不同变性淀粉对冷冻面团热力学特性的影响

采用差示扫描量热法(DSC)研究4种不同种类变性淀粉对冷冻面团热力学特性(玻璃化转变温度、冰晶融化特性和可冻结水含量)的影响。结果表明,冷冻面团的玻璃化转变温度在-30℃左右,不同变性淀粉对冷冻面团玻璃化转变基本无明显影响;添加5%马铃薯羟丙基淀粉、木薯羟丙基淀粉和木薯醋酸酯淀粉可以显著降低冷冻面团冰晶融化范围,面团中形成的冰晶大小更加均匀;冷冻面团可冻结水含量随着马铃薯醋酸酯淀粉和马铃薯羟丙基淀粉添加量的增加呈降低趋势,添加10%木薯羟丙基淀粉时,面团可冻结水含量显著低于空白组,而木薯醋酸酯淀粉对面团可冻结水含量无显著影响。     

乳化剂对冷冻面团水分状态和玻璃化转变温度的影响

乳化剂能通过改变面团中的水分状态来改变面团的玻璃化转变温度(Tg)和低温贮藏后的微观结构。利用低场核磁共振技术(LF-NMR)研究乳化剂对面团中水分状态的影响,并利用差示扫描量热法(DSC)和扫描电子显微镜(SEM)研究乳化剂对面团的Tg和低温贮存后面团微观结构的影响。结果表明：乳化剂能不同程度地降低面团中自由水含量,当加入0.15%双乙酰酒石酸单(双)甘油酯(DATEM)时,面团中自由水含量相对空白面团减少了5.78%;乳化剂也改变了面团的Tg,空白面团的Tg为－31.3℃,当加入0.50%的单甘酯时,面团的Tg为－17.3℃,提高了14℃,而山梨醇酐单硬脂酸酯(SP60)和卵磷脂在本实验的添加量范围内,未能将面团的Tg显著提高;乳化剂能不同程度的改善低温贮藏后面团的微观结构,尤其是加入0.50%单甘酯或0.15% DATEM后,面团实现玻璃化贮存,其微观结构得到了很好的保护。     

超细纤维合成革玻璃化温度影响因素的探讨

采用差示扫描量热法(DSC)对超细纤维合成革的各个组分进行测试,探讨了尼龙-6、聚氨酯PU含量和表面活性剂及其它助剂对超细纤维合成革玻璃化温度(Tg)的影响。试验结果表明:尼龙-6对合成革的Tg影响最大,聚氨酯也有一定影响,其它成分影响不明显,研究结果为改善超细纤维合成革的Tg和使用性能,提供一定的理论依据。     

赤藓糖醇对南美白对虾肉玻璃化转变温度与状态图的影响

南美白对虾肉（PV）冻藏期间极易出现蛋白质变性,为提高虾肉贮藏稳定性,研究了PV与按虾肉质量添加5%赤藓糖醇的虾肉（PV-E）的吸附等温线;测定了PV与PV-E的玻璃化转变温度（Tg）和冻结点温度（TF）。采用Gordon-Taylor方程与Chen’s方程拟合数据,探讨添加赤藓糖醇对虾肉状态图的影响。结果表明,PV与PV-E水分吸附均为III型等温线,GAB模型为描述虾肉水分吸附特性的最适模型。PV与PV-E的Tg随着湿基含水率升高而降低;相同含水率时,PV-E的Tg高于PV。PV与PV-E的TF随着固形物含量的增加而降低。PV与PV-E最大冷冻浓缩溶液时的玻璃化转变温度T’g分别为-77.09℃和-62.23℃,与之对应的溶质含量分别为0.672 g/g和0.686 g/g。赤藓糖醇可作为一种新型抗冻剂,用于提高虾肉冻藏期间的贮藏稳定性。      

