Bacterial Communities Changes during Food Waste Spoilage

Aeration promotes Proteobacteria over Firmicutes in macerated food waste, resulting in superior anaerobic digestion efficiency

Aeration is a common pretreatment method to enhance biogas production via anaerobic digestion of waste organic feedstocks such as unused food. While impacts on downstream anaerobic digestion have been intensively investigated, the consequence of aeration on the microbial community in food waste has not been characterized. Food waste has a low pH resulting from the dominance of lactic acid bacteria within the Firmicutes phylum. This excludes other phylotypes with a higher potential to hydrolyse complex biopolymers in food waste. In this study, we reveal that aeration of macerated food waste results in a dramatic shift away from Firmicutes towards dominance of Proteobacteria that are better known for extracellular enzyme production. Given that hydrolysis is the rate limiting step in anaerobic digestion, this explains why aeration improves the efficiency of biogas production from food waste. The discovery that Proteobacteria dominate microbial communities in aerated food waste opens up opportunities to manipulate extracellular enzyme production through gene expression mechanisms common among Proteobacteria such as quorum sensing.

Deeper insight into the storage time of food waste on black soldier fly larvae growth and nutritive value: Interactions of substrate and gut microorganisms

Biological treatment of food waste (FW) by black soldier fly larvae (BSFL) is considered as an effective management strategy. The composition and concentrations of nutrients in FW change during its storage and transport period, which potentially affect the FW conversion and BSFL growth. The present study systematically investigated the effect of different storage times (i.e., 0-15 d) on FW characteristics and its substantial influence on the BSFL growth. Results showed that the highest larvae weight of 282 mg and the shortest growth time of 14 days were achieved at the group of FW stored for 15 days, but shorter storage time (i.e., 2-7 d) had adverse effect on BSFL growth. Short storage time (i.e., 2-4 d) improved protein content of BSFL biomass and prolonged storage time (i.e., 7-10 d) led to the accumulation of fat content. The changes of substrate characteristics and indigenous microorganisms via FW storage time were the main reasons for BSFL growth difference. Lactic acid (LA) accumulation (i.e., 19.84 g/L) in FW storage for 7 days significantly limited the BSFL growth, leading to lowest larvae weight. Both the substrate and BSFL gut contained same bacterial communities (e.g., Klebsiella and Proteus), which exhibited similar change trend with the prolonged storage time. The transfer of Clostridioides from substrate to BSFL gut promoted nutrients digestion and intestinal flora balance with the FW stored for 15 days. Pathogens (e.g., Acinetobacter) in BSFL gut feeding with FW storage time of 7 days led to the decreased digestive function, consistent with the lowest larvae weight. Overall, shorter storage time (i.e., 2-7 d) inhibited the BSFL digestive function and growth performance, while the balance of the substrate nutrients and intestinal flora promoted the BSFL growth when using the FW stored for 15 days.

Timeframe of aerobic biodegradation of bioplastics differs under standard conditions and conditions simulating technological composting with biowaste

