Study On The Sterilization,Brittleness-keeping And "Nitrite Peak" Inhibition Technology Of Low-salt Picked Lettuce By Ultra-high Pressure Treatment

Pickle is a traditional table dish because of its convenient to eat and taste delicious. Vegetables pickled with low-salt are more conducive to human health, but due to the loss of the inhibitory effect of high-salt on microbial, low-salt pickles are easy to be polluted by harmful microorganism, hard to be storaged, and there is excessive nitrate (> 4 mg/kg).In this thesis, the ultra-high pressure (UHP) technology was utilized to process the low-salt pickled lettuce, under the premise of guarantee the low-salt pickle lettuce effective sterilization and without losing the crisp taste, inhibit its nitrite peak, evaluate its quality and to determine the best tasting period of the product. The main results are as follows:1) The low-salt pickle lettuce processed by UHP technology can be effective sterilization while maintain its crisp taste.The processing pressure and pressure holding time had significant effects on the sterilization effect of the low-salt pickled lettuce, the requirement of sterilization can be met under temperature of 25 ℃, pressure of 200 MPa and holding time of 20 min, the sterilization effect is better when the pressure is greater than or equal to 300 MPa.Brittleness and hardness of the UHP low-salt pickled lettuce was significantly better than that of the heat treated samples. After UHP processing, the hardness maximum loss rate of low-salt pickled lettuce is 10.16%, the brittleness loss rate is less than 14.02%, significantly better than heat treatment samples, and the lower the pressure, the better the taste crisp.2) The "nitrite peak" of the low-salt pickled lettuce could be significantly inhibited after pressure of 300 MPa treatment.The impact of UHP treatment on the "nitrite peak" of the low-salt pickled lettuce was investigated. The results show that the "nitrite peak" of the UHP low-salt pickled lettuce reached the minimum under pressure of 300 MPa, holding time of 15 min and temperature of 25 ℃, the "nitrite peak" was 2.76 mg/kg, decreasing by 65.24% compared to the untreated samples which "nitrite peak" was 7.71 mg/kg, indicating the differences are significant. And after treatment under this condition, the nitrate reductase activity and the total number of colonies were significantly reduced, while the nitrite reductase activity remained unchanged, what illustrates that the "nitrite peak" of the low-salt pickled lettuce can be effectively inhibited by adjusting the conditions of UHP treatment.3) The best tasting period of UHP low-salt pickled lettuce under temperature of 25 ℃ and 4 ℃ attain to 10 days and 30 days, respectively.The recommended best tasting period under 25 ℃ and 4 ℃ were 10 days and 30 days respectively. During this period, the samples did not occur the phenomenon of inflation, the sensory quality of products was good, the nitrite content is less than or equal to 2.76 mg/kg, and the hygiene requirements in line with NY/T 437-2012 "green food pickles" and GB29921-2013 " food pathogens in limited of food safety national standards".