Mechanism of action of three different glycogen branching enzymes and their effect on bread quality.

Bread staling adversely affects the quality of bread, but starch modification by enzymes can counteract this phenomenon. Glycogen branching enzymes (GBEs) used in this study were isolated from Deinococcus geothermalis (DgGBE), Escherichia coli (EcGBE), and Vibrio vulnificus (VvGBE). These enzymes were characterized and applied for starch dough modification to determine their role in improving bread quality. First, the branching patterns, activity on amylose and amylopectin, and thermostability of the GBEs were determined and compared. EcGBE and DgGBE exhibited better thermostable characteristics than VvGBE, and all GBEs exhibited preferential catalysis of amylopectin over amylose but different degrees. VvGBE and DgGBE produced a large number of short branches. Three GBEs degraded the starch granules and generated soluble polysaccharides. Moreover, the maltose was increased in the starch slurry but most significantly in the DgGBE treatment. Degradation of the starch granules by GBEs enhanced the maltose generation of internal amylases. When used in the bread-making process, DgGBE and VvGBE increased the dough and bread volume by 9 % and 17 %, respectively. The crumb firmness and retrogradation of the bread were decreased and delayed significantly more in the DgGBE bread. Consequently, this study can contribute to understanding the detailed roles of GBEs in the baking process.

Development of Freeze-Thaw Stable Starch through Enzymatic Modification.

The use of unmodified starch in frozen foods can cause extremely undesirable textural changes after the freeze-thaw process. In this study, using cyclodextrin glucanotransferase (CGTase) and branching enzymes, an amylopectin cluster with high freeze-thaw stability was produced, and was named CBAC. It was found to have a water solubility seven times higher, and a molecular weight 77 times lower, than corn starch. According to the results of a differential scanning calorimetry (DSC) analysis, dough containing 5% CBAC lost 19% less water than a control dough after three freeze-thaw cycles. During storage for 7 days at 4 °C, bread produced using CBAC-treated dough exhibited a 14% smaller retrogradation peak and 37% less hardness than a control dough, suggesting that CBAC could be a potential candidate for clean label starch, providing high-level food stability under repeated freeze-thaw conditions.

A study of the quality characteristics of frozen Korean rice cake by using different thawing methods.

The characteristics of frozen rice cakes after thawing them using different methods, such as standing at room temperature (NT), running water (RWT), pan-grill (PT), steam (ST), microwave (MWT), and superheated steam thawing (SHST), were compared. Frozen rice cakes treated by MWT or SHST showed the shortest thawing time of 3 min. The MWT treatment showed the largest thawing loss, while the ST treatment showed the highest moisture content. The ST, RWT, and MWT treatments showed the highest water activity values. The NT treatment exhibited the highest hardness values, whereas the ST treatment showed the lowest values, possibly due to the adverse effects of high temperature on them. Sensory evaluation showed differences in appearance, moistness, and tenderness according to the thawing method, but there was no significant difference in overall acceptability. This study suggests that the qualities of frozen rice cakes varied depending on the different thawing methods.

Impacts of nonpoint source pollutants on microbial community in rain gardens.

Low-impact development (LID) techniques are being applied to reduce non-point source (NPS) pollution which are generated from various land uses. Cost-effective LID design requires consideration of influent runoff properties as well as physical and ecological pollutant-removing mechanisms. However, current LID technology design has failed to reflect the different properties of influent water from various land uses, and the biological design factors in LID facilities causing low efficiency and difficulties in maintenance. This study was conducted to identify biological design factors by analyzing the impact of the pollutants included in influent runoff and physical environment on microbial growth in rain garden facilities applied to different land uses. The results showed that the non-point source pollutant loadings were about 1.5-3 times higher in the runoff from parking lots, which are frequently visited by automobiles than in roof runoff. Type of soil, chemical species, and chemical composition were assessed as internal environmental factors having significant impact on the phylum and the count of microorganisms in the facilities. The growth of Cyanobacteria, Streptophyta, Chlorophyta, Bacillariophyta, and Xanthophyceae was good when there was appropriate water content in the soil, light, and sandy soil. Based on these results, the future design of rain garden facilities should be performed by considering a microorganism appropriate to the properties of the influent pollutants, determining appropriate water content, nutrient content and soil type, and choosing plants that contribute to microbial growth.

Application of indices to evaluate LID facilities for sediment and heavy metal removal.