To determine the actual timeframe of biodegradation, bioplastics (BPs) (based on polylactic acid (PLA), starch (FS), polybutylene succinate (PBS), cellulose (Cel)) were degraded with biowaste (B), which simulates real substrate technological conditions during composting. For comparison, standard conditions (with mature compost (C)) were also applied. The 90-day aerobic tests, both with C or B, were carried out at 58 ± 2 °C. This comparison enables understanding of how BPs behave in real substrate conditions and how C and B affect the time or completeness of degradation based on oxygen consumption (OC) for BPs, the ratio of OC to theoretical oxygen consumption (OC/Th-O2), and the decrease in volatile solids (VS). Additionally, for deeper insight into the biodegradation process, microscopic, microbial (based on 16S rDNA), FTIR, and mechanical (tensile strength, elongation at break) analyses were performed. There was no association between the initial mechanical properties of BPs and the time necessary for their biodegradation. BPs lost their mechanical properties and remained visible for a shorter time when degraded with C than with B. OC for Cel, FS, PLA, and PBS biodegradation was 1143, 1654, 1748, and 1211g O2/kg, respectively, which amounted to 83, 70, 69, and 60% of the theoretical OC (Th-O2), respectively. Intensive OC took place at the same time as an intensive decrease in VS content. With C, Cel was most susceptible to biodegradation (completely biodegrading within 11 days), and PLA was least susceptible (requiring 70 days for complete biodegradation). With B, however, the time required for biodegradation was generally longer, and the differences in the time needed for complete biodegradation were smaller, ranging from 45 d (FS) to 75 d (PLA). The use of C or B had the greatest effect on Cel biodegradation (10 d vs 62 d, respectively), and the least effect on PLA (70 d vs 75 d). Specific bacterial and fungal community structures were identified as potential BP biodegraders; the communities depended on the type of BPs and the substrate conditions. In conclusion, the time needed for biodegradation of these BPs varied widely depending on the specific bioplastic and the substrate conditions; the biodegradability decreased in the following order: Cel ≫ FS ≫ PBS ≫ PLA with C and FS ≫ Cel = PBS ≫ PLA with B. The biodegradability ranking of BPs with B was assumed to be ultimate as it simulates the real substrate conditions during composting. However, all of the BPs completely biodegraded in less than 90 days.

An Overview of Advanced Antimicrobial Food Packaging: Emphasizing Antimicrobial Agents and Polymer-Based Films

The food industry is increasingly focused on maintaining the quality and safety of food products as consumers are becoming more health conscious and seeking fresh, minimally processed foods. However, deterioration and spoilage caused by foodborne pathogens continue to pose significant challenges, leading to decreased shelf life and quality. To overcome this issue, the food industry and researchers are exploring new approaches to prevent microbial growth in food, while preserving its nutritional value and safety. Active packaging, including antimicrobial packaging, has gained considerable attention among current food packaging methods owing to the wide range of materials used, application methods, and their ability to protect various food products. Both direct and indirect methods can be used to improve food safety and quality by incorporating antimicrobial compounds into the food packaging materials. This comprehensive review focuses on natural and synthetic antimicrobial substances and polymer-based films, and their mechanisms and applications in packaging systems. The properties of these materials are compared, and the persistent challenges in the field of active packaging are emphasized. Specifically, there is a need to achieve the controlled release of antimicrobial agents and develop active packaging materials that possess the necessary mechanical and barrier properties, as well as other characteristics essential for ensuring food protection and safety, particularly bio-based packaging materials.

A comprehensive study of food waste management and processing in the Czech Republic: Potential health risks and consumer behavior

Food waste is currently a widely discussed phenomenon with significant economic and social consequences. One third of the food produced in the world is wasted at various points along the food supply chain. This article presents a comprehensive study that examines consumer behavior in dealing with food waste and activities in the composting process that enable waste sanitation. The survey conducted as part of this study showed that consumers want to eliminate odors, are concerned about potential infections, and generally sort less food waste. This study suggested that the addition of appropriate additives could be a solution. The results indicated that additives could eliminate negative side effects such as unpleasant odors, the presence of insects and rodents, and act as a prevention of the occurrence of pathogenic organisms. Tea tree oil showed the best positive physical and chemical properties among the additives tested (CaCO3 and citric acid) with a significant effect on inhibiting the growth of bacterial strains such as Salmonella strains and had the strongest antibacterial effect, neutralized unpleasant odors, and stabilized the waste. The use of additives could be a future solution to meet consumer demands, improve the quality of food waste and advance the circular economy to improve the sustainability of agricultural systems.

