Structure and physicochemical properties of tuber starches modified by Lactobacillus reuteri 121 4,6-α-glucanotransferase GtfBdN
JIANG Tong1,2,3,4, JI Hangyan1,2,3,4, BAI Yuxiang1,2,3,4*
1(State Key Laboratory of Food Science and Technology,Jiangnan University,Wuxi 214122,China) 2(School of Food Science and Technology,Jiangnan University,Wuxi 214122,China) 3(Synergetic Innovation Center of Food Safety and Nutrition,Jiangnan University,Wuxi 214122,China) 4(International Joint Laboratory on Food Safety,Jiangnan University,Wuxi 214122,China)
Abstract: After the modification by Lactobacillus reuteri 121 4,6-α-glucanotransferase (4,6-α-GTase) GtfB, a water-soluble dietary fiber with probiotic potential can be obtained from starch. At present, the research has focused on the correlation between the structure of the product and its functional properties such as digestibility and probiotics. However, the research on the correlation between the structure and the physicochemical properties which are crucial for food processing has not yet been carried out. In this study, overexpressed GtfBdN with truncated N-terminal but full activity was used to modify tuber starches, including sweet potato starch, tapioca starch and potato starch. The structures and properties of the products were determined. The analysis results of nuclear magnetic resonance (NMR) spectroscopy, high performance size exclusion chromatography (HPSEC) and high performance anion exchange chromatography (HPAEC) showed that GtfBdN modification increased the ratio of (α1→6) bond in sweet potato starch, tapioca starch and potato starch to 20.7%, 19.5% and 26.6%, respectively; the relative molecular weight of the product was reduced, and the peak of molecular weight distribution was broader, the proportion of segments with DP>24 decreased, and the proportion of segments with DP 6-12 greatly increased. Tests such as rapid visco-analyzer (RVA), rheometer and differential scanning calorimetry (DSC) showed that the viscosity of the product dropped significantly, showing more fluid behavior, and the short-term and long-term retrogradation slowed down. This research provides theoretical and application basis for the application of 4,6-α-GTase modified tuber starch in food systems.
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