Barley starch behavior in the presence of rutin under subcritical water conditions

Abstract

Starch-flavonoid complexation has relevance for functional food applications; therefore, this study was carried out to understand the behavior of barley starch and the flavonoid rutin, via treatment in an environmentally friendly media known as subcritical water. Barley starches with varying amylose contents of 37%, 22%, and 0% with rutin (4.90 mg), and without rutin were heat-treated at 80 °C and subcritical water-treated at 100, 120, 140, and 160 °C and 70 bar for 30 min. The highest rutin content (0.87 ± 0.06 mg/g modified starch, dry matter) was obtained for 0% amylose starch at 100 °C. Loss of apparent amylose was an indication of V-amylose inclusion complexation in 37% amylose starch at 100 °C (7.16%), and 22% amylose starch at 120 °C (6.67%). FTIR analysis showed that the rutin complexation in the starches was related to the short-range order of the treated starches. All treated starches expanded but 37% amylose starch with rutin had the highest expansion of 6.10 ± 0.12 mL/g (392% increase) at 160 °C from 1.24 ± 0.01 mL/g of native 37% amylose starch at room temperature (25 °C). Viscoelastic characterization showed that the treated starches were weak gels with 37% amylose, showing higher elastic component than 22% and 0% amylose starch gels. There was no significant difference in storage modulus G’ for 0% amylose starch gels. Yellowness index was high in samples of 0% amylose at 100 °C (6.96 ± 0.00), and 22% amylose at 80 °C (6.60 ± 0.06).