Ice-cream without the crunch

A mixture of molecules obtained from gelatin could help to make food last longer in the freezer and make ice-cream creamier, a food scientist in the US has suggested. 

Many animals, ranging from fish to insects, produce their own specific antifreeze agents - usually proteins - that bind to very small ice crystals and stop them from growing. 

Food scientists have already explored the use of these ’ice-structuring proteins’ (ISPs) to minimise damage to food during freezing, storage and thawing, and to avoid the crunchy ice crystals that sometimes form in ice-cream after it is refrozen. Food and healthcare giant Unilever, for example, already sells products including ISPs. But their process of producing them from genetically modified yeast has drawn some unwanted attention from the anti-GM food movement. 

Now Srinivasan Damodaran, a professor of food chemistry at the university of Wisconsin at Madison has come up with a simpler way of producing food-compatible antifreeze. He started from gelatin, a common food ingredient used in jelly and marshmallows. 

Gelatin is made by partial degradation of the structural protein collagen, and can be produced in industrial amounts from slaughterhouse waste, such as cattle bones or pork skins. Damodoran subjected commercial gelatine samples to an enzymatic digestion using the enzyme papain. Analysing the resulting peptide fragments, he found that the smaller ones, with molecular weights below 3000 Dalton, display strong antifreeze activity [1]. 

Studying ice-cream samples with or without addition of these peptides, he showed that in trials mimicking the conditions of a typical home freezer, the gelatin peptides were able to suppress the growth of ice crystals very effectively. 

Mechanism mystery 

Damodaran claims that the peptides show some similarity to natural ISPs, as both tend to have repeating patterns of three amino acids. In particular, the ISPs of snow fleas, discovered in 2005 by the group of Peter Davies at Queen’s University at Kingston, Ontario, Canada, have triplets starting with glycine, as do the collagen peptides[2]. 

Davies told Chemistry World: ’The ice recrystallization inhibition obtained with the small peptides generated from gelatin by papain seems real and warrants further investigation.’ 

But he questioned Damodran’s proposed mechanism for the observed effects. ’The modelling shown in the paper is premature without this information, and the proposed mechanism for binding to ice seems too simplistic.’ 

Michael Gross