Quality characteristics of flood affected paddy (Oryza sativa L.) after milling

Introduction

For about half of the world's population, rice is one of the most essential staple foods, and it has an impact on the economics and way of life of several billion people. According to Suzanne, almost 154 million hectares of rice were harvested globally in 2010, with 137 million hectares (88.0%) of that total occurring in Asia. Just 48 million hectares, or 31.0% of the world's total rice harvest, were harvested in Southeast Asia. Since rice is a wet-season crop, it needs a lot of water. As a result, it is anticipated that the crop will be able to tolerate heavy rainfall and harsh watering circumstances with little impact on the rice quality. Yet, India is seeing an unusual occurrence of torrential rainfall and flooding at a time when the paddy was ready for harvesting because of climate change. Fields become inundated after five days of nonstop rain. This results in the rice crop being submerged and staying that way for four days. Every year, floods affect more than 20% of paddy fields of India (IRRI 2010) [7] . Degradative alterations, such as low head rice yield (HRY), poor physico-chemical, nutritional, sensory, and organoleptic quality changes, occur in the paddy that has been soaked by floods. The two most crucial factors affected during milling are kernel whiteness and head rice yield (HRY). Head rice is defined as rice kernels that retain at least 3/4 of their original length following a full milling operation (USDA, 1983) [16] . The quality of milled rice is determined by these two factors, which also affect its retail price. According to Conway et al. (1991) [6] , there is a high correlation between the size, shape, cleanliness, and whiteness of the rice and its transaction price. When compared to broken kernels, the price of head rice is nearly double or triple. Therefore, the rice milling industry's top goal is to maximize the percentage of head rice with the necessary level of kernel whiteness (Yadav and Jindal, 2008) [19] . When rice kernels have already been compromised by stress cracks (fissures) brought on by fast moisture adsorption, significant breaking happens during milling. Reduced head rice yields are the result of these cracked kernels typically breaking during subsequent hulling and milling processes. The produce of such fields is sold at low price causing small and marginal farmers to the economic loss. Moreover, rice millers prefer varieties with high milling out-turn (Merca and Juliano, 1981) [10] .

An estimated 4.0 million tons of paddy are lost annually as a result of flooding in Bangladesh and India alone, which is sufficient to feed 30 million people. The physical appearance of the grains are clearly impacted by agricultural floods. This caused us to conduct a thorough investigation of milling and cooking quality of flood affected paddy.

Materials and Methods

Paddy was procured from Raavulapaalem in West Godavari district of Andhra Pradesh which is one of the flood affected areas of India. The samples of the same variety were collected from both normal paddy and flood affected paddy. In case of flood affected paddy, the samples were collected from areas which were submerged under water for almost three days at fully matured stage. These samples were studied for its milling quality characteristics. Later, the samples were taken to Post Graduate and Research Centre (PGRC), Professor Jayashankar Telangana State Agricultural University, Rajendranagar, Hyderabad to carry out the study. Milling (Rice sheller-Indosaw) was carried out for the collected samples of both normal and flood affected paddy after bringing down the moisture content to 14%. For analyzing the quality characteristics of paddy such as husked rice percentage, head rice percentage, broken rice percentage and milling recovery percentage, milling was done which is an operation that transforms the materials by applying mechanical forces (Sahay and Singh 2005) [11] . The normal and flood affected paddy samples before and after milling are depicted in fig 1 and2.

Results and Discussion

The quality characteristics of normal paddy and flood affected paddy after milling are given in table 1 and fig 3 . Statistically significant difference at p<0.05 was observed between normal paddy as compared to that of flood affected paddy with regard to quality characteristics after milling. Husked rice and head rice exhibited higher percentage values for normal paddy (78.37% and 93.70% respectively). Lower percentage values were observed with flood affected paddy (75.47% and 84.88% respectively). In flood-affected paddy, the head rice percentage decreased the most, whereas in normal paddy, it decreased the least. Interestingly, paddy impacted by flooding had the highest percentage of small kernel fragments in whole milled rice but the lowest drop in head rice recovery. The development of fissures (stress cracks) in the rice kernel as a result of internal pressures brought on by drying and uneven moisture content, as well as changes in relative humidity during the rice kernel's ripening process, may be the source of the losses in head rice recovery. According to Kunze and Hall (1965) [8] , significant cracks that span the grain cross-section form when humidity levels fluctuate during the milling process. Flood-affected paddy in the current study displayed the emergence of huge fissures across the grain cross-section (Fig. 1), but it also displayed the existence of tiny fissures close to the grain tip (Fig. 2). This most likely explains why the samples under study showed various milling characteristics. According to Kunze and Prasad (1978) [9] , there are variations in the likelihood of cracks developing due to the grains' extreme fragmentation during milling and polishing which leads to decline in head rice recoveries. In contrast, the percentage of broken rice was higher for flood affected paddy (15.10%) as compared to normal paddy (6.28%). This might be due to prolonged period of submergence of paddy under floods which damaged the internal structure of grains and caused breakage of kernels. When stress cracks (fissures) brought on by rapid moisture adsorption has already damaged rice kernels, significant breaking occurs during milling. According to Banaszek and Siebenmorgen (1990) [2] , these cracked kernels typically shatter during hulling and milling processes, lowering head rice yields (HRYs). [1,18,17] . Different rice types are known to react differentially to moistureinduced kernel fissuring (Chen and Kunze, 1983; Bautista and Bekki, 1997) [5,3] . Therefore, it would be beneficial to comprehend how water adsorption affects the incidence of kernel fissures in current, widely produced cultivars in order to create pre-and post-harvest recommendations for maintaining milling quality. Brian and Terry (1999) [4] also demostrated that the environmental factors lead to shattering of rice kernels. It has been demonstrated that when milled rice kernels are subjected to specific environmental conditions, they quickly crack and eventually shatter. Depending on the temperature and relative humidity (RH) of the surrounding air, as well as the moisture content (MC) of the kernels, milled kernels quickly absorb or release moisture from their surroundings. The starchy endosperm of the milled kernel experiences compressive or tensile pressures as a result of this moisture movement into or out of the kernel. These forces can lead to kernel fissures during post-milling procedures, depending on the moisture gradient between the kernel and the equilibrium MC of the surrounding air.

