Effect of phosphorus fertilizer levels and parboiling of paddy on phytic acid and mineral content of three rice (Oryza sativa L.) cultivars

To study the effect of phosphorus levels (0, 40, 80 and 120 kg.ha-1) and parboiling of paddy on phytic acid and mineral content of three rice varieties, a field experiment was carried out as factorial arrangements in randomized complete block design with three replications at Rice Research Institute, Rasht, Iran, in 2012. Results showed that soil phosphorus deficiency decreased grain yield. The highest grain yield was observed at phosphorus levels of 80 and 120 kg.ha-1 and the least yield was obtained in phosphorus levels of 0 and 40 kg.ha-1. Results also showed that by increasing the soils phosphorus levels, phytic acid content increased but decreased Fe and Zn contents and availability. The highest phytic acid content was observed in Khazar cultivar and phosphorus level 120 kg.ha-1 (16.82 mg.g-1). A reduction in the phytic acid content was observed after parboiling, showing over 80% reduction in 3 rice cultivars. Least phytic acid content was observed in Gohar cultivar and 0 kg.ha-1 phosphorous (1.67 mg.g-1). Parboiling also increased mineral contents such as phosphorus, Fe and Zn in parboiled milled rice. During parboiling process phytase enzyme activity increased and the highest phytase activity was observed in 80 kg.ha-1 phosphorus in all rice cultivars. Results revealed that increased phosphorus content enhanced phytic acid content and decreases phytase activity and mineral nutrition content. However, parboiling reduced phytic acid content. Reduction of phytic acid during parboiling can be attributed to the enzymatic hydrolysis taking place during soaking and steaming and the breakdown of the ring structure of phytic acid during heat treatment of parboiling.