在食品结晶成核中应用超声探讨

总结了超声波应用于蔗糖、味精、谷氨酸、木糖醇等食品结晶的成核过程并分析其作用原理，然后以葡萄糖这种典型的具有同质异晶特性的食品结晶物系为研究对象。研究了超声波用于其中不同异构体成核的条件，最后给出了超声波用于食品结晶成核的一般结论。     

纳米二氧化钛对聚酯纤维结晶性能的影响

采用钛酸丁酯表面修饰纳米二氧化钛;并添加到聚酯酯过程中,以改性聚酯纤维,发现改性后的聚酯纤维上染速率提高了近3倍。针对这一现象,通过透射电镜和DSC差热仪进行观测,发现纳米二氧化钛较均匀地分散在聚酯内部,并提高了聚酯纤维的玻璃化温度,说明纳米粒子的表面修饰与聚酯有良好的相容性。进一步采用修正Avrami方程、Kissinger法和Jeziomy法对其非等温结晶过程进行发现,纳米二氧化钛降低了聚酯结晶活化能,提高了结晶速度,纳米粒子可作为晶核使聚酯部分转向异相结晶。研究结果表明,纳米二氧化钛改变了聚酯纤维结晶行为,促进了染料分子的吸附上染和热性能的提高。     

硫酸钠型矿盐卤水冷冻过程中芒硝结晶动力学的研究

采用连续稳态法对高浓度氯化钠水溶液中十水硫酸钠在MSMPR结晶器中的结晶过程进行了研究,测定了相关动力学参数,成核速率方程为:B0=1.245 E-63exp((-94 396.5)/(RT))ΔC2.907M0.111 5t,生长速率方程为:G=0.206 4exp((-15 825.46)/(RT))ΔC0.549 3.通过实验验证了动力学参数的可靠性,并对冷却结晶的影响因素进行了分析讨论.     

Control of ice crystal nucleation and growth during the food freezing process

Freezing can maintain a low-temperature environment inside food, reducing water activity and preventing microorganism growth. However, when ice crystals are large, present in high amounts, and/or irregularly distributed, irreversible damage to food can occur. Therefore, ice growth is a vital parameter that needs to be controlled during frozen food processing and storage. In this review, ice growth theory and control are described. Macroscopic heat and mass transfer processes, the relationship between the growth of ice crystals and macroscopic heat transfer factors, and nucleation theory are reviewed based on the reported theoretical and experimental approaches. The issues addressed include how heat transfer occurs inside samples, variations in thermal properties with temperature, boundary conditions, and the functional relationship between ice crystal growth and freezing parameters. Quick freezing (e.g., cryogenic freezing) and unavoidable temperature fluctuations (e.g., multiple freeze–thaw cycles) are both taken into consideration. The approaches for controlling ice crystal growth based on the ice morphology and content are discussed. The characteristics and initial mechanisms of ice growth inhibitors (e.g., antifreeze proteins (AFPs), polysaccharides, and phenols) and ice nucleation agents (INAs) are complex, especially when considering their molecular structures, the ice-binding interface, and the dose. Although the market share for nonthermal processing technology is low, there will be more work on freezing technologies and their theoretical basis. Superchilling technology (partial freezing) is also mentioned here.     

抗氧剂BHT结晶工艺研究

BHT结晶是以乙醇为溶剂，对不同浓度的乙醇，改变溶质与溶剂的物料配比，测定了BHT溶液的出晶点温度，结果表明，在乙醇浓度一定的条件下，出晶点温度随BHT与乙醇配比的增大而降低；而在相同物料配比的条件下，乙醇浓度越低，出晶点温度越高。     

L-抗坏血酸棕榈酸酯对椰子油结晶行为的影响

以椰子油作为模型，利用结晶动力学方程、X-射线衍射（XRD）分析、热力学分析以及偏振光显微镜（PLM）观察等方法研究了L-抗坏血酸棕榈酸酯（L-AP）对椰子油结晶行为的影响。结果表明：L-AP提高了椰子油的结晶速率，改变了晶体成核和生长机制；L-AP以“晶种”的方式诱导椰子油的结晶，对其结晶过程产生了促进作用； L-AP没有改变椰子油晶体的晶型以及堆积方式，却增加了晶体纳米片层的厚度；随着L-AP添加量的增加，晶体结构更加致密有序。     

