The effect of butter oil and whey proteins addition on viscoelastic properties of confectionary Dulce de Leche was evaluated. A two factors experimental design (0-8 % p/v of butter oil and 0-1 % p/v of whey proteins) was analysed. Frequency sweep tests were carried out and for all formulations studied a weak gel like behavior was observed. Therefore, results were interpreted using a weak gel model for foods. It was observed that the rheological behavior of the sample with addition of whey proteins and butter oil is significantly different than the others because rheological units interact with greater strength. Even more, the sample without butter oil and with whey proteins addition is composed by less rheological units than the others. It is concluded that the whole addition of butter oil and whey proteins generates a stronger gel matrix, more appropriate for use in confectionary.Fil: Olivares, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Pauletti, Miguel Sebastian. Universidad Nacional del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Costa, Silvia Claudia. Universidad Nacional del Litoral; ArgentinaFil: de Piante Vicin, Daniel Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Rubiolo, Amelia Catalina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Costa, Silvia Claudia

de Piante Vicin, Daniel Alberto

Olivares, María Laura

Pauletti, Miguel Sebastian

Rubiolo, Amelia Catalina

CONICET Digital

Latin American Applied Research  44:185-188 (2014) 185 EFFECTS OF BUTTER OIL AND WHEY PROTEINS ADDITION ON VISCOELASTIC PROPERTIES OF CONFECTIONARY DULCE DE LECHE   M.L. OLIVARES, M.S. PAULETTI Á, S.C. COSTAÁ,  D. DE PIANTE VICÍN   and   A.C. RUBIOLO  Instituto de Desarrollo Tecnológico para la Industria Química (UNL-CONICET)-Santa Fe- Argentina olivares@santafe-conicet.gov.ar ÁInstituto de Tecnología de Alimentos (UNL)- Santa Fe-Argentina  Abstract The effect of butter oil and whey pro-teins addition on viscoelastic properties of confec-tionary Dulce de Leche was evaluated. A two factors experimental design (0-8 % p/v of butter oil and 0-1 % p/v of whey proteins) was analysed. Frequency sweep tests were carried out and for all formulations studied a weak gel like behavior was observed. Therefore, results were interpreted using a weak gel model for foods. It was observed that the rheological behavior of the sample with addition of whey pro-teins and butter oil is significantly different than the others because rheological units interact with greater strength. Even more, the sample without butter oil and with whey proteins addition is composed by less rheological units than the others. It is concluded that the whole addition of butter oil and whey proteins generates a stronger gel matrix, more appropriate for use in confectionary. Keywords dulce de leche, rheology, whey pro-teins  I. INTRODUCTION Dulce de Leche (DL) is a sweet spread widely con-sumed as jam and as dessert. Also, is widely used in bakery and confectionery in the preparation of desserts and cakes as a cram. Argentina produces about 140,000 tons per year and 5.5 % of this production is exported to several countries (Ministerio de Ganadería, Agricultura, Pesca y Alimentos de la República Argentina, 2012). Argentinean food legislation (Código Alimentario Argentino, 2013 GHILQHV'/ DV ³WKH SURGXFW REWDLQHGby heat concentration, at normal or reduced pressure, of milk or reconstituted milk apt for human consumption, ZLWKWKHDGGLWLRQRIZKLWHVXJDU´6PDOODPRXQWVRIVo-dium bicarbonate is also added which increases the pH of the final product and avoids protein coagulation. Va-nillin is added as flavouring agent (Rovedo et al., 1991; Navarro et al., 1999). Maillard browning reactions oc-curs during this process; therefore the product has a dis-tinctive brown colour (Navarro et al., 1999). The heat treatment applied during DL manufacture generates chemical modifications leading to irreversible aggregation with formation of a gel with particular characteristics (Pauletti et al., 1996). The resulting mix-ture of carbohydrates, proteins and fats determines its structural properties, affecting its functional characteris-tics (Ranalli et al., 2012). For confectionery uses a firm texture is needed and for these purposes different hy-drocolloids are used. Therefore, rheological characteri-zation can be used as a quality control tool because the rheological parameters may be related to the desirable texture of confectionary DL.  