快速测定浓缩荔枝汁冰点温度的研究

以5种不同浓缩度的荔枝汁为原料,以冷冻浓缩机、热电偶、数据采集仪与计算机相联测量其冰点温度,确定冰点温度与荔枝汁浓度即可溶性固形物含量之间的关系,并建立相关数学模型,通过检测荔枝汁中可溶性固形物含量可以快速确定其冰点温度,为浓缩荔枝汁的保存及冷冻加工提供理论依据.结果表明:该方法简单可行,处理量大,准确度高,效率高,损失少.浓缩荔枝汁冰点温度与可溶性固形物含量呈显著负相关,回归方程为:Y=-0,00654X2+0.0855X-1.0981,相关系数R2=0.9998.     

草莓冻结点温度保鲜方法的探讨

本文探讨了冻结点温度下保鲜草莓的理论依据。并通过试验证明草莓在冻结点温度下的保鲜时间可达两个月以上,且感官品质与鲜果接近。草莓含水量与冻结点温度和可溶性固形物呈线性相关,回归方程分别为: =0.1009X1-110.6464 =-1.4092X2+99.1709 。据此可估算草莓的冻结点温度,误差小于0.1℃。该方法对于掌握草莓保鲜特性具有实际意义,也为其它果蔬的冻结点保鲜提供了借鉴。1y2y     

苹果汁电导率及介电损耗因子影响因素的研究

本文研究了苹果汁的电导率与可溶性固形物含量、温度、粘度和NaCl浓度等因素的关系,并通过电导率与介电损耗因子的关系,确定不同频率下与离子介导相关的苹果汁的介电损耗因子。结果表明,苹果汁的电导率随可溶性固形物含量的增加呈先增大后减小的抛物线趋势,随温度线性增大,粘度大小对电导率的影响很小,添加少量NaCl苹果汁电导率成倍增大。借助SPASS数据分析软件,得出电导率同可溶性固形物含量、温度的非线性回归方程：σ=-28.69C2+17.292C+0.02T+0.135,R2为0.974,拟合度良好。通过计算获得苹果汁在不同频率下（13.56、27.12、40.68 MHz）与离子介导相关的介电损耗因子。这些结果和数据,可为欧姆和射频加热技术用于苹果汁生产提供基础数据支持。     

用电导率法测定莲藕冻结点的研究

根据食品物料在温度改变时电导率变化的性质,用电导率仪对莲藕的冻结点进行测定.研究表明,莲藕的冻结点为-1.4～-1.9℃,经实际验证,误差小于±0.05℃.用电导率法测定莲藕冻结点的方法简单、精确和经济,在其他果蔬冻结点的测定方面有推广价值.对新鲜肉类和液态食品的冻结点测定具有借鉴作用.     

鸭梨的冻结特征及影响因素分析

运用自制热镀锡膜铜-康铜热电偶测温方法测定了鸭梨果实不同部位的冻结曲线,对鸭梨果实与汁液的冻结特点作了比较,并对冰点温度与部分品质参数的关系进行了探讨.试验结果表明,鸭梨果实的冻结曲线有3种形式,典型的形式具有过冷点、初始冰点、平衡冰点、终止冰点等关键特征点;果实不同部位的过冷点和冰点温度及其出现的时间顺序存在差异,越靠近果心,冻结速率越小,冰点温度越高;果实与果汁冻结特征的不同点在于果实有“特征小段”而果汁没有,且果汁较果实容易冻结;在一定范围内,鸭梨果实冰点温度与可溶性固形物含量呈极显著负相关,而与单果重、硬度相关性不显著.     

