方便米粉的水分吸附和热力学特性

为了给方便米粉的加工和贮藏过程提供理论指导,根据吸附原理,在环境温度分别为15、25 ℃和35 ℃时,采用静态称量法研究方便米粉的吸附等温线。采用7 个常见的非线性回归方程对吸附实验进行拟合,以决定系数、平均相对偏差和标准估计误差为评价指标,确定最佳拟合模型及其参数,探讨方便米粉水分吸附过程中净等量吸附热、微分吸附熵和焓熵互补等热力学性质的变化。结果表明,方便米粉的水分吸附特性属于II型等温线,Peleg和GAB模型都适合描述方便米粉的水分吸附特性。用GAB模型拟合得到的单分子层水分含量X0在15、25 ℃和35 ℃下分别为9.23%、8.34%和7.65%（干基）。在水分吸附过程中,方便米粉的净等量吸附热和微分吸附熵都会随着平衡水分含量的升高而明显下降;同时,存在焓熵补偿现象;根据实验结果绘制净等量吸附热与微分吸附熵的关系图,计算获得方便米粉的吸附过程属于焓驱动和自发过程。本研究对方便米粉贮藏条件选择和进一步评估不同贮藏条件下方便米粉的贮藏期具有指导作用。     

菊花粉水分吸附等温线及热力学特性

为提高菊花粉的贮藏稳定性,分别在20、30℃和40℃下,采用静态称量法对黄山贡菊粉和金丝皇菊粉的水分吸附等温线进行研究,同时探讨水分吸附过程净等量吸附热、微分熵、熵-焓互补理论、固体单位吸附表面积及有效孔径等热力学特性.结果表明,黄山贡菊粉和金丝皇菊粉的水分吸附遵循Ⅱ型等温线.Peleg模型最适合描述菊花粉水分吸附特性...     

花椒吸附等温线及热力学性质

采用静态称质量法,测定花椒在20、30、40 ℃,水分活度为0.005～0.982条件下的吸湿特性,绘制出花椒的吸附等温线。结果表明,花椒吸附等温线属于Ⅲ型等温线,在同一温度下,花椒的平衡含水率随水分活度的增加而增加。用8 种经典吸附模型对其进行拟合比较,Oswin模型效果最优,其次是GAB模型。Oswin模型的决定系数R2达到了0.999,平均相对误差E值为4.11%～8.13%。根据上述模型得到花椒的相对安全含水率与绝对安全含水率约为0.06 kg/kg与0.045 kg/kg。热力学性质显示,花椒属于毛细管多孔特性;当花椒的含水率超过0.08 kg/kg时,水同物料的结合能及净等量吸附热较低,花椒中的水分较易去除;花椒的平均单位质容量的范围为13～18 mol/J,可以根据平均单位质容量来选择最合理的预处理方法和干燥方法。     

Thermodynamic Analysis of Water Vapor Sorption Isotherms and Mechanical Properties of Selected Paper-Based Food Packaging Materials

ABSTRACT:  Adsorption isotherms of 3 selected paper-based packaging materials, that is, vegetable parchment (VP) paper, Kraft paper, and solid-bleached-sulfate (SBS) paperboard, were determined at 3 different temperatures (25, 40, and 50 °C). The GAB isotherm model was found to fit adequately for describing experimental adsorption isotherm data for the paper samples. The monolayer moisture content of the paper samples decreased with increase in temperature, which is in the range of 0.0345 to 0.0246, 0.0301 to 0.0238, and 0.0318 to 0.0243 g water/g solid for the MG paper, the Kraft paper, and the SBS paperboard, respectively. The net isosteric heats of sorption ( q_st ) for the paper samples decreased exponentially with increase in moisture content after reaching the maximum values of 18.51, 27.39, and 26.80 kJ/mol for the VP paper, the Kraft paper, and the SBS paperboard, respectively, at low-moisture content. The differential enthalpy and entropy of 3 paper samples showed compensation phenomenon with the isokinetic temperature of 399.7 K indicating that water vapor had been adsorbed onto the paper samples with the same mechanism. Depending on the paper material, tensile strength of paper samples was affected by moisture content.     

