US scientists, writing in the Journal of Food Process Engineering, report that short frying time and/or longer centrifuging time combinations would maximize oil removal from the chip's surface during vacuum frying.
According to the study, chips have increased oil content (OC) following vacuum frying and depressurization because of the rapid change in pressure (vacuum to atmospheric).
De-oiling, they note, is one of the most important steps in vacuum deep-fat frying to ensure quality products as it helps to remove the oil from the chip's surface before the process is pressurized.
The team, based at Texas A&M University and equipment supplier Blentech Corporation found the de-oiling system removed up to 81 per cent of the chip's surface oil when “centrifuged for 40 seconds at 750 rpm.”
And the researchers note that less oil was absorbed by the potato chips when the fryer was pressurized at lower rate (25 per cent open released valve) than at faster rate.
The authors claim their findings can help inform more effective design of vacuum frying systems to produce snacks with lower oil content.
Potato slices were fried at 120 and 140C oil temperatures and 1.33kPa pressure.
Noting a lack of data regarding de-oiling, pressurization rate and temperature history during vacuum frying of potato chips the scientists report that they monitored the temperatures of the fryer headspace and the centre of potato slices during frying.
They authors also studied the effects of varying the speed of the de-oiling mechanism and the pressurization rates on the oil absorption of potato chips. And they said they calculated convective heat transfer coefficient using the lumped capacity method for varying frying loads
The researchers note that pressure differential plays an important role in the uptake of oil in cases of vacuum frying:
“After completion of frying of potato slices in a vacuum fryer, the vessel must be depressurized for removal of chips. The major oil absorption takes place during this period of pressurization causing pressure gradient between capillaries and ambient conditions, which causes oil to move from the surface of the chips to within the product.”
The researchers concluded that de-oiling mechanism will remove more oil from the chip's surface “when the samples are centrifuged at higher speed for longer time.”
“The longer the chips remain immersed in the hot oil after most of the water has evaporated, the higher the oil absorption during frying. Therefore, short frying time and/or longer centrifuging time combinations would maximize oil removal from the chip's surface during the process,” they found.
Source: Journal of Food Process Engineering
Published online ahead of print: DOI: 10.1111/j.1745-4530.2011.00635.x
Title: Batch Vacuum Frying System Analysis for Potato Chips
Authors: A. Pandey, R. Moreira