Change rule of storage quality and optimization of storage condition for Camellia oleifera seeds

Abstract: Camellia oleifera seed, commonly known as the oil-seed camellia seed or oil-tea camellia seed, just like oil palm, olive and coconut, is one of the most prominent woody edible oilseeds. Camellia oleifera seed oil, one of the favorite cooking oil used wildly in China's southern provinces and Southeast Asia, has much in common with olive oil in chemical composition drawing great attention from the public, with high amounts of oleic acids (76.1%-83.3%) and linoleic acid (7.0%-11.03%) and was often titled as "Eastern Olive Oil". However, it is not easy to store the seeds because of the high total amount of unsaturated fatty acids up to 90% and high temperature and high humidity climate in Camellia oleifera seed producing area, which are tend to lead to the quality degradation during storage. In order to maintain good storage quality, the effects of storage conditions on quality of Camellia oleifera seeds and the reasons for them were explored in this study. Using moisture content of material (7%, 8.5%, 10%, 11.5%, 13%), air relative humidity (50%, 60%, 70, 80%) and storage temperature (4, 15, 20, 25℃) as single factors, the change in oil content, acid value and peroxide value of Camellia oleifera seeds were determined during the 8-months storage. At the same time, the lipase activity, lipoxygenase activity and the growth of microorganisms, which were highly related to the increases of acid value and peroxide value, were also investigated during storage. The change trend of oil content showed an increase in the beginning and decreased after the peak, indicating that there was a phenomenon of post-ripening observed during the storage. In this study, the post-ripening period of stored Camellia oleifera seeds was 3-4 months, which was similar to the post-ripening period of 2-3 months for peanut and was obviously longer than the post-ripening period of 10-20 days for corn. The acid value and peroxide value were increased with the increase of moisture content of material, storage temperature and storage time. The significantly positive correlation between the lipase activity and the acid value indicated that the increase for acid value of Camellia oleifera seeds during storage was mainly due to the accumulation of free fatty acids produced by hydrolysis of fat resulting from lipase. Within 6-months storage, only a few of molds of Camellia oleifera seeds were observed. However, once microorganisms grew in large quantities with the prolongation of storage time, lipase would be produced to further promote the increase of acid value. In addition, based on the above results, the effects of moisture content of material, air relative humidity, storage temperature and storage time on oil content, acid value and peroxide value were investigated using response surface method. The regression equation predicting quality variation was established and it proposed that suitable air relative humidity and storage temperature can promote the post-ripening of Camellia oleifera seeds during storage. The comprehensive optimization ranges of Camellia oleifera seed storage parameters, obtained using frequency analysis method from the regression analysis of standardized comprehensive score values, were as follows: air relative humidity of 57.6%-67.4%, temperature of 17.2℃-20.4℃, moisture content of 8.9%-10.4%, storage time of 62.2d-110.3d. Under the optimal conditions, the comprehensive qualities of Camellia oleifera seed oil are good. In order to make the best of post-ripening effect and improve the storage quality, it is suggested that in practical operation, air relative humidity of the storage during post-ripening period should be 1%-2% higher than the storage after the post-ripening stage, and the temperature should be 1℃-2℃ higher. This study can provide support for storage and the subsequent oil processing of Camellia oleifera seeds to improve the oil production rate and guarantee the quality.