We characterized SaHEX, which is a glycoside hydrolase (GH) family 20 exo-β-N-acetylhexosaminidase found in Streptomyces avermitilis. SaHEX exolytically hydrolyzed chitin oligosaccharides from their non-reducing ends, and yielded N-acetylglucosamine (GlcNAc) as the end product. According to the initial rate of substrate hydrolysis, the rates of (GlcNAc)3 and (GlcNAc)5 hydrolysis were greater than the rates for the other oligosaccharides. The enzyme exhibited antifungal activity against Aspergillus niger, which was probably due to hydrolytic activity with regard to chitin in the hyphal tips. Therefore, SaHEX has potential for use in GlcNAc production and food preservation.
Glass transition temperature (Tg) is an important parameter for the physical quality control of hard candies. In order to understand the applicability of calcium maltobionate to hard candy, effect of calcium maltobionate addition on the Tg of model and hand-made hard candies was investigated. Freeze-dried calcium maltobionate-sugar (sucrose containing a small amount of glucose-fructose mixture) and calcium maltobionate-reduced isomaltulose mixtures were prepared as model candies, and their anhydrous Tg was evaluated using a differential scanning calorimetry. The anhydrous Tg increased linearly with the molar fraction of calcium maltobionate. From these results, it was expected that calcium maltobionate can improve the physical stability of normal and sugarless candies. For comparison, various commercial candies were employed, and their Tg was evaluated using a thermal rheological analysis. The Tg values were in the range of 28–49 °C. The Tg values were higher than 25 °C, which is significant with respect to the physical stability of the candies. Calcium maltobionate-sugar and calcium maltobionate-reduced isomaltulose candies were prepared as hand-made candies. The calcium maltobionate-reduced isomaltulose candies had higher Tg than the calcium maltobionate-sugar candies at each calcium maltobionate content, although reduced isomaltulose has a lower Tg than sugar. At a high calcium maltobionate content, calcium maltobionate-reduced isomaltulose candy had an equivalent Tg to the commercial sugarless candies, and thus practically acceptable stability was expected. In the case of calcium maltobionate-sugar candies, there was a possibility that the hydrolysis of sugar reduced their Tg. Vacuum-concentration will be useful to improve the Tg of the candies.
Ethanol precipitation process for purification of branched dextrin (BD) in Nägeli amylodextrin from waxy rice starch was developed. Temperature and ethanol concentration for precipitation were main parameters affecting the recovery and purity of BD, and the purification condition at 4 °C and 10 % (v/v) ethanol in water was adopted. After four-time precipitation, the BD recovery was 34.6 %, whereas the purity improved from 78.5 % at the initial to 94.5 % at the four-time purified BD (BD4). BD4 mainly showed a chain length distribution between 18 to 35 with a mode length of 25, which shifted after enzymatic debranching with isoamylase to that between 9 and 20 with a mode length of 14. Each purified BD was solubilized in water, and each solution was mixed with methanol-water at 25 °C to a final methanol concentration of 16 M. The flakes of BD precipitated with 16 M methanol exhibited an A-type crystal structure by an X-ray diffraction analysis, and the speed generation of white flakes in 16 M methanol dramatically increased as the purification time increased. The effect of addition of highly branched cyclic dextrin (HBCD) or sodium tetraborate on BD aggregation in 16 M methanol was also investigated, where the former retarded aggregation but the latter had no effect on the velocity. Thus, the purified BD enables rapid characterization of aggregation of double helix structures of A-type crystal structure, and screening of compounds which could affect the phenomena for prediction of potentials in starch modification as well.
We have developed a novel low-molecular-mass oil-gelling agent that is electrically neutral, has no nitrogen atoms and consists only of cyclic sugar alcohols and saturated linear fatty acids. The cyclic sugar alcohols were 1,5-anhydro-D-glucitol (1,5-AG) and 1,5-anhydro-D-mannitol (1,5-AM) derived from starch via 1,5-anhydro-D-fructose. Various saturated linear fatty acids with 10 to 18 and 22 carbon atoms were introduced into all the hydroxy groups of 1,5-AG. Various saturated linear fatty acids with 13 to 18 and 22 carbon atoms were introduced into all the hydroxy groups of 1,5-AM. Initially, the gelling ability increased as the carbon number increased, but the gelling ability decreased as the carbon number increased beyond 17 carbons. This trend was similar for both 1,5-AG and 1,5-AM. A comparison of 1,5-AG and 1,5-AM derivatives revealed that 1,5-AG derivatives had greater gelling abilities for different kinds of oils at the same fatty acid length. Further, it was confirmed by SEM observations that a three-dimensional fibrous structure was formed, and this network structure formed the gel and held the oil. Here, we report the synthesis and characteristics of a novel low-molecular-weight gelling agent and its gelation mechanism.