The bacterial biota of laboratory-reared edible mealworms (Tenebrio molitor L.): From feed to frass

Polyurethane foam degradation combining ozonization and mealworm biodegradation and its exploitation

The biodegradation of polyurethane foam (PU foam) using a combination of oxidative pre-treatment (ozonization) and Tenebrio molitor (T. molitor) mealworms was conducted in this study. Different degrees of ozone oxidation (0%, 25%, and 50%) were applied to PU foam, which was subsequently fed to mealworms. The mealworms' survival and growth were then compared to mealworms receiving a normal diet (bran). Results showed that mealworms fed with non-oxidized PU foam (PUF0) exhibited a higher consumption rate (11.8%) than those fed with 25% (PUF25) and 50% (PUF50) oxidized PU foam (7.7% and 5.7%, respectively). The survival rate was similar across all the PU foam diets and the bran diet. Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) analyses revealed minor structural changes in the PU foam. The gut microbiota analysis showed a significant correlation between the PU foam and bran diets. Among the different oxidized PU, distinct microbial community profiles were also observed, with the genus Klebsiella consistently present across the PU foam diets. The ozone pre-treatment altered the palatability and degradation of the PU foam by mealworms, while the mealworm frass and chitin obtained could potentially be used as resources for agricultural and industrial applications that would close the circular bio-economy cycle.

Deciphering the Microbiota of Edible Insects Sold by Street Vendors in Thailand Using Metataxonomic Analysis

The aim of the present study was to investigate the microbiota of processed ready-to-eat (fried or boiled) edible insects sold by street vendors at local green markets in Thailand (Bangkok and Koh Samui). To this end, samples of 4 insect species (rhino beetle adults, silkworm pupae, giant waterbugs adults, and black scorpions) were collected and analyzed through viable counting and metataxonomic analysis. Enterobacteriaceae showed counts below 1 log cfu g-1 in all samples, except for black scorpions, which showed elevated counts reaching up to 4 log cfu g-1. Total mesophilic aerobes counts were up to 8 log cfu g-1 in all the analyzed samples. Counts below 1 log cfu g-1 were observed for Escherichia coli, Staphylococcus aureus, sulfite-reducing clostridia viable cells and spores, and Bacillus cereus. All the samples showed the absence of Listeria monocytogenes and Salmonella spp. According to metataxonomic analysis, 14 taxa were consistently present across all insect samples, including Dellaglioa algida, Latilactobacillus curvatus, Latilactobacillus sakei, Acetobacteraceae, Apilactobacillus kunkeei, Bombilactobacillus spp., Enterobacteriaceae, Gilliamella spp., Lactobacillus spp., Lactobacillus apis, Streptococcus thermophilus, Lacticaseibacillus rhamnosus, Lactiplantibacillus plantarum, and Weissella spp. Minority taxa included Alcaligenes spp., Brochothrix thermosphacta, Psychrobacter spp., Staphylococcus saprophyticus, Lactobacillus melliventris, Pediococcus spp., Levilactobacillus brevis, and Snodgrassella alvi.

Biotransformation of insect processing residues: Production of lactic acid bacterial biomass and associated partial removal of proteins from chitin

Processing of edible insects typically involves fractionating into high-value food ingredients, which results in by-products containing chitin and insoluble proteins. This study examined the effectiveness of lactic acid bacteria (LAB) in removing proteins from chitin in insect processing residues. Lesser mealworm processing residues were biologically treated for 48 and 120 h using LAB strains without added carbon sources. Results showed partial deproteinization, up to 29 % with Levilactobacillus brevis after 120 h. Most LAB grew up to 2 log10 colony-forming units/mL in the first 48 h. Confocal microscopy and Fourier-transform infrared spectra indicated that some protein remained attached to chitin. The molecular weight of solubilized proteins was affected by strain and time of incubation, with antioxidant activity increasing significantly after 120 h with Lacticaseibacillus paracasei. The biological treatment of insect processing streams can be a sustainable approach to producing high amounts of LAB biomass with subsequent protein solubilization and chitin release.

Analysis of Microbial Composition of Edible Insect Products Available for Human Consumption within the United States Using Traditional Microbiological Methods and Whole Genome Sequencing

Edible insects offer a promising protein source for humans, but their food safety risks have not been previously investigated within the United States. Therefore, the aim of this study was to investigate the microbial content of processed edible insect products. A total of eight different types of edible insect products, including diving beetles, silkworms, grasshoppers, Jamaican crickets, mealworms, mole crickets, whole roasted crickets, and 100% pure cricket powder, were purchased from a large online retailer for the analysis. All the products were purchased in August 2022 and examined between August 2022 and November 2022. Traditional microbiological methods were employed to determine microbial counts for each product type using three replicates (total number of samples = 24). This included assessing aerobic bacterial spore, lactic acid bacteria, Enterobacteriaceae, total viable counts, and the presence of Salmonella. Additionally, whole genome sequencing was employed to further characterize selected colonies (n = 96). Microbial counts data were statistically analyzed using one-way ANOVA, while sequence data were taxonomically classified using Sepia.Bacilluscereusgroup isolates underwent additional characterization with Btyper3. Product type significantly influenced total viable counts, bacterial spore counts, and lactic acid bacteria counts (P = 0.00391, P = 0.0065, and P < 0.001, respectively), with counts ranging from < 1.70 to 6.01 Log10 CFU/g, <1.70 to 5.25 Log10 CFU/g, and < 1.70 to 4.86 Log10 CFU/g, respectively. Enterobacteriaceae were only detected in mole crickets (<2.30 Log10 CFU/g) and house cricket powder (<2.15 Log10 CFU/g). All samples were negative for Salmonella. Whole genome sequencing revealed the presence of 12 different bacterial genera among the analyzed isolates, with a majority belonging to the Bacillus genus. Some of the isolates of Bacillus cereus group were identified as biovar Emeticus. Overall, although edible insects offer a promising food alternative, the presence of Bacillus cereus group in some products could raise concerns regarding food safety.

Antibiotic Resistance in Enterococci and Enterobacteriaceae from Laboratory-Reared Fresh Mealworm Larvae (Tenebrio molitor L.) and Their Frass

The occurrence of antibiotic-resistant bacteria in foodstuff involves a human health risk. Edible insects are a precious resource; however, their consumption raises food safety issues. In this study, the occurrence of antibiotic resistant bacteria in laboratory-reared fresh mealworm larvae (Tenebrio molitor L.) and frass was assessed. Antibiotics were not used during the rearing. Enterobacteriaceae and enterococci were isolated from 17 larvae and eight frass samples. In total, 62 and 69 isolates presumed to belong to Enterobacteriaceae and Enterococcus spp., respectively, were obtained and tested for antibiotic susceptibility via disk diffusion. Based on the results, isolates were grouped, and representative resistant isolates were identified at species level through 16S rRNA gene sequencing. For enterococci resistance, percentages higher than 15% were observed for vancomycin and quinupristin-dalfopristin, whereas Enterobacteriaceae resistance higher than 25% was found against cefoxitin, ampicillin, and amoxicillin-clavulanic acid. Based on the species identification, the observed resistances seemed to be intrinsic both for enterococci and Enterobacteriaceae, except for some β-lactams resistance in Shigella boydii (cefoxitin and aztreonam). These could be due to transferable genetic elements. This study suggests the need for further investigations to clarify the role of edible insects in the spreading of antibiotic resistance determinants through the food chain.

