Fernando García Barroso

This study evaluated the bioconversion of agro-industrial by-products (dry olive leaves, OL; full-fat dry olive pomace, OP; and quinoa husk, QH) by Tenebrio molitor larvae, included at different levels in the substrates. Wheat bran (control diet) was replaced with OL (15, 30, 50%), OP (30, 50, 70, 90%), or QH (15, 30, 50%). Productive performance, dietary and larval nutritional composition, and fatty acid profile were determined. Low to moderate inclusion levels (OL and QH up to 15%, and OP up to 30%) supported larval growth comparable to control diets. These formulations maintained or improved the nutritional composition of the larvae, by increasing protein content and reducing lipid levels. In contrast, high inclusion levels caused nutritional imbalances in the diets, likely due to excessive fibre and low protein (for OL and QH) or high lipid, fiber, ash and low carbohydrate contents (for OP), together with high phenolic contents (for OL and OP), which likely affected feed intake and larval development. Additionally, the dietary fatty acid appeared to influence larval lipid composition. Larvae fed OP tended to accumulate more oleic acid and less linoleic acid. Moreover, high dietary lipid and fiber contents due to OP seemed to increase larval oleic acid content while reducing linoleic acid, whereas carbohydrate-rich diets had the opposite effect. Therefore, olive and quinoa by-products in T. molitor feeding offer a sustainable valorisation strategy offer these side streams, if macronutrient balance is maintained when specific levels of the by-products are used to ensure optimal larval growth and feed efficiency.

In recent years, the potential of insects as a sustainable protein alternative to feed the growing world population has been explored. Differences in the ways insects are processed can affect their proximate composition and digestibility. This work studied the effects of the combination of different types of slaughter methods and drying temperatures on the proximate composition, organic matter digestibility (OMd), hydrolysis degree (DH/NH₂ and DH/100 g DM), total hydrolysis (TH), and hygienic and sanitary characteristics of BSFL (black soldier fly larvae) meal. Four types of slaughter methods were used including freezing (F), blanching + freezing (B), Melacide^® + freezing (M), and liquid nitrogen slaughter (N). Each of these was used with three drying temperatures (50, 70, and 90 °C). A negative correlation between the acid detergent fiber (ADF) and protein digestibility parameters was obtained. The most suitable drying temperature was 70 °C, as it produced higher values of protein digestibility (DH and TH), resulting in hygienic and sanitary conditions suitable for food use. Slaughtering with liquid nitrogen and blanching was more conducive to achieving high protein digestibility results than traditional freezing or the use of Melacide^®.

In recent years, the potential of insects has been explored as a sustainable protein alternative to sustain the growing world population. Differences in the way insects are processed can affect their proximate composition and digestibility. This work studies the effects of the combination of different types of slaughter methods and drying temperatures on the proximate composition, organic matter digestibility (OMd), hydrolysis degree (DH/NH2 and DH/100 g DM), total hydrolysis (TH) and hygienic sanitary study of BSFL (black soldier fly larvae). Four types of slaughter methods were used: frozen (F), blanched + frozen (B), Melacide® + frozen (M) and liquid nitrogen (N), each with three drying temperatures (50, 70 and 90 °C). A negative correlation between acid detergent fibre (ADF) and protein digestibility parameters was obtained. 70 °C was the most suitable drying temperature, as it reported higher values of protein digestibility (DH, TH), resulting in hygienic and sanitary conditions suitable for food use. Slaughtering with liquid nitrogen and blanching were more convenient than traditional freezing or the use of Melacide® to achieve higher protein digestibility results.

Rapid population growth is leading to an increase in the demand for high-quality protein such as fish, which has led to a large increase in aquaculture. However, fish feed is dependent on fishmeal. It is necessary to explore more sustainable protein alternatives that can meet the needs of fish. Insects, due to their high protein content and good amino acid profiles, could be a successful alternative to fishmeal and soybean meal traditionally used in sectors such as aquaculture. In this work, seven species of insects (Hermetia illucens, Tenebrio molitor, Acheta domestica, Alphitobius diaperinus, Gryllodes sigillatus, Gryllus assimilis, and Musca domestica) approved by the European Union (UE) for use as feed for farmed animals (aquaculture, poultry, and pigs) were studied. Their proximate composition, hydrolysis of organic matter (OMd), hydrolysis of crude protein (CPd), degree of hydrolysis (DH/NH₂ and DH/100 g DM), and total hydrolysis (TH) were analyzed. The results showed that Tenebrio molitor had digestibility similar to that of fishmeal, while Acheta domestica and Hermetia illucens provided similar digestibility to that of soybean meal. The acid detergent fiber (ADF) data were negatively correlated with all protein digestibility variables. The differences in the degree of hydrolysis (DH) results and the similarity in total hydrolysis (TH) results could indicate the slowing effects of ADF on protein digestibility. Further in vivo studies are needed.

