Annals of Sri Lanka Department of Agriculture. 2007.9:127-131.
EFFECT OF DIFFERENT HARVESTING INTERVALS ON THE QUALITY PARAMETERS OF RICE GRAIN B.P. RATNAYAKE, R.F. HAFEEL, D.K. PADMALATHA and E.M.R.D. EDIRISINGHE Rice Research and Development Institute, Batalagoda, Ibbagamuwa
ABSTRACT Appropriate time of harvesting is a critical factor which decides physical and other quality attributes of a harvested product. A study was carried out to investigate the correct harvesting time that retains the desirable rice grain quality parameters. Popular rice varieties Bg 360, Bg 357 and Bg 352 were selected with three replicates. Initially a study was conducted in 2003/04 maha starting to harvest the crop at the recommended harvesting time when 85% of paddy grain becomes golden brown in colour (physiological maturity) in the field. After 4, 7, 10 and 14 days intervals, samples were collected for grain quality testing. Having the data of the said season, same trial was established in 2004 yala. However initial harvest was done 4 days before physiological maturity. At physiological maturity, as well as 4 and 7 days after, the next samples were harvested. Samples were analyzed for milling quality, whiteness and cooking quality attributes. Delaying of harvesting lowered the accepted values of milling qualities. Further delaying, more than 10 days diminished the tenderness, and cooking quality. Bg 352 performed well compared to other two varieties in relation to some quality attributes. KEYWARDS: Grain quality characteristics, Harvesting time, Head grain, Rice.
INTRODUCTION Harvesting is one of the critical operations in rice production. Correct time of harvesting is very important for all agricultural commodities as the time of harvesting affects the yield as well as the quality of the product. Optimum stage of harvest is known to be the one when no more dry matter accumulation is possible in the grain. Harvesting paddy at optimum maturity is important for obtaining high milling recovery and good cooking quality. Studies have shown that for a better out put of head rice yield, harvesting moisture should be between 20-23% (Ali et al., 1993). Bal and Ojha (1975) recommended that rice should be harvested in the moisture range of 20 to 24% to obtain the maximum percent of head rice. Presently, rice is harvested based on the farmer experience as well as convenience. Farmers often harvest their crops at the incorrect stage of maturity which leads to qualitative and quantitative losses. Early harvesting of paddy leads to immature, partly filled or unfilled grain while late harvesting results in sun cracks which finally lowers the milling quality (Palipane, 2000). According to Finassi et al. (2002), some new cultivars had reached low grain moisture in the field and dried faster than some traditional varieties.
128 RATNAYAKE et al.
Economically, it is important to adopt measures to keep the potential whole kernel yield of rice at the highest level. Many studies were done to evaluate best moisture content at harvesting for better milling recovery or bulk density (Gupta et al., 2002 ; Fan et al., 1998; Ali et al., 1993). Several researchers have studied the relationship between average moisture content of rice at harvest and the subsequent head rice % and total milling yields when different drying procedures are used. These studies have shown that percent milled rice and percent head rice increased as the moisture content decreased at the early maturity stages. Present research was conducted to ascertain the best harvest time for desirable milling yield and other quality parameters among popular local varieties. MATERIALS AND METHODS A field trial was established using three popular rice varieties (Bg 360, Bg 357 and Bg 352) and replicated thrice during 2003/04 maha and 2004 yala. Samples were collected at different harvesting intervals. When visually 85% of golden brown paddy was observed in the field, which was considered as the recommended physiological maturity, the paddy was harvested and sampled (T). Then the other samples (T+4, T+7, T+10 and T+14) were harvested at 4, 7, 10 and 14 days after the 1 st harvest respectively. After studying the effect of above harvesting intervals, 2004 yala harvesting intervals were altered. First harvest (T-4) of 2004 yala was obtained calculating and predicting that in 4-5 days the crop might reach the physiological maturity which was the first harvest of 2003/04 maha. Since, the said stage was received after 4 days of first harvest the other harvests were done in 4 and 7 days after the second harvest respectively. They were sampled as above T+4 and T+7. In yala there were only 4 treatments and 5 in maha. Collected samples were shade dried until the moisture content drops to 13%. Each sample was tested for grain quality characteristics, 3 months after harvesting. Brown Rice percentage (BR%), Head Grain percentage (HG%), whiteness, grain elongation ratio and tenderness were evaluated. Samples were de-hulled and milled in a Mc-Gill sample mill for 1 minute. HG% of each variety was calculated according to Cruz and Kush (2000). To determine the whiteness of rice samples KETT digital whiteness meter was used. The whiteness meter was calibrated using the standard plate which has a value of 83.4. Then the whiteness of polished rice sample was measured after placing it in the whiteness meter. Standard plate was used in between each sample measurement. Grain elongation ratio was analyzed following Cruz and Kush (2000). Cooked rice tendency was measured by a trained sensory panel of six members.
