RICE TECHNOLOGY AND BIOCHEMISTRY

Work on Rice Technology was initiated during the Third Five Year Plan period. The objectives were to study all aspects of rice quality with particular emphasis on consumers' preference. These covered inter alia varietal differences in hulling, cooking quality and nutrient content, loss of proteins and vitamins in milling, influence of various fertilizer and cultural practices on the protein content, influence of storage on the physical and chemical changes that take place in stored grains, effect of moisture content, ageing, time and method of harvesting, drying etc., on the milling quality and the genetics of the various quality attributes.

Screening trials indicated that Taichung 65, Chianung 242, Tainan 3, CR 905, Changsan, JBS. 674 were characterized by high hulling out turn in the range of 79-83%. Short, globose grains with smooth hull were found to give high hulling outrun.

Hulling characteristics in rice was found to be polygenic in nature. Low protein was dominant over high protein with a large number of genes acting as modifiers. High amylose content was dominant over low amylose, with a single gene exerting major influence and with a large number of minor genes acting as modifiers. Transgressive segregations obtained for high hulling out turn and high protein content gave scope for combining these characters in breeding.

Study on the effect of nitrogen fertilizers on quality features showed that with increasing rates of nitrogen application, there was increase in 1000-grain weight, hulling percentage and protein content without appreciable deterioration in the cooking quality.

Harvesting between 27 to 33 days after flowering for early varieties and between 33 to 39 days after flowering for late varieties at high moisture levels and shade drying gave maximum head rice recovery. This information is of great use not only in increasing production but also in avoiding grain shedding in the fields and breakage losses in mills.

Rice quality

Quality attributes of four aromatic rice varieties (Kalimooch, Dubraj, Sitabhog, Badshabhog) and two non-aromatic varieties (Swarnaprabha, CR 181) were studied. Dubraj, an excellent traditional cultivar with intermediate amylose and gelatinization temperature and hard-gel,-consistency was comparable with the qualities of the variety, Betis of Spain. The two non-aromatic cultivars, Swarnaprabha, CR 181 with intermediate amylose content and other quality attributes were comparable with well traded rice varieties like Delta of France and Rea of Greece.

For evaluation of quality of long slender rice varieties, physical characters of cooked kernels are additive qualities that support consumer preference.

Cooking quality of long slender rice.

Culture/Variety

Amylose (%)

Kernel after cooking

 
   

Length (mm)

Breadth (mm)

Thickness (mm)

OR 1143-230

23

11.4

2.8

2.0

OR 362SP-15

22

10.6

3.0

2.0

R 321-71

22

10.7

2.8

2.0

R 2434-9-5-4

23

11.4

3.0

2.0

RP 263-29-5-5

23

10.0

3.0

2.0

RP 253-7122-9

22

10.6

2.9

2.0

RP2533-7487-15

23

11.0

2.6

2.0

Samalei (check)

21

10.4

3.3

2.2

The evaluation of quality characteristics in rice showed that SG 8, SG 22 and Dulahanaia possessed strong pleasant aroma and higher elongation ratio and were identified to be superior in quality and may serve as good donors in breeding programmes.

Grain quality studies were undertaken of the breeding material generated in the All India Co-ordinated Rice Improvement Project. Depending on biochemical, technological, cooking and eating (objective panel) test, several aromatic rice cultivars were identified. These are: UPRM 79-1, UPRM 500, Pusa 150-21-1, Pusa 150-9-3-1, Pusa 167-120-3-2, Pusa 150-21-1-1, Pusa 263-1-9-2-1, HAU 5-162-3, HAU 5-298-2, Basmati dwarf RPSC 26, Basmati dwarf RPSC 44 (Basmati x Sona), Basmati dwarf RP 55, Basmati dwarf RPSC 55, RPSC 25, RPSC 136, B 63 (Basmati 370 mutant), RPSC 55, RPSC 26, BK 770, RT VI-8A, RP 2144-108-5-3-2, and CRM 8-5708-388-712.

Physico-chmical characteristics of 12 long-slender rices including aromatic (9) and non-aromatic (3) were examined. Proportion of high density grain was positively associated with 100-grain weight, hulling, milling and head rice recovery.

Environment greatly influenced the quality of rice. The waxy nature of japonica rices was disturbed when grown at Cuttack as their amylose content was enhanced more than 10% when compared to those grown at Kulu Manali and other hilly terrains of Uttar Pradesh hills, Himachal Pradesh and Nagaland. Certain varieties like K 39(C), Norin 18(C), and Koshihikari when grown in Kulu terrain exhibited excellent quality comparable with japonica traits.

Protein quality, quantity and biosynthesis

With a view to understand the biochemical processes controlling biosynthesis of protein in rice endosperm, nucleic acid synthesis in developing kernels, fractionation of rice endosperm protein, and heterogenetics of rice glutelin were examined.

Major portion (80-90%) of DNA was synthesized within 13 days from anthesis. Optimum RNA was available up to 17 days from anthesis. The availability of DNA and RNA for a short period in developing rice kernels was responsible for low content of protein in rice endosperm. Glutelin constitutes the major component of rice endosperm protein. Electrophoresis studies confirmed that the heterogenetic nature of rice glutelin and its sub-units were attached with -SH bonds.

