Rice in human nutrition - Major processed rice products

Expanded (puffed, popped) rice products

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Puffed and popped rices are traditional breakfast cereals and snack foods (Juliano and Sakurai, 1985). Raw rice is traditionally popped by heating rough rice (13 to 17 percent moisture) at about 240C for 30 to 35 seconds or at 275C for 40 to 45 seconds or in an oil bath at 215 to 230C. The hull contributes to pressure retention before popping as evidenced by the lower popping percentage of brown rice. Good popping varieties have a tight hull and a significant clearance between hull and brown rice and when freshly harvested are free of grain fissures (Srinivas and Desikachar, 1973). Tightness of hull, grain hardness and degree of translucency could explain 80 percent of the variation in popping expansion among 25 rice varieties (Murugesan and Bhattacharya, 1991).

Flaked or beaten brown rice and parboiled milled rice may be converted to puffed rice by heating in hot air or roasting in hot sand (Juliano and Sakurai, 1985; Villareal and Juliano, 1987). With normal parboiled milled rice, puffed volume is directly proportional to the severity of parboiling

(equilibrium water content of steeped grain prior to parboiling) and is highest for waxy rice (Antonio and Juliano, 1973). Puffed waxy and low-amylose rices tend to have a higher puffed volume than intermediate- to high-amylose rices only when grains are incompletely parboiled or cooked before oil puffing (Villareal and Juliano, 1987). However, with increasing temperature and period of roasting of rough rice, high-amylose rice (specifically 27 percent) gives the maximum puffed volume for roasted beaten rice (Chinnaswamy and Bhattacharya, 1984). Puffed non-waxy rice and flattened waxy rice are caramelized and moulded and are common snack foods in the Philippines. A typical Japanese rice cake, okoshi, is made of puffed broken rice mixed and moulded with millet jelly, sugar and flavouring.

Gun-puffing of moist milled rice may be considered as puffing rather than popping since the grains are gelatinized prior to expansion. The expansion ratio was higher for waxy milled rice than for non-waxy rice (Villareal and Juliano, 1987). The expansion ratio for gun-puffed milled rice or oil-puffed parboiled or boiled milled rice correlated negatively with protein content, except for those rices parboiled at zero steam pressure before oil-puffing.

Continuous explosion-puffing of brown rice, developed in Japan in 1971, uses a long heating pipe wherein grains are dispersed and conveyed by a high-velocity stream of superheated steam (Sagara, 1988). After the rice has been heated and dried within 3 to 10 seconds, it is discharged into the atmosphere through a rotary valve to explosion-puff. A brown rice expansion ratio of 5.4 is obtained at 6 kg/cm2 pressure and an outlet steam temperature of 200C. The puffed product has a starch digestibility of 94 percent after 15 minutes of boiling. Thiamine is not destroyed at 200C or lower but is completely destroyed at an outlet steam temperature of 240C (Sagara, 1988).

In developed countries, dry rice breakfast cereals include rice flakes, ovenpuffed, gun-puffed or extruder-puffed rice, shredded rice cereal and multi grain cereals (Brockington and Kelly, 1972; Luh and Bhumiratana, 1980). These are of the ready-to-eat type in which the rice starch provides texture-modifying properties and rice also imparts its own special flavour. Among the important properties of a ready-to-eat cereal is "bowl life", or the ability to retain its texture and crispness in milk while being eaten.

Moisture-proof packaging is critical for optimum shelf-life. While low-amylose, low-GT rices are used for breakfast cereals in the United States, interrnediate- and high-amylose rices are used in the Philippines, but the degree of cooking must be controlled to obtain an acceptable puffed volume from the grain. Most cereals are enriched with B vitamins and with minerals, particularly iron.

