Rice starch is commonly isolated by alkaline (sodium hydroxide) extraction because this process provides high yield, high purity and is low in capital costs. This process produces an highly loaded alkaline effluent that contributes significantly to general costs of wastewater treatment. The present study attempted to develop an enzymatic procedure to isolate pure rice starch and to investigate the physico‐chemical properties in comparison with that of rice starch produced by an alkaline process of comparable scale. The isolation of starch from polished rice grain was effected by application of cellulase under slightly acidic conditions in order to degrade the cellular tissue, followed by protease (Corolase 7089 or papain) under neutral conditions in order to loosen the protein bodies that are associated with starch granules. In comparison with the alkaline process, the enzyme process provided rice starch with a slightly elevated protein content, but less damaged starch. No differences were found between the two proteases used. Washing the enzyme‐isolated starch with 0.2% sodium hydroxide or 0.5% sodium dodecylsulphate (SDS) solutions further improved the purity of rice starch. The physico‐chemical properties of the enzymatically‐isolated starches were mostly comparable with starch from the alkaline process. The developed process allows to replace the alkaline process and thus eliminates critical levels of mineral load in effluents of rice starch plants.
Acid modified, agglomerated starches offer specific advantages as fillers in production of pharmaceutical tablets. Spray drying can improve processing of tablet mixtures significantly. In order to investigate prerequisites in utilization of rice starch, non‐waxy and waxy types were partially hydrolyzed in 6% (w/v) HCl solution at room temperature for varied length of time to obtain rice starches with increased crystallinity (so‐called crystalline rice starches). Scanning electron micrographs of native and highly crystalline starches were used to study the morphological changes and to suggest the mode of acid attack during hydrolysis. Exo‐corrosion distributed over the surface of acid‐modified waxy rice starch (AWRS) was observed after 192 h of hydrolysis. In contrast, the surface of acid‐modified rice starch (ARS) remained unchanged at 192 h of acid hydrolysis. The amylose content and the median particle size (diameter) were reduced with increasing hydrolysis time. It was found by X‐ray diffraction that the relative crystallinity of acid‐modified starches at >95% relative humidity was clearly increased with prolonged hydrolysis time.For studying tablet properties spherical agglomerates of the native and acid modified starches were directly compressed at 4 kN to obtain tablets. Crushing strength and disintegration time of tablets increased with relative crystallinity. In contrast, tablet friability was reduced. Concerning tablet functionality, the crystalline starches were positioned in overlapping ranges between the common commercial tablet fillers (microcrystalline cellulose, pregelatinized starch and lactose, respectively).
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