Involvement of phenoloxidase in browning during grinding of Tenebrio molitor larvae

First Optimization of Tomato Pomace in Diets for Tenebrio molitor (L.) (Coleoptera: Tenebrionidae)

Tomato pomace (TP), an agricultural industrial waste product from the tomato processing industry, is valorized as a rearing substrate for Tenebrio molitor (L.). This study evaluated bran-based diets with increasing tomato pomace (0%, 27%, 41%, and 100%). Protein sources, such as brewer's spent grain and yeast, were used in TP27 and TP41 diets to ensure equal protein contents to the control diet. Results showed no different for larval and pupal weights between diets; however, the time of development significantly increases in TP100 compared to all diets. The feed conversion rate progressively increases from 2.7 to 4.3, respectively, from the control to the TP100 diet. Conversely, lycopene and β-carotene increase in the larvae. The fatty acid composition improves by increasing polyunsaturated fatty acids (mainly α-linoleic acid). Although the best nutritional quality was obtained in T100, the TP41 is the optimal diet for balance between larval performance and qualitative improvement of larvae. Therefore, tomato pomace is suitable for the formulation of mealworm diets, even in high dosages, when supplemented with sustainable protein and carbohydrate sources.

Optimization of the Heat-Drying Conditions of Drone Pupae by Response Surface Methodology (RSM)

Recent research has been conducted on various types of pre-processing methods for insects, including freeze-drying, microwave drying, hot air heat drying, and non-heat drying. This study aimed to identify the factors that have the greatest impact on heat drying conditions and establish the optimal heat drying conditions for drone pupae (Apis melifera L.) using response surface methodology (RSM) to minimize quality changes. Drone pupae were treated under various conditions, including blanching time (53-187 s) (X1), drying temperatures (41.6-58.4 °C) (X2), and drying time (266-434 min) (X3). The effect of these treatments on response variables, including the color parameter (WI, YI, BI, △E, and BD), AV, and TB of the dried drone pupae, was evaluated using a central composite design. The whole design consisted of 20 experimental points carried out in random order, which included eight factorial points, six center points, and six axial points. The optimal drying conditions for drone pupae were determined to be a blanching time of 58 s, a drying temperature of 56.7 °C, and a drying time of 298 min. The response variables were most affected by drying temperature and drying time and to a lesser extent by blanching time. The processed drone pupae using the optimized drying conditions resulted in the color parameters (WI, BI, YI, ΔE, and BD) being found to be 66.67, 21.33, 26.27, 31.27 and 0.13, respectively. And TB (log CFU/g) and AV (mg/g) values were found to be 3.12 and 4.33, respectively. The estimated and actual values for dried drone pupae showed no significant difference (p < 0.05). Comparing the physicochemical and microbiological properties of freeze-dried and optimal heat-dried drone pupae, the L and b value as well as PV were significantly lower in the heat-dried samples, while no significant difference was observed in the a value and AV (p < 0.05). Our study suggests that the model we developed can be applied to the large-scale production of drying conditions for use in the pharmaceutical and food industries.

Safety of UV-treated powder of whole yellow mealworm (Tenebrio molitor larva) as a novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on UV-treated powder of whole yellow mealworm (Tenebrio molitor larva) as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The term yellow mealworm refers to the larval form of the insect species T. molitor. The NF is the UV-treated powder of the whole, thermally dried yellow mealworm. The NF consists mainly of crude protein, fat, digestible carbohydrates and fibre (chitin). The Panel notes that the levels of contaminants in the NF highly depend on the occurrence levels of these substances in the insect feed. The Panel notes furthermore that there are no safety concerns regarding the stability of the NF if the NF complies with the proposed specification limits during its entire shelf life. The NF has a high protein content, although the true protein content in the NF is overestimated when using the nitrogen-to-protein conversion factor of 6.25, due to the presence of non-protein nitrogen. The applicant proposed to use the NF as an ingredient in various food products, such as bakery products, pasta, compotes of fruit/vegetables and cheese. The target population is the general population. The Panel notes that considering the composition of the NF, the proposed conditions of use and that the NF will not be the sole source of dietary protein, the consumption of the NF is not nutritionally disadvantageous. Despite the UV treatment, the Panel notes that the NF is not a significant dietary contributor of vitamin D3. The submitted toxicity studies from the literature did not raise safety concerns. The Panel considers that the consumption of the NF may induce primary sensitisation and allergic reactions to yellow mealworm proteins and may cause allergic reactions in subjects with allergies to crustaceans and dust mites. Additionally, allergens from the feed may end up in the NF. With the exception of possible allergenicity, the Panel concludes that the NF is safe under the proposed uses and use levels.