Heavy metal and sediments transported from the urban catchment are the prime interest among researchers these days due to its toxic behaviour and hazardous effect on the animals, plants and human. The inflow from urban catchments and outflow from the Low impact development technologies (LID) were evaluated using different types of indices. Indices like fd, fp and Kd showed that heavy metals like Pb, Cd and Ni were dominantly observed in the dissolved form. These metals possess higher threat to the water bodies receiving urban runoff without any treatments. The state of heavy metal was highly dependent on the particle size which was directly affected by the TSS EMC in urban area. The indices like fd, fp and Kd were good enough to understand the behaviour, nature and state of metal in urban inflow and outflow from the system. On the other hand, calculated MPI and PERI indices showed that runoff from urban areas without any treatment bare very strong risk to the environment. LID technologies were found to be the better option in reducing the risk of urban areas to the receiving water bodies. These indices could be valuable for the decision making before the selection of applicable LID types, plants and filter media. Furthermore, indices like these can be devised to measure the impact of LID system to the environment as well as the decision making tool before discharge of outflow to the nearby streams.

Effects of amylosucrase treatment on molecular structure and digestion resistance of pre-gelatinised rice and barley starches.

Structural modification of rice and barley starches with Neisseria polysaccharea amylosucrase (NpAS) was conducted, and relationship between structural characteristics and resistant starch (RS) contents of NpAS-treated starches was investigated. Pre-gelatinised rice and barley starches were treated with NpAS. NpAS-treated starches were characterised with respect to morphology, X-ray diffraction pattern, amylopectin branch-chain distribution, and RS content, and their structural characteristics were correlated to RS contents. Regardless of amylose contents of native starches, NpAS-treated (relative to native) starches possessed lower and higher proportions of shorter (DP 6-12) and intermediate (DP 13-36) amylopectin (AP) branch-chains, respectively. RS contents were higher for NpAS-treated starches relative to native starches, and maximum RS contents were obtained for NpAS-treated starches of waxy rice and barley genotypes. Amylose contents were not associated with RS contents of NpAS-treated starches. However, shorter and intermediate AP branch-chain portions were negatively and positively correlated to RS contents of NpAS-treated starches, respectively.

Role of maltogenic amylase and pullulanase in maltodextrin and glycogen metabolism of Bacillus subtilis 168.

The physiological functions of two amylolytic enzymes, a maltogenic amylase (MAase) encoded by yvdF and a debranching enzyme (pullulanase) encoded by amyX, in the carbohydrate metabolism of Bacillus subtilis 168 were investigated using yvdF, amyX, and yvdF amyX mutant strains. An immunolocalization study revealed that YvdF was distributed on both sides of the cytoplasmic membrane and in the periplasm during vegetative growth but in the cytoplasm of prespores. Small carbohydrates such as maltoheptaose and beta-cyclodextrin (beta-CD) taken up by wild-type B. subtilis cells via two distinct transporters, the Mdx and Cyc ABC transporters, respectively, were hydrolyzed immediately to form smaller or linear maltodextrins. On the other hand, the yvdF mutant exhibited limited degradation of the substrates, indicating that, in the wild type, maltodextrins and beta-CD were hydrolyzed by MAase while being taken up by the bacterium. With glycogen and branched beta-CDs as substrates, pullulanase showed high-level specificity for the hydrolysis of the outer side chains of glycogen with three to five glucosyl residues. To investigate the roles of MAase and pullulanase in glycogen utilization, the following glycogen-overproducing strains were constructed: a glg mutant with a wild-type background, yvdF glg and amyX glg mutants, and a glg mutant with a double mutant (DM) background. The amyX glg and glg DM strains accumulated significantly larger amounts of glycogen than the glg mutant, while the yvdF glg strain accumulated an intermediate amount. Glycogen samples from the amyX glg and glg DM strains exhibited average molecular masses two and three times larger, respectively, than that of glycogen from the glg mutant. The results suggested that glycogen breakdown may be a sequential process that involves pullulanase and MAase, whereby pullulanase hydrolyzes the alpha-1,6-glycosidic linkage at the branch point to release a linear maltooligosaccharide that is then hydrolyzed into maltose and maltotriose by MAase.

Modulation of substrate preference of thermus maltogenic amylase by mutation of the residues at the interface of a dimer.

To elucidate the relationship between the substrate size and geometric shape of the catalytic site of Thermus maltogenic amylase, Gly50, Asp109, and Val431, located at the interface of the dimer, were replaced with bulky amino acids. The k(cat)/K(m) value of the mutant for amylose increased significantly, whereas that for amylopectin decreased as compared to that of the wild-type enzyme. Thus, the substituted bulky amino acid residues modified the shape of the catalytic site, such that the ability of the enzyme to distinguish between small and large molecules like amylose and amylopectin was enhanced.