Effects of sub-denaturation extraction temperatures on the functional and nutritional characteristics of black soldier fly larvae protein

The growing interest in sustainable protein sources has led to the exploration of insect-derived proteins such as those from Black Soldier Fly Larvae (BSFL). This study aimed to evaluate how extraction at ambient and sub-denaturation temperatures (25, 35 and 45 °C) affects the physicochemical and functional properties of BSFL protein isolates produced using the alkaline extraction-acid precipitation (AEAP) method. The results show that elevating extraction temperature enhanced protein recovery, increasing the isolate yield from 22.29% at 25 °C to 31.93% at 45 °C, primarily due to increased alkaline solubility and mass transfer efficiency. However, higher temperatures also promoted the co-extraction of non-protein components, resulting in reduced protein purity (from 94.00% at 25 °C to 89.34% at 45 °C). Amino acid profiling revealed leucine, lysine and valine as the dominant essential amino acids, while sulphur-containing amino acids (methionine + cysteine) were limiting, yielding moderate protein quality as reflected by DIAAS values. Comparison with amino acid profiles of conventional protein sources indicates that BSFL protein extracted at lower temperatures closely resembles red meat protein, while extraction at higher temperatures yields a profile more comparable to chicken breast. Functional properties, including solubility and foaming capacity, improved with increasing temperature, whereas higher thermal exposure adversely affected oil and water holding capacities and emulsion stability, likely due to partial protein aggregation and structural destabilisation. Overall, these findings highlight that maintaining extraction under ambient and sub-denaturation conditions enables the production of BSFL protein isolates with enhanced functional performance while minimising further structural disruption and maintaining protein purity, underscoring low-temperature AEAP as a promising strategy for developing highly functional and sustainable insect-based protein ingredients.