Ammonium Sulfate and Repeated Freeze‐Thawing Recover Oil from Emulsion Separated from Salmon Skin Hydrolysate

Abstract

AbstractEmulsion separated by a disk stack centrifugal separator is the leftover from salmon skin hydrolyzed collagen production, in which oil can be recovered for further uses. Impacts of ammonium sulfate (AS) at different levels (0–10%, w/w) and freeze‐thawing with various cycles (0–7) on destabilization of emulsion separated from salmon skin (Oncorhynchus nerka) hydrolysate and quality of recovered oil are investigated. Emulsion added with AS shows larger oil droplet size (p < 0.05) with lower negative charge (p< 0.05). Oil yield and recovery are increased (p < 0.05) with augmenting concentrations of AS and freeze–thawing cycles. Highest yield (4.01%) and recovery (87.36%) (p < 0.05) are obtained for oil recovered from emulsion added with 10% AS in conjunction with freeze–thawing for three cycles. Oils recovered from emulsion added with AS (0–10%) and freeze–thawed for 0 and 3 cycles show no differences in hydrolysis, oxidation, and astaxanthin content (5.19–5.62 mg kg−1 oil). Furthermore, no marked differences in fatty acid composition and FTIR spectra are observed. Therefore, the use of 10% AS in conjunction with freeze–thawing (3 cycles) is a promising means for recovery of oil from emulsion, which can be an alternative source of nutraceutical.Practical applications: Oil–water emulsion is a by‐product separated from production of salmon skin hydrolysate with the aid of a disk stack centrifugal separator (DSCS). Retained peptides could act as emulsifier and stabilize oil droplets in emulsion. To recover oil from emulsion, the destabilization of emulsion is required. Addition of ammonium sulfate (AS) can destabilize emulsion via peptides precipitation, thus liberating the oil. Moreover, the repeated freeze–thawing in combination with AS under optimal condition is shown to enhance oil yield and recovery. Therefore, oil rich in astaxanthin and polyunsaturated fatty acid from the discarded emulsion can be recovered and further exploited.