Aquaculture struggles with sustainability due to the use of fishmeal, and insects are one potential alternative. Insects have low long-chain omega−3 polyunsaturated fatty acid content, and insect-fed fish reflect this in their composition. In total, 500 rainbow trout (Oncorhynchus mykiss, ~46 g) were fed until the fish reached a commercial size (~415 g). Five diets were used: one control based on fishmeal as main source of protein; two with a 50% replacement of fishmeal with yellow mealworm meal (Tenebrio molitor), one with full-fat insect, and another partially defatted; two other diets similar to the one with the full-fat insect, but with the addition of an experimental algal oil rich in omega−3 in two different concentrations (one equivalent to control, the other one to the defatted insect diet). Growth was unaffected, as well as texture and organoleptic profile of the fillets. Lightness, brightness and colour of the fillets were slightly modified by the experimental diets. An increase in omega−3 levels over those of the full-fat insect diet is described. An omega−3 sparing effect was highlighted, causing lipid accumulation in fillets and liver, and a mild increase in oxidative damage. More research is encouraged to evaluate the fatty acid profile of the liver.

A feeding trial was carried out on a shrimp farm located in the Santa Rosa province of El Oro, Ecuador, with four isonitrogenous and isolipidic experimental diets, designed with increasing levels of substitution of fish meal by P. voluvilis, (D-0), 15% (D-15), 25% (D-25), and 50% (D-50). The obtained results indicated that the 50% replacement with P. volubilis in practical diets had no noticeable negative effects on the growth performance of L. vanameii juveniles. The total weight of shrimps fed with 25% and 50% diets (16.04 g and 16.72 g, respectively) and the abdomen weight (10.32 g) of shrimps fed with the D-50 diet were high, with significant differences regarding those fed with the D-0 diet. No adverse effects on muscle composition were found. Significant differences were observed only in groups D-25 (for chymotrypsin) and D-50 (chymotrypsin and alkaline protease). Trypsin and amylase activity was not affected by the inclusion of P. volubilis. The results of this experiment indicated that P. volubilis cake is a possible alternative to fish meal in shrimp feeding; however, it should be studied in more depth to establish the maximum replacement percentage and to identify the adequate treatments to eliminate antinutritional factors.

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.

Fish discards are organic waste with high and good-quality protein levels, as well as a fatty acid profile rich in n−3 LCPUFAs, mainly eicosapentaenoic acid and docosahexaenoic acid. These discards can be used as food for Tenebrio molitor (Linnaeus, 1758) larvae, thus increasing the nutritional value of this insect. This study focused on increasing larval acceptance of fish through different pre-treatments of the diets provided, as well as increasing the accumulation of EPA and DHA in fish-fed larvae. Four different diets were prepared: control (broiler feed), DGF50: 50% dried ground fish (Pagellus bogaraveo, Brünnich, 1768) + 50% broiler feed, for different periods, FGF100: 100% fresh ground P. bogaraveo and DUF100: 100% dried whole unground P. bogaraveo. Growth, mortality, proximate composition, fatty acid profile and lipid nutritional indices were determined. Larvae fed with FGF100 displayed better results among treatments, doubling the initial weight, as well as increasing their protein level and decreasing fat levels. Regarding fatty acids, eicosapentaenoic acid and docosahexaenoic acid were only detected in larvae fed with a fish-based diet for a period longer than 5 days. These results show that pre-treatment of fish-based diets causes changes in the growth and compositional parameters of T. molitor larvae.

The demand of optimal protein for human consumption is growing. The Food and Agriculture Organization (FAO) has highlighted aquaculture as one of the most promising alternatives for this protein supply gap due to the high efficiency of fish growth. However, aquaculture has been facing its own sustainability problem, because its high demand for protein has been traditionally satisfied with the use of fishmeal (FM) as the main source. Some of the most promising and sustainable protein substitutes for FM come from insects. The present manuscript provides insight into an experiment carried out on rainbow trout (Oncorhynchus mykiss) with a 50% replacement of FM with different larvae insect meals: Hermetia illucens (HI), and Tenebrio molitor (TM). TM showed better results for growth, protein utilization and more active digestive function, supported by intestinal histological changes. Liver histology and intermediary metabolism did not show relevant changes between insect meals, while other parameters such as antioxidant enzyme activities and tissue damage indicators showed the potential of insect meals as functional ingredients.

Hermetia illucens and Tenebrio molitor were tested on account of their potential to replace fish protein in feed. Two levels of replacement for H. illucens, 30% and 50% (H30 and H50), and one for T. molitor, 50% (T50), as well as an additional diet with a modified fatty acid fraction (H50M), were investigated in relation to juvenile Sparus aurata growth indices, enzyme activities and gut microbiome. A T50 diet showed similar results to a control (C) diet, with no significant differences regarding morphological indices and minor differences for nutritional indices. Regarding the gut microbiome, H50M was the diet which showed the more similar prokaryotic community to C, which suggests that fatty acid fractions might influence the composition of the gut microbiome. Nevertheless, differences appeared to be related to a redistribution of dominant species, while changes in species affiliation were limited to minoritary species. The positive correlation between some of these minoritary species (Peptostreptococcus russellii, Streptococcus dysgalactiae and Weisella confusa) and several fish growth parameters might explain differences between control and insect diets. Deciphering such uncertainty and revealing the potential role these unusual species may play on fish performance should be addressed in future investigations.