Physicochemical properties of fish protein hydrolysates from invasive silver carp (Hypophthalmicthys molitrix) for use as value-added cryoprotectant ingredients

Jason Peter Mueller, Purdue University

Abstract

The physicochemical properties of the FPH were examined to characterize their functionality. FPH were produced by 30, 60, 90, 120, and 240 min hydrolysis with Protamex®, a commercially-available enzyme system. Degree of hydrolysis (DH) data showed substantial cleavage occurring during the reaction, especially in FPH from 120 (∼18% DH) and 240 min (∼53% DH). Mass distribution analysis using sodium-dodecyl sulfate (SDS-PAGE) electrophoresis and mass spectrometry revealed a relatively narrow molecular weight range for FPH-90 and 240 primarily less than 4 kDa, with larger peaks of 11 kDa (FPH-90) and 6.3 kDa (FPH-240) observed, respectively, suggesting a presumably high charge density of the FPH. Amino acid analysis demonstrated that FPH 90 and 240 retained all essential amino acids, including lysine at 10% total amino acid quantity. Desirable polar amino acids, including Asp and Glu, were observed to be in appreciable amount (∼10%) according to total amino acid analysis, whereas freed nonpolar amino acids Val, Met, Ile, Leu, and Phe increased across both treatments (which are known to promote F/T denaturation), but were notably higher in FPH-240. Surface hydrophobicity analysis suggested that FPH from silver carp may have evolving amphiphilic tendencies as the extent of hydrolysis increases; FPH-120 and 240 were noted to have the highest hydrophobicity values (P < 0.05) compared to all other FPH and the non-hydrolyzed (control) carp protein. Sulfhydryl resides were significantly lower (P < 0.05) for all FPH than the control, and this was correlated with near equal increases in disulfide linkages. The physicochemical properties of FPH from silver carp seem to imply a shifting balance in hydrophilicity vs. hydrophobicity as per the hydrolysis conditions. Thus, limited hydrolysis (i.e. up to 90 min) may promote beneficial water-binding of the FPH, while extensive hydrolysis seems to promote derogatory protein-protein interactions. Mince formulations consisted of 6% FPH (w/w) from each hydrolysis time condition, an untreated mince (CTRL), and 8% (w/w) 1:1 sucrose-sorbitol (SUSO), respectively. Mince formulations were evaluated before (Day 0/"D0") and after 6 freeze-thaw cycles (Day 7/"D7") for salt-extractable protein (SEP) content, expressible moisture (EM), antifreeze activity (AF) by differential scanning calorimetry, surface hydrophobicity, and quantities of sulfhydryl residues (SH) vs. disulfide linkages (SS). All FPH-treated mince samples were found to improve SEP recovery, while 240 min retained a significantly higher proportion (P < 0.05) of SEP at Day 7 compared to SUSO. At D7, all FPH treatments had significantly (P < 0.05) lower EM than both the control and SUSO formulations, indicating strong water holding capacity by the FPH. AF activity dropped in the control sample after freeze-thawing, from 20.3% to 5.5% unfrozen water, while the SuSo maintained AF activity at 20.4% (D7). Furthermore, all FPH imparted AF activity equal to or better than SUSO, with the FPH-90 exhibiting significantly higher (P < 0.05) AF activity at Day 7 with 43.9%. Surface hydrophobicity values did not significantly differ on D7 across treatments; however, FPH 30, 60, and 90 each retained a similar hydrophobicity from D0 to D7. FPH 60, 90, 120, and 240 retained total sulhydryl residues better than SUSO, though disulfide analysis returned inconclusive evidence. This evidence suggests that FPH from silver carp using the Protamex® system may have cryoprotectant capabilities in a frozen fish mince product.

Degree

M.S.

Advisors

Liceaga, Purdue University.

Subject Area

Food Science

COinS