Grasas y Aceites Vol. 55. Fasc. 3 (2004), 259-263 259
Color changes and 5-hydroxymethyl furfural formation in zile pekmezi during storage
By Ilkay Tosun
Ondokuz Mayis University, Faculty of Engineering, Department of Food Engineering, Samsun, Turkey, E-mail: [email protected]
RESUMEN and subsurface properties of the object (Ahmed et al., 2002). Cambios del color y formación de 5-hidroximetilfurfu- For many products, browning is desirable. ral durante el almacenamiento de zile pekmezi. However, in other foods browning is undesirable. El Zile pekmezi (pekmez duro blanco) es un alimento turco Browning is the most common quality problem in tradicional que se produce a partir del zumo del uva. El color, el pekmez. Color, flavour and HMF contents are the sabor y el contenido en 5-hidroximetilfurfural (HMF) son los pará- most important quality parameters in Zile pekmezi. metros de calidad más importantes en el Zile pekmezi. El pardea- White hard pekmez (Zile pekmezi) is particularly minto es el problema más común que afecta a la calidad del pekmez. produced from grape juice. The acidity of grape juice En este estudio se evalúa la cinética de formación del HMF is decreased with the application of CaCO3- determinándose los ordenes de reacción, las constatntes de for- containing special white soil, or CaCO alone, and mación y la energía de activación así como las variaciones en las 3 diferencias de color (∆E) en Zile Pekmezi, almacenado a 55, 65 y the grape juice is left to sediment. Acid-decreased 75 oC durante 9 dias. and clarified grape juice is concentrated to the Los resultados indicaron que la formación de HMF y la varia- desired Brix degree under atmosferic pressure, or by ción del color durante el proceso termal del Zile pekmezi siguieron una cinética de orden cero. Las energìas de activación calculadas a vacuum method. After addition of the white of an para HMF y el ∆E fueron de 158.63 kJ mol-1 y 40.04 kJ mol-1, res- egg, soapwort extract, former pekmez, or powdered pectivamente. sugar as bleaching agents, and pectin as gelling agent, the concentrated grape juice is stirred and PALABRAS-CLAVE: Color - Hidroximetilfurfural - Pekmez - beaten (Tosun and Ustun, 2003). Zile Pekmezi. Nonenzymatic browning reactions of pekmez occur SUMMARY either by caramelization or Maillard reaction. Maillard reaction takes place between amino and carbonyl Color changes and 5-hydroxymethyl furfural formation compounds. It results in undesirable changes and is in zile pekmezi during storage. followed by the formation of intermediates such as Zile pekmezi (white hard pekmez) is a traditional Turkish food 5-hydroxymethyl furfural (HMF), and finally brown which is produced from grape juice. Color, flavour and pigment formation (Bozkurt et al., 1999). 5-hydroxymethyl furfural (HMF) contents are the most important The color measurement can be used in an quality parameters in Zile pekmezi. Browning is the most common quality problem in pekmez. indirect way to estimate colored compounds of In this study, reaction orders, rate constants and activation food, since it is simpler and faster than chemical energies were evaluated for HMF formation and color difference analysis. Tristimulus color measurements have been o (∆E) variation in Zile pekmezi stored at 55, 65 and 75 C along 9 succesfully employed to calculate the rate constants days. The results indicated that HMF formation and ∆E variation and activation energies for nonenzymatic color during thermal processing of Zile pekmezi followed zero order development (López et al., 1997; Bates et al., 1998; reaction kinetics at 55, 65 and 75°C. Calculated activation energy Bozkurt et al., 1999). for HMF and ∆Ewere 158.63 kJ mol-1 and 40.04 kJ mol-1, respectively. Many studies concerned with the kinetics of the Maillard reactions, pigment and color degradation KEY-WORDS: Color - Hydroxymethylfurfural - Pekmez - (Bates et al.,1998; Bell et al., 1998; Buglione and Zile Pekmezi. Lozano, 2002). These studies major finding is that Maillard reactions follow zero order reaction kinetics (Bates et al., 1998; Bozkurt et al., 1999). 1. INTRODUCTION The purpose of this work was to determine the Color plays an important role in appearance, HMF formation and changes in color parameters in processing, and acceptability of food materials. Color Zile pekmezi (white hard grape pekmez) during is perceived as part of the total appearance, which is storage and evaulate reaction orders and the rate the visual recognition and assessment of the surface constants for HMF formation and ∆E. 260 Grasas y Aceites
2. MATERIALS AND METHODS & & 2.1. Samples & Zile pekmezi samples produced by a commercial factory in Tokat, Zile, were used. Upon production,
