MONITORING OF TRANSESTERIFICATION OF PALM OIL BY DIFFERENTIAL SCANNING CALORIMETRY

Chemical transesterification was conducted to obtain triacylglycerol ( TG) containing maximum concentrations of trisaturated and triunsaturated TG in palm oil. Catalyst (sodium methoxide) concentration of 0.1–0.5%, reaction temperature of 50–92C and reaction time of 30–480 min were applied in 20 treatments. Concentrations of trisaturated and triunsaturated TG, as well as melting points and iodine values were monitored by differential scanning calorimetric (DSC) techniques. The results showed that maximum trisaturated and triunsaturated TG achieved for refined-bleached-deodorized (RBD) palm oil were 17.10 and 7.50%, respectively, using 0.42% catalyst, at 58C in 389 min. These amounts were higher compared to control (untransesterified) RBD palm oil i.e 7.45 and 4.92%, respectively. The melting points of the products were higher compared to the control, while the iodine values were not significantly changed in all of the treatments.     

BOUND WATER DETERMINATION USING VACUUM DIFFERENTIAL SCANNING CALORIMETRY

SUMMARY– Using a vacuum differential scanning calorimeter, it was possible to measure the relative bound water content of several food stuffs. Freeze-dried beef powder, freeze-dried whole egg powder, modified corn starch powder and non-fat dry milk were used. Results indicate that the relative bound water of food stuffs can be determined, but determination of total water from water binding energy will require further experimentation.     

DIFFERENTIAL SCANNING CALORIMETRY OF STARCH12

At high water-to-starch (2:1) ratios a single endotherm was obtained for starch gelatinization. As the water-to-starch ratio was decreased the endotherm area decreased and the peak developed a trailing shoulder. At high water-to-starch ratios birefringence is lost over a temperature range of about 7°C. That narrow range increases to about 30°C at a low water-to-starch ratio. Starch and flour gave essentially the same endotherm initiation temperatures. In low-water systems the second DSC peak is much smaller with starch than with flour. It appears that in a starch system, water migrates during gelatinization. In dough, gluten limits that migration. As the level of sucrose was increased in a dough, the transition temperature increased and the gelatinization temperature range decreased. At the levels found in bread doughs both sugar and salt increase starch gelatinization temperatures.     

MEASUREMENT OF HEAT CAPACITY FOR BORAGE SEEDS BY DIFFERENTIAL SCANNING CALORIMETRY

Specific heat capacity of borage seeds was determined by differential scanning calorimetry (DSC) in the temperature range of 5 to 80C and moisture content range of 0.47 to 30.31 % wet basis. The specific heat ranged from 0.57 to 2.48 kJ/kgK. A multiple regression model with interaction terms correlated well the specific heat to temperature (T) and moisture content (M). It was found that the interaction terms T*M and T*M² were significant (α=0.01) and thus were included in the model, and the term M*T² was insignificant. Effect of measurement techniques with DSC were also investigated in this study to ensure that true specific heat values were obtained. Seal condition of the sample holders during DSC measurement had considerable effect on the specific heat of borage seeds. The difference between the specific heat of sealed and unsealed samples increased as seed moisture content increased, especially at higher temperatures. For the measurement of the specific heat of borage seeds by DSC in the above-mentioned temperature and moisture content ranges, an average of 5.75% deviation was found between the measurement with and without blank compensation.     

DIFFERENTIAL SCANNING CALORIMETRY DETECTION OF HIGH OLEIC SUNFLOWER OIL AS AN ADULTERANT IN EXTRA-VIRGIN OLIVE OIL

Differential scanning calorimetry (DSC) was employed to detect high oleic sunflower oil (HOSo) as an adulterant in extra-virgin olive oil (EVOo) by means of cooling and heating thermograms. Addition of HOSo did not significantly alter cooling profiles of EVOo except for onset temperature of crystallization, which was significantly shifted toward lower temperature at 40% of adulterant addition. At the same percentage of adulteration, the heating profile of EVOo was significantly changed as the major endotherm broadened and the minor event became smaller and less evident. Cooling thermograms of pure oils and their admixtures were deconvoluted into three constituent exothermic peaks in an attempt to detect addition of HOSo at levels lower than 40%. Thermal properties of the two lower-temperature exotherms (area percentage, offset temperature and range of transition) were significantly changed at ≥ 20% of HOSo substitution, suggesting that DSC can be employed to detect this oil as an EVOo adulterant.

