Valorisation of proteins and lipids from flax straw using combinations of microbial fermentation and black soldier fly larvae (Hermetia illucens)

Abstract The recovery of nutrients from underutilised agricultural byproducts offers a sustainable strategy to enhance food and feed production without major changes to existing supply systems. This current study examined the possibilities to use abundant agricultural byproducts, flax straw, to recover nutrients in the form of insect biomass. Flax straw was treated with Aspergillus oryzae-Lactobacillus plantarum or A. niger-Trichoderma koningii with and without autoclave pretreatments. Without the heating treatments, the straw was found a poor feed for the black soldier fly larvae. Their body mass only reached to 25.6 mg per larva in 15 days. Even with A. oryzae-L. plantarum fermentation, where we expected the better growth, the average weight per larva reached only 30.5 mg. These were much smaller compared to what can be achieved using rich feed, such as corn meal-based feeds. Rich feed typically allows a larva grow to 70+ mg after 15 days culture. When the straw was autoclaved, it supported a larvae growth to 34.5 mg. Fermentation of this cooked straw with cellulose-degrading microbes ( A. niger and T. koningii ) allowed even better growth. BSFL fed with cooked-fermented feed had a larva growing to 47.7 mg where proteins and lipids had 41.5 and 13.2% contents, respectively. The improvement of feed quality by cooking and fermentation is notable, given the inherently low nutrient bioavailability of straw. These results demonstrate the potential of microbial pretreatment and insect bioconversion to valorise underexploited agricultural byproducts within sustainable feed and food production systems.