Effect of Degree of Starch Gelatinization on Quality Attributes of Fried Tortilla Chips M.L

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 gelatinized 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 (5 109 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 20 C 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 C 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 30 C for 30 min to reach about 42% (w.b.) moisture con- deep-fat fried in oil at 190 C 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 C 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, shrinkage, 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-

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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). 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 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- 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) dimension of sample with frying time (mm). ing at 105 C overnight. The samples were scanned from 25 to 160 C with a heating rate of 10 C/min, a cooling rate of Solid Density 40 C/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 calculated from the equation: Bulk Density The bulk volume was measured using the liquid displace- DG(%) (( Hmasa Htreatment)/ Hmasa) 100 (1) ment technique (Wang and Brennan 1995; Lozano and others 1983). The apparatus was filled with toluene and closed where Hmasa enthalpy of gelatinization for the masa (kJ/ hermetically with a lid. It was turned upside down twice to kg), H 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 (K A R/W 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):

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 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. The area and perimeter of the pores were analyzed by Spring, MD) extraction with petroleum ether (AACC 1986). image analysis software called Scion Image (National Institutes The test was performed in triplicate. of Health, Bethesda, Md., U.S.A.). Pore-size distribution histo- Internal oil content: Oil content on the surface and the grams were developed to compare the different treatments. core of the tortilla chips was measured using the approach described by Moreira and others (1997). The surface oil was Texture washed out by dipping the tortilla chips for 1 s in a 600-mL Texture of the tortilla chips was evaluated with a Texture beaker containing petroleum ether. The oil collected in the Analyzer™ (TA-XT2, Texture Technology Corp., NY U.S.A.) beaker was defined as the surface oil, and the remaining oil using a 6.325-mm-dia ball probe and an 18-mm-dia hollow in the tortilla chips was defined as the internal oil (% w.b.) cylindrical base. The probe traveled at a velocity of 0.1 mm/s that was measured using Soxtec extraction with petroleum until it cracked the sample; the lowest possible speed that the ether (AACC 1986). The test was performed in triplicate. probe could travel was chosen to get a very jagged curve to measure crunchiness. About 20 flat chips from each treat- Degree of Shrinkage and Puffiness ment were tested. The effect of frying temperature and prefrying treatment on the diameter shrinkage and puffiness of tortilla chips dur- Crunchiness ing frying was analyzed. The diameter, thickness, and puff Crunchiness of tortilla chips fried at different times was

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Table 1—Effect of degree of gelatinization on oil distribution during frying of tortilla chips fried for 60 s at 190 oC*

Prefrying MCbf MCaf TOC IOCaf IOCac conditions (%w.b.) (%w.b.) (%w.b.) (%w.b.) (%w.b) Freeze-dried 42.981.02a 2.240.04a 38.240.31a 19.540.23a 32.020.18a (DG = 5%) Control 42.010.18a 2.040.11a 23.640.11b 9.490.61b 17.560.24b (DG = 45%) Steamed-baked 43.010.24a 2.600.02a 14.710.09c 1.8910.02c 4.010.07c (DG = 87%) Tests were performed in triplicate. Means with the same letter are not significantly different (p < 0.05). *Frying conditions: 8 tortillas/fryer, fresh soybean oil. DG =degree of starch gelatinization; % w.b. = % wet basis MC = moisture content; subscripts bf = before frying and af = after frying IOC = internal oil content; subscripts ac = after cooling TOC = total oil content

measured from the jaggedness or “noise” of the sample. Data files had a maximum of 10 points per s so the number of data points allowed by the program Fractals Surfaces was not exceeded (Russ 1994). This program synthesizes and ana- lyzes fractal surface images. The maximum distance traveled by the probe for each sample was recorded. The data for each sample was saved and used to obtain the fractal Kol- mogorov dimension of the mechanical signature. The Kol- mogorov dimension is called the “box counting” dimension because a grid of squares is placed over the boundary or line

Food Engineering and Physical Properties profile, and the number of squares through which any part of the line passes is counted. This process is repeated with different grids having different size squares, and the number of squares that passed the profile plotted against the length of the side of the square on a log-log scale (Russ 1994).