The earliest studies related to DL texture were car-ried out using shear viscometry (Moro and Hough, 1985; Hough and Moro 1988; Rovedo et al. 1991; Heimlich et al. 1994). These authors reported that DL presents a pseudoplastic behavior and it can be de-VFULEHG E\ &DVVRQ¶V DQG +HUVFKHO-Bulkley models. In addition, Pauletti et al. (1990) and Navarro et al. (1999) studied different types of DL by oscillatory rheometry and observed that its rheological behavior is intermedi-ate between a concentrated solution and a gel, depend-ing on the type of DL and the solid content. Recently, Ranalli et al. (2012) analyzed the physicochemical properties of four types of commercial DL (traditional, reduced calories, reduced fat and confectionary) and de-veloped a comprehensive study on the viscoelastic be-havior of these products. This behavior was modeled us-ing the Baumgartel-Scahusberger-Winter (BSW) and the mechanical relaxation spectrum in the linear viscoe-lastic range was predicted. The parameters of the BSW model were used to explain structural characteristics of the systems and, the dynamic data measured was also successfully converted into time and was validated us-ing creep and flow experiments.   Whey proteins, a byproduct from cheese and casein manufacture, are frequently used as functional ingredi-ents in many foods. They are now widely used as gel-ling agents, emulsifiers, texture modifiers, thickening agents and foaming agents. In addition, they have high nutritive value and are generally recognized as safe (Bryant and Mc Clements, 1998; Meza et al., 2010). Whey proteins ingredients may be purchased in several different forms. Whey proteins concentrates (WPC) contain between 20% and 89% of protein, being WPC with 35% of protein content the most common product (Tunick, 2008; Meza et al., 2010). In this sense, results of technological interest to explore the potential use of WPC as texture modifier in DL formulation and as fat replacer. Therefore, the objective of this work was to study the effect of whey proteins concentrate (WPC) and butter oil addition on viscoelastic properties of con-fectionary DL. Latin American Applied Research  44:185-188 (2014) 186 II. METHODS A. Dulce de Leche samples preparation Skim milk powder (Milkaut, Frank, Argentina), sucrose (Ledesma, Jujuy, Argentina), butter oil (Corlasa, Esperanza, Argentina) and a 35 % w/w whey protein concentrate (Milkaut, Frank, Argentina) were used as ingredients for DL manufacture. In addition, carragee-nan (Carragel, Gaiman, Argentina) and agar-agar (Chu-butagar, Gaiman, Argentina) were used as thickening agents.  Different DL samples were prepared, as listed in Table 1. Partial hydrolysis of lactose was carried out in order to avoid lactose crystallization by the addition of 0.015 kg of a commercial E-galactosidase enzyme extract (Maxilact, Delft, Holland) to the reconstituted milk at 37°C, one hour before manufacture. The manufacture of each sample was carried out in an open kettle commonly used by the industry. The in-gredients were mixed; the pH was fixed at 6.9 by addi-tion of Ca(OH)2 p.a. and then, the mixture was concen-trated at atmospheric pressure up to 70°Brix.  A refrac-tometer (ATAGO Master H80, Tokyo, Japan) was used for the measurement of °Brix during the concentration process. The obtained product was cooled at 70°C, packaged in containers of 250 g and storage for a week at room temperature prior analysis. As minimal variability between batches was ob-served previously (Pauletti et al., 1990, 1995), this study was carried out considering one batch of Dulce de Leche for each sample in order to significantly reduce the number of assays. B. Rheometrical measurements  A rheometer Haake RheoStress RS80 (Haake Instru-ment Inc., Paramus, NJ, USA) with parallel plates (35 mm diameter, 1 mm gap) was used for rheometrical measurements. The temperature of the lower plate was maintained at 25°C by circulating water from water bath. The DL sample was placed on the lower plate and then the upper plate was brought in contact with the