Journal of Food Engineering 59 (2003) 117–121 www.elsevier.com/locate/jfoodeng Effect of accelerated aging on the physicochemical and textural properties of brown and milled rice Hardeep Singh Gujral *, Vishal Kumar Department of Food Science and Technology, Guru Nanak Dev University, Amritsar 143005, Punjab, India Received 12 April 2002; accepted 28 October 2002 Abstract Accelerated aging of three different rice cultivars varying in length breadth ratio was carried out. Paddy was conditioned to 14%, 18% and 22% moisture content (wet basis) and then steamed for 30 min at atmospheric pressure. The paddy was dehusked to obtain brown rice and then polished to white rice. The physicochemical and textural properties of brown and milled rice were determined using an Instron Universal Testing Machine. Steaming at higher levels of moisture content increased elongation, width expansion, water uptake, cooking time and decreased solids loss. The hardness, cohesiveness and springiness of cooked rice increased whereas its adhesiveness decreased. Accelerated aged rice can be prepared by this short-time process to yield rice that has better and more desirable cooking properties. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Accelerated aging; Rice texture; Brown rice; Milled rice 1. Introduction The cooking and eating properties of rice change dramatically with its storage after harvest and this phenomenon is called aging of rice. It is a physicochemical process during which its properties like hydration, swelling, solubility, viscosity and pastiness change. Rice from freshly harvested paddy cooks to a pasty consistency, which is due to disintegration of fresh rice leading to dispersion of starch granules in the cooking water. Pastiness can be eliminated if the grain can be hardened so as to minimize the loss of solids in the gruel. The process of inducing the changes in rice in a short time to obtain cooking properties, which resemble that of naturally aged rice, is referred to as accelerated aging. Suitable wet heat treatment of freshly harvested paddy reduced the pastiness on cooking of rice (Desikachar & Subrahmanyan, 1957a, 1957b). Accelerated aging can also be accomplished by heating rough or milled rice to high temperatures (Bhattacharya, Desikachar, & Subrahmanyan, 1964; Iwasaki & Tani, 1967). * Corresponding author. Tel.: +91-183-258802x3429; fax: +91-183258820. E-mail address: hsgujral7@yahoo.co.in (H.S. Gujral). Parboiling has long been practiced as a method of improving the milling and cooking quality of rice. It is a lengthy process involving soaking, steaming and drying (Gujral, Singh, Sodhi, & Singh, 2002) and results in the complete gelatinization of starch and usually the fully parboiled rice is discolored. The accelerated aging treatment brings about only a partial gelatinization of the starch and the process is more economical than the traditional parboiling process. The objectives of the present investigation were to study the effect of paddy moisture content and steaming on the physicochemical and textural properties of brown and milled rice. 2. Materials and methods 2.1. Accelerated aging Three different varieties of freshly harvested paddy IR-8, Govinda and Sharbati were procured from a local rice sheller. The paddy samples were ground and moisture was determined using Halogen Moisture Analyzer (Model HG 53, Mettler, Toledo, Switzerland). The calculated amount of distilled water was added to weighed amount of paddy to bring its moisture content to 14% (wb). The paddy along with the calculated amount of water was shaken for 10 min in a PET jar and then kept 0260-8774/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0260-8774(02)00438-7 118 H.S. Gujral, V. Kumar / Journal of Food Engineering 59 (2003) 117–121 for 24 h for moisture equilibration in a refrigerator. Similarly paddy samples were conditioned to 18% and 22% moisture content (wb). The conditioned paddy (14%, 18% and 22% moisture content) was steamed for 30 min in an autoclave at atmospheric pressure and then allowed to dry to 9–11% moisture content in shade. 