真空冷冻干燥的羊乳及其分离产物的差示扫描量热法分析
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陕西师范大学食品工程与营养科学学院

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陕西省科技计划重大项目;陕西师范大学中央高校基本科研业务费专项; 陕西师范大学大学生创新创业训练项目


Differential Scanning Calorimetry Analysis of Vacuum Freeze Dried Goat Milk and Fractionation Products
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1.College of Food Engineering and Nutritional Science,Shaanxi Normal University,Xi’an 710119;2.China

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    摘要:

    为研究羊乳经冷冻干燥后的差示扫描量热法特征,指导羊乳生产加工。利用离心分离、等电点沉降过滤等方法分离生羊乳,得到各分离产物如:脱脂羊乳、乳脂、乳清、乳酪,经真空冷冻干燥48h后为粉状,用差示扫描量热仪对各冻干样品进行扫描,得到DSC热相图,并进行分析。结果表明,在羊乳及各分离产物的DSC热相图中,鉴定发现存在2个与脂肪熔融相关的吸热峰,1个与蛋白质熔融变性相关的吸热峰,1个与乳糖熔融产生的复杂放热峰,1个由乳糖引起的玻璃态转化温度Tg",1个由酪蛋白引起的玻璃态转化温度Tg",这些转化都不是单独出现的,无法在某单一组分中观察到上述所有热转化,这是由于不同成分之间存在着相互作用而产生的掩蔽、叠加、延迟等现象导致的。全脂乳粉分离为乳脂和脱脂乳粉后,乳糖的玻璃态转化温度、脂肪的吸热融化等指标发生了变化;脱脂乳粉分离为乳清和乳酪后,玻璃态转化温度、蛋白质变性吸热等指标发生了变化。DSC可作为一种研究评价冷冻干燥处理的羊乳粉物理性质以及鉴别乳组分、乳脂晶型和含量、乳蛋白种类、是否脱脂的工具。结果可为阐释冻干羊乳粉制品的独特特性、功能性和商业价值的开发提供理论支撑。

    Abstract:

    To study the characteristics of differential scanning calorimetry (DSC) of freeze-dried goat milk and guide the production and processing of goat milk, the fractionation of raw goat milk was carried out by means of centrifugal separation, isoelectric point sedimentation and filtration. The fractionation components, such as skimmed goat milk, cream, whey and caseins, were turned into powder after vacuum freeze-drying for 48 hours. The freeze-dried samples were scanned by differential scanning calorimeter to obtain and analyze the DSC thermal phase diagram. The results from DSC thermal phase diagram of the goat milk and each fraction showed two endothermic peaks (a, b) related to fat melting, one endothermic peak (c) related to melted protein denaturation, one complex exothermic peak (d) produced by lactose melting, one glass transition temperature Tg" induced by lactose, one glass transformation temperature Tg" caused by casein. All above-mentioned thermal transformations were not isolate and could not be observed in a single component, which was due to the phenomena of mutual masking, superposition and delay existed among different components. After the whole milk powder was fractionated into cream and skimmed milk powder, the glass transition temperature of lactose and the endothermic melting of fat were changed. After the fractionation of skimmed milk powder into whey and casein, the glass transition temperature, protein denaturation, heat absorption and other indexes were also changed. The DSC could be used as a tool to study and evaluate the physical properties of freeze-dried goat milk powder and to identify the milk components, the crystal and content of cream, the types of milk protein, and skimmed or not. These results might provide theoretical support to explain the unique characteristics, functions and commercial value of freeze-dried goat milk powder products.

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  • 收稿日期:2020-04-30
  • 最后修改日期:2020-12-29
  • 录用日期:2020-07-10
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