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Document Type

Campus-Only Access for One (1) Year

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

Year Degree Awarded

2019

Month Degree Awarded

February

First Advisor

Eric A. Decker

Second Advisor

Maria G. Corradini

Third Advisor

Guodong Zhang

Fourth Advisor

Zhenhua Liu

Subject Categories

Food Chemistry

Abstract

The first study focuses on impact of solid fat content (SFC) on lipid oxidation and micro-structure of low moisture crackers. A series of fats were formulated to have varying SFC but the same linoleic acid (18:2) and tocopherol compositions so the fats had similar susceptibility to oxidation. A comparison of the oxidative stability of interesterified soybean oil and a blend of fully hydrogenated soybean fat and soybean oil, the interesterified fat (13.7% SFC at 55 oC) resulted in a more oxidatively stable cracker than the fat blend (17.4% SFC at 55 oC). Similarly in crackers were made from different fat blends: fully hydrogenated soybean oil + interesterified soybean oil (HI, 32.0% SFC at 55 oC), fully hydrogenated soybean oil + sunflower oil (HS, 24.9% SFC at 55 oC), and palm shortening + sunflower oil (PS, 13.2% SFC at 55 oC) , lipid oxidation increased with increasing SFC. Confocal microscopy suggested that with increasing SFC, saturated fatty acids formed solid crystals which in turn would produce a fat phase that was more concentrated in polyunsaturated and thus more susceptible to oxidation.

The second study examined the influence of water activity (aw), sugars, and proteins on lipid hydroperoxides and hexanal lag phases of model crackers. Oxidative stability of crackers was in an order: aw 0.7 > aw 0.4 > aw 0.2 > aw 0.05. High water activities resulted in bigger differences between hydroperoxides lag phases and hexanal lag phases. Compared to non-reducing cyclodextrin and no added sugar controls, reducing sugars including glucose, maltose, and maltose dextrin at a same dextrose equivalence increased both hydroperoxides and hexanal lag phases. Crackers had glucose equivalence and oxidative stability in an order: maltose > maltodextrin > glucose > control. The antioxidant effectiveness of maltose increased with increasing concentrations from 1.1 to 13.8%. Increasing aw increased the antioxidant effect of maltose. Gluten showed to be able to inhibit lipid oxidation with activity increasing with increasing aw while casein showed no antioxidant impact. Antioxidant ability of gluten decreased when sulfhydryl groups in gluten were blocked by N-ethylmaleimide suggesting that cysteine was an important antioxidant component of gluten.

Available for download on Thursday, August 01, 2019

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