Thiamin stability in solids as affected by the glass transition

The stability of thiamin was evaluated in solid polyvinylpyrrolidone model systems as a function of water activity (a(W)) and the glass transition, In the glassy state, thiamin degradation rate constants correlated with the glass transition temperature (T-g), decreasing as T-g increased. Above a(W) 0.4, rate constants correlated better with a(W) rather than T-g. However, rate constants decreased in the rubbery state above a(W) 0.4, which could be attributed to glass transition induced structural collapse. Glass transition effects (mobility considerations, collapse) have a larger effect on thiamin stability than a(W), which should be recognized during the development of fortified food products.