The purpose of this research was to study the drying of purple rice (PR) at temperatures of 100 °C, 130 °C, and 150 °C using a fluidization technique in conjunction with storage in packaging consisting of a polypropylene woven bag (PPWB), laminated bag (LB) or laminated bag with an oxygen absorber (LBOA) to protect against a change in the quality of PR during storage for a period of 90 days. Drying at a temperature of 130 °C, other than showing a high drying rate, did not affect the quality in the aspects of the color, the anthocyanin content, the total phenolic content and the antioxidant activity of the PR. The application of such a temperature also made the free fatty acid (FFA) content decrease during the storage period. To maintain the PR at the highest expected quality after drying, it should be stored under LBOA conditions. Practical applications Drying conditions using a fluidization technique and the storage conditions used in the research were selected from the actual functional conditions used at present even though drying at high temperature might adversely result in the degradation of anthocyanins. Contrarily, the conditions selected positively resulted in inactivated lipase enzyme and prevented the hydrolysis lipids in the rice bran from becoming FFAs, which would subsequently give rise to rancidity. In addition, in this research, data comparisons were clearly made on the change in PR quality at various levels of storage conditions. After the tests, the conditions of drying and suitable storage that would attain the expected quality after harvest until the purple rice (PR) reached consumers would be maintained at the maximum quality. The data acquired will be useful and could be applied in the PR production process, which has been increasingly and continuously expanding.

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Paddy rice varieties harvested in the rainy season are generally at risk of fungal contamination. This includes the local paddy rice variety, Sang Yod, that is harvested annually and requires a specific climate and agricultural geography for growth (Ministry of Commerce, 2006). After maturity, most farmers in Thailand, who not have a large godown and equipment for rice production, will sell the paddy rice to the nearest rice community enterprise, cooperative, or factory immediately after harvesting. The paddy rice is sun-dried on a concrete yard to equilibrium moisture content. A small quantity of paddy rice is processed to brown rice, packed, and transported. The remaining paddy rice is stored to serve customer demand over the coming year. Any fungi that infect paddy rice pre-, during-, or post-harvest will usually develop during long-term storage, especially in the South of Thailand where the weather is hot and humid with heavy rainfall year-round. Most of these fungi belong to the genus Aspergillus (Bertuzzi, Romani, Rastelli, & Giorni, 2019). The fungi of this genus can cause contamination of the final product with mycotoxins, for example, aflatoxins and ochratoxin, which are carcinogens, mutagens, and teratogens-the main causes of cancer (Reddy, Reddy, Abbas, Abel, & Muralidharan, 2008). Inhibition and prevention of paddy rice fungi is necessary to reduce the potential losses and consumer health impacts.

This research was contemplated for two purposes: to study a consequent change in the free fatty acid (FFA) content of dried black glutinous rice by fluidization drying and to develop a mathematical equation for predicting FFA formation during storage. It was found that during the same storage period, the rice that passed through the drying process at temperatures of 100, 130 and 1508C accounted for less formation of FFA content than the referenced rice, and the FFA formation was reduced in accordance with the increasing drying temperature. In regard to the proposed equation, predicted FFA formation in rice during the storage period by zero-order rate reactions yielded the best fit with the values acquired from the experiment. PRACTICAL APPLICATIONSThe drying process, which uses fluidization with high temperature hot air, is a highly efficient drying method in reducing moisture of the paddy to a suitable level before transporting or storing. In addition, such a method could be applied to the inactivated lipase enzyme to prevent hydrolysis of lipids in rice bran that give rise to FFA, which results in undesirable rancidity for consumers. Data on the change in the FFA content acquired from the experiment would be used to develop a mathematical equation for predicting FFA formation in black glutinous rice during the storage period. The suitable drying condition and proposed mathematical equation would be beneficial as a drying guideline to control rancidity of rice during storage.