【作者】 赵金红；

【导师】 倪元颖；

【作者基本信息】 中国农业大学 ， 食品科学， 2014， 博士

【摘要】 本文采用了渗透脱水预处理和冻结联合应用加工芒果,研究不同预处理对冷冻芒果品质、多酚和挥发性成分的影响；同时,研究芒果渗透脱水—冻结的过程,以细胞为单元建立一维质量平衡方程和热平衡方程；将玻璃态贮藏理论应用在芒果冻藏中,研究芒果的玻璃化转变温度与状态图；并进一步验证玻璃态贮藏和渗透脱水—冻结对冻藏期内芒果品质的贮藏效果。得到的主要结果如下：(1)渗透脱水—冻结与传统冻结相比,芒果的冷冻时间减少,熔点下降,冷冻速率加快。渗透脱水—冻结芒果在色泽、硬度、汁液流失率、维生素C含量和其他生理指标方面都优于未处理和漂烫组。渗透脱水—冻结可使新鲜芒果的PPO活性下降,POD活性升高。(2)通过研究不同渗透脱水—冻结加工对芒果品质的影响,结果表明渗透液浓度越大,渗透脱水预处理样品的冻结速率越快。与新鲜芒果和芒果在蔗糖溶液中渗透预处理后相比,样品在葡萄糖和麦芽糖溶液中熔点(Tm)值较低。另外,渗透脱水—冻结样品在麦芽糖溶液中预处理后,维生素C含量增加了23.5～73.0%,总色差减少了2.6～39.2%以及汁液流失率降低了0.7～9.7%；样品在葡萄糖溶液中硬度增加了16.4～36.2%。通过主成分分析(PCA)和组间距离分析,得到45%的麦芽糖渗透脱水—冻结是芒果冷冻的最优条件。(3)渗透脱水—冻结与传统冻结相比,能够阻止芒果总酚含量的减少。与其他3种糖液预处理相比,葡萄糖渗透脱水—冻结后总酚含量最高。不同冷冻加工处理对芒果的各种酚类物质含量有显著性影响(P<0.05),没食子酸、芥子酸和槲皮素含量降低,对羟基苯甲酸和对香豆酸含量升高。与传统冻结相比,渗透脱水—冻结能够较好地保持芒果的多酚含量。(4)芒果经过不同渗透脱水—冻结加工处理后产生了一些新的挥发性成分。直接冷冻后有些挥发性成分未被检测到,并且有些成分含量降低。与传统冻结相比,渗透脱水—冻结能较好地保持芒果中酯类等其他香气成分。其中麦芽糖渗透脱水—冻结后,鉴定出的香气成分最多。(5)以细胞为单元建立了芒果一维渗透脱水质量平衡方程,与一维冻结过程的热平衡方程,通过实验值和模拟值的比较,证明本文建立的渗透脱水和冻结数学模型是可行的。本文预测了细胞内、外水质量浓度的分布,以及细胞外蔗糖质量浓度的分布。模拟结果得到细胞外水质量浓度分布曲线与细胞内水质量浓度分布曲线趋势相同,在任意位置任意时刻细胞外水质量浓度比细胞内水质量浓度较小。越靠近渗透液的位置细胞外蔗糖质量浓度越高,随着向中心位置方向移动,细胞外蔗糖质量浓度逐渐变小。(6)芒果粉末在25℃的吸附等温线符合GAB模型,单分子层水分含量(Xm)为0.109g/g湿基。通过DSC测量冻结点温度和玻璃化转变温度与水分含量的关系,建立了芒果状态图。从芒果状态图上,可以得到最大冻结浓缩状态时的固形物质量分数(Xs’)为0.84g/g湿基,对应的冻结终点特征温度(Tm’)为-33.0℃,特征玻璃化转变温度(Tg’)为-54.6℃。其他特征玻璃化转变温度Tg"值和TG’"值分别为-43.2℃和-36.8℃。对应芒果的非冻结水的水分含量为0.16g/g湿基(1-Xs’)。芒果的状态图既可以用来预测芒果冻藏过程中的稳定性,也可以预测芒果干燥条件下的稳定性,并且能提供最优的加工条件。(7)经过6个月的冻藏(-18℃)后,渗透脱水—冻结使得芒果的总色差降低了12.5～36.8%,硬度提高了35.8～65.5%,汁液流失率减少了11.3～44.5%,维生素C含量提高了21.2～134.8%。结果显示,较高浓度的渗透脱水前处理能够较好地保持冻藏芒果的品质,而40%的渗透液浓度是芒果冷冻保藏的最优条件。同时,芒果阴面(较硬)比阳面(较软)更适合于冷冻保藏。随着冻藏时间延长,渗透脱水前处理的冻藏芒果比直接冷冻的芒果品质下降缓慢。与普通冻藏(-18℃)相比,玻璃态贮藏(-55℃)能够提高芒果的色泽、硬度、汁液流失率、维生素C含量和其他生理指标。更多还原