Baked rice products

For those suffering from coeliac disease, a yeast-leavened bread of 100 percent rice flour has been successfully developed, consisting of 100 parts rice flour, 75 parts wafer, 7.5 parts sugar, 6 parts oil, 3 parts fresh compressed yeast, 3 parts hydroxypropyl methylcellulose and 2 parts salt (Bean and Nishita, 1985). Although all non-waxy rices produce breads of equivalent appearance, only lowamylose, low-GT rices give a soft-textured crumb. Intermediate-amylose, intermediate-GT rices give sandy, dry crumb characteristics. However, among lowGT rices low-amylose rice gave a lower loaf volume than did intermediate- and high-amylose rices (IRRI, 1976). Wet-milled flour gave a better texture than drymilled flour. An extended shelf-life should improve the popularity of this product.

A medium-grain low-amylose rice flour: waxy rice flour ratio of 3:1 in place of wheat flour produced satisfactory muffins for gluten-sensitive individuals (Stucy Johnson, 1988).

For bread baking in Japan, 10 to 20 percent rice flour is generally mixed with wheat flour as a diluent, depending on the gluten strength of the wheat flour (Tan), 1985). A recent Japanese formulation consisted of 60 percent rice flour, 30 percent wheat flour and 10 percent vital gluten. Similar dilutions of wheat flour with rice flour and other starchy flours have been developed for bread-making in several countries, but the GT of the starch should preferably be low (<70C), (Bean and Nishita, 1985).

Rice flour has also been used in making a Pakistani bread similar to roti, the flat unleavened bread commonly made from wheat flour (Juliano and Sakurai, 1985). The preferred bread, similar to a wheat chapatti, is puffed, semi-light, flexible, uniformly round and firm, but not rough. Red rices, such as Dwarf Red Gunja, are preferred in some Sind villages for Pakistani rice bread. Rice flour may also be added to wheat flour in a proportion of up to 15 percent; 21 percent rice flour in chapatti results in a still acceptable but difficultto-fold texture.

Fresh pregelatinized starch is used for the preparation of wheatless bread; the starch (16 percent by weight) acts as a binder in place of gluten, as in extruded rice noodles (Satin, 1988). The method is applicable to rice flour, but the crust properties are not as good as those of wheat bread and have to be improved. Dry, pregelatinized rice flour may possibly be used to produce this bread faster without any problem of incomplete starch gelatinization during baking in the presence of sucrose.

A layer-cake formula containing 100 percent rice flour was also developed for wheat-free diets (Bean and Nishita, 1985). It consists of 100 parts rice flour, 80 parts sugar, 15 parts oil and 5 to 7 parts double-acting baking powder. Lowamylose, low-GT rices are preferred for this formula; intermediate-amylose, intermediate-GT rices give a sandy, dry texture. A high sucrose level increases starch GT; thus in 50 percent sucrose low-GT rices have a GT of 80C while intermediate-GT rices have a GT of 92C. When the sucrose level is reduced to give a GT of 80C for the intermediate-GT rice, the volume and contour of the cakes improve, but the sandy texture remains. Hydrating the rice flour by intense mixing of the flour and water and folding of the hydrated mixture improve the texture and volume of the cake (Perez and Juliano, 1988).

Baked Japanese rice cakes or rice crackers include senbei and arare. A rare is a cracker made from boiled waxy rice pounded into rice cake, stored at 2 to 5C for two to three days to harden, cut, dried to 20 percent moisture at 45 to 75C and baked. Senbei is a cracker-like snack made of cooked non-waxy rice flour kneaded and rolled into sheets, cut, dried at 70 to 75C to 20 percent moisture, tempered for 10 to 20 hours at room temperature, redried at 70 to 75C to 10 to 12 percent moisture and baked at 200 to 260C, without the cooling treatment. Arare expands more during baking, has a soft texture and dissolves easily in the mouth. Senbei is harder and rougher. Sesame seeds, pieces of dried seaweed, peanuts, pulverized shrimp, cheese or spices may be mixed with the rice dough as desired. Extruder-type kneaders are used for mixing the gelatinized rice. Rice cracker production in Japan in 1983 was 103 000 t of arare and 118 000 t of senbei (Tani, 1985) and in 1987 was equivalent to 215 000 t of brown rice (Hirao, 1990).

Non-waxy rice cakes or crackers (xianggao) are prepared from both low- and high-amylose rices in China. The high-amylose cake is harder, whiter and more crispy than the low-amylose cake. A similar rice product made in the Philippines from intermediate- to high-amylose rice is called puto seko. These crackers break readily on handling.

