Inactivation of Baroduric Bacteria Isolated by High Hydrostatic Pressure in Pickle of Sichuan
|School||Sichuan Agricultural University|
|Course||Of Food Science|
|Keywords||High hydrostatic pressure Pickle Baroduric bacteria 16S rDNA Inactivation|
Sichuan pickles, are traditional lactic acid fermented vegetable products in China, which are very popular as its unique taste and high nutritional value. Fermented pickles, rich in nutrients, and also are one kind of low-salt, low-sugar, high water content products, which are very difficult to preserve. Traditional pasteurization of Sichuan pickles tend to have adverse effect on the quality of food, such as changing of color and taste, nutritional losses. Ultra-high pressure sterilization technique is able to give a good bactericidal effect, without influencing on small molecules of vitamins, pigments, flavor substances covalent bond, and also keeps the color, smell, taste, and nutrition.The purpose of this study is to isolate and to identify the baroduric bacteria from pickles after high pressure treatment, which could determine the target bacteria during the pressure treatment and provide a theoretical basis for ultra-high pressure technique in Sichuan Pickles. The6pickle samples were collected from Meishan City and Xindu district of Chengdu City in Sichuan as test raw materials. We first investigated the total number of colonies, mold and yeast in the2kinds of pickles at room temperature (20℃) under the conditions of different pressure and holding time. The result could indicate the validity of ultra-high pressure sterilization with the validity Sichuan pickles, and also to determine the pressure strain of HHP filter criteria. Then we used16S rDNA sequence to identify the residual pressure bacteria in the6pickle samples. In the end, we studied the lethal effect of the strains in the300-600MPa pressure in3-25min under20℃. The main results of this paper are as follows:1. Microbial mortality correlates to pressure and holding time positively, which also affect the lethal result of total bacterial count, yeast and mold. When the pressure is in the range of100-400MPa, the total number of colonies reduced, but the mold and yeast death rate increased sharply with the pressure increasing; the number of total bacteria slowly decreased in the500-600Mpa pressure range, after500MPa15min or600MPa5min pressure processing, molds and yeasts were no longer detectable. Hence, pressure level played a dominate role on the ultra-high pressure sterilization. Total number of colonies decresed with the time increaing at first20min, but would have not significant change afterward; Sterilize with400MPa for5-20min occurred a rapid decline in the number of fungal yeast, and there is no molds and yeasts were detected after25min. Longer holding time has little effect on bactericidal. When the pressure is higher than400MPa, with the holding time extended from20min to25min, the total number of colonies kept unchanged, with no molds and yeasts detected. Therefore,600MPa with the holding time of25min is selected as treatment treatment condition. 2. After6pickle samples treated with600MPa for25min, there are17of pressure-resistant strains were isolated, all of which were Gram-positive Bacillus. By16S rDNA sequence homology analysis, these17strains were identified as nine species, which are Bacillus subtilis (3strains), Bacillus sonorensis (1strain), Bacillus licheniformis (1strain), Bacillus pumilus (6strains), Bacillus cereus.(1strain), Bacillus megaterium (2strains), Bacillus the simplex (1strain), Bacillus fusiformis (1strain) and of Paenibacillus pabuli (1strain). These9species, including8Bacillus and1Paenibacillus, have more than99%homology with the corresponding reference strain based on the16S rDNA sequence. Bacillus pumilus, the largest proportion, accounting for35.29%of the17pressure-resistance strain in pickle samples, is the predominant strains.3. At room temperature (20℃) under300-600MPa pressure, the lethal effect on4representative strains, including Bacillus pumilus (B. pumilus), Bacillus subtilis (B. subtilis), Bacillus licheniformis (B. licheniformis), Bacillus sonorensis (B. sonorensis), were investigated. The order of the resistance to stress are Bacillus pumilus＞Bacillus licheniformis＞Bacillus Sonora＞Bacillus subtilis. When the pressure is between500-600MPa, to extend the holding time over15min does little on the bactericidal effect.