2.2. Milling The paddy samples, which were conditioned to 14% moisture content and then dehusked and polished, were referred to as control sample. The accelerated aged paddy after drying was again conditioned to 14% moisture content and dehusked in a McGill rice sheller (Rapsco, Brookshire, TX, USA) to obtain brown rice. The brown rice was polished in the McGill rice polisher to 8% degree of milling (Singh, Singh, Kaur, & Bakshi, 2000). Fig. 1. A typical texture profile analysis curve obtained from the Instron Universal Testing Machine. Solids Loss ð%Þ ¼ Increase in weight of dish  100 Weight of rice sample 2.3. Physicochemical properties 2.4. Texture profile analysis of cooked rice The length–breadth ratio was determined by dividing cumulative length of ten kernels by the cumulative breadth of ten kernels. The average of five replications was reported. Whole rice kernels (50, brown or milled) were taken in a test tube containing 20 ml of warm distilled water. The test tube was immersed in a boiling water bath and after 10 min of cooking a rice kernel was taken out after every 30 s and pressed between two microscope glass slides. The appearance of a chalky core indicated uncooked sample. The time (minutes) at which rice showed no chalky core was reported as cooking time. Elongation after cooking was determined using the following formula: Cooked rice (brown or milled) was subjected to texture profile analysis (TPA) using Instron Universal Testing Machine (Model 4464, Instron, Buckinghamshire, England). A single cooked rice kernel was placed on the platform of Instron Universal Testing Machine. A cylindrical plunger of 4 cm diameter attached to a 100 N load cell was used to compress the rice kernel to 50% of its original height at a crosshead speed of 10 mm/min twice in two cycles. The TPA curve (Fig. 1) was drawn from the force versus displacement data (Gujral, Kaur, Singh, & Sodhi, 2002). The values reported are the mean of ten replications. The following parameters were obtained. Elongation ð%Þ ¼ XL  Y L  100 YL where XL and YL are the cumulative length of 10 cooked and uncooked kernels respectively. Similarly width expansion was determined. The water uptake was determined using the following formula: Water uptake ð%Þ ¼ WC  WUC  100 WUC where WC and WUC is the weight of 50 cooked and uncooked kernels respectively. Solids loss: Whole rice (2 g, brown or milled) was taken in a test tube containing 20 ml of distilled water. The rice was cooked for optimum time in a hot water bath. The gruel was transferred into a dry and preweighed aluminium dish and kept at 100 °C for 24 h to remove moisture. The aluminium dish was cooled in a dessicator and weighed to determine the increase in weight of the dish. The average of three replications was reported. Cohesiveness ¼ A2 =A1 where A1 is the area under first compression and A2 is the area under second compression. Adhesiveness ¼ A3 ðN mmÞ where A3 is area under curve due to adhesion. Springiness ¼ Displacement ðmmÞ under the curve A2 Hardness ¼ Peak force of first compression ðNÞ 3. Results and discussion 3.1. Physicochemical properties Dehusked brown rice from IR-8, Govinda and Sharbati had length–breadth ratio of 2.76, 3.49 and 4.25 respectively. After polishing i.e. removal of bran IR-8, Govinda and Sharbati had length to breadth ratios of 2.9, 3.57 and 4.35 respectively. The increase in length to 119 H.S. Gujral, V. Kumar / Journal of Food Engineering 59 (2003) 117–121 fissures in the rice due to starch gelatinization. Hardness increased with increasing moisture content due to increased starch gelatinization. Brown rice was harder than the milled rice because of the presence of the fibrous bran layer around the kernel. Cooking time: All the three cultivars showed an increase in cooking time with increasing moisture levels of conditioning. Brown rice showed a longer cooking time breadth ratio is due to a lesser decrease in length of rice kernel as compared to breadth