sample to attain temperature equilibrium. The dynamic rheological data obtained included the 2 components of complex shear modulus (G*): the stor-age modulus (*¶), which is a measure of the energy stored and recovered per cycle of deformation (elastic component), and the loss modulus (*¶¶), which is a measure of the energy dissipated or lost as heat per cy-cle of deformation (viscous component) (Gunasekan and Ak, 2003). These parameters are related as follows: Table 1. Dulce de Leche samples studied. Ingredient Samples  S1 S2 S3 S4 Tap water (kg) 27 27 27 27 Skimmed milk powder (kg) 2.74 2.74 2.74 2.74 Sucrose (kg) 7.2 7.2 7.2 7.2 Whey Proteins  (% w/w) 0 1 1 0 Butter oil (% w/w) 0 0 8 8 Carrageenan (kg) 0.015 0.015 0.015 0.015 Agar-agar (kg) 0.01 0.01 0.01 0.01     2 2 2* ' ''G G G      (1) Frequency sweep tests were carried out from 0.01 to 1 Hz at strain amplitude of 0.01 r  5 x 10-4. The linear viscoelastic region was determined by performing strain sweep tests from 0.001 to 0.1 at 25°C for all samples studied. Moreover, the effect frequency on complex vis-cosity (|K*|=|G*|/Z, Z: frequency of oscillation) was analysed.  Each sample was analysed in triplicate. C. Data modelling Frequency dependency of |G*| for the DL samples was fitted by the weak gel model for foods (Gabriele et al., 2001), in which the structure of the material is modelled as a cooperative arrangement of flow units, to form a strand. According to this model, the complex modulus can be expressed by:    2 2 1* ' '' zFG G G A Z      (2) Where z is the interaction factor and AF is the gel strength. Values of z can be interpreted as the number of flow units interacting with one another in a three-dimensional structure to give the observed flow re-sponse of the material; AF can be interpreted as the strength of the interaction between flow units. D. Statistical analysis Data were analysed by ANOVA using Statgraphics (Statgraphics Inc., Rockville, MD, USA). When differ-ences between treatment effects were significant (P<0.05), a multiple comparison of means was per-formed. III. RESULTS AND DISCUSSION Figure 1 VKRZV FKDQJHV LQ *¶*¶¶ DV IXQFWLRQ RI IUe-quency of DL samples.  In samples S1, S3 and S4 the magnitudeVRI*¶ZHUHKLJKHUWKDQ*¶¶ZLWKRXWH[KLELt-ing no crossing point and both increased with increased in frequency, indicating dominant elastic properties. In sample S2 *¶DQG*¶¶DOVR LQFUHDVHGZLWK LQFUHDVHG LQfrequency but their values were similar in the whole frequency range evaluated, indicating similar elastic and YLVFRXV FKDUDFWHU *¶ a *¶¶ ,Q DGGLWLRQ *¶ DQG *¶¶values of the sample S2 were lower than those obtained from the other samples analysed. From a structure point of view, for true gels ln *¶*¶¶YHUVXVOQZ plots have zero slope because the molecular rearrangements within the network are very reduced over the time scales ana-O\VHGZKLOH WKHUHDUHSRVLWLYH VORSHVDQG*¶ LV JUHDWHUWKDQ*¶¶RYHUDZKROHIUHTXHQF\UDQJHVRIZ studied for weak gels and highly concentrated dispersions (Rao, 1999).  In weak gels there is a higher dependence on fre-quency for the dynamic moduli, suggesting the exis-tence of relaxation processes occurring even at short time scales, and lower difference between moduli val-ues, indicating that a lower percentage of the stored en-ergy is recovered (Rao, 1999). Therefore, mechanical spectra of all DL samples denote a weak gel structure.  These findings are in agreement with those reported by Navarro et al. (1999) and Ranalli et al. (2012).  M. L. OLIVARES, M. S. PAULETTI, S. C. COSTA, D. DE PIANTE VICÍN, A. C. RUBIOLO 187   Figure 1. Characteristics frequency sweeps of DL samples studied.  Figure 2. Characteristic loss tangent (tan G) as function of fre-quency corresponding to DL samples studied. The total resistance to flow of a material considered to be a viscous liquid refers to complex viscosity (|K*|) (Dimitreli and Thomareis, 2008). Fig. 1 also shows that |K*| of samples S1, S3 and S4 decreases across the fre-quency range which indicates shear-thinning behaviour. However, |K*| values of sample S2 were lower and less shear-thinning behaviour was observed.   