Inhibitory and fresh-keeping effects study of plant essential oil sodium alginate composite film on Agaricus bisporus

Abstract: Button mushroom (Agaricus bisporus) is one of the most popular mushrooms, traditionally cultivated in the world. Mushrooms are a good source of mannitol, vitamins, saccharides, organic bases and many mineral elements. However, button mushrooms only have a short shelf life, and they will lose their commercial value within a few days, due to browning, water loss, senescence and microbial attack. The short shelf-life of mushroom is an impediment to the distribution and marketing of the fresh product. Food spoilage and food poisoning caused by microbial infection during the harvesting, processing, transportation and storage of foods present an enormous threat to consumers and the development of food industry. Plant essential oil (EO) is an important volatile secondary metabolite in plants, which is well known for its high volatility, low residual generation, and very rare resistance problems. The purpose of this paper is to study the inhibitory effect of plant EOs on the main spoilage bacteria of mushroom during storage. Nine colonies were obtained by isolating and purifying the main spoilage microorganisms of mushroom. According to morphological identification, these colonies are 3 kinds of molds and 2 kinds of bacteria respectively. It was confirmed by pathogenicity test that the main pathogen of mushroom during storage was strain No. 3. The 18S rDNA sequence phylogenetic tree analysis of the pathogen showed that the pathogen No. 3 was closely related to Trichoderma sp. Four kinds of EO, which are Turmeric EO (TEO), Forsythia EO (FEO), Eucalyptus EO (EEO) and Angelica EO (AEO), were used to test the antibacterial activity against the Strain No. 3. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of preferred EO were determined by agar disk diffusion test. The results showed that EEO has the best inhibitory effect on Trichoderma sp., followed by FEO, while TEO and AEO have no obvious inhibitory effect. The MIC and MBC of EEO were 0.3125 and 0.625 μL/mL, respectively. The MIC and MBC of FEO were 0.625 and 1.25 μL/mL, respectively. Water vapor transmission rate, oxygen permeability, tensile strength and elongation at break of sodium alginate/EEO composite ?lm and sodium alginate single film were measured. The results show that the addition of EEO can significantly improve the gas barrier properties and mechanical properties of the membrane. The effects of four different packaging treatments on the physicochemical properties and microbial quality of mushrooms stored at 4°C for 12 d were investigated. The fresh mushrooms were packaged with the sodium alginate/EEO composite ?lm, sodium alginate single ?lm and PE film, and unpackaged mushrooms were used as control. The microbial levels and physicochemical properties such as weightloss, ?rmness, color, cell membrane permeability, and microbiological quality were measured. Although the highest weight loss (3.51%) was observed in the sodium alginate/EEO treatment at the end of storage, it was still lower than 5%. Mushrooms packaged in the sodium alginate/ EEO composite ?lm was signi?cantly (P<0.05) ?rmer than those packaged in the sodium alginate single film and PE ?lm. The cell membrane permeability the odium alginate/EEO ?lm was lower than those of the other treatments, and the browning index was similar. The sodium alginate/EEO ?lm was more effective in reducing microbial counts of mushrooms than the other two ?lms. The overall acceptability of mushrooms packaged in the sodium alginate/EEO ?lm remained good and within the limit of marketability after 12 d storage. The results suggested that the sodium alginate/EEO film could effectively reduce the senescence and pathogenic decay of mushrooms. The results of this study can provide a theoretical basis for the selection of antiseptic and natural bactericidal preservatives for mushroom during storage.