References

1. Adair CR, Bollich CN, Bowman DH, Jodon TH, Webb BD, Atkins JG. Rice breeding and testing methods in the United States. In: Rice in the United States: Varieties and Production. US Department of Agriculture Handbook No. 289 (revised). 1973. p. 22-27.
2. Banaszek MM, Siebenmorgen TJ. Head rice yield reduction rates caused by moisture adsorption. Am Soc Agric Eng. 1990;33(4):1263-1269.
3. Bautista RC, Bekki E. Grain fissures in rough rice drying: Differences in fissuring behavior of selected Japonica and Indica varieties. J Jpn Soc Agric Mach. 1997;50(4):87-108.
4. Lloyd BJ, Siebenmorgen TJ. Environmental conditions causing milled rice kernel breakage in medium-grain varieties. Cereal Chem. 1999;76(3):426-427.
5. Chen YL, Kunze OR. Effects of environmental changes on rice yield and particle size of broken kernels. Cereal Chem. 1983;60(3):238-241.
6. Conway JA, Sidik M, Halid H. Quality/value relationships in milled rice stored in conventional warehouses in Indonesia. In: Proceedings of the Fourteenth ASEAN Seminar on Grain Postharvest Technology; 1991 Nov 5-8;
7. International Rice Research Institute (IRRI). Scuba rice: Breeding flood tolerance into Asia's local mega rice varieties. Los Baños: IRRI and UK Aid; 2010. p. 1-6.
8. Kunze OR, Hall CW. Relative humidity changes that cause brown rice to crack. Trans ASAE. 1965;8(3):396-399,405.
9. Kunze OR, Prasad S. Grain fissuring potentials in harvesting and drying rice. Trans ASAE. 1978;21(2):361366.
10. Merca FE, Juliano BO. Physicochemical properties of starch of intermediate-amylose rice. Starch/Stärke. 1981;33:253-260.
11. Sahay KM, Singh KK. Unit operations of agricultural processing. 2nd rev. & enlarged ed. New Delhi: Vikas Publishing House Pvt Ltd; 2005. p. 273.
12. Siebenmorgen TJ, Jindal VK. Effects of moisture adsorption on the head rice yields of long-grain rough rice. Trans ASAE. 1986;29(6):1767-1771.
13. Siebenmorgen TJ, Counce PA, Lu R, Kocher MF. Correlation of head rice yield with individual kernel moisture content distribution at harvest. Trans ASAE. 1992;35:1879-1884.
14. Stahel G. Breaking of rice in milling in relation to the condition of the paddy. Trop Agric. 1935;12(10):255-260.
15. Redfern SK, Azzu N, Binamira JS. Rice in Southeast Asia: Facing risks and vulnerabilities to respond to climate change. Plant Production and Protection Division, FAO; 2013. p. 295-314.
16. United States Department of Agriculture (USDA). Standards for rice. Federal Grain Inspection Service. Washington (DC): USDA; 1983.
17. Wasserman T, Calderwood DL. Rough rice drying. In: American Association of Cereal Chemists. Cereal Crops. 1972. p. 166-187.
18. Witte GC. Conventional rice milling in the United States. In: Houston DF, editor. Rice Chemistry and Technology. St. Paul (MN): American Association of Cereal Chemists; 1972. p. 188-200.
19. Yadav BK, Jindal VK. Changes in head rice yield and whiteness during milling of rough rice (Oryza sativa L.). J Food Eng. 2008;86:113-121.