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Vacuum frying technology
- 1. Ranasalva N
- 2. • Originated - Frying foods - Middle East - two millennia before the birth of Jesus Christ 26 May 2015 2 Introduction Sautéing Shallow frying Deep frying
- 3. • High pressure • Atmospheric pressure • Low pressure/Vacuum 26 May 2015 3 Deep fat frying – carried out under
- 4. Penetrated oil Surface oil CRUST CORE 26 May 2015 4 Mode of heat and mass transfer during deep fat frying (DFF)
- 5. CRUST CORE Starch degradation Non enzymatic browning High temperatures Frying oil thermal degradation Beneficial compounds degradation Water vaporization Atmospheric conditions Frying oil oxidation Frying oil hydrolysis Moisture loss Oil uptake Key structural components changes 26 May 2015 5 Changes in product during DFF
- 6. FOOD OILUPTAKEDEHYDRATION WATER HYDROLYSIS OXYGEN OXIDATION Cyclisation Polymerization HIGH TEMPERATURES (140 -200°C) Isomerization HEAT Mono glycerides Di glycerides Glycerol Free fatty acids Aldehydes Ketones Acids Epoxides Dimers - trimers Hydro peroxides Polar CompoundsFRYING OIL Trans fatty acids Cyclic Compounds Dimers – trimers Polymers 26 May 2015 6 Changes in oil during DFF
- 7. 26 May 2015 7
- 8. 26 May 2015 8 Torricelli’s vacuum experiment in 1644. The level AB of mercury in both tubes C and D was equal, independent of the size of the additional volume E in tube D. Democritus - 460 to 375 B.C. Bronze statue around 250 B.C., National Museum in Naples History of vacuum science
- 9. 26 May 2015 9 Otto von Guericke in 1672 Inventor of vacuum pump principle Plenists Vs vacuists
- 10. Non condensable gas Non condensable gas VACUUM PUMP Liquid condensate Steam & Non condensable gas SPINNER MOTOR VACUUM FRYING CHAMBER OIL HEATER FRYING BASKET CHILLER LIFT ROD 26 May 2015 10 Vacuum frying system
- 11. 1. Depressurization - 1.33 - 10 kPa 2. Frying and De-oiling – Heat and mass transfer occurs and surface oil is removed 3. Pressurization – To atmospheric condition 4. Cooling – Product is cooled to room temperature and stored 26 May 2015 11 Stages of vacuum frying
- 12. • Process Factor – Pre frying – Frying – Post frying • Product factor • Oil factor 26 May 2015 12 Factors affecting vacuum frying
- 13. •Maltodextrin •Drying •NaCl2 soaking •Citric acid •Gelatinization •Freezing •Hydrocolloids 26 May 2015 13 Pre frying (pretreatments)
- 14. Paulo et al ,2008 26 May 2015 14 Properties influences Properties influenced by •Moisture content •Weight and moisture loss •Pore structure •Oil absorption •Pressure •Diameter shrinkage •Thickness - expansion •Penetration pressure Process temperature
- 15. Temperature at different locations within the product during frying process (T =185°C, T=20°C) Aman-Mohammad, 2009 Whole process (frying and cooling) Cooling period 26 May 2015 15 Process temperature
- 16. • Oil absorption • Browning Index • Color • Shrinkage • Moisture content 26 May 2015 16 Paulo et al ,2008 Process time
- 17. • The frying is carried out from 1.33 kPa to 90 kPa 26 May 2015 17 • Surface of food • Centre of the food • Head space of the chamber Paulo et al ,2008 Process pressure
- 18. 26 May 2015 18 DP – Depressurization; FR – Frying; PR – Pressurization; CL – Cooling; temperature of 120°C Carla, 2010 Centre Surface Head space Pressure Effects of process parameters
- 19. 26 May 2015 19 Temperature of 130°C Temperature of 140°C Carla, 2010 Effects of process parameters
- 20. • Oil absorption - 80% absorbed during cooling • Potato chips – 14% in core and 86% on the surface • Pressure gradient between the product and atmosphere cause intensive absorption of oil • De-oiling – under vacuum - centrifuging speed 350 – 1200 rpm for 30 s to 30 min (Garayo & Moreira, 2002, Moreira et al.,2009) 26 May 2015 20 Post frying process
- 21. • Size and shape - oil absorption increases thickness is reduced & product surface is increased • Ripeness of fruits – suitable for high sugar products • Taste – Stronger taste of high concentration of taste components • Surface roughness - Cells broken during cutting are a privileged location for oil absorption • Solid content – high density product shows reduced oil absorption • Moisture content 26 May 2015 21 Product factors
