New ideas and concepts
Rice bran: A nutrient-dense mill-waste for human nutrition
Rabbani GH¹, Ali M²

Introduction

Rice is the staple food for seventy percent of world population supplying as much as half of its energy needs (Chang TT 19 76). In Asian countries including China, India, Indonesia, Bangladesh, Vietnum, Japan, Thailand, Myanmar and Pakistan, rice is produced and eaten as the predominant source of energy.

Common rice, scientifically called Oryza sativa has more than 8,000 named species that are grown all over the world. Rice is sometimes classified as either short grain, medium grain or long grain. Short grain rice has the highest starch content and is stickiest when cooked as it contains more Amylopectin; while long grain is lighter and tends to remain separate when cooked.as it contains more Amylose . The characteristics of medium grain rice fall between the other two types.

Rice is also classified according to the degree of milling; brown rice is the whole grain with only its inedible outer hull removed keeping its nutrient-rich bran layer intact (Marshall 94). In contrast, white rice is both milled and polished, which removes the bran and germ contents along with all the nutrients that reside within these important layers.

White rice is the most popular form for human consumption although brown rice is eaten in some communities.

History

Rice is an ancient crop. It is believed that rice cultivation first began in China around 6,000 years ago, but this period could be as long as 9,000 years according to recent archaeological investigations based on discoveries of primitive rice seeds and farm tools (Plant Rice 2001, Marshall 94). Historically, rice is thought to be a staple grain  in Asia which was introduced to Greece by the Arab conquest of Asian land and to India by Alexander the Great.

During the Moorist conquent of Spain in the 8^th century rice appeared in the Spanish markets while the Crusaders brought it to France. In 17^th century rice was introduced to South America by the Spanish settlers in this continent. A significant proportion of world production of rice comes from Asian countries where it plays an important role in the food culture of the people. Thailand, Vietnam, India and Pakistan are the three largest exporters of rice worldwide

Rice Bran

Rice bran constitutes the brown covering of the grain beneath the outer husk. It constitutes 8% of the weight of the whole grain and contains most of the nutrients (65%). During milling process rice bran containing nutrients is completely removed. Around 60 million metric tons of rice bran is produced worldwide each year and almost all of it is either thrown away or used as low level animal and poultry feed. The cost of rice bran is 0.2 cent per pound in the international market and 0.1 cent (Tk. 5-7) in Bangladesh. Rice bran is a very rich source of nutrients containing vitamins, minerals, oils, wax, trace elements, antioxidants, phytosterols, and phytochemicals. It is also an energy-dense (373 cal/1 cup or118g), high protein (15.8 g/1cup), high fiber (99%), low sodium, low sugar (1.1 g) cereal containing zinc, iron, folic acid and other nutrients but no cholesterol. It is a good source of manganese, magnesium, vitamins B₁, B₂, B₆, and minerals i.e., potassium, calcium, phosphorus, and pantothenic acid. Recent information indicate that its high nutrient contents are hard to ignore.

Figure : Structure of mature rice grain

Brown rice

Brown rice is un-milled or partially milled rice with removal of the outermost layer of the rice grain (husk) which becomes rancid more quickly. Parboiling destroys partially or completely the lipase activity of the rice bran thus providing longer shelf life of brown rice and helps preventing development of rancidity. Parboiled brown rice was traditionally and historically been consumed in most part of Bangladesh. With the advancement of industrialization, milled white rice has taken over the place of parboiled brown rice in this setting in past few decades.

The limitations of using brown rice with intact bran are related to its unpalatability due to high fibre content and short shelf life resulting from rapid hydrolysis of its fat content by the grain enzyme lipase (Champagne 94). Within 1 hour of separating the bran from the grain during milling the material turns rancid liberating toxic free fatty acids. These shortcomings have now been overcome by reducing the fibre content and destroying the lipolytic activity using an advanced stabilizing technology; the resulting material thus obtained is called “stabilized” rice bran which has a good taste, readily soluble with a longer shelf life of 1 year.

Rice bran in its crude or stabilized form is a potential dietary source which can be used as a nutritional supplement to