UPGRADING BLACK SOLDIER FLY LARVAE MEAL FOR AQUATIC FEEDS USING A SUSTAINABLE MICROBIAL PROCESS

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2024

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Su, Wei Wen

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The current heavy reliance on fish meal (FM) in aquatic feed poses significant sustainability challenges. These ingredients are derived from wild stocks of marine forage fish and have traditionally been essential due to their complete nutritional profiles and wide availability. However, the increasing demand for seafood has driven up the cost of these feed components. With costs escalating due to increased demand and depleted fisheries, the urgency to find sustainable alternatives to FM as a primary protein source becomes more apparent. Over the past three decades, aquaculture has been the fastest-growing sector in global food production, further emphasizing the need for such alternatives. One promising source of proteins to replace costly and unsustainable FMs is the larvae of black soldier flies (Hermetia illucens; BSFL). This insect has received significant attention because its adults are not pests, and very dense larvae biomass can be produced on a large scale using organic wastes with relative ease. The main problem with using these highly nutritious insects is that their fat and chitin contents are as high as 58% and 9%, respectively. These properties negatively affect meal digestibility, trigger undesirable immune responses, cause liver damage, and alter microbiota in the fish; this prevents the incorporation of high proportions of the BSFLMs in aquaculture feeds. This study focuses on developing a sustainable microbial defatting process, instead of relying on costly mechanical and harmful chemical solvent extraction, to remove excess fat from the BSFLM. The solution to this problem is a simple solid-state fermentation process (SSF) process with the use of a filamentous fungus, Aspergillus oryzae, also known as “koji”. It is hypothesized that the enormous enzyme-producing capacity of this edible microbe can be exploited to upgrade BSFLM’s nutritional value in a straightforward and scalable process. Our study showed that koji can grow using BSFL fat as the sole carbon source in a minimal salt medium in liquid culture. We further demonstrated that SSF of BSFLMs with koji fungus is feasible, and it leads to significantly reduced overall fat content and increased protein content in the koji-fermented BSFLM. In this study, we validated and quantified the extent to which fat levels can be reduced and identified the optimal conditions for this low-cost microbial defatting process. Additionally, a simple SSF bioreactor system was developed to monitor and control the environment in which these fermentations were conducted. The system consists of autoclavable 1-liter polypropylene jars loaded with BSFLMs and inoculated with koji spores. They were incubated within an industrial proofer retrofitted to control temperature and humidity level of the fungal culture during SSF. An IR-based carbon dioxide gas sensor was incorporated into the fermentation jar to allow online monitoring of culture CO2 evolution rate, which was evaluated in this study and found to be suitable for indirect prediction of fungal growth during SSF of the BSFLM. Over 3 kg of fermented BSFLMs were successfully produced using the SSF system for use in a 12-week feed trial with tilapia hybrids (O. niloticus X O. mossambicus). From the tilapia feeding trial, the fermented (microbially defatted) BSFLM was found to be able to replace up to half of the fishmeal in feed formulations, potentially lowering production costs in feed manufacturing, and opening opportunities for the local production of a high-quality protein ingredient. In conclusion, the innovative approach of utilizing SSF with koji to defat and enhance the nutritional value of BSFLM presents a promising solution to the challenges posed by the heavy reliance on FM in aquatic feed.

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Bioengineering, Environmental engineering, Microbiology, aquaculture feed, black soldier fly larvae, insect meal, koji fermentation, microbial defatting

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108 pages

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