- 22. • Moisture content • Oil content • Microstructure • Diameter - shrinkage • Thickness - expansion • Bulk density • True density and • Porosity 26 May 2015 22 Changes in product
- 23. Stages of Moisture loss • Initial warm up period • Constant rate period • Falling rate period Moisture diffusion coefficient, De, 26 May 2015 23 (Broker et al., 1992) Mdb - moisture content in (g/g solid), Mo - initial moisture content (g/gsolid) Me- equilibrium moisture content (g/g solid), t - frying time (s) a - half thickness of the product slice (m) Moisture content
- 24. 26 May 2015 24 Effect of oil temperature and vacuum pressure (Garayo and Moreira, 2002) Shrinkage
- 25. Oil distribution pattern in vacuum fried potato slices at 130°C 26 May 2015 25 (Carla, 2010)
- 26. Vacuum frying Vs Traditional Frying 26 May 2015 26
- 27. Oil content within product 26 May 2015 27 S.No Frying temperature (°C) & method Internal oil content (g/g solid ) Surface oil Content (g/g solid ) Total oil content (g/g solid ) 1. Vacuum frying at 120 0.072 0.339 0.410 2. Vacuum frying at 130 0.062 0.413 0.475 3. Vacuum frying at 140 0.059 0.398 0.457 4. Atmospheric frying at 185 0.50 - - (Carla, 2010)
- 28. Oil content various products 26 May 2015 28 Comparison between oil content of product fried in vacuum and traditional fryers (white-bar: traditional fryer; and black-bar: vacuum fryer) (Paulo et al., 2008)
- 29. 26 May 2015 29 Blue potato fried - vacuum fryer Blue potato fried - traditional fryer Green bean fried - vacuum fryer Green bean fried - traditional fryer (Dueik et al., 2010) Color of product
- 30. 26 May 2015 30 Sweet potato fried - vacuum fryer Sweet potato fried - traditional fryer Mango fried - traditional fryerMango fried - vacuum fryer (Dueik et al., 2010) Color of product
- 31. 26 May 2015 31 (Dueik and Bouchon, 2011)
- 32. 26 May 2015 32 Oil properties affects Frying Oil properties get affected during Frying •Viscosity •Oxidation •Oil aging •Hydrolysis •Stability •Free fatty acids Oil property
- 33. Oil quality • TBHQ- SO - sunflower oil with synthetic antioxidant (tertiary- butylhydroquinone) •HOSO - sunflower oil with high oleic acid Quality Factors • Oil degradation • Fatty acid composition - PUFA and MUFA • ᾳ - Tocopherol Peroxide Value in TBHQ-SOv treatment, are higher than TBHQ- SOt at least 2.32 times in period 2 and 1.86 times in the period 3 26 May 2015 33 (Crosa et al., 2014) PUFA - Poly unsaturated fatty acid; MUFA - mono unsaturated fatty acid
- 34. S.No Quality parameters Traditional frying Vacuum frying TBHQ –SO HOSO TBHQ – SO HOSO 1. Free fatty acid (g oleic acid/100 g) 0.201 0.327 0.073 0.099 2. p- Anisidine (AnV) 207.0 82.0 25.8 33.3 3. Total polar compounds (%) 25.0 21.9 11.2 6.4 4. Reduction in ᾳ - Tocopherol (%) 53.62 99.76 4.90 96.87 *TBHQ- SO - sunflower oil with synthetic antioxidant (tertiary- butylhydroquinone) *HOSO - sunflower oil with high oleic acid content 26 May 2015 34 (Crosa et al., 2014) Comparison of quality parameters
- 35. • Preserves natural Color • Low moisture content - < 6% • Reduced Shrinkage • Low water activity - < 0.3 • Heat sensitive nutrients – preserves 90% of trans –carotene • Prevention of carcinogenic compounds formation – 97% less acrylamide in potato chips • Reduce the fat content – 80 – 85% less oil in potato chips • Suitable for high sugar content products • Less adverts effects on oil quality 26 May 2015 35 Granada et al, (2004), Clara. 2010., Merits of Vacuum frying
- 36. • Skilled person • Requires special packaging • Pre – frying steps – Battering, instant extrusion • Cost • Time 26 May 2015 36 Limitations
- 37. • The vacuum frying conditions (temperature and time) for various food products varied considerably and there was also a wide variation in the vacuum pressures used • The choice of the vacuum frying conditions for the food samples was dictated by a range of physical parameters, as well as pre-treatment conditions • There was no other way to design a vacuum frying process for a specific product except to carry out experiments to obtain an optimized process 26 May 2015 37 Summary
