Module 2. Cereal processing

Lesson 3

PROCESSED RICE PRODUCTS AND BY-PRODUCTS

3.1  Introduction

There are numerous uses of rice and rice flour for manufactured and for culinary preparations. Food uses of rice can be categorized into four groups: direct food use, brewing, seeds and others. The use of rice for direct food is the highest of the three uses. Milled rice, parboiled rice, brown rice are directly consumed after cooking. Rice and rice products are also used in manufacture of certain processed foods such as breakfast cereals, soup, baby food, packaged mixes, etc. Idli and Dosai are common foods in South India which is prepared from fermented batter of rice and black gram. Fermented beverage i.e. Sake is the traditional Japanese rice wine.

3.2  Modern Convenience Foods from Rice

Pre-cooked rice is used in rice-based convenience foods where non-rice ingredients are separately packaged and mixed only during heating. Such types of convenience foods provide convenience to the consumer as it requires much less time for preparation.

3.2.1  Precooked and instant rice (Quick cooking rice)

Because of the demand of the modern consumers, processes have been developed to manufacture quick-cooking rice. Quick cooking rice is precooked and gelatinized to some extent in water, steam or both. The cooked rice is usually dried in such a manner as to retain the rice grains in a porous condition. This pre-packed quick-cooking rice requires just 5 min for preparation compared to 20 – 30 min in case of conventional rice cooking. Process for the quick cooking rice involves soaking of rice in water, cooking to the moisture content of greater than 60%. The cooked rice is then dried to a moisture content of 14%. The finished product should consist of dry, individual kernels, substantially free of lumps or aggregates, and approximately 1.5 to 3 times the bulk volume of the raw rice.

Alternatively, precooked rice is freeze dried. The reconstitution property of freeze dried rice is excellent compared to heat cooked and dried rice.

Retort rice in Japan is made by hermatically sealing cooked non-waxy and waxy rice in laminated plastic or aluminum-laminated plastic pouches and retort processing at 120°C under processing. Steamed waxy rice with red beans accounts for 80% of retort rice in Japan. The aluminum-laminated plastic pouch is warmed directly in hot water for 10 to 15 minutes while plastic pouches may be punctured and heated in microwave oven for 1 to 2 minutes.

Many quick-cooking rice products, varying in texture, bulk volume, appearance, taste, etc., are designed specifically for certain consumer uses depending on the rehydration time and other requirements. Some of the special applications of quick-cooking rice are in dry soup mixes, rice puddings, casseroles, flavor-coated free flowing rice and other dry prepared mixes.

3.2.2  Canned rice products

Rice is used as one of the ingredients in various canned food products such as soups, baby foods, plain and flavoured cooked rice, rice-milk pudding, etc. Long grain varieties with high amylose content are suitable for canned rice products. Parboiled rice are also preferred as they retain integrity throughout the canning process. Lacquered tin cans and retortable flexible pouches are most commonly used packaging material for canned rice products.

In the soups or other canned foods, where the rice must remain in suspension, parboiled rice is cooked enough to prevent settling and then added to the mix. The most successful and well known canned rice product is pudding. If the rice and milk mixture are prepared separately and combined in the can aseptically, the flavour and texture of the product are preserved. Dry products such as fried rice and rice and beans can also be canned.

3.2.3 Puffed rice

Paddy is soaked in water to increase the moisture to about 20%. The moist paddy is puffed by subjecting to sudden heat treatment at 250-270°C for 30-40 seconds. The husk splits and the rice is puffed.

3.2.4 Flaked rice

Flaked rice is made from parboiled rice. Paddy is soaked in water for 2-3 days (or hot water 70-80°C for 20 min.) to soften the kernel, followed by boiling in water for few minutes. After cooking, the water is drained off and the paddy is heated (250-275°C) in a shallow earthen vessel till the husk break open, after which it is pounded by a wooden pestle, heavy iron rollers which flatten the rice kernel and remove the husk. Husk is removed by winnowing.

3.3 Processing of Rice Bran Oil

Rice bran makes up only some 2% of the paddy but it is a valuable source of edible oil and protein-rich animal feed. Rice bran consists of 12 – 15% protein, 15 – 20% lipid, 40 – 50% carbohydrates, 7 – 11% crude fiber and 6 – 9% ash. Heat generated during milling triggers enzymatic activity, resulting in the hydrolysis of lipid, and oxidative changes leading to rancidity. Hence, the bran must be stabilized as quickly as possible after production to prevent the rancidity. Stabilization of rice bran can be achieved by dielectric heating, treatment with hydrochloric acid and treatment with sodium metabisulfite. Recently, extrusion-cooking process has proved very successful and cheaper. Rice bran oil is extracted with light petroleum spirit (n – hexane); the process is thus hazardous. The flow diagram for extraction of rice bran oil is depicted in Fig. 3.1. An asterisk in the Figure indicates that the products are of value e.g. for soap manufacturing, etc.