Bacterial proximity effects on the transfer of antibiotic resistance genes within the alimentary tract of yellow mealworm larvae

The arthropod intestinal tract and other anatomical parts naturally carry microorganisms. Some of which are pathogens, secrete toxins, or carry transferable antibiotic-resistance genes. The risks associated with the production and consumption of edible arthropods are dependent on indigenous microbes, as well as microbes introduced during the processes of rearing. This mass arthropod production puts individual arthropods in close proximity, which increases the possibility of their exposure to antibiotic-resistant bacteria carried by bacteria from fellow insects, industry workers, or rearing hardware and substrates. The purpose of this study was to determine if the alimentary tract of the yellow mealworm provided an environment permitting horizontal gene transfer between bacteria. The effect of the concentration of bacterial exposure was also assessed. Antibiotic resistance gene transfer between marker Salmonella Lignières (Enterobacterales: Enterobacteriaceae) and Escherichia coli (Migula) (Enterobacterales: Enterobacteriaceae) introduced into the larval gut demonstrated that the nutrient-rich environment of the yellow mealworm gut provided favorable conditions for the transfer of antibiotic resistance genes. Conjugation frequencies were similar across inoculum concentrations; however, transconjugant production correlated positively to increased exposure concentration. The lowest concentration of bacterial exposure required enrichment to detect and thus may have been approaching a threshold level for the 2 bacteria to colocate within the expanse of the larval gut. While many factors can affect this transfer, the simple factor of the proximity of donor and recipient bacteria, as defined by the concentration of bacteria within the volume of the insect gut, likely primarily contributed to the efficiency of antibiotic gene transfer.

Local circular economy: BSF insect rearing in the Italian Agri-Food Industry

With a growing population, both food and waste production will increase. There is an urgent need for innovative ways of valorizing waste. The black soldier fly (Hermetia illucens L.) efficiently converts agri-food by-products (BPs) into high-quality materials; its rearing process yields larvae (BSFL) rich in fat and protein for feed purposes, with "frass" acting as organic fertilizer. While the insect rearing sector is expanding, few producers use BPs. Therefore, a case study approach was adopted to evaluate the potential for establishing an Italian BSFL production plant on BPs available on the territory. After contacting more than 115 agri-food companies (maximum 100 km from the BSFL plant), they were classified based on sector, distance, size, and BPs (quantity, seasonality, management). BPs with a low value (fruit and vegetable residues) were treated as waste, associated with costs and low valorization. By merging the available BPs on the territory and following the literature on BSFL nutritional needs' two diets (Scenario BSFL) were created, assessing their suitability comparing them to the current full-scale plant diet (Scenario 0). The exploitation of BPs for BSFL rearing reduced local waste production by 52 % compared to conventional composting (Scenario 0). In addition, integrating BPs into the larval feed formulation increased BSFL production value (+47 times). These results highlight the potential of locally-based insect rearing to valorize BPs and create a network of sustainable actors within the agri-food industry. Further investigations are needed to improve the connection between agri-food and insect industrial activities, expanding this framework to other regions.

Identification of fungi isolated from commercial bumblebee colonies

Fungi can have important beneficial and detrimental effects on animals, yet our understanding of the diversity and function of most bee-associated fungi is poor. Over 2 million bumblebee colonies are traded globally every year, but the presence and transport of viable fungi within them is unknown. Here, we explored whether any culturable fungi could be isolated from commercial bumblebee nests. We collected samples of various substrates from within 14 bumblebee colonies, including the honey, honey cup wall, egg cup wall, and frass then placed them on agar and recorded any growth. Fungal morphotypes were then subcultured and their ITS region sequenced for identification. Overall, we cultured 11 fungal species from the various nest substrates. These included both pathogenic and non-pathogenic fungi, such as Aspergillus sp., Penicillium sp., and Candida sp. Our results provide the first insights into the diversity of viable fungal communities in commercial bumblebee nests. Further research is needed to determine if these fungi are unique to commercial colonies or prevalent in wild bumblebee nests, and crucially to determine the ecological and evolutionary implications of these fungi in host colonies.

Molecular Characterization of Serratia marcescens Strain Isolated from Yellow Mealworms, Tenebrio molitor, in The Netherlands

Insect culture has developed rapidly worldwide; it faces important security and safety control issues, including animal infections and disease development. In the Netherlands, in 2021, a ~30% mortality of mealworms, Tenebrio molitor, occurred at one farm, where over-humid sites in the substrate were observed. Bacterial cultures from both the external and internal partsof fry and larger mealworms were identified by MALDI-TOF to predominantly Serratia marcescens, Staphylococcus xylosus and Staphylococus saprofyticus. Due to the important role of S. marcescens as a potential zoonotic bacterium, we performed a molecular characterization of the isolated strain. Genomic analysis showed a multidrug-resistant S. marcescens isolate carrying a tet (41), aac (6')-Ic, and blaSST-1 chromosomal class C beta-lactamase-resistantgenes, all located on the chromosome. Additionally, several virulence genes were identified. The phylogenetic tree revealed that the S. marcescens strain from this study was similar to other S. marcescens strains from different ecological niches. Although the entomopathogenic activity was not confirmed, this case demonstrates that T. molitor can act as a reservoir and as an alternative path for exposing clinically important antibiotic-resistant bacteria that can affect animals and humans. It underlines the need to keep management factors optimal, before insects and their products enter the feed and food chain.

Behaviour of Staphylococcus aureus in the Rearing Substrate of Tenebrio molitor Larvae

Tenebrio molitor (mealworm) is one of the most promising insect species to produce sustainable feed and food with high nutritional value. Insects may harbour microorganisms both in the gut and on the exoskeleton originating from the rearing environment. Staphylococcus aureus is a pathogenic microorganism frequently involved in food poisoning due to its enterotoxin production. This study aimed to evaluate the S. aureus growth and enterotoxins production following an experimental inoculation into the T. molitor rearing substrate (about 7 log CFU/g). Analyses on the substrate and larvae were performed over a testing period of seven days. The microbial population dynamics were also evaluated through total viable count and lactic acid bacteria count. The effects of fasting, washing, and cooking on the microbial loads of mealworms were evaluated. The results highlighted that mealworms and substrates can maintain their microbial loads of S. aureus over the tested period. Moreover, fasting and washing were generally not able to significantly reduce (p-value > 0.05) S. aureus count in mealworms. On the other hand, cooking significantly reduced (p-value < 0.001) the microbial load in almost all cases. No production of enterotoxins was revealed during the trial. Therefore, microbiological risks can be reduced by a wise choice of substrate, appropriate control measures, and thermal treatment of larvae.

Tenebrio molitor (Linnaeus, 1758): Microbiological Screening of Feed for a Safe Food Choice

As a result of the increasing focus on alternative protein sources which are ideally still sustainable, the yellow mealworm, Tenebrio molitor, has come into focus. To verify its suitability as a food source in relation to human health, an analysis of the microbiome of larvae of T. molitor is pertinent. Subsequently, the focus of this study was, on the one hand, to analyze the influence of the substrate on the microbial load of the larvae microbiome, and, on the other hand, to determine which processing methods ensure the risk-free consumption of mealworms. For this purpose, mealworms were grown on 10 different substrates derived from by-products of food production (malt residual pellets, corn germ meal, chestnut breakage and meal, wheat bran, bread remains, draff, nettle, hemp seed oil cake, oyster mushrooms with coffee grounds, pumpkin seed oil cake) and microbial loads were analyzed using different selective media. Further starvation/defecation and heating (850 W for 10 min) methods were used to investigate how the reduction of microorganisms is enabled by these methods. The results showed that there was no significant relationship between the microbial load of the substrate and the mealworm. Starvation and defecation led to a lower stock of microorganisms. Heating led to a significant microbial reduction in non-defecated mealworms. The group of defecated and heated mealworms showed no detectable microbial load. In conclusion, firstly, the choice of substrate showed no effect on the microbial load of larvae of Tenebrio molitor and secondly, heating and starvation allow risk-free consumption. This study makes an important contribution for evaluating the safety of mealworms as a sustainable protein source in human nutrition.