- 38. • Crosa, M. J, Verónica, S., Mónica, C., Laura, O., Roberto, S., Gabriela, S., and Marina, T. 2014. Changes produced in oils during vacuum and traditional frying of potato Chips. Food Chem. 146 (4) 603–607 • Dueik, V., Robert, P and Bouchon, P. 2010. Vacuum frying reduces oil uptake and improves the quality parameters of carrot crisps. Food Chem. 119 : 1143–1149 • Garayo, J., and Moreira, R. G. 2002. Vacuum frying of potato chips. J. Food Proc. Engng. 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. J. of Food Sci. 69(8): 405- 411 26 May 2015 38 References
- 39. • Mariscal, M. and Bouchon, P. 2008. Comparison between atmospheric and vacuum frying of apple slices. Food Chem. 107: 1561–1569 • Moreira, R.G., Da Silva, P.F., and Gomes, C. 2009. The effect of a de-iling mechanism on the production of high quality vacuum fried potato chips. J. of Food Engng. 92: 297-304 • Muanmai, A., Kuluma, C., Punnarai, S., and Noppawan, T. 2007. Effect of antibrowning agents on banana slices and vacuum-fried slices. J. of Food Agri.and Envi. Vol.5:151 -157 • Ophithakorn, T., & Yamsaengsung, R. 2003. Oil absorption during vacuum frying of tofu. In PSU-UNS international conference. Energy and the environment, December 2003, Hat Yai, Songkhla, Thailand • Paulo F. Da Silva and Rosana G. Moreira. 2008. Vacuum frying of high-quality fruit and vegetable-based snacks. Food Sci. and Technol.41 (8):1758 – 176726 May 2015 39
- 40. • Perez-Tinoco, M.R., Perez, A., Salgado-Cervantes, M., Reynes, M. and Vaillant, F. 2008. Effect of vacuum frying on main physicochemical and nutritional quality parameters of pineapple chips. J. of Sci. Food and Agri. 88: 945–953 • Rafael.H. V. V., Quiceno G. C. M., and Giraldo G. G. A. 2012. Effect of vacuum frying process on the quality of a snack of mango (Manguifera indica L.). ACTA AGRONÓMICA. 61 (1): 40- 49 • Shyu, S.L Lung-Bin, H., and Hwang, L. S. 1998. effect of vacuum frying on the oxidative stability of oils .J. American Oil Cor. Soc. 75 (10): 132 – 138 • Song X, Zhang M, Mujumdar A. S. 2007. Optimization of vacuum microwave pre-drying and vacuum frying conditions to produce fried potato chips. Drying Technol, 25: 2027-2034 • Sonntag, R.E., Claus, B., and Gordon, J. V.W., 2003. Fundamentals of Thermodynamics. John Wiley & Sons, Inc. USA. 1894- 192126 May 2015 40
- 41. 26 May 2015 41
- 42. 26 May 2015 42
Editor's Notes
- It's believed by experts that the technique of frying foods originated in the Middle East. The date is uncertain, but it's generally thought to be around two millennia before the birth of Jesus Christ. Frying is therefore age old, and involves the process of bringing oil or fat to a melting point. The reason fat or oils is used, is because they can reach such a high heat. Unlike with boiling water, fat or oil becomes so hot that they can sear the outside of foods. This keeps the moisture and flavour in the food, but also leaves the outside crisp. A criticism of frying food is from the health lobby, which maintain that frying lowers the nutrient value of food, and covers it in unhealthy fats, which can clog the arteries of the heart. Sautéing A cook will place a small amount of fat to layer the surface of a frying pan. With a high heat, usually with flipping the food, to quickly brown the food, but keeps the moisture and avoids absorbing the fat. Stir frying Just like with sautéing, only a small amount of oil is used. A technique which is used with woks, the food is stirred continually, so that it does not brown or burn. But, will make sure all the food is covered in any sauce added. In Chinese cooking there are numerous techniques with varying speeds of execution, heat used, and tossing done. Shallow frying Another style of pan frying, this time using more oil or fat. Whatever food is placed in the pan should be covered half way up with oil. A quick and less fussy way of achieving a similar result to deep frying. Deep frying
- Four stages - depressurization (DP), frying (FR), pressurization (PR), and cooling (CL) During the depressurization period, the potato slices are placed in the headspace of the frying vessel and waiting for the pressure value to go down to 1.33 kPa in order to start the second period; depressurization of the vessel takes approximately 90 to 100 seconds.
