Phytase activity in brown rice during steeping and sprouting

Phytase in brown rice will be activated and accumulated during seed germination. Changes of phytase activity in brown rice during two stages of germination (steeping and sprouting) affected by process conditions were studied. It was shown that steeping led to significant decrease of phytase activity (p < 0.01), varying with steeping temperature and steeping medium composition. Steeping respectively in demineralized water, 0.5 mM CaCl2 and 0.1 M H2O2 at 20 °C for 24 h led to the lowest phytase activity in brown rice, which was only 25% of that in raw rice. At steeping stage, steeping media had no significant effect. During the sprouting stage, phytase activity increased with prolonged time and gradually reached stable levels, and with higher temperature in the range of 15-25 °C. Phytase activity in brown rice reached 320-340 U kg-(1) after 5 d sprouting. The evolution pattern of phytase activity during sprouting differed with the solutes previously used during steeping. Steeping either with CaCl2 or H2O2 caused a delay followed by a rapid activation of phytase, while for control, a gradual accumulation of phytase activity was observed. Compared with acidic and alkaline steeping solutions, demineralized water at neutral (6.8) pH provided the best pre-treatment prior to sprouting at 25 °C, to activate maximum levels of phytase. Extreme conditions, either strong acidic or alkaline inhibited activation of phytase, and changed appearance of brown rice kernel as well.