Compositional Characteristics of Materials Recovered from Headed Gutted Silver Carp (Hypophthalmichthys molitrix) by Isoelectric Solubilization and Precipitation Using Organic Acids

Abstract

This research presents a reliable method for extracting nutritionally valuable fish protein and oils from otherwise hard to process fish and its byproducts. Replacing the traditionally used strong acids with organic acids might further accomplish bacterial load reduction while resulting in similar to or improved protein recovery yields. Therefore, this technology may increase the commercial viability of hard to process fish.

Calcium hydroxide as a processing base in alkali‐aided pH‐shift protein recovery process

“…A package of vacuum‐packaged fish containing 500 g paste was thawed at 4 °C for 24 h prior to processing. The thawed paste was diluted with distilled deionized water at a 1: 6 (fish: water) ratio in a glass beaker and homogenized (PowerGen 700, Fisher Scientific, Pittsburgh, PA, USA) for 5 min . Proteins were solubilized by increasing the pH of the solution to either 11.0, 11.5, 12.0 or 12.3 with 1 mol L −1 calcium hydroxide (Ca(OH) 2 ) or 10 mol L −1 sodium hydroxide (NaOH).…”

“…The solution was homogenized for 10 min after the final pH was reached and confirmed with a calibrated pH/ion analyzer (Oakton, Eutech Instruments, Singapore). The slurry was transferred into 1 L centrifuge bottles and centrifuged at 98 066.5 m s −2 for 15 min at 4 °C (Sorvall RC‐SB refrigerated superspeed centrifuge, Du Pont, Wilmington, DE, USA) to separate the lipids and insolubles (skin, bones and scales) from the protein solution . Following centrifugation, lipids formed the top layer, protein remained solubilized in the liquid fraction and the insoluble components were at the bottom.…”

“…This method accumulates large amounts of processing water and results in the recovery of 50–60 g 100 g −1 available fish protein . Another protein extraction method that is based on shifting the pH to solubilize and precipitate proteins does not generate as much waste water and has similar recovery yields: up to 66 g 100 g −1 of the available protein, depending on the protein solubilization strategy . This protein recovery method relies on pH shifts to separate impurities and lipids from myofibrillar protein by solubilizing at high or low pH and then precipitating it when the pH is adjusted to the protein isoelectric point, near pH 5.5.…”

“…Acidic solubilization takes place when the initial pH of fish and water solution is decreased to extremely low pH values such as pH 2–3, whereas alkali solubilization occurs when the pH is increased to high values such as 10.5–12 . Both strategies are effective in protein solubilization; however, alkali solubilization induces less protein denaturation, which is important if the final product is used for functional properties such as gelation …”

“…The proximate composition (protein, lipid and ash amounts) of recovered protein and lipid fractions, lipid and protein recovery yields, and mineral contents of recovered proteins at different alkali solubilization pH values (11.0, 11.5, 12.0 and 12.3), were determined and compared. Processing pH values were chosen based on results of previous studies that showed high protein recovery yields …”