Rice ranks first in terms of global production (603 million
tonnes) and used as a staple food for approximately 400 million people in the
developing countries. India exports 5% of the produced rice to the international
market and compete with Thailand, Vietnam, and Pakistan. About 10% of the
production of paddy
is converted to three rice products, namely, puffed rice, popped rice and
flaked rice. Among the rice based breakfast cereals, puffed rice is largely demanded
product for centuries in India because of its lightness and crispness. When
grains such as rice, paddy, corn, gram etc. are heated, vapour pressure of
water inside the grain increases. At a certain temperature and after certain
duration of time the vapour pressure becomes high which causes expansion of the
grain and the process is called puffing.
Preconditioning of rice is the most critical factor for
obtaining highly expanded smooth-surface puffed rice. The process comprises of
uniform and slow heating of moisture-salt-conditioned parboiled rice with
continuous turning until optimum moisture content of puffing (10% w.b.) is
attained. Non uniform heating of grain severely impairs the quality of product
with less expansion ratio in addition to rough and blistered surface. Further,
puffing efficiency for rice grain depends on several factors, including the
nature and concentration of salts diffused into the kernel.
Water activity of food material is determined as the ratio
of vapour pressure of water in the food to vapour pressure of pure water at the
same temperature. Many food deterioration reactions and the growth of important
microorganisms depend on the water activity of the food and water activity is
thus an important parameter to predict food stability. In order to determine
the storage conditions, it is necessary to know the relationship between the
equilibrium moisture content (EMC) in the rice and equilibrium relative
humidity of the aeration air at a given temperature.
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