Characterization of Starch Structures of 17 Maize Endosperm Mutant Genotypes with Oh43 Inbred Line Background'

Cereal Chem. 70(2): 179-183 Sorghum grains varying in grain hardness or endosperm texture (soft dispersion in hot water. Parboiled grain with soft endosperm texture and intermediate) and starch composition (nonwaxy and waxy) were contained less dispersible and soluble starch than parboiled grain with parboiled. Whole grain (one volume) and water (three volumes) were intermediate endosperm texture. The physical characteristics of the waxy boiled, soaked for 12 hr, and brought to boil again (boil-soak-boil process) cultivar were changed after parboiling; however, starch solubility and or, alternatively, soaked overnight and boiled for 10 min (soak-boil crystallinity decreased only slightly. Pasting properties of waxy sorghum process). The grain was dried at room temperature and decorticated. were not changed as dramatically by parboiling as were those of nonwaxy Parboiled kernels were darker, denser, smaller, and harder than noncultivars. Apparently, the absence of amylose in waxy starch substantially parboiled kernels. Parboiling decreased starch crystallinity and starch decreased retrogradation of starch polymers. Parboiling of rice is one of the most widespread food processes in the world. The hydrothermal process consists of soaking rough rice in water until it is saturated, draining the excess water, steaming or otherwise heating the grain to partially gelatinize the starch, and drying (Bhattacharya 1985). Sorghum (Sorghum bicolor (L.) Moench) is one of the most important staple foods in arid regions unsuitable for the cultivation of other crops. In 1989, world sorghum production was estimated at 58.0 million metric tonnes. Asia, North America, and Africa produced 32.7, 27.1, and 24.1% of the world's sorghum, respectively (FAO 1990). Rooney and Serna-Saldivar (1991) indicated that 30% of world production is consumed directly by humans, primarily as traditional foods. Sorghum is used as a substitute for rice in Mali and India (Subramanian et al 1982). In India, the ricelike product called annam or soru accounts for 10% of the total sorghum grain produced. Similar products have also been reported in Bangladesh (khicuri), Botswana (lehata wagen), China (kaohang mi fan), Ethiopia (nufio), and Nigeria (oko baba) (Subramanian and Jambunathan 1980). In most African countries, special types of sorghum with very hard, flinty endosperm are dehulled and used as a rice substitute. However, these special sorghums have small kernel size and low agronomic yields. Parboiling could allow consumers to use higher yield sorghums with intermediate or soft endosperm texture. Young et al (1990) adapted rice technology to produce a parboiled sorghum called SORI (SOrghum RIcelike product). The modified process was simply boiling, soaking for 12 hr. reboiling, and air-drying. Parboiled sorghum was then decorticated. The most important benefits of parboiling sorghum were: 1) increased yield of decorticated sorghum; 2) reduced amounts of broken 'Contribution TA 30669 from the Texas Agricultural Experiment Station, Texas A&M University, College Station. 2 Research group leader, CSIR, Division for Food Science and Technology, Pretoria, South Africa. 3 Research scientist, research associate, associate professor, and professor, respectively, Soil and Crop Sciences, Texas A&M University, College Station, TX 778432474. © 1993 American Association of Cereal Chemists, Inc. kernels during decortication; 3) improved texture of the boiled product (i.e., cooked SORI had a firmer, less-sticky texture compared to nonparboiled cooked sorghum); and 4) increased shelf-stability. The major disadvantage of parboiling is the energy the process uses, because the SORI needs longer cooking time than the raw grain. However, the decorticated grain can be cracked into various sizes of grits to produce a wide array of products for use in different food preparations such as thick porridges (couscous and to), making it a more diversified, marketable product. Parboiling trials conducted in Mali, at the village level, have shown that well-accepted products can be obtained by soaking the sorghum overnight, boiling it, and drying it. This saves energy and time and makes the process more practical (unpublished data). The physicochemical changes in sorghum starch during parboiling that are responsible for the improved characteristics have not been determined. Therefore, the objective of this study was to evaluate the effects of parboiling on starch crystallinity, birefringence, pasting properties, and dispersion in hot water using sorghum cultivars with different endosperm texture and starch composition. MATERIALS AND METHODS Sample Preparation Three sorghum cultivars with different endosperm texture were used in this study. In sorghum, endosperm texture refers to the proportion of hard to soft endosperm in the kernel. Grain samples of Dorado (nonwaxy, intermediate endosperm texture), P721Q (nonwaxy, higher lysine, soft endosperm texture), and ATx630* R3338 (waxy, intermediate endosperm texture) (Table I) grown at Halfway, TX, in 1987, were parboiled using two methods. Method I. Soak-boil (SB). Washed, whole grain (one volume) was soaked overnight in tap water (three volumes) and boiled in the same solution for 10 min at a rate of 5°C/min in an 1 -L steam-jacketed cooker (model TDC/2-20, Groen Div., Dover Corp., Elk Grove Village, IL). Method II. Boil-soak-boil (BSB). Washed, whole grain was brought to boil as in method I, soaked overnight, and brought to boil again in the same solution. The grain samples from both methods were dried for 48 hr Vol. 70, No. 2, 1993 179