Results and Discussion

Moisture Loss and Oil Absorption of Tortilla Chips Freeze-dried, steamed-baked, and control tortillas had a gelatinization percentage of 5%, 87%, and 45%, respectively. Freeze-drying caused no starch gelatination because no heat and water were available for gelatinization of the starch granules. Note that the 5% is due to the DMF that had some degree of starch gelatinized. On the other hand, cooking the product with steam and then baking it resulted in greatest degree of gelatinization before frying for the steamed-baked samples. For the control sample, the quick baking process caused only partial gelatinization of the starch granules in the chips. After frying, the gelatinization of the freeze-dried, steamed-baked, and control tortilla chips increased to 45%, 94%, and 93%, respectively. Note that even after frying, the freeze-dried sample still had ungelatinized starch granules.

Moisture Loss During Frying The effect of the degree of gelatinization (DG) on moisture loss during frying is shown in Fig. 1a. Initially, the 3 treatments of tortillas had about 42% (w.b.) moisture content (Table 1). All of them reached equilibrium moisture content of 2% to 3% in 60 s. The rate of moisture loss during frying was slower for the freeze-dried samples. Freeze drying is a slower process that results in a uniform drying. The frozen water during the process is not able to migrate and is evaporated (by sublimation) from its original site in all parts of the chip. The freeze-dried samples did not show any “pillowing” and very little puffiness (since there was no area of excess pressure buildup to cause puffing). This was the result of a Figure 1—Effect of starch gelatinization on (a) chips mois- uniform moisture loss during frying (Gamble and Rice 1987 ture content, (b) total oil content, (c) internal oil content that took place in all surface of the chip. during frying for 60 s in fresh soybean oil at 190 oC

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Total Oil Content During Frying causes the formation of a tight barrier on the outer surface The effect of the DG on total oil absorption can be seen of the chips due to the severe starch gelatinization during the in Fig. 1b. The total oil content was the highest for the process. After 60 s of frying, this outer layer formed a seal freeze-dried chips followed by the control and the that blocked the oil from flowing into the chips during cool- steamed-baked chips. After frying for 60 s, the freeze- ing resulting in low oil content and with most of the oil con- dried, control, and steamed-baked tortilla chips contained centrated at the surface as can be seen in Fig. 2. Note the 38.2%, 23.6%, and 14.7% (w.b.) total oil content, respec- bright area at the surface of the chips indicating oil content tively. Table 1 shows that the degree of starch gelatiniza- concentration. tion prior to frying significantly affects (p 0.05) the final oil content of tortilla chips. Fan and others (1997) showed that starch gelatinization and consequent swelling of the granules inhibited oil penetration (thus reducing oil content) in corn starch patties.

Internal Oil Content During Frying and Cooling The effect of prefrying treatment on the internal oil content of tortilla chips during frying and cooling is shown in Fig. 1c. The chips that were freeze-dried absorbed about 39% of the total oil content (38.2 0.3% w.b.) during frying (Table 1). About 76% of the total oil content was internal oil content after cooling (for 80 s) and 24% surface oil content. The steamed-baked tortilla chips absorbed about 11% of the total oil content (14.7 0.1% w.b.) during frying. After cooling, about 24% of the total oil content was internal oil content and 76% surface oil content. The internal oil content for the control chips was about 69% of the total oil content (23.6 0.1% w.b.) after cooling, and only 31% remained at the chip’s surface. The absorption rate of all samples was faster during cooling than during frying (Fig. 1c), with the freeze-dried samples showing the fastest rate followed by the control and the steamed-baked samples. Treating the chips by freeze-drying before frying resulted in no gelatinization of the starch, leaving the structure with open small pores that resulted in high final oil content. Most of the oil was located at the chip’s core. This result indicated that oil absorption is related to the pore size, that is, the smaller the pore size, the higher the final oil content of the