Ecotoxicological impacts of landfill sites: Towards risk assessment, mitigation policies and the role of artificial intelligence

Waste disposal in landfills remains a global concern. Despite technological developments, landfill leachate poses a hazard to ecosystems and human health since it acts as a secondary reservoir for legacy and emerging pollutants. This study provides a systematic and scientometric review of the nature and toxicity of pollutants generated by landfills and means of assessing their potential risks. Regarding human health, unregulated waste disposal and pathogens in leachate are the leading causes of diseases reported in local populations. Both in vitro and in vivo approaches have been employed in the ecotoxicological risk assessment of landfill leachate, with model organisms ranging from bacteria to birds. These studies demonstrate a wide range of toxic effects that reflect the complex composition of leachate and geographical variations in climate, resource availability and management practices. Based on bioassay (and other) evidence, categories of persistent chemicals of most concern include brominated flame retardants, per- and polyfluorinated chemicals, pharmaceuticals and alkyl phenol ethoxylates. However, the emerging and more general literature on microplastic toxicity suggests that these particles might also be problematic in leachate. Various mitigation strategies have been identified, with most focussing on improving landfill design or leachate treatment, developing alternative disposal methods and reducing waste volume through recycling or using more sustainable materials. The success of these efforts will rely on policies and practices and their enforcement, which is seen as a particular challenge in developing nations and at the international (and transboundary) level. Artificial intelligence and machine learning afford a wide range of options for evaluating and reducing the risks associated with leachates and gaseous emissions from landfills, and various approaches tested or having potential are discussed. However, addressing the limitations in data collection, model accuracy, real-time monitoring and our understanding of environmental impacts will be critical for realising this potential.

Evaluation of the Microbial Quality of Hermetia illucens Larvae for Animal Feed and Human Consumption: Study of Different Type of Rearing Substrates

In the context of climate change and depletion of natural resources, meeting the growing demand for animal feed and human food through sufficient, nutritious, safe, and affordable sources of protein is becoming a priority. The use of Hermetia illucens, the black soldier fly (BSF), has emerged as a strategy to enhance the circularity of the agri-food chain, but its microbiological safety remains a concern. The aim of the present study was to systematically review available data on the microbiological quality of BSF and to investigate the impact of using four different rearing substrates including classic options allowed by the EU regulation (cereals, fruits, vegetables) and options not allowed by EU regulations regarding vegetable agri-food (co-products, food at shelf life, and meat). A total of 13 studies were collected and synthesized, including 910 sample results, while 102 new sample results were collected from the present experiments in three farms. Both datasets combined revealed a high level of contamination of larvae, potentially transmitted through the substrate. The main pathogenic bacteria identified were Bacillus cereus, Clostridium perfringens, Cronobacter spp., Escherichia coli, Salmonella spp., and Staphylococcus aureus coagulase-positive, while Campylobacter spp. and Listeria monocytogenes were not detected. Any of these four substrates were excluded for their use in insect rearing; however, safety concerns were confirmed and must be managed by the operators of the sector using microbial inactivation treatment after the harvest of the larvae in order to propose safe products for the market. The results obtained will guide the definition of the control criteria and optimize the following manufacturing steps.

Revealing the effects of fermented food waste on the growth and intestinal microorganisms of black soldier fly (Hermetia illucens) larvae

The escalating global food waste (FW) issues necessitate sustainable management strategies. Black soldier fly larvae (BSFL) offer a promising solution for FW management by converting organic matter into insect protein. However, the fermentation of FW during production, collection, and transportation induces changes in FW's physicochemical properties and bacterial communities, requiring further exploration of its impact on BSFL growth and gut microbiota. The results showed that feeding FW fermented for different durations (0-10 d) slightly affected the BSFL yield. Feeding FW fermented for 8 d, characterized by a lower pH and higher biodiversity, resulted in a slight increase in larval biomass (222 mg/larvae). Nearly all groups harvested the peak larval biomass after 10 day's bioconversion. The fermentation significantly altered the microbial community of FW, with an increase in the abundance of unclassified_f_Clostridiaceae and a decrease in Lactobacillus abundance. As bioconversion progressed, intricate and mutualistic microbial interactions likely occurred between the BSFL gut and FW substrate, restructuring each other's microbial community. Specifically, the abundance of unclassified_f_Clostridiaceae increased in the BSFL gut, while its abundance in the initial larval gut was extremely low (<1 %). Despite the substrate microbial changes and interactions, a stable core gut microbiota was identified across all BSFL samples, primarily composed of nine genera dominated by Enterococcus and Klebsiella. This core gut microbiome may play a crucial role in facilitating the adaptation of BSFL to various environmental conditions and maintaining efficient FW bioconversion. These findings enhance our understanding of the role of BSFL gut microbiota in FW bioconversion.

