α-Glucosidase (Bacillus stearothermophilus) (Recombinant)

Introduction: Preparation of herbal mixtures from the traditional knowledge has been used for over centuries to improve and maintain health condition. Nonetheless, lack of scientific evaluations on regard to their bioactive metabolites as a mixture and their pharmacological effects have yet to be reported. Therefore, the objectives of this study are 1) to determine the effect of processing techniques (blending and juicing) on extracting polyphenols and 2) to determine the effect ratio of honey in herbal mixture (containing ginger, garlic, honey, apple cider vinegar, and lemon juice). Methods: Raw ingredients such as garlic, ginger, lemon and apple cider (1:1:1:1) were used as the base for this herbal mixture. The base was either blended using a blender or juiced using a juicer. The mixture was simmered (85°C-100°C) until reduced to half of the initial volume and cooled down before being added with honey in 1:1 (rA) or 1:3 (rB) ratio. The mixtures were tested for pH, total phenolic, total flavonoid content and alpha glucosidase inhibitory activities. Results: Both of juiced samples in both honey ratio (rA and rB) have lower acidity compared to blended samples. Total phenolic content (TPC) and total flavonoid content (TFC) also showed significantly higher levels (p <0.5) in juiced samples than blended samples especially in Jucier rB. The insignificant differences in α-glucosidase inhibitory activities of the mixtures. Conclusions: All of the results indicate that processing techniques and ratio can affect the pH and phenolic recovery.

Isomaltose-oligosaccharides (IMOs), as food ingredients with prebiotic functionality, can be prepared via enzymatic synthesis using α-glucosidase. In the present study, the α-glucosidase (GSJ) from Geobacillus sp. strain HTA-462 was cloned and expressed in Escherichia coli BL21 (DE3). Recombinant GSJ was purified and biochemically characterized. The optimum temperature condition of the recombinant enzyme was 65°C, and the half-life was 84 h at 60°C, whereas the enzyme was active over the range of pH 6.0-10.0 with maximal activity at pH 7.0. The α-glucosidase activity in shake flasks reached 107.9 U/mL and using 4-Nitrophenyl β-D-glucopyranoside (pNPG) as substrate, the K_m and Vmax values were 2.321 mM and 306.3 U/mg, respectively. The divalent ions Mn²⁺ and Ca²⁺ could improve GSJ activity by 32.1% and 13.8%. Moreover, the hydrolysis ability of recombinant α-glucosidase was almost the same as that of the commercial α-glucosidase (Bacillus stearothermophilus). In terms of the transglycosylation reaction, with 30% maltose syrup under the condition of 60°C and pH 7.0, IMOs were synthesized with a conversion rate of 37%. These studies lay the basis for the industrial application of recombinant α-glucosidase.

Lactobacillus reuteri strain ATCC 55730 (LB BIO) was isolated as a pure culture from a Reuteri tablet purchased from the BioGaia company. This probiotic strain produces a soluble glucan (reuteran), in which the majority of the linkages are of the α-(1→4) glucosidic type (~70%). This reuteran also contains α-(1→6)-linked glucosyl units and 4,6-disubstituted α-glucosyl units at the branching points. The LB BIO glucansucrase gene (gtfO) was cloned and expressed in Escherichia coli, and the GTFO enzyme was purified. The recombinant GTFO enzyme and the LB BIO culture supernatants synthesized identical glucan polymers with respect to linkage type and size distribution. GTFO thus is a reuteransucrase, responsible for synthesis of this reuteran polymer in LB BIO. The preference of GTFO for synthesizing α-(1→4) linkages is also evident from the oligosaccharides produced from sucrose with different acceptor substrates, e.g., isopanose from isomaltose. GTFO has a relatively high hydrolysis/transferase activity ratio. Complete conversion of 100 mM sucrose by GTFO nevertheless yielded large amounts of reuteran, although more than 50% of sucrose was converted into glucose. This is only the second example of the isolation and characterization of a reuteransucrase and its reuteran product, both found in different L. reuteri strains. GTFO synthesizes a reuteran with the highest amount of α-(1→4) linkages reported to date.