product (Moreira and Barrufet 1998). Gamble and Rice Food Engineering and Physical Properties (1987) demonstrated that a freeze-dried potato chip when fried had a uniform oil distribution around the entire chip’s surface. The oil was in very small deposits, with large amount of oils in the core of the chip. The insufficient moisture level impeded the starch to gelatinize during frying and increased the free volume in the chips, thus allowing more oil to enter the free space. On the other hand, treating the samples with steam before frying allowed the starch granules to swell, that is, gelatinize (due to the combination of water and heat), thus resulting in lower final oil content. The steaming-baking process

Figure 2—ESEM photomicrograph of the cross section of Figure 3—Effect of starch gelatinization on (a) the degree the steamed-baked tortilla chips (fried for 60 s in fresh of dia shrinkage, (b) the degree of puffiness, and (c) the soybean oil at 190 oC) porosity of tortilla chips during frying for 60 s in fresh soybean oil at 190 oC

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The control samples (93% gelatinization) had a more uni- The largest change was observed with the steamed-baked form oil distribution than the freeze-dried and steamed- chips, the lowest with the freeze-dried chips. Even though baked chips. The chips showed 17.6 % (w.b.) internal oil con- bulk density of the control and steamed-baked tortilla chips tent of a total of 23.6% (w.b.). was about the same after baking, the steamed-baked chips formed larger “puffy” areas during frying (Fig. 3c) that ac- Effect of the Degree of Starch Gelatinization on the counted for the increase in volume and therefore decrease PQA of Tortilla Chips in bulk density. The effect of starch gelatinization on the degree of dia Since solid density did not show a drastic effect, porosity shrinkage during frying is shown in Fig. 3a. The greatest de- played an important role in determining the bulk density. gree of shrinkage occurred during the 1st 5 s of frying. The Bulk density and porosity had an inverse relationship. There- steamed-baked chips shrunk the most (11%), followed by the fore, the steamed-baked chips had a higher porosity than the control (9.4%) and freeze-dried (7.3%) samples. It seems that freeze-dried. After frying, the freeze-dried, control, and the structure of the steamed-baked sample prior to frying steamed-baked chips had a porosity of 0.33, 0.55, and 0.70, was more deformable (thus softer) than the other samples, respectively. thus resulting in more shrinkage during the few s of frying. Figure 4 shows ESEM photomicrographs of freeze-dried, The effect of starch gelatinization on the degree of puffi- control, and steamed-baked tortillas. Freeze-dried tortillas ness of the tortilla chips is shown in Fig. 3b. The steamed- (Fig. 4a) did not show a significant amount of pores, and the baked chips showed the greatest puffiness (140.0 1.2%) and few that were found seemed small and apart from each oth- the freeze-dried chips the lowest (8.3 0.1%). Puffiness of the er. The steamed-baked tortillas (Fig. 4b) showed a greater steamed-baked samples caused by gelatinization was so large amount of small pores than the freeze-dried, but they were due to a strong barrier, that is, the crust that was formed dur- also isolated from each other. The control tortillas (Fig. 4c) ing steaming and baking that did not allow the water vapor to appeared to have a large amount of small pores and a small escape with ease. As the vapor tried to escape from the chip’s amount of large pores. The surface of the freeze-dried torti- interior, “puffs” or “pockets” were