Another useful rheometrical function in describing viscoelastic behaviour is the loss tangent (tan G=G´´/G´). It is dimensionless and gives a clear indica-tion of whether the material behaves as solid-like or liq-uid-like. The larger the tan G value, the more easily the DL flows. These results are presented in Fig. 2. The loss tangent values showed a predominantly elastic behav-iour (tan G < 1) in samples S1, S3, S4 over the whole range of frequency tested while a slightly viscous be-haviour was observed in sample S2 (tan G > 1). As it can be seen, the loss tangent clearly differentiated the vis-coelastic behaviour in two groups of samples. For sam-ples S1, S3 y S4 tan G presented values between 0.2 and 0.3 that correspond to amorphous polymers (Steffe, 1996). These values were also reported by Ranalli et al. (2012) for commercial DL. For sample S2 tan G pre-sented values between 0.9 and 1.4 that may correspond to a concentrated solutions or weak gels.  Therefore, in order to analyse the overall rheological behaviour, the response of complex modulus (|G*|) of DL samples was compared with the weak gel model for foods (Gabriele et al., 2001). Figure 3 shows character-istics experimental data and the fitted values obtained with Eq. (2), giving for all frequency sweeps analysed a fitting error  less than 5%. The obtained rheological pa-rameters are listed in Table 2. ANOVA indicated that the sample with whey pro-teins addition and without butter oil (S2) presented less number of rheological units than the others (z). This suggests that the structure of sample S2 is composed by OHVVQXPEHURIMXQFWLRQ¶V]RQHVLQWKHQHWZRUNJHQHUDt-ing a weaker matrix. The sample with addition of whey proteins and butter oil (S3) had a rheological behaviour significantly different than the others because presented higher gel strength between rheological units quantified by the parameter AF. Therefore, the whole addition of butter oil and whey proteins in sample S3 generates a stronger gel matrix.  Latin American Applied Research  44:185-188 (2014) 188  Figure 3.  Complex modulus (|G*|) as function of frequency of DL samples. Symbols are experimental values and lines correspond to predictions carried out with the weak gel model for foods. Table 2. Mean values of weak gel model parameters of DL samples* Sample Af.[Pa sz]  z[-]  S1 336.7a 6.6b,c S2 309.1a 1.7a S3 695.7b 6.1b S4 344.8a 6.8c * Mean values with different letters in a column indicate sig-nificant differences (P < 0.05). IV. CONCLUSION It is concluded that mechanical spectra of all DL sam-ples studied denote a weak gel structure. The DL micro-structure significantly changes with whey proteins and butter oil addition. When whey proteins are presents in absent of butter oil, the dynamic moduli of DL pre-sented higher dependency of frequency, suggesting a weaker matrix. This phenomenon was also observed when complex modulus of DL samples was compared with the weak gel model for foods. This model indicated that the structure of sample S2 is composed by less QXPEHURI MXQFWLRQ¶V zones in the network. The whole addition of butter oil and whey proteins in S3 generates a stronger gel matrix, more appropriate for use in con-fectionary. REFERENCES Bryant, C.M. and D.J. McClements, ³Molecular basis of protein functionality with special consideration of cold-set gels derived from heat-denatured whey´Trends Food Sci Tech, 9, 143-151 (1998). Código Alimentario Argentino, Available from: www. anmat.gov.ar/alimentos/codigoa/CAPITULO_VIII. pdf. Accessed january 2 (2013). Dimitreli, G. and A.S. Thomareis ³Effect of chemical composition on the linear viscoelastic properties of spreadable-type processed cheese´ Journal of Food Eng, 84, 368-374 (2008). *DEULHOH'%'H&LQGLRDQG3'¶$QWRQD³$ZHDNJHO PRGHO IRU IRRGV´ Rheol Acta, 40, 120-127 (2001). Gunasekaran, S. and M.M. Ak, Cheese Rheology and Texture, CRC Press, Boca Raton (2003). Heimlich, W., R. Bórquez and I. Céspedes ³Effect of milk replacement by whey protein concentrates on the rheological properties of dulce de leche´ Food Sci Technol-LEB, 27, 289-29 (1994). Hough G. and O. Moro, ³Flow properties of dulce de leche, a typical Argentine dairy product´ J. Dairy Sci, 71, 1783-1788 (1988). Meza, B.E., R.A. Verdini and A.C. Rubiolo, ³Effect of freezing on the viscoelastic behaviour of whey protein concentrate suspensions´ Food Hydrocol-loids, 24, 414-423 (2010). Ministerio de