This research strove to understand the relationship between physical structure and oxidative stability in crackers since mechanisms of lipid oxidation are poorly understood in low-moisture foods. Confocal microscopy showed that lipids formed a continuous matrix surrounding starch granules, and starch-lipid, lipid-air, and protein-lipid interfaces were observed. Unlike bulk oils, meats, and emulsions, lipid hydroperoxides exhibited greater stability in low-moisture crackers as hexanal formation was delayed >20 d. Iron, added at 10 times the concentrations normally found in enriched flour, did not increase oxidation rates compared to the control. EDTA may reduce endogenous iron activity but not as greatly as in other matrices. Addition of fatty acids up to 1.0% of total lipid weight did not statistically affect lipid oxidation lag phases. The unique structure of low-moisture foods clearly affects their resistance to metal-promoted lipid oxidation.
Keywords: antioxidants; confocal microscopy; crackers; free fatty acid; iron; lipid oxidation; low-moisture foods; prooxidant metals.