PRACTICAL APPLICATIONS

Adulteration of extra-virgin olive oil (EVOo) with cheaper oils from other vegetable sources or seeds, as well as with lower quality olive oils, is a serious concern for oil suppliers and consumers and requires the use of new analytical techniques for their detection. Differential scanning calorimetry (DSC) exhibits some advantages over the classical analytical methods as it does not require sample preparation and use of solvents, thus resulting in a reduced environmental impact. Results suggested that its application to the detection of EVOo adulteration with high oleic sunflower oil, a vegetable oil largely employed for this type of fraud, is promising with the support of the deconvolution analysis of cooling thermograms.     

STUDY OF SAGO STARCH (METROXYLON SAGU) GELATINIZATION BY DIFFERENTIAL SCANNING CALORIMETRY

Differential scanning calorimetry (DSC), at various heating rates (1–30C/min) and water:starch ratios (0.1:1–4:1), was used to study gelatinization phenomena of sago starch. The results showed that the gelatinization temperature and enthalpy (Δ H) of starches in excess water were 60–77C and 15.5–15.8 J/g, respectively. Δ H of gelatinization remained substantially the same at excess water contents, but decreased significantly beyond a water:starch ratio of 1.3:1. A single endothermic transition (G) that transformed into a double endotherm (G and M₁) and only M₁ occurred, respectively, at excess, intermediate and limited water contents. At 50% water content, evidence of the M₁ endotherm was observed, and 85C represented the effective conclusion temperature (T_m) at the end of melting for sago starch. The experimental data were treated thermody-namically by applying an equation describing phase transitions of semi-crystalline polymers. The calculated value for the melting point of the undiluted polymer (T_m) was 432 K (R²= 0.96).     

差示扫描量热技术及其在大豆蛋白分析中的应用

主要介绍了热分析技术，重点分析了差示扫描量热仪的原理、结构、输出信息以及影响测量结果的主要因素。并举例说明了差示扫描量热技术在大豆蛋白分析中的应用。     

SEMI-SOLID FAT BY INTERESTERIFICATION OF RED PALM OIL WITH OTHER VEGETABLE OILS

Interesterification of appropriate blends of vegetable oils offers an alternative method for obtaining semi-solid fats without hydrogenation. Random interesterification was carried out on blends of different oils, namely palm oil and sunflower oil (8:2, 7:3 and 6:4 w/w), palm oil and rice bran oil (8:2 and 7:3 w/w), palm oil and coconut oil (9:1 and 6:4 w/w), as well as palm oil and soybean oil (7:3 w/w), in the presence of sodium methoxide as a catalyst (0.2% w/v). The melting characteristic of the interesterified fat obtained from a blend of refined red palm oil and sunflower oil blend, in the ratio of 4:1 (w/w; slip melting point 41C) indicated that this combination could be an ideal margarine fat base.     

气相色谱法测定植物油中的苯线磷

植物油中苯线磷用丙酮提取,经液-液分配,用火焰光度检测器（FPD）检测,根据色谱峰的保留时间定性,外标法定量。     

DIFFERENTIAL SCANNING CALORIMETRY CAN DETERMINE KINETICS OF THERMAL DENATURATION OF BEEF MUSCLE PROTEINS

Differential scanning calorimetry (DSC) of beef muscle produced three large endotherms occurring at 55–57°C, 65–67°C and 81–83°C. Based on earlier DSC research on isolated proteins (Privalov 1979), the concept of cooperative units participating in thermal transition phenomena was applied to beef muscle endotherms. Analysis of these endotherms by the van't Hoff relationship and Borchardt and Daniels kinetics analysis revealed reaction orders of ca. 0.6 to 2.1, 3.5 to 5.1 and 1.5 to 3.1, respectively, for the three muscle endotherms. The reaction orders for these endotherms were influenced by muscle type, fiber sarcomere length and conditioning. Aging led to an increase in reaction order whereas increased sarcomere length was accompanied by a decrease in reaction order or number of cooperative units. Changes in the number of cooperative units participating in the endotherms is discussed in the context of meat tenderization and conditioning. It appears reaction order analysis of the T₃ transition (81–83°C) may correlate with meat tenderness.     

SPECIFIC HEAT CAPACITY OF AUSTRALIAN HONEYS FROM 35 TO 165C AS A FUNCTION OF COMPOSITION USING DIFFERENTIAL SCANNING CALORIMETRY

Modulated temperature differential scanning calorimetry was used to investigate the specific heat capacity (C _p ) of 10 Australian honeys within the processing and handling temperatures. The values obtained were found to be different from the literature values at certain temperatures, and are not predictable by the additive model. The C _p of each honey exhibited a cubic relationship (P < 0.001) with the temperature (T, C). In addition, the moisture (M, %), fructose (F, %) and glucose (G, %) contents of the honeys influenced their C_p. The following equation (r² = 0.92) was proposed for estimating C_p of honey, and is recommended for use in the honey industry and in research: