pH值对再制干酪功能特性的影响

利用质构仪、流变仪、扫描电镜分析pH值对再制干酪产品功能特性的影响,揭示了pH在再制干酪生产过程中的重要作用。结果表明,pH值影响再制干酪的融化性,但是这种影响没有呈现一定的规律性;随着pH值的升高,再制干酪产品的表观黏度也随之升高;在各质构参数中,硬度和咀嚼性随着pH值的升高而降低,pH值对弹性的影响显著(P<0.05);pH值影响水和乳化的过程,pH值越高,越利于水和乳化。     

Shift of pH-Value During Thermal Treatments in Buffer Solutions and Selected Foods

The pH value is one of the most important process parameters during thermal treatments, regardless if the medium is a simple buffer solution or a complex food matrix. When the temperature increases after an initial measurement of the pH at ambient temperature (25°C), a significant pH shift could occur, which could produce incomparable results in different buffer solutions or lead to side reactions during food preservation. Consequently, a measurement cell was constructed to record online the pH-value and temperature up to 130°C. By applying the Nernst equation, it was possible to exclude the temperature-dependent influence of the pH glass electrode on the total pH value. The pH shift was measured over a wide temperature range (ΔT 20–130°C) in the most commonly used buffer solutions and some selected food matrices. The ΔpH of certain buffer solutions, namely TRIS and ACES, showed a significant pH decrease of??2.01 ± 0.08 (ΔT 20–130°C) and??1.27 ± 0.1 (ΔT 20–130°C), respectively, whereas the pH of PBS buffer solution was nearly independent of temperature. The ΔpH decrease recorded in milk (?0.89 ± 0.6, ΔT 20–130°C) as well as commercial and self-made baby food (?0.56 ± 0.05, ΔT 20–130°C) is of special interest for the food industry to get a deeper insight in occurring reactions during thermal preservation processes.     

Flow Characteristics of Viscous, Non-Newtonian Fluids in Holding Tubes of HTST Pasteurizers

The type of flow and ratio of maximum to average velocity in the holding tube was studied for viscous, non-Newtonian fluids. Appropriateness of the salt test in water for holding time determinations was also studied. Sucrose and guar solutions were used to model rheological characteristics typical of ice cream mixes. Flow was observed using a dye stream and video photography. In straight-line flow, maximum velocity was 1.6 to 2 times faster than bulk-flow velocity for typical industrial settings (Re_g from 70 to 1900). When elbows were added, the dye stream was displaced from its centerline position and the ratio of dye stream to bulk-flow velocity decreased. No extrapolation could be made from salt tests in water to minimum holding time for viscous, non-Newtonian fluids.     

Osmolality and pH of commercially available contact lens care solutions and eye drops

PurposeThe physical properties of contact lens care solutions and Eye Drops (ED) may affect initial comfort and dry eye symptomatology in contact lens wearers, although these properties are not always provided by manufacturers. The present study aimed to measure and compare the osmolality and pH of commercially available contact lens care solutions and ED.MethodsForty-four solutions were tested (17 lens care solutions and 27 ED) and classified by the presence and/or combination of the viscosity/lubrication-enhancing ingredients. Solution osmolality was obtained with the Fiske 110 osmometer and pH was measured with a micro-pH 2000. Each measurement was taken ten times, following the manufacturer's instructions, while controlling for room temperature and humidity. Differences between the values of the physical properties of the solutions were analysed by type and viscosity/lubrication-enhancing agent subclassification.ResultsOsmolality ranged from 192.6 ± 2.17 to 364.6 ± 2.88 mOsm/Kg, while pH ranged from 6.35 [6.35–6.26] to 7.99 [7.99–8.00]. A significant difference in the osmolality and pH values of contact lens care solutions and ED was found when classified by type or viscosity/lubrication-enhancing agent (ANOVA and Kruskal-Wallis respectively, both p < 0.001).ConclusionsThe physical properties of some contact lens care solutions and ED are not readily available. The osmolality and pH values of various commercially available lens care solutions and ED vary significantly both by type and viscosity/lubrication-enhancing ingredients.     

CO_2超临界流体无污染制革技术研究超临界流体的基本原理及应用(I)

本文扼要介绍了ＣＯ２超临界流体的基本特性及相应的技术和装置，对其在制革工艺中应用的研究现状及前景进行了评述。     

超临界流体技术在造纸工业中的应用

综述了超临界技术尤其是超临界水氧化法在造纸生产过程、造纸污水和污泥的处理以及废水中痕量有害成分分析等方面的应用.     

