可可脂在非等温条件下结晶及融化特性的研究

采用差式扫描量热仪(DSC)研究了升降温速率和乳化剂时可可脂非等温结晶和融化过程中晶体衍变过程的影响.结果显示:可可脂结晶和融化过程都对温度变化速率(λ)敏感,随λ的提高,放热峰和吸热峰强度均增大,峰值(T_p)则分别降低和升高;单甘酯促进可可脂组分分离,降低结晶温度,改变晶体的融化特性;卵磷脂则提高可可脂结晶温度,对融化特性不产生影响.添加单甘酯和卵磷脂都使可可脂结晶量增加.     

Thermal Transitions of Actomyosin and Surimi Prepared from Atlantic Croaker as Studied by Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) was used to investigate thermal transitions of fish mince (surimi) and actomyosin from croaker. Three endothermic peaks were observed in DSC thermograms of surimi. After addition of salt, transition temperatures shifted to lower temperatures. Preheating samples containing 3% salt at various temperatures showed that 40°C heating caused the first peak to disappear, and preheating at temperatures higher than 50°C caused virtual disappearance of all transition peaks. Low temperature storage (4°C) of samples caused no significant change in thermograms of salted or unsalted surimi over a 5-day storage period. Evidence suggests that changes of fish protein during low temperature “setting” are different from those occurring during high temperature “setting.”     

A DSC determination of phase transitions and liquid fraction in fish oils and mixtures of triacylglycerides

The thermal phase transitions of 18 pure triacylglycerides (TAGs) and four fish oils were investigated using differential scanning calorimetry (DSC) and modulated DSC (MDSC) in the temperature range from − 150 to 80 °C. The dependence between the heat of fusions and the melting temperatures was determined for pure TAGs, and a regression equation was obtained. A liquid fraction in TAG mixtures and fish oils was determined by the partial integration of melting peaks enhanced by the regression equation. The method was considered to be beneficial for fish oils, because several pure TAGs did not show crystallization. These “unfreezable” TAGs were composited by polyunsaturated fatty acids with three or more double bonds. They showed a glass transition in the temperature range between − 113.9 and − 105.6 °C. The fish oils melted in the range between − 92.6 and 23 °C. The heat of melting was measured to be between 31.5 and 41.8 J g^− 1. The oils had a significant share of liquid fraction (between 40.0 and 58.0%) at temperatures down to − 110.0 °C when the glass transition appeared.     

Thermal and dynamic rheological properties of wheat flour fractions

A commercial high gluten flour (HGF) was fractionated into prime starch (PS), tailing starch (TS), and gluten (G). Fractions were examined alone or in various combinations. Dynamic rheological properties of samples were measured in an oscillatory rheometer (strain 0.02; frequency 0.1 Hz) during heating at 1°C/min. Thermal characteristics of samples were determined by differential scanning calorimetry (DSC) at a heating rate of 10°C/min. The loss (G″) and storage (G′) moduli of PS and mixed G/PS, G/TS, and G/PS/TS increased after 60°C, reaching peak values (e.g. 81, 301, 313, and 3000 Pa in G′, respectively) around 75°C after which the moduli decreased. HGF showed a steady increase in G′ from 32 to 2490 Pa as temperature increased from 65 to 90°C, indicating continuous formation of elastic networks. Cooling increased G′ for G/PS/TS, decreased G′ for HGF, and produced no rheological transitions for all samples. TS and G alone did not exhibit appreciable viscoelastic responses to the heating and cooling temperatures. DSC measurements revealed a major endothermic transition in HGF. This transition, with a peak around 60°C, was due to starch gelatinization. The presence of G or TS resulted in reduced melting enthalpies of starch in the PS fraction. Gluten or TS fractions alone or in combination did not exhibit any endothermic transitions.     

