THE HEAT AND MASS TRANSFER PROCESSESDURING THE VACUUM FRYING OF POTATO CHIPS 1

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1 POTATO CHIPS 1 The heat and mass transfer processes during the vacuum frying of potato chips NguyễnThịMỹChinh Nong Lam University Author note Nguyễn Th ị M ỹ Chinh, Food Technology, Nong Lam University Nguyễn Th ị M ỹ Chinh is studying Heat and Mass transfer principles project, Nong Lam University This research was supported the Heat and Mass transfer principles project to know more heat and mass transfer processesduring the vacuum frying of potato chips. Contact: mylienanlene@gmail.com

2 POTATO CHIPS 2 Abstract A heat and mass transfer were two processes which occurred during vacuum frying potato chips. The heat transfer process included the convection of heat from the surface to the product and the conduction of heat into the product. The mass transfer process was divided into two periods that are water loss and oil absorption. Oil absorption rate was related to the moisture loss rate during the vacuum frying process.from the heat and mass transfer processes, the increase in temperature of the product toward the boiling point of water (at the associated pressure) which followed by its steady increase toward the temperature of the oil was validated create the movement of water from the material and the osmotic of oil into the ingredients. These processes caused the modified physics and chemistry of potatoes and oil during frying. And the quality of potato chips also was affected by heat and mass transfer. Key words:heat transfer, mass transfer, vacuum frying, potato chips

3 POTATO CHIPS 3 Introduction Potato chips fried which is one of the most common products that can be found in everywhere. However, thechemical is formed when frying potatoes at high temperatures may increase the risk of harm to human health. In other to demand the rising health concern and the trends toward healthier snacks, vacuum frying may be an option for production of fruits and vegetables with low oil content and the desired texture and flavor characteristics. Because deep fried food occupy a large part of the food industry. The big problem with it is the high fat content that deep fried products have. Vacuum frying is a reasonably new technology which uses lower pressure and temperature rather than atmospheric deep fat frying to improve the quality attributesof food products. That is the technology reduces the fat content without compromising the edible quality which hasa large industrial potential today.

4 POTATO CHIPS 4 Purpose Vacuum frying is an alternative method to the deep frying that offers the health benefits of humans. Vacuum frying offers an alternative way to improve the quality of fried fruit and vegetables other than by atmospheric frying (Dueik and Bouchon, 2011a). The main factors that influence fried products are the frying time temperature combination of the cooking process; the correct combination of which is necessary to produce a food product with acceptable physical attributes (Andres Bello et al., 2011). Dueik and Bouchon (2011a) showed that vacuum frying significantly lowered the final oil content in comparison to atmospheric fried and it also slowed the rancidity of the oil. Most of the benefits of vacuum frying from the use of low temperatures and the minimal exposure to oxygen reduce the adverse effects on the oil quality (Shyu et al., 1998). The vacuum frying can reduce oil content in the fried product. Because the oil is absorbed less due to the difference between the pressure inside of product and the pressure vacuum frying can eliminate the oil sticks on the surface of the product in the final stages of frying.(garayo& Moreira, 2002). The product can keep the natural color, flavors(shyuand Hwang, 2001) and limit the loss of vitamins and minerals when fry in vacuum condition that are beneficial of the product due to the low temperature and oxygen content during the process (Da Silva và Moreira, 2008). Garayo and Moreira and Tychy (2004) demonstrated that vacuum frying could produce fried starchy products with a much lower acrylamide content than their counterparts fried at atmospheric pressure.

5 POTATO CHIPS 5 Method The potato chips have to be processed through steps: Classification > Washing >Peeling >Cutting >Cleaning >Blanching > Dehydration >Vacuum frying > Deoiling > Cooling > Mixing > Packaging To frying potato slices in vacuum condition, we used the vacuum fried equipment.when boiling oil, the raw material was enclosed into a specialized pressure vessel containing a deep fryer. The vessel was connected to a vacuum pump which was the equipment used to generate vacuum. Vacuum pumps generally can be considered as compressors in which the discharge, rather than the intake, is at atmospheric pressure. The vacuum in a chamber is created by physically removing air molecules and exhausting them from the system. Removing air from the enclosed system progressively decreases air density within the confined space, thus causing the absolute pressure of the remaining gas to drop.a vacuum environment is created due to the absolute maximum pressure difference that can be produced is equal to atmospheric pressure. After this the vessel depressurized. The raw material was immersed into frying oil within the vessel, fried at C for 5 20 minutes based on the size, thick slices of potato, fried furnace temperature and the amount of material.the potatoes completely submerged in oil andthe materials had to lower than the surface of the oil from 5 10 cm. During the frying process, we check the quality of the oil. If the index of acid is greater than four, we have to change the oil. If there are not burning smells, dark color, you can continue to fry, but we can not fry when the index of acid exceeds five.

6 POTATO CHIPS 6 Fig.1. Schematic of the vacuum frying system To determine the time stop frying, we rely on appearance, taste and level frying of products. In assessing the level frying, we evaluated by two level frying: The apparent frying: the ratio between the decrease of material after frying and the material before frying. It is used to check or calculate the indicators, technical and economic norms and yield of equipment. A: the mass of material before frying B: the mass of material after frying The fact frying: the total of the apparent frying with the oil which is absorbed into the material. It is the evaporation of material after frying. M: the ratio of oil is absorbed into the material

7 POTATO CHIPS 7 Finally the vessel is re pressurized again. The repressurization should be done quickly. A centrifugation step can also be inserted for removal of excess frying oil after the frying step before the pressurization. The heat and mass transfer processes during the vacuum frying of potato chips The vacuum frying is the frying process that is carried out under pressures well below atmospheric levels, preferably below 50 Torr(6.65 kpa). Due to the pressure lowering, the boilingpoints both of the oil and the moisture in the foods arelowered (Garayo and Moreira, 2002). The heat and mass transfer processes during vacuum frying of potato chips was reported by Yamsaengsung et al. (2008). The heat transfer process included the convection of heat from the surface to the product and the conduction of heat into the product. The mass transfer process was divided into two periods that are water loss and oil absorption. The heat transfer process The convective heat of the oil and the product surface Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it. The heat transfer of the oil and the product surface are forced convection due to the temperature increases in vacuum pressure condition. Under the impact oftemperature, heated oil expands and becomes more buoyant. Cooler, more dense oil near the surface descends and patterns of circulation can be formed, causing convection currents which transported energy. Therefore warmer oil rise, cooler oil drop and replaced the warmer oil.