Does the processing of black soldier fly larvae meal affect the amino acid solubility in Atlantic salmon (Salmo salar)?

Abstract

The present work aimed to evaluate protein and amino acid (AA) digestibility/solubility of different black soldier fly larvae (BSFL) based meals for Atlantic salmon in vivo and in vitro. Three types of insect meals that had been through different processing techniques were included: microwave full fat BSFL meal (BSFM), defatted BSFL meal with an enzymatic pre-treatment (BSFE) and a defatted BSFL meal without enzymatic pre-treatment (BSFH). For the in vivo digestibility studies only two ingredients (BSFE and BSFH) were used. The experimental diets for the different ingredients were prepared by mixing a control diet with BSFL meals at an 80:20 ratio. The in vitro method implied a two-stage hydrolysis involving both gastric simulation (acid hydrolysis) and gastrointestinal simulation (acid hydrolysis followed by alkaline hydrolysis), using enzymes extracted from salmon. The results showed that the AA solubility was higher in the gastrointestinal phases than the gastric phase alone, showing the importance of having both phases in vitro solubility for an effective protein breakdown. The AA solubility of different insect-based meals showed that neither partial defatting nor the addition of enzymatic treatment impacted the protein and AA solubility. The in vivo trial (56 days) recorded no differences between fish fed diets containing BSFE and BSFH for growth or body indices. The protein and AA apparent digestibility were similar for both BSFE and BSFH ingredients. Thus, in the current study no differences in nutrient digestibility were observed due to different processing methods employed to BSFL meal both in vivo and in vitro.