Insect biorefinery: A circular economy concept for biowaste conversion to value-added products

With rapid growing world population and increasing demand for natural resources, the production of sufficient food, feed for protein and fat sources and sustainable energy presents a food insecurity challenge globally. Insect biorefinery is a concept of using insect as a tool to convert biomass waste into energy and other beneficial products with concomitant remediation of the organic components. The exploitation of insects and its bioproducts have becoming more popular in recent years. This review article presents a summary of the current trend of insect-based industry and the potential organic wastes for insect bioconversion and biorefinery. Numerous biotechnological products obtained from insect biorefinery such as biofertilizer, animal feeds, edible foods, biopolymer, bioenzymes and biodiesel are discussed in the subsequent sections. Insect biorefinery serves as a promising sustainable approach for waste management while producing valuable bioproducts feasible to achieve circular bioeconomy.

Effect of Probiotics on Tenebrio molitor Larval Development and Resistance against the Fungal Pathogen Metarhizium brunneum

In recent years, the yellow mealworm (Tenebrio molitor L.) has demonstrated its potential as a mass-produced edible insect for food and feed. However, challenges brought on by pathogens in intensive production systems are unavoidable and require the development of new solutions. One potential solution is the supplementation of probiotics in the insect's diet to obtain the double benefits of improved growth and enhanced immune response. The aim of this study was to evaluate the effects of diet-based probiotic supplementation on T. molitor larval survival, growth, and resistance against a fungal pathogen. Three probiotic strains, namely Pediococcus pentosacceus KVL-B19-01 isolated from T. molitor and two commercialized strains for traditional livestock, Enterococcus faecium 669 and Bacillus subtilis 597, were tested. Additionally, when larvae were 9 weeks old, a pathogen challenge experiment was conducted with the fungus Metarhizium brunneum. Results showed that both P. pentosaceus and E. faecium improved larval growth and larval survival following fungal exposure compared to the non-supplemented control diet. Since B. subtilis did not improve larval performance in terms of either development or protection against M. brunneum, this study suggests the need for further research and evaluation of probiotic strains and their modes of action when considered as a supplement in T. molitor's diet.

Comparison of Gut Bacterial Communities of Locusta migratoria manilensis (Meyen) Reared on Different Food Plants

Simple Summary

Although locusts can cause major agricultural damage, they also constitute a valuable food resource. At present, L. migratoria manilensis has been largely domesticated, being considered an edible insect in China. Feeding variety is one of the main characteristics of L. migratoria manilensis. There are apparent differences in the capacity of locusts to adapt to different food plants. To elucidate the effect of different food plants (i.e., goosegrass, maize leaves, soybean leaves, and pakchoi) on the growth and development of L. migratoria manilensis, the gut bacterial community composition of L. migratoria manilensis fifth instars fed on different plants was analyzed by high-throughput sequencing. Gut bacterial communities were affected by food plants and may play an essential role in host adaption. Feeding on different food plants has significant effects on the growth and development of L. migratoria manilensis. The present study establishes a theoretical foundation for studying the interplay between gut bacteria structure and L. migratoria manilensis adaptation.

Abstract

Locusts, in particular Locusta migratoria manilensis (Meyen), have been associated with major damages in agriculture, forestry, and animal husbandry in China. At present, L. migratoria manilensis has been largely domesticated, being considered an edible insect in China. Feeding variety is one of the main characteristics of L. migratoria manilensis. It has been demonstrated that microorganisms inhabiting the insect gut impact nutrition, development, defense, and reproduction of the insect host. The aim of the present study was to search for the adaptation mechanism of L. migratoria manilensis feeding on four different food plants (goosegrass, maize leaves, soybean leaves, and pakchoi) and explore changes in the gut bacterial community structure of the insect at the fifth instar nymph stage. Proteobacteria and Firmicutes were the dominant phyla, whereas Kluyvera, Enterobacter, Pseudocitrobacter, Klebsiella, Cronobacter, Citrobacter, Lactococcus, and Weissella were the dominant genera in the gut of L. migratoria manilensis. Principal component analysis and permutational multivariate analysis of variance (PERMANOVA) revealed significant differences in the gut microbiota structure of L. migratoria manilensis fed on different food plants. Moreover, functional prediction analysis revealed that metabolic and cellular processes were the most enriched categories. Within the category of metabolic processes, the most enriched pathways were carbohydrate transport and metabolism; amino acid transport and metabolism; translation, ribosomal structure, and biogenesis; cell wall/membrane/envelope biogenesis; inorganic ion transport and metabolism; and energy production and conversion. Collectively, the present results revealed that the structure of gut bacterial communities in L. migratoria manilensis fed on different food plants is impacted by food plants, which may play an essential part in the adaptation of the host.

Colorado potato beetle exploits frass-associated bacteria to suppress defense responses in potato plants

BACKGROUND

Colorado potato beetle (CPB; Leptinotarsa decemlineata) is a destructive quarantine pest that develops broad physiological adaptations to potato plants. During feeding, CPB deposits a copious amount of wet frass onto the surface of leaves and stems that remains in place for long periods. Insect behaviors such as feeding, crawling and oviposition are able to mediate plant defenses. However, the specific role of CPB defecation-associated cues in manipulating plant defenses remains unclear.

RESULTS

CPB larval frass significantly suppressed potato polyphenol oxidase activity and enhanced larval growth on treated potato plants. The incorporation of antibiotics into larval frass triggered higher jasmonic acid (JA)-regulated defense responses in potato plants compared with antibiotic-free frass. Four bacterial symbionts belonging to the genera Acinetobacter, Citrobacter, Enterobacter and Pantoea were isolated from larval frass and suppressed plant defenses. After reinoculation of these bacteria into axenic larvae, Acinetobacter and Citrobacter were found to be highly abundant in the frass, whereas Enterobacter and Pantoea were less abundant probably due to the negative effect of potato steroidal glycoalkaloids (SGA) such as α-solanine. Furthermore, direct application of Acinetobacter and Citrobacter to wounded potato plants significantly inhibited the expression of genes associated with the JA-mediated defense signaling pathway and SGA biosynthesis.

CONCLUSION

Our findings demonstrate that CPB exploits frass-associated bacteria as a deceptive strategy of plant defense suppression, adding an interesting dimension to our understanding of how CPB successfully specializes on potato plants. © 2022 Society of Chemical Industry.

Effects of Agro-Industrial Byproduct-Based Diets on the Growth Performance, Digestibility, Nutritional and Microbiota Composition of Mealworm (Tenebrio molitor L.)