- The blue potato was fried at the shortest and the green beans at the longest time. Mangoes and sweet potatoes were fried for the same time, but the final moisture content was higher for sweet potato (lower moisture would result in much higher oil content) When frying under vacuum, a much lower temperature can be used (Garayo & Moreira, 2002) without affecting the product qualities. This is possible because as the water boiling point in vacuum frying is reduced, the water vapor in the product leaves earlier but at the same rate than in the traditional fryers thus resulting in a high-quality final product. The weight variation experienced by the samples fried under atmospheric conditions was around 44±2% with respect to initial weight while the mass variation experienced by fillets fried under vacuum conditions was 19±1% at 90 °C, 22.1±0.1% at 100 °C and 36±2% at 110 °C after 10 min of treatment. Changes in temperature within the frying chamber during vacuum frying The temperature during frying varies within the chamber also in the product. It depends on thickness and moisture content of the product to be fried and oil to product volume ratio of frying. The variation in temperature during frying of potato chips was studied by Paulo et al., (2008). The observation of his studies illustrates the reason for the change in temperature within the product and frying chamber. Temperature at the center of the chip - potato centre (PC) A fine thermocouple (0.254-mm diameter) was placed at the center of a potato slice of 1.6 mm thickness and 25.4 mm in diameter in order to study the temperature history during the vacuum frying process at various temperatures. It was noted that at all frying temperatures, temperature at the center of the potato has a subtle increase followed by a slight decrease during the depressurization period. The increase in temperature takes place when the potato is in the headspace of the vacuum vessel where the temperature is high (80-90ºC) due to heat irradiating from the oil, while the decrease in temperature is a consequence of lowering the pressure of the system, since the potato chip is trying to reach the saturation temperature at the new pressure. Once immersed in the oil, the temperature of the potato chip increased drastically and a temperature spike up to 104°C was observed during the first 10-15 seconds of frying, after this, the temperature starts lowering until it reaches a plateau which is known as the evaporation period. Water evaporated for a longer period of time when frying at the lowest temperature (120ºC); the length of the evaporation period was 70, 65, and 60 seconds corresponding to the frying temperatures of 120, 130 and 140°C, respectively. An interesting finding was that the evaporation temperature of water was between 86 and 94°C depending on the frying temperature. This evaporation temperature is well above the water evaporation temperature at the system pressure of 1.33 kPa (11.2°C). This behavior was also noted by Pandey (2009). It is believed that the high evaporation temperature is related to a difference in pressure between the system and the center of the potato chip, in which the pressure should be higher than 1.33 kPa in order for water to evaporate at those temperatures. For the remaining time of immersion in oil, the temperature at the center of the chip increased until it reached equilibrium with the frying medium; this period was also longer for the lower frying temperatures. During the final two steps of the process, pressurization and cooling, the temperature of the chip starts declining down to ambient temperature (~22°C). The rate of cooling during the pressurization period was slower than the one after the chips were out of the fryer, considering that during the pressurization step, the chips are suspended in the warm headspace of the vessel. Temperature at the surface of the chip (PS) The same thermocouple used to measure temperature at the center of the potato chip was used to measure temperature at the surface by placing it as close as possible to the surface of the chip. The history of the surface temperature was very close to the one for temperature at the center of the chip with some major differences at the beginning of the frying of the immersion frying period. During the depressurization step, the increase of temperature and slight decrease, mentioned in the previous section, was also noted. The most important difference between the center and surface temperature history is that the later does not show the temperature spike followed by the evaporation plateau seen in the center temperature history. The surface temperature rapidly got up to 104ºC in the first 15-20 seconds after immersion in oil, and then continued increasing at a slower rate until it reached the oil temperature. There was no constant temperature related to evaporation since water in the surface evaporates faster than the one in the core of the chip due to direct contact with the frying medium. The depressurization and cooling periods showed the same behavior as the temperature at the center, but with a slightly faster rate of cooling. Effect of frying method on temperature of product The temperature history for the center (PC) and the surface of a potato chip (PS), potato slices fried in a vacuum fryer at 120ºC and in a traditional fryer at 165ºC. The surface temperature history does not show difference between chips fried under the two methods; however a significant difference was noted in the history for temperature at the center of the chip. In traditional frying, the temperature at the center of the chip increased to a value of 107±2ºC once the slices were submerged into the oil; then the evaporation period occurs at 102±1ºC. Even though the center temperature during the first seconds of traditional frying is a slightly higher than the evaporation period, the spike is almost negligible when compared to the temperature spike seen in vacuum frying. This behavior was also observed in a study by Pandey (2009); it was suggested that there is less sudden variations in temperature history during traditional frying because of the negligible pressure difference.
