Studies on the soak water characteristics in various paddy parboiling methods

Parboiling of paddy is practised in rice mills, wherein paddy is soaked for varying periods, depending upon the parboiling method. Among the various methods of parboiling in vogue, soak water of the cold-soaking method followed in conventional rice mills showed a relatively higher population of total aerobic bacteria, staphylococci, lactic acid bacteria and yeasts than the other methods. The biochemical oxygen demand (BOD) of this soak water was also high. Although the soak water from the hot-soaking method adopted in modern rice mills exhibited a smaller microbial population, it showed higher concentrations of sugars, amino nitrogen and total phenolic compounds, and hence a higher chemical oxygen demand (COD). The continuous discharge of soak water around rice mills is of environmental concern.