1.1 Strains
Lactic acid bacteria: Enterococcus faecium HEW-A511; mold HEW-M1 were provided by Beijing Haoshiwo Biotechnology Co., Ltd.
1.2 Culture medium and materials
Medium: MRS broth medium, Bengal red medium, and potato dextrose medium were purchased from Beijing Aoboxing Biotechnology Co., Ltd., and MRS solid medium was purchased from Beijing Land Bridge Technology Co., Ltd.
Materials: Potassium sorbate was purchased from Ningbo Wanglong Technology Co., Ltd.
1.3 Experimental method
1.3.1 The effect of potassium sorbate on the growth and activity of lactic acid bacteria
Enterococcus faecium HEW-A511 glycerol was activated by streaking on the MRS solid plate, cultured at 37°C for 36 hours to form a single spot, then inserted the single spot into 50ml of MRS broth medium, and cultured at 37°C for 12 hours at 160rpm to prepare the seed solution. Take more than 1ml of the seed liquid and insert it into 100ml MRS broth medium with different concentrations of potassium sorbate, the concentration of potassium sorbate is 0%, 0.1%, 0.2%, 0.3%, 0.4%, initial pH=6.8, 37℃ Cultivate at 160rpm for 12h, dilute with 0.5ml of bacterial suspension to the power of 10-7, dilute with 0.85% normal saline, take 1ml of diluted bacterial suspension and use MRS solid medium to detect the activity of lactic acid bacteria, and count after 36 hours of incubation at 37°C .
1.3.2 The effect of potassium sorbate on mold
Introduce 0.1ml of the spore suspension of mold HEW-M1 into 50ml of potato dextrose medium, incubate at 28°C and 200rpm for 12h, dilute with 0.5ml of bacterial suspension to the power of 10-6, dilute with 0.85% normal saline, Take 1ml of the diluted bacterial suspension and use different concentrations of potassium sorbate Bengal red medium to detect the mold activity. The concentration of potassium sorbate is 0%, 0.1%, 0.2%, 0.3%, 0.4%, and cultured at 28°C for 72 hours After counting.
2.1 The effect of potassium sorbate on the growth and activity of lactic acid bacteria
Different concentrations of potassium sorbate were added to the MRS broth medium, and after culturing at 37°C and 160 rpm for 12 hours, the pH value of the medium was different, and the activity of lactic acid bacteria was also slightly different. The specific results are shown in Table 1.
Table 1 Effect of different concentrations of potassium sorbate on lactic acid bacteria
It can be seen from the table that the higher the concentration of potassium sorbate added, the higher the pH value of the culture medium, which also has a small impact on the activity of lactic acid bacteria.
2.2 Effect of potassium sorbate on mold
The mold was cultured using Bengal red medium containing different concentrations of potassium sorbate, and it was found that the inhibitory effect on the mold was obvious. The specific results are shown in Table 2.
Table 2 Effect of different concentrations of potassium sorbate on mold
The inhibitory effect of potassium sorbate on mold has a great relationship with the number of dissociated acid molecules. The higher the concentration of potassium sorbate, the more acid molecules dissociated, and the more obvious the inhibitory effect on mold.
2.4 Discussion
The antifungal mechanism of potassium sorbate is the same as that of sorbic acid, mainly through the combination of the dissociated acid molecule and the sulfhydryl group of the microbial enzyme system to destroy the action of many enzyme systems. The effect of potassium sorbate addition on lactic acid bacteria changes with the concentration and pH value, mainly because the dissociated acid molecules affect the metabolic pathway of lactic acid bacteria producing lactic acid, which affects the enzyme activity of acid production, so its fermentation The pH of the solution was higher than that of the control. The addition of 0.1% and 0.2% potassium sorbate has basically no effect on lactic acid bacteria, and the addition of 0.3% and 0.4% potassium sorbate has little effect on the activity of lactic acid bacteria.
Potassium sorbate is a commonly used antifungal agent, which is widely used in food, feed and other industries due to its safety and structural stability. However, potassium sorbate has certain limitations in its use due to its use under acidic conditions to better inhibit mold. This article found through research that adding 0.2% potassium sorbate has basically no effect on the activity of lactic acid bacteria, but it has a better inhibitory effect on mold.