Comparative study on endosperm protein between cultivars differing in protein content revealed that deep-seated protein bodies were present in high protein line. Translocation of soluble amino acids from flag leaf to panicle was faster in high protein line. At anthesis two multimolecular forms of glutamate dehydrogenase were observed in kernels of both high and low protein cultivars of rice. The activity of one isozyme was more in a high protein cultivar than in low protein cultivar. The greater activity of GDH isozyme, regulates the synthesis of high content of protein in high protein line.

Nature of biotic and abiotic stresses

Drought

Greater reductions in peroxidase and catalase due to water stress was noticed in drought sensitive cultivar CO 13 as compared to drought tolerant cultivar Lalnakanda-41. Amylase activity increased in both cultivars during moisture stress. Moisture stress caused an increase in pectin methyl esterase activity, and this increase was more in the sensitive cultivar. Drought induced the accumulation of greater amounts of free proline in the leaves of drought tolerant cultivars compared to the sensitive cultivar. Drought tolerant cultivar was characterized by higher amount of total lipids in the husk, bran, brown rice and in polished rice than in the sensitive cultivar. During germination, the seedlings (up to 7 days after germination) of tolerant cultivar contained higher amounts of lipids.

Waterlogging

Differential behaviour of oxidative enzymes like catalase, peroxidase and ascorbic acid oxidase was observed in rice roots submerged at different levels of water depth (up to 60 cm). With the increase of water depth from 3-5 cm to 55-60 cm at tillering, maximum tillering and flowering stage of the crop, catalase activity decreased in the roots of IET 4806 ( susceptible to waterlogging), while it increased in the roots of a tolerant cultivar (IET 6206). Tolerant cultivars contained higher concentrations of indole acetic acid in internodes than the susceptible cultivars.

Submergence

Submergence induces various biochemical properties in rice plants. A significant redcution in carbohydrates like starch and redcuing sugars was characteristic of submergence. This reduction was more in a tolerant, Hatipanjari than in sensitive varieties, Tulasi, CR 835-18-1. Correspondingly, greater activity of amylase was recorded in submergence tolerant variety than in sensitive varieties. However, acid phosphatase activity increased up to 6 days of submergence, and then, declined in all the cultivars examined including tolerant, CR 260-77 and sensitive Ratna and Samalei. Mechanism of submergence tolerance is presumably associated with the catabolism of reserved carbohydrate through hydrolytic enzymes.

Salinity

Salinity decreased the number of alpha amylase iso-enzymes and repressed hydrolytic enzymes in the early stage of seedling growth. Activity of hydrolytic enzymes was more in tolerant than in susceptible cultivars.

Disease and insect pests

Sheath blight and bacterial blight pathogens produced toxic principles in culture which were glycopeptide in nature. The toxin produced by sheath blight pathogen exhibited macerating activity in potato discs. The macerating activity of the toxin is believed to cause the typical sheath blight syndrome in the infected plants.

Rice processing and by-product utilisation

Harvesting, threshing and drying

Unscientific method of stacking of harvested paddy was shown to result in the production of mycotoxins in the grains, reduced the head rice recovery and initiated biodeterioration of the rice/paddy. Timely harvesting and proper drying reduced the possible production of mycotoxins.

Chemical analysis of straw, an important by-product of rice production, showed that it contained oxalic acid (1.0%), phytic acid (1.6%), which are toxic to ruminants. Simple alkali (1.0%) or calcium oxide (3.0%) treatment of pulverised straw reduced the content of these constituents substantially. Pulverised rice straw mixed with molasses and urea increased the protein content and palatability for ruminants.

Milling

The time required for 5% polish varied from variety to variety. Head rice recovery and time of polish were negatively correlated. It was observed that the time required to obtain 5% polish was maximum for short-bold grains. Between fine and super fine grains, the polishing time is more for fine grains than for super fine grains. Generally head rice yield was maximum in short-bold varieties. Maximum polish was obtained in raw rice followed by single and double parboiled rices in a fixed time.

Bran

Bran obtained from 5% polish is an excellent source of oil. Generally, rice bran contains 15-20% oil when solvent extraction was used. Rice bran oil is comparable to almond oil and butter fat in respect of certain chemical characters.

The de-oiled cake is an excellent source of protein (15-20%). Extract of de-oiled cake with alkali, and iso-electric precipitation yielded about 5% protein. Heating at 110oC for 10 min with 0.5 mm thickness of bran layer is an effective measure to control lipolytic enzyme, lipase. The resultant bran can be preserved for a month in polyethylene bag at room temperature without formation of free fatty acids.

Assessment of oilseeds quality raised in rice-based cropping system

Groundnut and sesamum are important components in the rice-based cropping system in Orissa. Several groundnut samples were analyzed for oil content and the de-oiled cake for protein content in order to select the suitable ones for recommendation. The oil content ranged from 44 to 54%, while the protein content of the de-oiled cake ranged from 38 to 49%. The variety ICGS 11, a moderate yielder showed higher oil content (54%) and protein (43%) content than the other varieties tested. Groundnut varieties, R 8808 and DRG 12 were identified as promising ones considering their higher pod yields and quality characters. Among the sesamum varieties tested, variety Vinayak showed an oil content of 50% in comparison to OM 7-10 (40%), Usha (40%), Kanaka (41%), Kalika (45%) and Uma (45%).