冷藏条件下甜玉米的糖份变化

在6℃温度贮藏5d后,3个品种甜玉米的总糖含量分别下降19.7%、25.7%和9.5%。其中蔗糖含量在贮藏后有较大下降,果糖和葡萄糖含量也都下降,麦芽糖含量在贮藏后有较大上升。糖度计读数(癇rix)不能用来估测玉米中的糖份含量。     

Crystallization and Drying in Thin Sucrose Films During Panning

Sucrose crystallization in thin films (50–55 μm) was studied, using a videomicroscopy technique, at conditions encountered during hard panning processes. No nucleation occurred in unseeded films, while a linear increase in seeded crystals occurred during drying. Crystal growth rate increased with temperature (25–30°C) and with air velocity (2.4–12.5 m/sec), but did not change with varying sucrose concentrations (70–76% w/w) and relative humidities (0–66% at 30°C). FD & C Yellow No. 5 food coloring in the dye form (0.05–0.5 g/100 mL) showed no effects while similar concentrations in the lake form inhibited crystal growth rate.     

Free Amino Acid Stability in Reducing Sugar Systems

Solutions of free amino acids were sterilized in different carbohydrate mixtures, at different pH values, and both browning and free amino acid content monitored at different storage temperatures. Results showed the expected behavior of a Maillard process, (e.g., increasing reaction rate with increases in pH, temperature and reducing sugar content). However, only three (tryptophan, histidine and lysine) of the amino acids tested (nine essential + taurine) were notably affected, even under stringent conditions (50°C storage, glucose containing solution at pH 7.5). Thus many free amino acids could probably be added to most food matrices without Maillard reactions affecting overall protein quality.     

Sugar Composition and lnvertase Activity in Prickly Pear Fruit

Sucrose was the predominant sugar in peel samples and present in lesser amounts in pulp and juice samples of prickly pear fruit. The relative total content of glucose and fructose differed among species and within fruit tissues. Acid invertase activity was found in all fruits examined while neutral invertase activity was found in two of the three species. Red-skinned fruits had no neutral invertase activity and yellow-skinned fruits had relatively high neutral invertase activity. When both invertase activities were added, a pattern of distribution of invertase activity that corresponded with sucrose levels within fruits was observed. The overall total invertase activity levels in red-skinned fruits were about twofold that of the yellow-skinned fruits and fourfold that of purple-skinned fruits.     

结晶原理和冰淇淋中的结晶现象

阐述了结晶原理在冰淇淋凝冻中的应用,详细叙述了结晶的目的和方法,晶核的形成原理,结晶体的成长,多晶现象,以及冰淇淋中的结晶现象.     

氢氧化镁结晶动力学研究

结晶动力学的研究是结晶器设计、结晶过程放大和优化的重要依据。文章研究了间歇反应过程中氢氧化镁结晶动力学,采用间歇动态法对结晶过程基本参数进行测试,根据粒数衡算和质量衡算关系,利用晶体成核生长经验公式拟合出氢氧化镁反应结晶动力学表达式。结果表明:氢氧化镁结晶过程晶体生长速率与粒度无关,得到了过饱和度、悬浮密度与成核速率之间的关系。     

Sugar and Cyclitol Determination in Vegetables by HPLC Using Postcolumn Fluorescent Derivatization

Nonreducing sugars such as sucrose, raffinose, myo-inositol, pinitol and galactinol were separated on a polyamine-bonded polymer gel (NH₂ type) column using acetonitrile-water as mobile phase. Sugars in the eluate were detected by periodate oxidation and the subsequent derivation of guanidine to fluorescent compounds. Detection limits were: sucrose 2.5, D-glucose 2.5 and pinitol 4 ng. This highly sensitive method was more accurate and rapid for determining sugar contents in immature soybean seeds, sweet corn kernels and chinese mustard leaves than the conventional method using refractive index detection. Also, this method reduced the injection volumes of extracts to the column and allowed to lengthen the column life.     