Canned rice

In the United States, the preferred canned rice product is white, with separate noncohesive grains, minimal longitudinal splitting and fraying of edges and ends and a clear canning liquor (Burns and Gerdes, 1985). Long-grain (intermediateamylose) parboiled rices are preferred in most canning formulations because of the required cooked rice stability. Non-parboiled high-amylose rices, particularly those with a hard gel consistency, are also suitable, but the texture may be too hard. A pH below 4.6 is recommended for canned rice to reduce microbial contamination because retorted canned rice may not be completely sterilized.

In Japan, low-amylose milled rice is placed in cans with water, broth or another seasoning, steamed for about 30 minutes and sealed and sterilized in a retort at 112C for 80 minutes (Juliano and Sakurai, 1985). Canned rice is heated in boiling water for 15 minutes before serving. Canned seasoned cooked rice is marketed primarily as military rations and as emergency foods. Intermediate-amylose rice is used in canned rice for the military in the Philippines. Annual production of canned rice in Japan was 1 472 t in 1983, but it is declining in popularity (Tan), 1985) with only 1 159 t produced in 1986 (Iwasaki, 1987).

Both wet- and dry-pack canned rices are produced in Taiwan (Chang, 1988). Daily production of wet-pack rice is 360 000 easy-to-open 340-ml cans, while the production of dry-pack rice is very limited. Wet-pack canned rice preparations, usually called rice congee, use waxy rice and are all sweetened; the most popular formula includes waxy rice as a base together with dried longans, red beans, peanuts, oatmeal and sugar. Low-amylose rice is used for dry-pack fried rice.

Fermented rice products

Various waxy rice wines are prepared by fermenting steamed waxy milled rice with fungi and a yeast starter (Steinkraus, 1983; Juliano and Sakurai, 1985). A sweet product is first produced, which is then converted to alcohol as fermentation progresses. The liquid is removed by decantation. Examples are Chinese laochao, Thai khaomak, Malaysian tapai, Indonesian tape ketan and Philippine tapuy. Red rices are preferred for tapuy and are often roasted before cooking (Sanchez et al., 1989). Ethanol conversion is higher for waxy and low-amylose rice than for intermediate- and high-amylose rice during tapuy production; undigested starch is mainly amylose (Sanchez et al., 1988).

Rice wine production in Taiwan uses 67 000 t of milled rice annually and uses either Aspergillus oryzae (shao-hsing wine) or Rhizopus sp. (hua-tiao) for saccharification (Chang, 1988). Overmilled waxy rice (20 percent bran polish) is washed, steeped in water, steamed, inoculated with A. oryzae spores and incubated for 45 hours at 35 to 38C for a low-amylose brown rice starter.

Ragi-type starters (bubod in the Philippines) are available in the markets of most Asian countries (Steinkraus, 1983). They are usually small (3 to 6 cm), round, flattened cakes of rice flour on which the desired microorganisms have been grown. The cakes are either air-dried or sun-dried and the dehydration occurs simultaneously with growth of the organisms. Micro-organisms include the mould Rhizopus sp. or combinations of the essential yeasts and moulds required for the different types of alcoholic fermentations.

Rice is the sole cereal substrate in Japanese rice wine such as sake (Yoshizawa and Kishi, 1985). The raw material is highly milled rice (25 to 30 percent bran polish by weight of brown rice) with low arnylose, low GT and a white core, characteristics that facilitate swelling, cooking and penetration by the mycelia of A. oryzae. Overmilling lowers protein (5 to 6 percent) and non-starch lipids (0.1 percent) and also potassium and phosphorus levels. Steamed rice is inoculated with koji, a culture of A. oryzae grown on steamed rice and seed mash. Sake yeast is grown on koji steamed rice containing 70 ml lactic acid per 100 litres of water at 12C.

Three more additions of materials are made to maintain fermentation. About 500 000 t of milled rice were used for sake in Japan in 1985 (Tan), 1985).