The aim of this study was to evaluate the effects of agro-industrial byproduct-based diets on the productive parameters, digestibility, insect composition, and gut microbiota of mealworm (Tenebrio molitor) larvae. Three formulations corresponding to three different levels of starch and protein were tested: one formulation based on bread remains and brewer’s yeast, representing a diet of high starch (61.1%) and low crude protein (18.5%) (HS-LP); and two formulations in which an additional four byproducts (courgette (Cucurbita pepo) remains, tigernut (Cyperus scelentus) pulp, brewer’s spent grains, and rice straw) were incorporated in different proportions, consistent with a diet of both moderate starch (29.8%) and crude protein (21.0%) (MS-MP); and another corresponding to a diet of low starch (20.0%) and high crude protein (26.3%) (LS-HP). A total of 1920 young larvae (average weight = 0.65 mg per larva) were used in this study. The larvae were randomly distributed into 16 replicates per treatment (boxes of 22.5 cm × 14.0 cm × 4.75 cm). Ten replicates for the growth performance−digestibility trial and six replicates for the complementary trial to determine uric acid levels in the frass were assigned per treatment. For growth performance, the diets were administered ad libitum during the experiment. The average number of days for the larvae to start pupating was lower in those reared on the HS-LP and LS-HP diets (88.90 and 91.00 days, respectively) than those on the MS-MP diet (120.09 days) (p < 0.001). The final individual weight was higher (p < 0.001) in larvae of the LS-HP group (168.69 mg) compared to those of the other groups (100.29 and 112.99 mg for HS-LP and MS-MP, respectively). However, the feed conversion ratio was better (p < 0.001) in the HS-LP group with the lowest value (1.39 g/g), with dry matter digestibility being the highest for the same diet (70.38%) (p < 0.001). Mealworms reared on LS-HP and MS-MP diets had a higher crude protein content than those reared on the HS-LP diet (p = 0.039). The most abundant phyla in the gut microbiota of larvae were Tenericutes, Proteobacteria, and Firmicutes, with their abundance depending on the rearing substrate. The representation of Tenericutes phylum was higher (p < 0.05) in the mealworms reared on MS-MP and HS-LP diets, whereas Proteobacteria and Cyanobacteria were higher in abundance (p < 0.001) in the insects reared on LS-HP. In conclusion, the larval growth, digestibility, insect composition, and gut microbiota of Tenebrio molitor were found to depend on the composition of the administered diet, and the results suggest great potential for the use of agro-industrial byproducts in their rearing and production.

Benefits and Challenges in the Incorporation of Insects in Food Products

Edible insects are being accepted by a growing number of consumers in recent years not only as a snack but also as a side dish or an ingredient to produce other foods. Most of the edible insects belong to one of these groups of insects such as caterpillars, butterflies, moths, wasps, beetles, crickets, grasshoppers, bees, and ants. Insect properties are analyzed and reported in the articles reviewed here, and one common feature is nutrimental content, which is one of the most important characteristics mentioned, especially proteins, lipids, fiber, and minerals. On the other hand, insects can be used as a substitute for flour of cereals for the enrichment of snacks because of their high content of proteins, lipids, and fiber. Technological properties are not altered when these insects-derived ingredients are added and sensorial analysis is satisfactory, and only in some cases, change in color takes place. Insects can be used as substitute ingredients in meat products; the products obtained have higher mineral content than traditional ones, and some texture properties (like elasticity) can be improved. In extruded products, insects are an alternative source of proteins to feed livestock, showing desirable characteristics. Isolates of proteins of insects have demonstrated bioactive activity, and these can be used to improve food formulations. Bioactive compounds, as antioxidant agents, insulin regulators, and anti-inflammatory peptides, are high-value products that can be obtained from insects. Fatty acids that play a significant role in human health and lipids from insects have showed positive impacts on coronary disease, inflammation, and cancer. Insects can be a vector for foodborne microbial contamination, but the application of good manufacturing practices and effective preservation techniques jointly with the development of appropriate safety regulations will decrease the appearance of such risks. However, allergens presented in some insects are a hazard that must be analyzed and taken into account. Despite all the favorable health-promoting characteristics present in insects and insects-derived ingredients, willingness to consume them has yet to be generalized.

Nanopore-Sequencing Characterization of the Gut Microbiota of Melolontha melolontha Larvae: Contribution to Protection against Entomopathogenic Nematodes?

This study focused on the potential relationships between midgut microbiota of the common cockchafer Melolontha melolontha larvae and their resistance to entomopathogenic nematodes (EPN) infection. We investigated the bacterial community associated with control and unsusceptible EPN-exposed insects through nanopore sequencing of the 16S rRNA gene. Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundant bacterial phyla within the complex and variable midgut microbiota of the wild M. melolontha larvae. The core microbiota was found to include 82 genera, which accounted for 3.4% of the total number of identified genera. The EPN-resistant larvae differed significantly from the control ones in the abundance of many genera belonging to the Actinomycetales, Rhizobiales, and Clostridiales orders. Additionally, the analysis of the microbiome networks revealed different sets of keystone midgut bacterial genera between these two groups of insects, indicating differences in the mutual interactions between bacteria. Finally, we detected Xenorhabdus and Photorhabdus as gut residents and various bacterial species exhibiting antagonistic activity against these entomopathogens. This study paves the way to further research aimed at unravelling the role of the host gut microbiota on the output of EPN infection, which may contribute to enhancement of the efficiency of nematodes used in eco-friendly pest management.

Microbial dynamics in rearing trials of Hermetia illucens larvae fed coffee silverskin and microalgae

In the present study, Hermetia illucens larvae were reared on a main rearing substrate composed of a coffee roasting byproduct (coffee silverskin, Cs) enriched with microalgae (Schizochytrium limacinum or Isochrysis galbana) at various substitution levels. The microbial diversity of the rearing substrates, larvae, and frass (excrement from the larvae mixed with the substrate residue) were studied by the combination of microbial culturing on various growth media and metataxonomic analysis (Illumina sequencing). High counts of total mesophilic aerobes, bacterial spores, presumptive lactic acid bacteria, coagulase-positive cocci, and eumycetes were detected. Enterobacteriaceae counts were low in the rearing diets, whereas higher counts of this microbial family were observed in the larvae and frass. The microbiota of the rearing substrates was characterized by the presence of lactic acid bacteria, including the genera Lactobacillus, Leuconostoc and Weissella. The microbiota of the H. illucens larvae fed Cs was characterized by the dominance of Paenibacillus. H. illucens fed diets containing I. galbana were characterized by the presence of Enterococcus, Lysinibacillus, Morganella, and Paenibacillus, depending on the algae inclusion level, while H. illucens fed diets containing S. limacinum were characterized by high relative abundances of Brevundimonas, Enterococcus, Paracoccus, and Paenibacillus, depending on the algae inclusion level. Brevundimonas and Alcaligenes dominated in the frass from larvae fed I. galbana; the predominance of Brevundimonas was also observed in the frass from larvae fed Schyzochitrium-enriched diets. Based on the results of the present study, an effect of algae nutrient bioactive substances (e.g. polysaccharides, high-unsaturated fatty acids, taurine, carotenoids) on the relative abundance of some of the bacterial taxa detected in larvae may be hypothesized, thus opening new intriguing perspectives for the control of the entomopathogenic species and foodborne human pathogens potentially occurring in edible insects. Further studies are needed to support this hypothesis. Finally, new information on the microbial diversity occurring in insect frass was also obtained.