the samples arriving to the laboratory were identified DYDOXH by several physical and chemical properties. Samples were placed into glass tubes in duplicate and closed tightly and held in temperature-controlled laboratory ovens at three different temperatures (55, 65 and 75 oC). Analyses were made in duplicate 7LPH GD\V and average values were used. Initially, Zile pekmezi had a pH 5.53, Brix 83.20o, total sugar 76.9%, invert sugar 68.4% and crude protein 2.41%. Figure 2 Change in Hunter a during storage at different temperatures 2.2. Apparatus ∆ ∆ ∆ HMF was determined with a JASCO UV-Visible where a = a-a0; b = b-b0 ; and L = L-L0. Subscript V-530 spectrophotometer. Color was evaluated by ‘0’ indicates initial color. means of a reflectance colorimeter (CR 300, Chromometer, Minolta, Japan). 2.3. Statistical analysis Regression analyses were performed to 2.3. Methods determine reaction order and rate constants for HMF and ∆E. Correlation analyses were performed to HMF was determined following the procedure determine the relationship between color parameters described by the IFFJP (1964), based on the and HMF during storage at different temperatures. colorimetric reaction between barbituric acid, Both regression and correlation analyses were p-toluidine and HMF, forming a red colored complex. carried out with SPSS 11.0 statistical package The intensity of the red colour was measured at 550 programme. nm with the spectrophotometer. Color was evaluated by measuring Hunter L 3. RESULTS AND DISCUSSION (lightness, 100:White, 0: Black), a (+, red; -, green), b This study was carried out along 9 days at three (+, yellow; -, blue) parameters by means of the o different temperatures (55, 65 and 75 C). Changes colorimeter. A white tile (No: 21733001) was used to in color of samples during storage are shown in standardize the instrument. Hue angle (H) and color Figures 1-5. As can be seen, lightness L and hue difference (∆E) were calculated according to the angle decreased during storage. As storage following equations: temperature is increased, L value and hue angle
-1 decreased. These results revealed that the rate of H = tan (b/a) (1) the browning reaction increased with increasing ∆ ∆ 2 ∆ 2 ∆ 2 1/2 temperature. Decreased lightness indicated E = ( L + a + b ) (2) browning reaction. & & & & & &
/ YDOXH
EYDOXH
7LPH GD\V 7LPH GD\V
Figure 1 Figure 3 Change in Hunter L during storage at different temperatures. Change in Hunter b during storage at different temperatures Vol. 55. Fasc. 3 (2004) 261
& & & & & & +XH DQJOH
+0) SSP 7LPH GD\V 7LPH GD\V
Figure 4 Figure 6 Change in Hue angle during storage at different temperatures Change in HMF content during storage at different temperatures
Redness (+a) showed different behaviour at The Arrhenius relationship was applied to estimate activation energies. The Arrhenius equation different temperatures. While yellowness (+b) tends to stabilize from the third day at 55 oC, it decreased at relating rate constant with temperature is 65 and 75 oC during storage (Figure 3). represented by: The HMF content increased with temperature and (-Ea/RT) heating time (Figure 6). The following equation was k = ko e (4) used to fit both HMF formation and ∆E data by using where k is the rate constant, ko is the constant inde- linear regression analysis: pendent of temperature (frequency factor), Ea is the C - C = k t (3) activation energy, R is the universal gas constant, 0 and T is the absolute temperature. where C is the concentration at a given time, C is the Calculated activation energy for HMF formation 0 ∆ concentration at time zero, k is the rate constant and and E variation are given in Table I. As shown in the Table, the activation energy for HMF formation in Zile t is the time. -1 Calculated rate constants for HMF formation are pekmezi was 158.63 kJ mol . Activation energies given in Table I. HMF formation during thermal reported for color development due to Maillard reactions are generally in the range 65 to 170 kJ processing of Zile pekmezi followed zero order -1 reaction kinetics at 55, 65 and 75oC. The kinetic rate mol (Lee et al., 1984; Baisier and Labuza, 1992; constant values increased when increasing heat Bates et al., 1998; Bozkurt et al., 1999). Bozkurt et al. (1999) calculated the activation treatment temperatures. The reaction order for HMF -1 accumulation of boiled grape juice (pekmez) was energy of HMF in pekmez as 103 kJ mol . As seen, found to be zero (Bozkurt et al., 1999) and 0.3 the calculated activation energy in Zile Pekmezi was (Gögüs et al., 1998). higher than that reported by Bozkurt et al. (1999), but it was similar to other researchers’ reports. This difference may be due to the composition and & structure of food systems. Zile pekmezi is rich in & sugar and protein. Bates et al. (1998) reported that & as the water content of food is decreased, the activation energy increases. Color differences (∆E) increased linearly with "( treatment time at 55 and 65oC and followed during storage zero order equation (Eq.3), but didn’t follow at 75oC. It can be observed that the fittings are not very well correlated, but at an acceptable level is obtained. Similar results were reported for brown pigment formation by Carabasa-Giribet and 7LPH GD\V Ibarz-Ribas (2000) who studied it for aqueous glucose systems. Calculated activation energy of ∆E in Zile Figure 5 Pekmezi was 40.04 kJ mol-1. López et al. (1997) who Change in color difference during storage at different temperatures studied it on hazelnut obtained that the activation 262 Grasas y Aceites
Ta bl e I Rate constant and activation energy values (mean ± SD) for HMF and ∆E at different temperatures
Parameters Temperature (0C) k (concentration day-1)R2 Ea (kJ mol-1)