Rice milk has been used as a substitute for animal milk and milk powder and may be prepared either from puffed rice flour or from wet milled flour with sugar and peanut oil for flavouring. Brown rice gives a better-quality milk than milled rice, and a formulation of 3.5 percent (wt/vol.) of brown rice, 2 percent peanut oil and 7.5 percent sugar gave the best sensory score (Lin, Shao and Chiang, 1988). Rice milk contains 87.7 percent moisture, 0.8 percent protein, 0.8 percent fat, 0.1 percent crude fibre, O. I percent ash and 10.4 percent carbohydrate; it has 11 percent total solids and viscosity of <3 poise. Use of bacterial amylases to hydrolyse the starch can increase the solids content of the milk without unduly increasing the milk viscosity (Mitchell, Mitchell and Nissenbaum, 1988).

Mirin is a clear, sweet drink made by adding steamed waxy rice and koji to shochu, a gin-like alcoholic beverage obtained by distilling a type of sake made from broken indica rice. The mixture is allowed to ferment in the presence of 40 percent ethanol from shochu until the rice starch is converted to sugars (two months at 25 to 30C). After filtration and treatment with tannin and gluten and refiltering, the bottled mirin contains 14 percent ethanol and 45 percent sugars. It is used either for drinking (sweetened sake) or for seasoning Japanese dishes. Mirin production in 1986 in Japan was 78 000 kl (Sagara, 1988).

Rice vinegar results from the completion of the rice starch fermentation and is a traditional Japanese and Chinese product (Iwasaki, 1987). Acetic acid fermentation is carried out by mixing seed vinegar with the rice wine and takes one to three months. The product is ripened, filtered, pasteurized and bottled (Lad, Chang and Luh, 1980). It has 4 to 5 percent total acidity (mostly acetic acid, plus some lactic and succinic acids). Rice vinegar production in Japan was 40 000 kl in 1983 (Tani, 1985) and 52 000 kl in 1986 (Sagara, 1988).

Broken rice, together with maize grits, is an adjunct in beer manufacture in the United States and Japan (Yoshizawa and Kishi, 1985). Rice is preferred to maize because of its lower protein and fat content (<1.5 percent). Broken rice is obtained from regular milling of brown rice in most countries, except in Japan, where it is milled from broken brown rice. Broken rice must be free from bran contamination to reduce protein and fat content. Low-GT, low-amylose rices are used because intermediate-GT, intermediate-amylose rices are relatively resistant to starch liquefaction. Rice seed is not used for malting in place of barley because of its lower a-amylose production (IRRI, 1988b).

Other fermented rice products include Japanese miso, Sierra rice (amarillo or requemado) from Latin America and angkak (anka, red rice). Miso is a traditional Japanese brown seasoning paste principally used for a breakfast soup. It is prepared from koji (A. oryzae) from milled rice mixed with cooked and minced soybean, salt and a starter of cultured yeast and lactic acid bacteria. The ingredients are fermented in covered vats at 25 to 30C for one to three months (Wang, 1980). The rice-to-soybean ratio is about 2: 1. Japanese miso production in 1986 was 471 000 kl (Sagara, 1988). Sierra rice is derived from moist rough rice fermented by the micro-organisms that are naturally present with heating up to 50 to 70C. The grain becomes yellow to brown and is essentially precooked and predigested. Angkak may be produced by Monascus purpureus mould on cooked rice at 35 percent moisture and pH 6.5 at room temperature (Dizon and Sanchez, 1984). It is used as a colouring agent for food, such as fermented fish (Hesseltine, 1979).

Rice flours and starch

Rice flour in Japan is made from both waxy and non-waxy rices and from both raw and gelatinized rice. It is milled by rolling, pounding, shock-milling, stone-milling, milling in a lateral steel mill and wet milling in a stone mill. In 1985, rice flour production in Japan included 67 000 t from raw rice plus 140 t from pregelatinized rice (Tani, 1985). In 1987, rice flour production used 105 000 t of brown rice (Hirao, 1990).

A tea prepared from roasted brown rice in Japan used 23 800 t of non-waxy and 1 200 t of waxy rice in 1985 (Tan), 1985). Production in 1986 was 20 000 t (Sagara, 1988).