A biochemical analysis of Black Soldier fly (Hermetia illucens) larval frass plant growth promoting activity

Black Soldier fly (Hermetia illucens) larval (BSFL) frass was examined for its nutrient nitrogen, phosphate and potassium (N:P205:K2O), phytohormone and biogenic amine content, its plant growth promoting activity, and screened to test the hypothesis that bacteria characteristic of the genus Enterococcus (present in the biome of decaying catering waste and the larval gut) are excreted by BSFL in their frass. Frass plant growth promoting activity was measured by comparing the growth of winter wheat berry (Triticum aestivum) in frass treated soil to that of untreated (control) soil. The N:P205:K2O percent dry matter average, biogenic amine and phytohormone content of frass was determined by standard soil analysis, HPLC and HPLC/GC-MS methodologies, respectively. All were at too low of concentrations to account for its plant growth promoting activity. Frass added to soil induced a 11% increase in aerial mass and shoot length in treated plants over controls. Numerous colonies of Enterococci growing out on BEA (bile-esculin-agar) plates were detected in frass collected directly from larvae confirming the hypothesis that viable Enteroccoci are passing from the larval gut into their frass. Since a number of rhizobacteria, including Enterococci, have previously been identified as part of the larval gut biome, the passage of Enterococci from the larval gut into frass in the face of only trace N:P205:K2O percent dry matter averages, biogenic amine and phytohormone content is consistent with the hypothesis that Enterococci exhibiting rhizobacterial activity have a role in conferring to frass its plant growth promoting activity.

Converting food waste into soil amendments for improving soil sustainability and crop productivity: A review

One-third of the annual food produced globally is wasted and much of the food waste (FW) is unutilized; however, FW can be valorized into value-added industrial products such as biofuel, chemicals, and biomaterials. Converting FW into soil amendments such as compost, vermicompost, anaerobic digestate, biofertilizer, biochar, and engineered biochar is one of the best nutrient recovery and FW reuse approaches. The soil application of FW-based amendments can improve soil fertility, increase crop production, and reduce contaminants by altering soil's chemical, physical, microbial, and faunal properties. However, the efficiency of the amendment for improving ecosystem sustainability depends on the type of FW, conversion method, application rate, soil type, and crop type. Engineered biochar/biochar composite materials produced using FW have been identified as promising amendments for soil remediation, reducing commercial fertilizer usage, and increasing soil nutrient use efficiency. The development of quality standards and implementation of policies and regulations at all stages of the food supply chain are necessary to manage (reduce and re-use) FW.

Highly efficient oriented bioconversion of food waste to lactic acid in an open system: Microbial community analysis and biological carbon fixation evaluation

The valorization of organic solid waste to lactic acid (LA) in open fermentation systems has attracted tremendous interest in recent years. In this study, a highly efficient oriented LA bioconversion system from food waste (FW) in open mode was established. The maximum LA production was 115 g/L, with a high yield of 0.97 g-LA/g-total sugar. FW is a low-cost feedstock for LA production, containing indigenous hydrolysis and LA-producing bacteria (LAB). Saccharification and real-time pH control were found to be essential for maintaining LAB dominantly in open systems. Furthermore, microbial community analysis revealed that Enterococcus mundtii adapted to complex FW substrates and dominated the subsequent bioconversion process. The oriented LA bioconversion exhibited the capacity for biological carbon fixation by reducing CO₂ emissions by at least 21 kg per ton of FW under anaerobic conditions.

