Insight into the effects and biotechnological production of kestoses, the smallest fructooligosaccharides

Neokestose suppresses the increase in plasma glucose caused by oral administration of sucrose in a streptozotocin‑induced diabetic rat

Neokestose is considered to have a prebiotic function. However, the physiological activity of neokestose remains unknown. Neokestose has a blastose, a sucrose analog, in its structure. We previously demonstrated that oral administration of blastose to diabetic rats suppressed the increase in plasma glucose (PG) concentration after sucrose administration. Therefore, neokestose might have a similar effect. In this study, we investigated the effects of neokestose on PG concentrations and the mechanism of its action. We first administered neokestose orally to streptozotocin-induced diabetic rats and observed that the expected consequent increase in PG concentration was significantly suppressed. Next, we examined the inhibitory effect of neokestose on glycosidase activity, but observed only a slight inhibitory effect. Therefore, we hypothesized that neokestose might be hydrolyzed by gastric acid to produce blastose. We performed an acid hydrolysis of neokestose using artificial gastric juice. After acid hydrolysis, peaks corresponding to neokestose and its decomposition products including blastose were observed. Therefore, we suggest that neokestose and blastose, a decomposition product, synergistically inhibit glycosidase activity. These findings support the potential use of neokestose as a useful functional oligosaccharide that can help manage plasma glucose concentrations in patients with diabetes mellitus.

Production, modification and degradation of fructans and fructooligosacharides by enzymes originated from plants

Non-starch polysaccharides exhibit numerous beneficial health effects but compounds belonging to FODMAP (Fermentable Oligo- Di- and Monosaccharides and Polyols) has been recently connected to several gastrointestinal disorders. This review presents integrated literature data on the occurrence and types of fructans and fructooligosaccharids (classified as FODMAPs) as well as their degrading enzymes present in plants. Plants from the family Asteraceae and many monocotyledones, including families Poaceae and Liliaceae, are the most abundant sources of both fructans and fructan-degrading enzymes. So far, vast majority of publications concerning the application of these specific plants in production of bakery products is related to increase of dietary fibre content in these products. However, there is limited research on their effect on FODMAP content and fibre balance. The authors emphasize the possibility of application of enzyme rich plant extract in food production casting light on the new scientific approach to fibre modification.

Recent developments in the production of prebiotic fructooligosaccharides using fungal fructosyltransferases

Prebiotic nutritional ingredients have received attention due to their health-promoting potential and related uses in the food and nutraceutical industries. Recent times have witnessed an increasing interest in the use of fructooligosaccharides (FOS) as prebiotics and their generation using microbial enzymes. FOS consumption is known to confer health benefits such as protection against colon cancer, improved mineral absorption, lowering effect on serum lipid and cholesterol concentration, antioxidant properties, favourable dietary modulation of the human colonic microbiota, and immuno-modulatory effects. Comparative analysis of molecular models of various fructosyltransferases (FTases) reveals the mechanism of action and interaction of substrate with the active site. Microbial FTases carry out transfructosylation of sucrose into fructooligosaccharides (kestose, nystose, and fructofuranosylnystose), the most predominantly used prebiotic oligosaccharides. Furthermore, FOS has also been used for other purposes, such as low-calorie sweeteners, dietary fibres, and as the substrates for fermentation. This review highlights the occurrence, characteristics, immobilisation, and potential applications of FOS-generating fungal FTases. Production, heterologous expression, molecular characteristics, and modelling of fungal FTases underpinning their biotechnological prospects are also discussed.

Inherent molecular characteristics and effect of garlic polysaccharides on dough micro- and mesoscopic properties

Directional control of the process of doughs with nutrition fortification is challenging. Thus, this study aimed to develop non-starch polysaccharides that can modify the quality of flour products. Polysaccharides were extracted from three different garlic cultivars, evaluated for physicochemical properties and used to enrich doughs for microstructure and mesoscopic characteristics analysis. We assessed the moisture distribution, texture characteristics, thermodynamic properties, dynamic viscoelastic properties, protein structure, microstructure and molecular interaction of the doughs and demonstrated a relatively high molecular weight, lower steric hindrance of molecular chains and higher cross-linking ability with the dough network in the supernatant polysaccharide from Yunnan single-clove-garlic (SGSOS) fraction. These features of SGSOS fraction improved the rheological, thermodynamic, texture characteristics, and water distribution of doughs. These findings provide information on the use of garlic polysaccharides during the processing and manufacturing of foods to enhance their processing adaptability and qualities.