HMF 55 9.07 ± 0.67 0.996 158.63 ± 3.73
65 59.49 ± 0.41 0.989 R2=0.997
75 255.64 ± 0.93 0.993
'E 55 1.94 ± 0.14 0.964 40.12 ± 5.24
65 4.15 ± 0.21 0.987 R2=0.830
75 4.49 ± 0.17 0.910
Ta bl e I I Correlation matrix of color parameters and HMF value
LabHue'E
L1.00
a-0.802**
b0.809** -0.367
Hue 0.995** -0.781** 0.850**
'E -1.000** 0.805** -0.803** -0.994**
HMF -0.859** 0.409 -0.940** -0.879** 0.856**
** Correlation is significant at the 0.01 level.
energy of ∆E in hazelnut was between 28 and 39 kJ show in Table II, ∆E had a highly negative correlation mol-1. On the other hand, Bates et al. (1998) working with lightness. with a Starch-Glucose-Lysine system reported an activation energy of ∆E of 66.5 kJ mol-1. As a result, 4. CONCLUSSION calculated activation energy of ∆E in Zile Pekmez Results indicated that temperature is an was below Bates et al. (1998), and similar to that important parameter affecting the quality of Zile obtained by López et al. (1997). pekmezi which should have a maximum HMF In order to assess relationships between various content of 25 ppm. L value and hue angle decreased color parameters and HMF, Pearson correlation while ∆E and HMF values increased during storage. coefficients were calculated. It can be found that HMF formation during thermal processing of Zile there were negative correlations between hue angle pekmezi followed zero order reaction kinetics at 55, (r = -0. 879**), L (r = -0.859**) and b (r=-0.940**) o 65 and 75 C. Calculated activation energy for HMF values with HMF values (p<0.01), and were positive was 158.63 kJ mol-1. between ∆E (r = 0.856**) and a (r=0.409) values with Negative correlations were found between hue HMF values (p<0.01) during storage (Table II). As angle, L and b values with HMF (p<0.01), and Vol. 55. Fasc. 3 (2004) 263
positive correlation between ∆E and HMF values Carabasa-Giribet, M. and Ibarz-Ribas, A. (2000). Kinetics (p<0.01) were obtained during storage. of colour development in aqeous glucose systems at high temperatures. J. Food Engineering, 44, 181-189. Gögüs, F., Bozkurt, H. and Eren, S. (1998). Kinetics of REFERENCES Maillard reactions between the major sugars and Ahmed, J., Kaur, A. and Shivhare, U. (2002). Color amino acids of boiled grape juice. degradation kinetics of spinach, mustard leaves, and Lebensm.-Wiss.u.-Technol., 31, 196-200. mixed puree. J. Food Sci., 67, 1088-1091. IFFJP (International Federation of Fruit Juice Producers Baisier, W.M. and Labuza, T.P. (1992). Maillard browning Methods) (1964). Analsen-analyses; Fruit-Union kinetics in a liquid model system. J. Agric. Food Chem., Suisse Assoc. Svizzera Frutta Zug Switzerland, 12, 40, 707-713. 1-4. Bates, L., Ames, J.M., MacDougall, D.B. and Taylor, P.C. Lee, C.M., Sherr, B. and Koh, Y-N. (1984). Evaluation of (1998). Laboratory reaction cell to model Maillard color kinetic parameters for a glucose-lysine Maillard development in a starch-glucose-lysine system. J. reaction. J. Agric. Food Chem., 32, 379-382. Food Sci., 63, 991-996. López, A., Pique, M.T., Boatella., J., Romero, A., Ferrán, A. Bell, L.N., White, K.L. and Chen, Y.H. (1998). Maillard and García, J. (1997). Influence of drying conditions on reaction in glassy low-moisture solids as affected by the hazelnut quality: III. Browning. Drying Technology, buffer type and concentration. J. Food Sci., 63, 15, 989-1002. 785-788. Tosun, I. and Ustun, N.S. (2003). Nonenzymic browning Bozkurt, H., Gögüs, F. and Eren, S. (1999). Nonenzymic during storage of white hard grape pekmez (Zile browning reactions in boiled grape juice and its models pekmezi). Food Chem., 80, 441-443. during storage. Food Chem., 64 , 89-93. Buglione, M. and Lozano, J. (2002). Nonenzymatic browning and chemical changes during grape juice Recibido: Abril 2003 storage. J.Food Sci., 67, 1538-1543. Aceptado: Enero 2004