Rice Bran

Rice is in the form of paddy (where the kernel is fully enveloped by the rice hull) when harvested from the field (Saunders, 1990). After being dried, the first stage in milling is removal of the hull, yielding brown rice. In the second state, the outer brown layer is removed from the brown rice kernel by abrasive milling operation to yield the familiar white rice. The separated brown layer is designated rice bran, which includes the germ in the United States. Under normal milling conditions, when brown rice is milled to white rice, the oil in the bran and a potent lipase also in the bran come into contact, resulting in rapid degradation of the oil. The bran thus produced is unpalatable and only fit as a feedstuff.

However, if the bran is subjected to a short-term high temperature heat treatment g the lipase activity is destroyed and a stabilized bran is produced. The compositions of rice brans are summarized in Table 5.

Rice bran has a number of unique properties (Saunders, 1990). Rice bran ^

protein is of relatively high nutritional value. Protein efficiency ratio values reported for bran generally range from 1.6 to 1.9 compared to casein value of 2.5. | Digestibility of protein in rice bran is about 75 percent. The bran usually contains 16-22 percent oil, although this value is higher in parboiled bran due to the absence of broken starch fragments. The three major fatty acids in rice bran are palmitic, oleic, and linoleic and they make up more than 90 percent of the total fatty acids. Rice bran oils contain 3-4 percent waxes and about 4 percent unsa-ponifiable lipids. Rice bran oil has a higher content of unsaponifiable material

Sources and Uses of Fiber

Table 5 Typical composition of rice bran

Atribute

Stabilized Rice Bran

Parboiled Rice Bran

Table 5 Typical composition of rice bran

Atribute

Stabilized Rice Bran

Parboiled Rice Bran

Moisture

8

-12%

7

-9%

Protein

12

-16%

14

-20%

Fat

16

-22%

23

-32%

Ash

7

-10%

8

-13%

Total Dietary Fiber

20

-25%

31

-33%

Soluble Dietary Fiber

2

-3%

2

-3%

Calories/g

3.2

3.5

From Saunders (1990).

From Saunders (1990).

than other vegetable oils. The unsaponifiable fraction consists of compounds such as oryzanols, beta-sitosterol, and tocopherols, which may have cholesterol-lowering activity. The major carbohydrates in commercial rice bran are cellulose, hemicellulose, and starch. Starch is not present in the outer pericarp layers, but because of endosperm breakage during milling it appears in the bran. The quantity varies according to the amount of breakage and degree of milling, but values of 10-20 percent are typical. Hemicellulose and cellulose have been reported to comprise 8.7-11.4 percent and 9.6-12.8 percent of the bran. Beta-glucans in the bran are present at levels of less than 1 percent.

The functional properties of rice bran are compatible with a wide variety of food uses (Barber and Benedito de Barber, 1980; Saunders, 1990). The water and oil absorption capacities are 2.0 and 1.5 g/g, respectively. Bran from parboiled food-grade rice bran is normally finely granulated, light tan in color, and possesses a relatively bland flavor with a nutty, toasted overtone. Its applications include use in baked goods, breads, cookies, breakfast cereals, granola-type bars, snacks, muffins, many other product. Parboiled rice bran appears to be a good dietary fiber supplement for bakery products (Skurray et al., 1986).

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