Sensory Evaluation and Model Prediction of Vacuum-Packed Fresh Corn during Long-Term Storage

The postharvest shelf life of fresh corn largely depends on the packaging method and storage temperature. This study investigated the effect of vacuum packaging (VP) with high-barrier (HB) or ordinary (OR) nylon/nylon/polypropylene (PP) composite films and the impact of storage temperature (4, 25, and 38 °C) on the shelf life of fresh corn. The sensory quality and color changes of the corn were evaluated, indicating a significant improvement in the glossiness (GL), sourness (SO), and color changes compared to corn packaged using OR films. The results showed that the HB films preserved corn freshness under refrigerated and normal temperature storage conditions, delaying color changes and SO development. A shelf-life model was established based on the Arrhenius equation. The predicted values of the corn at different temperatures were compared with the experimental data, indicating that the model could accurately predict the shelf life. The shelf life observed via sensory evaluation was more than 50% shorter than the results obtained by instrumental measurements. Therefore, sensory evaluation could be applied to determine shelf life and avoid food waste.

Domestic refrigerators: An overlooked breeding ground of antibiotic resistance genes and pathogens

Domestic refrigerator is a widely used appliance to keep food fresh and retard food spoilage in household. However, our understanding of microbial health risk associated with food under such circumstance still remains very poor. Here, typical types of food (vegetable, fish, and pork) were kept in a domestic refrigerator at 4 °C for 3-30 days. Temporal dynamics of antibiotic resistome, pathogens, bacterial and fungal communities during this period were investigated via high-throughput quantification and Illumina sequencing technologies. Results showed that a large number (21-134) of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) were detected across the three food types, including 10.06 % of high-risk ARGs classified by their risk ranks. Moreover, four bacterial pathogens (i.e., Bacillus cereus, Cronobacter spp., Klebsiella pneumoniae and Staphylococcus aureus) targeted by marker genes including the pathogen-specific genes or virulence factor genes, and some potential fungal pathogens (e.g., Fusarium, Candida, and Aspergillus) were detected, indicating the occurrence of microbial risk even at the normally regarded safe storage temperature. Among all food types, the total bacterial density and ARG abundances in fish rapidly increased after only 3 days, much faster than vegetable and pork after 10 days. In addition, fish samples contained the highest ARG and pathogen abundances, indicating its potentially higher health risk than other food types. Finally, the shifts of ARG pattern were mainly contributed by bacterial communities and MGEs. This study highlights that food preserved in refrigerator at 4 °C could still be an unneglected microbial risk, and raises awareness of improving food safety in domestic environment.

Cold chain relevance in the food safety of perishable products

The food cold chain is an effective tool that allows food markets to maintain food quality and reduce losses. Poor logistics may result in foodborne disease outbreaks and greenhouse gas emissions caused by organic matter decay. The ongoing pandemic of COVID-19 makes it necessary to study the chances of SARS-CoV-2 transmissions in food products. This study reviews cold chain logistics as a handy tool for avoiding food safety risks, including COVID-19. The cold chain of perishables and its proper management make it possible to maintain quality and safety at any stage of the food supply chain. The technology covers each link of the food chain to prevent microbial spoilage caused by temperature fluctuations and the contamination with SARS-CoV-2 associated with perishable foods. Given the lack of knowledge in this field in Latin America, the region needs new research to determine the impact of the cold chain on perishable foodstuffs. The perishable cold chain is only as strong as its weakest link, and the national and international markets require new traceability protocols to minimize the effect of COVID-19.

Temporal variation of antibiotic resistome and pathogens in food waste during short-term storage

