Available online at ScienceDirect. Agriculture and Agricultural Science Procedia 2 ( 2014 )

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1 Available online at ScienceDirect Agriculture and Agricultural Science Procedia 2 ( 2014 ) ST26943, 2nd International Conference on Agricultural and Food Engineering, CAFEi2014 Gel Strength and Stability Characterization of Ultrasound Treated Whey Protein Foams Mei Ching Tan a, Nyuk Ling Chin a, *, Yus Aniza Yusof a, Farah Saleena Taip a, Jaafar Abdullah b a Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Malaysia, UPM Serdang, Selangor, Malaysia b Plant Assessment Technology Group, Malaysia Nuclear Agency (Nuclear Malaysia), Bangi Kajang, Selangor, Malaysia Abstract Ultrasound treated whey protein foam at 10% concentration was characterized rheologically for its gel strength and stability. The 400 W ultrasound treatment at 20, 40 and 60% amplitude for 5, 15 and 25 minutes had increased gel strength up to 31% and improved foam stability with reduced foam drainage by 31%. The continuous network of the treated whey protein foam remained as a weak gel with tan δ values > 0.1 although the overall treated sample had a slight increase of gel strength from 121 to 147 Pa s 1/z compared to the untreated at 112 Pa s 1/z The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Scientific Committee of CAFEi2014. Peer-review under responsibility of the Scientific Committee of CAFEi2014 Keywords: Whey protein foam; weak gel; gel strength; foam drainage; ultrasound 1. Introduction Proteins are one of the main constituents that perform critical functions in food systems such as thickening, gelation, emulsification, foaming, texturization and water binding (Bryant and McClements, 1998; García-Garibay et al., 2008). These functional properties contribute to the sensorial properties of foods and influence the structural properties in foods. Proteins are the most complex food ingredients and they play important roles in baking. The effective of use of protein ingredients in baking depends upon its abilities to satisfy specific functional requirements * Corresponding author. Tel.: ; fax: address: chinnl@upm.edu.my The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Scientific Committee of CAFEi2014 doi: /j.aaspro

2 Mei Ching Tan et al. / Agriculture and Agricultural Science Procedia 2 ( 2014 ) such as emulsion stabilizer, foam stabilizer and gel structure (Chou and Morr, 1979) as to build up food structure. During baking, protein is necessary to form foam with viscoelastic network which has good gas-retaining properties to give rise in volume of product. The foam must be stable enough to hold the other ingredients until a stable matrix of protein is developed during heat coagulation in baking (Indrani and Rao, 2008). This study focused on characterizing gelling properties and foam stability of whey protein foams with ultrasound treatment. 2. Materials and methods 2.1. Protein suspension preparation Whey protein concentrate (Textrion PROGEL 800, DMV International, BA Veghel, Netherlands) in powder form with composition of 80% protein, 6.5% lactose, 6.3% fat, 4.4% ash, and 4.9% moisture at ph 6.5 was used. A 10% concentration protein suspension was prepared by dispersing 25 g of protein powder in 225 g of distilled water in a 500 ml beaker. It was then stirred using a mechanical stirrer (RW20 DZM.n S2, IKA Works (Asia) Sdn. Bhd., Malaysia) at 335 rpm for 20 minutes until homogeneous Foam preparation and ultrasound treatment The protein suspension was sonicated using a high intensity ultrasound probe (400 W, 20 khz, Digital Sonifier Model 450, Branson Ultrasonics Corporation, Danbury, Connecticut, USA) up to 60% amplitude for 25 minutes where maximum temperature increase in sample was up to 55 C, which is below protein denaturation temperature of 80 C (Chen and Dickinson, 1998). The 1 inch probe was immersed to half level at the center of the suspension. The protein suspension was then whipped with a mixer (5K5SSS, Kitchen Aid Inc., St. Joseph, Michigan, USA) at 330 rpm for 15 minutes at room temperature. The control samples were without ultrasound treatment Rheological measurement Rheological measurement on foam was performed using a rheometer (AR-G2, TA Instruments, New Castle, USA) with a 40 mm diameter serrated plate-plate geometry set at a constant gap height of 2.4 mm at 25 o C (Mleko et al., 2007). Frequency sweep tests over the range of Hz were conducted within its linear viscoelastic region at 1% strain to measure the storage modulus, and loss modulus, as to determine the complex modulus, of foam. A fresh sample was prepared for each test and the experiment was repeated once Gel characteristic of whey protein foam The type of gel formed was determined by loss tangent values, tan δ (Ikeda and Nishinari, 2001) as in Eq. (1) (Seta et al., 2012). The calculated complex modulus, of foam was modelled as weak gel food following Eq. (2) (Gabriele et al., 2001; Ikeda and Nishinari, 2001; Meza et al., 2011). The gel strength, (Pa s 1/z ) represents the strength of the interaction between the flow units of molecules that build up the gel network. The interaction factor, is the number of interaction between the flow units in a three-dimensional structure. Both gel strength, and interaction factor, values were obtained through curve fitting for the best fitted line by adopting the Generalised Reduced Gradient (GRG2) nonlinear optimization code (Chin et al., 2009). The goodness of fit, R 2 was calculated following Eq. (3) with minimum sum of square errors (SSE) and total corrected sum of squares (SST) values (Walpole et al., 2002). The angular frequency, is from rad s -1 from the set frequency of Hz. (1) (2) (3)