upon polishing. Brown rice from IR-8, Govinda and Sharbati had a thousand kernel weight of 24.02, 18.25 and 14.31 g which was lowered to 22.09, 16.79 and 13.16 g upon polishing. Hardness of raw rice: Accelerated aging lead to an increase in the hardness of raw rice (Tables 1–3). This may be attributed to the filling up of air spaces and Table 1 Effect of moisture content on the physicochemical and textural properties of IR-8 Control Hardness (N) raw Cooking time (min) Elongation (%) Width expansion (%) Water uptake (%) Solids loss (%) Cohesiveness Springiness (mm) Hardness (N) cooked Adhesiveness (N mm) 14% 18% 22% Brown Milled Brown Milled Brown Milled Brown Milled 82.92a 35.0a 32.3a 47.82a 84.69a 6.8a 0.133a 0.383a 6.995a 0.0232a 61.55a 13.0a 38.7a 50.61a 108.57a 10.8a 0.206a 0.483a 5.38a 0.0551a 111.99b 42.0b 35.3b 48.0a 108.69b 2.4b 0.188b 0.450b 7.435b 0.0092b 105.84b 18.0b 45.9b 52.38b 126.06b 3.5b 0.229b 0.491a 5.504a 0.0151b 167.29c 47.0c 35.36b 50.8b 125.44c 1.4c 0.206c 0.540c 8.474c 0.0005c 158.69c 23.0c 49.18c 57.14c 135.63c 2.8c 0.248c 0.899b 5.750b 0.0024c 317.03d 51.0d 35.4b 51.8b 136.75d 1.1c 0.250d 1.033d 10.939d 0.0001d 257.73d 25.0c 51.61c 61.9d 140.21d 2.4c 0.273d 1.140c 6.074c 0.0007d Milled Brown Superscripts with the same letters are not significantly different (P > 0:05). Table 2 Effect of moisture content on the physicochemical and textural properties of Govinda Control Brown Hardness (N) raw Cooking time (min) Elongation (%) Width expansion (%) Water uptake (%) Solids loss (%) Cohesiveness Springiness (mm) Hardness (N) cooked Adhesiveness (N mm) a 72.00 34.0a 10.14a 50.0a 88.49a 3.9a 0.139a 0.249a 1.958a 0.0462a 14% Milled a 42.084 12.0a 26.13a 50.45a 90.58a 6.7a 0.155a 0.253a 1.445a 0.2403a 18% Brown b 124.78 44.0b 16.17b 55.0b 93.42b 2.8b 0.144a 0.261a 2.353b 0.0162b Milled b 96.662 21.0b 37.5b 55.56b 144.78b 2.8b 0.175b 0.424b 2.425b 0.0126b 22% Brown c 217.29 46.0b 17.6b 57.5c 110.95c 2.0c 0.207b 0.433b 2.860c 0.0008c c d 125.04 23.0b 38.95b 58.34c 151.93c 2.6b 0.248c 0.666c 2.448b 0.0046c 233.67 53.0c 19.4c 60.0d 127.39d 0.7d 0.301c 0.816c 3.101d 0.0004d Milled 178.73d 24.0b 44.0c 61.11d 153.12c 1.0c 0.371d 0.911d 2.540c 0.0042c Superscripts with the same letters are not significantly different (P > 0:05). Table 3 Effect of moisture content on the physicochemical and textural properties of Sharbati Control Hardness (N) raw Cooking time (min) Elongation (%) Width expansion (%) Water uptake (%) Solids loss (%) Cohesiveness Springiness (mm) Hardness (N) cooked Adhesiveness (N mm) 14% 18% 22% Brown Milled Brown Milled Brown Milled Brown Milled 93.78a 35.0a 8.82a 50.0a 80.99a 4.5a 0.108a 0.199a 1.969a 0.0243a 64.27a 13.0a 32.3a 113.34a 131.0a 11.0a 0.177a 0.293a 1.568a 0.0356a 120.17b 42.0b 11.76b 54.0b 85.88b 2.4b 0.111a 0.257b 1.99a 0.0056b 108.26b 18.0b 38.46b 53.0b 163.43b 3.8b 0.220b 0.368b 1.61b 0.0082b 217.39c 47.0c 14.7c 70.0c 115.23c 1.9c 0.115a 0.332c 2.75b 0.0018c 184.39c 23.0c 43.07c 73.4c 179.39c 2.3c 0.226b 0.586c 1.657b 0.0029c 312.78d 51.0d 16.17d 75.0d 118.02d 1.5c 0.172b 0.333c 3.345c 0.0004d 291.78d 25.0d 46.15d 86.67d 184.95d 1.8c 0.242c 0.691d 2.301c 0.0021c Superscripts with the same letters are not significantly different (P > 0:05). 120 H.S. Gujral, V. Kumar / Journal of Food Engineering 59 (2003) 117–121 as compared to the milled rice because of the presence of outer branny layers, which leads to slower moisture diffusion and starch gelatinization during cooking. The cooking time increased by 92.3%, 100% and 92.3% in milled IR-8, Govinda and Sharbati aged at 22% moisture content. Pushpamma and Reddy (1979) reported that the optimum cooking time for milled rice was 4–6 min longer after six months of storage than it was at harvest. Elongation and width expansion: The aged rice showed higher elongation and width expansion upon cooking than rice from freshly harvested paddy. As the moisture content before steaming was increased, the elongation and width expansion of rice increased. Both elongation and width expansion was greater