Phenolic Compounds and Antioxidant Properties during Production of Bread from Purple-Colored Wheat Grains
L. YU (1), T. Beta (2). (1) Univ of Manitoba, Winnipeg, MB, Canada; (2) University of Manitoba, Winnipeg, MB, Canada
Even though increasing evidence indicates the health potential of wheat to reduce the risk of oxidative-stress related chronic diseases, food manufacturing may compromise the beneficial properties, resulting in loss of antioxidant activities. Therefore, changes in phenolic acids, the most abundant antioxidants, and anthocyanins, the distinct pigmentation of colored grain, were investigated during bread-making. Bread inside, crust as well as samples collected after mixing, 30min and 65min fermentation, and baking were examined. Phenolic content, total anthocyanin content (TAC), DPPH• scavenging capacity and ABTS•+ decolorization ability were employed. The subgroups under phenolic acids and anthocyanins were identified and quantified using HPLC. Free phenolic content (105.4~113.2 mg FA equiv./100g) significantly (p<0.05) increased during mixing, fermentation and baking (65%~68%), while bound phenolics slightly decreased after 30min fermentation (7%~9%) compared to the dough after mixing, but increased significantly during 65min fermenting and baking (16%~27%). Their antioxidant activities were corresponded to their TPC trends. The bread crust demonstrated increased free (103%~109%) but decreased bound (2%~3%) phenolic content, whereas inner-side of the bread exhibited a reversal of result. TAC significantly decreased after mixing (21%); however, gradually increased to 90% of their original levels after fermenting. Baking significantly decreased TAC by 55% with a lowest TAC in bread crust (0.8 to 4.4 mg cyn-3-glu equiv./100g). p-Hydroxybenzoic, vanillic, p-coumaric and ferulic acids were detected in free- while protocatechuic, caffeic syringic and sinapic were additional acids in bound- phenolic extracts. The bread-making process significantly increased the phenolic content and antioxidant activities; however, it compromised the anthocyanin content of purple wheat bread.
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