苹果酒酿造工艺及高级醇的气相色谱分析

以富士苹果为原料,利用安琪葡萄酒活性干酵母、丹宝利高活性干酵母和Y1酵母(本实验室自选)分别在18、23、28℃3种条件下进行苹果酒发酵试验,主发酵结束后用气相色谱测定高级醇含量并对苹果酒的质量进行感官评定。试验结果表明:利用安琪葡萄酒高活性干酵母,在23℃条件下发酵酿造的苹果酒感官评定分数最高;以安琪葡萄酒高活性干酵母和丹宝利酵母为菌种发酵时,高级醇的含量随着发酵温度的增加逐渐增加,而Y1酵母在低温条件下发酵时高级醇含量较高;苹果酒中异丁醇等高级醇含量(X)和感官评定分数(Y)呈线性相关,其回归方程为y=-6×10-5x+92.4,相关系数r=0.7846(p<0.01);苹果酒中异丁醇等高级醇以在发酵过程中形成为主。     

鳜鱼肌肉品质评价的初步研究

以7尾健康成年鳜鱼(体重383g±12·6g)为实验对象,测定鱼肉品质的相关指标,包括:肌肉水分含量、脂肪含量、胶原蛋白含量、肌肉pH、电导率、滴水损失、肌肉渗出性损失、肌纤维直径、肌肉质构。结果表明,鳜鱼肌肉水分含量为78·93%±0·61%,脂肪含量为1·59%±0·47%,胶原蛋白含量为0·98%±0·12%,肌肉pH为(6·00±0·16),鱼体垂直电导率为(1·93±0·69)S,鱼体水平电导率为(5·60±0·36)S,滴水损失为10·48%±2·69%,肌肉渗出性损失为32·92%±1·71%,肌纤维直径为(107·36±11·17)μm;在肌肉质构指标中,硬度为(716·73±136·35)g,弹性为(0·86±0·04),凝聚性为(0·53±0·05),黏性为(369·82±79·59),咀嚼力为(317·61±77·41)g,回复力为(0·36±0·02)。在上述指标中,鳜鱼肌纤维直径(Y)与肌肉硬度(X)呈显著负相关(P0·05):Y=-9·6397X2+596·83X-8181·5(R2=0·968);肌肉脂肪含量(Y)与硬度(X)之间呈显著负相关(P0·05):Y=(2×106)X2-88589X+1764·2(R2=0·878);肌肉咀嚼力(Y)与pH(X)呈极显著正相关(P0·01):Y=1853X2-21274X+61286(R2=0·928)。本研究表明,肌纤维直径、脂肪含量、肌肉pH等是评价鳜鱼肌肉品质的重要指标。     

用电导率法测定莲藕冻结点的研究

本文根据食品物料在温度改变时电导率变化的性质,用电导率仪对莲藕的冻结点进行测定。研究表明,莲藕的冻结点为-1．4～-1．9℃,经实际验证,误差小于0．05℃。用电导率法测定果蔬冻结点的方法具有较为简单、精确和经济的特点。该方法对新鲜肉类和液态食品的冻结点测定具有借鉴作用和推广价值。     

米粉种类及添加量对蛋糕品质的影响

以籼米、粳米、糯米为原料,用一定比例的米粉替代面粉制作蛋糕.采用感官、质构、比容等指标评价米粉种类及添加量对蛋糕品质的影响,建立米粉物性指标与蛋糕品质指标间的相关性.结果表明,米粉的种类及添加量对蛋糕的感官、质构、比容等均有显著性影响;米粉物性指标与蛋糕品质指标间均有一定相关性,其中蛋糕的口感、弹性分别与米粉添加量呈极显著负相关(-0.910)与极显著相关(0.811);蛋糕比容分别与米粉水分含量、脂肪含量均呈极显著正相关(0.823、0.764);回归分析得蛋糕感官总分的回归方程为:Y感官总分=1.63+0.990X蛋糕口感+1.646X米粉添加量-8.058X米粉水分含量+0.136X蛋糕外观-0.23X蛋糕比容.     

梅州金柚食用后期的苦味来源分析

金柚美味可口,营养丰富,深受消费者喜爱。随着储藏时间的延长,金柚会产生苦味,严重影响其产业的健康发展。为深入探究来源,本研究以梅州金柚为研究对象,深入探究其长时间存放后的苦味来源。对其进行分级后,同步测定金柚可滴定酸、可溶性固形物、最大粘附力、柠檬苦素含量、诺米林含量、柚皮苷的含量,借助randomforest等方法分析各项指标的相关性。结果表明,金柚的可溶性固形物与感官评分呈极显著正相关(R=0.78);诺米林与感官评价呈极显著负相关(R=-0.69)、柚皮苷与感官评价呈显著负相关(R=-0.59),食用后期金柚的苦味与可溶性固形物的含量密切相关。该研究可为金柚脱苦、金柚品质快速判断等研究提供一定的理论依据。     

