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.
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.
La friture profonde peut être d efinie comme une cuisson par immersion dans une huile ou une mati ere grasse comestible a une temp erature au-dessus du point d' ebullition de l'eau. C'est un proc ed e rapide de transfert simultan e de chaleur et de mati eres. Il peut être utilis e comme une op eration de s echage. Au-del a des applications alimentaires, ce proc ed e est utilis e pour s echer, pour stabiliser, des carcasses de viande, des boues d' epuration ou encore du bois. La friture profonde reste une op eration complexe a cause des deux transferts de mati ere de direction oppos ee au sein du mat eriau : pour les produits a base d'amidon, de l'eau et quelques solut es s' echappent du produit et l'huile entre dans l'aliment. Parfois, même de la mati ere grasse peut s' echapper du produit vers le bain d'huile. C'est le cas pour des mat eriaux pr esentant un taux de mati ere grasse significatif tels que la viande ou le poisson (Oroszvari et al., 2005). De plus, pendant la friture, le mat eriau est soumis a des transformations chimiques et physiques a haute temp erature. Aspects nutritionnelsLes produits frits sont d'une grande vari et e. Si on consid ere les produits a base d'amidon, deux produits pr edominent : les frites de pommes de terre ou de plantain o u la d eshydratation est seulement partielle. L' epaisseur du produit aura une grande influence. En g en eral, les produits de faible epaisseur pr esentent une teneur en eau tr es faible. Ils peuvent donc être conditionn es facilement pour la conservation et la distribution. Cependant comme les produits fins pr esentent un taux de mati ere grasse elev ee (30 a 40 %), la stabilit e de l'huile pendant la conservation doit être g er ee avec pr ecaution pour eviter le d eveloppement d'arômes ind esirables (rancidit e) dans le produit. Les produits epais, quant a eux, pr esentent une teneur en eau interm ediaire d' a peu pr es 30 a 50 % mais avec une faible teneur en mati ere grasse (inf erieure a 15 %). Typiquement, ils ont une croûte croustillante et un coeur moelleux comme de la pomme de terre cuite.Ces produits peuvent être obtenus a partir d'ingr edients frais ou surgel es, ayant souvent subi une pr efriture. Cette pr efriture consiste g en eralement en une Abstract: Deep-fat frying process: oil-product interactions 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 a major 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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