Effect of germination time and temperature on bioactive compounds of purple corn (Zea mays L.)

Abstract

Purple corn is a pigmented variety of Zea mays L. that constitutes a rich source of phenolic compounds, mainly anthocyanins with recognized antioxidant and anticarcinogenic activities. Germination enhances the phytochemical content of cereal grains, being the extent of these changes dependent on germination conditions. Studies on the effect of germination on purple corn phytochemical composition are scarce. The objective was to optimize germination time and temperature for production of purple corn sprouts with the highest levels of gamma-aminobutyric acid (GABA), total phenolic compounds (TPC) and antioxidant activity. Optimization was carried out using Response Surface Methodology (RSM) with a 22 central composite rotational design. The phenolic composition of purple corn sprouts obtained in the optimal conditions was analysed by HPLC-DAD-ESI/MS. The GABA, TPC and antioxidant activity of purple corn seeds were 15.27mg GABA/100g dw (dry weight), 1679.72 mg GAE/100g dw and 4837.06 mg TE/100g dw, respectively. Temperature and time were key factors affecting the content of bioactive compounds and the antioxidant activity of purple corn. GABA increased after seed germination ranging from 22.40 to 53.17mg/100g dw (P<0.05). In contrast, TPC and antioxidant activity decreased (P<0.05), regardless germination temperature and time. In the optimal germination conditions (26°C and 63 h) a 3.5-fold increase of GABA and reduction of total non-anthocyanin compounds (30%) and antioxidant activity (14%) were observed (P<0.05) while total anthocyanin content remained constant. Anthocyanins were the most abundant phenolic class in purple corn sprouts detected mainly as cyanidin, pelargonidin and peonidin glycosides. These antocyanins were also detected as acylated with malonic acid and condensed with flavanols by C-C linkages. Hydroxycinnamic derivatives and flavonols such as quercetin and kampferol glycosides were also detected as minor compounds in purple corn sprouts. In summary, purple corn sprouts have an excellent potential as sources of health promoting compounds such as GABA and anthocyanins.