Characterization of product quality attributes of tortilla chips during the frying process

Abstract

Tortilla chips were prepared from commercially nixtamalized dry mesa flour. The effect of initial moisture content, frying oil temperature, flour particle size distribution, and degree of starch gelatinization on the moisture loss, oil absorption, changes in geometric dimensions, texture, porosity, and pore size distribution of tortilla chips during frying was studied. Isotherm, glass transition, and pore size distribution models during frying of tortilla chips were also developed. Tortilla chips with a high initial moisture content had a high rate of water loss and oil absorption during frying. As water evaporated tortilla chips shrank (in diameter) to a large extent and the chips' thickness increased. Tortilla chips fried in a higher oil temperature showed a higher degree of shrinkage and a lower degree of expansion. Crust formation occurred faster thus creating puffiness at the chips' surface. Higher oil temperature produced chips with a higher practicability and grouchiness. Oil temperature did not affect the final oil content of tortilla chips. The chips made from fine grain flour formed small pores during frying which accounted for the large amount of oil absorption. The coarse grain chips had the highest fracturability and the least crunchiness. Tortilla chips with a high starch gelatinization prior to frying shrank (in diameter) the most and no thickness expansion occurred. These chips absorbed a very small amount of oil that was deposited on the surface. Various models were fitted to determine which one predicted the experimental data of water activity the best. The Crapiste and Rotstein model (1986) provided the best correlation at the entire range of moisture content and temperatures. The equilibrium moisture content decreased as temperature and oil content increased for the same water activity value. The glass transition temperatures were fitted using the Gordon and Taylor equation. The glass transition curve for the fried chips with total oil content is higher than the one for the chips with partial oil content. A model was developed using the Extreme Value distribution to predict the pore size distribution of tortilla chips during frying. Pore size increases during frying and becomes more uniformly distributed as frying continues.