Rice Cultivation and Compostion

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Rice is one of the most versatile crops and constitutes a principal source of calories for Asia, Africa, and South America and this trend will continue well into the 21st century (Pingali et al. 1997). Rice is planted on about 150 million ha of land annually (11% of the world’s arable land); it is cultivated worldwide under a wide range of agro-climatic conditions ranging from irrigated, rain-fed low land, rain-fed upland and flooding ecosystems.
Global rice production has been increased due to introduction of high yielding varieties and improved agricultural practices. According to the FAO, global milled rice production was estimated to increase from 491.1 million tons in 2012 to 493.9 million tons in 2013 which was by around 0.6% (http://oryza.com/news/rice-news/fao-estimates-2014-global-rice-trade-383-million-tons-3-last-year).
Appearance, eating, cooking, milling and nutritional qualities are the primary components of rice grain quality. The values of each of these components are determined by the physiochemical properties and other socio-cultural factors such as the history and traditions of the localities where rice is grown. According to Unnevehr et al., (1992) and Juliano and Villareal (1993) the appearance quality of rice is determined by grain dimensions, specifically by grain length, width, width-length ratio, and the shape and translucency of the endosperm. Rice can be classified into different grain types based on grain dimensions including short, medium, and long types. McKenzie and Rutger 1983 has reported that medium and short grain cultivars tend to be low amylose rice and exhibit high gelatinization temperatures and moist, chewing cooking properties. In contrast, long grain rice generally contains high amylose ...

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...sopyranosyl chains with α-1,6-bonds. Amylopectin molecules are highly branched and constitute the skeleton of the starch granules (Kossmann and Llyod 2000). The basic structure of amylopectin was defined by Peat and others (1956) based on linear A, B, and C chains. A, the outer chains, are attached through their potential reducing end to B chains. However, B chains are linked in the same way and carry one or more A chains. In contrast, the C chains are single reducing group of the amylopectin molecule and carry other chains. The cluster model has been refined on the basis of the A-, B-, C- chain terminology of Peat and others (1956) and Hizukuri (1986). (B-chains that are present within a single cluster as designated are B1 chains, whereas, long B-chains that interconnect clusters are referred to as B2, B3, and B4, depends on the number of clusters interconnected).

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