Functional properties of caprine whey protein concentrates obtained from clarified cheese whey

Small Ruminant Research 110 (2013) 52–56

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Functional properties of caprine whey protein concentrates obtained from clarified cheese whey Beatriz Sanmartín, Olga Díaz, Laura Rodríguez-Turienzo, Angel Cobos ∗ Área de Tecnología de Alimentos, Departamento de Química Analítica, Nutrición y Bromatología, Facultad de Ciencias de Lugo, Universidad de Santiago de Compostela, 27002 Lugo, Spain

a r t i c l e

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Article history: Received 30 May 2012 Received in revised form 21 September 2012 Accepted 12 November 2012 Available online 4 December 2012 Keywords: Caprine whey protein concentrates Thermocalcic precipitation Solubility Foaming and emulsifying properties

a b s t r a c t Functionality (solubility, foaming and emulsification properties) of caprine whey protein concentrates was evaluated. The caprine whey was clarified by thermocalcic precipitation. Next, it was ultrafiltrated/diafiltrated, and then, the lyophilisation of the retentate was carried out. The functionality of these powders was compared with those of untreated ultrafiltrated/diafiltrated whey protein concentrates, clarification by-products (aggregates) and a commercial bovine whey protein concentrate. The clarification treatment increased the emulsifying capacity at pH 7. Other functional properties were not improved by the clarification procedure. Both caprine whey protein concentrates showed higher solubility and emulsifying stability than commercial bovine whey protein concentrate. The clarified whey protein concentrates also showed higher emulsifying capacity than commercial bovine whey protein concentrate. Caprine whey protein concentrates and bovine whey protein concentrate did not show foaming capacity. The aggregates could also be useful in food manufacturing due to their functionality (solubility and emulsifying properties). © 2012 Elsevier B.V. All rights reserved.

1. Introduction Whey proteins are well known for their high nutritional value and their excellent functional properties in food products (De Wit, 1998). The use of whey protein concentrates (WPC) as functional ingredients by the food industry represents one of the best means for utilization of whey proteins (Morr and Foegeding, 1990). Commercial whey protein concentrates derived mainly from bovine whey. Caprine milk products are suitable as potential substitutes for bovine milk products in the diets of children with cow milk allergies (Pandya and Ghodke, 2007). The allergy to bovine milk proteins affects primarily infants, but may also persist throughout adulthood and can be very

∗ Corresponding author. Tel.: +34 982 824070; fax: +34 982 285872. E-mail address: [email protected] (A. Cobos). 0921-4488/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.smallrumres.2012.11.029

severe (Lara-Villoslada et al., 2005). Caprine WPC could be an interesting alternative to bovine WPC in foods for allergic people. However, little information on the functional properties of caprine WPC is available. Casper et al. (1999) reported that caprine WPC produced from sweet whey showed better emulsifying capacity than bovine WPC. The presence of residual lipid (mainly phospholipoproteins) impairs functionality of WPC (Pearce, 1992); hence, its removal by means of thermocalcic precipitation (TP) (Fauquant et al., 1985) is very beneficial. The aggregates separated by this method could exhibit interesting functional properties such as good emulsifying properties (Rosenberg, 1995; Díaz et al., 2004). In a previous work (Sanmartín et al., 2012), we studied the effect of clarification by TP and the composition of different caprine WPC and aggregates. Caprine whey protein concentrates with high protein content (74%) and low lipid content (6%) were obtained. The clarification procedure increased the ash and calcium contents whereas the

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protein composition and the proportion of phospholipids were not influenced by this pre-treatment. The aggregates showed a different protein profile with the highest levels of immunoglobulin G and caseinomacropeptide. The purpose of this work was to evaluate the effects of the clarification by thermocalcic precipitation on functionality (solubility, foaming and emulsifying properties) of caprine whey protein concentrates produced by ultrafiltration followed by diafiltration. These properties were

 Overrun (%) =

compared with those of the clarification by-products (aggregates) and those of a commercial bovine whey protein concentrate.

