Degradation during application of ultrasound in food processing: A review

The oil palm tree is an ancient tropical plant that originated from West Africa. Palm oil has centuries׳ long use as food and medicine. This review covers the recent significant materials found in the literature on palm oil processing, refining, and use in frying especially in blends with other vegetable oils. Crude palm oil (CPO) is obtained from the fruit of the oil palm tree (Elaeis guineensis). The oil is rich in palmitic acid, β-carotene and vitamin E. CPO has been fractionated mainly into liquid palm olein and solid palm stearin in order to diversify its food applications. Palm oil is highly stable during frying especially due to the synergistic activity of β-carotene and tocotrienol. In recent years there has been a shift from the use of animal fats and hydrogenated vegetable oils in frying and other food applications. The use of naturally stable oils such as palm oil and composite oils like blends of palm oil and other fats and oils is practiced to ensure that maximum benefits are derived from the oils. Blending offers functional, nutritional and technical advantages, such as tailoring the oil to suit frying applications. The objective of this review is to combine and condense the body of research on the processing, characterization and use of palm oil especially in frying as well as suggest areas that need further research.

Palm oil: Processing, characterization and utilization in the food industry – A review

Deep-fat frying is a rapid and low cost process widely used to prepare tasty food. During this cooking process, oil is used both as the heating medium and as an ingredient producing calorific products. Nutrition has become a major health issue, especially in developed countries where increasing obesity is a problem, particularly among children. Many food research projects involving snack food industries therefore attempt to understand oil uptake during the frying process in order to control and reduce the fat content of fried products without deteriorating their desirable organoleptic characteristics. The main objectives of this paper are to review the literature on the frying process and more precisely the mechanisms and parameters involved in the oil uptake phenomenon. Both products and processes will be considered and their influence via experimental results will be discussed.

Review of mechanisms, conditions, and factors involved in the oil uptake phenomenon during the deep-fat frying process

The changes in regular canola oil as affected by frying temperature were studied. French fries were fried intermittently in canola oil that was heated for 7 h daily over seven consecutive days. Thermo-oxidative alterations of the oil heated at 185 ± 5 or 215 ± 5 °C were measured by total polar components (TPC), anisidine value (AV), color components formation, and changes in fatty acid composition and tocopherols. Results showed that TPC, AV, color and trans fatty acid content increased significantly (P < 0.05) as a function of frying temperature and time. The oil polyunsaturated fatty acids (PUFA) decreased in direct proportion to frying temperature and time. After 7 days of frying, the amount of PUFA was reduced by half and the trans isomers contribution increased 2.5 times during frying at 215 °C. Of the parameters assessed, total polar component and color had the highest correlation, with correlation coefficients of 0.9650 and 0.9302 for frying at 215 and 185 °C, respectively. TPC formation correlated inversely with the reduction of tocopherols.

Degradation and nutritional quality changes of oil during frying.

In this review, the concept of phenolic antioxidants, mechanisms of action, and applications have been reviewed. Phenolic compounds (PCs) acts as an antioxidant by reacting with a variety of free radicals. The mechanism of antioxidant actions involved either by hydrogen atom transfer, transfer of a single electron, sequential proton loss electron transfer, and chelation of transition metals. In foods, the PCs act as antioxidants which are measured with several in vitro spectroscopic methods. The PCs have been found in milk and a wide range of dairy products with sole purposes of color, taste, storage stability, and quality enhancement. The role of PCs in three types of food additives, that is, antimicrobial, antioxidant, and flavoring agents have been critically reviewed. The literature revealed that PCs present in a variety of foods possess several health benefits such as antibacterial, antihyperlipidemic, anticancer, antioxidants, cardioprotective, neuroprotective, and antidiabetic properties. PRACTICAL APPLICATIONS: Phenolic compounds are strong antioxidants and are safer than synthetic antioxidants. The wide occurrence in plant foods warranted continuous review applications. This review, therefore, presented an updated comprehensive overview of the concept, mechanism, and applications of phenolic antioxidants in foods.

Concept, mechanism, and applications of phenolic antioxidants in foods.

The effects of temperature, heating time (continuous or discontinuous mode), and water steam on sunflower oil deterioration have been investigated. Oil was heated at three temperatures, 120, 150, and 190 7C, during a total period of 60 h to achieve a wide range of degradation degrees. At 190 7C, 9 h of discontinuous heating were achieved, and oil degradation was compared to the previous treatment. Water steam treatment was investigated at two oil temperatures, 120 and 150 7C, by frying food model samples that provided a vapor flow of 1.2 g/min during about 30 h. Energy consumptions of the fryers have been measured for each experiment. Thermooxidative degradation of heated oils was evaluated by the measurement of conjugated dienes,
viscosity and total polar compounds. All these indicators showed that for the same heating time, oil degradation was more important at 190 7C, and most of all for an intermittent heating. However, the results showed a good correlation between oil degradation and the fryer energy consumption for all the heating experiments, continuous or discontinuous. The presence of water seemed to modify this correlation. These
results highlight the complexity of oil degradation during frying, depending on oil temperature, heating mode and presence of water, which can be expressed in energy consumption.

Effect of energy transfer conditions on the chemical degradation of frying oil

Among the many thermal processes used to prepare tasty food, deep fat frying is one of the fastest and cheapest. Oil serves both as an ingredient and as a heating medium. Recently, nutrition became amajor health issue especially in developed countries where obesity is widespread. Fried products being often considered as too calorific, many research projects try to understand the underlying mechanisms of oil uptake in the fried product. There is a difficult challenge in reducing fat content without altering texture and taste. This papers aims at reviewing most interesting researches published on oil uptake.

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Isabelle Trezzani

Papers

Review of mechanisms, conditions, and factors involved in the oil uptake phenomenon during the deep-fat frying process

Effect of energy transfer conditions on the chemical degradation of frying oil

Friture profonde : les interactions huile-produit

Deep-fat frying process: oil-product interactions