Investigation of kinetics of mass transfer parameters during deep fat frying of native gum coated potato chips

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1 Investigation of kinetics of mass transfer parameters during deep fat frying of native gum coated potato chips Zamani Ghaleshahi, Atefeh M.Sc. student, Department of Food Science and Technology, Ferdowsi University of Mashhad Mashhad, Iran Alavi rafiee, Somayeh Ph.D student, Department of Food Science and Technology, Ferdowsi University of Mashhad Mashhad, Iran Meshkani, Mahdi M.Sc. student, Department of Agronomy, Azad University of Sabzevar Sabzevar, Iran stract: The objective of this study was to evaluate the effect of two different coatings on mass transfer during deep-fat frying of potato strips. The effect of Basil seed gum (BSG) and methylcellulose (MC) (1%, w/w), frying temperature and time on mass transfer were determined. The least fat absorption was observed when samples were coated with BSG 1% fried at 190 C (0.14 d.b). The first order kinetics based on the Fick s law was used to describe the moisture transfer phenomenon. The effective moisture diffusivity ranged from to m 2 /s. The rate of fat transfer constants was between and s 1. Keywords: Coating; deep-fat frying; mass transfer; potato strips; oil uptake. Introduction Deep-fat frying is a widely used food process, which consists basically of immersion of food pieces in hot vegetable oil.the high temperature causes partial evaporation of the water, which moves away from the food and through the surrounding oil, and a certain amount of oil is absorbed by the food. Frying is often selected as a method for creating unique flavors and texture in processed foods that improve their overall palatability(1,2). Quick and easy preparation, good sensory properties such as color, texture, aroma and flavor of fried food can increase the utility of their palatability. However, these products may contain high amounts of oil. Other adverse effects that are as a result of this process, and is caused by high temperatures and the presence of oxygen, are degradation of nutrients and formation of compounds toxic molecules in oil or food (3,4). Interest in low fat product has recently increased as excess fat consumption is considered to heighten blood cholesterol, high blood pressure and coronary heart disease (5). Oil uptake is a function of temperature and time of frying, moisture content of the product, number and size of pores and pre-treatments before and after frying process. Suitable hydrocolloid coating is expected (mainly long chain 1

2 polysaccharides) will lead to lower oil uptake during deep-frying (6,7,8). Used hydrocolloids include proteins, cellulose derivatives, alginate, pectin, starch and other types of poly phospholipids. Garcia, et al. (2000) when using methyl cellulose and hydroxy propyl methyl cellulose in order to lowering oil uptake in potato chips reported that coating with methylcellulose was more effective in reducing oil absorption (9). Susanne and Gauri (2002) indicated that hydrocolloids like gelatin, Kappa- carrageenan, methyl cellulose, pectin and whey protein isolate can reduce oil uptake in fried products (10). Garmakhany, et al (2008) used hydrocolloids as edible coatings to produce low-fat crisps (11). Basil seed (Ocimum basilicum L.) is cultivated in large quantities in different regions of Iran. This seed has reasonable amounts of gum with good functional properties which is comparable with commercial food hydrocolloids. Literatures indicate lack of the scientific data on the use and effect of Iranian native gums in reducing potato oil uptake (12). Evaluation of reaction kinetics includes study of velocities and consequently the mechanisms in which the chemical species converts to other species. In order to obtain low-fat potato chips, it is useful to understand the mechanisms involved during the frying process,so that oil migration into the structure can be minimized. Numerous studies have shown that most of the oil is confined to the surface region of the fried potatoes(13). The main objective of this study was to comparing potato oil uptake treated with basil with traditional gums and investigation the effect of coating on kinetics of moisture loss and oil uptake during deep-frying process. Materials and methods Materials Potatoes and basil seeds were obtained from a local supermarket in Mashhad. Methyl cellulose was purchased from Sigma-Aldrich company. Oil extracted with hexane. Virgin olive oil and canola oil were obtained from local market. Basil seed preparation and analysis Basil seed wich obtained from Isfahan had the higher extraction efficiency (%15.42) (12). Therefore the basil seed used in this study were obtained from the city. The basil seeds were carefully cleaned removing dusts, stones and chaffs. The cleaned seeds were then packed in plastic bags, sealed and preserved in a dry and cool place until the gum extraction step. Optimum extraction conditions of Basil seeds consisted of temperature, 1 ± 67 C, ph 8 and ratio of water to grain (65:1). Concentration of 1% methylcellulose in deionized water was prepared. Such as methyl cellulose is soluble in cold water, to prepare its solution, water with a temperature of 25 C was used. The solution for 15 minutes until complete homogeneity was stirred at high speed mixer. Then, to complete hydration was kept overnight in the treatment room. Frying conditions and coating Potatoes after skinning were cuted into ± 0.2cm incisions. Slices blanched in hot water at 85 C for 3.5 min. Then the samples immediately washed in cold water and were immersed in gum solutions for two minutes. The slices were removed from water and were dried for 3 minutes at oven with 150 C to reduce the moisture level. Ten slices per sample time of each pre-treatment were deep fried in 8 l of hot oil contained in an electrical fryer (Moulinex,Toucan Automatic) at each of the three temperatures tested : 160, 180 and 190 C for 0,1,2,3,4,5 and 6 minutes. 2

