Abstract:
Damaged and cracked grains are abundant in combine harvesting method due to
subsequent harvesting and threshing operations at high speeds. Cracks on grains
adsorb moisture from the storage environment and impose negative effects on head
rice yield due to high moisture contents (over 18%). Milling of same paddy with
favourable moisture contents after 2-5 months shows high broken rice percentage.
Thermal pre-treatments, prior to milling, is effective in minimizing the broken rice
percentages by maintaining the favourable moisture contents in mechanically
harvested paddy. It is expected to find out the best thermal treatment condition for
mechanically harvested paddy to reduce the broken rice percentage. Paddy samples
harvested mechanically using a combine harvester were subjected to thermal pre treatments at 50 °C, 60 °C and 70 °C using a hot air oven. Thermal exposure time
durations of paddy samples were one, two and three hours. The effects of the
mechanical drying treatments were evaluated on percentage of brown rice,
percentage of polished rice, percentage of broken rice, hardness of brown rice and
moisture content. Mechanically harvested paddy samples, subjected to direct milling,
were maintained control of the experiment. Control rice samples reported highest
significant broken rice percentage of 35.55 and lowest significant hardness value of
2.91. The control samples reported brown rice percentage of 78.92 and polished rice
percentage of 90.49. Subjecting mechanically harvested paddy to 60 °C for two hours
has shown lowest significant broken rice percentage of 21.9 and highest significant
hardness (N) of 5.02±0.01. The same treatment reported the brown rice percentage
of 74.28 and polished rice percentage of 90.43. The grain moisture content of the
samples after the treatment was 12.01%. The results revealed that the broken rice
percentage had been greatly reduced and hardness of milled rice is increased with the
introduction of mechanical drying at 60 °C for two hours.