The massive food wastes pose a growing health concern for spreading of antibiotic resistance and pathogens due to food spoilage. However, little is known about these microbial hazards during collection, classification, and transportation before eventual treatment. Here, we profiled the temporal variations of antibiotic resistance genes (ARGs), pathogens, bacterial and fungal communities across four typical food wastes (vegetable, fish, meat, and rice) during storage at room temperature in summer (maximum 28-29 °C) of typical southeast city in China. A total of 171 ARGs and 32 mobile genetic elements were detected, and the absolute abundance of ARGs significantly increased by up to 126-fold with the storage time. Additionally, five bacterial pathogens containing virulence factor genes were detected, and Klebsiella pneumoniae was persistently detected throughout the storage time in all food types except rice. Moreover, fungal pathogens (e.g., Aspergillus, Penicillium, and Fusarium) were also frequently detected. Notably, animal food wastes were demonstrated to harbor higher abundance of ARGs and more types of pathogens, indicating a higher level of hazard. Mobile genetic elements and food types were demonstrated to mainly impact ARG profiles and pathogens, respectively. This work provides a comprehensive understanding of the microbial hazards associated with food waste recycling, and will contribute to optimize the food waste management to ensure biosecurity and benefit human health.

Physical, chemical, and microbial contaminants in food waste management for soil application: A review

Currently, 1.3 billion tonnes of food are thrown away each year, most of which are incinerated or landfilled causing large environmental, social, and economic issues. Therefore, the utilisation of food waste as biofertilisers, such as composts and digestates, is a solution to reduce the problems created by incineration and landfilling whilst simultaneously amending soils. The improper disposal of food wastes and bulking materials can contribute to high levels of contaminants within the end-product. Moreover, the food waste and bulking materials, themselves, may contain trace amounts of contaminants. These contaminants tend to have long half-lives, are easily mobile within soil and plants, can accumulate within the food supply chain, and have moderate to high levels of toxicity. This review aims to examine the current and emerging contaminants of high concern that impact the quality of food-waste fertilisers. The paper presents the volume of current and emerging contaminants of plastics, other physical (particulate) contaminants, heavy metals, pesticides, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), per- and polyfluoroalkyl substances (PFAS), and pathogens within food-waste composts and digestates. Due to the large extent of organic chemical contaminants and the unknown level of toxicity and persistence, the risk assessment of organic chemical contaminants in the food-supply chain remains largely unknown. This study has presented available data from literature of various contaminants found in food waste, and composts and digestates derived from food waste, and evaluated the data with current regulations globally. Overall, to reduce contaminants in composts and digestates, more studies are required on the implementation of proper disposal separation, effective composting and digestion practices, increased screening of physical contaminants, development of compostable plastics, and increased regulatory policies on emerging, problematic contaminants. Moreover, examination of emerging contaminants in food-waste composts and digestates is needed to ensure food security and reduce future human-health risks.

The pathogenic and spoilage bacteria associated with red meat and application of different approaches of high CO2 packaging to extend product shelf-life

With the fast-global development of packaging techniques, the potential antimicrobial effect of CO₂, as a safe, cheap and readily available gas, makes it the integral component for packaging of meat products. The associated spoilage and/or pathogenic bacteria on raw meat may respond in different ways to elevated CO₂ concentrations. The growth of some aerobic Gram-negative bacteria such as Pseudomonas spp. is significantly inhibited but some LAB bacteria may be allowed to grow faster and dominate the product. The antimicrobial efficacy of enriched CO₂ packaging is attributed to the rate of CO₂ solubility in the product which is itself affected by the level of headspace CO₂, product pH, temperature and the ratio of headspace gas to product (G:P). This review, first, explores the varied range of beef and sheep meat spoilage and pathogenic bacteria and the intrinsic and extrinsic parameters that may influence the pattern of microbial growth and meat spoilage rate during storage. Then, the antimicrobial mechanism of elevated CO₂ packaging will be discussed and the different approaches of achieving enriched CO₂ packaging i.e. the traditional technique of flushing a desired gas mixture and/or using the new commercially developed CO₂ emitters will then be compared in terms of their strengths, limitations and technical mode of action.

