Food Materials Science: RH-Temperature Phase Diagrams of Deliquescent and/or Hydrate Forming Crystals, Effects of Sweeteners on Starch Gelatinization, and the Water Activity of Wines

Matthew C Allan, Purdue University


The field of food materials science explores the roles of food solids and liquids in structuring processes in foods, and works to improve the understanding of structure-function relationships in different environments by applying the laws of thermodynamics and kinetics. This dissertation encompasses three food materials science related objectives: 1) to develop RH-temperature phase diagrams of hydrate forming deliquescent crystalline ingredients, 2) to investigate the effects of sweeteners on the gelatinization temperature (Tgel) of starch, and 3) to determine the water activity (aw) of wine, accounting for the effects of solutes. RH-temperature phase diagrams from 20-50˚C were developed for sodium sulfate, glucose, citric acid, caffeine, trehalose, and lactose. These findings are the first to document not only these phase boundaries, but also to show that the deliquescence of an anhydrous crystal can precede and accelerate hydrate formation, and that solution mediated equilibration in aw-controlled ethanol-water solutions can be utilized for precise and accelerated identification of the anhydrate-hydrate phase boundary. From investigating the effects of 19 sweeteners on the Tgel of starch, the most comprehensive comparative study to date, it was determined that the Tgel increased as sweetener concentration increased and that the sweetener solution viscosity, which was indicative of sweetener-starch intermolecular interaction potential, was the greatest predictor of Tgel. The increased starch Tgel in the presence of sweeteners was attributed to sweetener-starch intermolecular interactions in the starch amorphous regions, with supporting evidence including how sweeteners affected starch annealing and how pH affected starch-glucuronic acid interactions and measured Tgels. Historically, measuring the aw of samples containing significant amounts of volatiles was impossible; however, recent advances in instrumentation enabled the measurement of the aw of wine (n=679). The measured aws ranged from 0.860-0.968 and were highly correlated to the alcohol and sugar concentrations in the wines. While the three objectives of this dissertation covered different aspects of food materials science, findings from each provide useful information for better understanding the systems studied: the RH and temperature dependence of anhydrate/hydrate transitions, the mechanisms by which sweeteners increase the starch Tgel, and the effects of ethanol and residual sugars on the aw of wine.




Mauer, Purdue University.

Subject Area

Food Science

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