Slowly digestible starch--a review

The link between carbohydrate intake and health is becoming increasingly important for consumers, particularly in the areas of glycemic index (GI) and extended energy-releasing starches. From a physiological point of view, slowly digestible starch (SDS) delivers a slow and sustained release of blood glucose along with the benefits resulting from low glycemic and insulinemic response. SDS has been implicated in several health problems, including diabetes, obesity, and cardiovascular diseases (metabolic syndromes). It may also have commercial potential as a novel functional ingredient in a variety of fields, such as nutrition, medicine, and agriculture. The present review assesses this form of digestion by analyzing methods to prepare and evaluate SDS, and factors affecting its transformation, its health benefits, and its applications.

The osteogenic potential of ligament fibroblasts is greater in ankylosing spondylitis patients than in patients with osteoarthritis

BACKGROUND

The goal of the present study was to investigate the osteogenic potential of ligament fibroblasts from patients with ankylosing spondylitis (AS).

MATERIALS AND METHODS

Ligament fibroblasts were isolated from tissues harvested from AS patients and patients with aseptic necrosis of the femoral head (ANFH) who had undergone total hip arthroplasty (THA). Cells were cultured in osteogenic induction medium (OIM) with or without bone morphogenetic protein 2 (BMP-2) for 30 days. During this time, the levels of alkaline phosphatase (ALP) and osteocalcin (OC) were determined as markers of osteogenesis.

RESULTS

Ligament fibroblasts isolated from patients with AS exhibited significantly greater potential for differentiation than those isolated from patients with osteoarthritis (ANFH).

CONCLUSION

These findings illuminate osteogenesis as a new pathway for studying the mechanism underlying ankylosis in AS patients. Factors which cause localized stromal remodeling at the enthesis significantly influence formation of new bone and further research is required to determine the mechanisms responsible for the osteogenic potential of enthesis cells and ligament fibroblasts in AS patients.

Intracellular synthesis of glutamic acid in Bacillus methylotrophicus SK19.001, a glutamate-independent poly(γ-glutamic acid)-producing strain

BACKGROUND

Bacillus methylotrophicus SK19.001 is a glutamate-independent strain that produces poly(γ-glutamic acid) (γ-PGA), a polymer of D- and L-glutamic acids that possesses applications in food, the environment, agriculture, etc. This study was undertaken to explore the synthetic pathway of intracellular L- and D-glutamic acid in SK19.001 by investigating the effects of tricarboxylic acid cycle intermediates and different amino acids as metabolic precursors on the production of γ-PGA and analyzing the activities of the enzymes involved in the synthesis of L- and D-glutamate.

RESULTS

Tricarboxylic acid cycle intermediates and amino acids could participate in the synthesis of γ-PGA via independent pathways in SK19.001. L-Aspartate aminotransferase, L-glutaminase and L-glutamate synthase were the enzymatic sources of L-glutamate. Glutamate racemase was responsible for the formation of D-glutamate for the synthesis of γ-PGA, and the synthetase had stereoselectivity for glutamate substrate.

CONCLUSION

The enzymatic sources of L-glutamate were investigated for the first time in the glutamate-independent γ-PGA-producing strain, and multiple enzymatic sources of L-glutamate were verified in SK19.001, which will benefit efforts to improve production of γ-PGA with metabolic engineering strategies.

Improving the catalytic behavior of inulin fructotransferase under high hydrostatic pressure

BACKGROUND

The demand for difructose anhydride III (DFA III), a novel functional sweetener, is growing continuously. It is produced from inulin by inulin fructotransferase (IFTase). In this study, high hydrostatic pressure (HHP), as a clean technology, was first applied to further improve the catalytic efficiency of IFTase in the process.

RESULTS

The maximum activity of IFTase was obtained under 200 MPa at 60 °C. Meanwhile, HHP lowered the energy barrier necessary for the enzymatic reaction and decreased the volume between the reactants and the transition state. Under this condition, the optimal pH for the enzymatic reaction shifted from 5.5 to 6.0. The activity was further enhanced by 65.2% in the presence of 1.5 mol L(-1) NaCl.