in milled rice as compared to brown rice. The greater increase in width expansion of milled rice as compared to brown rice may be attributed to presence of outer branny layers, which limit the expansion of brown rice. The elongating property of basmati type riceÕs also improves during storage and increases in volume expansion and water absorption during cooking (Desikachar & Subrahmanyan, 1959; Pushpamma & Reddy, 1979). Water uptake: Water uptake of rice increased with increasing moisture content of conditioning before steaming. The water uptake increased by 29.14%, 69.04% and 41.18% in milled IR-8, Govinda and Sharbati aged at 22% moisture content. Increases in volume expansion and water absorption of aged rice had also been reported by Barber (1972) and Indhudhara Swamy, Sowbhagya, and Bhattacharya (1978). Expansion and water uptake are desirable economically for the food service industry as they lead to a fuller plate for the same amount of rice. Solids loss: There was substantial decrease in solids loss both in milled and brown rice after accelerated aging. The solids loss decreased with the increasing moisture contents of conditioning before steaming. Aged rice grains were more resistant to disintegration during grain swelling leading to the reduced solids loss. Pastiness has been shown to be due to disintegration of fresh rice leading to dispersion of the starch granules in the cooking water and the formation of a viscous sticky gruel. Suitable wet heat treatment of the paddy or an incipient parboiling of rice prior to cooking reduced the pastiness, on cooking, of rice (Desikachar & Subrahmanyan, 1959). from IR-8 (control) had a cohesiveness of 0.206, which increased to 0.229, 0.248 and 0.273 for the samples conditioned and steamed at 14%, 18% and 22% moisture content respectively. Similarly, brown rice from Govinda control and aged samples had cohesiveness values of 0.139, 0.144, 0.207 and 0.301 respectively and their corresponding milled rice had cohesiveness values of 0.155, 0.175, 0.248 and 0.371 respectively. Brown rice from Sharbati (control) and samples conditioned and steamed at 14%, 18% and 22% moisture content had cohesiveness values of 0.1088, 0.111, 0.115 and 0.172 respectively and their corresponding milled rice had cohesiveness values of 0.177, 0.220, 0.226 and 0.242 respectively. Cohesiveness is the extent to which a sample tends to retain its shape (texture) after compression. The above discussion reveals that the cooked brown rice has lower cohesiveness compared to cooked milled rice. The lower cohesiveness of brown rice may be attributed to the presence of outer fibrous branny layers, the structure collapses after first compression and prevents the rice from retaining its shape after compression. The increased gelatinization of the starch may be responsible in increasing the cohesiveness of the cooked brown and milled rice. The increase in moisture content of conditioning increased the springiness of both brown and milled rice. Milled rice has more springiness compared to brown rice. The springiness increased by 136.02%, 260.0% and 135.83% in milled IR-8, Govinda and Sharbati aged at 22% moisture content. Brown rice from all the three rice cultivars showed more hardness as compared to milled rice both from control and aged samples. As described, earlier, increased moisture levels of conditioning were the cause of increased raw rice hardness due to more starch gelatinization, which ultimately led to increased cooked rice hardness. The hardness increased by 12.89%, 75.77% and 46.74% in milled IR-8, Govinda and Sharbati aged at 22% moisture content. Perez and Juliano (1982) reported increases in hardness of cooked aged rice. Increasing the moisture content of conditioning decreased the adhesiveness of both brown and milled rice. The adhesiveness decreased by 98.72%, 98.25% and 94.1% in milled IR-8, Govinda and Sharbati aged at 22% moisture content. Cooked aged rice was harder and less sticky than cooked freshly harvested rice, as measured by texturometer (Okabe, 1979). Short-time steaming of rough rice was also effective in reducing the stickiness of cooked, treated and milled rice (Fellers & Deissinger, 1983). 