Hydrothermal Changes of Starch Monitored by Combined NMR and DSC Methods

The thermal, dynamic, and structural properties of wheat starch–water systems with different levels of water content (11, 35, 40, 42, 45, and 50%, wet basis) were investigated. ¹H time domain nuclear magnetic resonance (TD-NMR) spectroscopy was used to interpret and quantify the water transfer and starch transformations in terms of water uptake, granule swelling, amylose leaching, and melting of starch polymers in relation to the different levels of water content. Complementary differential scanning calorimetry (DSC) experiments were performed to study the effects of water content on the degree of starch gelatinization. In particular, this twofold approach was applied to the first endotherm to study the mechanisms of gelatinization with a common heating range both in NMR and DSC. It was shown that the trend of the enthalpy changes in the first phase transition in starch–water (SW) mixtures was strongly correlated with the loss of solid content measured by NMR in the corresponding temperature range (55–70 °C). Based on the evolution of the relative amplitudes of T ₂, structural transformations of starch were shown to occur in both crystalline and amorphous regions within SW samples, supporting the fact that the amorphous phase of starch also plays a significant role in the phase transition of granules during gelatinization. This dynamic and hydrothermal approach provided the first NMR-based interpretation of the first endotherm measured by DSC.     

THERMAL CHARACTERISTICS OF POLYLACTIC ACID/WHEAT GLUTEN BLENDS

The interaction between polylactic acid (PLA) and wheat gluten (gluten) has been studied using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction and phase contrast microscope. The primary DSC thermogram of gluten showed one glass transition (Tg) at 63C. Neat (pure) PLA also showed a Tg around the same temperature range followed by crystallization (Cry) and a melting (Mel) transition. Different PLA : gluten blends (20:80, 50:50, 80:20) showed a Tg followed by PLA Cry and immediate Mel transitions. However, subsequent heating‐cooling cycling of the blend demonstrated a decrease in PLA Cry and Mel transitions and the appearance of a second Tg. The presence of gluten reduced the number of cycles needed to change PLA Cry structure to mostly amorphous. The low PLA Cry indicates an interaction between the two polymers. The TGA data showed slower PLA degradation compared with gluten, where 10% was degraded at 316C while 10% of the gluten degraded at 254C. Solid‐state FTIR showed that amide I and II peaks significantly decreased signifying gluten‐heat degradation. A strong peak, corresponding to ester formation between gluten and hydrolyzed gluten molecules, appeared at 1750/cm. The esterification increased in the presence of PLA. The phase contrast microscope demonstrated that the melting of PLA starts at 150C, which means that the continuous phase between 150 and 250C was the melted PLA. At 220C, gluten formed a thin layer; and at about 245C, it aggregated.     

Kinetics of Protein Degradation and Physical Changes in Thermally Processed Atlantic Salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>)

Protein denaturation is the main reason for physicochemical changes in muscle foods during thermal processing. The purpose of this study was to understand the kinetics of quality degradation and protein denaturation of Atlantic salmon (Salmo salar) during thermal pasteurization. Findings indicate that cook loss, area shrinkage, and protein denaturation parameters (both dielectric loss and differential scanning calorimetry (DSC) studies) were best fitted to a first-order reaction. In addition, color parameters followed zero-order kinetics. Fourier transform infrared spectroscopy (FTIR) results showed that increasing heating time and temperature reduced the α-helix peak, indicating protein denaturation. At the same time, the β-sheet peak intensity increased, which is related to protein aggregation. Correlation loading plots from FTIR spectra showed that protein denaturation was dominant below 75 °C. Above this transition temperature, protein denaturation occurred rapidly and protein aggregation became more obvious. The dielectric properties in cooked salmon at different times and temperature increased with increasing heating time and temperature, while penetration depth decreased significantly (P < 0.05). The kinetics of protein denaturation from DSC showed that the activation energy of 300.6 kJ/mol and k ₀ was 1.1 × 10⁴² min^?1. Our findings on kinetic data from protein denaturation and physical changes may be used to improve the processing schedule in the production of safe, high-quality pasteurized salmon.     

