Junko Matsuki

Effects of Environmental Temperature on Structure and Gelatinization Properties of Wheat Starch

ABSTRACT The effects of environmental temperature on gelatinization properties and amylopectin structures of wheat endosperm starch were examined by isolating starches from four wheat cultivars matured in growth chambers at daytime temperatures of 15, 20, 25, or 30°C. Kernel weight and starch content per kernel were reduced by high maturation temperature. Amylose content showed no significant change at high maturation temperature in some cultivars; in other cultivars, there was a slight increase. Principal component analysis of data on relative peak areas of debranched amylopectin showed that amylopectin from wheat grown at a lower temperature had a greater proportion of shorter chains. Amylopectin branch chains were classified into three groups based on the correlation coefficients between the data of branch chain length distribution and principal component scores, degree of polymerization (DP) of 6–12, DP 13–34, and DP ≥ 35. The gelatinization temperature of starches increased markedly at a higher matur...

Comparison of Physical Properties of Wheat Starch Gels with Different Amylose Content

ABSTRACT The effects of amylose content and other starch properties on concentrated starch gel properties were evaluated using 10 wheat cultivars with different amylose content. Starches were isolated from grains of two waxy and eight nonwaxy wheat lines. The amylose content of waxy wheat lines was 1.4–1.7% and that of nonwaxy lines was 18.5–28.6%. Starch gels were prepared from a concentrated starch suspension (30 and 40%). Gelatinized starch was cooled and stored at 5°C for 1, 8, 16, 24, and 48 hr. The rheological properties of starch gels were studied by measuring dynamic viscoelasticity with parallel plate geometry. The low-amylose starch showed a significantly lower storage shear modulus (G′) than starches with higher amylose content during storage. Waxy starch gel had a higher frequency dependence of G′ and properties clearly different from nonwaxy starches. In 40% starch gels, the starch with lower amylose showed a faster increase in G′ during 48 hr of storage, and waxy starch showed an extremely s...

Pretreatment of microcrystalline cellulose flakes with CaCl2 increases the surface area, and thus improves enzymatic saccharification.

Glucose production from cellulose flakes with cellulases was improved after pretreatment with saturated CaCl2 at room temperature. When pretreated microcrystalline cellulose flakes (Funacel II, Funakoshi Co., Ltd, Tokyo, Japan) were saccharified with the cellulases, 76.8% of the substrate was converted into glucose within 5 h, whereas the corresponding conversion rate of water-pretreated cellulose flakes was 33.8%. To clarify the mechanism of the promotion, cellobiohydrolase I purified from Trichoderma longibrachiatum was used as the model cellulase, which degraded CaCl2-pretreated cellulose more quickly than the water-pretreated cellulose under tested conditions. The maximum amount of the enzyme bound to CaCl2-pretreated cellulose at 37 degrees C was estimated as 1.14 nmol/mg of cellulose, whereas that to water-pretreated cellulose was 0.527 nmol/mg of cellulose. The specific activity of the bound enzyme greatly decreased with the increase of the surface density (rho) of the bound enzyme, and no significant positive effects of the CaCl2-pretreatment on the specific activity could be observed at the same rho value, suggesting that the promotion was attributed mainly to the increase of the surface area of cellulose. The effect was also observed with dewaxed cotton or filter paper, but not with nata de coco cellulose or bagasse cellulose as the substrates. This suggests that the CaCl2-pretreatment serves to increase the surface area of cellulose flakes via liberation of cellulose particles which were artificially aggregated during harsh drying processes of the flakes.

Characterization of Starch Granules in Rice Culms for Application of Rice Straw as a Feedstock for Saccharification

Rice plants are known to accumulate starch in leaf sheaths and culms, and in some cultivars significant amounts of starch are present at the mature stage. This can be considered as potential feedstock for the recovery of fermentable sugars. We isolated starches from the culms of cultivars Yumeaoba, Koshihikari, and Leafstar to investigate their structural and physical features. Yumeaoba culm starch contained 20.2% amylose, whereas Koshihikari and Leafstar contained 25.8% and 25.2%. Yumeaoba culm starch was found by chain-length distribution analysis to contain higher amounts of short chains, resulting in lower gelatinization temperature by 7 °C, as compared to Koshihikari and Leafstar. Consequently, the rate of enzymatic hydrolysis of Yumeaoba culm starches reached maximum at a lower temperature than Leafstar. Rice culm starch, with a lower gelatinization temperature, can provide an advantageous material for feedstock for bioethanol production in terms of energy conservation.

Development of a Simple Method for Evaluation of Water Absorption Rate and Capacity of Rice Flour Samples

A simple method employing a commercially available canister was developed for the determination of mode of water absorption of rice flour samples. The samples prepared by four different grinding methods were used to analyze water absorption. The total amount of water in a flour sample was described by using an exponential model. Capacity and rate of water absorption of the samples were determined, and the relationship to baking quality of partially substituted rice bread was investigated. The water absorption was highly dependent on the method of grinding. Flours produced by wet jet-milling of the grains, which absorbed a small amount of water at high speed, were most suitable for rice bread. The method was applicable to other food powders, provided that flour particles do not stick together or swell immediately upon contact with water.