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where SPC, supernatant protein concentration (mg/ml); SW, sample weight (mg); and SP, sample protein concentration (%). 2.2.2. Foaming properties Foaming capacity and foam stability of the samples and of ovalbumin (used as reference) at pH 4 and 7 were determined in duplicate using the method of Phillips et al. (1990). Dispersions of 5% (w/v)protein (CWP, UWP, bovine WPC and ovalbumin) and of 1% (w/v) protein(aggregates) were whipped for 15 min at ambient temperature in a Braun mixer mod. ˜ Esplugues de Llobregat, Spain) at maximum MR550 (Braun Espanola, speed (10,000 rpm) using the whipping accessory. Foaming capacity was expressed as the percentage overrun in the resulting foam and was calculated as follows: (Weight of 100 ml protein dispersion) − (Weight of 100 ml foam) (Weight of 100 ml foam)



× 100

The foam stability was measured by monitoring volume of liquid drained from the resulting foam at ambient temperature for 30 min (Patel et al., 1988). The foam stability (FS) was determined as follows:



FS (%) = 100 −

Volume of liquid drained after 30 min Initial volume of foam



× 100

2. Materials and methods 2.1. Sample preparation Sweet caprine whey was obtained from a local cheese-making farm. Caprine whey was obtained from a rennet-coagulated cheese that had been produced from pasteurized whole milk. After the collection, the curd fines were separated from the whey using a filter (20 ␮m of pore diameter) and then, the whey was pasteurized at 63 ◦ C for 30 min (initial whey). Approximately 80 l of whey were used in each trial. 30 l were processed through ultrafiltration–diafiltration (UF/DF), and 50 l, after determining the calcium content by a colorimetric method using a commercial kit (Spinreact S.A., Girona, Spain), were used for thermocalcic precipitation-separation of aggregates by centrifugation followed by UF/DF. More details and a diagram of the process can be found in Sanmartín et al. (2012). The whey obtained after separation of aggregates (clarified whey; 40 l) and the initial whey (30 l) were submitted to UF and DF using a Centramate lab tangencial flow system equipped with an Omega (polyethersulfone) membrane cassette (0.09 m2 surface area, 10 kDa MW cut-off) (Pall Corporation, Ann Arbor, MI, USA). The diafiltration retentates and the aggregates were freeze dried in a Lyph-LockTM (Labconco Corporation, Kansas City, USA) freeze dryer. Three products were obtained: the aggregate powder (aggregates), the diafiltration retentate powder from the clarified whey (CWP) and the diafiltration retentate powder from the unclarified whey (UWP). All experiments were made in triplicate. Chemical, lipid and whey protein compositions of the three types of caprine products (aggregates, CWP and UWP) and a commercial bovine WPC (BWPC) are described in Sanmartín et al. (2012). The protein contents were also determined by the Bradford method (Kruger, 1996) and they were 56.73% for CWP, 29.88% for UWP, 5.35% for aggregates and 68.12% for BWPC. 2.2. Functional properties 2.2.1. Solubility The solubility of protein at pH 4 and 7 was determined in duplicate using the method of Morr et al. (1985). About 500 mg of powder were dissolved in 40 ml of 0.1 M NaCl. Immediately after obtaining a complete dispersion, the pH was adjusted to 4.0 or 7.0 with 0.1 N HCl or NaOH solution. The dispersion was stirred for 1 h; during this period, pH was monitorized and adjusted when necessary. After that, the dispersion was transferred into a 50 ml volumetric flask and diluted to the mark with additional 0.1 M NaCl solution. An aliquot of the dispersion was centrifuged 15 min at 2260 × g and 4 ◦ C and the resulting supernatant fraction was filtered through Whatman No. 1 filter paper. The protein content of the filtrate and the original dispersion was determined by Bradford method (Kruger, 1996). The solubility of the products was calculated as:

 Protein solubility (%) =

SPC × 50 SW × (SP/100)