Ganadería, Agricultura, Pesca y Alimentos de la República Argentina, Available from: http://www.minagri.gob.ar. Accessed: au-gust 27 (2012). Moro, O. and G. Hough, ³Total solids and density measurements of dulce de leche, a typical Argen-WLQH 'DLU\ SURGXFW´ J. Dairy Sci, 68, 521-525 (1985). Navarro, A.S., C. Ferrero and N.E. Zaritzky, ³Rheologi-FDO FKDUDFWHUL]DWLRQ RI ³'XOFH GH /HFKH´ E\ Gy-namic and steady shear measurements´ J. Texture Stud., 30, 43-58 (1999). Pauletti M.S., A. Venier, N. Sabbag and D. Stecchina ³5KHRORJLFDO&KDUDFWHUL]DWLRQRIGXOFHGHOHFKHDconfectionery dairy product,´J. of Dairy Sci., 73, 601-603 (1990). Pauletti M.S., E.L. Castelao, N. Sabbag and S. Costa. ³Color development rate in dulce de leche,´Food Sci Technol Int., 1, 137-140 (1995). Pauletti, M.S., E.L. Castelao and E. Seguro, ³Kinetics of heat coagulation of concentrated milk proteins at high sucrose contents´ J. Food Sci, 61, 1207-1210 (1996). Ranalli, N., S.C. Andrés and A.N. Califano, ³Physico-chemical and rheological characterization of dulce GHOHFKH´, J.Texture Stud., 43, 115-123 (2012). Rao, M.A., Rheology of fluids and semisolid foods. Principles and applications, Gaithersburg, Aspen (1999).  Rovedo, C.O., P.E. Viollaz and C. Suarez, ³The effect of pH and temperature on the rheological behavior of dulce de leche, a typical dairy argentine prod-uct´ J. Dairy Sci, 74, 1497-1502 (1991). Steeffe, J.F., RheologicalMethods in Food Processing Engineering, 2nd Ed. Freeman Press, East Lansing (1996). Tunick, M.H. Whey protein production and utilization: a brief history. In C. I. Onwulata and P. J. Huth (Eds.), Whey processing, functionality and health benefit, John Wiley & Sons, Iowa (2008).  Received: March 27, 2013 Accepted: November 6, 2013  Recommended by Subject Editor: María Luján Ferreira 

Effects of butter oil and whey proteins addition on viscoelastic properties of confectionary Dulce de leche

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

Latin American Applied Research  44:185-188 (2014) 185 EFFECTS OF BUTTER OIL AND WHEY PROTEINS ADDITION ON VISCOELASTIC PROPERTIES OF CONFECTIONARY DULCE DE LECHE   M.L. OLIVARES , M.S. PAULETTI , S.C. COSTA ,  D. DE PIANTE VICÍN    and   A.C. RUBIOLO   Instituto de Desarrollo Tecnológico para la Industria Química (UNL-CONICET)-Santa Fe- Argentina olivares@santafe-conicet.gov.ar Instituto de Tecnología de Alimentos (UNL)- Santa Fe-Argentina  Abstract  The effect of butter oil and whey pro-teins addition on viscoelastic properties of confec-tionary Dulce de Leche was evaluated. A two factors experimental design (0-8 % p/v of butter oil and 0-1 % p/v of whey proteins) was analysed. Frequency sweep tests were carried out and for all formulations studied a weak gel like behavior was observed. Therefore, results were interpreted using a weak gel model for foods. It was observed that the rheological behavior of the sample with addition of whey pro-teins and butter oil is significantly different than the others because rheological units interact with greater strength. Even more, the sample without butter oil and with whey proteins addition is composed by less rheological units than the others. It is concluded that the whole addition of butter oil and whey proteins generates a stronger gel matrix, more appropriate for use in confectionary. Keywords  dulce de leche, rheology, whey pro-teins  I. INTRODUCTION Dulce de Leche (DL) is a sweet spread widely con-sumed as jam and as dessert. Also, is widely used in bakery and confectionery in the preparation of desserts and cakes as a cram. Argentina produces about 140,000 tons per year and 5.5 % of this production is exported to several countries (Ministerio de Ganadería, Agricultura, Pesca y Alimentos de la República Argentina, 2012). Argentinean food legislation (Código Alimentario Argentino, 2013by heat concentration, at normal or reduced pressure, of milk or reconstituted milk apt for human consumption, o-dium bicarbonate is also added which increases the pH of the final product and avoids protein coagulation. Va-nillin is added as flavouring agent (Rovedo et al., 1991; Navarro et al., 1999). Maillard browning reactions oc-curs during this process; therefore the product has a dis-tinctive brown colour (Navarro et al., 1999). The