3 Canola oil / Palm olein /Olive oil (ratio of 75:15:10, respectively) were used as the frying medium (14). After this time, samples were removed from oil, immediately. Then oil was separated from the surface with absorbent paper and for the following tests were cooled to room temperature. Oil was changed every 4 hours (15). Determination of physicochemical properties fried potato chips Replacing in Eq. (1), we have the model proposed in this work: Where K represents the specific rate of uptake of this model. For short times, this model has a linear behavior with time, while for long times becomes time independent. The second model is a first-order kinetics model (5) Moisture content Mean moisture content of potato chips was measured by drying the samples in a convection oven until constant mass at 105 C (16). The moisture content was calculated on a dry weight basis. Oil content Oil content of samples was measured by AOAC (2005)(17). A certain amount of sample (3 g) were weighed. Fat extraction using hexane solvent were performed for 4 hours. The oil content also was calculated on dry weight basis. Modeling of kinetics of mass transfer Two kinds of empirical models were used to describe oil uptake during frying. In first the one, for oil content during frying can be stated where O is the oil content at time t (dry basis, oil free); O eq is the oil content at equilibrium (or maximum content) (dry basis, oil free) at t= and O * is the oil content to be uptaken between t and t=. It is assumed that O * /O is inversely proportional to frying time Wher Oeq 1 is the equilibrium oil content and K 1 the specific rate for the first-order model. In both models at t=0, oil content is null, and for long times, oil content becomes the equilibrium value. The parameters of Eqs. (3) and (4) were obtained by nonlinear regressions by means of the soft ware Statgraphics Plus for Windows, version 4.0 (Manugistics Inc., Statistical Graphics Corporation, Rockville, USA), using as objective function the residual sum of squares (RSS). The relationship for the variation of equilibrium oil content with the frying temperature T is that due to Arrhenius, which has the form wher e E A is the activation energy, R is the gas constant an d A is the pre-ex ponential factor associated with the collision factor in terms of absolute reaction rates. Statistical analysis Investigation the effect of coating on oil uptake and quality parameters of fried chips was carried out 3

4 based on the factorial experimental in a completely randomized design (CRD) with three replications. All analysis were performed to the Minitab (15). Significant differences between means were determined by Duncans's multiple range tests. P values less than 0.05 were considered statistically significant. Results and discussion Moisture desorption Covered potato slices in comparison with control samples had a higher moisture content during frying (Figure 1). Samples coated with 1% basil seed had the the maximum moisture content at the end of frying process. This can be due to the high binding water capacity and film forming ability by this coating. With increasing frying time, the moisture content of the samples decreased. Due to the sample surface moisture removal, decreasing trend in the early minutes process was faster. Other researchers reported similar finding in their studies (18,19). Oil uptake As figure 2 shows, during frying time to reach equilibrium the amount of oil absorbed increased and then was constant. Sharp increase in the oil absorption at the beginning of the process of frying was due to the fast moisture desorption and increasing the porosity. At the end of process, due to the blockage of pores and film formation by oil saturation, porosity decreased and the oil uptake decreased (20). Similar increasing trend in the amount of oil absorbed by the potato slices treated with different gums during the process of frying temperatures was observed, but oil absorption between the samples were found to be significantly different. Samples coated with 1% Basil seed oil had the lowest oil content. This is probably due to the better thermal gel and less permeable film forming from gum basil oil. Kinetic of mass transfer during frying process kinetic parameters of potato slices treated with Basil seed and methyl cellulose gum are shown in table 1. K values shows moisture diffusion coefficient and D ef values are effective penetration coefficients. Temperature has a positive effect on the effective penetration coefficient. Moisture diffusion coefficients and effective penetration coefficient depends on the type of coatings (21,22). Effective penetration coefficient for potato slices coated with different gums has reported between m2/s. At 190 C, potato slices coated with basil seed gum had the lowest moisture diffusion and effective penetration coefficients. Due to the high capacity connection to the water and film forming ability, basil seed gum act as a barrier against moisture out. As data shows, basil seed gum has the similar moisture maintenance with methyl cellulose. Although the resuls show no significant differences between moisture content of potato slices coated with these gums, but the values for basil seed gum were higher. Investigation of kinetic parameters during oil measurements (table 2) shows that exception 160 C, there were significant differences between O eq values among samples coated with basil seed gum and control samples. It should be noted that however there was no differences between these values among basil seed and methyl cellulose gum, samples coated with basil seed gum had the lower O eq. It can be due to the lower moisture desorption. Conclusion 4

5 In this research, the effects of coating by Basil seed gum (BSG) (1%, w/w) compared to that by methylcellulose (MC) on the oil uptake, moisture removal, oil absorption and kinetic parameters in deep-fat fried potato strips were investigated. With regard to the controlling role of water in oil uptake, the oil content in all coated samples was less than that of the control (uncoated potato strips). The least fat absorption was observed when samples were coated with BSG 1% fried at 190 C (0.14 d.b). The potatoes treated with the gum experimented showed that the moisture content in all coated samples was higher than that of the control. Sample moisture loss during frying process increased with increasing time and temperature of frying. Basil seed gum had the lowest oil content and was more effective than methyl cellulose gum. REFERENCES 1. Pedreschi, F and Moyano, P.C Kinetics of oil uptake during frying of potato slices: Effect of pre-treatments. LWT - Food Science and Technology, 39: BeMiller, J. N., & W histler, R. L Carbohydrates. In O. W. Fennema (Ed.), Food chemistry, (3rd ed.). New York: Marcel Dekker, Inc. 3. Singthong, J. and Thongkaew, C Using hydrocolloids to decrease oil absorption in banana chips. LWT - Food Science and Technology, 42: Krokida, M.K., Orepoulou, V., Maroulis, Z.B., and Marinos-Kouris, D. 2001a. Colour changes during deep fat frying. Journal of Food Engineering, 48: Krokida, M. K., Oreopolou, V., Maroulis, Z. B., & M arinos-kouris, D Deep fat frying of potato strips quality issues-. Drying Technology, 19: Bouchon, P., Hollins, P., Pearson, M., Pyle, D. L., and Tobin, M. J Oil distribution in fried potatoes monitored by infrared microspectroscopy. Journal of Food Science, 66: Moreira, R.G., Sun, X., and Chen, Y Factors affecting oil uptake in tortilla chips in deep-fat frying. Journal of Food Engineering, 31: Saguy, I.S., and Pinthus, E.J Oil uptake during deep-fat frying: factors and mechanism. Food Technology, 41: Garcia, M. A., Ferrero, C., Bertola, N., Martino, M. and Zaritzky, N Methylcellulose coatings applied to reduce oil uptake in fried products. Food Science and Technology International, 10: Susanne, A. and Gauri, S.M Comparative evaluation of edible coatings to reduce fat uptake in a deep-fried cereal product. Journal of Food Research International, 35: Garmakhany, A. D., Mirzaei, H., Kashani Nejad, M., Maghsudlo, Y Study of oil uptake and some quality attributes of potato chips affected by hydrocolloids. Eur. Journal Lipid Science Technology, 110: Razavi, S.M.A., Mortazavi, S.A., Matia-Merino, L., Hosseini-Parvar, S.H., Motamedzadegan, A., & Khanipour, E Optimization study of gum extraction from Basil seeds (Ocimum basilicum L.), International Journal of Food Science & Technology, 44, Pedreschi, F., Aguilera, J. M., & Arbildua, J. J CLSM study of oil location in fried potato slices. Microscopy and Analysis, 37, Farhoosh, R., Esmaeilzadeh Kenari, R., Poorazrang, H Frying Stability of Canola Oil Blended with Palm Olein, Olive, and Corn Oils. Journal of the American Oil Chemists Society, 86: Blumenthal, M. M A new look at the chemistry and physics of deep fat frying. Food Technology, 45(2), AACC Moisture content. In approved methods of the American Association of Chemists. St Paul, MN: AACC. 17. AOAC Official Methods of Analysis. Association of Official Analytical Chemists. Washington. DC. 18. Adedeji, A.A., Ngadi, M.O. and Raghavan, G.S.V Kinetics of mass transfer in microwave precooked and deep fat fried chicken nuggets. Journal of Food Engineering, 91:

6 19. Ngadi, M., Li, Y. and Oluka, S Quality changes in chicken nuggets fried in oils with different degrees of hydrogenatation. LWT- Food Science and Technology, 40: Pedreschi, F., and Moyano, P Oil uptake and texture development in fried potato slices. Journal of Food Engineering, 70(4): Troncoso, E., and Pereschi, F Modeling water loss and oil uptake during vaccum frying of pre-treated potato slices. Lebensmmitte - Wissenschaft und-technologie, 42:

7 a ab 1.50 b moisture content (d.b.) Figure 1. Moisture content changes during the time Oil content (g/g db) a c b Figure 2. Oil content changes during the time 7

8 Table 1. Kinetic parameters in during moisture measurements Control BSG (%1) Mc (%1) 160 Ba 2.75±0.45P 2.56±0.46P 2.29±0.73P -3 K ( 10P P) 180 ABa 3.05±0.52P 2.34±0.36P 2.38±0.36P ±0.72P 2.88±0.70P 2.76±0.69P 160 Ba 10.21±1.64P 9.34±1.65P 8.38±2.67P -7 R( 10P DRef P) 180 ABa 11.16±1.90P 8.54±1.32P 8.68±1.31P ±2.66P 10.51±2.54P 10.05±2.49P Table 2. Kinetic parameters in during oil measurements Control BSG (%1) Mc (%1) 160 Ba ±0.007P ±0.000P ±0.000P Ba Bb -3 K ( 10P P) ±0.52P ±0.36P ±0.36P Bb ±0.005P ±0.002P ±0.001P Bb ±1.64P 0.18±1.65P 0.20±2.67P -7 R( 10P OReq P) ±0.001P 0.17±0.000P 0.18±0.005P ±0.003P 0.14±0.007P 0.18±0.001P 8