- Browning index Lower frying temperature and shorter frying time would result in a product with a lower browning index. This is due to samples processed at these conditions having less browning changes when compared with the unprocessed samples. This is contrary with observations of Ihns et al. (2011) for drying apricot slices at different temperatures. The differences were probably due to the drying time involved which was not constant for each temperature where shorter drying time was used for higher temperature. the moisture content of vacuum-fried apricot slices decreases with increasing frying temperature (Fig. 1a,b), frying time (Fig. 1a,c) and MD level (Fig. 1b,c). Higher frying temperature and a longer frying time would result in a product with lowermoisture content. This is due tomore evaporation occurring in the sample resulting in lower product moisture content. The same phenomena were also observed by Diamante et al. (2011). for vacuum-fried gold kiwifruit; Higher frying temperature and longer frying time would result in a product with a higher penetration pressure indicating increase in crunchiness. This is due to the drying out of the sample, which therefore hardens it, resulting in a much higher pressure to penetrate the sample. The same phenomena were also observed by Diamante et al. (2011), for vacuum-fried gold kiwifruit; Perez-Tinoco et al. (2008), for vacuum-fried pineapple chips; Fan et al. (2005), for vacuum fried carrot chips; and Shyu and Hwang (2001), for vacuumfried apple chips.
- A pressure transducer was attached to the lid and recorded the pressure inside the vessel during the frying process. Knowing the pressure history during frying allows a better understanding of the vacuum frying process and is a determining parameter in the study and modeling of oil absorption (Mir-Bel et al, 2009). The pressure history showed the same behavior and values for the three temperatures studied with a minor difference right after immersion of the potato chips. During the depressurization period, the pressure is lowered from 101.6±0.15 kPa to 1.4±0.06 at a rate of 1.9±0.06 kPa/s. Once the desired pressure is achieved, the potato slices are submerged into the oil causing vapor release and a short increase in pressure of about 7 to 10 kPa; the raise in pressure was more pronounced at the highest frying temperature (140ºC) due to faster water vapor loss to the headspace. The vacuum pump rapidly accounted for the increased in pressure and efficiently adjusted the pressure back to the lowest level, from this moment, pressure remained constant until the end of the frying. In the pressurization step, the system recovered ambient pressure at a rate of 1.5±0.17 kPa/s.
- It is observed that 80% of oil absorption of fried product takes place only during pressurization period The pressurization step plays an important role in reducing the oil absorption during vacuum frying. It can increase or decrease oil absorption in the product depending on the amount of surface oil and free water presented in the product After frying in vacuum, the pressurization step due to pressure gradient between the product and atmosphere cause intensive absorption of oil De-oiling is very much essential usually carried out with centrifuging speed 350 – 1200 rpm for 30 s to 30 mins
- Size and shape - oil absorption increases significantly when product thickness is reduced and product surface is increased Surface roughness - cells broken during cutting are a privileged location for oil absorption Using good quality blades for cutting can therefore reduce the surface roughness of the product and thus the surface area, resulting in lower oil uptake. Solid content – high density product shows reduced oil absorption. Initial solid content in the product is a factor that influences oil uptake during frying because of the relationship between water loss and oil uptake (Yamsaengsung & Moreira, 2002). High density potato (1103 kg.m-3 compared to 1093 kg.m-3) can reduce oil content by about 10% (Ufheil & Escher, 1996).
- Oil viscosity is very influential in the oil absorption mechanism but is involved both in adhesion and draining dynamics. Moreover, the frying oil may contain a portion of fat that solidifies upon cooling and be harder to drain or shake from the food as well as being less likely to penetrate deeply into crust pores. Fat content can be considered to be a sum of both fat penetration into the crust and fat crystallization on the surface. High oil viscosity shows slow oil migration. Initial oil viscosity depends on the oil type but also on the temperature and oil quality. An increase in interfacial tension leads to an increase in oil uptake the addition of surfactants (surface-active agents or wetting agents) such as Tween80 (Polysorbate) and Span80 (Sorbitan monooleate) Oil aging Oil aging causes increase in viscosity and this contributes to an increase in oil quantity on the food surface. alpha-tocopherol reduction were TBHQ-SO (4.90%) and HOSO (96.87%) in vacuum frying and HOSO (99.76%) and TBHQ-SO (53.62%) in traditional frying. vacuum frying maintains the quality of oil appreciably Initial oil viscosity depends on the oil type but also on the temperature and oil quality An increase in interfacial tension leads to an increase in oil uptake the addition of surfactants (such as Tween80 (Polysorbate) and Span80 (Sorbitan monooleate) Oil aging Oil aging causes increase in viscosity and this contributes to an increase in oil quantity on the food surface