A Technique to Measure Firmness in Potato Tissue during Frying

Abstract

The suitability of a cylinder fabricated from stainless steel was investigated for measuring the textural changes in potato during frying. The cylinder was attached to a TA.XT2 texture analyzer. A circulating heating bath was suitably connected to the cylinder. Initially, sunflower oil in the heating bath was brought to 180 'C without allowing it to circulate into the cylinder. A cube of potato tissue was positioned at the center of the cylinder with the help of a metal plate. The metal plate also allowed a thermocouple to be inserted into a potato cube to measure sample temperatures. The texture analyzer was then set to cause a continuous 20% strain. Heated sunflower oil from the bath was then circulated into the cylinder, thereby achieving complete immersion of potato tissue during force measurements. The circulating heated oil rapidly raised the tissue temperature from 20 'C to about 85 0C in 30 s, and, thereafter, a slow increase was observed. Firmness, expressed as the force required to cause 20% strain in the cube of potato tissue, slightly decreased during initial frying followed by a rapid decline. In separate hot-stage microscopy experiments, temperatures corresponding to swelling of starch granules and cell disruption were examined and compared with the firmness data. The stainless steel cylinder certainly allowed continuous circulation of heated oil and also kept the food sample in direct contact with oil during force measurements. This technique has limitations if absolute values of firmness are required. However, for zomparing texture profiles of different food samples during frying, the technique allows continuous measurements to be made.