浅述用差示扫描量热法研究食品的玻璃化转变

食品材料所处的状态———玻璃态或橡胶态会对食品体系的粘度、脆度、结晶、塌陷以及冰晶的形成等物理化学及质构等性质产生重要的影响。介绍了差示扫描量热法(DSC)测定玻璃化转变温度在食品中的一些运用。     

Glass Transition Temperatures Determined using a Temperature-Cycling Differential Scanning Calorimeter

Glass transition temperatures, T_g, of polystyrene, polyvinylpyrrolidone, polydextrose, gelatin, corn flakes, pasta, and aqueous glucose/glycine solutions were determined using a differential scanning calorimeter which cycled the temperature while the net temperature increased at a constant rate. Operating conditions of the modulated differential scanning calorimeter^(tm) (MDSC^(tm)) for optimizing the endothermic baseline shift associated with the glass transition were a scan rate of 5°C/min with an amplitude of ± 1°C over a modulation period of 60 or 100 sec. The MDSC successfully separated the glass transition from other irreversible thermal changes in simple food ingredients. While the MDSC did not distinctly determine T_g of complex food systems at low moisture contents, glass transitions were observed for solutions and food systems at higher moisture contents. T_g values from MDSC were reproducible and similar to those from standard DSC.     

花生壳/仁的吸附等温线与热力学特性

为了解花生壳与花生仁的含水率、水分活度(a_w)与温度的关系,提高花生的贮藏稳定性。研究花生壳与花生仁在10、20、30℃时的吸附等温线;探讨花生壳与花生仁的净等量吸附热(q_(st))、微分熵(S_d)、扩张压力、积分熵、积分焓、熵-焓互补、玻璃化转变温度(T_g)等热力学特性。结果表明,花生壳与花生仁的水分吸附呈Ⅲ型等温线。温度一定时,花生壳与花生仁的干基含水率随a_w增加而增加。描述花生壳与花生仁吸附特性的最适模型为GAB模型。花生壳与花生仁的q_(st)与S_d均随含水率增加而降低。扩张压力随a_w增加而升高,但随温度升高而降低。积分焓随含水率增加而降低,而积分熵随含水率增加而升高。花生壳的q_(st)和S_d均高于花生仁,而同一温度条件下花生仁的扩张压力高于花生壳。含水率相同时,花生仁积分焓低于花生壳,而花生仁的积分熵则高于花生壳。花生壳与花生仁水分吸附过程均为焓驱动、自发过程。花生壳与花生仁的T_g随含水率增加而降低,相同含水率时,花生壳的T_g值高于花生仁。根据状态图得到温度为10℃时,花生壳与花生仁的临界水分活度与临界含水率分别为0.80、0.175 4 g/g与0.68、0.095 5 g/g。研究结果可为花生干制工艺及其干制品贮藏稳定性提供理论依据。     

共混对淀粉玻璃化转变特性的影响

采用DSC曲线分析法对各种添加刑与淀粉的相容性进行了判断，首次给出了这些添加剂与淀粉的相客性结果。对黄原肢与淀粉的共混体系的玻璃化转变行为进行了实验研究，根据高分子聚合物的共混模型对糯米淀粉与黄原胶共混物的玻璃化转变实验数据进行了拟合，得到适用于此体系的经验关联式，并应用玉米等其他淀粉与黄原胶共混后的实验数据进行验证，表明该关联式可用于定量预计淀粉与黄原肢共混后的玻璃化温度。     

分子量对淀粉玻璃化转变温度的影响

采用相对黏度法及TDA与DSC法测定了淀粉同系物的黏均分子量和玻璃化转变温度,得到分子量对淀粉同系物的玻璃化转变的影响关系:即随着分子量的增加玻璃化转变温度也增加,当分子量增加到一定程度以后玻璃化转变温度增加趋于平缓,并得到实验关联式。根据这种关系我们可在一定的范围内根据实际生产、加工及贮存的需要,用改变淀粉体系的分子量分布的方法来改变其玻璃化转变温度。     