HARVESTING TIME AFFECTS RICE QUALITY 129
RESULTS AND DISCUSSION
Brown Rice%
The percentages of Brown rice and head grain with treatments are shown in Figures 01 and 02 respectively. Even the BR% was maximum at 85% of maturity, during maha, it was higher at four days before the same stage during yala (Fig. 1). After the said period, the harvested rice has shown a decreasing pattern in BR%. Similarly HG% also showed a decreasing trend after 85% golden brown maturity (Fig. 2). But HG% at first harvest during yala was less than the said harvest, differing to BR% of the same season. Ali et al. (1993) observed that head rice recovery was low at both early and late maturity. A similar study done by Gupta et al. (2002), showed that white head rice% decreased with decreasing harvest moisture content. Usually after 85% maturity, moisture content decreases during a sunny period. Before the physiological maturity at 85%, the moisture content is much higher than the said stage. 81 80 79 78 77 76 75 -4
85%
4 7 Day of harvest maha
10
14
yala
Figure 1. Brown rice content at each harvest.
Head grain%
70 65 60 55 50 -4
85%
4
7
10
14
Day of harvest maha
yala
Figure 2. Head grain content of rice at each harvest.
Other quality parameters such as whiteness value, grain elongation ratio and tenderness did not vary significantly at different harvests during yala season. But there was a slight variation between treatments in whiteness value and tenderness during maha (Table 1). Ali et al. (1993) reported that elongation ratio increased with increase in days to harvesting
130 RATNAYAKE et al.
after 50% flowering. Late harvesting, more than ten days from said period decreases tenderness significantly. Harvesting around 85% of maturity (4 or 7 days) does not affect tenderness. Table 1. Rice grain quality parameters at each harvest during maha and yala. Time of harvesting Whiteness Elongation ratio Tenderness maha* yala* maha* yala* maha* yala*
Brown Rice%
T-4 42.3a 1.69a 4.3a T 41.0b 42.4a 1.72a 1.64a 4.8a 4.2a T+4 41.5b 43.6a 1.70a 1.63a 4.7a 3.7a T+7 42.0b 45.2a 1.66a 1.67a 5.0a 3.7a T+10 42.5a 1.73a 4.3b T+14 42.7a 1.79a 4.0c *Means with the same letters along the column are not significantly different. 81 80 79 78 77 76 75 Bg 360
Bg 357
Bg 352
Varieties maha
yala
Figure 3. Brown rice content of rice varieties during maha and yala.
1.7 ratio
Grain elongation
1.8
1.6 1.5 Bg 360
Bg 357
Bg 352
Varieties
m aha
yala
Figure 4. Grain elongation ratio of rice varieties during maha and yala.
During both seasons, there was a significant interaction within treatment and three rice varieties. Bg 352 obtained the highest brown rice percentages. But the values of other two varieties varied (Fig. 3). Bg 360 had the best tenderness during both seasons, differing significantly from other two varieties (Table 2). Bg 352 showed the best elongation ratio followed by Bg 360 and Bg 357 having values of 1.8, 1.7 and 1.6 respectively (Fig. 4). Other parameters such as head grain percentage and whiteness did not show any pattern related to their values.
HARVESTING TIME AFFECTS RICE QUALITY 131 Table 2. Grain quality parameters of three varieties during maha and yala. Varieties Head grain% Whiteness Tenderness maha yala maha yala maha yala Bg 360 60.8b 68.1a 38.4c 35.1b 5.6a 4.6a Bg 357 57.4c 59.9c 46.1a 47.1a 5.0b 3.7b Bg 352 67.1a 64.2b 41.7b 47.8a 3.0c 3.7b Means with the same letters along the column are not significantly different.
CONCLUSIONS Timely harvesting, at the correctly observed physiological maturity enhances some rice milling quality parameters. Delaying the harvest by 10 days after the physiological maturity affects most of the quality parameters. Until the seventh day of physiological maturity, whiteness and tenderness remained the same. Bg 352 was scored as the best variety on brown rice percentage and tenderness. REFERENCES Ali, A., M.A. Kasim, A. Majid, G. Hassen, L. Ali and S.S. Ali. 1993. Grain quality of rice harvested at different maturities. International Rice Research News. 18 (2): 11. Bal, S. and T.P. Ojha. 1975. Determination of biological maturity and effect of harvesting and drying conditions of milling quality on paddy. J. Agric. Eng. Res. 20(4); 353-362. Cruz, N.D. and G.S. Kush. 2000. Rice grain quality evaluation procedures. In: Eds. R.K. Singh and G. S. Khush. Aromatic Rices. Oxford and I.B.H publishing Co. Pvt. Ltd., New Delhi. 15-27 pp. Fan, J., T.J. Siebenmorgen, T.R. Garman and D. R. Gardisser. 1998. Bulk density of long and medium grain rice varieties as affected by harvest conditions and moisture contents. Cereal Chemistry. 75(2)254-258 Finassi, A, P. Noris and F. Vidotto. 2002. The effect of weather on whole-kernel milling yield of selected cultivars of Oryza sativa L. grown in the po valley of Italy. J.E. Hill and B. Hardy. 471-479pp. Gupta, R., M.C. Kahyap, M.K. Garg and Yadvika. 2002. Effect of harvesting moisture content on development of fissure and gead rice recovery in Basmati paddy. Journal of Agriculture Engineering. 39(1):21-26. Palipana, K.B. 2000. Milling and quality improvement in rice. Rice Congress 2000. Department of Agriculture, Peradeniya, Sri Lanka. 142-153pp.