Potential Environmental and Human Health Risks Caused by Antibiotic-Resistant Bacteria (ARB), Antibiotic Resistance Genes (ARGs) and Emerging Contaminants (ECs) from Municipal Solid Waste (MSW) Landfill

The disposal of municipal solid waste (MSW) directly at landfills or open dump areas, without segregation and treatment, is a significant concern due to its hazardous contents of antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARGs), and metal resistance genes (MGEs). The released leachate from landfills greatly effects the soil physicochemical, biological, and groundwater properties associated with agricultural activity and human health. The abundance of ARB, ARGs, and MGEs have been reported worldwide, including MSW landfill sites, animal husbandry, wastewater, groundwater, soil, and aerosol. This review elucidates the occurrence and abundance of ARB, ARGs, and MRGs, which are regarded as emerging contaminants (ECs). Recently, ECs have received global attention because of their prevalence in leachate as a substantial threat to environmental and public health, including an economic burden for developing nations. The present review exclusively discusses the demands to develop a novel eco-friendly management strategy to combat these global issues. This review also gives an intrinsic discussion about the insights of different aspects of environmental and public health concerns caused due to massive leachate generation, the abundance of antibiotics resistance (AR), and the effects of released leachate on the various environmental reservoirs and human health. Furthermore, the current review throws light on the source and fate of different ECs of landfill leachate and their possible impact on the nearby environments (groundwater, surface water, and soil) affecting human health. The present review strongly suggests the demand for future research focuses on the advancement of the removal efficiency of contaminants with the improvement of relevant landfill management to reduce the potential effects of disposable waste. We propose the necessity of the identification and monitoring of potential environmental and human health risks associated with landfill leachate contaminants.

Impact of Processed Food (Canteen and Oil Wastes) on the Development of Black Soldier Fly (Hermetia illucens) Larvae and Their Gut Microbiome Functions

Canteens represent an essential food supply hub for educational institutions, companies, and business parks. Many people in these locations rely on a guaranteed service with consistent quality. It is an ongoing challenge to satisfy the demand for sufficient serving numbers, portion sizes, and menu variations to cover food intolerances and different palates of customers. However, overestimating this demand or fluctuating quality of dishes leads to an inevitable loss of unconsumed food due to leftovers. In this study, the food waste fraction of canteen leftovers was identified as an optimal diet for black soldier fly (Hermetia illucens) larvae based on 50% higher consumption and 15% higher waste reduction indices compared with control chicken feed diet. Although the digestibility of food waste was nearly twice as high, the conversion efficiency of ingested and digested chicken feed remains unparalleled (17.9 ± 0.6 and 37.5 ± 0.9 in CFD and 7.9 ± 0.9 and 9.6 ± 1.0 in FWD, respectively). The oil separator waste fraction, however, inhibited biomass gain by at least 85% and ultimately led to a larval mortality of up to 96%. In addition to monitoring larval development, we characterized physicochemical properties of pre- and post-process food waste substrates. High-throughput amplicon sequencing identified Firmicutes, Proteobacteria, and Bacteroidota as the most abundant phyla, and Morganella, Acinetobacter, and certain Lactobacillales species were identified as indicator species. By using metagenome imputation, we additionally gained insights into the functional spectrum of gut microbial communities. We anticipate that the results will contribute to the development of decentralized waste-management sites that make use of larvae to process food waste as it has become common practice for biogas plants.

Identification of Bacteria in Two Food Waste Black Soldier Fly Larvae Rearing Residues

Significant economic, environmental, and social impacts are associated with the avoidable disposal of foods worldwide. Mass-rearing of black soldier fly (Hermetia illucens) larvae using organic wastes and food- and agro-industry side products is promising for recycling resources within the food system. One current challenge of this approach is ensuring a reliable and high conversion performance of larvae with inherently variable substrates. Research has been devoted to increasing rearing performance by optimizing substrate nutrient contents and ratios, while the potential of the substrate and larval gut microbiota to increase rearing performance remains untapped. Since previous research has focused on gut microbiota, here, we describe bacterial dynamics in the residue (i.e., the mixture of frass and substrate) of black soldier fly larvae reared on two food wastes (i.e., canteen and household waste). To identify members of the substrate and residue microbiota, potentially associated with rearing performance, bacterial dynamics were also studied in the canteen waste without larvae, and after inactivation by irradiation of the initial microbiota in canteen waste. The food waste substrates had similar microbiota; both were dominated by common lactic acid bacteria. Inactivation of the canteen waste microbiota, which was dominated by Leuconostoc, Bacillus, and Staphylococcus, decreased the levels of all rearing performance indicators by 31-46% relative to canteen waste with the native microbiota. In both food waste substrates, larval rearing decreased the bacterial richness and changed the physicochemical residue properties and composition over the rearing period of 12 days, and typical members of the larval intestinal microbiota (i.e., Providencia, Dysgonomonas, Morganella, and Proteus) became more abundant, suggesting their transfer into the residue through excretions. Future studies should isolate members of these taxa and elucidate their true potential to influence black soldier fly mass-rearing performance.

