THESIS

2 Rice starch
2.1 Rice production
Rice (Oryza sativa L.) is the most important cereal crop and the stable
food of over half the world’s population. The majority of rice varieties grown in
Thailand are long grain. In Thailand, rice varieties are divided into 3 types according
to custom and usage, such as waxy rice, low amylose rice, and high amylose rice.
Rice varieties commonly used in commercial rice flour production in Thailand are
waxy and high amylose rice. In 2003 – 2004, Thailand produced 26.124 million
metric tons of rice and exported 6.62 million metric tons. Food ingredient usage of
rice accounts for 22% of domestic rice sales. The use of rice as a food ingredient has
also increased by 3.7% due to the rising popularity and availability of snacks, frozen
dish, rice pudding, package mixes and beverage. More research on rice functionality,
physical and chemical properties is needed in order to meet the food industry’s
demand for low-fat, hypoallergenic and nutritious food ingredient. The rice grain
(Figure 1) comprises the hull (16-28% dry mass basic) and the caryopsis. The mass
distribution of the rice caryopsis is 1-2 % pericarp, 4-6% aleurone plus seed coat and
nucellus, 2-3% embryo and 89-94% starchy endosperm (Hoseney, 1990). Further
milling to remove the pericarp, seed coat, testa, aleurone layer and embryo to yield
milled or white rice results in a disproportionate loss of lipid, protein, fiber, reducing
sugars and total sugars, ash, and minor components including vitamins, free amino
acids and free fatty acids (Park et al. 2001). Diastatic, proteolytic and lipolytic were
also reduced by milling. On the other hand available carbohydrates, mainly starch,
were higher in milled rice than in brown rice. Starch is the major constituent of milled
rice at about 90% of the dry matter. Protein and lipid contents are also significant. The
endosperm cells are thin-walled and packed with amyloplasts containing compound
starch granules which are evenly distributed, although they are smaller in size near the
periphery of the endosperm (Blanshard 1987). The two outer most cell layers (the sub
aleurone layer) are rice in protein and lipid and have smaller amyloplasts and
compound starch granules than the inner endosperm.
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