Starch is an insoluble glucose polymer that forms semi-crystalline granules. Insight into the relationships between the physicochemical properties of starch and its structure is limited. A deeper knowledge of these relationships is necessary for understanding the starch properties of mutant lines. Starch synthase (SS) and starch branching enzyme (BE) play central roles in the biosynthesis of starch. To explore the relationships between the physicochemical properties of starch, morphology of starch granules, starch crystallinity, and the function of SS and BE isozymes expressed in rice endosperm, we analyzed these traits in starches isolated from the double mutant lines [ss1/be1 and ss1L/be2b (ss1L means leaky ss1 mutant)]. Deficiency of SSI and BEI lead to an increase and decrease in gelatinization temperature, respectively. A significant increase in gelatinization temperature results from deficiency of BEIIb, as has been shown in previous studies in rice and maize, and this phenomenon is pronounced in the reduction of SSI activity. Deficient BEIIb expression also had a significant impact on the morphology of starch granules in the endosperm and changed the A-type diffraction pattern of the granules to a B-type pattern, while deficiency of SSI and/or BEI did not affect these traits.
The CaCCO process (Park et al., 2010), a sugar platform for herbaceous lignocellulosics, was modified and evaluated for fermentable-sugar recovery in solution, using rice straw (RS) as well as stems and leaves of Erianthus arundinaceus (ER), one of the strategic energy crops in Japan. Continuous wet milling of a mixture of feedstock, water and Ca(OH)2, with a weight ratio of 3/7/0.3, was adopted, not only to evaluate the applicability for wet feedstocks, but also for simultaneous Ca(OH)2 mixing with the milled feedstocks. We also applied low temperatures of 95-100°C for the alkali pretreatment to save energy. Enzymatic-saccharification tests were performed for the pretreatment slurries from 10 kg feedstocks for 72 h at 40°C under a CO2-pressurized atmosphere at 0.9 MPa with high-solid loadings of 28.4% (w/w) for RS and 27.8% (w/w) for ER. These tests successfully solubilized 80.6% (RS) and 68.1% (ER) of the total glucose- and xylose residues in the solids. Following centrifugation, the solubilized-sugar concentrations in the recovered solutions were 16.9% (w/v) for RS and 15.5% (w/v) for ER. Thus, we demonstrated that the CaCCO process could be a simple and flexible platform for preparation of dense sugar solutions from dry- and wet feedstocks, which could stimulate a new agricultural bio-industry for vitalizing rural areas.