Preparation Of Active Edible Membrane And The Function On Apple Preservation

Apples contain plenty of nutrients and have appealing flavor, so that they are increasingly important in people's daily life and well received by people. But apples have regional and time limits, and apples have short shelftime at room temperature. The mould are one of the important reasons for apple rot, such as Penicillium expansum. Chemical fungicides can reduce the disease incidence effectly. But because of the worries from the public about pesticide residues and pathogen resistance to fungicides, most countries start to limit the use of chemical fungicides even forbidden. So people pay more attention to find a safe and simple preservation method. The study made coating freshness technique and BIOLOGical preservation technique together and all the objects used were natural and non-poisonous. A defined active edible membrane was made with marine antagonistic yeast into AGC-GG blending membrane, which was used in fruit preservation, in order to provide material to new technology of apple preservation. The results were as follows:Firstly, it was purposive and pointive to screen marine yeast which could inhibit the growth of Penicillium expansum under large range of temperature and oligotrophy. So a suitable yeast strain was screened in the definite depth of seawater in order to adapt to the micro-environment on the surface of apples, meantime, the strain could hardly produce ethanol under anaerobic fermentation. Then the screened yeast was identified by BIOLOG system and 26S molecule method as Candida orthopsilosis. Finally, the relating experiments were carried on about the basic properties and growing condition of the marine yeast, and it showed that the yeast cell was spheroidal, and it could form cell string and had great reproductive performance. It could reach biomass of 10~8 CFU/mL after 16 h, and it could grow on the barren culture medium. The best medium components were: 3 % glucose, 3 % maltose, 1.5 % yeast extract, 0.15 % KH2PO4,0.03 % CaCl2,0.2 % MgSO4 and 0.35 % NaCl. Meantime, the relative experiments of inhibiting Penicillium expansum were carried on in apples, and the result showed that the main inhibiting part was yeast cells, while yeast zymotic fluid could not exhibit inhibition abilities. In addition, the abilities of inhibition were relative with yeast concentration and inoculation interval. The yeast inoculated before the mould and the bigger concentration of yeast existed, the greater abilities of inhibition showed.Secondly, the antifungal mechanisms of the marine antagonistic yeast were investigated, in order to express the ability of inhibiting Penicillium expansum. It was compared with C. laurentii which was considered as the yeast with great abilities of inhibiting the mould. The result showed that the marine antagonistic yeast could inhibit mould for a long time, and the inhibition zone was even 8 mm after 7 d. But C. laurentii could not inhibit after 3 d and there were full of spores after 7 d. Meantime, the marine antagonistic yeast could supass the abilities of C. laurentii on inhibiting spore germination, inhibiting germ tube elongation, competition in space and nutrition with the mould. From the experiments in apples, it showed that both of the marine antagonistic yeast and C. laurentii could inhibit the growth of Penicillium expansum significantly. They could decrease the rot rate and rot extent, and decreased the rot extent of apples from 31.3 mm of control group to 12.9 mm and 14.4 mm. The marine antagonistic yeast showed greater abilities of inhibition. In addition, two yeasts could inhibit mould (Penicillium expansum, aspergillus niger and aspergillus flavus) to some extent, but could hardly inhibit bacteria (escherichia coli, staphylococcus aureus, clostridium perfringens, bacillus subtilis and pseudomonas fluorescens). It showed that the inhibition spectrum was similar between the two yeasts. But for the MIC experiment, the MIC of the marine antagonistic yeast was 106 CFU/mL which is much lower than that of C. laurentii (108 CFU/mL), so the inhibiting abilities of the marine antagonistic yeast were greater. On anoter aspect, the marine antagonistic yeast could multiply to more biomass quickly under low temperatures and oligotrophy comparing with C. laurentii.Thirdly, many kinds of edible membrane (gellan gum, gelatin, carrageenan, xanthan gum, gum tragon, carboxymethyl cellulose, konjac glucomannan and high methoxyl pectin) blending with sodium alginate (AGS) were studied, and AGS - gellan gum (GG) (1 : 9) was chosen as the experimental edible membrane through orthogonal optimization test. Meantime, aiming at improving the stability of the membrane which could gurantee it from dissolution by condensed water to keep the sensory effect of apples, the crosslinking method with CaCl2 was adopted into the edible membrane so that it could adhere to the surface of apples greatly. Finally, micro-testings such as infrared detection, DSC and EMS were carried on, and it was found that the edible blending membrane had good compatibility and performed multilayer and network configuration. The result also showed that the edible membrane has little thickness, low level of water vapor permeability and oxygen permeability and good mechanical properties, so that it could be well used in apple preservation.Fourthly, the marine antagonistic yeast was added into the AGS-GG blending membrane to make a active edible membrane smearing to apple surface, and then the membrane was crosslinked by CaCl2 and used in apple preservation experiment. The result showed that the active edible membrane could play the roles of edible membranes and antagonists, so it could decrease the weightloss rate and decay rate, maintain the high level of fruit firmness and compressive strength, contain much soluble solid content, and have good physical properties. In addition, active edible membrane could slow down the decrease rate of VC content, polysaccharide content and titratable acid content and it could also surpress the raise of MDA. The marine antagonistic yeast could induce apples to produce some protective enzymes, such as SOD, CAT and so forth. Therefore, the active edible membrane could effectly control the happeness of natural decay and microbial contamination, and keep the qualities of apples.