Abstract:
Refrigerated convenient rice has been gradually recognized as one of the main forms of food products at present, due to its simple processing and excellent taste. Nevertheless, there is the serious decrease in rehydration, taste, and nutritive value, as the storage time prolongs. Physical and chemical means have been utilized to inhibit the rice regeneration for better quality, such as the storage temperature, moisture content, and additives. Particularly, the safe and natural additive control technology can be applied to inhibit rice regeneration. Among them, maltitol is often obtained by the hydrogenation of maltose, due to its low sweetness, strong moisture absorption, and excellent water retention. Meanwhile, maltitol has been widely utilized in the food industry as a sweetener, water-retaining agent, and stabilizer. This research aims to clarify the optimal quantity of maltitol addition for the high quality of rice and starch during rice refrigeration. The aging of starch was then delayed to extend the shelf life of rice starch products. Soaking treatment was performed on the different mass fractions of maltitol solution. The additional amount of maltitol was adjusted to determine the water absorption, hardness, iodine blue value, taste value, crystal structure, and microstructure of cooked rice. The results indicated that soaking rice in maltitol solution enhanced the water absorption and viscosity of rice, and the taste value of cooked rice, whereas, the hardness of rice was reduced to inhibit the aging and regeneration of rice during refrigeration. The hydroxyl groups in the maltitol solution interacted with water to form the hydrogen bonds. The penetration of water molecules into rice improved the water absorption rate of rice, thereby inhibiting the reorganization of starch molecules for the rice regeneration. Once the rice was immersed in 1% maltitol solution, the water absorption of the rice was 17.60%, which was 1.84 percentage points higher than that of the control group. On the third day of storage at 4 ℃, the iodine blue value of rice decreased significantly, indicating the relatively outstanding regeneration. The highest iodine blue value of rice starch was observed in the 1% maltitol treatment group. The degree of rice rejuvenation was the lowest, followed by the control group. Compared with the control group, the hardness of rice soaked with a 1% mass fraction of maltitol solution was significantly different from the 5th day after cooking and stored in the refrigerator at 4 ℃ to the 7th day. Furthermore, the hardness of rice tended to be stable, when the rice was stored on the 7th day. Among them, the hardness of rice in the 4 treatment groups increased to different degrees when the storage was extended from the 3rd day to the 5th day, but the hardness of rice after soaking in 1% maltitol solution increased less. On the 3rd day of storage, the hardness value is 1446.14 N, and on the 7th day of storage, the hardness value is 1714.31 N. There was a much more effective performance to inhibit rice regeneration. There was no significant difference crystallinity of rice starch soaked by maltitol of different mass fractions, compared with the control group (
P > 0.05). However, there was a decrease in the crystallinity of rice starch soaked by a 1% mass fraction of maltitol, compared with the rest treatment. Specifically, the crystallinity was reduced from 4.68% to 2.84%. The microstructure of rice samples soaked by 1% and 2% maltitol presented a dense porous structure, with uniform distribution and excellent microstructure on the surface. Therefore, the maltitol solution with the low mass fraction was more easily permeated into rice grains, thus inhibiting the recrystallization of starch grains, and the aging and rejuvenation of rice. The soaking in maltitol solution with a low mass fraction can be expected to effectively inhibit the rice rejuvenation for high quality. The finding can also provide a strong reference for the low-dose sweetener (maltitol) to inhibit rice rejuvenation in food products.