Induction Time of Crystallization in Vegetable Oils, Comparative Measurements by Differential Scanning Calorimetry and Diffusive Light Scattering

ABSTRACT: In this work we compared the induction time of crystallization (τ_i. measured by DSC (τ_iDSC) and scanning diffusive light-scattering (SDLS, τ_iSDLS) in a vegetable oil blend. Several crystallization temperatures and cooling rates (1,10, and 30 °C/min) were investigated. Additionally, rheograms obtained during the crystallization of the oil blends were obtained to differentiate the stages of nucleation and crystal growth. The results obtained showed that independent of cooling rate and crystallization temperature, SDLS provided an earlier detection of triacylglycerides'(TAGS) nucleation than DSC. Furthermore, τ_iSDLS was more consistent (that is, lower standard deviation) than τ_iDSC particularly at high crystallization temperatures and cooling rates. The rheograms showed that τ_iDSC involves a measurement of crystal growth, while τ_iSDLS is associated with the early formation of a solid phase in the oil blend (that is, TAGS nucleation). When the Fisher-Turnbull equation was therefore used to calculate the free energy of nucleation (ΔG_c), τ_iSDLS provided a better estimate of ΔG_c than that obtained by τ_iDSC     

Mg2+,K+//Cl-,SO2-4-H2O体系硫酸钾结晶动力学研究

文章依据硫酸镁转化法制取硫酸钾相图,配制25℃下Mg2+,K+∥Cl-,SO2-4-H2O体系硫酸钾饱和溶液,用结晶槽法研究了该体系溶液在不同过饱和度下,硫酸钾晶体的线生长速率.硫酸钾结晶动力学实验结果表明,所研究溶液体系硫酸钾晶体生长由表面反应过程控制.     

Free sugars determination by HPLC in pineapple products

Free sugars have been determined by HPLC in fresh pineapple fruit, freshly extracted pineapple juice (home-made), pineapple juice concentrate (for industrial use), commercial pineapple juices and nectars. In natural samples, intermediate products and commercial juices the dominant sugar was sucrose, followed by fructose and glucose, both of which were found in similar concentrations. However, the sugar content of nectars analyzed was highly variable. The presence of maltose in nectar samples is a clear indication of the addition of sugars from corn syrup. We have found a fructose/glucose ratio close to 1, and the coefficient fructose plus glucose/sucrose close to 1, both of which are a good index of authenticity of pineapple juices.     

Sugar content of swedes for stockfeeding

The sugar content was determined of 19 cultivars of swede (Brassica napus ssp rapifera L) grown in rows 50 and 75 cm apart. Sugar concentration ranged from 54.3 to 78.7 g kg^?1 fresh weight and was positively correlated with dry matter content which ranged from 90.4 to 138.7 g kg^?1 fresh weight. The average concentration of fructose, glucose and sucrose in the dry matter was 225.0, 328.4 and 34.5 g kg^?1 DM, respectively. The high-dry-matter cultivars tended to have less fructose and more sucrose than the low-dry-matter ones, but total sugar concentration in the dry matter was not associated with dry-matter content. Row width had little effect on sugar content compared with the differences between cultivars. The implications for the feeding value of swedes are discussed.     

配料对巧克力品质影响的研究进展

巧克力浆料是由非脂相,如糖、可可粉、乳粉等物质分散于以油脂为连续相而形成的悬浮液体系。可可脂、可可液块和糖是巧克力的主要成分,这些组分会影响巧克力浆料的流变性、质构及其微观结构等,从而影响巧克力及巧克力制品的品质。研究巧克力品质的影响因素对于调整产品配方,改善加工工艺,提高产品品质具有重要的指导意义。本文主要从产品配方如原料油、糖类及微量组分对巧克力品质的影响进行了综述,期待能为巧克力生产提供一定的指导作用。      

Mg~(2 ),K~ //Cl~-,SO_4~(2-)-H_2O体系硫酸钾结晶动力学研究

文章依据硫酸镁转化法制取硫酸钾相图,配制25℃下Mg2 ,K //Cl-,SO2-4-H2O体系硫酸钾饱和溶液,用结晶槽法研究了该体系溶液在不同过饱和度下,硫酸钾晶体的线生长速率。硫酸钾结晶动力学实验结果表明,所研究溶液体系硫酸钾晶体生长由表面反应过程控制。