| In this research, we introduced biology method to prevent browning. Firstly, lactic acid bacteria (LAB) of anti-browning were screened out from peas fermentation broth and characteristics of anti-browning metabolites of LAB were analyzed. Secondly, culture conditions of LAB anti-browning metabolites in MRS medium had been optimized. Finally, preservation effect of LAB fermentation supernatant which could be used as natural anti-browning inhibitor on lotus root was studied. The main research results were as follows:1. Five LAB strains which could inhibit BD and PPO activity of lotus root were screened out from peas fermentation broth. According to biochemical/physiological traits and sequence analysis of 16SrDNA, L5, L8 and L11 were identified as Lactobacillns pentosus, L6 and L10 were identified as Lactobacillus planatarum. Furthermore, L5, L8 and L11 reached 100% similarity with Lactobacillus pentosus JCM8339, L6 and L10 reached 99% similarity with Lactobacillus planatarum CG4.2. Characteristics of strains anti-browning metabolites were analyzed and made sure the substances of inhibiting lotus root browning mainly included acid, hydrogen peroxide, protein substances. Metabolites could show good anti-browning effect only under acidic conditions(itself pH when fermentation was completed). In addition, the decline of inhibition rate of metabolites on lotus root BD and PPO activity was not significant (P>0.05) than that of undiluted solution after treated at 80℃, while the inhibition rate significantly decreased (P＜0.05) after treated at 90℃, 100℃,121℃, which illustrated metabolites had a certain of thermal stability, but the anti-browning effect would be significantly affected when temperature exceed 80℃.3. Different factors were investigated such as initial pH, inoculating amount, temperature and time on the inhibition rate of PPO activity so as to optimize strains cultural conditions. The results were as follows:The optimum culture conditions of strains L8 were initial pH 6.0, inoculating amount 2%, temperature 30 ℃, time 16h and the inhibition rate of metabolites on PPO activity increased by 19.43%.The optimum culture conditions of strains L10 were initial pH 7.0, inoculating amount 5%, temperature 30 ℃, time 22h and the inhibition rate of metabolites on PPO activity increased by 18.37%.4. The experiment on other culture medium of preferable LAB showed:when choosing simple carbon and nitrogen sources as culture medium, the anti-browning effect of L8 and L10 metabolites was lower than that in MRS medium. When selecting peas serosity as culture medium, L8 and L10 enhanced the inhibition rate of metabolites on PPO activity of lotus root after inoculation and the influence of different incubation time on metabolites inhibiting PPO activity had significant difference (P＜0.05) at 30℃. However, inhibitory effect of metabolites was still lower than that in MRS medium. Respectively choosing peas serosity and MRS as culture medium at 20℃, inhibitory effect of metabolites on PPO activity didn’t have significant difference (P>0.05). At 20 ℃, inhibition rate of metabolites from peas serosity (undiluted solution), undiluted solution+L8, undiluted solution+L10 were higher than that at 30℃, which indicated low-temperature fermentation was more conducive to the generation of anti-browning metabolites when choosing peas serosity as culture medium.5. Fresh-cut lotus root (FLR) were to do preservation experiment. BD, PPO, POD, total phenol, firmness and soluble solids were determined during storage, the results showed metabolites of L8 and L10 could retard tissue browning of FLR and maintain a good quality. The effect processed by fermentation supernatant was better than ascorbic acid (Vc) and control treatment. Different percentages of the same strains fermentation supernatant didn’t have significant difference (P>0.05) on the six indicators, while the influence on the measured indicators was significant difference (P<0.05) at different strains fermentation supernatant, and among different strains fermentation supernatant and Vc, control treatment. In summary, L8 fermentation supernatant had stronger anti-browning effect than L10. Taking into account the color and expenses of MRS liquid medium, it was more suitable to choose low-concentration fermentation supernatant to do preservation of FLR. |
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