CONCLUSION

The catalytic reaction of IFTase was performed under HHP for the first time. HHP, as a promising green technology for bioconversion, significantly accelerated the enzymatic reaction under the appropriate operational conditions.

Polysaccharide Modification through Green Technology: Role of Endodextranase in Improving the Physicochemical Properties of (1→3)(1→6)-α-D-Glucan

The structure and properties of bioengineered (1→3)(1→6)-α-D-glucan subjected to endodextranase treatment were investigated. Upon enzyme treatment, OD220 and Mw decreased substantially during the first 60 min and thereafter slowed as the modification progressed. Compared to the native glucan, the modified sample solution had a lighter opalescent, bluish-white color. The morphological analysis revealed that bioengineered glucan produced quite a few small particles after hydrolysis. The molecular weight distribution curve gradually shifted to the low Mw region with a significant broadening distribution, and the chain hydrolysis reaction followed a combination of zeroth- and first-order processes. The NMR results showed some specific α-1,6 linkages of glucan chains were cleaved with enzyme treatment. The viscosity of modified glucan solution was markedly reduced, and the Newtonian plateaus were also observed at high shear rates (10-100 1/s). The above results suggested that the modified (1→3)(1→6)-α-D-glucan showed a tailor-made solution character similar to that of arabic gum and would be used as a novel food gum substitute in the design of artificial carbohydrate-based foods.

The tomato DDI2, a PCNA ortholog, associating with DDB1-CUL4 complex is required for UV-damaged DNA repair and plant tolerance to UV stress

CULLIN 4 (CUL4)-DAMAGED DNA binding protein 1 (DDB1)-based ubiquitin E3 ligase modulates diverse cellular processes including repair of damaged genomic DNA. In this study, an uncharacterized gene termed as DDB1-Interacting protein 2 (DDI2) was identified in yeast two-hybrid screening with bait gene DDB1. The co-immunoprecipitation (co-IP) assays further demonstrated that DDI2 is associated with tomato DDB1-CUL4 complex in vivo. It appears that DDI2 encodes an ortholog of proliferating cell nuclear antigen (PCNA). Confocal microscope observation indicated that DDI2-GFP fusion protein was localized in nuclei. The expression of DDI2 gene is constitutive but substantially enhanced by UV-C irradiation. The transgenic tomato plants with overexpression or knockdown of DDI2 gene displayed the increased or decreased tolerance, respectively, to UV-C stress and chemical mutagen cisplatin. The quantitative analysis of UV-induced DNA lesions indicated that the dark repair of DNA damage was accelerated in DDI2 overexpression lines but delayed in knockdown lines. Conclusively, tomato DDI2 gene is required for UV-induced DNA damage repair and plant tolerance to UV stress. In addition, fruits of DDI2 transgenic plants are indistinguishable from that of wild type, regarding fresh weight and nutrient quality. Therefore, overexpression of DDI2 offers a suitable strategy for genetic manipulation of enhancing plant tolerance to UV stress.

Purification and characterization of an intracellular levansucrase derived from Bacillus methylotrophicus SK 21.002

An intracellular levansucrase from Bacillus methylotrophicus SK 21.002 was isolated, purified, and characterized. The final specific levansucrase activity was 135.40 U/mg protein with an 11.78-fold enrichment and a 9.28% recovery rate. The molecular weight of the enzyme was approximately 60,000 Da as evaluated by gel filtration and SDS-PAGE. Both the maximum transfructosylation and hydrolytic activities were observed at pH 6.5. The enzyme exhibited optimum transfructosylation activity at 40 °C, whereas the optimum temperature of hydrolytic activity was 45 °C. Cu(2+), Fe(2+), Zn(2+), and Ni(2+) inhibited both the transfructosylation and hydrolytic activities up to 100%, whereas Mn(2+) inhibited only hydrolytic activity. Ca(2+) and Mg(2+) stimulated both transfructosylation and hydrolytic activities. The chemical modifiers (n-bromosuccinimide and phenylmethanesulfonyl fluoride) strongly inhibited hydrolytic and transfructosylation activity of the levansucrase. The Km and Vmax values of the purified levansucrase were 117.2 mM and 33.23 μmol/mg·Min, respectively. When the fructose concentration was below 0.2 M, higher fructose concentrations promoted the transfructosylation and inhibited the hydrolytic activity.

