C Aochen, SR Assumi, A Seyie, AW Yanthan, H Verma, H Kalita
ICAR, Nagaland Centre, Medziphema
Rice, a staple food for approx. 3.5 billion people across the world, is emerging as much more than a source of carbohydrates. Asia accounts for more than 90% of the world's rice production and consumption. Rice is also a good source of dietary protein which is naturally gluten-free, making rice suitable for infants and people with celiac disease or gluten allergies. It is consumed in several forms, including brown, milled and parboiled rice, as well as flour and fermented products.
Rice bran
Rice bran, the hard outer layer of the grain, is removed during milling and polishing to produce white rice. However, the layer contains a wide range of valuable nutrients and bioactive compounds, particularly flavonoids and phenolic compounds, which are known for their antioxidant activity. Colored or pigmented rice varieties - including black, purple and red rice - are attracting increasing interest because of their higher concentrations of anthocyanins and other bioactive compounds localized in the bran layer. These whole or unpolished pigmented rice holds potentially valuable source of nutraceutical and health-promoting compounds.
Brown rice and White rice
Brown rice (unpolished rice) retains its nutrient-rich bran and germ layer, which is the tiny nutrient-dense embryo found in the grain, while milled white rice has those outer layers removed or polished off. Processing improves the appearance, texture and shelf life of the grain but can simultaneously remove the nutrient-rich layers. Removing rice bran is reported to lower total dietary fiber by 40% and about 70–80 % reduction in minerals, and an average nutrient loss up to 70%. Despite this, polished rice remains the predominant form of rice consumption, and potentially contribute to hidden hunger, in which people may consume sufficient calories but lack essential vitamins and minerals, unless their diet is supplemented with adequate fruits and vegetables.
Parboiled rice
Parboiling is a process in which paddy is soaked in warm water, steamed and subsequently dried. The process increases the solubility of nutrients in the rice bran and helps transfer them into the starchy endosperm. The practice is particularly significant in India, where around 60% of marketed paddy rice is estimated to be parboiled.
Glycemic Index (GI)
GI is an important measure of how carbohydrate-containing foods affect blood glucose levels. Foods with a high GI (>70) are digested rapidly and can cause sharp increases in blood sugar, while foods with low-GI (<55) produce a slower rise. Rice is a major contributor to the glycemic load for billions of people and its association with an increased risk of type 2 diabetes mellitus (T2DM). Sticky, glutinous or waxy rice has a high GI of approximately 87–90, making it a rapidly digested carbohydrate. Short-grain rice also exhibit more glycemic responses than long-grained rice. Meanwhile non-glutinous high-amylose varieties, including some whole-grain and parboiled rice - are expected to digest more slowly and produce lower glycemic responses.
Resistant starch
Another nutritional factor is resistant starch, a type of carbohydrate that escapes digestion in the small intestine and is fermented in the large intestine. Research indicates that cooling cooked rice can increase its resistant starch content. Rice refrigerated for 24 hours and subsequently reheated has been found to contain approximately 2.5 times more resistant starch than freshly cooked rice. Heating and cooking alter the structure of starch, while cooling allows some of it to form a structure that is more resistant to digestion.
Cooking Methods
Among cooking methods reviewed, pressure cooking is observed to result in good nutrient retention, with preserved proteins, antioxidants and bioactive compounds. More so because it requires less time than conventional boiling, thus reducing some nutrient losses. Also its sealed environment may also limit the loss of water-soluble vitamins and minerals. However, heat-sensitive nutrients such as folate and vitamin B1 may still undergo some degradation depending on cooking temperature and duration. Besides, cooking processes such as boiling or frying might further diminish bioactive chemical availability. Extended boiling significantly increased the GI across all rice types. Parboiling is also a reliable technique for enhancing the nutritional value of rice while lowering its GI. Pressure cooking is found particularly beneficial for brown rice and other whole grains, where nutrient retention is a priority. Overall, selecting nutrient-rich rice varieties and adopting gentle cooking methods can maximize health benefits.
Conclusion
Nagaland is home to hundreds of traditional rice landraces reported, which can potentially provide recommended nutritional requirements as in dietary fibre, proteins, vitamins, minerals and bioactive compounds. The ICMR-National Institute of Nutrition, Hyderabad in its recent study in landraces from Nagaland have reported the appreciable nutrition in unmilled brown rice and has recommended up to 5% milling or slight polishing to minimize nutrient loss. The findings highlight the importance of preserving traditional rice diversity while reconsidering how rice is processed and prepared. For consumers, choosing less-polished or whole-grain varieties and adopting appropriate cooking methods could gather maximum nutrition and health benefits from this humble staple. While this knowledge may not be uniformly applicable across myriads of rice landraces and varieties, it can help inform individuals regarding dietary choices involving rice.
