J Integr Plant Biol. ›› 1955, Vol. 4 ›› Issue (4): -.

• Research Articles •    

A Study of Safe Moisture Content of Rice Grains during Storage

Chao Tung-fang and Wang Ming-chi   

Abstract: Four quantifies of a late variety of unglutinous flee, Lao-lai-ching, harvested in the current year (1954) were sunned/or different periods of time to have their respective moisture contents reduced to 13.6%, 15.2%, 17.2%and 19.6%. From each of them six equal portions were taken and placed in six replicated 1000-ml bottles, three aerated and three sealed up. These 24 bottles were equally grouped and stored in three incubators at different temperatures, 15℃, 25℃ and 35℃, and they were arranged in such a way that one pair of bottles (one aerated and one sealed up)from each of the above-mentioned four groups with different percentages of moisture content were put in one incubator. Three months later, determinations of the percentage of germination and fatty acid, the vitamin B1 content, the number and kinds of molds and the grade of the dehulled rice turned out therefrom were made. From the results thus obtained we find as follows: 1. From the standpoint of the maintenance of the germination percentage, the appropriate moisture content of rice grains during storage should be less than 13% at 35℃, not over 15% at 25℃ and no more than 17% at 15℃. 2. Laboratory storage of rice with different moisture contents for three months under both sealed-up and aerated conditions at different temperatures showed differences in fatty acid content from the original samples. The factors favouring the increase in fatty acid content are: (1) high temperature and (2) high moisture content. 3. There are certain relations between the fatty acid content and the grade of the dehulled rice. Generally, the higher the fatty acid content is, the lower will be the grade of rice. As regards the vitamin B1 content, however, only very slight changes were noticed. 4. The number of mold spores per gram of rice grains stored under the aerated condition was notoably different from that of mold spores per gram of rice grains stored under the sealed-up condition. Further analysis showed more tremendous differences at different temperatures in the aerated bottles than in the sealed-up bottles. 5. The molds isolated most often from the rice grains were Aspergillus sp. Alternaria tenuis, Brachysporium sp., Cladosporium herbarum, Cephalothecium roseum, Curvularia lunata,Fusarium spp., Helminthosporium oryzae, Helicoceras sp., Nigrospora oryzae Mucor spp., Penicillium spp., Phoma sp., and Trichoconis Padwickii. At 35 ℃, isolations made from rice grains under the aerated condition gave birth chiefiy to Aspergillus spp., Mucor spp., and Penicillium spp., and those from the sealed-up ones brought forth Penicillium spp., and Tricoconis Padwickii. At 25 ℃ and 15℃, all the 14 genera of molds listed above were isolated from individual rice kernels in both the aerated and dealed-up bottles with the agar-plate method. 6. It is a general .experience that the newly-harvested Lao-lai-ching offers superior white unglutinous rice when dehulled. If one intends to maintain this high grade for three months or longer, he has to keep the moisture content of rice grains at less than 14% at 35℃, not over 14% at 25℃ and around 15% at 15℃. This paper discusses certain complex interrelationships amoung the percentage of germination, the fatty acid content., the vitamin B1 content, the number and kinds of molds, and the grade of the dehulled rice. It points out the necessity for further physiological and biochemical investigations in connection with grain storage.

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