Vozzo, Simone (2024) Black soldier fly: Growth Performance and Nutritional Pro file on Different Types of Organic Substrates. Possible Implications and Uses for Sustainable Production. [Tesi di dottorato]

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Abstract

The expansion of animal-derived protein production to meet global demand presents significant environmental challenges, including heightened greenhouse gas emissions, increased water consumption, and extensive land requirements. In both developing and developed nations, the issue of sourcing alternative protein sources is becoming increasingly urgent. Urban population growth in developed regions necessitates the development of large-scale production systems with minimal land use, which in turn leads to increased consumption and a corresponding rise in organic waste production. One of the main and strongest answers nowaday seems to be the circular economy model, which can provide to the consumption of the great amount of waste and at the same time evaluate it producing value and work. Insects seem to be a great candidate in this sense: due to their evolutionary adaptation to diverse environments, many insect species have the potential to be used in sustainable systems for biomass conversion. Insect farming offers substantial environmental advantages compared to conventional livestock production in terms of power consuption, land and water. Among the most studied bioconverting insects the black soldier fly (Hermetia illucens, Linnaeus, 1758) has garnered significant attention for its ability to efficiently convert a wide range of organic waste into high-quality biomass. The H. illucens larvae are rich in proteins, lipids, and bioactive compounds, such as chitin, lauric acid, and antimicrobial peptides, which have demonstrated beneficial effects on intestinal health and overall animal welfare. This PhD project aims to study Hermetia illucens, analyzing its growth performance and nutritional profile at the larval stage on different types of organic substrates. The project will evaluate the potential applications and implications for the sustainable production of this species on a large scale. Each study contributing to this work focuses on a different chemical analysis of BSFL (Black Soldier Fly Larvae) grown on various substrates, in order to assess the insect's potential. Therefore, one of these works aimed to evaluate how different food wastes used as growth substrates affected the lipid composition of Hermetia illucens larvae; the relationship among substrates, larvae, and frass fatty acid (FA) composition was studied. Six thousand five-day-old Hermetia illucens larvae were allotted to one of four different substrates named CTRL (a control substrate made of broiler feed), V50 + B50 (vegetable and butchery wastes, 1:1 ratio), V75 + B25 (vegetable and butchery wastes, 3:1 ratio), and V100 (entirely composed of vegetables). Saturated FAs (SFAs) prevailed in all the groups. The CTRL larvae had the highest SFA (64.3%), while the V100 and V50 + B50 larvae had the lowest percentages. The V100 frass recorded a significantly higher SFA value (44.8%) than the others. Lauric acid (C12:0) was high in CTRL (0.2%) and V100 (0.3%) substrates and amount at 7.6 and 9.6% in their correspondent frass, respectively. 2 However, C12:0 content was higher in the CTRL larvae than in the V100 ones (36.7 and 24.5%, respectively), while it had an intermediate value (28.9%) in the V75 + B25 larvae. Finally, the n-3 polyunsaturated FAs (PUFAs) level was high in the V100 substrate and larvae but not in the V100 frass. The relationship between frass FAs and their correspondent amounts in substrates and larvae was significant for C12:0, C18:2n-6, MUFAs, and n-6 PUFAs. There was a positive relationship for C12:0 and MUFAs with both substrates and larvae, while for C18:2n-6 and n-6 PUFAs, the relationship was positive for substrates but negative for larvae. In the end the V100 substrate appeared to be the most suitable treatment for rearing Hermetia illucens because of the positive effects on the fatty acid content of larvae (low SFA and high n-3 PUFA content) and frass (optimal lauric acid levels for fertilizers). After the fatty acids, the second work shown how BSFL amino acid composition is strictly related to the amino acid composition of the substrates themselves. For this research the same substrates as the fatty acid one were used, and their influence on larvae amino acid profile was evaluated: vegetable and butchery wastes show interesting potential for BSF larvae, in terms of growth and amino acid composition. As result of larvae growth, the insect frass (excreta, exuviae and residual substrate) resulting at the end of the production cycle, offers new and interesting aspects, from the perspective towards circular economy. In BSF, the amount of protein ranged from 20.0% in V75B25 to 43.7% in V100 (P < 0.01). The