Oleyl potato starch (OA-PS) was prepared by lipase-catalyzed solid-phase synthesis. PS retaining AY-Amano 30G as a lipase (PS/Lip) was prepared by immersing in the lipase solution, and by dehydrating with ethanol before air-drying. PS/Lip and oleic acid (OA) were incubated in n-hexane or without a solvent, and then unreacted OA was thoroughly eliminated by washing with n-hexane before air-drying to respectively obtain OA-PS or OA-PS (solvent-free). The OA-PS samples respectively showed the structural compositions of PS (as glucose residue) of OA = 30:1 and 286:1 (molar ratio). Their crystallinity evaluated by polarizing microscopic observation and X-ray diffractometry and their digestibility with α- and β-amylase were similar to those of PS. The OA-PS samples acquired significantly higher thermal structural stability, as evaluated by DSC, than that of the PS and control samples, and exhibited improved pasting properties in terms of a markedly lower swelling index and peakviscosity by RVA, as well as easier vaporization of water from the gelatinized suspension and higher heat-resistance for maintaining the swollen starch granules at 110°C for 30 min than those of the PS and control starches. In particular, OA-PS was superior to OA-PS (solvent-free) in these structural and pasting characteristics. OA-PS also exhibited a decreased surface tension with increasing concentration. Oleylation with lipase should thus be valuable for improving the multiple functional properties of starch.
One-pot enzymatic production of nigerose was demonstrated from abundantly available sugar resources, including maltose, cellobiose, sucrose and starch. (i) 319 mM nigerose was generated from 500 mM maltose by the combined actions of maltose phosphorylase and nigerose phosphorylase, which share the same β-D-glucose 1-phosphate, in the presence of phosphate. The yield was 62% based on the concentration of maltose as the starting material. (ii) 129 mM nigerose was produced from 250 mM cellobiose by cellobiose phosphorylase and nigerose phosphorylase in the presence of phosphate, in combination with the enzymatic pathway to convert α-D-glucose 1-phosphate to β-D-glucose 1-phosphate via D-glucose 6-phosphate by the combined actions of α-phosphoglucomutase and β-phosphoglucomutase, resulting in a yield of 52%. (iii) 350 mM nigerose was produced from 500 mM sucrose by substituting cellobiose phosphorylase with sucrose phosphorylase and adding xylose isomerase, giving a yield of 67%. (iv) 270 mM nigerose was generated from 100 mg/mL starch and 500 mM D-glucose by the concomitant actions of glycogen phosphorylase, isoamylase, α-phosphoglucomutase, β-phosphoglucomutase and nigerose phosphorylase, in the presence of phosphate. In addition, 280 mM 3-O-α-D-glucopyranosyl-D-galactose was produced by substituting D-glucose with D-galactose. Based on the concentrations of D-glucose and D-galactose as the starting materials, the yields were calculated to be 52 and 56%, respectively. These one-pot enzymatic approaches can be extended to include practical production of a variety of oligosaccharides by substituting nigerose phosphorylase with other β-D-glucose 1-phosphate-forming phosphorylases together with various carbohydrate acceptors.
The physicochemical properties of starches from 10 sweetpotato varieties differing in tuberous root traits, recently bred in Japan, were examined using our standard experimental methods. Pasting and gelatinization properties determined by a rapid visco-analyser and a differential scanning calorimeter, respectively, grouped the sweetpotato starches roughly into two types. One was an ordinary sweetpotato starch type, well known as traditional sweetpotato starch; the other was a starch type, having low gelatinization temperature as represented by Quick Sweet. The apparent amylose contents of the starches were similar ranging from 18.6 to 20.7%, whereas phosphate contents and granular sizes ranged widely from 1.13 to 7.53 μmol/g and from 12.8 to 18.6 μm, respectively. The chain length distributions of the starches were classified into two types, similar to the pasting and gelatinization types. In this study, for the quantitative comparison of chain length distribution, we successfully performed an analysis yielding a number-based chain length distribution of amylopectin, estimated by gel permeation chromatography with a refractive index detector and using calibration with commercial pullulan standards. With respect to functional properties, retrogradation of starch pastes and digestibility of starch granules by glucoamylase showed measurably large differences among the starches, depending on minor differences in structural properties.
Dextransucrase reacts with sucrose to produce dextran and fructose. Dextransucrase is known to form a complex with the dextran product at the active site. Using this characteristic, dextran was introduced to the surface of magnetite through the dextransucrase reaction by reaction with sucrose to obtain dextran-conjugated magnetite. This modified magnetite was applied in an aqueous two-phase system for protein purification with the aid of an applied magnetic field. Two sizes of the magnetite used were 320 nm and 5.0 μm. Dextran-conjugated magnetite (320 nm), assembled magnetically, was able to rapidly extract hemoglobin with a high yield because the dextran on the surface of the magnetite has an entangled structure with a high density for capturing hemoglobin.
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