The Microbial Diversity of Non-Korean Kimchi as Revealed by Viable Counting and Metataxonomic Sequencing

Kimchi is recognized worldwide as the flagship food of Korea. To date, most of the currently available microbiological studies on kimchi deal with Korean manufactures. Moreover, there is a lack of knowledge on the occurrence of eumycetes in kimchi. Given these premises, the present study was aimed at investigating the bacterial and fungal dynamics occurring during the natural fermentation of an artisan non-Korean kimchi manufacture. Lactic acid bacteria were dominant, while Enterobacteriaceae, Pseudomonadaceae, and yeasts progressively decreased during fermentation. Erwinia spp., Pseudomonasveronii, Pseudomonasviridiflava, Rahnellaaquatilis, and Sphingomonas spp. were detected during the first 15 days of fermentation, whereas the last fermentation phase was dominated by Leuconostoc kimchi, together with Weissellasoli. For the mycobiota at the beginning of the fermentation process, Rhizoplaca and Pichia orientalis were the dominant Operational Taxonomic Units (OTUs) in batch 1, whereas in batch 2 Protomyces inundatus prevailed. In the last stage of fermentation, Saccharomyces cerevisiae, Candida sake,Penicillium, and Malassezia were the most abundant taxa in both analyzed batches. The knowledge gained in the present study represents a step forward in the description of the microbial dynamics of kimchi produced outside the region of origin using local ingredients. It will also serve as a starting point for further isolation of kimchi-adapted microorganisms to be assayed as potential starters for the manufacturing of novel vegetable preserves with high quality and functional traits.

Control of Biological Hazards in Insect Processing: Application of HACCP Method for Yellow Mealworm (Tenebrio molitor) Powders

Entomophagy has been part of human diets for a long time in a significant part of the world, but insects are considered to be a novel food everywhere else. It would appear to be a strategic alternative in the future of human diet to face the challenge of ensuring food security for a growing world population, using more environmentally sustainable production systems than those required for the rearing of other animals. Tenebrio molitor, called yellow mealworm, is one of the most interesting insect species in view of mass rearing, and can be processed into a powder that ensures a long shelf life for its use in many potential products. When considering insects as food or feed, it is necessary to guarantee their safety. Therefore, manufacturers must implement a Hazard Analysis Critical Control plan (HACCP), to limit risks for consumers' health. The aim of this case study was to develop a HACCP plan for Tenebrio molitor larvae powders for food in a risk-based approach to support their implementation in industry. Specific purposes were to identify related significant biological hazards and to assess the efficiency of different manufacturing process steps when used as Critical Control Points. Then, combinations of four different processes with four potential uses of powders by consumers in burger, protein shake, baby porridge, and biscuits were analyzed with regard to their safety.

Suitability of Black Soldier Fly Frass as Soil Amendment and Implication for Organic Waste Hygienization

Because of its nutritious properties, the black soldier fly has emerged as one of the most popular species in advancing circular economy through the re-valorization of anthropogenic organic wastes to insect biomass. Black soldier fly frass accumulates as a major by-product in artificial rearing set-ups and harbors great potential to complement or replace commercial fertilizers. We applied frass from larvae raised on different diets in nitrogen-equivalent amounts as soil amendment, comparing it to NH4NO3 fertilizer as a control. While the soil properties did not reveal any difference between mineral fertilizer and frass, principal component analysis showed significant differences that are mainly attributed to nitrate and dissolved nitrogen contents. We did not find significant differences in the growth of perennial ryegrass between the treatments, indicating that frass serves as a rapidly acting fertilizer comparable to NH4NO3. While the abundance of coliform bacteria increased during frass maturation, after application to the soil, they were outcompeted by gram-negatives. We thus conclude that frass may serve as a valuable fertilizer and does not impair the hygienic properties of soils.

Identification of bacterial endospores and targeted detection of foodborne viruses in industrially reared insects for food

With edible insects being increasingly produced, food safety authorities have called for the determination of microbiological challenges posed to human health. Here, we find that the bacterial endospore fraction in industrially reared mealworm and cricket samples is largely comprised of Bacillus cereus group members that can pose insect or human health risks. Hepatitis A virus, hepatitis E virus and norovirus genogroup II were not detected in the sample collection, indicating a low food safety risk from these viral pathogens.

Salmonella Typhimurium Level in Mealworms (Tenebrio molitor) After Exposure to Contaminated Substrate

Findings of viable Salmonella spp., which are important foodborne pathogens, are seemingly not reported in mealworms (Tenebrio molitor) for feed and food. Still, the bacterial load of mealworms is naturally high and includes members of the Enterobacteriaceae family to which Salmonella belong. This indicates that Salmonella may be able to thrive in mealworms if introduced into the production. Therefore, this study aimed to assess the quantitative level of Salmonella enterica serovar Typhimurium (ST) in mealworms over a 14-day course after exposure to substrate contaminated with ST levels from 1.7 to 7.4 log CFU/g at start (i.e., day 0). The level of ST found in larvae was below the quantitative detection level (1 or 2 log CFU/g) on day 1 in larvae exposed to contamination levels of 1.7, 3.4, and 3.6 log CFU/g opposed to contamination levels of 5.4, 5.6, and 7.4 log CFU/g, respectively. The maximum level of ST detected in individual 1-g larvae samples was 5.8 log CFU/g, but the level varied among the triplicate samples from each sampling, and the highest average value was 5.3 ± 0.3. Beyond day 7, only larvae exposed to the contamination level of 7.4 log CFU/g were >1.0 log CFU/g in the triplicate samples. However, qualitative testing (10 g) showed the presence of ST in larvae until the end of the experiment on day 14 except for the lowest contamination level of 1.7 log CFU/g. Parallel testing of surface disinfected larvae indicated that some larvae may be ST-positive due to Salmonella residing on the surface only. Still, any detection of Salmonella is of concern from a food safety perspective. In substrate with contamination levels below 3.6 log CFU/g, the level of ST was below the quantitative detection limit within a few days. Still, ST was detected until the end of experiment on day 14 except for the lowest contamination level of 1.7 log CFU/g. This study indicates the importance of avoiding introduction of Salmonella into the production, e.g., via contaminated substrate in order to avoid Salmonella-positive larvae as they remained positive for at least 14 days (except at the lowest contamination level).

A comprehensive assessment of microbiome diversity in Tenebrio molitor fed with polystyrene waste

Recently it was demonstrated that mealworm (Tenebrio molitor) larvae consume and biodegrade polystyrene. Thus, in this study a breeding investigation with various types of polystyrene was performed to follow the changes in the gut microbiome diversity. Polystyrene used for packaging purposes (PSp) and expanded polystyrene (EPS) were perceived as more favorable and attacked more frequently by mealworms compared to raw polystyrene (PS) and material commercially available for parcels (PSp). Although our studies showed that larvae could bite and chew selected materials, they are not able to degrade and use them for consumption purposes. In a next-generation sequencing experiment, among all samples, seven classes, Gammaproteobacteria, Bacilli, Clostridia, Acidobacteria, Actinobacteria, Alphaproteobacteria and Flavobacteria, were indicated as the most abundant, whereas the predominant genera were Enterobacter, Lactococcus and Enterococcus. Additionally, we isolated three bacteria strains able to use diverse types of bioplastic as a sole carbon source. The strains with biodegradable activity against bioplastic were identified as species of the genera Klebsiella, Pseudomonas and Serratia. The presence of a bacterial strain able to degrade bioplastic may suggest a potential niche for further investigations.