【Abstract】 The objectives of this study were to use the combining osmotic dehydration pre-treatment with freezing technique to improve the quality of frozen mango. The effects of different pre-treatments on the quality attributes, phenolic compounds and volatile flavor compositions of frozen mango were investigated. Moreover, in order to simulate the whole processes of osmotic dehydration and freezing, a successive one-dimensional mass and heat transfer modeling approach based on mango cell as a basic unit was developed. In addition, glass transition temperature and state diagram of mango were investigated to predict the storage stability of frozen mangoes. Moreover, the effects of storage at glassy state and osmo-dehydrofreezing on the quality attributes of frozen mangoes during storage were also investigated. The main results and conclusions were made as follows:(1) The osmo-dehydrofrozen mangoes obtained a shorter freezing time, a lower melting point and a higher freezing rate than that of the conventionally frozen samples. The osmotic dehydration pretreatment significantly improved the quality attributes of frozen mango in terms of color, hardness, drip loss, vitamin C content and other physical properties compared with the untreated or the blanched ones. In addition, the osmo-dehydrofreezing can inhibit the polyphenol oxidase activity, but activate the peroxidase activity.(2) Freezing time of the osmotic-dehydrated mangoes was reduced by increasing osmotic concentration due to less water to be frozen. The melting temperature of mango cuboids dehydrated in glucose and maltose solutions was lower than that of fresh samples and samples in sucrose solution. In addition, the dehydrofrozen samples pretreated in maltose had higher quality in vitamin C content (increasing by23.5-73.0%), color (color change reducing by2.6-39.2%) and drip loss (reducing by0.7～9.7%) than those pretreated in other osmotic solutions. The cuboids pretreated in glucose displayed higher hardness (increasing by16.4-36.2%). Based on principal component analysis (PCA) and group distance, osmotic dehydration in45%maltose was proposed as the most favorable freezing conditions.(3) The osmo-dehydrofreezing could prevent total phenolic losses of mangoes compared with conventional freezing. The dehydrofrozen samples pretreated in glucose had higher content of total phenolic than other sugars. After different freezing processes, there were significant differences (p<0.05) in the content of individual phenolic compounds; some phenolic compounds (including gallic acid, quercetin, and sinapic acid) decreased, while others (including p-hydroxybenzoic acid and p-coumaric acid) increased. The current work indicates osmo-dehydrofreezing improves the content of individual phenolic compounds in frozen mangoes.(4) The new volatile compounds were present in osmotically pretreated mangoes after freezing. Some compounds present in fresh samples tended to decrease or disappear after conventional freezing. The osmo-dehydrofreezing could improve the esters and other major aroma compounds of frozen mangoes compared with conventional freezing. The dehydrofrozen samples pretreated in maltose had more volatile compounds identified than other sugars.(5) The one-dimensional mass balance equations and thermal balance equations were established. And a good agreement was obtained between the simulated and experimental results, proving that two models were practical. Numerical results could describe the distribution of water and sucrose in the intracellular and extracellular volumes of mangoes during osmotic dehydration. The distribution of water in the intracellular was similar with that of water in the extracellular volumes. The density of water in the extracellular volumes was lower than in the intracellular volumes. In addition, the density of sucrose in the extracellular volumes was higher when the distance was close to the interface, and it gradually become lower when the distance was close to the center.(6) The water sorption isotherm of freeze-dried mango (25℃) was established by GAB model and the monolayer moisture content was found to be0.109g water/g sample (d.b.) as the stability criteria by water activity concept. The state diagram provided an estimate of maximal-freeze-concentrated solutes at0.84g solids/g sample (w.b.)(Xs’) with the characteristic temperature of end point of freezing (Tm’) being-33.0℃and the characteristic glass transition temperatures Tg’being-54.6℃. Other characteristic glass transition temperatures Tg "and Tg’"were-43.2℃and-36.8℃, respectively. The unfreezable water in mango was obtained as0.16g water/g sample (w.b.)(1-Xs’). The state diagram can be used in predicting the storage stability of frozen and dried mangoes as well as in providing the optimum processing conditions.(7) The osmotic dehydration pretreatment can improve the quality attributes of frozen mango in terms of color (total color difference reducing by12.5～36.8%), hardness (increasing by35.8～65.5%), drip loss (reducing by11.3～44.5%) and vitamin C content (increasing by21.2～134.8%) compared with the untreated ones after6months of frozen storage (-18℃). Pretreatment with higher solution concentration showed smaller alterations in the quality attributes of samples. Through comprehensive analysis, dehydration in osmotic solution of concentration40%was considered as the optimum pretreatment conditions for frozen storage. In addition, the quality was better maintained in shaded side (firmer) of mangoes than the sun-exposed side (softer). With progression of storage time, although there was a reduction in the quality of samples, mangoes pretreated by osmotic dehydration showed less reduction than the untreated. The quality attributes of frozen mango could be improved at glassy state during frozen storage (-55℃).更多还原