Structural changes and shrinkage of potato during frying

Abstract

Summary Light microscopy was used to study changes in cell size, blister formation and crust evolution during potato frying. Frying experiments with both French fries and crisps of different thickness (1–5 mm) were performed at temperatures of 140 and 180 °C. Thickness, volume and density changes were also measured. The formation of crust in French fries starts after the potato surface reached approximately 103 °C, and then the crust thickness increased linearly with the square root of frying time, this increase being faster at 180 °C. The potato volume decreased during frying, although in the late stages the volume may increase because of oil uptake and cell separation caused by entrapped water vapour. Shrinkage was adequately described by the Weibull model with a residual value, with shrinkage rate increasing with temperature and decreasing with potato thickness. The residual volume was not affected by temperature (65% for French fries and 59–30 for crisps, depending on thickness). Volume appeared to decrease mainly as the result of water loss, except for very low water content, and thus potato density changes were very small.

Effect of pre-drying and par-frying conditions on the crispness of French fries

“…Both sensory evaluation and texture analysis showed that the highest value for crispness resulted from par-frying at 180 • C. In microscopic analysis, however, the typical cell structure associated with a crispy crust did not occur more often in samples that were par-fried at 180 • C than those that were par-fried at 160 and 170 • C. The enhanced crispness may be explained by the temperature difference between surface and core. The core temperature remains at 103 • C because of the presence of water [3,13]. A higher frying temperature, therefore, results in a larger temperature difference and a thicker crust.…”

“…The interior of French fries consists of cooked and slightly dehydrated cells [13], and the texture is similar to cooked potatoes. Microscopic analysis of potato strips, fried in dyed oil, showed that the oil is located in the crust region only [14].…”

Effect of pulsed electrical fields on the structural properties that affect french fry texture during processing

“…The crust develops when the surface temperature reaches ~103 o C (Costa, Oliveira, & Boutcheva, 2001). Crust is formed within seconds of frying, as the outer cells of the chips are damaged during cutting and undergo rapid release of vapour and subsequent dehydration.…”

“…Blister structures can form under the crust as vapour pressure is released, forming pockets. Blisters increase with temperature and cooking time (Costa, Oliveira, & Boutcheva, 2001). …”

Study of a new energy efficient process for French fries production

“…The resistance to the release of water vapour increases and this leads to pressure build-up below the surface. Water vapour is released by the bursting of a few localized sites that break under the stress caused by pressure, resulting in a porous structure [19]. After frying, oil enters the crust because of the capillary pressure difference and the interfacial tension between the oil and the gas within the pores [20].…”