Effects of microwave heating on changes in chemical and thermal properties of vegetable oils

Abstract

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...

Oxidative changes of vegetable oils during microwave heating

“…The acid value changes were negligible (less than 0.2 mg/g between the original sample and the last one) under the experimental conditions of this study in preliminary experiments. This observation is in agreement with the literature data (TAN et al 2001). Therefore, the acid value was not included as a marker of deteriorative changes in our experiments.…”

“…during the first 10 min, no changes were observed, but pronounced changes followed afterwards (VIEIRA & REGITANO-D'ARCE 2001). The power of the microwave oven had a great effect on the changes of corn and soybean oils (TAN et al 2001).…”

Microwave Heating: A Time Saving Technology or a Way to Induce Vegetable Oils Oxidation?

“…In opposition, virgin olive oils, being obtained only by physical processes at low temperature, could have naturally a higher acidity value, due to the lipases interaction with the triglycerides, and their prices reflect the care given to maintain the acidity as low as possible. Several author's studied the effect of microwave heating on the free acidity of different vegetable oils: Portuguese virgin and extra virgin PDO olive oils (Malheiro et al, 2009); olive oil (refined + virgin olive oil) (Caponio et al, 2002); Spanish virgin olive oils (Brenes et al, 2002), and Italian extra-virgin olive oils (Cossignani et al, 1998), coconut, palm and safflower oils (Yoshida et al, 1991); peanut, high oleic sunflower and canola oils (Chiavaro et al, 2010); corn and soybean oils (Tan et al, 2001); virgin olive oil, olive oil, sunflower oil, high oleic sunflower oil, and lard (Albi et al, 1997 a,b). All the results provide clear evidence that microwave heating causes a slight increase in the free fatty acids amounts, higher than that obtained by conventional heating.…”

Efeito da incorporação de folhas de oliveira (Olea europaea L.) no desenvolvimento e qualidade da carne de frangos

“…As coxas e sobrecoxas de frango dos três tratamentos analisados apresentaram ausência de Listeria monocytogenes durante os 12 dias, atestando segurança do produto quanto à listeriose. Gökmen et al (2014) O efeito antimicrobiano das folhas de oliveira em diversas bactérias, conforme relatado em estudos realizados LEE, 2010;PEREIRA et al, 2007;CARDOSO et al, 2005;OWEN et al, 2003;BENAVENTE-GARCIA et al, 2000) com relação à atividade antimicrobiana das folhas de oliveira, o que, conforme mencionado por e verificados nesta pesquisa, pode ser atribuído à presença de compostos fenólicos como a oleuropeína, que apresenta-se em grande concentração nas folhas de oliveira (TAN et al, 2003). Savournin et al (2001), relataram que folhas de oliveira podem conter até 10% de polifenóis, principalmente oleuropeina e hidroxitirosol.…”

“…Ao investigar a atividade in vitro de um extrato comercial de folhas de oliveira (Olea europaea L.) que continha 4,4 mg/mL de oleuropeína, diante de uma vasta gama de micro-organismos, Sudjana et al (2009) Ubabef (2012), a região sul do Brasil é responsável por 61,53% do volume de frango produzido, cujo principal destino é o Oriente Médio, na forma de cortes, frango inteiro, frango industrializado e outros produtos. Porém, esta carne em condições não adequadas de processamento e armazenamento pode se tornar veículo de transmissão de inúmeros micro-organismos, alguns deles patógenos ao homem.…”