| Food spoilage caused by microorganisms has brought great economic losses to food processing enterprises, and even harm to human health. With the improvement of people’s safety awareness, it is necessary to seek a safe, efficient and green natural preservative. China is rich in bamboo resources with a wide range of planting area. Essential oil (EO) from bamboo leaf is a kind of secondary metabolites, which has broad spectrum of antimicrobial activity. It can be used as a natural preservative with broad application prospects. Bamboo leaf essential oil (BLEO) as the research object and the common food-related microorganisms (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Saccharomyces cerevisiae) as tested microbies, the antimicrobial activity of BLEO and its combination was investigated, firstly. Then the chemical components and the antimicrobial stability of BLEO and its combination were studied. Finally from the cellular level (apparent morphology, cell contents, cell fatty acid composition) to explore the mechanism of the antimicrobial activity of BLEO and BLEO-combination. The main contents and results of this paper are as follows:(1) To compare the antimicrobial activity of BLEO, cinnamon EO and oregano EO by the bacteriostatic circle method, we found that three kinds of EOs have strong antimicrobial activity against four food-related microorganisms. In combination with the MIC, the results showed that E.coli was the most sensitive one to EOs. So, we choose the E.coli bacteria as subject to combine BLEO with cinnamon EO and oregano EO. Through antimicrobial activity assay and sensory evaluation, the best antimicrobial effect was the one that BLEO to oregano EO is 8:2 (V/V, concentration is 36.00 mg/mL), and the inhibition zone diameter of E.coli is 15.83±0.31mm. The MIC of BLEO-combination against four tested microorganisms is 0.28-0.56mg/mL. Its antimicrobial activity is 2-4 times more than that of BLEO.(2) Chemical components of EOs were analyzed and identified by GC-MS:Forty-one compounds consisting up to 97.36% of the BLEO were identified. Hexadecanoic acid (19.35%), phytol (10.54%) and pentacosane (9.89%) were found to be major components. The GC-MS analysis revealed 73 compounds representing 94.53% of the BLEO-combination containing carvacrol (25.82%), phytol (7.42%), pentacosane (6.38%) and hexadecanoic acid (6.25%).The BLEO-combination had the same acids as BLEO, but its content reduced from 25.23% to 10.09%, and the degree of reduction is more than half; the content of ketones, aldehydes, alcohols and hydrocarbons were significantly decreased, but the kinds of those components were increased, and the increasing species of them are mainly compounds with unsaturated double bond and hydroxyl. Carvacrol and thymol were detected in BLEO-combination, which are not detected in BLEO. In addition, the species and content of ester components increased.(3) By comparing the effects of pH, temperature and ultraviolet irradiation on antimicrobial activity of EOs, the results showed that the antimicrobial effect of BLEO and BLEO-combination was decreased with the increase of pH, and it was stable to high temperature and ultraviolet radiation.(4) Through test of microbial growth curve, the release of cell constituents, the content of sugar and protein, the changes in the percentage of cell fatty acids and the observation of atomic force microscope, the antimicrobial mechanisms of EOs from bamboo leaves and its combination were studied. Results showed that the mechanism of antimicrobial activity of BLEO and BLEO-combination against the tested strains, on the one hand, EOs disrupt the growth of microbes by inhibiting the absorption and utilization of nutrients;On the other hand, they damage the structure of cell membrane and increase the cell membrane permeability, leading to the leak out of cell contents and the death of cell. |