Rheological Properties of Solutions and Emulsions Stabilized with Xanthan Gum and Propylene Glycol Alginate

The rheological effects of propylene glycol alginate (PGA) added to solutions and model emulsions containing xanthan gum (XG) were studied using controlled stress rheometry with concentrations appropriate for salad dressings. For samples with XG and XG + PGA blends, solutions and emulsions showed a Newtonian plateau at low shear stresses. The Newtonian plateau of a solution accurately predicted (r²= 1.00) the Newtonian plateau for an emulsion of equivalent gum concentration. Addition of PGA to constant levels of XG showed a more than additive increase in the Newtonian plateau viscosity for solutions and emulsions. For XG aqueous solutions, pseudoplasticity decreased upon addition of PGA. Storage and loss moduli increased with addition of PGA to XG for solutions and emulsions, although G’ for solutions of PGA alone were negligible.     

Use of Positron-Emission Particle Tracking (PEPT) Technique for Velocity Measurements in Model Food Fluids

ABSTRACT Positron-emission particle tracking (PEPT) is a method of following particles in opaque fluids inside metal equipment. Comparison of experimental and theoretical velocity distributions obtained in aluminum pipes indicated that PEPT can be used to measure velocity distributions in viscous fluids for conditions of relevance to the food industry. Velocities were also measured for a fluid containing starch particles using 2 tracers having diameters of 600 and 240 μm. Velocity profiles were not significantly different, but the smaller tracer passed closer to the flow boundaries. PEPT was also used to quantify the effect of headspace on the velocity distributions of rotating cans containing soup. While in fully filled cans, fluid moved in circular motion, addition of air altered this, resulting in D-shape velocity contours.     

柚皮果胶的提取方法比较及其粘流性能研究

比较了从江永柚皮中提取果胶的不同方法。研究了柚皮果胶溶液的粘流性能,测定了果胶的特性粘度并由此计算出果胶的分子量。结果表明:盐酸逆流萃取法为从柚皮中提取果胶的较好方法,果胶溶液的粘流活化能约为17.14kJ/mol(依赖于果胶浓度大小),采用逆流萃取法提取的果胶特性粘度为4.492ml/g,果胶分子量为7.17×104。     

Recovery and Properties of Muscle Proteins Extracted from Tilapia (Oreochromis niloticus) Light Muscle by pH Shift Processing

ABSTRACT: Functional proteins can be extracted from fish muscle using acid- or alkali-aided solubilization and recovered with isoelectric precipitation. It was of interest to evaluate acid- and alkali-aided solubilization/precipitation on muscle material from the warm-water fish tilapia. Higher levels of proteins were extracted with high compared with low pH ( P < 0.05) because of higher protein solubility at high pH. Protein extraction was not influenced by the specific low or high pH tested or homogenization time. Similar protein types were extracted for the low and high pH solubilization, while proteolysis was observed at low pH. Viscosity was significantly higher at pH 2.3 to 2.9 compared with pH 10.8 to 11.4 ( P < 0.05) and varied greatly at low pH indicating a more unstable system. Two different low (pH 2.5 and 2.9) and high (pH 11 and 11.2) solubilization pH values were selected and protein recovery investigated in the pH range 5.1 to 5.7. The alkali-extracted proteins had more solubility at pH 5.1 to 5.7 ( P < 0.05) and thus less protein ( P < 0.05) was precipitated compared with the acid-aided process. More protein was recovered as pH increased from 5.1 to 5.7 ( P < 0.05). More protein types were found in the supernatant after precipitation for the alkali-aided treatment, and soluble proteins were similar to those of untreated tilapia muscle homogenate. Viscosities of the acid- and alkali-extracted proteins at pH 5.1 to 5.7 were significantly higher than the viscosity of native proteins at that pH ( P < 0.05). While this study demonstrated significant differences in protein extractability and precipitation of the 2 processes, no statistical difference ( P > 0.05) was found for overall protein recovery (61% to 68% for alkali-aided process and 56% to 61% for acid-aided process) of the 2 processes.     