3 146 Mei Ching Tan et al. / Agriculture and Agricultural Science Procedia 2 ( 2014 ) Foam drainage Foam drainage at room temperature was measured to determine the stability of foam by using a filter funnel with dimension of 7.5 cm inner top diameter, 0.4 cm inner stem diameter and 7.0 cm stem length. 100 ml of foam was loaded on a small plug of glass wool which was placed at the top of the funnel stem (Jambrak et al., 2009). The drainage of the liquid into a measuring cylinder was recorded after 30 minutes. The samples were in triplicates and the experiment was repeated once Statistical analysis Mean and standard deviation were calculated using Microsoft Excel 2010 (Window 7, Microsoft Corporation, USA) and the error bars in graphs are the standard deviation of means. Two-way analysis of variance (ANOVA) was performed to determine the significance difference of the responses measured which is indicated by the P-value. 3. Results and discussion 3.1 Gel type of protein The loss tangent, tan δ is a measure of relative contribution of viscous components to the mechanical properties of the material where tan δ < 0.1 indicates conventional gel type and tan δ > 0.1 for weak gel type (Ikeda and Nishinari, 2001). Fig. 1 shows that all tan δ values are in the range of , thus the gel networks formed around the air bubbles in whey protein foam are of a weak gel type. The ultrasound treatment with respect to its amplitude and sonication duration did not give significant impact to altering the gel type. 3.2 Gel strength of protein network Fig. 1. tan δ value of foam treated at various ultrasound amplitude and sonication time. Fig. 2 shows that the ultrasound treated whey protein foams have higher values than the non-treated. The values increased with ultrasound amplitude (P < 0.005) and sonication time (P < 0.5). The higher of the treated whey protein gels indicate an increase in force interactions due to bonding of molecules in the gel network (Baldino et al., 2014). The increased gel strength was due to denaturation of whey protein molecules induced by ultrasound (Iametti et al., 1996; Qi et al., 1997; Lee and Feng, 2011; Meza et al., 2011). Iametti et al. (1996), Qi et al. (1997), Totosaus et al. (2002) and Lee and Feng (2011) explained that during protein denaturation the polypeptide chain will

4 Mei Ching Tan et al. / Agriculture and Agricultural Science Procedia 2 ( 2014 ) unfold and expose its hydrophobic amino acid groups, which lead to protein aggregation and contribute to the gel strength (Meza et al., 2011). For the interaction factor,, ultrasound did not give significant effect (P > 0.1) (Fig. 3). All and values were obtained with good correlation of R 2 > 0.95 following the weak gel model in Eq. (2). Fig. 2. Gel strength of foam treated at various ultrasound amplitude and sonication time. 3.3 Foam drainage Fig. 3. Interaction factor of foam treated at various ultrasound amplitude and sonication time. Fig. 4 shows that the ultrasound treated whey protein foams had lower drainage. The drainage decreased with ultrasound amplitude (P < 0.001) and sonication time (P < 0.001) due to the increased gel strength of the protein film (Fig. 2) which provided a more stable foam system. This characteristic is important in providing volume in processing of aerated food product with gas bubbles retained (Sahi and Alava, 2003).