Protein, lipid, and chitin fractions from insects: Method of extraction, functional properties, and potential applications

Edible insects are accepted as food and feed ingredients in many parts of the world. Insects account for more than 80% of animal kingdom providing rich biodiversity of protein and lipid profiles compared to conventional livestock. Insect biomasses contain an average of 35-62% protein, 3-57% lipid, and 3-12% chitin, and their nutritional values are widely recognized due to their presence, including minerals, and vitamins. While whole insects are consumed as eggs, larvae, pupae, or adults, there has been a recent uptick in interest to use fractions, e.g., protein, lipid, and chitin, as food and feed ingredients. To utilize these fractions in various food and feed preparations, a deeper understanding of the physicochemical as well as functional properties of the ingredients is required, which are generally impacted by extraction and preparation processes. Thus, the methods of extraction/purification are important to preserve the quality and functional properties of these ingredients. This paper discusses the extraction methods for insect protein, lipid, and chitin, their functional properties, and potential applications in food and feed applications.

Insect phenoloxidase and its diverse roles: melanogenesis and beyond

Insect life on earth is greatly diversified despite being exposed to several infectious agents due to their diverse habitats and ecological niche. One of the major factors responsible for their successful establishment is having a powerful innate immune system. The most common and effective method used by insects in recognizing pathogen and non-self-substances is the melanization process among others. The key enzyme involved in melanin biosynthesis is the copper containing humoral defense enzyme, phenoloxidase (PO). This review focused on understanding about PO and that had been in research for nearly a century. The review elaborates about evolutionary significance of PO in arthropods, its relationship with mammalian tyrosinases, various substrates, activators and inhibitors involved in the activation of phenoloxidase cascade, as it requires an integrated system of activation that vary among insect species. The enzyme also plays a vital role in insect immunity by involving in several other immune functions like sclerotization, wound healing, opsonization, encapsulation and nodule formation. Further, gene knock down or knock out of PO genes and inhibition of PO-melanization cascade by several mechanisms can also be considered as promising future alternative to control serious pests by making them highly susceptible to any targeted attack.

In Vitro Crude Protein Digestibility of Insects: A Review

The high protein content of insects has been widely studied. They can be a good food alternative, and therefore it is important to study the effect of digestion on their protein. This review examines the different in vitro protein digestibility methodologies used in the study of different edible insects in articles published up to 2021. The most important variables to be taken into account in in vitro hydrolysis are the following: phases (oral, gastric and intestinal), enzymes, incubation time and temperature, method of quantification of protein hydrolysis and sample preprocessing. Insects have high digestibility data, which can increase or decrease depending on the processing of the insect prior to digestion, so it is important to investigate which processing methods improve digestibility. The most commonly used methods are gut extraction, different methods of slaughtering (freezing or blanching), obtaining protein isolates, defatting, thermal processing (drying or cooking) and extrusion. Some limitations have been encountered in discussing the results due to the diversity of methodologies used for digestion and digestibility calculation. In addition, articles evaluating the effect of insect processing are very limited. It is concluded that there is a need for the standardisation of in vitro hydrolysis protocols and their quantification to facilitate comparisons in future research.

Safety of frozen and freeze‐dried formulations of the lesser mealworm (Alphitobius diaperinus larva) as a Novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on frozen and dried formulations from whole lesser mealworm (Alphitobius diaperinus larva) as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The term lesser mealworm refers to the larval form of the insect species Alphitobius diaperinus. The NF comprises the frozen and freeze‐dried formulations of the lesser mealworm as whole or in the form of a paste or powder. Apart from water in the frozen formulations (whole, paste), the main components of the NF are crude protein and fat, besides smaller amounts of digestible carbohydrates and fibre (chitin). The Panel notes that the levels of contaminants in the NF depend on the concentration of such substances in the insect feed. The Panel notes furthermore that the true protein levels in the NF are overestimated when using the nitrogen‐to‐protein conversion factor of 6.25, due to the presence of non‐protein nitrogen from chitin. The applicant proposed to use the NF formulations added as an ingredient to various food products such as cereal bars, pasta, meat imitates and bakery products. The target population is the general population. Additionally, the applicant proposed to use the NF as a food supplement in adults. The Panel notes that, considering that the NF will not be the sole source of dietary protein, and the composition of the NF and the proposed conditions of use, the consumption of the NF is not nutritionally disadvantageous. The submitted subchronic 90‐day toxicity study with the NF as testing material did not raise safety concerns. The Panel considers that the consumption of the NF may induce primary sensitisation and allergic reactions to lesser mealworm proteins and may cause allergic reactions in subjects with allergy to crustaceans and dust mites. Additionally, allergens from the feed may end up in the NF. Allergenicity aside, the Panel concludes that the NF is safe under the proposed uses and use levels.