滑石颜料高剪切流变性能的研究

使用毛细管高剪切黏度仪研究了滑石颜料分散体系的高剪切黏度性能,以及pH值、固含量、不同分散剂和润湿剂、不同粒径分布对滑石分散体系高剪切黏度的影响。同时还研究了滑石与GCC及高岭土混合浆料的高剪切黏度性能。结果表明,滑石含量越高、粒度越细,其分散浆料的高剪切黏度值越大。同时发现,滑石高剪切黏度受分散剂和润湿剂的影响不大。提高pH值有利于降低滑石分散体系的高剪切黏度。滑石与GCC混合浆料的高剪切黏度随着GCC粒度的变细而降低。当滑石与GCC的体系中加入高岭土后,混合浆料的高剪切黏度大幅增大,且随着GCC粒度的变细而增大。     

Recrystallization in Aqueous Fructose Solutions as Affected by Locust Bean Gum

Rates of ice recrystallization were measured in aqueous fructose solutions containing locust bean gum (LBG). The effects of temperature, ice phase volume and LBG concentration were determined. Decreasing temperature reduced the recrystallization rate: the dependency followed Williams Landell Ferry kinetics. An increase in ice phase volume resulted in an increase in the recrystallization rate. Addition of LBG reduced the recrystallization rate up to a concentration of 0.3% (w/w); further addition resulted in no further decrease. The hypothesized mechanism of action of LBG is via weak adsorption of the polysaccharide to the ice crystal. Freeze concentrated solution viscosity did not correlate with observed recrystallization rates.     

整体包装解决方案初探

针对当前国内整体包装解决方案现状进行分析,提出整体包装解决方案的优势所在以及存在的问题,并为CPS企业如何发展提出一些建议。     

Potato Starch Paste Behavior as Related to Some Physical/Chemical Properties

Potato starch with anomalous stable (constant with time) paste viscosity has been proposed as a natural replacement for cross-linked starch, but its behavior and the influencing factors are not well understood. Starch from 44 samples of potato tubers representing 34 genotypes was analyzed for phosphorus, mean granule diameter, amylose, calcium, magnesium, sodium, and potassium. Except for granule diameter, sodium, and potassium, each of those properties correlated significantly with one or more of five paste characteristics determined using the Brabender Visco-amylograph. Three samples had a stable viscosity in 1 yr of the study, but their behavior was not associated with unusual values of the other measured properties. The stable viscosity is probably a heritable trait influenced by cultural and climatic factors.     

草浆高浓黑液的流变性与粘流温度效应

利用Rheometrics RFSII流体粘弹仪测量了蔗渣浆黑液多聚物体系的剪切应力，表现粘度与剪切速率的关系，由实验得出了蔗渣浆高浓黑液在工程剪切速率范围（10^-1～10^3s^-1)内属剪切稀化流体，浓度和温度越高，黑液的剪切稀化现象越显著。此外，利用Brookfield粘度仪测定了黑液的剪切粘度与温度的关系，得出蔗渣浆黑液的粘度与温度的关系符合指数递规律。粘度越大，黑液粘度对温度的依赖性越强。     

蛋白质溶液表面张力及其与功能性质的关系

为了探讨蛋白质溶液表面张力的变化规律，本文利用表面张力计和食品流变学方法系统地研究了蛋白质溶液表面张力随液滴停留时间的变化及其与功能性质的关系。结果表明：高浓度时，液滴停留时间与表面张力的变化遵循下列一次方程In[（θt-θe）/（θw-θe）]=-kt。对同一蛋白质来说，k值随浓度的增加而增大。蛋白质起泡力与k值呈极显著的线性关系，泡沫稳定性与k值呈正相关。蛋白质的乳化性低浓度时与表面张力呈正相关；高浓度时，乳化性与k值呈正相关。     

Beet Pulp and Isolated Pectin Physicochemical Properties as Related to Freezing

Any potential effects of postharvest freezing storage of beets on physicochemical characteristics of isolated pectin and beet pulp were determined. Fresh beets were stored at -20°for up to 3 mo. At the end of storage, beets were thawed and shredded, and sucrose was extracted. Pectin was isolated using a combination of enzyme treatment and acid extraction. Yield, galacturonic acid content, methoxyl ester content, and molecular mass distributions of the isolated pectin were determined. Neutral and acidic sugar compositions in the nonstarchy polysaccharides (NSP) of the beet pulp were determined using enzyme hydrolysis and gas chromatography. Results showed that physicochemical characteristics of isolated pectin, and sugar composition of the NSP in the beet pulp were not notably influenced by the freeze/thaw cycle.     

果仁糖果用高质量分数糖浆的流变特性

采用R/S plus流变仪对不同质量分数（80%～92%）的果仁糖果用蔗糖-麦芽糖混合糖浆在不同温度下的流变特性进行研究。结果表明：温度对黏度的影响可用阿累尼乌斯（Arrhenius）方程表示,质量分数对黏度的影响可用幂函数的形式表示。通过回归分析,给出在研究的温度和质量分数范围内黏度随温度、质量分数各自变化的函数式以及温度和质量分数对黏度的综合方程式。所建立的方程式能够成功地描述在相应质量分数和温度范围内的数据。