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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 Food Engineering and Physical Properties Introduction Materials and Methods HE FRYING TECHNOLOGY IS IMPORTANT TO THE SUPPLIERS OF Toils, food-service operators, food industries, and manu- Samples Preparation facturers of frying equipment. The amounts of fried food Raw tortillas were prepared from nixtamalized dry masa and oil used at commercial and industrial levels are large. flour (NDMF) for tortilla chips (tortilla chip 1Y, Valley Grain The U.S. produces more than 2.5 million metric tons (MMT) Products, Muleshoe, Texas, U.S.A.). The procedure is detailed (5 ϫ 109 lb) of snack food per year, the majority being fried in Moreira and others (1997). (Snack Food Association 1997). The effect of starch gelatinization on oil distribution (in- Numerous reports are available in the literature related to ternal and total), moisture content, shrinkage, puffiness, po- factors that affect oil distribution in tortilla chips, however, rosity, pore-size distribution, and texture during frying was such phenomenon of oil absorption during the process has determined by pretreating the raw tortillas before frying. To not yet been thoroughly understood. Manufacturers of fry- be able to compare tortilla chips with different degrees of ing equipment still lack enough knowledge about what hap- starch gelatinization, the pretreated tortillas contained the pens within a product during frying. same initial moisture content (approximately 42% (w.b.)) as Manufacture of tortilla chips involves boiling the corn in the other samples. lime solution, quenching it, and steeping it overnight. The Freeze-dried tortillas: A monolayer of raw tortillas was cooked corn is washed to remove excess alkali and loose frozen at Ϫ20 ЊC for 8 h. The frozen tortillas were placed on pericarp. It is then stone-ground to produce masa, which is a basket inside a freeze drier (Freeze Dry-5, Labconco Cor- sheeted, cut, and baked at 300 to 315 ЊC for about 1 min. The poration, Kansas City, MI U.S.A.) and were freeze dried at baked tortillas are cooled at ambient temperature and then Ϫ30 ЊC for 30 min to reach about 42% (w.b.) moisture con- deep-fat fried in oil at 190 ЊC for 1 min. Many factors affect tent. These tortillas had a degree of gelatinization of approxi- oil uptake, including frying temperature and duration, prod- mately 5%. uct shape, product composition, porosity, and pre-frying Control tortillas: Control tortillas were prepared as de- treatments. scribed above. These tortillas had a degree of gelatinization Oil content in fried foods has been related to initial moisture of 45%. content (Gamble and others 1987; Moreira and others 1995), Steamed-baked tortillas: Over-gelatinized tortillas were prefrying treatment (Gamble and Rice 1987), structural changes prepared by steaming the raw tortillas and then baking them during baking (Lee 1991; McDonough and others 1993; Rock- in a convection oven. A round flat sieve was placed on the Dudley 1993), and cooling time (Sun and Moreira 1994). top of an 8-quart sauce pot filled with 4 quarts of boiling wa- Understanding the oil distribution in tortilla chips is im- ter. The raw tortillas, initially containing approximately 54% perative before trying to assess good quality control. It is hy- (w.b.) moisture content, were placed on the sieve for 45 min. pothesized to be related to the degree of starch gelatiniza- The tortillas were cooked during the process, resulting with tion prior to frying. However, little is known about the effect an increased final moisture content of about 64% (w.b.). The of degree of starch gelatinization on the oil absorption and tortillas were then transferred to a baking oven set at 90 ЊC thus the quality attributes of tortilla chips during frying. In for 27 min to reduce the moisture content to 42% (w.b.). this study, the effect of degree of starch gelatinization prior These tortillas had a degree of gelatinization of 87%. to frying on product quality attributes (PQA) that is, shrink- age, puffiness, texture, pore-size distribution, and porosity of Degree of Starch Gelatinization tortilla chips was studied. The degree of starch gelatinization (DG) of different torti- 300 JOURNAL OF FOOD SCIENCE—Vol. 66, No. 2, 2001 © 2001 Institute of Food