Study On The Key Techniques Of Proeessing For Fresh-cut Carrot

The objective of this master thesis have been studied aiming to breakthrough thelimitation and be applied for industrialization based on the research of vacuum per-cooling process, new type of disinfectant and modified atmosphere packaging.As for the study about vacuum per-cooling, the effect of different thicknesses offresh-cut carrots and end-temperatures during vacuum pre-cooling were studied. Thevariations of weight loss rate, respiratory intensity, firmness and color of fresh-cutcarrots were determined during storage after the treatment of vacuum pre-cooling.The results showed that6mm-thickness disks of fresh-cut carrot and end-temperatureof6℃was the optimized condition of vacuum pre-cooling. Under this pre-coolingcondition, the weight loss rate of1.3%, the central temperature of1.5℃in the fresh-cut carrot and duration time of7.3min were obtained. Moreover, pre-cooling couldeffectively inhibit respiratory intensity, reduce weight loss rate and maintain sensoryquality of fresh-cut carrots compared with the intact carrots during storage.As for the study of new disinfectant on fresh-cut carrot, the optimal condition ofdimethyl dicarbonate (DMDC) sterilization on fresh-cut carrots was investigatedusing Box-Behnken model of response surface methodology (RSM)(version8.0.5b).The optimum processing parameters of DMDC sterilization were as following:sterilizing concentration200mg/L, ratio of material to sterilizing solution1:3,sterilizing time2min. The optimum reductions (log10) of bacteria and mould offresh-cut carrot treated by DMDC were3.515and2.632respectively.At the bottom of the optimal sterilization condition of DMDC, the reduction ofmicroorganisms and variation of nutritional and physiological quality in fresh-cutcarrot treated by DMDC was evaluated. The results showed the total aerobic platecount (TAPC) and count of total yeasts and moulds in the fresh-cut carrot treated byDMDC were significantly reduced (P <0.05) by3.01and3.43log CFU g-1respectively, in comparison with control (the fresh-cut carrot washed by sterile water).DMDC could also inhibit the activity of polyphenol oxidase (PPO) and peroxidase(POD) and be beneficial to the maintenance of vitamin C level, quality of fresh-cutcarrot during storage at10℃. DMDC made no marked impact on the β-carotenecontent of fresh-cut carrot. Therefore, DMDC was an effective disinfectant in fresh-cut carrot.High oxygen modified atmosphere packaging was one of the hottest packagingtechniques on fresh-cut fruit and vegetables in recent years. The aim of this study was to investigate the effects of super atmospheric oxygen modified combined with highbarrier film packaging on the quality of fresh-cut carrot during storage at differenttemperature (4℃、15℃、25℃), the packaging box filled with air as control. Theresults showed the loss of weight, loss of vitamin C and total carotene and therespiratory intensity of fresh-cut carrot packaged by super atmospheric oxygen weresignificantly increased than the control. But the content of phenol compounds infresh-cut carrot was higher than the samples packaged with air. In general, the qualityof fresh-cut carrot was not effectively maintained by super atmospheric oxygenmodified atmosphere combined with high barrier film packaging.