heat treatment applied during DL manufacture generates chemical modifications leading to irreversible aggregation with formation of a gel with particular characteristics (Pauletti et al., 1996). The resulting mix-ture of carbohydrates, proteins and fats determines its structural properties, affecting its functional characteris-tics (Ranalli et al., 2012). For confectionery uses a firm texture is needed and for these purposes different hy-drocolloids are used. Therefore, rheological characteri-zation can be used as a quality control tool because the rheological parameters may be related to the desirable texture of confectionary DL.  The earliest studies related to DL texture were car-ried out using shear viscometry (Moro and Hough, 1985; Hough and Moro 1988; Rovedo et al. 1991; Heimlich et al. 1994). These authors reported that DL presents a pseudoplastic behavior and it can be de--Bulkley models. In addition, Pauletti et al. (1990) and Navarro et al. (1999) studied different types of DL by oscillatory rheometry and observed that its rheological behavior is intermedi-ate between a concentrated solution and a gel, depend-ing on the type of DL and the solid content. Recently, Ranalli et al. (2012) analyzed the physicochemical properties of four types of commercial DL (traditional, reduced calories, reduced fat and confectionary) and de-veloped a comprehensive study on the viscoelastic be-havior of these products. This behavior was modeled us-ing the Baumgartel-Scahusberger-Winter (BSW) and the mechanical relaxation spectrum in the linear viscoe-lastic range was predicted. The parameters of the BSW model were used to explain structural characteristics of the systems and, the dynamic data measured was also successfully converted into time and was validated us-ing creep and flow experiments.   Whey proteins, a byproduct from cheese and casein manufacture, are frequently used as functional ingredi-ents in many foods. They are now widely used as gel-ling agents, emulsifiers, texture modifiers, thickening agents and foaming agents. In addition, they have high nutritive value and are generally recognized as safe (Bryant and Mc Clements, 1998; Meza et al., 2010). Whey proteins ingredients may be purchased in several different forms. Whey proteins concentrates (WPC) contain between 20% and 89% of protein, being WPC with 35% of protein content the most common product (Tunick, 2008; Meza et al., 2010). In this sense, results of technological interest to explore the potential use of WPC as texture modifier in DL formulation and as fat replacer. Therefore, the objective of this work was to study the effect of whey proteins concentrate (WPC) and butter oil addition on viscoelastic properties of con-fectionary DL. Latin American Applied Research  44:185-188 (2014) 186 II. METHODS A. Dulce de Leche samples preparation Skim milk powder (Milkaut, Frank, Argentina), sucrose (Ledesma, Jujuy, Argentina), butter oil (Corlasa, Esperanza, Argentina) and a 35 % w/w whey protein concentrate (Milkaut, Frank, Argentina) were used as ingredients for DL manufacture. In addition, carragee-nan (Carragel, Gaiman, Argentina) and agar-agar (Chu-butagar, Gaiman, Argentina) were used as thickening agents.  Different DL samples were prepared, as listed in Table 1. Partial hydrolysis of lactose was carried out in order to avoid lactose crystallization by the addition of 0.015 kg of a commercial -galactosidase enzyme extract (Maxilact, Delft, Holland) to the reconstituted milk at 37°C, one hour before manufacture. The manufacture of each sample was carried out in an open kettle commonly used by the industry. The in-gredients were mixed; the pH was fixed at 6.9 by addi-tion of Ca(OH)2 p.a. and then, the mixture was concen-trated at atmospheric pressure up to 70°Brix.  