Batch-Mode Analysis of Thermophilic Methanogenic Microbial Community Changes in the Overacidification Stage in Beverage Waste Treatment

Biogasification by methane fermentation is an important and effective way to utilize beverage wastes. Beverage wastes are good feedstocks for methane fermentation because of their richness in sugars and proteins, although overacidification and inhibition of methane production caused by high substrate loading often become problematic. This study investigated changes in microbial communities in the overacidification state of the thermophilic methane fermentation process with beverage waste by establishing a simulated batch culture. We assessed 20 mL-scale batch cultures using a simulant beverage waste mixture (SBWM) with different amounts of addition; high cumulative methane production was achieved by adding 5 mL of SBWM (11358 mg-chemical oxygen demand-COD/L of organic loading), and overacidification was observed by adding 10 mL of SBWM (22715 mg-COD/L of organic loading). The results of 16S rRNA amplicon sequence analysis using nanopore sequencer suggested that Coprothermobacter proteolyticus, Defluviitoga tunisiensis, Acetomicrobium mobile, and Thermosediminibacter oceani were predominantly involved in hydrolysis/acidogenesis/acetogenesis processes, whereas Methanothrix soehngenii was the major acetotrophic methane producer. A comparison of microbial population between the methane-producing cultures and overacidification cultures revealed characteristic population changes especially in some minor species under 0.2% of population. We concluded that careful monitoring of population changes of the minor species is a potential indicator for prediction of overacidification.

Non-sterile fermentation of food waste with indigenous consortium and yeast - Effects on microbial community and product spectrum

This work presents examples of non-sterile mixed culture fermentation of food waste with a cultivated indigenous consortium (IC) gained from food waste, which produces lactic and acetic acids, combined with Saccharomyces cerevisiae, which produces ethanol. All results are flanked by microbial analysis to monitor changes in microbial community. At pH 6 and inoculated with yeast or IC, or both mixed sugars conversion was equal to 71%, 51%, or 67%, respectively. Under pH unregulated conditions metabolic yields were 71%, 67%, or up to 81%. While final titer of acetic acid was not affected by pH (100-200 mM), ethanol and lactic acid titers were. Using mixed culture and pH 6, sugars were almost equally used for formation of ethanol and lactic acid (400-500 mM). However, under pH unregulated conditions 80% of the substrate was converted into ethanol (900-1000 mM).

Techno-economic assessment of non-sterile batch and continuous production of lactic acid from food waste

Non-sterile lactic acid (LA) fermentation of highly viscous food waste was demonstrated in batch and continuous flow fermentations. With Streptococcus sp., an indigenous consortium, and/or applied glucoamylase, food waste was fermented without addition of external carbon or nitrogen sources. Experimental results were used for economic and energy evaluations under consideration of different catchment area sizes from 50,000 to 1,000,000 inhabitants. During batch mode, addition of glucoamylase resulted in a titer (after 24 h), yield, and productivity of 50 g L^-1, 63%, and 2.93 g L^-1h^-1, respectively. While titer and yield were enhanced, productivity was lower during continuous operation and 69 g L^-1, 86%, and 1.27 g L^-1h^-1 were obtained at a dilution rate of 0.44 d^-1 when glucoamylase was added. Both batch and continuous flow fermentations were found economically profitable with food waste from 200,000 or more inhabitants.