Characterization, production optimization, and fructanogenic traits of levan in a new Microbacterium isolate

Levan is a high-valued β-(2,6)-linked fructan with promising physicochemical and physiological properties and has diverse potential applications in the food, nutraceutical, pharmaceutical and cosmetic industry, but its commercial availability is still restricted to the relatively high costs of production. In this study, a strain identified as Microbacterium sp. XL1 was isolated from soil and highly produced exopolysaccharide (EPS). HPLC, FTIR and NMR spectroscopy revealed XL1-EPS is a levan-type fructan connected by β-(2, 6) linkages. SEM, DLS and TGA-DSC analysis showed that XL1-EPS processed high morphological versatility, narrow size distribution in its solutions and excellent thermal stability. The levan yield reached 83.67 ± 4.06 g/L with corresponding productivity of 3.49 ± 0.17 g/L/h and a conversion yield of 39.8 ± 1.9 % using sucrose (210 g/L) as substrates under the optimal cultivation conditions concluded by the response surface methodology (RSM). More strikingly, the XL1 strain also has multi-type fructanases to generate levanbiose, kestose, DFA IV and other L-FOSs. These results suggest Microbacterium sp. XL1 is a promising strain to produce levan and can provide various levan/inulin-degrading enzymes to create a great diversity of FOSs.

Effect of Humic Acid on Soil Physical and Chemical Properties, Microbial Community Structure, and Metabolites of Decline Diseased Bayberry

In recent years, bayberry decline disease has caused significant damage to the bayberry industry. In order to evaluate whether humic acid can be used to effectively control the disease, this research examined the nutritional growth and fruit quality of bayberry, soil physical and chemical properties, soil microbial community structure, and metabolites. Results indicated that the application of humic acid not only improved the vigor and fruit quality of diseased trees, but also increased the diversity of microbial communities in the rhizosphere soil. A great increase was observed in the relative abundance of bacterial genus Mycobacterium and Crossiella; fungal genus Fusarium and Coniosporium. In contrast, a significant decrease was observed in the relative abundance of bacterial genus Acidothermus, Bryobacter, Acidibacter, fungal genus of Geminibasidium and Mycena. Analysis of redundancies (RDA) for microbial communities and soil characteristics showed that the main four variables, including available nitrogen, phosphorus, potassium, and calcium, had a great effect on the composition of bacterial and fungal communities in bayberry rhizosphere soil at the genus level. The main four variables had a greater effect on bacterial communities than on fungal communities. In addition, ABC transporter, arginine and proline metabolism, galactose metabolism, and glutathione metabolism were significantly affected by humic acid, which changed the content of 81 metabolites including 58 significantly down-regulated metabolites such as isohexonic acid and carinitine, and 23 significantly up-regulated metabolites such as acidic acid, guaninosuccinate, lyxose, 2-monoolein, epicatechin, and pentonolactone. These metabolites also significantly correlated with rhizosphere soil microbiota at the phylum, order, and genus levels. In conclusion, the results demonstrated the role of humic acid on plant growth and fruit quality, as well as rhizosphere soil characteristics, microbiota, and secondary metabolites, which provides novel insights into the control of bayberry decline disease.

Directionally modulating the product chain length of an inulosucrase by semi-rational engineering for efficient production of 1-kestose

Microbial inulosucrase as a transfructosylation tool has been used to produce inulin and inulin-type fructooligosaccharides with various polymerization degrees. Tailor-made oligosaccharides could be generated by inulosucrase via chain length modulation. In this study, a semi-rational design based on the modeled structure of Lactobacillus reuteri 121 inulosucrase was carried out to screen and construct variants. The residues Arg541 and Arg544 were determined to be significant to the product chain elongation of L. reuteri 121 inulosucrase. The variant R544W altered the product specificity of inulosucrase and produced short-chain fructooligosaccharides with 1-kestose as the main component. Molecular dynamic simulations verified an increased binding free energy of variant R544W with 1-kestose than the wild-type enzyme with 1-kestose. After optimization, 1-kestose and total short-chain fructooligosaccharides production reached approximately 206 g/L and 307 g/L, respectively. This study suggests the great potential of variant R544W in the biotransformation from sucrose to functional sugar.