3.2. Texture profile analysis of the cooked rice As the moisture content of conditioning was increased the cohesiveness of both brown and milled rice increased. Brown rice from IR-8 (control) had a cohesiveness of 0.133 which increased to 0.188, 0.206 and 0.250 for the samples conditioned and steamed at 14%, 18% and 22% moisture content respectively. Milled rice 4. Conclusion The physicochemical properties of rice like water absorption, swelling capacity and cooking time increased markedly after accelerated aging whereas solids loss of cooked rice decreased. The textural properties of H.S. Gujral, V. Kumar / Journal of Food Engineering 59 (2003) 117–121 cooked rice like cohesiveness, springiness and hardness increased whereas adhesiveness of cooked rice decreased significantly. The extent to which these changes occur seem to depend upon the moisture content of the paddy before steaming. At higher moisture levels, the severity of the treatment increases due to increased starch gelatinization. In natural aging these changes take a long time to occur which is not economically feasible for the industry. The extent to which these changes are desired may be controlled by changing the moisture content of paddy before accelerated aging or by the duration of the accelerated aging treatment. References Barber, S. (1972). Milled rice and changes during aging. In D. F. Houston (Ed.), Rice chemistry and technology (first ed., pp. 215–236). St. Paul, MN: American Association of Cereal Chemists. Bhattacharya, K. R., Desikachar, H. S. R., & Subrahmanyan, V. (1964). Curing of freshly harvested rice by heat treatment. Indian Journal of Technology, 2, 378–380. Desikachar, H. S. R., & Subrahmanyan, V. (1957a). The curing of freshly harvested paddy: Part I––Principles of curing. Journal of Scientific and Industrial Research, 16A, 365–367. Desikachar, H. S. R., & Subrahmanyan, V. (1957b). The curing of freshly harvested paddy: Part II––Applications. Journal of Scientific and Industrial Research, 16A, 368–370. 121 Desikachar, H. S. R., & Subrahmanyan, V. (1959). Expansion of new and old rice during cooking. Cereal Chemistry, 36, 385–391. Fellers, D. A., & Deissinger, A. E. (1983). Preliminary study on the effect of steam treatment of paddy on milling properties and rice stickiness. Journal of Cereal Science, 1, 147–157. Gujral, H. S., Singh, J., Sodhi, N. S., & Singh, N. (2002). Effect of milling variables on the degree of milling of unparboiled and parboiled rice. International Journal of Food Properties, 5(1), 193– 204. Gujral, H. S., Kaur, A., Singh, N., & Sodhi, N. S. (2002). Effect of liquid whole egg, fat and textured soy protein on the textural and cooking properties of raw and baked patties from goat meat. Journal of Food Engineering, 53, 377–385. Indhudhara Swamy, Y. M., Sowbhagya, C. M., & Bhattacharya, K. R. (1978). Changes in physicochemical properties of rice with aging. Journal of Science of Food and Agriculture, 29, 627–639. Iwasaki, T., & Tani, T. (1967). Effect of heating on brown rice composition and quality. Cereal Chemistry, 44, 204–210. Okabe, M. (1979). Texture measurements of cooked rice and its relationship to the eating quality. Journal of Texture Studies, 10, 131–152. Perez, C. M., & Juliano, B. O. (1982). Physicochemical changes of the rice grain in storage: A brief review. In Documentation of the seminar paddy deterioration in the humid tropics, Baguio City, Philippines, 1981 (pp. 180–190). Eschborn, Germany: German Agency for Technical Cooperation. Pushpamma, P., & Reddy, M. U. (1979). Physicochemical changes in rice and jowar stored in different agroclimatic regions of Andhra Pradesh. Bulletin of Grain Technology, 17, 97–108. Singh, N., Singh, H., Kaur, K., & Bakshi, M. S. (2000). Determining the effect of degree of polish and ash distribution in brown rice using conductivity. Food Chemistry, 69, 147–151.