Studies On Nitrite Degradation In Radish (Raphanus Sativus L) Pickling Process And Preservation Technology

The radish pickle is one of the consumer’s favorite, but its safety has been concerned widespreadly. The variation and control of nitrite and nitrosamines during vegetable picking process have become a hot topic. In this dissertation, the pickling radish processing and preservation technology were investigated. Lactic acid bacteria (LAB) strains reducing nitrite were isolated from radish pickle made from natural fermentation, and the optimization of incubation conditions of pickle fermentation was carried out. Then, changes of essential substances in radish during pickle fermentation and ultra high pressure processing were analyed. Finally, the changes of microbe number, nitrite content, color and pH value in pickled radish during storage were observed. The main results were as follows:Eighteen lactic acid bacteria strains reducing nitrite were isolated from the radish pickle made by traditional fermentation method. Of which, two strains of B1 and C2 which showed higher nitrite reducing ability in culture medium with high nitrite content were obtained. Identification tests indicated that B1 and C2 belonged to Lactobacillus plant arum strain.They could reach the stable phase after 16h and their optimum growth conditions were:temperature 30℃, pH value 6.0, salt concentration 0-5% and nitrite concentration 0-0.4%. The results of nitrite degradation by LAB showed:in the early fermentation stage, enzymolysis was the main controller and then acid splitting became the controller.Radish(Raphanus sativus L) was used as the material in producing inoculated fermentation pickle. The optimization conditions of inoculated fermentation were carried out with Box-Behnken design of response surface methodology. The optimum condition included the following parameters:culture temperature 29.45℃, salt concentration 4.08% and inoculum number 11.48%. Under these conditions, the nitrit decreased down to 2.59±0.01 μg/g and the activity of nitrite acid reductase decreased down to 11.61±0.42 μg/(g·h).Changes of essential substance content in radish were analyed during traditional nature fermentation and artificial inoculated fermentation process of radish. Nitrite content of nature fermentation period was significantly higher than that of inoculated fermentation. Nitrite content during nature fermentation period increased rapidly, but remained low during inoculated fermentation period. After fermentation three days, nitrite content of nature and inoculated fermentation processing were 271.24 μg/g and 0.39 μg/g, respectively. Nitrite acid reductase activity in radish during nature and inoculated fermentation process decreased. After fermentation for three days, nitrite acid reductase content of nature fermentation was 26.03 times higher than that of inoculated fermentation. The results showed that amino nitrogen, soluble protein and reducing sugar content were decreased by both fermentation methods. With fermentation time prolonged, total acidity content was increased, and the content of inoculated fermentation was much higher than that of nature fermentation. After fermentation three days, total acidity content of nature fermentation was 1.28 times higher than that of inoculated fermentation.Effects of nature and inoculated fermentation on the quality of radish pickle treated with ultrahigh-pressure were investigated. The results showed that with pressure increased from atmospheric pressure to 500 MPa, the total number of bacteria was reduced from 104 to 102. Under 300 MPa or more, mold yeast were undetectable. With the pressure-holding time prolonged, the bacteriostatic effect increase within a certain range. Under 300 MPa for 5min to 15min, the total number of bacteria decreased to 65.59%. Under 300 MPa for 15min or more, the mold and yeast were undetectable. The results showed that ultrahigh-pressure could well restrained total number of bacterial count, mold, yeast and coliform, but nitrit content, color and pH had no significantly changes.Effects of different storage temperature on radish pickle qualities were investigated. Ultrahigh-pressure and refrigeration temperature storage can well restrained total number of bacterial count, mold, yeast and coliform, but nitrit, color and pH had no significantly changes. After 120 days storage, the total number of bacteria in room temperature storage was 1.37 times than that in refrigeration temperature storage. With ultrahigh-pressure, the total number of bacteria in refrigeration temperature storage was 0.37 times than that in room temperature storage. Nitrit content decreased during storage. The L*-value, the a*-value, the b*-value and pH-value increased. N-nitrosamines were not detected.