Journal
FOODS
Volume 8, Issue 10, Pages -Publisher
MDPI
DOI: 10.3390/foods8100452
Keywords
starch; alpha-glucan branching enzyme (GBE); branching activity; in vitro digestibility
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Funding
- Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Science, ICT and Future Planning [NRF-2013R1A2A2A01068096, NRF-2016R1A2B4011554]
- NRF [NRF-2018R1D1A1B07041112]
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Two thermophilic 1,4-alpha-glucan branching enzymes (GBEs), CbGBE from Caldicellulosiruptor bescii and PhGBE from Pyrococcus horikoshii, which belong to the glycoside hydrolase family 13 and 57 respectively, were cloned and expressed in Escherichia coli. Two GBEs were identified to have alpha-1,6 branching activity against various substrates, but substrate specificity was distinct. Starch was modified by two GBEs and their in vitro digestibility and structural properties were investigated. Short-branched A chains with a degree of polymerization (DP) of 6-12 increased with CbGBE-modified starch, increasing the proportion of slow digestible and resistant starch (RS) fractions. PhGBE-modified starch resulted in an increase in the RS fraction only by a slight increase in part of A chains (DP, 6-9). Compared to the proportion of control not treated with GBE, the proportion of alpha-1,6 linkages in CbGBE- and PhGBE-modified starch increased by 3.1 and 1.6 times. C-13 cross polarization/magic angle sample spinning (CP/MAS) NMR and XRD pattern analysis described that GBE-modified starches reconstructed double helices but not the crystalline structure. Taken together, CbGBE and PhGBE showed distinct branching activities, resulting in different alpha-1,6 branching ratios and chain length distribution, and double helices amount of starch, ultimately affecting starch digestibility. Therefore, these GBEs can be used to produce customized starches with controlled digestion rates.
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