【作者】 刘倩；

【导师】 张慜；

【作者基本信息】 江南大学 ， 农产品加工及贮藏工程， 2014， 硕士

【摘要】 青菜含有丰富的矿物质和维生素，但鲜嫩易萎蔫，制成软包装调理产品可以有效延长青菜的贮藏期。目前软包装调理产品主要以禽肉类食品为主，很少以绿色叶菜作为原料，究其原因主要是因为绿色叶菜类调理产品加工及贮藏期间极易变色变软，而且其杀菌方式主要以高压蒸汽灭菌等热杀菌为主，会对绿色叶菜的色泽和质构产生不良的影响，影响其感官品质。针对以上问题，本论文研究了调理青菜加工及保藏的关键工艺，在保证产品品质的前提下提高了货架期。为解决青菜加工及贮藏过程中易变色变软的问题，本文首先研究了热烫前处理和护色保脆预处理。青菜经95℃/2min热烫处理后，过氧化物酶（相对残余活力8.53%）和多酚氧化酶（相对残余活力1.24%）的活性可以得到很好的抑制，这不仅消除了酶促褐变的隐患，又可以减少热烫对青菜品质的影响。以质构和感官评价为指标，确定青菜保脆处理的工艺条件为采用0.45%海藻酸钠和0.3%氯化钙进行减压渗透浸泡；通过单因素试验和正交试验得到最佳护色工艺为由5%氯化钠、10%甘油和0.4%羧甲基纤维素钠组成的混合溶液浸泡45min。该工艺安全高效，不仅可以起到很好的护色效果，还能满足人们对调理青菜口感的要求。为解决调理青菜杀菌保藏难的问题，在保证产品品质的基础上控制微生物的生长，本文研究了纳米ZnO抑菌和介电（微波和射频）杀菌。纳米ZnO分散液的贮藏稳定性较好，且微波处理对其稳定性无不利影响。纳米ZnO具有良好的抑菌效果，当添加量为0.01～0.03g/kg时，随着添加量的增加杀菌效果逐渐增强。采用915MHz和2450MHz两种频率的微波杀菌方式处理调理青菜，在一定的微波条件下，调理青菜的颜色变得更加鲜绿。调理青菜经微波杀菌后质构会变差，且风味也有轻微的变化，但合理控制杀菌条件能使产品的感官品质仍在可接受的范围。当微波条件为400W150s（2450MHz）时，产品温度在114℃左右，可获得最佳的杀菌效果。采用27.12MHz射频处理调理青菜，射频处理前后产品的色泽、质构和风味等品质没有显著性差异，与微波杀菌相比更有利于保持产品的感官品质。当射频条件为20mm/20min时，产品的温度在62℃左右，杀菌效果最佳，但不及微波杀菌。此外，纳米ZnO联合介电杀菌的效果远高于单一杀菌处理，杀菌条件为微波加热400W150s（2450MHz）与添加纳米ZnO（0.02g/kg）相结合时可使调理青菜达到商业无菌的条件。因此，调理青菜的杀菌条件最终确定为微波加热400W150s（2450MHz）与添加纳米ZnO（0.02g/kg）联合处理。为预测调理青菜的货架期，本文以菌落总数为指标，利用Gompertz模型对调理青菜冷藏期间的微生物生长情况进行拟合，得到货架期为104d，而且在此货架期内产品的各项品质指标均符合冷藏调制食品行业标准（SB/T10648-2012）的要求。更多还原

【Abstract】 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).更多还原