The microbial safety of seaweed as a feed component for black soldier fly (Hermetia illucens) larvae

Farmed insects can offer an environmentally sustainable aquafeed or livestock feed ingredient. The value of black soldier fly (Hermetia illucens) (BSF) larvae could be improved by enrichment in omega-3 through the dietary inclusion of seaweed. However, the industry practice of drying seaweed at low temperatures to retain nutritional properties may benefit the survival of human pathogenic bacteria, particularly if the seaweed has been harvested from contaminated water. Here we have demonstrated that E. coli and E. coli O157:H7 died-off in seaweed dried at 50 °C, although both were detected in the dried powder following 72 h storage. V. parahaemolyticus fell below the level of detection in stored seaweed after drying at ≥ 50 °C, but L. monocytogenes remained detectable, and continued to grow in seaweed dried at ≤60 °C. Therefore, drying seaweed at low temperatures risks pathogen carry-over into insects destined for animal feed. BSF larvae reared on an artificially contaminated seaweed-supplemented diet also became contaminated by all four bacteria present in the supplement. Water quality at seaweed harvesting sites, seaweed desiccation, and insect rearing practices, represent critical points where development of regulatory standards could achieve targeted control of pathogenic hazards.

Addition of Olive Pomace to Feeding Substrate Affects Growth Performance and Nutritional Value of Mealworm (Tenebrio Molitor L.) Larvae

The well-recognized efficiency of Tenebrio molitor larvae to convert low quality organic matter into a nutritionally valuable biomass was exploited to manage solid wastes coming from the olive oil industry, which represent a severe environmental challenge in the Mediterranean area. Three organic pomace-enriched substrates (mixtures middlings/pomace 3:1, 1:1, and 1:3) were assessed, together with 100% organic wheat flour and 100% organic middlings as control feeds. A feeding substrate made up of 25% olive pomace and 75% wheat middlings appeared to be the best compromise between growth performance (larval and pupal weights, survival rate, development time) and nutritional properties of mealworm larvae. In fact, larvae fed the 3:1 feed showed the highest dry matter (DM) yield (38.05%), protein content (47.58% DM), and essential/non-essential amino acids ratio (1.16). Fat content (32.14% DM) and fatty acid composition were not significantly different than those of larvae fed more pomace-enriched feeds.

Evolution and taxonomy of nematode-associated entomopathogenic bacteria of the genera Xenorhabdus and Photorhabdus: an overview

Entomopathogenic bacteria from the genera Photorhabdus and Xenorhabdus are closely related Gram-negative bacilli from the family Enterobacteriaceae (γ-Proteobacteria). They establish obligate mutualistic associations with soil nematodes from the genera Steinernema and Heterorhabditis to facilitate insect pathogenesis. The research of these two bacterial genera is focused mainly on their unique interactions with two different animal hosts, i.e. nematodes and insects. So far, studies of the mutualistic bacteria of nematodes collected from around the world have contributed to an increase in the number of the described Xenorhabdus and Photorhabdus species. Recently, the classification system of entomopatogenic nematode microsymbionts has undergone profound revision and now 26 species of the genus Xenorhabdus and 19 species of the genus Photorhabdus have been identified. Despite their similar life style and close phylogenetic origin, Photorhabdus and Xenorhabdus bacterial species differ significantly in e.g. the nematode host range, symbiotic strategies for parasite success, and arrays of released antibiotics and insecticidal toxins. As the knowledge of the diversity of entomopathogenic nematode microsymbionts helps to enable the use thereof, assessment of the phylogenetic relationships of these astounding bacterial genera is now a major challenge for researchers. The present article summarizes the main information on the taxonomy and evolutionary history of Xenorhabdus and Photorhabdus, entomopathogenic nematode symbionts.

Changes in the gut microbiome and enzymatic profile of Tenebrio molitor larvae biodegrading cellulose, polyethylene and polystyrene waste

Recent studies have demonstrated the ability of mealworm (Tenebrio molitor) for plastic degradation. This study is focused on changes in microbiome structure depending on diets. Microbial community obtained from oat and cellulose diet formed similar group, two kinds of polyethylene formed another group, while polystyrene diet showed the highest dissimilarity. The highest relative abundance of bacteria colonizing gut was in PE-oxodegradable feeding, nevertheless all applied diets were higher in comparison to oat. Dominant phyla consisted of Proteobacteria, Bacteroides, Firmicutes and Actinobacteria, however after PS feeding frequency in Planctomycetes and Nitrospirae increased. The unique bacteria characteristic for cellulose diet belonged to Selenomonas, while Pantoea were characteristic for both polyethylene diets, Lactococcus and Elizabethkingia were unique for each plastic diet, and potential diazotropic bacteria were characteristic for polystyrene diet (Agrobacterium, Nitrosomonas, Nitrospira). Enzymatic similarity between oatmeal and cellulose diets, was shown. All three plastics diet resulted in different activity in both, digestive tract and bacteria. The enzymes with the highest activity were included phosphatases, esterases, leucine arylamidase, β-galactosidase, β-glucuronidase, α-glucosidase, β-glucosidase, chitinase, α-mannosidase and α-fucosidase. The activity of digestive tract was stronger than cultured gut bacteria. In addition to known polyethylene degradation methods, larvae may degrade polyethylene with esterase, cellulose and oatmeal waste activity is related with the activity of sugar-degrading enzymes, degradation of polystyrene with anaerobic processes and diazotrophs.

Hermetia illucens in diets for zebrafish (Danio rerio): A study of bacterial diversity by using PCR-DGGE and metagenomic sequencing

In the present research, bacterial diversity was studied during a 6-month feeding trial utilizing zebrafish (Danio rerio) fed Hermetia illucens reared on different substrates with an emphasis on fish gut bacterial diversity. A polyphasic approach based on viable counting, PCR-DGGE and metagenomic 16S rRNA gene amplicon target sequencing was applied. Two different H. illucens groups were reared on coffee by-products (C) or a mixture of vegetables (S). Viable counts showed a wide variability based on substrate. PCR-DGGE and Illumina sequencing allowed the major and minor bacterial taxa to be detected. Both samples of larvae and their frass reared on the S substrate showed the highest richness and evenness of bacterial communities, whereas zebrafish (ZHC) fed H. illucens reared on substrate C and zebrafish (ZHS) fed H. illucens reared on substrate S had the lowest bacterial richness and evenness. A stimulating effect of bioactive compounds from coffee by-products on the occurrence of Lactobacillaceae and Leuconostoccaceae in H. illucens reared on substrate C has been hypothesized. Zebrafish gut samples originating from the two feeding trials showed complex microbial patterns in which Actinobacteria and Alteromonadales were always detected, irrespective of the diet used. Enterobacteriaceae in fish guts were more abundant in ZHS than in ZHC, thus suggesting an influence of the bioactive compounds (chlorogenic and caffeic acids) in the substrate on Enterobacteriaceae in fish guts. ZHC showed a higher abundance of Clostridia than did ZHS, which was likely explained by stimulating activity on the bacteria in this class by the bioactive compounds contained in H. illucens reared on substrate C. An influence of the microbiota of H. illucens or insect-derived bioactive compounds on the gut microbiota of zebrafish has been suggested. The presence of bacteria consistently associated with zebrafish guts has been found irrespective of the diet, thus attesting to the likely stability of the core fish microbiota.

