Retrogradation behavior of extruded whole buckwheat noodles: An innovative water pre-cooling retrogradation treatment

Abstract

In this study, effects of different retrogradation treatments including room temperature retrogradation (25-RT), 4 °C refrigerator retrogradation (4-LT), 4 °C water pre-cooling for 10 s (4-WP), 4 °C water pre-cooling for 10 s plus 4 °C refrigerator retrogradation (4-WP+4-LT) on the starch fine structure, noodle microstructure, cooking characteristics and in vitro starch digestibility of extruded whole buckwheat noodles were investigated. Results showed that 4-WP could facilitate the formation of starch gel network structure and retention of water molecules in noodles. The combined treatment of 4-LT and 4-WP+4-LT at 120 min had the highest retrogradation enthalpy (124.46 J/g) and highest degree of retrogradation which reflected by infrared ratio of absorbance at 1047 cm−1/1022 cm−1 (0.82) and relative crystallinity (24.93%). Scanning electron microscopy (SEM) showed that large pores in noodle cross-sections disappeared and the microstructure was significantly improved after 4-WP+4-LT treatment, resulting in lowest noodle cooking loss (11.57%) and broken rate (2.22%), and highest hardness (1895.87 g). In addition, 4-WP also resulted in the highest springiness of 0.97. In vitro starch digestibility results showed that recrystallized structure formed by amylose reduced the catalytic efficiency of amylase, resulting in decreasing predicted glycemic index (pGI) from 79.33 to 71.85. These findings indicated that treatment of 4-WP+4-LT showed the great potential to produce whole buckwheat noodles with higher quality characteristics.