Effects of Intermittent Liquid Nitrogen Immersion Freezing on the Freezing-cracking Rate and Sensory Quality of Dumplings

To explore the effect of intermittent liquid nitrogen immersion freezing on the color difference,texture,sensory quality and microstructure of dumplings,in this paper the effect of liquid nitrogen immersion time,interval time and immersion times on dumplings with the index of freezing-cracking rate were studied. The effect of liquid nitrogen immersion freezing on the color,texture,sensory properties and microstructure of dumplings compared with the cryogenic refrigerator freezing and spiral tunnel freezing was studied by means of color difference meter,texture meter and scanning electron microscope. The results showed that when the single immersion time of liquid nitrogen was 2 s,the interval time was 10 s and the total immersion time was 86 s,the time was the shortest and the central temperature reached below-18 ℃ and the freeze-crack rate of dumplings was 0. Compared with the traditional cryogenic refrigerator freezing and spiral tunnel freezing,the L^* of dumplings increased significantly after the immersion freezing with liquid nitrogen(P<0.05),the color and appearance were significantly improved,and the hardness,adhesion and chewability significantly reduced(P<0.05). The taste was more similar to the quality of fresh untreated dumplings. The SEM results showed that the number of pores in the dumpling skin was the smallest and the most in the liquid nitrogen freezing treatment group,and the excessive holes might damage the gluten network structure,resulting in poor boiling resistance of dumplings. This study provides a certain theoretical basis and technical support for the application of liquid nitrogen freezing in rice noodle products.