Eiji Yamazaki

Dynamic oscillation rheometry in combination with repeating freeze–thaw (FT) cycles (DOR‐FT) was applied to evaluate the rheological change of starch gel caused by long‐term retrogradation. The gels prepared from corn, wheat, rice, potato, and sweet potato starch pastes (6%, w/w) were formed on a dynamic rheometer plate and the rheological changes induced by the FT cycles were measured while their gels remained on the rheometer plate. Comparing with the storage modulus (G′) at 25°C of each starch gels without FT, G′ of corn, wheat, rice, potato, and sweet potato starch gels after three FT cycles increased by 341, 474, 167, 1368, and 631%, respectively. The DOR‐FT method enabled the evaluation of the rheological changes caused by the long‐term retrogradation within 1 h, which is much shorter than with the conventional puncture test. Moreover, G′ versus FT cycles could be expressed as an exponential function model, indicating that the function model would show the FT cycle dependence for the rheological change of starch gels.

Pectic substances were extracted from Japanese pepper (Zanthoxylum piperitum DC) fruit with hot diluted HCl (90°C, pH 2.2). The yield of the pectic substances was 8.4% (w/w) based on dry material. The contents of total carbohydrate, anhydrogalacturonic acid, ash, protein, and moisture of the pectic substances were 84.1, 66.9, 3.6, 2.7, and 9.6% (w/w), respectively. The degree of methylation was estimated to be 80.3% by using alcohol oxidase test. This indicated that the pectic substances are high methoxyl pectins and have an ability to form sugar gels. The jelly grade of the pectic substances was estimated to be 130 (USA-SAG) at standard condition. Viscosity-average molecular weight was relatively low (30.3 kDa). When the molecular weight distribution was checked by gel-permeation chromatography on Sepharose CL-4B, the elution profile of the pectic substances was highly polydispersed extending from 40 kDa (or less) to 2000 kDa.

Kinetics of fatty acid binding ability of glycated human serum albumin (HSA) were investigated by fluorescent displacement technique with 1-anilino-8-naphtharene sulphonic acid (ANS method), and photometric detection of nonesterified-fatty-acid (NEFA method). Changing of binding affinities of glycated HSA toward oleic acid, linoleic acid, lauric acid, and caproic acid, were not observed by the ANS method. However, decreases of binding capacities after 55 days glycation were confirmed by the NEFA method in comparison to control HSA. The decrease in binding affinities was: oleic acid (84%), linoleic acid (84%), lauric acid (87%), and caproic acid (90%), respectively. The decreases were consistent with decrease of the intact lysine residues in glycated HSA. The present observation indicates that HSA promptly loses its binding ability to fatty acid as soon as the lysine residues at fatty acid binding sites are glycated.