A refrac-tometer (ATAGO Master H80, Tokyo, Japan) was used for the measurement of °Brix during the concentration process. The obtained product was cooled at 70°C, packaged in containers of 250 g and storage for a week at room temperature prior analysis. As minimal variability between batches was ob-served previously (Pauletti et al., 1990, 1995), this study was carried out considering one batch of Dulce de Leche for each sample in order to significantly reduce the number of assays. B. Rheometrical measurements  A rheometer Haake RheoStress RS80 (Haake Instru-ment Inc., Paramus, NJ, USA) with parallel plates (35 mm diameter, 1 mm gap) was used for rheometrical measurements. The temperature of the lower plate was maintained at 25°C by circulating water from water bath. The DL sample was placed on the lower plate and then the upper plate was brought in contact with the sample to attain temperature equilibrium. The dynamic rheological data obtained included the 2 components of complex shear modulus (G*): the stor-age modulus ( ), which is a measure of the energy stored and recovered per cycle of deformation (elastic component), and the loss modulus ( ), which is a measure of the energy dissipated or lost as heat per cy-cle of deformation (viscous component) (Gunasekan and Ak, 2003). These parameters are related as follows: Table 1. Dulce de Leche samples studied. Ingredient Samples  S1 S2 S3 S4 Tap water (kg) 27 27 27 27 Skimmed milk powder (kg) 2.74 2.74 2.74 2.74 Sucrose (kg) 7.2 7.2 7.2 7.2 Whey Proteins  (% w/w) 0 1 1 0 Butter oil (% w/w) 0 0 8 8 Carrageenan (kg) 0.015 0.015 0.015 0.015 Agar-agar (kg) 0.01 0.01 0.01 0.01  2 2 2* ' ''G G G     (1) Frequency sweep tests were carried out from 0.01 to 1 Hz at strain amplitude of 0.01  5 x 10-4. The linear viscoelastic region was determined by performing strain sweep tests from 0.001 to 0.1 at 25°C for all samples studied. Moreover, the effect frequency on complex vis-cosity (| *|=|G*|/ , : frequency of oscillation) was analysed.  Each sample was analysed in triplicate. C. Data modelling Frequency dependency of |G*| for the DL samples was fitted by the weak gel model for foods (Gabriele et al., 2001), in which the structure of the material is modelled as a cooperative arrangement of flow units, to form a strand. According to this model, the complex modulus can be expressed by: 2 2 1* ' '' zFG G G A    (2) Where z is the interaction factor and AF is the gel strength. Values of z can be interpreted as the number of flow units interacting with one another in a three-dimensional structure to give the observed flow re-sponse of the material; AF can be interpreted as the strength of the interaction between flow units. D. Statistical analysis Data were analysed by ANOVA using Statgraphics (Statgraphics Inc., Rockville, MD, USA). When differ-ences between treatment effects were significant (P<0.05), a multiple comparison of means was per-formed. III. RESULTS AND DISCUSSION Figure 1 e-quency of DL samples.  In samples S1, S3 and S4 the magnitude t-ing no crossing point and both increased with increased in frequency, indicating dominant elastic properties. In sample S2 frequency but their values were similar in the whole frequency range evaluated, indicating similar elastic and  values of the sample S2 were lower than those obtained from the other samples analysed. From a structure point of view, for true gels ln  plots have zero slope because the molecular rearrangements within the network are very reduced over the time scales ana- studied for weak gels and highly concentrated dispersions (Rao, 1999).  In weak gels there is a higher dependence on fre-quency for the dynamic moduli, suggesting the exis-tence of relaxation processes occurring even at short time scales, and lower difference between moduli val-ues, indicating that a lower percentage of the stored en-ergy is recovered (Rao, 1999). Therefore, mechanical spectra of all DL samples denote a weak gel structure.  These findings are in agreement with those reported by Navarro et al. (1999) and Ranalli et al. (2012).  M. L. OLIVARES, M. S. PAULETTI, S. C. COSTA, D. DE PIANTE VICÍN, A. C. RUBIOLO 187   Figure 1. Characteristics frequency sweeps of DL samples studied.  Figure 2. Characteristic loss tangent (tan ) as function of fre-quency corresponding to DL samples studied. The total resistance to flow of a material considered to be a viscous liquid refers to complex viscosity (| *|) (Dimitreli and Thomareis, 2008). Fig. 1 also shows that | *| of samples S1, S3 and S4 decreases across the fre-quency range which indicates shear-thinning behaviour. However, | *| values of sample S2 were lower and less shear-thinning behaviour was observed.   