larvae on V100 had the highest (P < 0.01) amount of essential and non-essential amino acids (EAA) except for hydroxyproline which has been detected only in V75B25 group. V75B25 group had the lowest amount (P < 0.05) for almost all the AA. Out of the composition, BSF larvae appeared to be a useful tool for the bioconversion of a wide range of food wastes although significant differences in protein fraction and amino acid profile have been observed depending on the rearing substrate. In a third work, with same substrates that were previously used in fatty acid and amino acid research, the mineral profile of the larvae and frass, and the potential bioaccumulation of toxic elements (As, Cd, Pb, Hg) were valuated. The V100 larvae had the highest concentrations of all minerals, except for Se and P, higher in the control group (poultry diet as substrate) (p<.01). The V50B50 and V75B25 larvae showed lower (p<.01) mineral concentrations than the other groups. The V50B50 group had the highest (p<.01) bioaccumulation factor (BAF) for Cd (8.52%), the V100 for Pb (p<.01). The equations to estimate the mineral content of larvae from the substrate were significant only for Ca and Mg (p<.05). The V100 frass had the highest (p<.01) levels of As, Cd, Pb, Fe, K and Mg, while the control group showed the highest (p<.01) levels of Se, Zn, Ca, P and K. Toxic elements can accumulate in black soldier fly larvae and frass, with the exception of Hg. However, organic wastes from V and B had a very low content of toxic elements and that strongly reduced the risk of excessive bioaccumulation in larvae. Indeed, the 3 content of toxic elements in larvae is lower than the maximum values established for feed materials by EU regulations. In conclusion, organic substrates from vegetables or butchery wastes can be used for BSF larvae growth without the risk of accumulation of toxic elements. The latest contribution to this PhD project aimed to observe how BSF larvae behave, under a nutritional and bioconvertion profile, with pet food, specifically with cat wet food. This work was born looking at some data about the great petfood industry: the European pet population is substantial, with an estimated 340 million animals, comprising 26% dogs and 25% cats, so is the pet food industry as a business, with annual sales of approximately 10.9 million tons, and a growth rate of 5.1% over the last three years. The market is expected to continue growing in the coming years. As the global pet industry expands, it is likely that waste generation from this sector will also increase, including expired products, so this trend is expected to have significant environmental implications. For this purpose, a total of 4 substrates were used in the trial. A commercial broiler diet was used for the control group. The other three substrates were represented by three wet complete food for adult cats named beef, chicken and salmon mousses. In terms of growth performance the results showed that the larvae fed on salmon-based cat food had a shorter life cycle (20 days) and higher final weight (+14.98% and +8.24% compared to beef and chicken, respectively) than the other two groups. Moreover, the mortality rate of the salmon group was significantly lower (-19.7%) compared to the control group. The diverse growing substrates affected the chemical-nutritional characteristics of the resulted larvae. The decrease of larval protein content due to use of beef substrate is in line with the previous reasearch in larvae grown on butchery waste, consisting of meat from the trimming of bovine carcasses and cuts of meat, in comparison to larvae grown on a vegetable diet. However, the amount of protein content in larvae ranged from 43.12 to 45.64 %. The lipid content of the larvae on the diverse substrates was not different and only larvae on beef had a lower lipid content and, despite the similar carbohydrate content than the other substrates, larvae on beef cat food showed a lower amount of lipids stored in the body. Among all the results, one of the most interesting to see was the presence of polyunsaturated lipids: the control and salmon group showed a higher content of total PUFA than the other two groups, in particular the PUFA n-3 content in the diet and, as a consequence, improve the n6/n3 ratio, confirming that the fatty acid profile of BSF larvae can be modulate according to the fatty acid profile of the substrates. The results also indicate that not all cat foods, despite similar chemical-nutritional characteristics, can produce the same outcomes. A closer examination of the ingredients reveals that the main difference among the three cat foods is the inclusion of specific animal proteins from chicken, beef, or salmon. Therefore, it is likely that the differences in larvae growth can be attributed to the varying ability of the larvae to utilize these protein sources.

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