Hydrolyzates produced from mackerel Scomber japonicus skin by the pressurized hydrothermal process contain amino acids with antioxidant activities and functionalities

Abstract

The production of amino acids with antioxidant activities and functional properties from protein hydrolyzates of freeze-dried and supercritical carbon dioxide (SC-CO2)-extracted mackerel skin by pressurized hydrothermal hydration (PHH) at different temperatures (150–240 °C) and pressures (12–210 bars) was investigated. The highest yield of amino acid in freeze-dried and SC-CO2-extracted mackerel skin hydrolyzates was 121.93 ± 1.80 and 122.96 ± 2.84 mg/g, respectively, at 240 °C and 210 bars. Nine essential amino acids were identified in both skin hydrolyzates, of which histidine was the most abundant. All essential amino acids showed a temperature stability up to 240 °C, with the exception of threonine and histidine. The antioxidant activity of the hydrolyzates, as demonstrated in the DPPH, ABTS, hydroxyl radical, metal chelating, and reducing power assays, increased with increases in temperature and pressure; it was high in both hydrolyzates at 240 °C and 210 bars. In terms of functional properties, hydrolysis at different temperatures and pressures increased protein solubility to above 59 % over a wide pH range (3.5–9.5). When the temperature and pressure increased, the emulsifying activity index, emulsion stability, foaming capacity, and foam stability of both hydrolyzates decreased, possibly caused by the shorter peptide chain length. We conclude that protein hydrolyzates produced from mackerel skin can be used in food-related industries as good additives.