Impact of laccase-induced protein cross-linking on the in vitro starch digestion of black highland barley noodles

Abstract

The aim of this work is to evaluate the influence of laccase (LAC) on protein cross-linking and the in vitro starch digestion of black barley noodles (BHBN). In addition, the mechanisms underlying the impacts of protein cross-linking induced by LAC on the starch digestion were further elucidated. When the addition of LAC from 0% to 0.4%, in vitro starch digestion curves showed that the rate of in vitro starch digestion within the initial 60 min (k1) significantly (P < 0.05) decreased from 0.0161 to 0.0083, and the maximum hydrolysis extent at 300 min (C∞) significantly (P < 0.05) decreased from 58.55% to 48.48%. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) revealed that LAC induced an increasingly continuous and compact protein network, which wrapped starch granules more tightly. Meanwhile, a significantly (P < 0.05) decreasing trend of sodium dodecyl sulfate extractable protein (SDSEP) content under reducing and non-reducing conditions was observed, indicating that LAC addition promoted the degree of protein cross-linking in BHBN. Furthermore, the content of dityrosine increased by 12%, along with the decrease of free sulfhydryl and phenolic (17% and 42%, respectively), when LAC addition was increased (0–0.4% black highland barley flour). Significant correlations (P < 0.05) were observed between LAC addition, SDSEP (the degree of protein cross-linking) and in vitro starch digestion. These results can enrich theory research in the field of protein cross-linking in the starch digestion of noodle, and also promote the development of noodles with low glycemic index values.