Effect of Moisture Content on the Melting of Wheat Starch

The effect of water on heating wheat starch-water mixtures of water content (between 2.8% and 90%) has been observed by differential scanning calorimetry. Four endothermic transitions were observed for wheat starches heated in the presence of limited water (moisture levels of 40,50%). These transitions appears to be due to melting of amylopectin crystallites, amylose-lipid, and amylose. The heat decomposition temperature range of wheat starch were 253-302°C and the plasticization effect according to the amount of water was small. The melting temperature obtained by extrapolation to zero volunme fraction of water were 234°C for M1 DSC endotherm, 254.3°C for M2 DSC endotherm, 267.8°C for M3 DSC endotherm.     

THERMAL AND DYNAMIC-MECHANICAL PROPERTIES OF FROZEN WHEAT DOUGHS WITH ADDED SUCROSE,NaCl, ASCORBIC ACID,AND THEIR MIXTURES

The effects of sucrose, NaCl, and ascorbic acid on the physical state of wheat dough at sub-zero temperatures were investigated using Differential Scanning Calorimetry (DSC) and Dynamic-Mechanical Analysis (DMA). The DSC thermograms were obtained for annealed samples by scanning from ?80 to 10°C at 5°C/min. Added sucrose and NaCl decreased the onset of ice melting of doughs, and they were found at ?26°C. Added sucrose and NaCl increased the relative amount of unfrozen water in doughs, while added ascorbic acid had not noticeable effects. DMA measurements were made for annealed samples at a heating rate of 1°C/min from ?150 to 10°C. The loss modulus, G″, of DMA showed an α-relaxation (glass transition), two low temperature relaxations (β and γ), and melting of ice in all doughs with added ingredients.     

The Effect of Hybrid Carrageenan on the Thermo-rheological Properties of Gluten-Free Flour Doughs Using a Modified Kneading Protocol

Thermo-rheological behaviour of chestnut flour doughs supplemented with kappa/iota-hybrid carrageenan (HC) (up to 2.0%, flour basis (f.b.)) and sodium chloride (1.8%, f.b.) was determined at both target (C1) and final (C5) mixing peaks. For this purpose, small amplitude oscillatory shear (0.01 to 100 Hz), creep–recovery (loading of 50 Pa for 60 s, 30 °C), temperature sweeps (from 30 up to 180 °C) and heating/cooling cycles (between 30 and 60 °C) were conducted on a controlled stress rheometer. Previously, the thermal-mixing behaviour at proposed mixing temperature (50 °C) was conducted on Mixolab® apparatus. Results showed that the dough stability (from 2.2 to 5.8 min) in mixing stage and starch heat resistance to dough processing were significantly improved at proposed mixing temperature, even in the absence of HC. No statistical differences in rheological properties were observed for doughs evaluated in C1; however, those analysed in C5 were significantly modified in the presence of HC, mainly in terms of viscous behaviour (from 52.1 × 10⁶ to 39.1 × 10⁶ Pa s). Creep–recovery data sets, successfully fitted using Burgers model, revealed that the elasticity (J _r/J _max from 73.3 to 87.6%) of doughs analysed in C5 improved with HC addition. Thermal tests showed that the starch transitions were significantly promoted and stabilized with HC addition.     

Understanding and Modifying Water Uptake of Seed Coats Through Characterizing the Glass Transition

The glass transition temperature (Tg) of seed coat was studied in relation to water uptake behavior. Tg values of seed coats were determined using differential scanning calorimetry (DSC) for selected pea and bean varieties. Rapidly hydrating samples showed a sharp Tg near ambient temperature with a range spanning 4–10°C. Samples that demonstrated a lag and consequently slow hydration exhibited a broad Tg above ambient temperature with a range spanning 22–33°C. Slow hydrating samples were processed via cyclic heating and cooling above and below Tg, resulting in elimination of the lag phase and markedly improved hydration rates. This research showed that Tg can be related to water uptake behavior and can be used as a parameter to determine processing conditions for improving water uptake in seeds.     

