| The aim of this paper was to investigate the synergistic sterilization effect of naringin andpulsed electric fields (PEF) treatment on Saccharomyces cerevisiae. Firstly, naringin waschelated with two kinds of metal salts, and then the inhibitory effects and mechanisms ofnaringin and its metal complexes were explored. Meantime, the lethal and sub-lethal effects ofPEF treatment on Saccharomyces cerevisiae were investigated., Finally, the synergisticsterilization effect of naringin and PEF on Saccharomyces cerevisiae was systematicallyexamined. The results showed that naringin was successfully chelated with zinc acetate andcopper acetate in optimum conditions. The UV and IR analysis of the two naringin-metalcomplexes indicated that the chelating groups of naringin were4-carbonyl and5-hydroxyl.There was a good consistence between the theoretic and analytic data of the composition ofthree main elements (carbon, hydrogen, metal)..Inhibition zone method and double dilution method were used to study the antibacterialactivities of naringin and its metal complexes. The results indicated that the antibacterialactivities of narigin-metal complexes were much stronger than narigin. The inhibition effects ofdifferent products against various organisms are as follows: E. coli, naringin-Zn (Ⅱ)> naringin-Cu (Ⅱ)> naringin; Staphylococcus aureus, naringin-Zn (Ⅱ)> naringin-Cu (Ⅱ)> naringin;Aspergillus niger, naringin-Cu (Ⅱ)> naringin-Zn (Ⅱ)> naringin; Saccharomyces cerevisiae,naringin-Zn (Ⅱ)> naringin-Cu (Ⅱ)> naringin.Naringin and its metal complexes could accelerate the death of Staphylococcus aureus,increase the permeability of its cell membrane and cause the leakage of its electrolyte, proteinsand nucleic acids. The normal physiological metabolism of the bacterial cell was affected so thatthe cell dies.PEF sterilization causes a part of microorganisms being sub-lethal, and the number ofwhich is larger with higher electric field strength. However, when the electric field strengthreaches a critical value, the destruction effect to the cell membranes is so strong that irreversibledamages increase. With the decreasing of the cell self-repairing ability, the number of sub-lethal cells decreases.There were two synergistic methods：1) Saccharomyces cerevisiae mixed with naringinsolution, followed by PEF treatment. The colony reduction index of Saccharomyces cerevisiaetreated by0.7g/L naringin for5h along with PEF (20kV/cm) for2400，3600and4800μsreached0.45、0.70and1.21, respectively, which were almost3times of the index by PEF treatment alone, and4times by naringin alone.2) Saccharomyces cerevisiae treated by PEF wascultured in the medium containing naringin and metal complexes. The germicidal effects weresignificantly improved and was close to the (4%NaCl) selective medium. A large number ofdamaged microorganism cells were further damaged by naringin and its metal complexes, cells’slef-repairing ability was weakened, leading to the death of Sub-lethal microorganisms, and thesub-lethal rate caused by PEF decreased. |
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