PREDICTION OF FREEZING TIMES FOR FOODS AS INFLUENCED BY PRODUCT PROPERTIES

This investigation utilizes a computer simulation technique to predict the freezing times and temperature history curves for food products. The input information consists of the product properties for temperatures above the initial freezing point, freezing medium conditions and the initial product temperature. It has been established that food products with lower initial freezing points, higher initial water contents and higher initial product densities will have longer freezing times. The prediction of freezing time is most sensitive to the accuracy of the measurement of the product density and the initial freezing point if the freezing point is above ?0.5°C. The influence of the accuracy of unfrozen product thermal conductivity data on the freezing time is not important in the range of 0.45 to 0.55 W/m°K investigated. The combined influence of inaccuracy in measuring these product properties on the freezing time prediction will be significant even if the influence of an individual product property is small.     

Relationship Between Static Electrical Conductivity and Unfrozen Water Content in Food Products

The static electrical conductivity measurements on frozen foods such as citrus juice and varieties of cheese showed that both conductivity and unfrozen water content in food products varied directly with temperature. In describing the log σ vs 1/T curve, where σ is the conductivity and T is the absolute temperature, it was found that the linear portion of the curves at low temperature was related to bound water content which was independent of temperature, whereas the non-linear portion in the temperature range between the freezing point and 10 or 35 degrees below the freezing point was related to the unfrozen free water content which was dependent on temperature.     

反演法求小麦面团在冻结温度范围内的热导率

为确定小麦面团在冻结温度范围内的热导率,采用差式量热扫描法测量了3个不同水分含量面团的比热,然后利用COMSOL软件反演求出面团在-30~30℃范围内的热导率。结果表明,面团热导率随水分含量增大(38%~44%)而逐渐升高;且随着温度的降低,面团的热导率逐渐降低,但是当面团的温度降至冰点后,面团的热导率急剧上升,然后又呈缓慢上升趋势。通过对面团热导率与水分含量关系的进一步分析,建立了速冻温度范围内面团热导率随温度和水分含量变化的数学模型。     

电导率仪测定食品冰点方法的研究

通过观测多种液态和固态食品物料的温度和电导率的关系,发现当温度降至食品物料冰点时,电导率就急剧下降。本试验测定出王老吉凉茶、可口可乐、玉米浓浆的冰点分别为-1.8,-2.0,-2.2℃;新鲜罗非鱼片、南美白对虾、黄冠梨的冰点分别为-1.3,-1.5,-1.2℃。     

A Novel Method for Simultaneous and Continuous Determination of Thermal Properties during Phase Transition Applied to Calanus finmarchicus

Abstract: The thermal properties of a product are the most important parameters for practical engineering purposes and models in food science. Calanus finmarchicus is currently being examined as a marine resource for uncommon aquatic lipids and proteins. Thermal conductivity, specific heat, enthalpy and density were measured over the temperature range from −40 to +20 °C. The initial freezing point was determined to be −2.3 °C. The thermal properties were recorded continuously on 4 samples using a new method, and the results were compared with predictive models. The accuracy of the new method is demonstrated by different calibration runs. Significant differences in the thermal conductivity of the frozen material were found between the parallel-series model and the data, whereas the model of Pham and Willix (1989) or the Maxwell–Euken adaption showed better agreement. The measured data for specific heat, enthalpy, and density agreed well with the model. Practical Application: The thermal data obtained can be used directly in food engineering and technology applications, for example, in a thin layer model for freezing food for which precise thermal data for each layer are now available, enabling the more accurate prediction of freezing times and temperature profiles. Dimensionless numbers (such as the Biot number) can also be based on measured data with minor deviations compared to more general modeled thermal properties. Future activities will include the generation of a comprehensive database for different products.     