5 148 Mei Ching Tan et al. / Agriculture and Agricultural Science Procedia 2 ( 2014 ) Conclusions Fig. 4. Drainage of foam treated at various ultrasound amplitude and sonication time. The aerated whey protein foam is a weak gel formed in a continuous phase of protein network and is well described using the weak gel model for foods. The increased values shows that the protein network has increased gel strength with ultrasound treatment at increasing amplitude and sonication time. Whey protein foams with higher gel strength also have increased foam stability. Acknowledgements This work was supported by the Ministry of Education (MOE), Malaysia through the Fundamental Research Grant Scheme (FRGS/2/2013/TK05/UPM/02/5). References Baldino, N., Gabriele, D., Lupi, F.R., de Cindio, B., Cicerelli, L., Modeling of Baking Behavior of Semi-Sweet Short Dough Biscuits. Innovative Food Science and Emerging Technologies. doi: /j.ifset Bryant, C.M., McClements, D.J., Molecular Basis of Protein Functionality with Special Consideration of Cold-set Gels Derived from Heatdenatured Whey. Trends in Food Science and Technology 9(4), Chen, J., Dickinson, E., Viscoelastic properties of heat-set whey protein emulsion gels. Journal of Texture Studies 29, Chin, N.L., Chan, S.M., Yusof, Y.A., Chuah, T.G., Talib, R.A., Modelling of Rheological Behaviour of Pummelo Juice Concentrates using Master-curve. Journal of Food Engineering 93(2), Chou, D.H., Morr, C.V., Protein-water Interactions and Functional Properties. Journal of the American Oil Chemists Society 56(1), A53- A62. Gabriele, D., de Cindio, B., D Antona, P., A Weak Gel Model for Foods. Rheological Acta 40(2), García-Garibay, M., Jiménez-Guzmán, J., Hernández-Sánchez, H., Whey Proteins: Bioengineering and Health, in Food Engineering: Integrated Approaches. In: Gutiérrez-Lopez, G. F., Welti-Chanes, J., Parada-Arias, E. (Eds.). Springer New York, pp Iametti, S., De Gregori, B., Vecchio, G., Bonomi, F., Modifications occur at Different Structural Levels during Heat Denaturation of β- lactoglobulin. European Journal of Biochemistry 237, Ikeda, S., Nishinari, K., Weak Gel -Type Rheological Properties of Aqueous Dispersions of Nonaggregated κ-carrageenan Helices. Journal of Agricultural and Food Chemistry 49(9), Indrani, D., Rao, G.V., Function of Ingredients in the Baking of Sweet Goods, in Food Engineering Aspects of Baking Sweet Goods. In Sumnu, S.G., Sahin, S. (Eds.). Taylor and Francis Group, USA, pp Jambrak, A.R., Lelas, V., Mason, T.J., Krešić, G., Badanjak, M., Physical Properties of Ultrasound Treated Soy Proteins. Journal of Food Engineering 93(4), Lee, H., Feng, H., Effect of Power Ultrasound on Food Quality, in Ultrasound Technologies for Food and Bioprocessing. In: Feng, H., Barbosa-Cánovas, G., Weiss, J. (Eds.). Springer New York, New York, pp Meza, B.E., Chesterton, A.K., Verdini, R.A., Rubiolo, A.C., Sadd, P.A., Moggridge, G.D., Wilson, D.I., Rheological Characterisation of

6 Mei Ching Tan et al. / Agriculture and Agricultural Science Procedia 2 ( 2014 ) Cake Batters Generated by Planetary Mixing: Comparison between Untreated and Heat-treated Wheat Flours. Journal of Food Engineering 104(4), Mleko, S., Kristinsson, H.G., Liang, Y., Gustaw, W., Rheological Properties of Foams Generated from Egg Albumin after ph Treatment. LWT Food Science and Technology 40(5), Qi, X.L., Holt, C., McNulty, D., Clarke, D.T., Brownlow, S., Jones, G.R., Effect of Temperature on the Secondary Structure of β- lactoglobulin at ph 6.7, as Determines by CD and IR Spectroscopy: A Test of the Molten Globule Hypothesis. Biochemical Journal 324, Sahi, S.S., Alava, J.M., Functionality of Emulsifiers in Sponge Cake Production. Journal of the Science of Food and Agriculture 83(14), Seta, L., Baldino, N., Gabriele, D., Lupi, F.R., de Cindio, B., The Effect of Surfactant Type on the Rheology of Ovalbumin Layers at the Air/Water and Oil/Water Interfaces. Food Hydrocolloids 29(2), Totosaus, A., Montejan, J.G., Salazar, J.A., Guerrero, I., A Review of Physical and Chemical Protein-gel Induction. International Journal of Food Science and Technology 37, Walpole, R.E., Myers, R.H., Myers, S.L., Ye, K., Probability and Statistics for Engineers and Scientists (7th ed.). Prentice Hall, New Jersey, USA. Accepted for oral presentation in CAFEi2014 (December 1-3, 2014 Kuala Lumpur, Malaysia) as paper 141.