Parboiled Rice

1. 5/6/2017
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Parboiled Rice
• 25% of the world rice is parboiled
• Growing interest due to its higher vit B (Thiamin) content whose
deficiency causes “beri-beri”.
Md rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
• The process consists of three consecutive steps, performed either on paddy or
brown rice.
(i) Steeping at approx. 60°C. The relative high temperature results in short
steeping times. Also, germination and microbial growth are avoided. After
steeping, the excess water is removed.
(ii) During the consecutive steam treatment, the rice starch is gelatinized and the
kernel sterilized. Upon gelatinization, part of the vitamins migrate form the bran to
the endosperm. In addition, enzymes are to large extent inactivated during the
steam treatment. Important in this respect is the destruction of lipase.
(iii) Drying of the steamed rice: rice is quickly dried to 18-20% moisture and then
further dried at slower pace to avoid cracks and fissures.
Md rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

2. 5/6/2017
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Nutritional changes in parboiled rice
1) Starch losses its polarisation cross.
2) The solubility of the protein is reduced due to denaturation.
3) The fat content of the parboiled product is lower than that of normal
rice.
4) It is assumed that migration of water to the kernel of the rice kernel is
accompanied by migration of fat in opposite direction.
Md rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
The advantages of parboiled rice can be summarised as follows:
• A higher ‘head rice’ yield after milling because the parboiled rice is more
resistant to breakage (5-12.5%). This can partially be ascribed to the
disappearance of cracks that were present in rice prior to parboiling. The
reason for this disappearance is starch gelatinisation.
• Higher resistance of rice against insects;
• Increased nutritional quality of the parboiled rice due to higher contents
of vitamin B1(thiamine).
Md rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

3. 5/6/2017
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The "parboiling"-process also has some disadvantages:
(i) A darker rice colour;
(ii) A slightly different taste, and
(iii) Increased susceptibility to oxidative rancidity, in spite of inactivation of
lipases. This is due to the fact that ‘parboiling’ destroys natural antioxidants.
(iv) An additional property that is changed by parboiling is consistency:
parboiling leads to less sticky rice.
Md rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Quick cooking rice
• Preparation (cooking) of white rice takes approx. 20 to 35 min. This
relatively long time is caused by the slow diffusion of water in the
rice kernel. Indeed, to soften the kernel, water (and heat) has to
migrate to the centre of the kernel.
• In order to produce quick cooking rice, a procedure is needed that
results in the formation of pores in the rice, allowing faster water
uptake.
Md rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

4. 5/6/2017
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• A first method consists of partially precooking the rice to a moisture
content of 60% (cooked rice contains 80% moisture) and slow
drying of the precooked kernels to a moisture content of 8%. This
treatment results in a more porous structure of the rice.
• In a second method, rice with a moisture content of 12% is heated
rapidly. This results in fissures and cracks in the rice kernel, allowing
faster water penetration when the rice is eventually cooked.
Md rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST