Heat Gelation Properties of Actomyosin and Surimi Prepared from Atlantic Croaker

Comminuted mixtures of fish muscle (surimi) and salt undergo a sol-gel transformation when subjected to heat processing which is responsible for the textural characteristics of fabricated imitation shellfish meats. Upon “setting” a fish muscle sol at temperatures below those conventionally used for heat processing meat products, a fine translucent gel network is formed which imparts strength and resiliency to the subsequently cooked gel product. Increased firmness and opacity, as well as some loss in cohesiveness, were noted upon processing surimi sols at higher temperatures. The low temperature “setting” property of fish proteins necessitates rapid forming or extrusion of the product prior to the initiation of network formation to insure a firm texture in the final product.     

Thermal Denaturation and Aggregation of Actomyosin from Atlantic Croaker

The denaturation of croaker actomyosin was studied with respect to the important role of coagulation and gelation phenomena in the manufacture of gel-type meat and fish products. Measurements of turbidity (A₆₀₀), viscosity, calcium ATPase activity, total sulfhydryl groups and protein coagulation of croaker actomyosin solutions during heating at a constant temperature increase of 1°C/min revealed no loss of enzymic activity nor evidence of protein aggregation prior to reaching a temperature of 37–40°C, at which point the protein coagulated with corresponding loss of ATPase activity and sulfhydryl groups and an increase in turbidity. The degree of protein coagulation was highly dependent on the protein concentration. An observed increase in the apparent viscosity over the 30–35°C temperature range was postulated to result from interaction of protein molecules due to noncovalent forces.     

Phase and State Transitions in Granular Starches Studied by Dynamic Differential Scanning Calorimetry

Phase and state transitions of granular starches heated in water are studied by dynamic differential scanning calorimetry (DDSC). The DDSC results of various granular starches show a stepwise heat capacity (C_p) change in the storage C_p curve, which starts at the beginning of melting or immediately preceding gelatinization and ends before the melting reaches its peak temperature. Annealing reduces the magnitude of this stepwise change in storage C_p. After the amorphous phase is selectively removed by acid, the stepwise storage C_p is greatly reduced. The stepwise storage C_p increase is not observed when recrystallized linear short chains from enzyme‐debranched waxy maize starch are heated in water. The results show that the stepwise change in C_p observed on the granular starch is a unique property associated with the phase transition of granular structure and reflects a glass transition of the rigid amorphous regions in starch granules. The glass transition of the mobile amorphous phase in granular starch is believed to extend over a broad range of temperatures before gelatinization. A small glass transition below 0°C is directly detected by DDSC and is attributed to part of the mobile amorphous fraction in granular starch.     

Effect of Moisture on the Thermal Behavior of Strawberries Studied using Differential Scanning Calorimetry

Differential scanning calorimetry was used to determine the thermal transitions in fresh and freeze-dried strawberries and the moisture dependence of these transitions. The freeze-dried strawberry samples had a glass transition at 30–60°C, and the melting endotherm of the dried products was similar to that for freeze-dried sugars. The glass transition temperature of humidified samples was a linear function of the water activity; it decreased with increasing moisture content. Ice was found to melt at a moisture content of 21.4% or above. The melting of ice in strawberries was similar to that in sugar solutions and fruit juices.     

DSC法研究6种莲子淀粉糊化和老化特性

利用差示扫描量热仪(DSC)结合Avrami 方程研究在4℃、储存两周的条件下,6种莲子淀粉的糊化和老化特性,探讨直链淀粉以及贮存时间对其热力学行为产生的影响,并用SPSS软件计算其相关性。结果表明：6种莲子淀粉的糊化温度、ΔH、老化焓、老化度以及老化速率存在着一定的差异,老化速率的大小顺序为太空莲＞美人红＞大紫红＞武植2号＞鄂莲＞洪湖莲,太空莲淀粉的老化速率是洪湖莲淀粉的1.36 倍;6种莲子淀粉的成核方式均为瞬间成核;4℃条件下贮存两周的莲子淀粉的老化度随着贮存时间的增加而增大;直链淀粉含量与Avrami 指数n值呈负相关,与速率常数k值、ΔH、老化焓以及冰融溶焓呈正相关。     

Subzero Glass Transition of Waxy Maize Starch Studied by Differential Scanning Calorimetry

A mixture of waxy maize starch and water (1:2, w/w) was heated in a differential scanning calorimeter (DSC) pan to different temperatures to obtain different degrees of gelatinization. Each pan was then quenched to ‐30°C and rescanned, and the subzero glass transition temperature (T_g′) of the content was determined. A three‐phase model of a starch granule—a mobile amorphous phase, a rigid amorphous phase, and a crystalline phase—was used to interpret results and explain the glass transitions in starch. Waxy maize starch had an onset gelatinization temperature (T_o) of 61.5°C, peak temperature (T_p) of 70.3°C, and completion temperature (T_c) of 81.7°C. The T_g′ was clearly noted after the starch and water mixture was heated to T_p and T_c, but was small and barely observable when the mixture was heated up to T_o and immediately cooled to ‐30°C. When the starch and water mixture was heated to 55°C, which was 6°C below the T_o, and held for 2 h, a T_g′ was observed. Moreover, T_g′ began to appear and was observable if the starch and water mixture was heated to 10°C below gelatinization onset temperature (51°C) and annealed for 2 h without any gelatinization. Further holding at ‐7°C showed a clear subzero glass transition of annealed native starch granules.     

Phase Transitions and Unfreezable Water Content of Carrots, Reindeer Meat and White Bread Studied using Differential Scanning Calorimetry

Differential scanning calorimetry was used to measure the phase transitions and unfreezable water of carrots, reindeer meat, and white bread. The incipient melting point (T_im), incipient intensive melting point (T′_im), the onset temperature of melting (T_m), latent heat of melting (ΔH_m), specific heat (C_p) and enthalpy (ΔH) were determined from the melting curves. T′_im, T_mΔH_m and ΔH and the unfreezable water were found to be functions of moisture. The T_im, temperatures were ? 39°C, ?33°C, ?40°C; T′_im, ?11.8°C, ?13.3°C ?17.3°C T_m, ? 3.4°C, ? 3.1°C, ? 12.2°C for carrot, reindeer meat, and white bread, respectively. The unfreezable water was 8.3% for carrots, 15.1% for reindeer meat, and 22.5% for white bread, determined from ΔH_m and 3.4%, 6.4% and 2.9%, determined from ΔH. The lowest water detectable from ΔH_m was 26.4% and from ΔH 3.6%.     

差示扫描量热技术研究甘油二酯的热力学性质

甘油二酯是存在于各种动植物油脂中的天然微量成分,因其具有安全、营养、人体相容性高和加工适应性好等优点而被作为一种多功能添加剂,广泛应用于食品和化妆品等行业中。甘油二酯的热力学性质对其功能性有很大的影响,不同来源的甘油二酯的初始结晶温度、峰值温度和热晗值等热力学性质不同。差示扫描量热技术是甘油二酯热力学性质研究中应用最广泛的热分析技术之一,具有灵敏度高、分辨率高、适用范围广、操作简单、快速和重现性好等优点。主要对差示扫描量热技术的原理和分类进行论述,进一步对该技术在甘油二酯的热力学性质的研究方面进行综述。     

Study of Thermal Properties of Oat Globulin by Differential Scanning Calorimetry

The thermal behavior of oat globulin was studied by differential scanning calorimetry (DSC). The effects of pH, salts, and of various structure perturbants upon thermal characteristics were determined. Raising or lowering pH from near neutrality reduced denaturation temperature. (T_d), enthalpy (ΔH) and cooperativity indicated by increase in width at half height (ΔT_1/2). The effect of salts on thermal stability was related to their position in the lyotrophic series and suggests involvement of hydrophobic interaction in the thermal stability of oat globulin. Increasing concentrations of urea progressively lowered T_d and ΔH and increased ΔT_1/2; sodium dodecyl sulfate (SDS) lowered ΔH without affecting T_d; ethylene glycol (EC) lowered T_d without changing ΔH. Dithiothreitol did not affect DSC characteristics suggesting that disulfide bonds do not contribute to the thermal response of oat globulin.     

用差示扫描量热法测定调温针织物的热性能

介绍了差示扫描量热法（DSC）的原理、用途及用法,测定了罗纹空气层织物的相变温度和相变焓,得到了其DSC曲线图。结果表明该织物具有良好的温度调节功能。     

Studies of Thermal Denaturation of Oat Globulin by Differential Scanning Calorimetry

Thermal denaturation of oat globulin was studied by differential scanning calorimetry (DSC). Prior heat treatments at 100°C and 110°C resulted in a progressive decrease in enthalpy (ΔH) indicating partial denaturation. Marked increase in denaturation temperature (T_d) and onset temperature (T_m) and decrease in width at half peak height (ΔT_1/2) suggest that the preheated protein assumed a more compact conformation or associated to a complex structure with higher thermal stability and cooperativity. The heated globulin was segregated into soluble and insoluble fractions containing native and denatured protein respectively. The denaturation kinetics of oat globulin was studied and results show a reaction order of 2.5 and an activation energy of 505 KJ/mol. Heat treatments caused a pronounced increase in activation energy and pre-exponential factor.     

Measurement of Food Thermal Conductivity Using Differential Scanning Calorimetry

To measure thermal conductivity of foods, an attachment to a differential scanning calorimeter was constructed. A needle probe with a 40 gauge type-T thermocouple was used to measure the temperature of a cylindrical food sample. The DSC heating pan temperature was maintained at 40°C, and then raised to 50°C. The average thermal conductivities of rutabagas, radish, parsnip, turnip, potato, green apple, and carrot were 0.447, 0.499, 0.392, 0.480, 0.552, 0.405, and 0.564 W/m°C, respectively, for a temperature range between 40–50°C. The DSC method was reliable, precise, and a relatively rapid technique for determining thermal conductivity of foods.     

基于差示扫描量热法研究喷雾干燥鸡蛋全粉热转变温度

研究含非冻结水（较低水分含量）喷雾干燥鸡蛋全粉与含冻结水（较高水分含量）样品的热转变温度,以及鸡蛋全粉的吸附等温线,为蛋制品干燥或冷冻加工的稳定性提供数据支持。采用差示扫描量热仪检测样品,结果发现含非冻结水样品中有两个吸热峰,分别是卵转铁蛋白和卵白蛋白的变性峰,二者的变性温度（Td）都随湿基水分含量的增大而减小。对于含冻结水的样品,冻结温度（TF）与湿基水分含量之间的关系采用Clausius-Clapeyron方程描述,由冰晶熔融焓值得到非冻结水的湿基水分含量为0.18 g/g,再通过Clausius-Clapeyron方程得到其对应的冻结终点温度（Tm’）为－14.6 ℃。只有当湿基水分含量为0.22 g/g时,才检测到其玻璃化转变温度（－46.3 ℃）。此外,还研究了喷雾干燥鸡蛋全粉的吸附等温线,采用GAB模型进行非线性拟合,结果表明鸡蛋的吸附等温线为II型,其单分子层干基水分含量为0.043 g/g。本研究结果能为蛋制品的最适干燥或冷冻加工条件提供理论依据。     

Gelling Properties of Atlantic Croaker Surimi Processed by Acid or Alkaline Solubilization

ABSTRACT: Textural properties of gels from Atlantic croaker surimi recovered by isoelectric precipitation, following acid (AC) or alkaline (AL) solubilization, were compared with that of conventionally washed (CW) surimi. Gel strengths were in the order of AL > AC > CW, with higher gel strength and deformability induced by microbial transglutaminase addition. None of the surimi treatments evidenced endogenous TGase activity. Salt (2% NaCl) addition had variable effects. Proteolysis was evident by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in gels from all treatments when preincubated at 30 °C or 40 °C.     

Determination of Amylose by Differential Scanning Calorimetry

A differential scanning calorimetry (DSC) method for the determination of amylose as its amylose-L-α-lysophosphatidylcholine (LPC) complex is described. Potato amylose/amylopectin mixtures covering the range of 0–95% amylose were heated in the presence of LPC, cooled and then reheated to follow melting of the amylose-LPC complexes formed during the cooling phase. A linear relationship (r = 0.98) was obtained between the amylose content of the mixtures and the enthalpies of the amylose-lipid complexes. This linear calibration was used to predict the amylose content of various native starches, rice flours, wheat flour, durum wheat semolina, and lyophilized raw potato on the basis of the melting enthalpy of their amylose-LPC complexes. Except for the potato samples, amylose contents determined by the DSC method were in good agreement with those obtained from a colorimetric assay.     

Rigidity and Viscosity Changes of Croaker Actomyosin During Thermal Gelation

Two types of thermal scanning rigidity monitors (TSRM) were developed which are nondestructive and capable of monitoring rigidity or viscosity changes during heating of proteins over a wide range of concentrations. Thermal transitions which occur during gelation of croaker actomyosin were studied by these TSRM devices and the Brookfield viscometer during constant rate heating (1°C/min). Gelation of actomyosin occurred only at protein concentrations above 5.5% under these conditions. In plots of rigidity versus temperature, three transitions were observed during gelation, occurring near 38°C 46°C and 60°C. At lower concentrations, only one peak was observed, occurring near 36°C. A relationship between the 36–38°C transition in rheological properties and the high temperature “setting” phenomenon of fish proteins is postulated.     

Retrogradation of Rice Starches Studied by Differential Scanning Calorimetry and Influence of Sugars, NaCl and Lipids

In waxy and nonwaxy rice starch gels the retrogradation process was a function of time. The enthalpy for rice starch gel with high amylose content was higher than those for low amylose content or for waxy starch samples. In all rice starch gels, samples stored under 25°C had lower enthalpy and higher endothermic onset temperature. In presence of sucrose, extent of retrogradation increased, while in presence of NaCl, it decreased. Effects of maltose, glucose and lipids were dependent on rice starch gel and storage temperature.     

Effects of Added Egg White or Whey Protein Concentrate on Thermal Transitions in Rigidity of Croaker Surimi

Rigidities of surimi [refined minced fish (MF)] sols, alone and in combination with egg white (EW) and whey protein concentrate (WPC) were measured during constant-rate heating by a nondestructive technique. Each of the protein types tested showed measureable changes due to variation of the heating rate or NaCl concentration of the sol. Rigidity and differential scanning calorimetric (DSC) thermograms for mixtures resembled composites of the individual protein source profiles, indicating that no major changes occurred in thermal gelling properties of the component proteins due to mixing. Maximum rigidity values indicated more favorable gelation of MF/WPC than MF/EW combinations.     

Gelatinization Transitions of Acid‐modified Tapioca Starches by Differential Scanning Calorimetry (DSC)

Tapioca starch was partially hydrolyzed by 6 % and 12 % hydrochloric acid (w/v) at room temperature for various length of time. The gelatinization transitions of the acid‐modified tapioca starches were studied using Differential Scanning Calorimetry. Starch suspensions (67 % moisture) were heated at 5 °C/min to follow melting transition of amylopectin. As the hydrolysis time increased, onset (T_o), peak (T_p) and conclusion (T_c) temperatures of gelatinization have been observed to increase, in the same order of relative crystallinity, until reaching some critical values, then decreased with the large broadening of the endotherms. The increasing of the transition temperatures corresponded to the retrogradation of the remaining partially hydrolyzed amylose followed by a decrease of these parameters corresponding to the reduction of the length of the chains of double helices amylopectin.     

Effect of Extraction Method on the Oxidative Stability of Camelina Seed Oil Studied by Differential Scanning Calorimetry

Camelina seed is a new alternative omega‐3 source attracting growing interest. However, it is susceptible to oxidation due to its high omega‐3 content. The objective of this study was to improve the oxidative stability of the camelina seed oil at the extraction stage in order to eliminate or minimize the use of additive antioxidants. Camelina seed oil extracts were enriched in terms of natural antioxidants using ethanol‐modified supercritical carbon dioxide (SC‐CO₂) extraction. Oxidative stability of the camelina seed oils extracted by ethanol modified SC‐CO₂ was studied by differential scanning calorimeter (DSC), and compared with cold press, hexane, and SC‐CO₂ methods. Nonisothermal oxidation kinetics of the oils obtained by different extraction methods were studied by DSC at varying heating rates (2.5, 5, 10, and 15 ° C/min). Increasing ethanol level in the ethanol‐modified SC‐CO₂ increased the oxidative stability. Based on oxidation onset temperatures (T_on), SC‐CO₂ containing 10% ethanol yielded the most stable oil. Oxidative stability depended on the type and content of the polar fractions, namely, phenolic compounds and phospholipids. Phenolic compounds acted as natural antioxidants, whereas increased phospholipid contents decreased the stability. Study has shown that the oxidative stability of the oils can be improved at the extraction stage and this may eliminate the need for additive antioxidants.