Browsing by Subject "Vacuum frying"
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Item Characterization of Product Quality Attributes and Thermal Properties of Potato Chips during Vacuum Frying(2010-10-12) Yagua Olivares, Carla VeronicaVacuum frying is an alternative processing method for producing high quality snacks with the advantages of lower processing temperature, enhanced organoleptic quality, and reduced acrylamide content. Vacuum frying (1.33 kPa), with the aid of a deoiling mechanism, was used to produce low-fat potato chips. The kinetics of oil absorption and oil distribution in the potato chips (total, internal, and surface oil content) was studied so that effectiveness of the de-oiling system could be established. An analysis of product quality attributes (PQA) such as moisture content, oil content, microstructure, diameter shrinkage, and thickness expansion, as well as, bulk density, true density, and porosity of chips fried at different temperatures (120, 130, and 140 degrees C) was performed in order to evaluate the effect of process temperature on the product. Moreover, heat capacity of the chips and convective heat transfer coefficient at the oil-chip interface were determined for the same temperature range. The final oil content of the potato chips was 0.072?0.004, 0.062?0.003, and 0.059?0.003 g/g solid for frying temperatures of 120, 130, and 140 degrees C, respectively. These values are lower (80-85 percent less) than those found in traditionally-fried potato chip which indicates that the de-oiling mechanism is crucial in vacuum frying processing. A significant difference (P<0.05) was observed in oil content and oil distribution within temperatures. It was found that the rate of change in PQAs is greatly affected by temperature; however, the final values of moisture content, bulk density, true density, porosity, diameter shrinkage, and thickness expansion were not affected by temperature. During vacuum frying, the specific heat of potato chips decreased with time as water decreases. The convective heat transfer coefficient changed considerably as frying progresses; moreover, it increased with temperature reaching a maximum between 2,200 and 2,650 W/m2K depending on frying temperature.Item Design and Optimization of Condenser and Centrifuge Units for Enhancement of a Batch Vacuum Frying System(2011-02-22) Pandey, AkhileshA batch vacuum frying system, which processes fruits and vegetables, includes a frying pan, a surface-condenser, and a vacuum pump. With health and safety issues in mind, this research focused on developing a modified surface-condenser to prevent cavitation of the vacuum pump. The final oil-content was reduced by centrifugal de- oiling of the product under vacuum, which make the product healthier than what is currently available. The de-oiling mechanism consists of a centrifuge with a motor attached to the basket shaft, rotating up to 750 rpm (63 g units). The condenser consists of a (counter- flow) spiral-coil heat exchanger (SHE) connected to a refrigeration system that uses R404a refrigerant. De-oiling for 40 s at 300 and 750 RPM removed up to 67% and 72% of the chip?s surface oil, respectively. At 750 RPM for 10 s, 40 s, and 60 s the oil-content was reduced by 38%, 44%, and 51%, respectively. The convective heat transfer coefficient (h) of the frying oil was determined at 120?C and 140?C using the lumped capacitance method. The h-values were 217?13 W/m2K (120?C) and 258?37 W/m2K (140?C) using a copper-ball thermocouple. The h- values increased to 3.6 times during the boiling period. COMSOLTM Multiphysics was used to model the heat transfer in the vacuum fryer pan. Based on the simulation results, a 1.5 cm thick insulation material was installed in the fryer to reduce the energy losses. The refrigeration system operates at Tevap = -26?C and Tcond = 50?C with 26?C sub-cooling. Sensitivity analysis showed that the system Coefficient of Performance (COP) was about 3.87 at these conditions and compressor power requirement (CPR) was 74 W (85% efficiency) when frying 30 g of potatoes slices. The best results were obtained at Tevap = -10?C and Tcond = 40?C with 26?C sub-cooling and superheat of 5?C. The predicted COP was 4 and the CPR 70 W. The ice-formation on coils reduced the condensation rate. Reducing the refrigerant temperature to -10?C (from -26?C) reduced the condensation rate by 30%. These results show a more effective vacuum frying system for high-quality fruits and vegetables than the system previously used.