CALCULATION of INITIAL FREEZING POINT,EFFECTIVE MOLECULAR WEIGHT and UNFREEZABLE WATER of FOOD MATERIALS FROM COMPOSITION and THERMAL CONDUCTIVITY DATA1

A procedure was developed for simultaneous determination of the effective molecular weight, unfreezable water, and initial freezing point of foods based on composition and thermal conductivity data. Freezing properties were determined by trial and error and optimized by minimizing the difference between calculated and reported values of thermal conductivity. the procedure involved determination of the ice fraction at several temperature levels. Corresponding thermal conductivity values at each temperature level were then calculated. Results showed that calculated values of effective molecular weight, unfreezable water, and initial freezing point for various types of meat and fish are comparable to those published. the parallel-perpendicular model was found an excellent predictor of thermal conductivity of frozen meat and fish with muscle fibers oriented toward the direction of the heat flow.     

脆肉鲩低温相变区热特性的研究

采用差示扫描量热仪,研究脆肉鲩鱼肉在低温相变区的冰点、表观比热和热焓以及NaCl、NaCl 与蔗糖混合物添加量对脆肉鲩热特性的影响。结果表明,脆肉鲩鱼肉的冻结相变温区为－ 12.5～－ 11℃,熔融相变温区为－ 1.9～0.1℃,冰点为－ 0.2℃,冰点的表观比热和热焓值分别为130.56J/g·℃、305.57J/g。随着NaCl、NaCl和蔗糖混合物添加量的增加,脆肉鲩肌肉的相变温区向低温方向移动,冰点的表观比热和热焓值下降。鱼肉中NaCl添加量较低时,添加蔗糖可减缓相变温度的下降,当NaCl 添加量大于2% 时,添加蔗糖对鱼肉相变区温度的影响不大,NaCl 起主导作用。     

Determination of Dextrose Equivalent Value and Number Average Molecular Weight of Maltodextrin by Osmometry

ABSTRACT:  Dextrose equivalent (DE) value is the most common parameter used to characterize the molecular weight of maltodextrins. Its theoretical value is inversely proportional to number average molecular weight ( M_n ), providing a theoretical basis for correlations with physical properties important to food manufacturing, such as: hygroscopicity, the glass transition temperature, and colligative properties. The use of freezing point osmometry to measure DE and M_n  was assessed. Measurements were made on a homologous series of malto-oligomers as well as a variety of commercially available maltodextrin products with DE values ranging from 5 to 18. Results on malto-oligomer samples confirmed that freezing point osmometry provided a linear response with number average molecular weight. However, noncarbohydrate species in some commercial maltodextrin products were found to be in high enough concentration to interfere appreciably with DE measurement. Energy dispersive spectroscopy showed that sodium and chloride were the major ions present in most commercial samples. Osmolality was successfully corrected using conductivity measurements to estimate ion concentrations. The conductivity correction factor appeared to be dependent on the concentration of maltodextrin. Equations were developed to calculate corrected values of DE and M_n  based on measurements of osmolality, conductivity, and maltodextrin concentration. This study builds upon previously reported results through the identification of the major interfering ions and provides an osmolality correction factor that successfully accounts for the influence of maltodextrin concentration on the conductivity measurement. The resulting technique was found to be rapid, robust, and required no reagents.     

特殊医学用途配方食品渗透压的不同检测方法和结果比较分析

研究了不同仪器、不同检测方法检测特殊医学用途配方食品的渗透压的检测结果差异情况和现阶段国内外各类特殊医学用途配方食品渗透压状况。收集国内外各类特殊医学用途配方食品样品38个,采用德国GONOTEC 3000-D渗透压仪进行检测,同时选择部分代表性样品使用其他冰点法仪器和露点法仪器进行仪器比对和方法比对。冰点法检测的38个样品的渗透压检测结果范围为89 mOsmol/kg~869 mOsmol/kg,相对标准偏差为0.25%~0.97%;进行比对的样品中,冰点法检测结果平均值的范围为168 mOsmol/kg~640 mOsmol/kg,相对标准偏差为0.18%~1.70%;露点法检测结果平均值的范围为162 mOsmol/kg~594 mOsmol/kg,相对标准偏差为0.61%~4.81%。渗透压较高的样品以氨基酸配方和全营养配方为主,专门用于婴儿的配方样品渗透压检测结果较低;露点法的检测结果低于冰点法,检测结果的稳定性和重复性不及冰点法。检测过程中保持环境温湿度和仪器的稳定性,使用合理的进样量能够减小检测误差。