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Vacuum Frying - A Lower cooking Temperature
By Rosana G. Moreira, Professor in Food Engineering, Texas A&M University
Vacuum frying is an efficient method of reducing the oil content in fried snacks, maintaining product nutritional quality, and reducing oil deterioration. It is a technology that can be used to produce fruits and vegetables with the necessary degree of dehydration without excessive darkening or scorching of the product. In vacuum frying operations, food is heated under reduced pressure (< 60 Torr - 0.0789 atm) causing a reduction in the boiling points of the oil and the moisture in the foods.
French fries processed in a vacuum fryer can achieve the necessary degree of dehydration without excessive darkening or scorching of the product. Jagoba and Moreira (2002) showed that vacuum fryers could produce potato chips with lower oil content and the same texture and color characteristic of those fried in conventional (atmospheric) fryers. Ophithakorn and Yamsaengsung (2003) proved that vacuum frying produces lighter color tofu products with lower oil contents. The frying oil showed lower amounts of free fatty acid (FFA) and a slightly lighter color after 30 batches of frying. Yamsaengsung and Rungsee (2003) found that vacuum fried potato chips and guava slices had lower oil content and more natural colorations than those fried in conventional fryers.
Another important use of this technology is in the area of safety. Acrylamide, a carcinogen found to cause cancer in laboratory rats, is present in carbohydrate-rich foods cooked at high temperatures, such as fried/baked chips, bread, etc. Acrylamide could be created by a reaction between an amino acid called asparagine, which occurs naturally in relatively high levels in potatoes and other cereals, and sugar. Tests confirmed that when the amino acid is heated, it does react with sugar to create acrylamide, a process called the Maillard reaction. This occurs at temperatures above 100°C (212°F).
Recent research to come out of the US Texas A&M University confirms these findings, revealing that lowering cooking temperature is an "easy and effective way" to reduce acrylamide in fried foods. Granda et al. (2004) demonstrated that vacuum frying could produce potato chips with 97% reduction in acrylamide content than the traditionally fried chips.
A couple of Asian companies have developed vacuum fried a system for the process of fruit (apple, pineapple, grapes, banana, guava, mango, peach, etc.) and vegetables (sweet potato, potato, pumpkin, carrots, etc) into chips and fried fishes and shellfishes (octopus and cattlefish). An example is the batch vacuum frying system that has been developed by I-Tung Machinery Industry (Taipei, Taiwan). It has a capacity of 50-100 kg potato chips/h and 20-50 kg of fruits/h and operates at a vacuum of 10.7 Torr (0.0141 atm).
Continuous vacuum frying was a concept developed by Florigo (H&H Industry Systems B.V., The Netherlands) in the early 1970's to produce high quality French fries. Due to the improvement in quality of the raw materials and blanching techniques, the use of vacuum fryers almost died out with exception of one or two production companies who still insist in producing a non-blanched product. Today, the Florigo automatic continuous vacuum fryers are used mainly to produce fruit-chips and very delicate snack products.
References:
Garayo, J. and R.G. Moreira. 2002. Vacuum frying of potato chips. J. of Food Engr. 55(2): 181-191.
Granda, C.; Moreira, R.G. and Tichy, S.E. 2004. Reduction of acrylamide formation in potato chips by low-temperature vacuum frying. Journal of Food Science. 69(8):405-411.
Yamsaengsung, R. and Rungsee, S. 2003. Vacuum frying of fruits and vegetables. Manuscript - #1-2003 - Department of Chemical Engineering, Prince of Songkla University, Hat Yai, Songkhla 90112.
Yamsaengsung, R. and Moreira, R.G. 2002. Modeling the structural change during deep-fat frying of foods. Part I: Model development. Journal of Food Engineering. 53:1-10.
Rosana Moreira is a Professor in Food Engineering at Biological and Agricultural Engineering Department, Texas A&M University. In 1998, she was promoted to Associate Professor and in 2004 to Professor. Rosana has over 60 publications in respected professional journals, is the author of several book chapters, a book in 'deep-fat frying' and another on 'process control for the food industry'. For article feedback, contact Rosana at: rmoreira@tamu.edu
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