High-protein rice flours for early childhood feeding may be obtained from cooked milled rice by destarching treatment with a-amylase (Resurreccin,

Juliano and Eggum, 1978; Hansen et al., 1981). A high-fructose rice syrup and a high-protein rice flour have been produced from broken rice using a-amylase, glucoamylase and glucose isomerase. This procedure obtained an 80 percent glucose yield from brokers (91 percent starch basis) which was converted to 50 percent glucose, 42 percent fructose and 3 percent maltose (Chen and Chang, 1984). The high-protein flour (28 percent protein) was recovered in 30 to 32 percent yield. Others have obtained 80 percent protein flour Resurreccin Juliano and Eggum, 1978). Maltodextrins are also produced from milled rice flour at 80C using heat-stable a-amylase (Griffin and Brooks, 1989).

Rice starch production involves mainly wet milling of brokers with 0.3 to 0.5 percent sodium hydroxide to remove protein (Juliano, 1984). Brokens are steeped in alkali solution for 24 hours and are then wet milled in pin mills, hammermills or stone-mill disintegrators with the alkali solution. After the batter is stored for 10 to 24 hours, fibre (cell wall) is removed by passing it through screens; the starch is collected by centrifugation, washed thoroughly with water and dried. Protein in the effluent may be recovered by neutralization and the precipitated protein used as a feed supplement.

In the European Economic Community (EEC), about 8 800 t of broken rice are processed annually to about 7 000 t of starch in five to six plants in Belgium, Germany, Italy and the Netherlands (Kempf, 1984). The starch is used exclusively as a human food, largely for baby foods and also in extruded noodles. Egypt, Syria and Thailand also produce rice starch.

Rice bran and rice-bran oil

Rice bran has been an extremely popular source of dietary fibre because of the hypocholesterolaemic property of its oil fraction. Stabilized rice bran has been made available by the use of the Brady extruder in the United States to stabilize the full-fat bran by inactivating its lipase (Saunders, 1990). It is finding application in breakfast cereals, snack foods and bakery products. Stabilized rice bran has been incorporated into whole-wheat bread, muffins, peanut butter cookies and oatmeal cookies at levels of up to 20 percent. The 3 to 8 percent sugar content of rice bran may also contribute to oven browning. The high water absorption capacity of rice bran helps maintain moisture and freshness and therefore improves shelf-life. Its foaming capacity aids in air incorporation and leavening.

In tropical Asia, food applications of rice bran will have to await the reduction of hull contamination of rice bran from the use of Engelberg mills. However, stabilized rice bran is a good poultry feed since its trypsin inhibitor has been inactivated by extrusion cooking.

Rice-bran oil production was about 679 000 t in 1990 (FAO Statistics Division data) or about 13 percent of potential production based on 7 percent bran from rough rice, 15 percent oil recovery from bran and a world rice production of 507 million tonnes. The principal producers of rice bran oil are India (370 000 t), Japan (83 000 t) and China, including Taiwan (122 000 t).

Rice-bran oil has an iodine absorption number of 92 to 115 and contains 29 to 42 percent linoleic acid and 0.8 to 1.0 percent linolenic acid (Jaiswal, 1983). It is considered a salad oil rich in vitamin E and in various plant sterols (Juliano, 1985b).

Rice types preferred for rice products

Most rice products have a preferred amylose type which is related to the preferred rice type for boiled rice consumption in the country (Table 45). All rice types are used for parboiled rice, but usually intermediate- and high-amylose rices are used in Thailand and the United States. High-amylose rices are used in Bangladesh, India, Pakistan and Sri Lanka. Canned, precooked and quick-cooking rices, expanded rice products, rice cereals and snacks are of the type preferred for boiled rice. Low-GT rices are preferred for fermented products since the rice starch can be gelatinized at 70C and therefore requires less cooling before inoculation. Low-fat or highly milled rice, preferably freshly milled to minimize rancid odours, is preferred for rice products. Waxy rices are preferred for desserts and sweets because of the slower rate of hardening of the boiled or steamed rice starch.

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