Effect Of Thermal And Other Processing To The Quality Of Zongzi

Zongzi (rice dumpling wrapped in reed leaves) is a famous traditional food. However problems such as short shelf life, half-cooked rice inside and glutinous retrogradation and aging have restricted the industrialization of zongzi. This paper focused on several problems during the producing process. Based on glutinous zongzi, the effects of soaking, mixing, cooking and sterilizing on the quality of zongzi during processing were studied. The research tried to analyze the factors influencing the quality of the zongzi and therefore getting the best condition in zongzi producing.Parameters changed most violently in the first 60 minutes when glutinous rice was soaked and the change came to be gentle in 60~120 min. There is no significant difference between samples soaked in different temperature. As soaking time increased to 60 min water content of glutinous rice increased to be around 55%. Dry matter changed most violently in the first 60 minutesand as well and decreased about 16% after soaking. The color of the zongzi increased with L* value and decreased in with a* value. With the increase of immersion time rice aroma was decreased and bamboo incense rose for the sensory evaluation. Sample of rice soaked for 60min showed the highest score with the moderate taste.As the percentage of adding Dongbei rice increased, water content inside zongzi decreased, and the weight, L* value increased as well. However a* value decreased with the increasing percentage in Dongbei rice. Hardness of zongzi increased as content of Dongbei rice increased. Adhesiveness and sensory evaluation score of zongzi showed a change of increasing at the beginning and then reducing with a peak as content of Dongbei rice increased. When Dongbei rice reached 40% of total, zongzi got the highest score in sensory evaluation.Higher water content will help water and heat transfer during cooking process. With the increase of initial water content, water content inside zongzi increased in the same cooking condition. But F value of cold-point decreased as the increase of initial water content. Cooking with higher temperature and pressure, temperature of cold-point increased faster, and F value rose up more quickly. Hardness decreased while adhesiveness rises up at the beginning and reduced with a peak as cooking temperature raised. L* value increased and a* value decreased during cooking. When water content appeared to between 130% to 135% zongzi tasted better. When soaked rice for 60 min, and cooked in 115℃(0.07 MPa)for 30 min, the size of 100g zongzi tasted best.With the increase in initial water content, water content in the center of zongzi decreased faster. And water content in the center of zongzi decreased more for a longer sterilizing time. Hardness decreased after sterilization. And adhesiveness increased rise up at the beginning and reduced with a peak after sterilization. Sterilized for 20min the number of colonies in zongzi can achieve the commercial sterility requirements. Sterilization time shows impact a* value greater than cooking and soaking. Priorities of factors affect F value during sterilization process were C (sterilization time)> A (soak time)> B (cooking time). According to sensory evaluation of the orthogonal test, the best producing process of zongzi is A3B2C3, which means soaked 60 min, cooking 120 min and sterilized 25 min.