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In this study, 10 different vegetable oils were oxidized at four different isothermal temperatures (383, 393, 403, and 413 K) in a differential scanning calorimeter (DSC). The protocol involved oxidizing vegetable oils in a DSC cell with oxygen flow. A rapid increase in evolved heat was observed with an exothermic heat flow appearing during initiation of the oxidation reaction. From this resulting exotherm, the onset of oxidation time (T o ) was determined graphically by the DSC instrument. In our experimental data, linear relationships were determined by extrapolation of the log (T o ) against isothermal temperature. The rates of lipid oxidation were highly correlated with temperature. In addition, based on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (E a ), activation enthalpies (∆H ‡ ), and activation entropies (∆S ‡ ) for oxidative stability of vegetable oils were calculated. The E a , ∆H ‡ , and ∆S ‡ for all vegetable oils ranged from 79 to −104 kJ mol −1 , from 76 to −101 kJ mol −1 , and from −99 to −20 J K −1 mol −1 , respectively. Based on the results obtained, differential scanning calorimetry appears to be a useful new instrumental method for kinetic analysis of lipid oxidation in vegetable oil.

Diacylglycerol (DAG) oil has beneficial effects on obesity and weight-related disorders. A survey of literature has shown the effects of DAG on the reduction in the accumulation of body fat in both animals and humans. The physiological effect of DAG is believed to be attributed to its metabolic pathway, which is different from triacylglycerol (TAG) metabolism. Physicochemical properties, such as melting and smoke points and polymorphic forms, of DAG are also distinct from TAG. Various patented processes for DAG oil production from several reaction routes are discussed. A review of patent literature of commercial products based on DAG oils and fats is also provided.

Partial hydrolysis using Lipozyme RMIM lipase in a solvent-free system was used to produce a diacylglycerol (DAG)-enriched palm olein. Response surface methodology (RSM) was applied to model and optimize the reaction conditions namely water content (30-70 wt% of enzyme mass), enzyme load (5-15 wt% of oil mass), reaction temperature (45-85 C) and reaction time (6-16 h). Well fitting models were successfully established for both DAG yield (R2 = 0.8788) and unhydrolysed triacylglycerol (TAG) (R2 = 0.8653) through multiple linear regressions with backward elimination. Chi-square test indicated that there were no significant (P > 0.05) differences between the observed and predicted values for both models. All reaction conditions had positive effects on DAG yield and negative effects on unhydrolysed TAG. Optimal reaction conditions were: 50 wt% water content, 10 wt% enzyme load, 65C of reaction temperature and 12 h of reaction time. The process was further up-scaled to a 9 kg production in a continuous packed bed bioreactor. Results indicated that upscaling was possible with a similar DAG yield (32 wt%) as in lab scale. Purification of the DAG oil using short path distillation yielded a DAG-enriched palm olein with 60 wt% DAG and 40 wt% TAG which is suitable for margarine, spread or shortening applications.

The effects of microwave heating on the cooling profiles of two vegetable oils (corn oil and soybean oil) were studied using differential scanning calorimetry (DSC) and compared to changes in chemical parameters. These oils were exposed for several periods of time to three controlled treatments: low-, medium-, and high-power settings, respectively. The DSC results were derived from the cooling curve of oils at a scanning rate of 5°C/min. The chemical analyses of the oils included peroxide value, anisidine value, free fatty acid content, iodine value, and C18:2/C16:0 peak area ratio. A statistical comparison was carried out between DSC and the chemical parameters. In general, correlations were good between these parameters. Likewise, the experimental data showed that, for a given microwave power setting, a good correlation existed between DSC curve parameters and heating periods. These results indicate that DSC can be used as an objective nonchemical, instrumental technique to monitor lipid oxidation in both traditionally heated and microwave-heated oils.Microwave heating is one of the most commonly used methods of food preparation today because of its convenience, rapidity, and economy (1). Advances in equipment design, trends in electrical energy costs, and research on food properties have provided a basis for modeling microwave heating patterns that should stimulate the development of new and improved commercial food processes. In the food industry, microwave heating operations have been used with increasing success in baking, blanching, cooking, drying, pasteurization, sterilization, and thawing of various food products (2,3). George (4) reviewed the application of microwave heating in food processing with reference to the advantages and limitations for a range of food processing operations.Microwave penetration depths within a product are determined by the electrical and physical properties, heating patterns, microbial inactivation, and safety (5) and can vary significantly with chemical composition, product temperature, and the frequency at which the microwave operates. Industrial microwave systems are available in both batch and continuous design configurations and use magnetrons that develop either 915 or 2450 MHz (6). Lassen and Ovesen (7) reviewed the effects of microwave heating on the nutritional constituents of foods and concluded it does not change the nutrient content of food to any greater extent than conventional cooking.The chemical constituents of oils that degrade during microwave heating do so at rates that vary with heating temperature and time, as with other domestic processing methods (e.g., frying, steaming, and roasting). Suitable quality parameters therefore can be used as time-temperature integrators of quality deterioration of oils during microwave heating. Monitoring of many of these parameters makes extensive use of chemicals. Also, the methods for measuring such components can be relatively complex and time-consuming, which can be a major drawback in industrial applications. Instrum...