Characterization of Product Quality Attributes of Tortilla Chips During the Frying Process Marie Louise Kawas A, Rosana G
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Journal of Food Engineering 47 (2001) 97±107 www.elsevier.com/locate/jfoodeng Characterization of product quality attributes of tortilla chips during the frying process Marie Louise Kawas a, Rosana G. Moreira b,* a Research and Development, Frito-Lay, Inc., Plano, TX-75024, USA b Department of Agricultural Engineering, Texas A & M University, 310 Scoates Hall, College Station, TX 77843-2117, USA Received 3 March 2000; accepted 19 June 2000 Abstract Characterization of product quality attributes (PQA) of tortilla chips during frying will provide critical information that can be used to develop fundamental models to describe the structural changes of a fried product during frying. Tortilla chips were prepared from nixtamalized dry-masa ¯our and fried in fresh vegetable oil for 60 s. The results indicated that most diameter shrinkages of tortilla chips happened during the ®rst 5 s of frying. The chip's thickness increased as a result of crust formation and some bubbles developed at the surface due to gas expansion. The chips become more porous (pore size increased in number and size). The pore size distribution became more uniform (normal) as frying time increased. The chips became crunchier as moisture decreased during frying. The combination of all these quality attributes is responsible for producting the best ®nal product as oil content is greatly aected by the mechanism of structure formation thus resulting in the desired product texture. Fundamental properties such as isotherms and glass transition temperatures were also evaluated. The Crapiste and Rotstein model provided the best correlation at the entire range of moisture content and temperatures. The glass transition termperatures were ®tted 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. Ó 2000 Elsevier Science Ltd. All rights reserved. Keywords: Pores; Texture; Shrinkage; Expansion; Properties 1. Introduction the dough. Many manufacturers use dry-masa ¯our, as opposed to fresh masa, as it does not require much labor In the United States, the two most popular masa- and equipment. However, fresh masa is less expensive based snack products are tortilla chips and corn chips. and has a richer alkaline ¯avor (Serna-Saldivar, Gomez, Corn chips are fried directly from masa and contain & Rooney, 1990). more oil than tortilla chips. Tortilla chips are baked and Tortilla chips vary in oil content from 21% to 34% then fried, making them absorb less oil and have a (w.b.) depending on corn variety, cooking processes, ®rmer texture and a stronger alkaline ¯avor than corn grinding conditions, baking time, cooling time after chips. baking, and others (Lee, 1991). Nixtamalization is the process of cooking and steep- Moreira, Palau, and Sun (1995) observed that ing corn in alkaline solution, and then washing it to moisture loss and oil absorption rates were faster produce nixtamal. The nixtamal is stone-ground to form during the ®rst 15 s of frying, and became constant as a soft, moist dough called masa. Masa is then the raw frying continued; moisture loss rate increased as tem- material used to make tortilla chips. Dry-masa ¯our is a perature increased. The eect of temperature on oil product made by drying and grinding the fresh masa absorption was not signi®cant during the ®rst 15 s of into ¯our. Dry-masa ¯our has a longer shelf life (around frying, although, the ®nal oil content was higher for 1 yr) than fresh masa and requires only water to produce tortilla chips fried at 190C than at 150C for the some frying time. Moreira, Sun, and Chen (1997) measured the oil * Corresponding author. Tel.: +1-979-847-8794; fax: +1-979-845- 3932. content on the surface and at the core of tortilla chips to E-mail address: [email protected] (R.G. Moreira). determine the oil distribution during frying and cooling. 0260-8774/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 0 - 8 7 7 4 ( 0 0 ) 0 0 104-7 98 M.L. Kawas, R.G. Moreira / Journal of Food Engineering 47 (2001) 97±107 During frying, only 20% was absorbed by the chips, and 2.2.2. Oil content 80% remained on the chip's surface. During cooling, 2.2.2.1. Total oil content. The total oil content of tortilla about 64% of the total oil content was absorbed by the chips was determined by using the Soxtec System HT chips, and 36% remained on the chip's surface. (Pertorp, Silver Spring, Maryland) extraction with pe- Oil content in fried foods has been related to initial troleum ether (AACC, 1986). The test was performed in moisture content (Gamble, Rice, & Selman, 1987; triplicate. Moreira, Palau, Sweat, & Sun, 1995), pre-frying treat- ment (Gamble & Rice, 1987), structural changes during 2.2.2.2. Internal oil content. The oil content on the sur- backing (Lee, 1991; McDonough, Gomez, Lee, Wan- face and at the core of tortilla chips was measured using iska, & Rooney, 1993; Rock-Dubley, 1993), and cooling the approach described by Moreira et al. (1997). The test time (Sun & Moreira, 1994). was performed in triplicate. Understanding the oil distribution in tortilla chips is imperative before trying to access good quality control. 2.3. Degree of shrinkage/expansion and puness Changes in structure and texture of tortilla chips during frying can greatly aect the mechanism of oil absorption The diameter, thickness, and pu height were mea- during cooling (Moreira, Castell-Perez, & Barrufet, sured using a steel caliper (MG Tool Company, NY). 1999). Therefore, it is important to fully characterize About 20 readings were made for ®ve samples of each tortilla chips during frying so that an accurate mathe- treatment. matical model can be developed to predict quality The degree of diameter shrinkage Si was calculated changes. The objectives of this study were to: by · Characterize product quality attributes (PQA) such do d t as, shrinkage/expansion, puness, texture, pore size dis- Si 100 1 tribution, and porosity of tortilla chips during frying. do · Measure fundamental properties such as isotherms The degree of thickness expansion and puness Ei was and glass transition. calculated by · Develop a predictive model of pore size distribution d tdo during frying. Ei 100 2 do where do is the original dimension of baked sample (mm) and d t is the dimension of sample with frying time (mm). 2. Materials and methods 2.1. Sample preparation 2.4. Solid density Tortilla chips were prepared from nixtamalized dry To obtain the solid volume of tortilla chips, the pre- masa ¯our (NDMF) for tortilla chips (tortilla chip 1Y, weighed samples were ground using a coee grinder Valley Grain Products, Muleshoe, TX). The procedure (Braun, Model KSM2) and placed in a compressed he- is carefully detailed in Moreira et al. (1997). The tortillas lium gas multi-pycnometer (Quantachrome & Trade, 3 were fried in fresh vegetable oil for 60 s. Samples were NY). Solid density, qs kg=m , was determined by di- collected at 5, 10, 20, 30, 40, 50 and 60 s frying time viding the weight of the sample by its solid volume. The interval for testing. The dry-masa ¯our used to make test was performed in triplicate. tortilla chips had a combination of 69% coarse particles (amount of particles that did not pass a US #70 sieve), 2.5. Bulk density 21% intermediate (amount of particles that passed the US #70 but not the US #100), and 10% ®ne (amount of The bulk volume was measured using the liquid dis- particles that passed a US #100 sieve). placement technique with toluene (Wang & Brennan, 1995; Lozano, Rotstein, & Urbicain, 1983). Bulk den- sity, q kg=m3, was then determined by dividing the 2.2. Sample analysis b weight of the chip by its bulk volume. The test was performed in triplicate. 2.2.1. Moisture content Tortilla chip samples were ground in a coee grinder (Braun, Model KSM2) after frying. The moisture con- 2.6. Porosity tent of tortilla chips was determined by weight loss after drying 5 g samples in a forced air oven at 103±105C Porosity, /, was calculated as q (AACC, 1986) for 24 h. The test was performed in / 1 b 3 triplicate. qs M.L. Kawas, R.G. Moreira / Journal of Food Engineering 47 (2001) 97±107 99 2.7. Pore size distribution England) at an air¯ow rate of 1.2 m/s. The samples were dried at 10 min intervals up to 240 min when approxi- Three tortilla chip samples were analyzed for every mately 2% (w.b.) moisture content was reached. Water treament. Each tortilla chip sample was broken into nine activity was measured out using the Rotronic Hygro- pieces (10 mm L Â 7 mm W) for which three photomi- skop DT (Model DT-2, Rotronic Instrument , NY) crographs were taken in dierent regions to have a good coupled to a Rotronic Measurement Station (Model representation of the treatement. The small pieces were WA-40TH, Rotronic Instrument, NY) for the mea- mounted on aluminum stubs with conductive adhesive surement of equilibrium relative humidity following the and viewed with no further sample preparation in an method described in Crapiste and Rotstein (1982). Electroscan Model E-3 ESEM (Electroscan, Wilming- Moisture content was determined by the forced air oven ton, MA) with an accelerating voltage of 15 kV. The method (AACC, 1986) previously explained in Section area and perimeter of the pores were analyzed by an 2.2.1. Isotherms were obtained at 25C, 48.8C, and image analysis software called Scion Image (National 68.8C.