Optimisation of hydrolysis conditions and fractionation of peptide cryoprotectants from gelatin hydrolysate

The inhibition of ice crystal growth in an ice cream mix by gelatin hydrolysate produced by papain action was studied. The ice crystal growth was monitored using a cold stage by thermal cycling between −14 and −12 °C at a rate of one cycle per 3 min. Optimum conditions for producing cryoprotective peptides from bovine gelatin (Type 225B40) was investigated by incubating gelatin with papain at pH 7.0 for various times (10–60 min), temperatures (37, 45, and 55 °C), and enzyme-to-gelatin (E/S) ratios (1:10 to 1:100). The hydrolysate obtained after 30 min at 37 °C and pH 7.0 (E/S ratio of 1:10) substantially inhibited ice crystal growth in an ice cream mix. The molecular weight range of ice crystal growth inhibiting peptides was determined by matrix-assisted laser desorption ionisation – time of flight (MALDI-TOF) mass spectrometry after fractionation on Sephadex G-50 and SP-Sephadex C-25 chromatography columns. Cationic gelatin peptides with average molecular mass in the range of 700–1400 Da significantly reduced ice crystal growth in an ice cream mix by a factor of ten under identical experimental conditions.