TmDorX2 positively regulates antimicrobial peptides in Tenebrio molitor gut, fat body, and hemocytes in response to bacterial and fungal infection

Dorsal, a member of the nuclear factor-kappa B (NF-κB) family of transcription factors, is a critical downstream component of the Toll pathway that regulates the expression of antimicrobial peptides (AMPs) against pathogen invasion. In this study, the full-length ORF of Dorsal was identified from the RNA-seq database of the mealworm beetle Tenebrio molitor (TmDorX2). The ORF of TmDorX2 was 1,482 bp in length, encoding a polypeptide of 493 amino acid residues. TmDorX2 contains a conserved Rel homology domain (RHD) and an immunoglobulin-like, plexins, and transcription factors (IPT) domain. TmDorX2 mRNA was detected in all developmental stages, with the highest levels observed in 3-day-old adults. TmDorX2 transcripts were highly expressed in the adult Malpighian tubules (MT) and the larval fat body and MT tissues. After challenging the larvae with Staphylococcus aureus and Escherichia coli, the TmDorX2 mRNA levels were upregulated 6 and 9 h post infection in the whole body, fat body, and hemocytes. Upon Candida albicans challenge, the TmDorX2 mRNA expression were found highest at 9 h post-infection in the fat body. In addition, TmDorX2-knockdown larvae exposed to E. coli, S. aureus, or C. albicans challenge showed a significantly increased mortality rate. Furthermore, the expression of 11 AMP genes was downregulated in the gut and fat body of dsTmDorX2-injected larvae upon E. coli challenge. After C. albicans and S. aureus challenge of dsTmDorX2-injected larvae, the expression of 11 and 10 AMPs was downregulated in the gut and fat body, respectively. Intriguingly, the expression of antifungal transcripts TmTenecin-3 and TmThaumatin-like protein-1 and -2 was greatly decreased in TmDorX2-silenced larvae in response to C. albicans challenge, suggesting that TmDorX2 regulates antifungal AMPs in the gut in response to C. albicans infection. The AMP expression profiles in the fat body, hemocytes, gut, and MTs suggest that TmDorX2 might have an important role in promoting the survival of T. molitor larvae against all mentioned pathogens.

Comparison of Six Commercial Meat Starter Cultures for the Fermentation of Yellow Mealworm (Tenebrio molitor) Paste

In this study, six commercial meat starters, each consisting of a pure strain of a lactic acid-fermenting bacterium (including Lactococcus lactis, Lactobacillus curvatus, L. farciminis, L. plantarum, L. sakei, and Pediococcus acidilactici), were tested for their ability to ferment a paste produced from the yellow mealworm (Tenebrio molitor). During fermentation, microbial counts, pH, and the bacterial community composition were determined. In addition, UPLC-MS was applied to monitor the consumption of glucose and the production of glutamic (Glu) and aspartic (Asp) acid. All tested starters were able to ferment the mealworm paste, judged by a pH reduction from 6.68 to 4.60–4.95 within 72 h. Illumina amplicon sequencing showed that all starters were able to colonize the substrate efficiently. Moreover, the introduction of the starter cultures led to the disappearance of Bacillus and Clostridium species, which were the dominant microorganisms in un-inoculated samples. Of the six cultures tested, Lactobacillus farciminis was most promising as its application resulted in the largest increase (±25 mg/100 g of paste) in the content of free glutamic and aspartic acid. These amino acids are responsible for the appreciated umami flavour in fermented food products and might stimulate the acceptance of insects and their consumption.

Investigating Antibiotic Resistance Genes in Marketed Ready-to-Eat Small Crickets (Acheta domesticus)

The present investigation was aimed at evaluating the occurrence of transferable genes conferring resistance to tetracyclines, macrolide-lincosamide-streptogramin B (MLS_B ), vancomycin, beta-lactams, and aminoglycosides in 32 samples from eight batches of ready-to-eat crickets (Acheta domesticus) commercialized by four European Union producers (two batches per producer). Bacterial DNA extracted directly from the insects was subjected to optimized polymerase chain reaction (PCR) and nested-PCR assays for the qualitative detection of 12 selected antibiotic resistance (AR) genes. Microbial enumeration demonstrated high counts of spore-forming bacteria and total mesophilic aerobes. Statistical analyses revealed significant differences between different producers and insect batches. Regarding AR genes, a high prevalence of genes conferring resistance to tetracycline [tet(M), tet(O), tet(K), tet(S)] was observed, together with the presence of genes conferring resistance to erythromycin [erm(B), erm(C)], beta-lactams (blaZ and mecA), and aminoglycosides [aac(6')-Ie aph(2")-Ia]. We performed a principal component analysis based on the AR gene frequencies that differentiated samples of batch 1 from those of batch 2. This analysis provided evidence for a difference between the producer from France and all the other producers among the batch 1 samples. PRACTICAL APPLICATION: Overall, an intrabatch variation was seen in the transferable resistances among different producers. This evidence, coupled with the observed differences in the viable counts, suggests a low standardization of the production processes. Hence, a prudent use of antimicrobials during the rearing of insects destined for human consumption is strongly recommended, as well as a need for a full standardization of production technologies.

Examining the Presence of Cronobacter spp. in Ready-to-eat Edible Insects

Edible insects present a potential solution to increasing global food insecurity. However, there is limited research on the microbial hazards they may pose. These include opportunistic pathogens like Cronobacter spp. (formerly Enterobacter sakazakii). In this study, nine types of ready-to-eat edible insect products purchased in the UK were examined for their microbial load (total aerobic count, total Enterobacteriaceae count), and screened for the presence of Cronobacter sakazakii(C. sakazakii) by selective enrichment and plating on chromogenic agar. While microbial load was generally low, presumptive Cronobacter spp. were detected in five of the edible insect products. Four of the isolates were identified as C. sakazakii, using the Remel RapID ONE biochemical test kit. Genotypic characterisation of the isolates by ITS-PCR, however, demonstrated that the isolates may be other species of Cronobacter instead. Further studies into understanding microbial hazards linked to edible insects for human consumption are required.

Entomophagy: Nutritional, ecological, safety and legislation aspects

Globally, there is a need to seek alternative sources of protein in addition to meat. This has led to considerable interest in edible insects. Such insects form part of cultures and diets in many Asian and African countries, and are an excellent source of essential nutrients, minerals, vitamins and proteins. Furthermore, they have been reported to be sustainable. The ecological importance of insects is related to their short life cycles when reared and farmed. This makes them ideal in mitigating greenhouse gas emissions, cutting land uses and polluted water, and reducing environmental contamination. However, the use of edible insects as food in Europe is minimal. To ensure safety of insects when eaten as food, considerations should be made on: microbiological contamination; toxicological hazards, e.g. chemical hazards and antinutrients; allergenicity issues that are related to different exposures, including injection, ingestion, inhalation and skin contact. In this review, we summarize the nutritional and sustainable values of edible insects, look at safety and legislative measures and we finally discuss future issues.

Microbiological Profile and Bioactive Properties of Insect Powders Used in Food and Feed Formulations

Microbiological, nutritional and bioactive properties of edible powders obtained from Acheta domesticus (house cricket) and Tenebrio molitor (mealworm) were investigated. Except for the enterobacteria, viable bacteria were at a higher concentration in mealworm flour. The diversity evaluation carried out using MiSeq Illumina that mainly identified Citrobacter and Enterobacteriaceae in mealworm powder and members of the Porphyromonadaceae family in house cricket powder. Enterococci were identified and characterized for their safety characteristics in terms of the absence of antibiotic resistance and virulence. Both powders represent a good source of proteins and lipids. The fatty acid profile of mealworm powder was characterized by the predominance of the monounsaturated fatty acids and house cricket powder by saturated fatty acids. The enzymatic hydrolysis produced the best results in terms of percentage of degree of hydrolysis with the enzyme Alcalase, and these data were confirmed by SDS-PAGE electrophoresis. Furthermore, the results showed that the protein hydrolysate of these powders produces a significant antioxidant power.