Interaction mechanism between green tea extract and human α-amylase for reducing starch digestion

This study evaluated the inhibitory effects of the green tea extract on human pancreatic α-amylase activity and its molecular mechanism. The green tea extract was composed of epicatechin (59.2%), epigallocatechin gallate (14.6%) and epicatechin gallate (26.2%) as determined by HPLC analysis. Enzyme activity measurement showed that % inhibition and IC50 of the green tea extract (10%, based on starch) were 63.5% and 2.07 mg/ml, respectively. The Michaelis-Menten constant remained unchanged but the maximal velocity decreased from 0.43 (control) to 0.07 mg/(ml × min) (4 mg/ml of the green tea extract), indicating that the green tea extract was an effective inhibitor against α-amylase with a non-competitive mode. The fluorescence data revealed that the green tea extract bound with α-amylase to form a new complex with static quenching mechanism. Docking study showed the epicatechin gallate in the green tea extract presented stronger affinity than epigallocatechin gallate, with more number of amino acid residues involved in amylase binding with hydrogen bonds and Van der Waals forces. Thus, the green tea extract could be used to manipulate starch digestion for potential health benefits.

Metabolic mechanism of phenyllactic acid naturally occurring in Chinese pickles

Phenyllactic acid, a phenolic acid phytochemical with the antimicrobial activity, was rarely reported in food besides honey and sourdough. This study evidenced a new food source of phenyllactic acid and elucidated its metabolic mechanism. Phenyllactic acid naturally occurred in Chinese pickles with concentrations ranged from 0.02 to 0.30 mM in 23 pickle samples including homemade and commercial ones. Then, lactic acid bacteria capable of metabolizing phenyllactic acid were screened from each homemade pickle and a promising strain was characterized as Lactobacillus plantarum. Moreover, the investigation of the metabolic mechanism of phenyllactic acid in pickles suggested that the yield of phenyllactic acid was positively related to the content of phenylalanine in food, and the addition of phenylalanine as precursor substance could significantly promote the production of phenyllactic acid. This investigation could provide some insights into the accumulation of phenyllactic acid in pickle for long storage life.

Elucidation of substituted ester group position in octenylsuccinic anhydride modified sugary maize soluble starch

The octenylsuccinic groups in esterification-modified sugary maize soluble starches with a low (0.0191) or high (0.0504) degree of substitution (DS) were investigated by amyloglucosidase hydrolysis followed by a combination of chemical and physical analysis. The results showed the zeta-potential remained at approximately the same value regardless of excessive hydrolysis. The weight-average molecular weight decreased rapidly and reached 1.22 × 10(7) and 1.60 × 10(7) g/mol after 120 min for low-DS and high-DS octenylsuccinic anhydride (OSA) modified starch, respectively. The pattern of z-average radius of gyration as well as particle size change was similar to that of Mw, and z-average radius of gyration decreased much more slowly, especially for high-DS OSA starch. Compared to native starch, two characteristic absorption peaks at 1726.76 and 1571.83 cm(-1) were observed in FT-IR spectra, and the intensity of absorption peaks increased with increasing DS. The NMR results showed that OSA starch had several additional peaks at 0.8-3.0 ppm and a shoulder at 5.56 ppm for OSA substituents, which were grafted at O-2 and O-3 positions in soluble starch. The even distribution of OSA groups in the center area of soluble starch particle has been directly shown under CLSM. Most substitutions were located near branching points of soluble starch particles for a low-DS modified starch, whereas the substituted ester groups were located near branching points as well as at the nonreducing ends in OSA starch with a high DS.