Solving Gritty Problems in Ice Cream

A University of Wisconsin, Madison, researcher has discovered how gelatin hydrolysate may provide ice cream makers with a way to minimize unwanted ice-crystal growth that leads to unacceptable, gritty texture in ice cream.

The study, “Inhibition of Ice Crystal Growth in Ice Cream Mix by Gelatin Hydrolysate,” (Srinivasan Damodaran J. Agric. Food Chem., 55 (26), 10918–10923 10.1021/jf0724670) investigated the effectiveness of low-molecular-weight peptides derived from enzymatic hydrolysis of gelatin on the inhibition of ice-crystal growth in ice cream mix, assuming that these peptides bind to ice nuclei and crystals. The research was based on prior studies that indicated an specific enzymatic modification of gelatin with papain resulted in an edible product that exhibited antifreeze properties.

The size of ice crystals influences the texture and mouthfeel of frozen foods. For example, ice crystals ranging from 15 to 20 µm give a desirable smooth texture to ice cream, but those larger than 40 µm make it coarse and grainy. Typical storage temperatures in household freezers (over -20°C) and the temperature cycling created by automatic defrost systems increases water mobility that promotes rapid ice-crystal growth, thus adversely affecting ice cream quality.

Damodaran conducted a controlled study using batches of ice cream prepared with and without the peptide compound, showing that ice cream containing the antifreeze developed significantly smaller and fewer ice crystals than batches prepared without the compound. The gelatin was hydrolyzed by papain into peptides with a range of molecular weight, and the peptides separated into fractions based on molecular weight. Testing indicated that gelatin polypeptides with a size greater than 7000 Da poorly inhibited ice-crystal growth in the ice cream mix, and that peptides smaller than 3000 Da appear to be largely responsible for the antifreeze properties of gelatin hydrolysate. He theorized that specific molecular structures might be responsible for the antifreeze effects, stating, “Further elucidation of the molecular interactions responsible for ice crystal growth inhibition by peptides from gelatin hydrolysate may lead to rationale designing of peptide cryoprotectants with greater antifreeze activity.”