The Primary Constituent Of Milled Rice Biology Essay


The primary constituent of milled rice is starch and it can be found in the endosperm of rice grains. Apart from starch, carbohydrate and protein are some of the main components found in grains. With the many different varieties found worldwide, isolation of starch from each variety results in different structures, hence possessing different functional behaviours and can be used in various processing applications (Vandeput et al., 2004). Starch granules found in rice were small (2-7 µm). Compared to other starches, rice has one of the smallest particles making it very permeable. Rice starch is well known for being used in various ingredients in food processing due to its versatility, smooth and stand-alone taste as it does not interfere with other tastes found in other components. The food industry for babies utilizes starch as it's hypoallergenic, easily digestible and is a good thickening agent. It is also used in the production of low fat food as it has a smooth, milky and rich mouth feel which imitates the dairy industry.

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Based on its amylose content, rice starch could be divided into non-waxy rice starch (1.64% of amylose) and waxy rice starch (above 21-30%) (Jiranuntakul et al., 2011). The variation in starch content in rice was mainly due to environment and genetic factors. Rice starch has a polyhedral shape and tends to combine together to form clusters when heated. It is whiter compared to other starches and is easily digestible. Rice starch is generally more stable in cold conditions, therefore can be incorporated in food which uses the freeze/thaw cycle.

2.6.2 Gelatinization

Starch gelatinization is a crucial factor in determining the rheological properties of various foods as it affects the structure and texture (Ubwa et al.,2012). Changes caused by gelatinization are irreversible as starch granules undergo swelling, loss of birefringence and solubility. Hydration is a common term used to explained gelatinization as the starch granules viscosity starts to increase. Larger granules tend to expand in size first as compared to smaller granules. The presence of lipid, protein, sugar and other foreign material found in the aqueous medium influences the time, temperature and energy required for gelatinization (Delcour et al., 2000).

When starch is heated in the presence of water till it reaches its gelatinization temperature, starch will absorb water, thus causing the granules to swell. The molecules will start to vibrate thus causing the disruption of hydrogen bonds between granules. New bonds will then be formed between water and the hydroxyl group of starch (Murphy, 2009). There is a strong attraction amongst starch molecules and water. Maaruf et al., (2001) states that gelatinization is a process which causes disorder in the molecular arrangement of starch granules. This process can only happen when water, heat and starch are present.

The crystalline region of starch which does not allow the access of water, will slowly lose its nature and start dissociating to form an amorphous phase. Once this happens, crystallite melting, solubility and birefringence is lost (BeMiller et al., 2009). Starch is believed to have form paste (gel) when a large amount of starch granules has lost its structure. Birefringence can be observed when starch granules are viewed using a microscope in the presence of polarized light. The crystalline region of starch will exhibit the Maltese cross when refracted with polarized light. When 98% of the maltese cross is lost, the gelatinization temperature of starch is known (Goering et al., 1974).

The gelatinization temperature for starch granules varies accordingly as size of granules has an impact on temperature. Smaller granules will take a longer time to gelatinize as it absorbs water slower when compared to larger granules. Factors such as starch concentration and variation in granules have an effect on the starting point and gelatinization temperature of starch (Singh and Medina, 1988). Apart from that, chemical components which possess strong water affinity may prevent gelatinization by forming hydrogen bonds with water thus, preventing any interaction with starch.

Retrogradation plays an important role in establishing consumers' utility of food products. It is usually described as recrystallization of starch molecules during storage. When starch retrograde, the intermolecular distance between molecules decreases (Sobolewska-Zielińska and Fortuna 2010). The degree of starch retrogradation is influence by storage time, temperature and also starch concentration (Liu et al., 1998).

2.7 Antioxidant Properties

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Antioxidants are an assorted group of compounds which can act against oxidative damage induced in the body, as well as degradation of fatty acids which results in undesirable colour changes and rancidity. Free radicals are produced when our body cells uses oxygen, thus causing damage as its reactivity with other compounds can be detrimental. Free radicals are usually the cause of many age related diseases such as Alzheimer's and Parkinson's disease. Oxygen is one of the most active elements found as it can combine with various compounds. This usually happens in the bloodstream where various biochemical reactions take place. Hence, antioxidants play an active role in defending and protecting the body against the damages caused by free radical (Ismail et al., 2010).

Antioxidant compounds act as free radical scavengers thus preventing and repairing the damage caused by terminating the chain reaction. Antioxidants can either be obtained naturally or synthetically (Zheng and Wang, 2001).Natural antioxidants can be found in fruits, vegetables, cereals and legumes. It has been reported that the antioxidant compound found in cereals, have a high content of phenolic compounds in their bran (Zhang et al., 2010).

There are many different kinds of rice consumed by humans; however, white rice is by far the most popular followed by brown rice, red, purple or black rice. (Nanri et al., 2010; Sompong et al., 2011). Coloured rice is used as a constituent in many Asian cuisines as it has its own particular texture and flavour (Rhee et al., 2000). Recent studies have found an excellent source of natural antioxidants which includes many different kinds of phenolic compounds which can be found from the gramineae family of cereals (Chotimarkorn et al., 2008; Gani et al., 2012). Other compounds with antioxidants actions such as tocopherols, tocotrienols and γ-oryzanol have also been associated with rice (Iqbal et al., 2005).

