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Open Access Dissertation
Doctor of Philosophy (PhD)
Year Degree Awarded
David Julian McClements
Food Science | Nutrition
Low-moisture snacks account for much of the saturated fat in the diet, making them a key target for improving consumers’ health. However, it is not currently feasible to maintain the same shelf life when replacing saturated fats with unsaturated fats in these products.
The first study characterized the microstructure of a low-moisture cracker model system and determined the impact of iron, chelators, and free fatty acids (FFA) on lipid oxidation kinetics. Confocal microscopy showed that lipids form a continuous layer surrounding the small and/or minimally gelatinized starch granules. Lipid-starch, lipid-air, and starch-lipid-protein interfaces all existed. Oxidation studies showed a large difference between the rates of hydroperoxide and headspace hexanal formation in crackers. Crackers containing 10X the usual amount of reduced iron were as oxidatively stable as the control. FFA decreased hexanal lag phases only when added at concentrations greater than 1.0% (w/w) of the total lipid weight. Metal chelators (citric acid, desferoxamine, and ethylenediaminetetraacetic acid) were mildly effective at extending the headspace hexanal lag phage. These results suggested that transition metals were not as strongly prooxidative in the crackers as they are in oil-in-water emulsions and bulk oil.
The second study examined antioxidant efficacy in the low-moisture cracker model system. Rosmarinic acid esters of varying polarity exhibited different partitioning behavior (viewed with confocal microscopy) and antioxidant activity. Surprisingly, the 20-carbon ester of rosmarinic acid exhibited the strongest antioxidant activity as determined by lipid hydroperoxides and headspace hexanal generation compared to oil-in-water emulsions where the 20-carbon ester is a very poor antioxidant. Degradation of the 20-carbon ester was slower than the other rosmarinic acid derivative’s as determined by HPLC. The activity of the 12-carbon ester of rosmarinic acid varied as a function of how it was added to the cracker model with increased effectiveness observed when the antioxidant was added to the lipid phase prior to formation of the dough. Synthetic, commercial antioxidants followed a similar trend with the most nonpolar being the most effective. This research highlights the need to gain a better understanding of lipid oxidation in low-moisture foods so more effective antioxidant technologies can be developed.
Barden, Leann M., "Understanding Lipid Oxidation in Low-Moisture Food" (2014). Doctoral Dissertations. 155.