Effects of storage and heat processing on the content and composition of free fatty acids in oats

The effects of storage and heat processing on the content and composition of free fatty acids (FFA) in oats (Avena sativa L.) have been studied. Samples of three cultivars (Kapp, Mustang, and Svea) were stored at 30, 55, and 80% rh for 3.5 and 15.5 months before heat processing of hulled and dehulled grains. Results from gas chromatographic analysis of individual FFA were closely correlated (r = 0.962) with measurements of acidity by titration of ethanol extracts. No significant differences in acidity were detected among the cultivars studied. After 3.5 months, the FFA content in the cultivar Kapp was 3.5 and 6.6 mg/g of dry matter when stored at 30 and 80% rh, respectively. After 15.5 months, FFA content increased to 5.4 and 11.3 mg/g of dry matter when stored at 30 and 80% rh, respectively. Measurement of acidity by titration was less specific and resulted in smaller relative differences. During processing, the FFA content and fat acidity was reduced by an average of 50%. This reduction in FFA is probably due to complexing of fatty acids, while the relative reduction in linolenic acid during storage and processing is related to an increasing content of volatile oxidation products, of which hexanal is an indicator. The total lipid content of oats did not change significantly during processing. After 15.5 months of storage, the lipid content was lower at 80% rh than at 30% rh; the content of ether-extractable lipids was 0.77 percentage points lower, while the content of total fatty acids was 0.43 percentage points lower. No such differences were detected by ether extraction after acid hydrolysis.