formed. The control chips llas seemed undamaged since the starch granules retained had a gradual increase in puffiness during frying and reached their original shape, and that of the steamed-baked tortillas Food Engineering and Physical Properties about 100.0 1.0% after 60 s of frying. The freeze-dried chips looked rough in comparison to the control (baked) tortillas. did not show any change during the 1st 30 s of frying, after The baking process created a smooth surface in the chips, as which puffiness increased to about 8.3 0.1% and remained can be seen in Fig. 4c. the same for the rest of frying time. So freeze-drying causes After frying, the freeze-dried chip (Fig. 4d) had a greater the formation of a structure that facilitates vapor to escape amount of small pores close to each other. The steamed- from the chips during frying. The values after 60 s of frying baked chip (Fig. 4e) had very few large pores. For the control were significantly different (p 0.05). chips, both the small and large pores became larger during Figure 3c shows the effect of starch gelatinization on the frying (Fig. 4f). Therefore, the different starch matrix forma- porosity of tortilla chips during frying for 60 s at 190 C. The tion and chips’ structure formed prior to frying affected the freeze-dried chips had a larger bulk density than the control oil absorption mechanism during frying and cooling. and steamed-baked chips. The bulk density for the freeze- Figure 5a shows that the freeze-dried tortilla had few pores dried, control, and steamed-baked chips was about 970, 880, with about 45% with a size of 40 m and about 35% with a size and 890 kg/m3 before frying, respectively. During frying, the of 55 m. The rest were not larger than 110 m. Figure 5b bulk density of the freeze-dried, control, and steamed-baked shows that the amount of pores found in the steamed-baked samples decreased to 830, 580, and 440 kg/m3, respectively. tortilla was about 2.5 times that found in the freeze-dried tortilla. It had about 60% of the pores with a dia size of 25 m and about 35% with a size of 40 m. The rest were not larger than 80 m. The control chips (Fig. 5c) had about 60% pores with 38 m in dia, about 22% had a dia of 63 m, and the rest were in the range of 88 and 138 m in dia. After frying, the freeze-dried samples (Fig. 5d) had a large amount of small pores with nearly 5.5 times the amount of pores than the steamed-baked chips had. About 95% of the total amount of pores were in the range of 25 to 55 m; the rest were larger pores. The steamed-baked chip (Fig. 5e) had a small amount of small and large pores. It had pores in the range of 55 to 300 m, of which 40% had a size of 70 m, and about 40% were in the range of 190 to 300 m. The control chips (Fig. 5f) showed a normal pore-size distribution with a large amount of pores around 88 and 113 m. In general, frying increased the amount of pores in the freeze-dried samples, but the pore size remained the same. Frying of the steamed-baked tortillas made the pores size larger, and it reduced the number of pores. The optimum texture and oil content is obtained when the pore size shows a normal distribution as found in the control tortilla chip. Figure 4—ESEM photomicrographs of freeze-dried (a), The effect of starch gelatinization on crunchiness of torti- steamed-baked (b), control (c) tortillas chips before frying lla chips is shown in Fig. 6. The steamed-baked chips were and freeze-dried (d), steamed-baked (e), control (f) torti- the least crunchy (9.6% less crunchy than the control), the llas chips after frying for 60 s at 190 oC freeze-dried were crunchier than the steamed-baked sam-

