The oil in full-fat rice bran can become rancid during storage due to the presence of a lipolytic enzyme that becomes active when the bran is separated from the rice. Rancidity rapidly increases the free fatty acid content. The free fatty acid content of bran from parboiled rice is below 3% immediately after milling but increases at the rate of about 1% per hour. Apart from extraction of the oils, the rancidity process can be delayed by heating or drying immediately after milling. Heating to 100°C for four or five minutes with live steam is sufficient to retard the increase in free fatty acids. The rice bran can also be heated dry if spread out on trays at 200°C for ten minutes. The same effect can be obtained by reducing the moisture content to below 4%. Most chemical inhibitors are ineffective (Göhl, 1982).
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