Abstract: In this study, five wheat flour samples with different processing degrees were selected and stored at 40℃ and relative humidity of 70% for 6 months. The effect of processing degree on the storage stability of wheat flour was investigated through analyses of changes in their lipids (glyceride contents and fatty acid compositions) and physicochemical properties related to lipids (fatty acid values, peroxide values, and malondialdehyde contents) during storage. The contents of triglycerides and diglycerides in wheat flour samples decreased while the contents of monoglycerides and fatty acids increased with storage time, indicating that the lipids were hydrolyzed. After 6 months of storage, the increase in fatty acid value of sample 5 was 16.22 times higher when compared with sample 1. The lower the processing degree, the higher the degree of hydrolysis of the lipids. Both peroxide values and malondialdehyde contents showed an upward trend with storage time, indicating that oxidation of the lipids occurred accompanied by their hydrolysis. After 6 months of storage, the increase in peroxide value and malondialdehyde content of sample 5 was 4.81 and 7.44 folds when compared with sample 1, respectively. The lower the processing degree was, the greater the increase in peroxide value and malondialdehyde content was, and the faster oxidative rancidity occurred. The wheat flour samples with different processing degrees had similar fatty acid compositions, and both saturated and unsaturated fatty acid compositions of crude lipids extracted from the wheat flour samples did not obviously change with storage time.

Key words: wheat flour, lipid, fatty acid, peroxide value, malondialdehyde