Changes of starch during microwave treatment of rice

Abstract

Rice (Oryza sativa L.), a major cereal crop, is the staple food source for half of the world population. Rice is an excellent source of energy, in the form of starch, and it gives the benefit of providing proteins with a higher nutritional quality than those of other cereal grains (M���������� et al. 1998). At present, many possible applications of microwave (MW) energy in the food industry are known. MW drying was demonstrated to be an alternative means for the rice drying (W�������� & K����� 1986). Major components and the enzymic system of rice can be influenced during MW treatment. Since starch comprises approximately 90% of the dry matter of the rice endosperm, the research on rice cooking behaviour has focused on this fraction. W�������� and K����� (1986) used two long-grain cultivars and one medium-grain cultivar of rice for drying under vacuum by means of MW energy to determine the effects on the physicochemical properties and eating characteristics. Amylographic characteristics were used to obtain more information on the influence of the starch fraction of rice on its cooking behaviour. No significant differences were found in both maximum viscosity and setback viscosity between the air-dried controls and MW dried rice. M������ and T������ (1993) reported the effect of MW treatment on the contents of total and enzyme resistant starch in white and brown rice (three Australian cultivars -Calrose, Doongara and Waxy). The starch content was maintained or increased by cooking in a MW oven except with cv. Waxy. The increase was consistent with starch gelatinisation and therefore, with greater susceptibility to enzymic attack. Cooked rice had a higher content of resistant starch than the corresponding raw product, possibly because of the production of retrograded starch. It can be concluded that although the content of the resistant starch in rice increased by the techniques known to increase the resistant starch in other foods (heating, cooking, cooling and freezing), the impact was not as great. Z���� et al. (1996) treated two japanase cultivars of rice (700 W, 3 min, 500 g batches) with MW and determined physicochemical properties, cooking quality and enzyme activities. It was found that both cultivars of rice had debranching enzymes, and that α-amylase activities were significantly lower than those of the untreated controls. Cooking qualities, such as water absorption capacity, pH, and iodine blue value of cooking water, β-amy- The properties of rice after microwave irradiation were evaluated by means of amylograph and enzymic determination of the total and the damaged starch. The content of the total starch was not affected by the immediate energy output used for irradiation but that of the damaged starch increased with microwave energy absorbed and the temperature of treatment, mainly at the moisture of 30% and the temperature of 100°C. The results of damaged starch determination are in accordance with the amylographic readings of changes at maximum viscosity. Amylographic characteristics suggest mini...

Correlation between grain nutritional content and pasting properties of pre-gelatinized red rice flour

“…Conversely, in the Table 3, the factor cooking time caused changes in the starch structure of all genotypes of red rice studied, altering significantly the rheological behavior of the pregelatinized flours, reducing the peak viscosity and retrogradation, with irregular behavior of the viscosity breakdown. Pinkrová et al, (2003) and Yu & Wang (2007) also noted this type of viscous behaviour, but for rice starch irradiated in microwave oven and with gamma rays, respectively.…”

Inactivation of Endogenous Rice Flour β-Glucanase by Microwave Radiation and Impact on Physico-chemical Properties of the Treated Flour

“…Instead, longer treatments (4 min) induced the opposite effect, and a decrease in the viscosity was noted. A decrease of the maximum (peak) viscosity was also observed by Pinkrová et al (2003) by increasing temperature of microwave treatment of the rice grain and increasing power output at a moisture content of 30 %. Roman et al (2015) have examined the effect of MW on flour structure.…”

“…These authors reported rearrangements of the molecular structure upon microwave heating that could explain the significant changes in viscosity properties of both waxy and non-waxy starches. Pinkrová et al (2003) have observed that the peak viscosity of rice flour decreased as temperature and microwave power level applied to rice grain increased. On the other hand, Fan et al (2012) reported that microwave irradiation had no effect on the optical and thermal properties of rice starch during gelatinization compared to conventional heating.…”

Effect of Microwave Treatment on Physicochemical Properties of Maize Flour

“…Rearrangements of the molecular structure during microwave heating produced significant changes in viscosity properties of both waxy and non-waxy starches. Furthermore, Pinkrová et al (2003) reported that the peak viscosity of rice flour decreased as temperature and microwave power level applied to rice grain increased.…”