Influence of extrusion on the bioactive compounds and the antioxidant capacity of the bean/corn mixtures

The aim of this investigation was to examine the influence of extrusion on the bioactive compounds and the antioxidant capacity of bean/corn mixtures. Whole bean flour and nixtamalized corn were mixed in a 60:40 proportion and extrusion was performed in different moisture (14.5%, 15.4%, 17.1% and 18.0%) and temperature (150 degrees C, 160 degrees C, 170 degrees C, 180 degrees C and 190 degrees C) conditions in order to find the optimal extrusion conditions. According to their functional properties and antioxidant status, the mixtures 142 degrees C/16.3% H, 170 degrees C/16.3% H and 198 degrees C/16.3% H were defined as optimal, moderate and bad, respectively. Total polyphenols and flavonoids in the mixture of 142 degrees C/16.3% H (15.09 +/- 1.7 mg gallic acid equivalent [GAE]/g dry weight [DW] and 1.57 +/- 0.2 mg catechin equivalent [CE]/g DW) were significantly higher (P < 0.05) than in the sample 170 degrees C/16.3% H (9.42 +/- 1.1 mg GAE/g DW and 1.4 +/- 0.1 mg CE/g DW) and the mixture 198 degrees C/16.3% H (6.46 +/- 0.8 mg GAE/g DW and 0.78 +/- 0.1 mg CE/g DW). The antioxidant activity (37.02 +/- 3.8 and 25.01 +/- 2.5 mu M Trolox equivalent [TE]/g DW) of mixture 142 degrees C/16.3% H, determined by the cupric reducing antioxidant capacity with Trolox equivalent antioxidant capacity and beta-carotene-linoleic acid (beta-carotene,% of inhibition) assays, was significantly higher (P < 0.05) than in 170 degrees C/16.3% H (25.69 +/- 2.8 and 17.02 +/- 1.8 mu M TE/g DW) and in mixture 198 degrees C/16.3% H (13.93 +/- 1.5 and 8.94 +/- 0.9 mu M TE/g DW), respectively. The free polyphenols, flavonoids and the antioxidant activities showed lower results than the hydrolyzed ones. The correlation coefficients between polyphenols, flavonoids, and cupric reducing antioxidant capacity capacities were between 0.93 and 0.99. In cereal proteins extracted and separated by electrophoresis, some differences were found in the sodium dodecyl sulfate-protein bands in the region from 36 to 45 kDa for 142 degrees C/16.3% H, in comparison with other samples. Therefore, there is a need to find such conditions for the extrusion procedures that would take into consideration the contents of the bioactive compounds and the antioxidant capacity in the end product.