Another useful rheometrical function in describing viscoelastic behaviour is the loss tangent (tan =G´´/G´). It is dimensionless and gives a clear indica-tion of whether the material behaves as solid-like or liq-uid-like. The larger the tan value, the more easily the DL flows. These results are presented in Fig. 2. The loss tangent values showed a predominantly elastic behav-iour (tan  < 1) in samples S1, S3, S4 over the whole range of frequency tested while a slightly viscous be-haviour was observed in sample S2 (tan  > 1). As it can be seen, the loss tangent clearly differentiated the vis-coelastic behaviour in two groups of samples. For sam-ples S1, S3 y S4 tan  presented values between 0.2 and 0.3 that correspond to amorphous polymers (Steffe, 1996). These values were also reported by Ranalli et al. (2012) for commercial DL. For sample S2 tan  pre-sented values between 0.9 and 1.4 that may correspond to a concentrated solutions or weak gels.  Therefore, in order to analyse the overall rheological behaviour, the response of complex modulus (|G*|) of DL samples was compared with the weak gel model for foods (Gabriele et al., 2001). Figure 3 shows character-istics experimental data and the fitted values obtained with Eq. (2), giving for all frequency sweeps analysed a fitting error  less than 5%. The obtained rheological pa-rameters are listed in Table 2. ANOVA indicated that the sample with whey pro-teins addition and without butter oil (S2) presented less number of rheological units than the others (z). This suggests that the structure of sample S2 is composed by t-ing a weaker matrix. The sample with addition of whey proteins and butter oil (S3) had a rheological behaviour significantly different than the others because presented higher gel strength between rheological units quantified by the parameter AF. Therefore, the whole addition of butter oil and whey proteins in sample S3 generates a stronger gel matrix.  Latin American Applied Research  44:185-188 (2014) 188  Figure 3.  Complex modulus (|G*|) as function of frequency of DL samples. Symbols are experimental values and lines correspond to predictions carried out with the weak gel model for foods. Table 2. Mean values of weak gel model parameters of DL samples* Sample Af.[Pa sz]  z[-]  S1 336.7a 6.6b,c S2 309.1a 1.7a S3 695.7b 6.1b S4 344.8a 6.8c * Mean values with different letters in a column indicate sig-nificant differences (P < 0.05). IV. CONCLUSION It is concluded that mechanical spectra of all DL sam-ples studied denote a weak gel structure. The DL micro-structure significantly changes with whey proteins and butter oil addition. When whey proteins are presents in absent of butter oil, the dynamic moduli of DL pre-sented higher dependency of frequency, suggesting a weaker matrix. This phenomenon was also observed when complex modulus of DL samples was compared with the weak gel model for foods. This model indicated that the structure of sample S2 is composed by less  zones in the network. The whole addition of butter oil and whey proteins in S3 generates a stronger gel matrix, more appropriate for use in con-fectionary. REFERENCES Bryant, C.M. and D.J. 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Andrés and A.N. Califano, Physico-chemical and rheological characterization of dulce , J.Texture Stud., 43, 115-123 (2012). Rao, M.A., Rheology of fluids and semisolid foods. Principles and applications, Gaithersburg, Aspen (1999).  Rovedo, C.O., P.E. Viollaz and C. Suarez, The effect of pH and temperature on the rheological behavior of dulce de leche, a typical dairy argentine prod-uct  J. Dairy Sci, 74, 1497-1502 (1991). Steeffe, J.F., RheologicalMethods in Food Processing Engineering, 2nd Ed. Freeman Press, East Lansing (1996). Tunick, M.H. Whey protein production and utilization: a brief history. In C. I. Onwulata and P. J. Huth (Eds.), Whey processing, functionality and health benefit, John Wiley & Sons, Iowa (2008).  Received: March 27, 2013 Accepted: November 6, 2013  Recommended by Subject Editor: María Luján Ferreira 

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Effects of butter oil and whey proteins addition on viscoelastic properties of confectionary Dulce de leche

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