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  • Title: Wheat Starch with Low Retrogradation Properties Produced by Modification of the GtfB Enzyme 4,6-α-Glucanotransferase from Streptococcus thermophilus.
    Author: Li X, Fei T, Wang Y, Zhao Y, Pan Y, Li D.
    Journal: J Agric Food Chem; 2018 Apr 18; 66(15):3891-3898. PubMed ID: 29582651.
    Abstract:
    A GtfB enzyme 4,6-α-glucanotransferase from Streptococcus thermophilus lacking 761 N-terminal amino acids was heterologously expressed in Escherichia coli. Purified S. thermophilus GtfB showed transglycosylation activities toward starch, resulting in branch points of (α1→6)-glycosidic linkages plus linear chains of (α1→4)-glycosidic linkages. After wheat starch was modified at a rate of 0.1 g/mL by 1-4 U/g starch GtfB at pH 6.0 and 40 °C for 1 h, the weight-averaged molecular weight decreased from 1.70 × 107 g/mol to 1.21 × 106 to 3.41 × 106 g/mol, the amylose content decreased from 22.07 to 16.34-17.11%, and that of amylopectin long-branch chains decreased from 26.4 to 10.25-15.64% ( P < 0.05). After the GtfB-modified wheat starches were gelatinized and stored at 4 °C for 1-2 weeks, their endothermic enthalpies were significantly lower than that of the control sample ( P < 0.05), indicating low retrogradation rates.
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