Phase Transitions of Amorphous Sucrose and Frozen Sucrose Solutions

Amorphous sucrose showed typical thermal transitions of amorphous materials. The temperatures of those transitions, glass transition, crystallization and melting, decreased with increasing moisture content. The glass transition temperature of dry amorphous sucrose at 57°C was decreased to -46°C as the sucrose was plasticized with excess water. That value remained constant due to maximal freeze-concentration with 72-73% sucrose in the unfrozen matrix which showed ice melting at -34°C. Concentrated solutions may become supercooled resulting in partial freeze-concentration with resultant lowering of glass transition temperature.     

Combination of NMR and MRI Techniques for Non-invasive Assessment of Sea Cucumber (<Emphasis Type="Italic">Stichopus japonicas</Emphasis>) Tenderization During Low-Temperature Heating Process

The purpose of this study was to develop and test the combination of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) method to assess the proton changes of sea cucumber body wall during low-temperature heating process. NMR relaxometry and MRI measurements indicated a significant proton change in the internal structure for sea cucumber body wall when the heating temperature increased from 45 to 55 °C. Differential scanning calorimetry (DSC) analysis revealed that the denaturation temperature of sea cucumber body wall was in the range of 45–55 °C with an endothermic peak at 51 °C, which is in accordance with the result observed in NMR and MRI. Rheological study showed similar trend to the DSC thermogram. The band change in amide I region of Fourier transform infrared (FTIR) spectra indicated the decrease in α-helix content and possible formation of other secondary structures. Scanning electron microscopy (SEM) further confirmed that the low-temperature heating did induce microstructure changes. The analysis of the Ringer?s soluble fraction (RSF), enzyme-labile fraction (ELF), and total unaltered fraction (TUF) for sea cucumber body wall during low-temperature heating provided more detailed information on the cause of structure change observed in NMR and MRI. The NMR parameters were highly correlated with the rheology storage modulus (G′), relative enzymatic assay parameters, RSF, ELF, and TUF. All these results demonstrated that it could be possible to use NMR and MRI to assess sea cucumber tenderization during low-temperature heating process.     

Differential scanning calorimetry of porcine adipose tissues

Differential scanning calorimetry (DSC) was used for the direct analysis of melting properties in porcine subcutaneous, intermuscular, and kidney leaf adipose tissue by heating at a constant ratio of +5 °C/min from 4 to 90 °C. Melting curves for adipose tissues as well as fat extracted from the associated tissues by chloroform–methanol were generated using DSC. Major peaks in DSC curves were similar among types of adipose tissue but the temperatures of the melting peak and conclusion point differed among types of adipose tissues. From the visual appearance of fat samples it appeared that the major DSC peak corresponded to phase transition of the fat. The direct DSC analysis of porcine adipose tissues may be useful to determine melting properties.     

Characteristics of fat,and saponin and tannin contents of 11 varieties of rambutan (Nephelium lappaceum L.) seed

Rambutan seed is discarded during fruit processing. However, the seed contains a considerable amount of crude fat. Hence, the objective of this study was to determine two anti-nutritional constituents, namely saponin and tannin, and to characterize the fat of the seeds of 11 varieties of rambutan fruit. Results showed that the range of crude fat content is fairly narrow (36.13–39.13 g/100 g dried seeds). The iodine value and free fatty acid content of the fat were 38.50–50.61 g I₂/100 g fat and 0.99–2.18% as oleic acid, respectively. Oleic (33.35–46.64%) and arachidic (26.03–33.27%) acids were the main fatty acids in the fat. HPLC analysis showed that the fat comprised mainly five unknown triacylglycerols (83.94–95.33%). The melting and crystallization curves showed that the fat exhibited four to nine non-distinct peaks. The complete melting and crystallization onset temperatures of the fat were 24.8–50.6°C and 24.1–39.4°C, respectively, while the melting and crystallization enthalpies of the fat ranged from 71.2 to 141.7 J/g and from 60.4 to 88.9 J/g, respectively. At 0°C, the solid fat index of the fat ranged between 87.4% and 91.6% and the fats of some varieties melted completely at human body temperature. The saponin and tannin contents of the seed were 14.27–18.96 mg soya saponin/100 g and 4.40–26.68 mg catechin equivalent/100 g, respectively. Findings showed that rambutan seed fat has potential to be used in various sectors of food industry.     

