Increased rice cropping intensity, due to shorter maturity varieties and shorter turn around times between crops, has lead to an increase in burning of rice straw. This can have significant short and long term effects on the productivity of the rice cropping system. A glasshouse experiment was conducted using an Aquic Haplustalf soil to study the release of S from different rice residues (straw and ash) under different water management conditions (non-flooded and flooded), and with and without the addition of S fertilizer. Rice straw residues (0.086 and 0.108%S) and ash produced from them (0.168 and 0.374%S), labelled with 35S, were used to investigate the importance of residue form and residue S concentration for the release of S. A loss of approximately 60% of the S from low-S straw and 40% from high-S straw was recorded on burning. The results showed that the addition of 6 kg S ha-1 as gypsum significantly increased grain yield across treatments. The addition of gypsum resulted in an increased S release from high-S straw residue under non-flooded conditions as measured by plant uptake, suggesting a priming effect of gypsum on S release from residues. The incorporation of straw and ash resulted in significantly increased grain yield in some but not all treatments. The percentage recovery of S in plants was higher in ash than in straw treated soil, but since S had been lost during burning, the absolute amount recovered (soil+plant) was higher in straw than in ash-treated soil. The 35S data indicate that if there is a critical S level for mineralization of rice straw, this level is less than the 0.086% in the residues used in this experiment.

Cereal Chem. 87(3):214-220Cross-linked carboxymethyl rice starches (CL-CMRS) were prepared from reactions between a native Klong Luang 1 (KL1) rice starch and varied concentrations (2.5-15% w/w) of sodium trimetaphosphate (STMP) in simultaneous carboxymethylation and cross-linking reactions set up using methanol as a solvent. Physicochemical as well as pharmaceutical properties of CL-CMRS were evaluated in relation to the amount of STMP used and the degree of cross-linking (DCx). At a low DCx, the viscosity of CMRS solution was enhanced through the formation of cross-linked polymeric network and chain entanglement. At higher concentrations in the preparation reaction, STMP caused proportional de-creases in the water solubility and ≤70-fold of the solution viscosity, but promoted swelling and water uptake of the modified starches. Rheological behavior of the nonsoluble but swellable CL-CMRS was similar to that of commercial superdisintegrants sodium starch glycolate (SSG), and cross-carmellose sodium (CCS). The swelling and water uptake of CL-CMRS were 5-7 and 6-25 times higher, respectively, than that of the native starch. Disintegration test of tablets containing 1 and 3% w/w of native and modified rice starches showed that M-KL1-5 and M-KL1-10 could be developed as tablet disintegrants.

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Cereal Chem. 84(4):331-336Carboxymethyl rice starches (CMRS) were prepared from nine strains of native rice starches with amylose contents of 14.7-29.1%. The reaction was conducted at 50°C for 120 min using monochloroacetic acid as a reagent under alkaline conditions and 1-propanol as a solvent. After determining the degree of substitution (DS), the physicochemical properties including water solubility, pH, and viscosity of 1% (w/v) solution, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses of the granules, as well as some pharmaceutical properties of CMRS powders and pastes were investigated. The DS range was 0.25-0.40. All CMRS dissolved in unheated water and formed viscous gel. A good positive correlation was observed between amylose content and DS (r = 0.9278) but not viscosity. SEM and XRD concurrently revealed significant physical alteration of CMRS granules compared with those of native starches, which reflected the changes in the properties of CMRS. At 3% (w/w), CMRS can function as tablet binder in the wet granulation of both water-soluble and water-insoluble diluents. The tablets compressed from these granules showed good hardness with fewer capping problems compared with those prepared using the pregelatinized native rice starch as a binder. In addition, most CMRS pastes formed clear films with varying film characteristics, depending upon the amylose content of the native starches. This type of modified rice starch can potentially be employed as a tablet binder and film-former for pharmaceutical dosage formulations.