COOKING QUALITY OF MILLED RICE (ORIYZA SATIVA)


Cooking is a science: cooking is an important characters that determines consumers preference, these properties determines the cooked texture  Khatum  et  al,   (2003).   Cooking  quality  of  rice   is   mainly determined by water uptake/ volume expansion, kernel elogation Becker (2003) cooking quality of rice depends on the amylose content and gelatinization temperature Juliano (1979) However, still on preference, high volume expansion and lengthwise expansion of kernel during cooking are more desirable traits of good quality rice high volume expansion on cooking is still considered to be good
quality of milled rice by the working class people who do not care whether the expansion is lengthwise or crosswise. Sood and Sadiq (1979). Urban people on the other hand prefers the varieties that expand more in length than in breath. Choudlum (1972).

Therefore the economic important of rice depends on its cooking and processing quality. When water is present at sufficiently high temperature, the starch undergoes a gelatiniation reaction Takeuchi (1984), for temperature below 500C, the grains absorb a limited amount of water up to approximately 30% moisture content (Wet basis). The resulting grains are not cooked because the starch has not undergone gelatinization from human experience with small sample, it is known that soaking rice grain in water at 25% for about one hour is required before cooking at a temperature above 70°c for 20 minutes or more. As water is taken up by a rice particle, the starch undergo a gelatinization reaction. The term used to describe the swelling and hydration of the starch granules (Whistler 1984).

Rice starch is usually digested quite rapidly compared to other foods  Starch foods such as a noodles, sweet potato or cassava, this leads to  a prompt and pronounced increased of the blood glucose level (high glycemic index ) after the ingestion of rice Frei and Beaker  (2004) .
Rapid starch digestion can cause a sensation  of hunger only shortly after the ingestion of rice  and the energy released  is quickly used, farmers cultivating  rice land races in the Philippines  reported a relatively long feeling of sensation after  the  ingestion of certain varieties Oko et al (2012)
Thus far, most of the published research on cooking quality in rice has focused on physico-chemical properties i.e Amylose content (AC) Gel consistency (GC) and gelatiruzation temperature (GT) which are directly related to rice cooking quality. (Perez 1987)
Amylose content
Amylose content is apparently, reported for rice samples to ranges from 24.6-28.8% and the level vary within each location. Amylose consists of linearly linked glucose molecules and is relatively resistant to digestion, hence the term "resistance starch" This means that rice with greater proportion of starch in the form of amylose tend to have a lower glycemic index. Amylose content of milled rice has been found to correlate positively with hardness values of cooked rice and negatively with stickness value (Perez et al  1987)  amylase content also makes difference between cooked rice that is moist and sticky or cooked rice that is dry or flaky.  Tester and Morrison (1990) reported  that Milled rice amylose content can be classified into:
v High  amylose  content:  If  the  rice  grain  will  show   high   volume expansion (not necessarily elogation) and a high degree of flakiness, the rice grain cooks dry, they are less tender and becomes hard upon cooking 25-30 percent amylose content is classified as high.
v Intermidate   amylose   content 20-30  percent  amylose  is   classified as intermidate amylose content, which is preferred in most rice growing areas of the world.
v Low amylose content 10-20 percent amylose content is classified as low. (www.knowledgebank.irriorg) 

2.6.2          Gel consistency
The gel consistence measures the tendency of the cooked rice to harden after cooking, it was developed to index cooked rice hardeness (Juliano 1973) Research has provide that amylopectin contributed more than amylose to starch gel consistency and viscosity (Juliano 1993) If the gel of the cooked rice is hard, the cooked rice tends to be sticky, harder gel consistency is associated  with harder cooked rice and thus future is particularly evidence in high amylose rice, also if the gel constancy is soft , the cooked rice has a higher degree of tenderness, this is a preferred characteristic by most consumers (www.knowledgebankirri.org) 

 Gelatinization temperature
Gelatinization temperature determines the time required for cooking in rice. Where as Juliano (1993) refers to final gelatiniazation temperature of starch as the water temperature at which, at least 90% of the starch
granules have gelatinized or swollen irreversibly in hot water. Based on this gelatinization temperature of milled rice is classified as low, intermediate and high. Tester, and Morrison (1990).
v Low   gelatinization   temperature:   Varieties   with   gelatinization temperature of 70°c have low gelatinization temperature
v Intermediate gelatinization temperature of between 70-74°c

v High gelatinization temperature: varieties with gelatinization temperature greater than 74 °c.

However if gelatinization temperature is very high, than the rice will becomes excessively soft and disintegrates when over cooked. It will also requires more cooking water than rice with lower gelatinization temperature (www.knowledgebankirri.org).
The difference in quality which are mainly attributed to difference in colloidal structure and the extent of swelling of any variety of rice on cooking have always been used as index of its quality Oko  et al. (2012).
Therefore, milled rice nutrients are lost through some cooking method such as washing before cooking which is normally done  to remove dirt but affects composition of cooked rice and cooking in excess water (Kernedy 2004). Washing rice prior to cooking is estimated to lead to losses of protein (2-7%), potassium (14-20%), Thiamine (22-59%), riborflavin (11-26%) and miacin (20-60%) (Juliano 1993), losses from washing and cooking methods used in Indian calculated as follows protein 10%, iron 75%, calcium and phosphorous 50% (Grist 1986). Cooking in excess water than is desired can lead to loss of thiamin 30-50%, riboflourin 25-35% and niacin 25-50% (Saunders, 1979). This is to show that however nutritional a food material may be, it will not be accepted by the consumer unless It satisfied specific culinary characteristics. Thus the  grains of cooked rice should be  non-sticky as well  separated qualities that can be Judge by swelling number water uptake and  amylase content  (pushpamma  and  Uma  Reddy 1979). Cooking    improves their digestibility, promotes palatability as well as making the rice soft  to eat.  Rice starch  has to be gelatinize during cooking or else rice is too firm  to be eaten comfortable USA Rice Federation,( 2002).Heat also  help to sterilize the food by killing harmful bacteria and other micro organisms and it increase the availability of nutrient.
These nutrient may be lost during  cooking in two  ways, first  by degradation,  which  can occur by destruction or by other chemical  changes such as oxidation or secondly by  leaching into the cooking  medium. Vitamins are susceptible to both losses while minerals are affected  only by leaching. Rice varieties with high  protein tend to have worse flavor, and less tender, less cohesive when cooked in  some amount of  water and longer cooking times are needed because of water  absorption USA Rice Federation ( 2002). Since consumers choice of rice varieties are largely based on  grain and cooking  quality, the high rate of influx of hybrid  varieties and other new rice varieties to local farmers in the three  zones of Ebonyi  state  who abandon their hitherto  cherished  indigenous varieties without  critical  comparison is unacceptable.
Share on Google Plus

Declaimer - Unknown

The publications and/or documents on this website are provided for general information purposes only. Your use of any of these sample documents is subjected to your own decision NB: Join our Social Media Network on Google Plus | Facebook | Twitter | Linkedin

READ RECENT UPDATES HERE