Technologists jfsv66n2p0300-0306ms20000236.p65 300 4/19/2001, 4:10 PM Black Starch Gelatinization on Fried Tortillas . lla samples was tested to relate it to moisture loss, oil ab- height were measured using a steel caliper (MG Tool Compa- sorption, and PQA. ny, New York, N.Y., U.S.A.). About 20 readings were made for The enthalpy of tortilla chips with different degrees of 5 samples of each treatment. starch gelatinization was determined with a Differential Degree of diameter shrinkage (Si) was calculated by: Scanning Calorimeter (DSC) (Perkin Elmer DSC-4). ϭ Ϫ ϫ The control, steamed-baked and fried, and freeze-dried Si (do d(t)/do) 100 (3) and fried tortilla chips were ground with a coffee grinder (Braun, Model KSM2) to obtain a powder-looking sample. Degree of puffiness (Ei) was calculated by: Four mg tortilla chip samples were placed into aluminum ϭ Ϫ ϫ DSC pans (Model 219-0062, Perkin Elmer), and distilled water Ei (d(t) do/do) 100 (4) was added with a micropipette to give a water to sample ra- ϭ tio of 4:1. The weight of the dry sample in each pan was de- where do original dimension of baked sample (mm), and termined by puncturing the pan after scanning and then dry- d(t) ϭ dimension of sample with frying time (mm). ing at 105 ЊC overnight. The samples were scanned from 25 to 160 ЊC with a heating rate of 10 ЊC/min, a cooling rate of Solid Density 40 ЊC/min, and a DSC operating range of 50 mcal/s. To obtain the solid volume of tortilla chips, the pre- The control baked, steamed-baked, and freeze-dried tor- weighed samples were ground using a coffee grinder and tillas were mashed using a spatula to obtain a homogeneous placed in a compressed helium gas multi-pycnometer sample. The tortilla samples were not crushed in a coffee (Quantachrome Corporation Boynton Beach, Fla., U.S.A.). ␳ 3 grinder to avoid any starch gelatinization from frictional Solid density, s(kg/m ), was determined by dividing the forces of the blades. About 4 mg tortilla chip samples were weight of the sample by its solid volume. The test was per- placed into aluminum DSC pans (Model 219-0062, Perkin formed in triplicate. Elmer) and treated as described previously. Enthalpy was cal- culated from the equation: Bulk Density The bulk volume was measured using the liquid displace- ϭ ⌬ Ϫ ⌬ ⌬ ϫ DG(%) (( Hmasa Htreatment)/ Hmasa) 100 (1) ment technique (Wang and Brennan 1995; Lozano and oth- ers 1983). The apparatus was filled with toluene and closed ⌬ ϭ where Hmasa enthalpy of gelatinization for the masa (kJ/ hermetically with a lid. It was turned upside down twice to kg), ⌬H ϭ enthalpy of gelatinization for the treated measure the volume displacement with and without the pre- treatment ␳ tortilla or chip (kJ/kg). The test was performed 20 times. weighed sample immersed in the toluene. Bulk density, b (kg/m3), was then determined by dividing the weight of the ⌬H ϭ (K ϫ A ϫ R/W ϫ S) (2) chip by its bulk volume. The test was performed in triplicate. where ⌬H = enthalpy (kJ/kg), K = calibration constant, 1.011, Porosity A = area under the sample peak (m2), R = range control set- Porosity, ␾ , can be defined as the volume of pores occupied ting, W = sample weight (kg), and S = chart speed. by air divided by the volume of the product (bulk volume): ϩ ϩ ϭ Ϫ ␳ ␳ Sample Analysis Va/(Vs Vw Va) 1 ( b/ s) (5) Food Engineering and Physical Properties Moisture content Pore-size distribution Tortilla chip samples were ground in a coffee grinder Three tortilla chip samples were analyzed for every treat- (Braun, Model KSM2) after frying. Moisture content of torti- ment. Each tortilla chip sample was broken into 9 pieces (10 lla chips was determined by weight loss after drying 5-g sam- mm L ϫ 7 mm W) for which 3 photomicrographs were taken ples in a forced-air oven at 103 to 105 ¼C (AACC 1986) for 24 in different regions to have a good representation of the treat- h. The test was performed in triplicate. ment. The small pieces were mounted on aluminum stubs with conductive adhesive and viewed with no further sample Oil Content preparation in an Electroscan Model E-3 ESEM (Electroscan Total oil content: Total oil content of tortilla chips was de- Corp., Wilmington, Mass., U.S.A.) with accelerating voltage of termined by using the Soxtec System HT (Pertorp, Inc., Silver 15 kV.

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