 × 100

2.2.3. Emulsifying properties The turbidimetric method of Pearce and Kinsella (1978), modified by Patel and Kilara (1990), was used to determine the emulsifying capacity. Dispersions of 2%(w/v) protein (CWP, UWP and BWPC samples) and 0.5% (w/v) protein(aggregates) were prepared. The pH was adjusted to 4.0 or 7.0 pH with 0.1 N HCl or NaOH, respectively. Volumes of 50 ml of dispersion (pH 7.0 and 4.0) were used as a continuous phase and the dispersed phase was 150 ml of sunflower oil. The emulsions were prepared using a Polytron PT-20 homogeneizer (Brikman Instruments, Westbury, USA) at 17,200 rpm for 2 min followed (except in aggregates) by homogeneization in a Rannie homogeneizer (Mini-lab type 8.30 H) at 20 MPa. An aliquot was diluted 1/3,000 using a 0.1% SDS solution and the absorbance of the diluted emulsion was determined at a wavelength of 500 nm in a spectrophotometer Zuzi mod. UV-4210 (Auxilab, Beriain, Spain). The emulsifying capacity, expressed as emulsifying activity index (EAI), was calculated as follows: EAI (m2 /g) =

2 × 2.303 × A500 ×L×C

where A500, absorbance of dilute emulsion at 500 nm; , volume fraction of dispersed phase; L, path length of cell (in metres); and C, weight of product per unit volume of product dispersion (in g/m3 ). The method of Tornberg and Hermansson (1977) was used to determine the emulsifying stability rating (ESR) of the samples. Aliquots of 4 g and 30 g of the emulsions were prepared as previously described. Aliquots of 30 g were stored at 20 ◦ C for 24 h and afterwards, were centrifuged 15 min at 180 × g. Aliquots of 4 g were taken from the bottom fraction. The fat contents of the initial emulsion and of the bottom fraction were evaluated by the method of Bligh and Dyer (Hanson and Olley, 1963). ESR was computed by dividing the fat content of the bottom fraction by the fat content of the initial emulsion and multiplying by 100. All measurements were made in duplicate. 2.3. Statistical analysis The data from caprine powders were analysed by one-way ANOVA and the means were compared using the least significant difference test with significance at p < 0.05(SPSS version 12.0 for Windows, 2004, SPSS Inc., Chicago, IL, USA).

3. Results and discussion 3.1.1. Solubility Protein solubility of caprine cheese whey powders and bovine WPC are shown in Table 1. Solubility values found for caprine WPC (CWP and UWP) at pH 7 were similar to those described by Casper et al. (1999) in caprine WPC

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Table 1 Protein solubility (% of protein in samples), emulsifying activity index (EAI, m2 /g) and emulsifying stability rate (ESR, %) of caprine cheese whey powders and bovine whey protein concentrate. CWP Protein solubility pH 7 pH 4 EAI pH 7 pH 4 ESR pH 7 pH 4

102.57 ± 3.11a 67.62 ± 3.54b

UWP

Aggregates

Bovine WPC

103.14 ± 2.08a 84.60 ± 10.22a

93.98 ± 4.47b 95.69 ± 6.11a

73.88 ± 3.53 59.08 ± 0.53

60.24 ± 6.35a 48.55 ± 16.59

19.30 ± 3.61b 49.89 ± 7.86

48.89 ± 8.27a 49.90 ± 5.00

48.92 ± 0.89 30.27 ± 1.66

99.12 ± 1.78 95.86 ± 1.29b

100.86 ± 1.66 96.39 ± 3.64b

102.52 ± 2.63 103.15 ± 0.97a

95.16 ± 0.92 80.40 ± 4.38

CWP: clarified whey powders; UWP: unclarified whey powders; aggregates: aggregates powders; bovine WPC: bovine whey protein concentrate. Values within the same row with different superscript differ significantly (p < 0.05). Mean values ± standard deviation (n = 3).