Safety of frozen and dried formulations from whole yellow mealworm (Tenebrio molitor larva) as a novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on frozen and dried formulations from whole yellow mealworm (Tenebrio molitor larva) as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The term yellow mealworm refers to the larval form of the insect species Tenebrio molitor. The NF comprises the frozen and freeze-dried formulations of the yellow mealworm, whole or in the form of powder. The frozen formulation consists mainly of water, crude protein and fat whereas the freeze-dried formulations of crude protein, fat, digestible carbohydrates and fibre (chitin). The Panel notes that the levels of contaminants in the NF depend on the occurrence levels of these substances in the insect feed. The Panel notes furthermore that there are no safety concerns regarding the stability of the NF if the NF complies with the proposed specification limits during its entire shelf-life. The dried formulations of the NF have a high protein content, although the true protein levels in the NF are overestimated when using the nitrogen-to-protein conversion factor of 6.25, due to the presence of non-protein nitrogen from chitin. The applicant proposed to use the NF as whole frozen or whole dried insect, or in the form of powder, added as an ingredient to various food products such as cereal bars, pasta, meat imitates and bakery products. The target population is the general population. The Panel notes that, considering that the NF will not be the sole source of dietary protein, and the composition of the NF and the proposed conditions of use, the consumption of the NF is not nutritionally disadvantageous. The submitted toxicity studies from the literature did not raise safety concerns. The Panel considers that the consumption of the NF may induce primary sensitisation and allergic reactions to yellow mealworm proteins and may cause allergic reactions in subjects with allergy to crustaceans and dust mites. Additionally, allergens from the feed may end up in the NF. The Panel concludes that the NF is safe under the proposed uses and use levels.

Safety of dried yellow mealworm (Tenebrio molitor larva) as a novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on dried yellow mealworm (Tenebrio molitor larva) as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The term yellow mealworm refers to the larval form of the insect species Tenebrio molitor. The NF is the thermally dried yellow mealworm, either as whole dried insect or in the form of powder. The main components of the NF are protein, fat and fibre (chitin). The Panel notes that the levels of contaminants in the NF depend on the occurrence levels of these substances in the insect feed. The Panel notes that there are no safety concerns regarding the stability of the NF if the NF complies with the proposed specification limits during its entire shelf life. The NF has a high protein content, although the true protein levels in the NF are overestimated when using the nitrogen-to-protein conversion factor of 6.25, due to the presence of non-protein nitrogen from chitin. The applicant proposed to use the NF as whole, dried insect in the form of snacks, and as a food ingredient in a number of food products. The target population proposed by the applicant is the general population. The Panel notes that considering the composition of the NF and the proposed conditions of use, the consumption of the NF is not nutritionally disadvantageous. The submitted toxicity studies from the literature did not raise safety concerns. The Panel considers that the consumption of the NF may induce primary sensitisation and allergic reactions to yellow mealworm proteins and may cause allergic reactions in subjects with allergy to crustaceans and dust mites. Additionally, allergens from the feed may end up in the NF. The Panel concludes that the NF is safe under the proposed uses and use levels.

Impacts of Killing Process on the Nutrient Content, Product Stability and In Vitro Digestibility of Black Soldier Fly (Hermetia illucens) Larvae Meals

The black soldier fly (BSF, Hermetia illucens) is considered a potential sustainable insect alternative source of protein for animal feed. The quality of a BSF meal is greatly influenced by the killing method and the purpose of this article is to compare the influences of different killing methods. BSFs at the 18-day-old prepupae stage were separated into six different killing methods with three replicates: 1. blending, 2. freezing, 3. CO2 treatment, 4. vacuum, 5. blanching and 6. CO2 plus blanching. After killing, BSF larvae meals were obtained by hot air oven drying and grinding. The chemical composition and in vitro digestibility calculated from sediments were not affected by the killing method, except that blending provided the worst BSF quality for all measured parameters (p < 0.05). The highest quality of BSF was obtained from the heat treatment procedures (blanching and the CO2 plus blanching methods), as they produced lower acidity after killing, total viable counts, browning reaction (enzymatic and non-enzymatic), darkness, moisture, fat acidity, protein and lipid oxidation during storage compared with other killing procedures (p < 0.05). Interestingly, the highest free amino acids in the supernatant after in vitro digestibility of BSF samples was observed with the CO2 plus blanching killing method (p < 0.05), whereas other parameters were similar to those obtained with blanching. The CO2 plus blanching method did not produce clearly different outcomes to blanching; therefore, the selection of one of these techniques over the other should depend on the regulations in each country.