水分含量及添加剂对面团玻璃化转变温度的影响

本实验应用差示扫描量热仪(DSC),测量了不同水分含量的面团的玻璃化转变温度以及NaCl、卵磷脂、抗坏血酸、明胶、海藻糖、单干酯及黄原胶等常见食品添加剂对面团玻璃化转变温度的影响。结果表明:水分含量为40%的纯精粉面团的玻璃化转变温度为-27.75℃,水分含量在38%～45%的玻璃化转变温度有逐渐降低的趋势。NaCl、抗坏血酸、海藻糖分别以5%、1%、3%加入面团以后,面团玻璃化转变温度分别为-13.68、-12.73、-15.74℃。加入明胶、单干酯、黄原胶时,面团的玻璃化转变温度提高并不明显,而卵磷脂的加入却降低了面团的玻璃化转变温度。     

Thermal characterisation of gelatin extracted from yellowfin tuna skin and commercial mammalian gelatin

Glass transition and other thermal characteristics of gelatin from different sources were studied by differential scanning calorimetry (DSC) and modulated DSC (MDSC). The initial glass transition temperatures of equilibrated gelatin samples at 11.3% relative humidity, determined from reversible heat flow thermogram of MDSC, were 23, 75 and 59 °C, respectively, for tuna skin, bovine and porcine gelatin. When gelatin samples were equilibrated at higher relative humidity of 52.9%, glass transition temperature of fish skin and bovine gelatin decreased to −3 and 57 °C, respectively. Further increase of equilibration relative humidity to 75.3% showed increased value in the case of tuna skin, whereas bovine and porcine did not show any significant change. DSC and MDSC results indicated that tuna gelatin showed lower glass transition compared to mammalian source gelatin equilibrated at the same constant relative humidity. In general glass transition measured by DSC was found lower than the values measured by MDSC. The results in this study showed that the degree of plasticization varied with the source of gelatin as well as their extraction methods.     

低聚异麦芽糖为基质挤压法制备玻璃化抗坏血酸胶囊

采用挤压法制备了低聚异麦芽糖为基质的抗坏血酸(AA)玻璃化胶囊.选择了10%和16%两种AA质量分数的配方,在螺杆转速60 r/min,喂料速度1 kg/h的条件下,研究了3种挤压腔温度时的挤压工艺.探讨了挤压过程中电机扭拒、模头压力等的变化规律.差式扫描量热法、X射线对产品性质进行了表征.对挤压产品产率和载量等理化指标进行了分析.结果表明:提高挤压腔温度可以减小电机扭矩和模头压力.AA质量分数对3种温度条件下的电机扭矩影响较小.当挤压腔为中温和低温时,AA质量分数的增加可以使模头压力减小.两种质量分数的AA得到了很好的包埋,挤压产物的玻璃化转变温度随着AA质量分数增加而降低.X射线表明AA以溶解形式分散于基质中,形成了固溶体.     

淀粉的玻璃化转变温度与含水量的关系

采用热膨胀法测定不同含水量下四种淀粉的玻璃化转变温度,得到了不同含水量下淀粉的玻璃化转变温度Tg实验值,探讨了水的增塑作用及影响机理,得到了含水量与Tg的定量表达式,为预测淀粉体系的玻璃化转变温度及对淀粉的储藏加工提供了依据。     

Thermal Transitions in Gelatinized Wheat Starch at Different Moisture Contents by Dynamic Mechanical Analysis

Gelatinized starch was analyzed by DMA and the resulting overlapped tan 5 curve was characterized. At high moisture contents (>30% w/w), transitions around ice melting region of tan 5 peak (>50°C wide) showed skewness at the low temperature side. After deconvolution, a symmetrical, sharp, main peak was correlated with the ice melting endotherm but the cause of the lower temperature asymmetrical peak was not identified. At <30% moisture, two deconvoluted Gaussian peaks indicated at least two separate, broadly distributed domains (slightly frequency dependent). Transitions (other than ice melting), if caused by glassy rubbery transitions, were small in tan 5 and broad (50–100°C wide).