30C-20 |
Effects of ascorbic acid and its degradation products on the molecular weight and solubility of gelatin when stored at low moisture |
A. FARAHNAKY1, S. E. Hill, D. A. Gray, and J. R. Mitchell. (1) Food Sciences Division, Sutton Bonington Campus, University of Nottingham, Loughborough, Leics, LE12 5RD, England Alteration of gelatin's molecular properties affects its functionality. It is known that processing can reduce gelatin's molecular weight while chemicals can cause crosslinking. Vitamin C is regularly added to food and pharmaceuticals that are prepared and stored at different water contents. Ascorbic acid (AA) has the potential to act as a crosslinker or a chain breaker. It may generate free radicals leading to chain breaking, or could form crosslinks as shown to occur using reducing sugars. Studies were performed to elucidate the effects on gelatin of materials based on ascorbic acid (MAA) i.e. AA, dehydroascorbic acid, 2,3-diketo-gulonic acid and glyoxal. Gelatin (Type B, pI 5.5) was intimately mixed with MAAs 1% (w/w). Products were then stored at different relative humidities for 6 hours at 80 ºC and 3 months at 50 ºC. Apparent viscosity, color, free lysine content and protein solubility in water and SDS were measured. Using dynamic mechanical thermal analysis (DMTA) the Tgs of the samples were obtained. Test samples with 8.7, 24 and 48% moisture after 6 hours storage showed increases in viscosity and color and falls in free lysine and solubility. Samples at < 4% moisture showed no significant changes, except for color. The DMTA analysis showed that samples stored at 50 ºC and 13% moisture would be glasses. Samples stored under these conditions with AA or dehydro-AA showed a doubling of molecular weight after 12 and 1 weeks storage, respectively. All ascorbic acid products tested apparently crosslink gelatin and cause insolubility. The mechanism appears to be based on the Maillard reaction. Storage, when gelatin is in the glass, dramatically slows the reaction, but it still is able to proceed. As well as diffusion of Maillard products there must be sufficient mobility of sidechains and backbone of the protein to allow the proposed mechanism.
Session 30C, Food Chemistry: Proteins
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