300 JOURNAL OF FOOD SCIENCE—Vol. 66, No. 2, 2001 © 2001 Institute of Food Technologists Food Engineering and Physical Properties JFS: Food Engineering and Physical Properties Effect of Degree of Starch Gelatinization on Quality Attributes of Fried Tortilla Chips M.L. KAWAS AND R.G. MOREIRA ABSTRACT: The effect of degree of starch gelatinization on the quality attributes of tortilla chips was studied. Three different samples were prepared: control (45% of starch gelatinized before frying), freeze-dried (5% of starch gelati- nized before frying), and steamed-baked tortilla chips (87% starch gelatinized before frying). Compared to the control chips, the steamed-baked tortillas produced chips with lower oil content. They shrunk the most and showed a high degree of puffiness and lower crunchiness. Their texture was harder and not very crunchy. The majority of the oil in these chips was located at the surface. The freeze-dried tortilla yielded chips with high oil content. The texture was soft, and the porosity was very low, providing unacceptable characteristics in tortilla chips. Key Words: freeze-drying, steaming, crunchiness, puffiness, oil content Introduction T HE FRYING TECHNOLOGY IS IMPORTANT TO THE SUPPLIERS OF oils, food-service operators, food industries, and manu- facturers of frying equipment. The amounts of fried food and oil used at commercial and industrial levels are large. The U.S. produces more than 2.5 million metric tons (MMT) (5  10 9 lb) of snack food per year, the majority being fried (Snack Food Association 1997). Numerous reports are available in the literature related to factors that affect oil distribution in tortilla chips, however, such phenomenon of oil absorption during the process has not yet been thoroughly understood. Manufacturers of fry- ing equipment still lack enough knowledge about what hap- pens within a product during frying. Manufacture of tortilla chips involves boiling the corn in lime solution, quenching it, and steeping it overnight. The cooked corn is washed to remove excess alkali and loose pericarp. It is then stone-ground to produce masa, which is sheeted, cut, and baked at 300 to 315 °C for about 1 min. The baked tortillas are cooled at ambient temperature and then deep-fat fried in oil at 190 °C for 1 min. Many factors affect oil uptake, including frying temperature and duration, prod- uct shape, product composition, porosity, and pre-frying treatments. Oil content in fried foods has been related to initial moisture content (Gamble and others 1987; Moreira and others 1995), prefrying treatment (Gamble and Rice 1987), structural changes during baking (Lee 1991; McDonough and others 1993; Rock- Dudley 1993), and cooling time (Sun and Moreira 1994). Understanding the oil distribution in tortilla chips is im- perative before trying to assess good quality control. It is hy- pothesized to be related to the degree of starch gelatiniza- tion prior to frying. However, little is known about the effect of degree of starch gelatinization on the oil absorption and thus the quality attributes of tortilla chips during frying. In this study, the effect of degree of starch gelatinization prior to frying on product quality attributes (PQA) that is, shrink- age, puffiness, texture, pore-size distribution, and porosity of tortilla chips was studied. Materials and Methods Samples Preparation Raw tortillas were prepared from nixtamalized dry masa flour (NDMF) for tortilla chips (tortilla chip 1Y, Valley Grain Products, Muleshoe, Texas, U.S.A.). The procedure is detailed in Moreira and others (1997). The effect of starch gelatinization on oil distribution (in- ternal and total), moisture content, shrinkage, puffiness, po- rosity, pore-size distribution, and texture during frying was determined by pretreating the raw tortillas before frying. To be able to compare tortilla chips with different degrees of starch gelatinization, the pretreated tortillas contained the same initial moisture content (approximately 42% (w.b.)) as the other samples. Freeze-dried tortillas: A monolayer of raw tortillas was frozen at -20 °C for 8 h. The frozen tortillas were placed on a basket inside a freeze drier (Freeze Dry-5, Labconco Cor- poration, Kansas City, MI U.S.A.) and were freeze dried at -30 °C for 30 min to reach about 42% (w.b.) moisture con- tent. These tortillas had a degree of gelatinization of approxi- mately 5%. Control tortillas: Control tortillas were prepared as de- scribed above. These tortillas had a degree of gelatinization of 45%. Steamed-baked tortillas: Over-gelatinized tortillas were prepared by steaming the raw tortillas and then baking them in a convection oven. A round flat sieve was placed on the top of an 8-quart sauce pot filled with 4 quarts of boiling wa- ter. The raw tortillas, initially containing approximately 54% (w.b.) moisture content, were placed on the sieve for 45 min. The tortillas were cooked during the process, resulting with an increased final moisture content of about 64% (w.b.). The tortillas were then transferred to a baking oven set at 90 °C for 27 min to reduce the moisture content to 42% (w.b.). These tortillas had a degree of gelatinization of 87%. Degree of Starch Gelatinization The degree of starch gelatinization (DG) of different torti-