Protein carbonylation in dopaminergic cells exposed to rotenone

Rotenone is an environmental neurotoxin that induces degeneration of dopaminergic neurons and the most common features of Parkinson's disease in animal models. It acts as a mitochondrial complex I inhibitor that impairs cellular respiration, with consequent increase of reactive oxygen species and oxidative stress. This study evaluates the rotenone-induced oxidative damage in PC12 cells, focusing particularly on protein oxidation. The identification of specific carbonylated proteins highlighted putative alterations of important cellular processes possibly associated with Parkinson's disease. Carbonylation of ATP synthase and of enzymes acting in pyruvate and glucose metabolism suggested a failure of mechanisms ensuring cellular energy supply. Concomitant oxidation of cytoskeletal proteins and of enzymes involved in the synthesis of neuroactive molecules indicated alterations of the neurotransmission system. Carbonylation of chaperon proteins as well as of proteins acting in the autophagy-lysosome pathway and the ubiquitin-proteasome system suggested the possible formation of cytosolic unfolded protein inclusions as result of defective processes assisting recovery/degradation of damaged molecules. In conclusion, this study originally evidences specific protein targets of rotenone-induced oxidative damage, suggesting some possible molecular mechanisms involved in rotenone toxicity.

Iron-polyphenol complexes cause blackening upon grinding Hermetia illucens (black soldier fly) larvae

Insects are a promising alternative protein source. One of the bottlenecks in applying insects in food is the fast darkening initiated during grinding. Besides enzymatic browning, non-enzymatic factors can cause off-colour formation, which differs between species. This study investigates the impact of iron, phenoloxidase, and polyphenols on off-colour formation in insect larvae. Hermetia illucens showed a blackish colour, whereas Tenebrio molitor turned brown and Alphitobius diaperinus remained the lightest. This off-colour formation appeared correlated with the iron content in the larvae, which was 61 ± 9.71, 54 ± 1.72 and 221 ± 6.07 mg/kg dw for T. molitor, A. diaperinus and H. illucens, respectively. In model systems, the formation of iron-L-3,4-dihydroxyphenylalanine (L-DOPA) bis- and tris-complexes were evidenced by direct injection into ESI-TOF-MS, based on their charges combined with iron isotope patterns. The reversibility of the binding of iron to phenolics, and thereby loss of blackening, was confirmed by EDTA addition. Besides complex formation, oxidation of L-DOPA by redox reactions with iron occurred mainly at low pH, whereas auto-oxidation of L-DOPA mainly occurred at pH 10. Tyrosinase (i.e. phenoloxidase) activity did not change complex formation. The similarity in off-colour formation between the model system and insects indicated an important role for iron-phenolic complexation in blackening.

Development of a new method for collecting hemolymph and measuring phenoloxidase activity in Tribolium castaneum

Objective

Hemolymph plays many important roles in the physiology of an insect throughout its lifetime; however, for small-bodied insects, studies are lacking because of the difficulties encountered while collecting hemolymph. The objective of our study was to develop a method to collect hemolymph plasma from various stages of Tribolium castaneum and to evaluate phenoloxidase activity in the plasma samples. We first designed a procedure for easily and quickly collecting clear hemolymph plasma from T. castaneum.

Results

By using this method, we collected approximately 5 µl plasma from 30 individuals at the larval, pupal or adult stages. And then, we studied the expression of phenoloxidase by performing western blot analysis of the plasma samples and found that phenoloxidase is present in hemolymph in each developmental stage. We also measured phenoloxidase activity in control plasma and plasma treated with Gram-positive bacteria, Micrococcus luteus. Phenoloxidase activity was greater in some of the M. luteus-treated plasma samples compared with control samples. Thus, we developed a method to collect hemolymph plasma that is suitable for studies of phenoloxidase activity.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-4041-y) contains supplementary material, which is available to authorized users.

Targeted Inhibition of Enzymatic Browning in Wheat Pastry Dough

Enzymatic browning primarily affects fruits and vegetables but also occurs in wheat-based food. Herein, the browning behavior in wheat pastry dough was investigated aiming toward a targeted inhibitory treatment without influencing the pastry dough properties such as workability or taste. Dough discoloration is attributed to several subsequent enzyme-substrate reactions, which can selectively be inhibited by food additives. In most cases, an effective and lasting inhibition is only guaranteed by compounds acting upon multiple inhibition pathways. Despite their effectiveness, the unlimited use of commercial inhibitors is nondesirable due to necessary labeling, thus sustainable and natural inhibitors usually occurring as conventional food ingredients are of interest. It is shown that white wine combined with lemon juice revealed itself as an ideal combination for prevention of enzymatic browning in pastry dough.