Measurement of physical properties during processing of french fries

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Agblor, Amewushika
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A puncture test was used to measure the effects of blanching, drying and frying conditions on the mechanical properties (peak force, peak deformation and post-puncture energy consumption) of french fries. Potato cultivars (Russet Burbank and Shepody) grown at Portage and Carberry, Manitoba in 1994 and 1995, and stored for 11 months were used. For texture, high peak force, large peak deformation and low post-puncture energy consumption were assumed to be associated with improved quality. French fry colour was measured using the lightness (L) scale on a Hunterlab colorimeter. For a given unit operation, french fries processed by the standard conditions, which mimic industrial french fry operations, were compared to fries processed by a low-temperature long-time (LTLT) and a high-temperature short-time (HTST) regime. Processing conditions were found to have varying effects on french fry quality. With the exception of the LTLT blanching conditions, which improved both colour and textural quality, and the LTLT drying conditions which decreased these properties, a compromise has to be made between improved colour and improved textural quality. French fry quality was influenced by storage period, cultivar and site. French fries processed from potatoes at 11 months storage had improved colour and textural quality compared to potatoes at 9 months storage whereas fries processed at 3 months were darker in colour but firmer in texture than french fries processed from potatoes at 1 month. For cultivar, no significant differences (p $\leq$ 0.05) were found in peak force of fries made from Russet Burbank and Shepody potatoes but fries from Shepody potatoes were darker than those from Russet Burbank potatoes. For site, fries from Portage potatoes were darker in colour but firmer in texture than fries from Carberry potatoes. Strip position within the tuber was a major source of variation for mechanical properties. Peak force, peak deformation and post-puncture energy consumption were greater for blanched french fry strips located in the pith of the tuber (inner strips) than for outer strips taken from the cortex of the tuber. Examination of the microstructure of these french fry strips revealed that parenchyma cells in the outer strips had a 'balloon-like' appearance due to the magnitude of starch swelling pressure generated by swollen granules. For inner strips, this "balloon-like" appearance was less evident. The measured volume of cell agglomerate obtained upon maceration of strips was significantly higher (p $\leq$ 0.001) for outer strips than for inner strips. It was concluded that a differential blanching treatment should be used, in which inner strips are blanched by HTST conditions and outer strips by LTLT conditions. (Abstract shortened by UMI.)