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。     

大豆水分解吸-吸附等温线拟合模型

为给在干燥、贮藏及运输过程中保证大豆的品质提供理论依据,实验测定了大豆在室温（25 ℃）条件下的水分解吸-吸附等温线。采用非线性回归分析,应用常见的5 种模型Oswin、Halsey、Hendenson、GAB、Chung-Pfost对大豆在室温条件下测得的水分进行解吸-吸附等温线拟合分析,以确定最佳拟合模型及其参数。结果表明：大豆的解吸等温线属于第Ⅱ种类型;吸附等温线属于第Ⅲ种类型;在整个水分活度范围内,大豆的解吸-吸附等温线均存在着滞后现象;最佳的解吸-吸附等温线拟合方程都是Oswin模型,它们的决定系数均高于0.993;Oswin模型拟合大豆解吸等温线的参数A和B分别为0.075和0.500,吸附等温线的参数A和B分别为0.075和0.498。     

外源蛋白改良剂对米面团热力学性能及面包品质的影响

以小麦面包为对照,探究大豆分离蛋白、豌豆分离蛋白、玉米醇溶蛋白、乳清浓缩蛋白和蛋清蛋白5种外源植物和动物蛋白质对米面团及面包的混合特性、糊化特性、流变学特性、比容和感官分析的影响。结果表明,加入外源蛋白可以降低米面团的回生值到最小为211 cP,使面包的比容增加至1.810 mL/g,硬度下降约55.3%,胶着性降低至2 710.12 g。其中植物蛋白中添加量为12%的大豆蛋白组面包气孔数量最多,质地细腻且颜色均匀,持水性及感官品质最好。动物蛋白中9%的乳清浓缩蛋白组面包硬度显著下降,约2 032.9 g(P<0.05),此时面团硬度最接近于小麦面团,弹性为0.82%,口感较软,对米面包质构特性改善效果最佳。结论：在植物蛋白中大豆蛋白添加量为12%、动物蛋白中乳清浓缩蛋白添加量为9%的条件下可以改善米面包品质。     

稻谷吸附与解吸等温线影响因子的研究

研究了稻谷的品种、初始含水量、稻谷的类型(籼稻、粳稻和糯稻)和加工程度(原稻、糙米和白米)等因素对稻谷吸附与解吸等温线的影响。结果表明，不同品种的籼稻的吸附与解吸等温线间没有明显的差异；而初始含水量、稻谷的类型以及加工程度显著影响稻谷的吸附与解吸等温线。     

五种饲料原料水活性等温吸附曲线研究

通过研究5种常用饲料原料(玉米、豆粕、菜粕、鱼粉和麸皮)的水活性等温吸附曲线,评价了5种常用的数学模型对这几种饲料原料水活性等温吸附曲线的拟合效果,发现玉米的水活性等温吸附曲线效果:Chungpfost方程在(25±1)℃和(17±1)℃时拟合最好,直线方程在(11±1)℃条件下拟合效果最好;豆粕的水活性等温吸附曲线:Henderson方程在(25±1)℃和(17±1)℃时拟合效果最好,直线方程在(11±1)℃条件下拟合效果最好;菜粕的水活性等温吸附曲线:Henderson方程拟合各个试验温度条件下的效果均最好;鱼粉的水活性等温吸附曲线:在(25±1)℃条件下Halsey方程拟合效果最好,Chungpfost方程在(17±1)℃条件下拟合效果最好,而Henderson方程在(11±1)℃条件下拟合效果最好;麸皮的水活性等温吸附曲线:Halsey方程在(25±1)℃条件下拟合的效果最好,Chungpfost方程在(17±1)℃、(11±1)℃条件下拟合效果最好。并选择拟合最好的数学模型计算出各种饲料原料的绝对安全水分含量和相对安全水分含量,以期为饲料储存和饲料生产做出指导。     

Water Sorption Enthalpy-Entropy Compensation Based on Isotherms of Plum Skin and Pulp

ABSTRACT: The net isosteric heat and entropy of water sorption were calculated for plum, based on sorption isotherms obtained by the static gravimetric method at different temperatures (20 to 70 °C). The Guggenheim-Andersonde Boer model was applied to the experimental data giving a good agreement between experimental and calculated values. The net isosteric heat of water sorption, estimated by applying Claussius-Clapeyron equation to sorption isotherms, was found to be different for plum skin and pulp, mainly at low moisture contents, and could be well adjusted by an empirical exponential relationship. Plots of enthalpy in contrast to entropy provided the isokinetic temperatures for skin and pulp, indicating an enthalpy-controlled sorption process. Thermodynamic data on water sorption for plums are not found in literature, as opposed to prunes for which the data are abundant.     

