Effect Of Moisture Migration Changes On Quality Of Cereal Food

Moisture plays a very important role in rice and other relative products such as Zongzi, rice cake. The critical process affecting quality and shelf life of cereal food is the interaction between water and starch during manufacture, including the migration of moisture, the combination and sepatation of water with starch and protein, changes of water states, changes on the characteristics of starch itself and so on. The transverse relaxation time(T2) of cereal food can be detected by the application of Low Field-Nuclear Magnetic Resonance(LF-NMR) during manufacture and storage, and much important information of water mobility and distribution in samples can be acquired to provide relative evidence of quality changing mechanism in cereal food, so that to guide its manufacture process.Moisture migration changes and the quality of cereal food (glutinous rice, japonica rice, indica rice and Zongzi) were researched in this paper to investigate their effects on the quality of Zongzi. The results are as fellows:1. Changes of moisture status in rice during soaking processThe changing research of water distribution in glutinous rice during soaking was as follows:The shortest time was 35min for the water to reach the center of glutinous rice, the ratio of water to rice was at least 35%; When the soaking temperature increased by 5℃, the soaking time could be shortened by 10 min in the range of 15-30℃.It was found that water distribution in different breeds of rice were significantly different during soaking. The amounts of free water was characterized by T23 The T23 of glutinous rice was 37.64ms, japonica rice was 52.63ms, while the indica rice was 59.94ms after soaking for 1 hour. Compared with non-aged glutinous rice, the aged glutinous rice had higher relaxation time of T21, but the amplitude of T21 was smaller during soaking process.2. Change of water status and its effects on the quality of rice and Zongzi during cooking processT23 of the 3 kinds of rice increased first and then decreased rapidly in the cooking process; Compared with the japonica rice and indica rice, T22 relaxation time and T22 amplitude of cooked glutinous rice were higher; the amylose content had significant positive correlation with the hardness of cooked rice, but the viscosity was significantly negatively correlation. Soaking time had a significant effect on the hardness and sticky of the cooked rice (P<0.05). The hardness of the cooked rice was lower after 24h excessive-soaking, but the viscosity was higher.T21 amplitude of aged glutinous starch decreased during gelatinizing, the viscosity lowed down significantly, the hardness of the cooked rice increased while the viscosity decreased, so the quality of cooked rice was affected significantly.Water status changes of surface and center rice in Darou Zong during cooking were significantly different:T21of surface rice increased from 1.64ms to 4.57ms, at 80℃, droped sharply to 1.02ms. While center rice increased from 1.65ms to 3.80ms, began to decline at 90℃, T21reduced to 1.02ms after pressure; Keeping pressure 30min, T22 and T22 amplitude of Darou Zong and Dousha Zong were higher than Baimi Zong.3. The relationship between water status and rice quality during rice retrogradationThe velocity of T22 within 12h of three kinds of rice were as follow: glutinous cooked rice (0.671), japonica cooked rice (1.023) and indica cooked rice (1.134), the velocity of T22 become larger with the increased amylose content, the hardness of rice increased and the viscosity decreased in the retrogradation process. The velocity of T22 within 12h and 10d of aged glutinous cooked rice were (1.141 and 0.147, respectively) greater than non-aged glutinous cooked rice (0.671 and 0.105, respectively). 4. The relationship between changes of water status and quality of Zongzi during its shelf-lifeThe hardness, adhesiveness and chewiness were used to characterize of the texture changes in Zongzi during storage.The results of the changes of water status and texture of Zongzi during 6d storage were as follows:T21 changed a little, T22 decreased, The hardness, adhesiveness and chewiness showed rising tendency; Compared with Baimi Zong, the T21 and T22 proton density of Darou Zong and Dousha Zong were higher, meanwhile the texture were more soft; Darou Zong and Dousha Zong started to have the free water composition (T23>100ms) after 4d storage, meanwhile the hardness, adhesiveness and chewiness showed decreasing tendency.