Study On The Processing And Preservation Technology Of Prepared Caixin

Caixin (Brassica chinensis L.) is a popular green-leafy vegetable in China, which isreported to contain high concentrations of vitamins and minerals. It is well known that there isa big challenge to maintain the freshness of green leafy vegetables during processing andstorage. Soft packaging is an effective way to extend the shelf life of green-leafy vegetables.In the current market, most of the soft packaged prepared-foods are poultry products butalmost no green vegetables are available. This is mainly because the prepared foods arepreserved by high-pressure steam sterilization or other conventional heat sterilization methodsthat may have negative effects on the color and texture properties of green vegetables. Withthe aim of improving the shelf life and keeping the product quality of prepared Caixin, theprocessing and preservation technology were researched in this study.To solve the softening and discoloration problems of prepared Caixin during processingand storage, the pretreatments of blanching, crisp-preserving and color-protectiontechnologies were studied. The results showed that the activity of peroxidase (the relativeresidual activity,8.53%) and polyphenol oxidase (the relative residual activity,1.24%) hadbeen well suppressed when Caixin was blanched for2min at95℃and then quickly cooled inice water bath, which could not only eliminate enzymatic browning, but also keep the productquality. With texture and sensory evaluation as indicators, the samples were treated with0.45%sodium alginate and0.3%calcium chloride to preserve a crisp texture; The bestcolor-protection technology got through single factor and orthogonal experiments was thatsocking samples with sodium chloride,10%edible glycerol and0.4%sodium carboxymethylcellulose for45min. The formulation was safe and efficient, and it could not only play a partin the color protection, but also meet people’s requirements for prepared Caixin.To solve the sterilization problem of prepared Caixin, controlling the growth of microbeson the basis of ensuring product quality, ZnO nanoparticles and dielectric sterilization werestudied. ZnO nanoparticle suspension had good storage stability and microwave heating didnot have bad effect on the dispersion stability. ZnO nanoparticles had good antibacterialactivity, and the sterilization effect increased with the increasing of ZnO nanoparticles(0.01-0.03g/kg). The method of microwave sterilization with two frequencies of915MHzand2450MHz were used for Caixin samples sterilization respectively, the color of preparedCaixin could become greener with certain microwave sterilization conditions. Microwavesterilization had some effect on the texture and flavor of prepared Caixin, but the sensoryquality of it was still within the acceptable ranger with appropriate sterilization conditions.Prepared Caixin had the best sterilization effect with the microwave condition of400W150s(2450MHz) with the temperature of about114℃. Radio frequency heating at27.12MHz wasselected for samples sterilization. The sensory evaluation results indicated that there were nosignificant differences among the RF treated and control samples on the sensory quality ofcolor, texture, flavor, taste and overall acceptability, it was more conducive to maintain theproduct quality compared with microwave sterilization. RF treatment of20mm/20min hadsignificantly reduced the total colony number of prepared Caixin with the temperature of about62℃, but its sterilization effect was less than microwave sterilization. Additionally, thecombined effect of ZnO nanoparticles and dielectric sterilization was better than the singlesterilization treatment. When the sterilization condition was400W150s microwave heating(2450MHz) combined with the addition of0.02g/kg ZnO nanoparticles, the total colonynumber of prepared Caixin could decrease to the degree of commercial sterility. Based on theabove results, the best sterilization condition of prepared Caixin was400W150s microwaveheating (2450MHz) combined with the addition of0.02g/kg ZnO nanoparticles.In order to predict the shelf life of prepared Caixin, with the total colony number as anindicator, the Gompertz equation was used to fit the growth of microbes in prepared Caixinduring cold storage, and the shelf life was concluded as104d. Additionally, the productquality of prepared Caixin could meet the industry standards for chilled prepared foods withinstorage period (SB/T10648-2012).