Comprehensive utilization of sucrose resources via chemical and biotechnological processes: A review

Sucrose, one of the most widespread disaccharides in nature, has been available in daily human life for many centuries. As an abundant and cheap sweetener, sucrose plays an essential role in our diet and the food industry. However, it has been determined that many diseases, such as obesity, diabetes, hyperlipidemia, etc., directly relate to the overconsumption of sucrose. It arouses many explorations for the conversion of sucrose to high-value chemicals. Production of valuable substances from sucrose by chemical methods has been studied since a half-century ago. Compared to chemical processes, biotechnological conversion approaches of sucrose are more environmentally friendly. Many enzymes can use sucrose as the substrate to generate functional sugars, especially those from GH68, GH70, GH13, and GH32 families. In this review, enzymatic catalysis and whole-cell fermentation of sucrose for the production of valuable chemicals were reviewed. The multienzyme cascade catalysis and metabolic engineering strategies were addressed.

Crystal Structure of Levansucrase from the Gram-Negative Bacterium Brenneria Provides Insights into Its Product Size Specificity

Microbial levansucrases (LSs, EC 2.4.1.10) have been widely studied for the synthesis of β-(2,6)-fructans (levan) from sucrose. LSs synthesize levan-type fructo-oligosaccharides, high-molecular-mass levan polymer or combinations of both. Here, we report crystal structures of LS from the G^--bacterium Brenneria sp. EniD 312 (Brs-LS) in its apo form, as well as of two mutants (A154S, H327A) targeting positions known to affect LS reaction specificity. In addition, we report a structure of Brs-LS complexed with sucrose, the first crystal structure of a G^--LS with a bound substrate. The overall structure of Brs-LS is similar to that of G^-- and G⁺-LSs, with the nucleophile (D68), transition stabilizer (D225), and a general acid/base (E309) in its active site. The H327A mutant lacks an essential interaction with glucosyl moieties of bound substrates in subsite +1, explaining the observed smaller products synthesized by this mutant. The A154S mutation affects the hydrogen-bond network around the transition stabilizing residue (D225) and the nucleophile (D68), and may affect the affinity of the enzyme for sucrose such that it becomes less effective in transfructosylation. Taken together, this study provides novel insights into the roles of structural elements and residues in the product specificity of LSs.

The β-Fructofuranosidase from Rhodotorula dairenensis: Molecular Cloning, Heterologous Expression, and Evaluation of Its Transferase Activity

The β-fructofuranosidase from the yeast Rhodotorula dairenensis (RdINV) produces a mixture of potential prebiotic fructooligosaccharides (FOS) of the levan-, inulin- and neo-FOS series by transfructosylation of sucrose. In this work, the gene responsible for this activity was characterized and its functionality proved in Pichia pastoris. The amino acid sequence of the new protein contained most of the characteristic elements of β-fructofuranosidases included in the family 32 of the glycosyl hydrolases (GH32). The heterologous yeast produced a protein of about 170 kDa, where N-linked and O-linked carbohydrates constituted about 15% and 38% of the total protein mass, respectively. Biochemical and kinetic properties of the heterologous protein were similar to the native enzyme, including its ability to produce prebiotic sugars. The maximum concentration of FOS obtained was 82.2 g/L, of which 6-kestose represented about 59% (w/w) of the total products synthesized. The potential of RdINV to fructosylate 19 hydroxylated compounds was also explored, of which eight sugars and four alditols were modified. The flexibility to recognize diverse fructosyl acceptors makes this protein valuable to produce novel glycosyl-compounds with potential applications in food and pharmaceutical industries.