Consuelo M. Perez

Indicators of eating quality for non-waxy rices

Abstract Although amylose content is the major determinant of the eating quality of milled rice, varieties of similar amylose content may differ in eating quality. Stickiness of cooked rice, as measured with an Instron food tester, gave a better correlation with amylose content than did hardness. Among rices of similar amylose content (high, intermediate or low) differences in hardness of cooked rice were shown to be generally related to differences in gel, and amylograph consistency, final gelatinisation temperature, or both. A higher rice concentration improved the differentiation among low-amylose samples for gel and amylograph consistency.

Grain size, sucrose level and starch accumulation in developing rice grain

Abstract Five rices ( Oryza sativa L.) differing in final grain size were studied at the midmilky stage to determine if any factor could be identified which might limit rate of starch accumulation. Only UDP glucose pyrophosphorylase activity increased with increasing grain size. Detached rice panicles incubated in liquid medium containing 1% sucrose and 0.1% glutamine, in addition to minerals and vitamins, produced grains similar to those on intact plants. Sucrose level (0–1.5%) in the medium determined the extent of dry matter and starch accumulation and influenced physiological development of the ripening grains. Chemical and enzymic composition of the grain were similar to previously reported levels in grains of intact panicles analysed at regular intervals after anthesis. Addition of 3-P glycerate or K + to the medium did not improve dry matter accumulation in the developing grain.

Extruded rice noodles: Starch digestibility and glycemic response of healthy and diabetic subjects with different habitual diets

Abstract High amylose rice variety was extruded to noodles and the starch digestibility and glycemic response of one healthy and two non-insulin dependent diabetic groups (Quezon City, Philippines and Toronto, Canada) with different habitual diets were determined. Rice extrusion significantly reduced the starch digestibility by 15% and the glycemic index in healthy volunteers by 36%. In both diabetic populations, the reduction in glycemic index was similar at 24%, suggesting that the effect was reproducible, and also that glycemic response was not affected by previous daily exposure of the subjects to rice. The effect of extrusion appears to be related to the starch gelatinization and retrogradation which occurred during processing as indicated by the lower amylograph viscosity and softer gel consistency of the rice noodles compared to the milled rice, as well as by the retrogradation test. The low glycemic response to high amylose rice and particularly the rice noodles suggests that these foods may have health benefits to both normal and diabetic individuals.

Eating quality indicators for waxy rices

Abstract A study of the properties of raw and cooked waxy milled rices from the Republic of Korea, the Philippines and Thailand verified that the hardness and stickiness values of cooked rices, as measured by an Instron food tester, tended to be related to final gelatinisation or birefringence end-point temperature (BEPT), neutral gel consistency or both properties of raw rices. Actual texture determination of cooked rice is required among the low final BEPT rices that have similar gel consistency and alkali test values. Intermediate final BEPT waxy rices as cooked rice had hardness and stickiness properties similar to those of high final BEPT rices.

Kinetic studies on cooking of tropical milled rice

Abstract Four aged tropical milled rices differing in amylose content and/or starch gelatinization temperature (GT) were presoaked for 30 min and cooked in calculated weights of water based on amylose content at 80, 90, 100, 110 and 120°C. Differences in cooking rates were evident below 100°C. Activation energy of cooking, derived from Arrhenius plots of cooking rate constant and reciprocal temperature, ranged from 76 to 121 kJ/mole at 80–90°C and 31–57 kJ/mole at 90–120°C. Cooking rates were lower and activation energy values were higher for intermediate GT samples than for low GT samples.

Properties of Thai cooked rice and noodles differing in glycemic index in noninsulin-dependent diabetics

Glycemic index responses of two cooked rices and six types of cooked noodles consumed by eight noninsulin-dependent diabetics correlated positively with in vitro starch digestibility of food slurry and negatively with amylose content of the food. Glutinous (waxy) rice had the highest values, and mung bean noodles the lowest.

Varietal differences in properties of extrusion-cooked rice flour

Ten milled rices differing in starch properties were extrusion cooked through a twin screw extruder at 15% moisture and 120, 135 and 150°C. Instron hardness values of extrudate were lowest at 150°C. Extrusion cooking drastically reduced viscosity in 0·2n KOH and in water without any decrease in amylose content and with little increase in reducing sugars. Spherical protein bodies were intact in the protein masses uniformly dispersed in the gelatinized starch matrix. Amylose content and gel consistency of raw rice flour were significantly correlated with expansion ratio only at 135°C, water absorption and solubility indexes at all temperatures and with gel viscosity of extrudates. Only gel consistency of raw flour correlated with cold paste viscosity of extrudate. Final gelatinization temperature of starch was not significantly correlated with any extrudate property.

Effect of extrusion cooking on nutritional value of rice flour

Abstract Extrusion cooking, in a twin-screw extruder, of milled rice batter at 15% moisture and 120–150°C reduced total lysine content 11–13%, true digestibility 3%, biological value 4–5% and NPU 7–8% in growing rats.

Effect of treatment on composition and protein and energy utilization of rice and mung bean by rats

Yellow rice derived from stack-burned unthreshed grains had lower lysine content than white milled rice. Stack burning did not affect energy digestibility in growing rats but decreased true nitrogen digestibility and net protein utilization (NPU). Increasing parboiling time from 20 to 60 min had no adverse effect on energy and protein utilization of parboiled milled rice. Defatting of rice bran-polish with petroleum ether at 50°C had no effect on protein utilization but decreased energy content and utilization. Mechanical dehulling of mung bean (Vigna radiata [L.] Wilczek) reduced fiber content, increased energy and protein digestibility but decreased biological value (BV) and NPU. Toasting and winnowing the bean reduced lysine content, improved digestible energy but decreased BV and NPU. Cooking the bean preparations improved the biological value only in mechanically dehulled bean with resultant higher NPU than that of whole bean.

Effects of nitrogen fertilizer treatment and source and season on grain quality of IR64 rice.

The effects of nitrogen fertilizer treatment and source (prilled urea, urea supergranule, fresh azolla, rice straw or sesbania or rice straw compost and their combinations) on grain quality were studied in the 1987 crops of variety IR64 at IRRI. Although fertilizer application improved grain yield, it improved protein content only in the case of urea supergranule, azolla and rice straw. Lysine contents of brown rice protein were similar in samples with no N fertilizer and those with the highest protein content in both seasons. Fertilizer treatment regardless of source tended to decrease weight and increase translucency of brown rice in both seasons. Effects on other grain properties were not consistent in both seasons. Season affected more grain properties than fertilizer treatment did, particularly translucency which was higher in the dry season than in the wet season.