Glass transition behaviour of fructose

The glass transition temperature and the second transition (the endothermic change between the glass transition and melting temperatures) of fructose were studied. The thermal history strongly affected both transitions of fructose. Storage for 10 days at 22 °C increased the dynamic glass transition temperature from 16 to 25 °C and decreased the second transition of fructose from 110 to 98 °C in the first differential scanning calorimetric (DSC) scan. The amplitude of the second transition increased slightly with storage time and reached 260% of the first transition for vacuum oven dried samples. The effect of thermal history on the glass transition temperature of fructose can be removed by scanning the sample in a DSC to 130 °C. The effects of water content, glucose and sucrose on the two transitions were also investigated.     

Characterization of Thermal Properties of Pig Hair Fiber

Hair fiber is a key by-product of humane slaughter of pigs with considerable economic value. In the present study, we investigated the thermal properties of pig hair fiber using Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC curve showed a broad endotherm (around 50–80°C) initially, followed by denaturation doublet peaks (229°C and 239°C) and finally a pyrolysis endotherm. The melting enthalpy of pig hair fiber was 9.93 J/g on dry basis. During TGA, distinct phases of initial weight loss due to loss of moisture and later through thermal degradation of protein around 238–240°C were observed. Mean thermal insulation and conductivity values of pig hair fiber were 0.068 ± 0.004 m²K/W and 0.029 ± 0.003 W/m/K, respectively. The thermal characteristics of pig hair fiber were similar to other keratin fibers of animal origin.     

Milk fat thermal properties and solid fat content in emmental cheese: a differential scanning calorimetry study

The experiments reported in this study give deeper insight into the crystallization of milk fat in Emmental cheese, which is the most widely consumed hard cheese in France. Differential scanning calorimetry (DSC) was used to monitor the thermal properties of milk fat after the main stages involved during manufacture of Emmental cheese. By heating the samples to 60°C to eliminate their thermal history and cooling them at 2°C/min, the liquid → solid phase transition of fat was investigated. Confocal laser scanning microscopy was used to characterize in situ the supramolecular organization of milk fat dispersed in the casein matrix. The destabilization of fat globules by aggregation or coalescence and the formation of free fat during the manufacture altered the thermal properties of milk fat by increasing the initial temperature of crystallization and by the formation of 2 overlapping exotherms. The melting properties of the crystalline structures formed by fat at the temperatures used for ripening (12, 21, and 4°C) were examined. Differential scanning calorimetry was used to determine the ratio of solid to liquid fat; that is, the amount of fat that is crystallized, by dividing the partial enthalpy of melting of the fat for ripening temperature by the total enthalpy of melting of the same fat extracted from cheese. This study shows, for the first time, that milk fat is partially crystallized in Emmental cheese: about 55.7 ± 3.5% of fat is solid at 4°C at the end of ripening. Polymorphic phase transitions of milk fat are also suggested during ripening of Emmental cheese.     

Infrared Heating as a Disinfestation Method Against <Emphasis Type="Italic">Sitophilus oryzae</Emphasis> and Its Effect on Textural and Cooking Properties of Milled Rice

Infrared (IR) heating method against rice weevils (Sitophilus oryzae) in an egg stage was investigated. A kinetic model was developed to describe insect mortality in a temperature range of 40–60 °C. Effects of IR heating temperature (50–60 °C) and exposure time (1–3 min) on insect mortality and quality attributes of the treated rice were evaluated. The optimized condition obtained by means of the response surface method was used to analyze rice quality before and after IR treatment with storage. The results showed that the 0.5th-order thermal death kinetic equation was the most suitable model, and the S. oryzae eggs had less heat tolerance than the adults and some other species. Mortality achieved 100 % after 2 min for all temperatures. Both IR heating parameters significantly affected the treated milled rice qualities. The minimal changes in rice quality before and after storage could be obtained using optimized temperature and exposure time of 53.6 °C and 1.2 min, respectively.