Effect of drying schemes using superheated-steam and hot-air as drying media on the quality of parboiled chalky rice compared to conventional parboiling

Various drying techniques were tested on two rice cultivars (Plai Ngahm Prachin Buri and Prachin Buri 2) that typically have severe chalkiness and milling quality problems. The main aims were: (1) to apply multi-stage intermittent drying technique using superheated-steam and hot-air as drying media to reduce the chalkiness and low head-rice yield problems of chalky rice and (2) to compare the quality of different rice products to that of single-stage drying and conventional parboiling process. The results showed that the head-rice yields improved from below the national standard (6.19% for Plai Ngahm Prachin Buri and 29.46% for Prachin Buri 2) to high milling quality levels (up to 61.38% and 68.22%, respectively) by applying hot water soaking together with multi-stage intermittent drying technique. The textural characteristics of the rice dried using multi-stage intermittent drying technique were similar to those for conventionally parboiled rice; however, the rice hardness was significantly lower by 33% and 20% for Plai Ngahm Prachin Buri and Prachin Buri 2, respectively. This study demonstrated that the hot water soaking combined with multi-stage intermittent drying method using superheated-steam drying followed by either hot-air drying at 50 degrees C or fluidized-bed drying at 80 degrees C resulted in parboiled rice products whose quality was comparable or superior to that from conventional parboiling and the commercial parboiled rice product.

Automated summary

The study demonstrates that hot water soaking combined with multi-stage intermittent drying technique can improve head-rice yields of chalky rice while maintaining rice texture, reducing rice hardness. The quality of parboiled rice products produced using this method is comparable or superior to that from conventional methods.