Effects of exogenous enzymes and capsaicin on food waste treatment and larval growth of black soldier fly

Abstract: Food waste has been an international problem in recent years, due to odor and disposal challenges. Globally, the United Nations Environment Program (UNEP) estimated that about 17% of food was wasted at the retail and consumer levels. It was estimated that 91 million tons of food waste were produced in China in 2020. Fortunately, it is a promising way to convert carbon and nutrients (N, P, and K) in food waste into usable products. The multiple benefits can then be gained for nutrient recycling, public health, and reduction in the emission of greenhouse gases. However, the available cost-effective techniques are still lacking in food waste treatment, particularly in the ever-increasing demand. This research aimed to assess the potential performance of the black soldier fly (Hermetia illucens L.) for food waste (rice with spicy soup) treatment and nutrient recycling. A series of cultural experiments were indoor simulated to investigate the effects of exogenous enzymes (amylase and catalase) and capsaicin on the degradation of food waste and the growth of black soldier fly (Hermetia illucens L.) at different life phases (the first, second, and fifth instar larvae). Nevertheless, there was a low performance of the newly hatched larvae of the black soldier fly (Hermetia illucens L.) to decompose the rice residue with the spicy soup. The amylase was then added to accelerate the decomposition of starch in the food waste into sugars. A favorable condition was created for the newly hatched larvae to grow. The life phases were also selected as the second or fifth instar larvae, where the insects were in rapid growth or at mature stages. Furthermore, capsaicin was added as a seasoner to stimulate the appetite of the black soldier fly (Hermetia illucens L.), thereby increasing the food intake for the higher growth rate and biomass accumulation during this time. The addition of α-amylase (at the ratio of food waste: α-amylase of 10 000:1) and catalase (at the ratio of food waste: peroxidase of 100 000:1) at the first instar larvae of the black soldier fly (Hermetia illucens L.), followed by adding the capsaicin (at the ratio of food waste: capsaicin of 80:1) at the fifth instar larvae, increased the degradation rate of food waste by 6.49 %, the live weight of the insect by 29.70 %, and the dry weight of the insect by 38.22 %, compared with the control. Besides, the protein and fat contents of the insect biomass were raised by 18.81 % and 20.97 %, respectively. The results also demonstrate that a trace amount of exogenous enzymes (amylase and catalase) and capsaicin were effective to accelerate food waste degradation, particularly for the higher growth of the black soldier fly (Hermetia illucens L.). As such, the quality of the black soldier fly (Hermetia illucens L.) biomass was improved to serve as the high-protein and high-fat feed. In the field experiment thereafter, the fresh biomass of the insect was fed, such as chickens. The dry biomass was used as an ingredient of feed for the fish to replace the plant protein, and the meal was liked by fish species in the aquaculture tanks. Anyway, the finding can guide the conversion of rice food waste to high-protein animal feed, particularly for the reuse and reduction of food waste.