稻谷吸附与解吸等温线的拟合模型及其参数的研究

评价了拟合稻谷等温线的4种最常用的数学模型对我国不同类型的稻谷（籼稻、粳稻、糯稻）、糙米和精米吸附与解吸等温线数据的拟合效果。结果表明,Strohman—Yoerger模型最适合拟合籼稻（包括糙米和精米）、粳稻的吸附与解吸等温线及糯稻的吸附等温线,而修正Oswin模型（MONE）最适合拟合糯稻的解吸等温线。     

Effect of Freezing and Hot Water Soaking on the Functional Properties of Rice Flour Derived from four Sri Lankan Traditional Rice Varieties

Rice cultivation nowadays has become as major concern to Sri Lanka due to high dependency of chemical fertilizers. There is an interest to promote utilization of rice obtained from traditional rice varieties which are well adopted to Sri Lankan environmental conditions, such varieties are highly nutritious and less dependent on agrochemicals. Thus they are ideal candidates in promoting organic food products without chemical inputs. Rice flour is a good substitute for imported wheat flour in bakery industry. However due to lack of gluten protein, rice flour cannot be used directly in bakery products without any modifications. In this study rice grains derived from four traditional rice varieties namely Madathuwalu, Kaluhenati, Pachaperumal and Ratdal were subjected to freezing at -20^oC (24 hours and 48 hours), hot water soaking at 80^oC (5 minutes and 10 minutes) individually and in dual combinations. Untreated rice flour served as the control and experiments were conducted in triplicates. Water Absorption Index (WAI), Water Solubility (WS), Swelling Power (SP) and pH values were measured in both treated and untreated rice flour. Results showed that these physical treatments to the rice grains brings about a significant difference (p< 0.05) on the functional properties of rice flour both individual and in dual combinations. Strong correlation (p=0.000) was obtained between WAI and SP. Dual modification treatments were found to be highly effective in improving functional properties of all selected traditional rice varieties compared to the single modification. Freezing at -20^oC for 48 hours was more effective than the 24 hours freezing to improve the functional properties. Therefore, this study proves that simple physical treatment methods such as freezing and hot water soaking could bring about a significant effect on the functional properties of traditional rice flour.     

Water Vapor Adsorption Isotherms of Guava, Mango and Pineapple

Isotherms were determined at 25° and 50°C, using an electronic water activity meter. For the 3 fruits temperature had practically no effect on the isotherms. Sorption capacity of freeze-dried pineapple was higher than that for vacuum dried. The higher sorption capacity of mango and pineapple in comparison to guava corresponded to the respective sugar contents of the fruits.     

魔芋不可逆凝胶的流变学性质

对魔芋不可逆凝胶的流变学特性进行研究,考察不同品种魔芋粉、魔芋粉添加量、加热温度以及胶凝剂的种类和添加量对魔芋不可逆凝胶强度的影响。通过动态黏弹性实验测定魔芋不可逆凝胶的各项流变学参数。结果表明：花魔芋、白魔芋、珠芽魔芋干法加工（干粉）和花魔芋湿法加工（湿粉）的4 种魔芋粉形成的凝胶中,白魔芋干粉品质最佳。魔芋不可逆凝胶化过程中,随着魔芋粉添加量的增大,凝胶化时间缩短,储能模量的平台值也随之增大,升高温度也能加快魔芋粉凝胶化的速率。在温度为80 ℃、pH值为11～13之间,体系的储能模量达到最大值,即可形成品质较好的凝胶。当凝胶剂Na2CO3、Ca(OH)2、Na3PO4添加量分别为0.6%、0.5%、1.0%时,凝胶体系储能模量达到最大值,与损耗模量差值相应也最大,最利于凝胶的形成,且形成凝胶体系所需的时间短。     

稻米淀粉的理化特性研究Ⅰ.不同类型稻米淀粉的理化特性

以籼稻、粳稻和糯稻为原料,研究了稻米淀粉的理化特性及稻米类型对理化特性的影响.结果表明籼稻、粳稻和糯稻淀粉的颗粒特性相似,粒径1.90～2.53μm,粒形为多面体,酶解力(0.032OD/g淀粉)和结晶度(28%～40%)较接近.三种稻米在组成上以直链淀粉含量的差异较大,其他成分差异不明显.籼稻的糊化温度(68℃-77℃)最高,在自然水分下加热时晶体熔解所需热量(2.795J/g)最低,凝胶稠度(35.0mm)、特性粘度(132.38mL/g)最小,碘兰值(0.232 OD/0.1g淀粉)最大.糯稻的糊化温度(57℃～65℃)最低,在自然水分下加热时晶体熔解所需热量(28.276J/g)最高,凝胶稠度(91.5mm)、特性粘度(167.45mL/g)最大,碘兰值(0.059 OD/0.1g淀粉)最小.