| Dynamic high-pressure processing is considered as one of the most potential and promising physical modification technologies in the latest food processing and preservation development.In the process of ultra-high pressuree homogenization(UHPH) can not only kill food-borne microorganisms,but bring less detriment to food compounds such as nutrients,pigments,and flavoring agents,et al.Aussie bean is a full-nutrient food due to have abounding proteins and rational amino acids.So Aussie bean proteins are commonly used as a functional ingredient and additive for food formulation because of its excellent function properties and good nutritional values.Thermal preservation results in denaturation of proteins and precipitation of beverage containing protein,thus affects the quality of products.The lupin-milk has been studied by multiple analysis ways.The effects of high pressuree homogenization on the physicochemical and microstructural characteristics of lupin-milk have been analyzed,in order to provide the reference for the application of soybean products,modification of soybean protein,and food safety. Combined effect of lysozyme and high pressure homogenization on microorganism in model systems based on skim milk was discussed,too.And try to seek for a novelty nonthermal pasteurization technology.The experimental results of this paper are summarized showed as follows:1.Effects of ultra high pressure homogenization(UHPH) on physicochemical, microbial and microstructural characteristics of lupin-milkThe effects of ultra high pressure homogenization(UHPH) on physicochemical, microbial and microstructural characteristics of lupin-milk was studied and compared with lupin-milk(control) processed with conventional homogenization pressure(25MPa) used in industry.UHPH treated lupin-milks were compared with the control lupin-milk,and the result of microbiological quality showed that UHPH was reducing the total number of bacteria,reaching reductions of 4 logCFU/mL at 175MPa with 6 passes and results of levels of orthogonal experiment showed the pressure was the most effective on sterilization. Physicochemical parameters assessed in lupin-milk were viscosity,color,and particle size. Color differences between UHPH treatment and control were found that the UHPH treatments increased the L*,a*and△E* values and reduced the b* value of treated lupin-milk,moreover the maximum difference value of△E* between the treated and control was 1.63 which was noticeable difference.And the UHPH treatments induced a reduction in viscosity valuesk and a enhencement in physical stability index values of treated soymil compared with control.With the higher the pressure and the more passes employed,the smaller was the particle size.Images of transmission electron microscopy showed the distribution and general characteristics of the particles and structures of samples. No structures in coalescence process were observed after UHPH treatment.Differences of size and distribution of globules depending on the treatment applied to lupin-milk could be seen.More detailed images of protein could be observed,evidencing that the protein fraction in the continuous phase appeared more disperse that in UHPH lupin-milks.2.Combined effects of ultra high pressure homogenization and lysozyme on microorganismIt was studied the reduction of a population of Gram positive and Gram negative species inoculated in in skim milk by the combination of ultra-high pressure homogenization(UHPH) treatment and the use of lysozyme as antimicrobial.The minimum inhibitory concentration(MIC) of lysozyme against bacteria showed that lysozyme had a different extent of inhibition against Gram positive and Gram negative species.Escherichia coli.Lactobacillus plantarum were the most pressure resistant species,while Bacillus subtilis,Pseudomonasputida,Staphylococcus aureus were found to be very sensitive to the hyperbaric treatment.The enzyme addition enhanced the instantaneous pressure efficacy on almost all the considered species as indicated by their instantaneous viability loss following the treatment.Moreover,the combination of the enzyme and high pressure homogenization significantly affected the recovery and growth dynamics of several of the considered species.The enzyme addition enhanced the treatment efficacy on the Gram negative species as indicated by the comparison of data relative to surviving cells of samples homogenized at different pressures in the presence or absence of lysozyme.HPH-treated lysozyme(75MPa) reduced the cell load after 10h from treatment of 1.93 logcfumL in comparison with the control.On the other hand,a treatment at 100 MPa enhanced the lysozyme activity and induced,after an incubation of about 6 h,an increase of the L. plantarum deactivation rate with respect to the control.These results preliminary evidence that the interaction lysozyme-high pressure homogenization should not be attributed only to the effect of pressure on the integrity of the cell walls or outer membrane for the Gram negative species.As shown by the SEM(scanning electron microscopy) micrographs,at the pressure level applied(130 MPa) severe damages,including shrinkage of surface,rupture of parital cell wall,also the discharge of cytoplasmic content and even breakage of microbial cells,were observed.These results suggested that the combined effects of the process and enzymes cannot be attributed to a mere sum of their individual actions but to their synergetic effect. |
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