Mechanistic insights into high-intensity ultrasound-induced debittering and umami-enhancing of Antarctic krill peptides during ultrasound-assisted flavourzyme hydrolysis: Integrating E-tongue, multi-spectroscopy, and label-free peptidomics.

The bitterness of protein hydrolysates negatively affects the utilization of protein-rich by-products from Antarctic krill after oil extraction. The debittering and umami-enhancing effects as well as the underlying mechanisms of high-intensity ultrasound on Antarctic krill peptides (AKPs) during ultrasound-assisted flavourzyme hydrolysis were unveiled by integrating E-tongue, multi-spectroscopic, and peptidomic approaches. Results revealed that appropriate high-intensity ultrasound allowed ordered conformations (α-helices and β-sheets) to convert into disordered conformations (mainly β-turns), promoting the unfolding of structural proteins (mainly myofibrillar proteins) and cleavage of exposed hydrophobic residues during enzymolysis, which improved the protein recovery and degree of hydrolysis (DH) of AKPs. These changes led to the small-molecular weight (MW) proportion (<3 kDa) increase, peptide length shortening, N-terminal/C-terminal hydrophobic residues reduction, hydrophobic/bitter residues (especially Phe, Ile, Leu, Met, Pro, and Val) content decline, and hydrophilic/umami residues (mainly Asp and Glu) amount augment of AKPs, contributing to the generation of fewer underlying bitter peptides and release of more potential umami peptides, which resulted in the bitterness-associated perceptions (bitterness, bitter aftertaste, and astringency) attenuation and umami-related tastes (umami and richness) enhancement. However, overhigh-power (>400 W) high-intensity ultrasound could disturb α-helices degradation along with exposure and cleavage of hydrophobic residues during enzymolysis, which would decrease the DH and protein recovery, leading to the bitterness enhancement and umami decline of AKPs through augmenting average MW, increasing hydrophobic/bitter residues proportion, and reducing hydrophilic/umami residues content. These findings provided insights into the high-intensity ultrasound-induced taste-improving mechanism of peptides and facilitated the high-value utilization of defatted Antarctic krill by-products.