Effects of Early Harvesting of Grains on Taste Characteristics of Cooked Rice.

Abstract

In order to clarify the effects of early harvesting of rice grains on the taste characteristics of cooked rice, especially on the taste items of "sweetness" and "deliciousness," we compared "early-harvest" rice which was harvested 10 days before the ordinary harvest time and "ordinary-harvest" rice which was harvested at the usual time. From the results of sensory tests, the cooked early-harvest rice was evaluated as being sweeter and more delicious than the cooked ordinary-harvest rice. The greater sweetness in the former rice was primarily due to the formation of glucose, maltose and maltoligosaccharides from starch, probably by starch degradation enzymes during soaking and/or cooking. The cooked early-harvest rice also contained more L-glutamic acid than the cooked ordinary-harvest rice. From these results, it was concluded that when rice is harvested 10 days before the ordinary time of harvesting, the cooked rice will be sweeter and more delicious.Keywords: early harvesting, cooked rice, sweetness, maltoligosaccharides, starch degradation enzymeThe time of harvesting rice grains has conventionally been determined from the standpoints of attaining a good external appearance, getting sufficient yield and making the harvesting work easier, without taking the eating quality of the harvested grains into account. On the other hand, when the harvesting time of rice has been extremely retarded or advanced the taste of cooked rice has been reduced; suggesting that the time of harvest of the grains can have a critical influence on the quality of cooked rice. To identify an optimum harvesting time to assure rice of good eating quality, many studies have examined factors related to taste such as the contents of amylose and protein in milled rice (Taira et al., 1978;Asaoka et al., 1985;Tamaki et al., 1989a;Matsue et al. 1991;Takebe et al., 1994) and the texture parameters of cooked rice (Ebata et al., 1982;Tamaki et al., 1989a) in relation to the time of harvesting. It has been asserted in these studies that an adequate period of time for harvesting rice grains to obtain cooked rice of good quality is about 40 days after heading (Ebata et al., 1982).More, recent reports showed that in addition to such taste components as amylose and protein, other characteristics of sweetness and deliciousness greatly contribute to the quality of cooked rice (Tamaki et al., 1989b;Matsuzaki et al., 1992;Sugiyama et al., 1995;Arai et al., 1997). However, the optimum time for harvesting grains with special reference to the taste characteristics of cooked rice has scarcely been examined to date.The objective of the present study was thus to clarify the effects, which the harvest time, especially early harvest, has on these previously unevaluated taste characteristics of cooked rice, as well as on taste characters, which have already been subjected to research. Materials and MethodsPlant materials Rice plants (Oryza sativa L. cv. Koshihikari) grown at Nita-cho in Shimane Prefecture in 1997 were used. Developing grains were sampled at 32 and 4...

Effects of Harvesting Time on Sweetness of Cooked Rice and Activity of Starch-Degradation Enzymes of Rice Grains

“…These results are in agreement with a previous report (Arai and Itani, 2000). In Nakateshinsenbon, however, maltotriose was again detected in 46-and 49-DAH rice.…”

“…From these results, we concluded that the effect of early harvesting on the texture of cooked rice varies with the rice variety. Effect of harvesting time on free-sugar content of cooked rice In this study, we measured the content of free sugars in the outer layer (glutinous substance) and remaining rice grains (residual grains) of cooked rice separately, because we previously observed a difference between them (Arai and Itani, 2000). In Koshihikari (Figure 4), the content of free sugars in the glutinous substance of cooked rice was the highest in the rice harvested extremely early (28-DAH rice), and it decreased as the harvesting time was delayed.…”

“…Besides glucose and sucrose, maltose and maltoligosaccharides such as maltotriose and maltotetraose, which add a refined sweetness to cooked rice, were detected in the cooked rice when harvested early. Maltoligosaccharides in cooked rice are assumed to be produced by the action of ce-amylase during soaking and/or cooking (Arai et al , 1997;Arai and Itani, 2000;Tajima et al , 1994;Maruyama, 2002).…”

“…We therefore reevaluated the optimum time of harvest from the viewpoint of the taste factors of cooked rice. In a previous report (Arai and Itani, 2000), we compared the taste factors of cooked rice between the rice grains harvested at 42 DAH, which was considered as the most suitable harvesting time, and those harvested 10 days earlier. As a result, we found that the eating quality is improved by harvesting 10 days earlier than the optimum harvesting time (42 DAH).…”

Karakteristik Flavor Beras Varietas Padi Aromatik dari Ketinggian Lokasi yang Berbeda

“…Selain dipengaruhi oleh gen, mutu beras aromatik juga dipengaruhi oleh kondisi pertanaman (Champagne 2008), baik ketinggian lokasi, tekstur tanah, maupun hara tanah (Itani et al 2004, Sagar andAli 1993) dan proses pascapanen (Arai andItani 2000, Champagne et al 2005). Faktor tanah mempengaruhi senyawa volatil, tetapi mekanismenya belum diketahui secara pasti (Singh et al 2003).…”