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ples by about 5%, and the control were the most crunchy. Crunchiness increased as frying time increased, and the final Kolmogorov dimensions for the steamed-baked, freeze- dried, and control was 1.13, 1.19, and 1.25, respectively. The steamed-baked chips reached a value of 1.13 after 30 s of frying and remained the same during frying. At this point, moisture loss had stabilized, and the pores were very large, which did not allow the chips to become crunchy. The freeze-dried chips were crunchier than the steamed-baked because moisture evaporated continuously, and there were small pores close to each other making the chips crunchy. The control chips were crunchier than the freeze-dried because the freeze-dried samples had more oil absorption making the latter less crunchy.

Conclusions HE DEGREE OF STARCH GELATINIZATION, AND THEREFORE THE Tstructure formed in the tortillas before frying, affects the final oil content of the chips and the oil distribution in the chips. In general, the steamed-baked chips (94% gelatinization) had a very low total oil content and internal oil absorption during frying and cooling. The freeze-dried chips (45% gelatinization), which did not undergo starch gelatinization during freeze-drying, had a large amount of total oil and a fast internal oil absorption. The control chips (93% gelatinization) had a more uniform oil distribution than the other 2 samples. Freeze-drying resulted in tortillas with a uniform structure and large amount of small pores that facilitated oil absorption during frying and cooling. Little dia shrinkage and no puffiness contributed to the chips higher oil content, which in turn resulted in low porosity (0.33). These chips were also crunchier than the steamed-baked tortillas. Steam baking, on the other hand, produced a structure with larger pores than those from freeze-drying and the control treatments. These chips shrunk and puffed the most, resulting in higher oil content at the surface and low at the core. Due to the larger degree of starch gelatiniza-

tion, the total chip oil content was lower than the freeze- Food Engineering and Physical Properties dried and control samples. The chips were also harder and thus less crunchy. These results provide valuable understanding on the mechanisms of oil absorption during frying of tortilla chips.

Figure 5—Effect of gelatinization on pore-size distribution of tortillas after baking for 60 s in a 3-tier convection oven at 343, 222, 220 oC [freeze dried (a), steamed-baked (b), Figure 6—Effect of gelatinization on the Kolmogorov di- control (c)] and on tortilla chips after frying for 60s at 190 mension of tortilla chips during frying (60 s in fresh soy- oC [freeze dried (d), steamed-baked (e), control (f)] bean oil at 190 oC) (The bars indicate standard error.)

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The implications are that structure formation prior to frying during deep-fat frying. J Food Sci 58(3):199-203. Moreira RG, Palau J, Sweat V, Sun X. 1995. Thermal and physical properties of have a great impact on how oil is absorbed and distributed in tortilla chips as a function of frying time. J Food Proc Pres 19:175-189. tortilla chips during cooling. Moreira RG, Sun X, Chen Y. 1997. Factors affecting oil uptake in tortilla chips in deep-fat frying. J Food Eng 31(4):485-498. Moreira RG, Barrufet MA. 1998. A new approach to describe oil absorption in References fried foods: a simulation study. J Food Eng 27(2):205-220. AACC. 1986. Approved methods of the American Association of Cereal Chem- Rock-Dudley P. 1993. The effect of processing parameters on oil content of corn ists. MN. tortilla chips [MS thesis]. College Station, Texas: Texas A&M University. Fan J, Paul Singh R, Pinthus EJ. 1997. Physicochemical changes in starch during Russ JC. 1994. Fractal surfaces. New York: Plenum Press. 309 p. deep-fat frying of a model corn starch patty. J Food Proc Pres 21:443-460. Snack Food Association. 1997. State of the snack food industry report. Alexan- Gamble MH, Rice P. 1987. Effect of pre-fry drying on oil uptake and distribution dria, Va.: Snack Food Association. in potato chip manufacture. Intl J Food Sci Technol 22:535-548. Sun X, Moreira RG. 1994. Oil distribution in tortilla chips during deep-fat frying. Gamble MH, Rice P, Selman JD. 1987. Relationship between oil uptake and mois- ASAE Meeting. St. Joseph, Mich. Paper #94-6506. ture loss during frying of potato slices from UK tubers. Intl J. Food Science Wang N, Brennan JG. 1995. Changes in structure, density and porosity of potato Technol 22:233-241. during dehydration. J Food Eng 24(4):61-76. Lee JK. 1991. Effect of processing conditions and maize varieties on physico- Ms. 20000236 chemical characteristics of tortilla chips [PhD dissertation]. College Station, Texas: Texas A&M University. Author Kawas is with Research and Development for Frito-Lay, Inc., Plano, Lozano JE, Rotstein E, Urbicain MJ. 1983. Shrinkage, porosity, and bulk density TX 75024. Author Moreira is with the Dept. of Agricultural Engineering, Texas of foodstuffs at changing moisture content. J Food Sci 48(5):1497-1502, 1553. A&M Univ., College Station TX 77843-2117. Direct correspondence to R.G. McDonough C, Gomez MH, Lee JK, Waniska RD, Rooney LW. 1993. Microstructure Moreira (E-mail: [email protected]). Food Engineering and Physical Properties

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Black