Ice crystal growth inhibition by peptides from fish gelatin hydrolysate

Ice crystal growth inhibition in an ice cream mix matrix and in sucrose solutions by peptides derived from alcalase (also known as subtilisin) hydrolyzed fish gelatin was investigated. Hydrolysis of fish gelatin at an optimum hydrolysis condition (i.e. 20% w/w gelatin solution treated with Alcalase at an enzyme-to-substrate ratio of 0.176 Anson units/g gelatin at pH 9.0 for 25 min at 45 degrees C) released peptides with maximum ice crystal growth inhibition activity. Fractionation of gelatin hydrolysate using size exclusion and ion exchange chromatography resulted in isolation of a cationic peptide fraction containing two prominent peptides having 1850.82 Da and 2036.88 Da molecular masses. This cationic fraction had the highest ice crystal growth inhibition activity. The amino acid sequences of these peptides showed no sequence similarity other than that they both contained -GTPG- and -GPP((OH))G-motifs and 3 to 5 hydroxyl containing amino acid residues. The results of this study supported the hypothesis that short collagen/gelatin polypeptides in the molecular mass range of 1000-2500 Da, regardless of their source, would have the ability to inhibit ice crystal growth in frozen systems. The results also suggested that the mechanism of ice crystal growth inhibition by gelatin peptides might involve three steps, namely, initial nonspecific electrostatic interaction of cationic peptides with the negatively charged ice surface, followed by structural realignment to optimally hydrogen bond with the oxygen-oxygen lattice on the ice surface, and stabilization of the electrostatic and hydrogen bonding in the peptide ice crystal complex by a partial nonpolar environment created by neighboring hydrophobic residues of the peptide. (C) 2017 Elsevier Ltd. All rights reserved.