A Glimpse into the Microbiota of Marketed Ready-to-Eat Crickets (Acheta domesticus)

The present study was aimed to get an insight into the bacterial biota of ready-to-eat small crickets (Acheta domesticus) already marketed in the European Union. 16S rRNA gene of the DNAs extracted from thirty-two samples of ready-to-eat crickets commercialized by 4 European Union producers located in Austria, Belgium, France and the Netherlands (2 batches per producer) was analyzed by Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE). The species belonging to the genera Hespellia, Ruminococcus and Clostridium were detected in samples from Austria, while those from genera Lysobacter, Staphylococcus and Clostridium were detected in samples from Belgium. Moreover, samples from France were characterized by Staphylococcus, Pseudomonas, and Hydrogenophilus genera. Finally, the genera Staphylococcus, Hydrogenophilus, Clostridium and Ruminococcus were identified in the samples produced in the Netherlands. When insects are intended for commercialization, rearing, processing and handling could affect the presence of the occurring microbial species. Hence, to assure a safe product, the need for a full standardization of production technologies, including feed supply as well as rearing and processing practices, is recommended.

Current knowledge on the microbiota of edible insects intended for human consumption: A state-of-the-art review

Because of their positive nutritional characteristics and low environmental impact, edible insects might be considered a 'food of the future'. However, there are safety concerns associated with the consumption of insects, such as contaminating chemical and biological agents. The possible presence of pathogenic and toxigenic microorganisms is one of the main biological hazards associated with edible insects. This review presents an overview of the microbiota of edible insects, highlighting the potential risks for human health. Detailed information on the microbiota of edible insects from literature published in 2000-2019 is presented. These data show complex ecosystems, with marked variations in microbial load and diversity, among edible insects as well as stable and species-specific microbiota for some of the most popular edible insect species, such as mealworm larvae (Tenebrio molitor) and grasshoppers (Locusta migratoria). Raw edible insects generally contain high numbers of mesophilic aerobes, bacterial endospores or spore-forming bacteria, Enterobacteriaceae, lactic acid bacteria, psychrotrophic aerobes, and fungi, and potentially harmful species (i.e. pathogenic, mycotoxigenic, and spoilage microbes) may be present. Several studies have focused on reducing the microbial contamination of edible insects by applying treatments such as starvation, rinsing, thermal treatments, chilling, drying, fermentation, and marination, both alone and, sometimes, in combination. Although these studies show that various heat treatments were the most efficient methods for reducing microbial numbers, they also highlight the need for species-specific mitigation strategies. The feasibility of using edible insects as ingredients in the food industry in the development of innovative insect-based products has been explored; although, in some cases, the presence of spore-forming bacteria and other food-borne pathogens is a concern. Recent studies have shown that a risk assessment of edible insects should also include an evaluation of the incidence of antibiotic-resistance (AR) genes and antibiotic-resistant microorganisms in the production chain. Finally, as proposed in the literature, microbial hazards should be limited through the implementation of good hygienic practices during rearing, handling, processing, and storage, as well as the implementation of an appropriate HACCP system for edible insect supply chains. Another issue frequently reported in the literature is the need for a legislative framework for edible insect production, commercialisation, and trading, as well as the need for microbiological criteria specifically tailored for edible insects. Microbiological criteria like those already been established for the food safety and hygiene (e.g. those in the European Union food law) of different food categories (e.g. ready-to-eat products) could be applied to edible insect-based products.

Listeria monocytogenes contamination of Tenebrio molitor larvae rearing substrate: Preliminary evaluations

Today, edible insects represent a hot topic as an emerging and eco-friendly source of protein. The mealworm (Tenebrio molitor L.) is among the most employed insects for human consumption and feed purposes. So far Listeria monocytogenes, have never been detected either in products sold on the market or during the rearing process. In this study, the substrate employed for mealworm rearing was deliberately contaminated with L. monocytogenes and the bacterium was enumerated during the rearing period and after technological treatments of the larvae. L. monocytogenes persisted during the rearing period. Washing the larvae did not produce any significant effect, while fasting the larvae for 24 or 48 h reduced the L. monocytogenes load (P < 0.001). Oven cooking eliminated L. monocytogenes cells from the product, reducing the risk associated to this foodborne pathogen to zero.

Assessing the Microbiota of Black Soldier Fly Larvae (Hermetia illucens) Reared on Organic Waste Streams on Four Different Locations at Laboratory and Large Scale

This study aimed to gain insight into the microbial quality, safety and bacterial community composition of black soldier fly larvae (Hermetia illucens) reared at different facilities on a variety of organic waste streams. For seven rearing cycles, both on laboratory-scale and in large-scale facilities at several locations, the microbiota of the larvae was studied. Also samples of the substrate used and the residue (= leftover substrate after rearing, existing of non-consumed substrate, exuviae and faeces) were investigated. Depending on the sample, it was subjected to plate counting, Illumina Miseq sequencing and/or detection of specific food pathogens. The results revealed that the substrates applied at the various locations differed substantially in microbial numbers as well as in the bacterial community composition. Furthermore, little similarity was observed between the microbiota of the substrate and that of the larvae reared on that substrate. Despite substantial differences between the microbiota of larvae reared at several locations, 48 species-level operational taxonomic units (OTUs) were shared by all larvae, among which most belonged to the phyla Firmicutes and Proteobacteria. Although the substrate is assumed to be an important source of bacteria, our results suggest that a variety of supposedly interacting factors-both abiotic and biotic-are likely to affect the microbiota in the larvae. In some larvae and/or residue samples, potential foodborne pathogens such as Salmonella and Bacillus cereus were detected, emphasising that decontamination technologies are required when the larvae are used in feed, just as for other feed ingredients, or eventually in food.

Portable Rice Disease Spores Capture and Detection Method Using Diffraction Fingerprints on Microfluidic Chip

Crop diseases cause great harm to food security, 90% of these are caused by fungal spores. This paper proposes a crop diseases spore detection method, based on the lensfree diffraction fingerprint and microfluidic chip. The spore diffraction images are obtained by a designed large field of view lensless diffraction detection platform which contains the spore enrichment microfluidic chip and lensless imaging module. By using the microfluidic chip to enrich and isolate spores in advance, the required particles can be captured in the chip enrichment area, and other impurities can be filtered to reduce the interference of impurities on spore detection. The light source emits partially coherent light and irradiates the target to generate diffraction fingerprints, which can be used to distinguish spores and impurities. According to the theoretical analysis, two parameters, Peak to Center ratio (PCR) and Peak to Valley ratio (PVR), are found to quantify these spores. The correlation coefficient between the detection results of rice blast spores by the constructed device and the results of microscopic artificial identification was up to 0.99, and the average error rate of the proposed device was only 5.91%. The size of the device is only 4 cm × 4 cm × 5 cm, and the cost is less than $150, which is one thousandth of the existing equipment. Therefore, it may be widely used as an early detection method for crop disease caused by spores.