at pH 7. These authors attributed the excellent solubility properties to the low degree of denaturation associated with lyophilisation and the low lipid content of WPC (0.2–0.3%). Patel and Kilara (1990) reported that lipids can reduce solubility of proteins. This reduction could be due to the hydrophobic interactions between lipids and proteins (Vojdani, 1996). Nevertheless, the solubility values of UWP were not affected negatively by the high content of lipids (53.18%) [datum reported in Sanmartín et al. (2012)]. This lipid content of UWP was due to the high lipid concentration of the caprine whey (0.84%) and the lack of whey skimming before UF (Sanmartín et al., 2012). Caprine WPC at pH 4 showed lower protein solubility than at pH 7. Solubility of whey proteins depends on pH and is lower at pH around the isoelectric point (4–5) (Zayas, 1997). At this pH, attractive forces predominate, therefore protein–protein interactions increase resulting in a loss of solubility (Morr and Ha, 1993; Vojdani, 1996; Zayas, 1997). Casper et al. (1999) observed similar solubility of proteins in caprine WPC at pH 3 and 7. This was probably due to the different acid pH used for the evaluation of this property; it has been observed that for pH below the isolectric point the solubility of whey proteins increases (Pelegrine and Gasparetto, 2005). Caprine aggregates also showed good solubility properties. Solubility values found for caprine aggregates were similar to those observed by Díaz et al. (2004) in ovine microfiltration retentate powders using a 0.20 ␮m pore size membrane after thermocalcic precipitation. Caprine aggregates showed similar solubility at pH 4 and 7. The high levels of calcium and ash in these powders (Sanmartín et al., 2012) could be beneficial for solubility, due to the “saltingin” effect which decreases protein–protein interactions, while protein-water interactions are increased, and consequently, solubility is improved (Patel and Kilara, 1990; Vojdani, 1996). Clarified whey powders (CWP) did not show higher protein solubility than unclarified whey powders (UWP). Even UWP showed significantly higher protein solubility than CWP at pH 4. Therefore, thermocalcic precipitation followed by centrifugation did not improve solubility for caprine WPC probably related with the high protein solubility of unclarified whey powders. Caprine WPC and aggregates showed higher solubility values thancommercial bovine WPC. These higher solubility properties could be attributed to the low degree

of denaturation associated with manufacturing process of caprine WPC; whey was pasteurised at 63 ◦ C for 30 min and the products were freeze dried (Sanmartín et al., 2012). It is possible that denaturation of whey proteins could be higher in manufacturing process of commercial bovine WPC. Casper et al. (1999) observed similar protein solubility in caprine and bovine WPC when the same manufacturing process was used. 3.1.2. Foaming properties Neither caprine products nor bovine WPC produced foams in assayed conditions. When foaming properties of solutions of ovalbumin (used as control) were determined, overrun of this protein was 259% at pH 7 and 281% at pH 4 and foam stability was 56% at pH 7 and 48% at pH 4. So, clarification pretreatment did not make possible to produce foams from caprine whey. Our results are in agreement with those described by Kim et al. (1989) where no foaming propertieswas observed when thermocalcic precipitation was followed by centrifugation in bovine WPC. Casper et al. (1999) observed foaming properties (foam overrun and foam stability) in caprine WPC. These differences could be due to the lipid content of WPC. The fat content (0.2–0.3%) of caprine WPC studied by Casper et al. (1999) was lower than those observed in CWP (5.9%) and UWP (53.2%) [data reported in Sanmartín et al. (2012)]. The absence of foaming properties in bovine WPC could also be due to their lipid content (4.3%) (Sanmartín et al., 2012). Fat content plays an important role in foaming properties. The presence of lipids, even small amounts, has a detrimental effect on this functional property (De Wit et al., 1988; Karleskind et al., 1995; Heino et al., 2007). Lipids impair the foaming properties of WPC due to several mechanisms: their high surface activity and the sliming effect on interface protein film, the reduction of the surface hydrophobicity of proteins and the inhibition of protein adsorption in the interface (Damodaran, 1996; Zayas, 1997). 3.1.3. Emulsifying properties Table 1 shows the EAI and ESR at pH 4 and 7 of the emulsions prepared with caprine cheese whey powders and bovine WPC.