Apart from that, anthocyanin compounds can also be found in the pericarp of coloured rice, such as brown and black rice (Chaudhary et al., 2003). The inhibition of free radical damage and health benefits associated with these compounds has been long known. Coloured rice varieties have anti-inflammatory properties and is known to prevent cancer, anti-aging, heart and nerve diseases (Kehrer et al., 1993, Tsuda et al., 2002, Manosroi et al., 2012, Kayahara et al., 2000). Much interest has been generated in search for various biological activities due to the presence of various antioxidant compounds in rice. Various solvent systems has been used for extraction, however the yield of each solvent is different, as extracted antioxidant compounds are greatly influenced by the type of solvent used .

2.8 Problems with rice

There are many problems associated with rice cultivation due to natural forces such as flash floods which then causes the paddy to drown hence generating an increase in price, due to the supply and demand reaction (Lawrence, 2008). Drought seasons can also cause paddy to dry up and lower its yield. Rice is grown in many third world countries; henceforth farmers tend to use varieties which produce a lower yield and traditional methods due to the lack of awareness and funds. Rice producing countries like India struggle with labour issues, abuse of insecticides and pesticides, scarcity of land and many other issues which varies from place to place (The Independent, 2011).

In order to increase harvest, rice is planted three times a year as compared to one huge harvest. There are many downsides associated with it as soil nutrients will be completely lost. This is because; crop rotation to replenish the soil with nutrients will no longer be practiced. Nutrients such as phosphorus, nitrogen and potassium will then be supplied by using large amounts of synthetic fertilizers to make it whole again. Many different organisms such as nitrogen-fixing algae, humus building agents, organisms which ward of rice pests have been identified in rice crops. Abuse usage of various chemicals such as insecticides, herbicides, fertilizers has also decreased and destroyed most of these beneficial parasites and predators. Aquatic animals such as fish, frogs and many others are also affected as the water source becomes contaminated and polluted.

Certain methods have been proposed to reduce the environmental impacts of using large doses of fertilizers by rotating crops with legumes to improve, increase and meet nitrogen requirements. Using rainy season crops and mixing it with other crops during drought season will reduce methane discharge, boost soil characteristics and obstruct growth of rice pests (Rao et al., 2006).

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Looking from another perspective, the three fold increase in rice pricing in 2008 is not due to environmental forces but caused by the soaring increase of global oil prices which affects and increases the transportation and production cost of rice (Lawrence, 2008). Compared to other staple food, very few countries export rice and it is usually grown for domestic usage. Hence it is a very unpredictable crop due to the small trading market. Some rice producing countries like India, Vietnam and a few others have restricted rice exports to help combat soaring prices and inflations (Lawrence, 2008). China and India are the biggest consumers and producers of rice, which accounts for more than half of the total crop production (Khoso et al., 2008).

2.9 Rice Pricing

Rice traded internationally is one of the most misrepresented commodity stock market. This is due to the fact that there is a very low percentage of rice traded internationally. Being the staple food, there is a strong attachment for both consumers and producers in terms of ensuring financial and food security. The rice market has been identified as thin, inconsistent, disconnected and seriously distorted (Narayanan and Gulati, 2002).

Malaysia relies heavily on rice imports compared to other countries. As Malaysia has not been able to meet the increasing needs for rice, plans have been put in place to ensure that Malaysia becomes independent and less reliant on imported rice. Major exporters of rice to Malaysia are Thailand and Vietnam. Policies have been implemented as it plays a part in the national economy, contributes job opportunity and involvement of foreign exchange due to trading. Subsidies, taxes and buffer stocks help control the inconsistent price of rice in the world market (Vengedesalam et al., 2011).

Foreign rice sold in Malaysia is more expensive than locally grown rice. A price check in the local hyper markets shows that the price of imported rice such as basmati, glutinous and black rice was 20-30% more expensive than locally grown rice. This is because of the import quotas imposed by various rice bodies in Malaysia. Back in the 1960's an average Malaysian typically spends about 21.5 % of their salary on rice (Ani, 1968). That's not the case anymore as the average household income of Malaysian's has increase in recent years. However the amount spend on rice by Malaysians are still relatively high compared to other countries like the United States as rice sold there is almost half the price of what it is here.

2.10 Rice Noodles

Asian noodles are widely consumed as one of the oriental cultures especially among Japanese and Chinese. Japanese white salted noodles and the Chines yellow alkaline noodles are the common types of Asian noodles (Ingett , 2005). Asian noodles can be made from various ingredients such as rice, wheat, and starches obtained from mung bean and potato.

Rice noodles generally contain a lower percentage of digestible starch as it is made from rice; hence it's good in preventing constipation. Wheat noodles have better characteristics than rice noodles as it contains gluten. Gluten helps to improve texture and limits cooking loss from noodles (Park and Baik, 2009). Since rice does not contain gluten, it relies on its protein and starch content to make high quality noodles. The functionality of protein found in rice is limited as compared to wheat gluten, hence limiting the usage of rice flour (Chung et al., 2012). Starch content found in rice influences the noodle production and quality through its physiochemical properties (Chen et al., 2003). Rice noodles are usually produced through sheeting of a rice batter (Fu, 2008).

Rice noodles cannot be stored long as it is freshly prepared. Once refrigerated, it loses its elastic texture and tends to disintegrate thus affecting the eating quality of noodles. Rice noodles can be found in various sizes depending on how its cut. Fresh rice noodles has a high moisture content (>60%) and it is produced by steaming the rice batter. The surface of rice noodles is usually sticky, thus oil is added to the surface to prevent it from sticking before being packaged (Fu, 2008). It can be used straight for preparation of various dishes without boiling the noodles due to its high moisture content.