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The clarification treatment improved significantly the emulsifying activity of caprine WPC at pH 7. This result seems to be related to the lipid content of the samples. Patel and Kilara (1990) observed that the emulsifying capacity of WPC with high lipid contents (9–14%) was significantly lower than that of the WPC with low lipid content (4–5%). Emulsifying properties are negatively modified by lipids, mainly phospholipids and monoglicerides. This can be attributed to the reduction of the amount of protein adsorbed in the interface caused by competitive mechanisms and to the direct reaction with proteins, which cause their instability and can promote aggregation (Damodaran, 2005; McClements, 2008). However, the emulsifying activity of caprine WPC at pH 4 was not improved by the clarification probably due to the different effect of pH in WPCs. CWP and bovine WPC at pH 7 showed higher emulsifying activity than at pH 4. Nevertheless, UWP at pH 7 showed lower emulsifying activity than at pH 4. Casper et al. (1999) observed higher emulsifying capacity at pH 8 than at pH 3. ␤-Lactoglobulin, the main whey protein, shows a higher emulsifying capacity than other whey proteins and their capacity of emulsify oil is higher at pH 7 than at pH 4–5 (Klemaszewski et al., 1992; Zayas, 1997); this is in agreement with the results observed for CWP and bovine WPC. Shimizu et al. (1985) reported that ␤-lactoglobulin showed lower emulsifying and surface activity at acid pH than at pH 7 because its conformation was more rigid and resistant to denaturation at acid pH than at pH 7. On the contrary, UWP showed better EAI at acid pH. The likely explanation for this improvement at pH 4 may be related with the fact that lipids interact more with proteins through hydrophobic bonds at the isoelectric point (Borderías and Montero, 1988). The probability of protein–lipid interaction could increase in emulsions prepared with UWP due to its high lipid content, improving the emulsifying activity at pI. The emulsifying stability at pH 7 and 4 were not improved by the clarification. Other authors (Rinn et al., 1990; Vaghela and Kilara, 1996) also reported that the emulsifying stability of bovine WPC was not influenced by thermocalcic precipitation followed by centrifugation. The stability of an emulsion is influenced by the protein concentration (Zayas, 1997) and by the protein composition (Klemaszewski et al., 1992). The lack of differences in ESR between CWP and UWP could probably be due to the similar protein content and protein composition of the emulsions. Dispersions of the same protein concentration [2%(w/v) protein] were prepared for both CWP and UWP, and no significant differences between the protein composition from CWP and UWP were observed (Sanmartín et al., 2012). The EAI of caprine products were higher than for bovine WPC. Casper et al. (1999) also observed higher emulsifying capacity of caprine WPC than bovine WPC at pH 8 and 3. They explain the higher emulsifying capacity of caprine WPC than bovine WPC at pH 3 by the higher content of ␣-lactalbumin in caprine WPC. However, CWP has similar content of ␣-lactalbumin than bovine WPC (Sanmartín et al., 2012). The emulsifying capacity is also improved by the increase in protein concentration (Zayas, 1997); a high content of ␤-lactoglobulin has also a positive effect due to

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its better emulsifying properties compared to other whey proteins (Klemaszewski et al., 1992). However, the protein concentration and composition of CWP were similar than those observed in bovine WPC (Sanmartín et al., 2012). Probably, the lower solubility of bovine WPC could explain the differences in the emulsifying capacity between caprine and bovine WPCs. In relation to the emulsifying stability (ESR), caprine WPC showed very high values (around 100%). These values were higher than those observed in bovine WPC (80–95%). No available information about emulsifying stability of caprine WPC has been found. Emulsion stability has been positively correlated with protein solubility (Patel and Kilara, 1990). The lower solubility of bovine WPC could explain the differences in emulsifying stability between caprine and bovine WPCs. Caprine aggregates also showed good emulsifying properties. No significant differences were observed in emulsifying properties (EAI and ESR) between CWP and aggregates except in ESR at pH 4, where the aggregates showed significant higher values. Díaz et al. (2004) observed that the ovine microfiltration retentate powders after thermocalcic precipitation showed higher values in EAI than the unclarified and clarified-diafiltrated powders. Thermocalcic aggregation produces the precipitation of fat globule membrane proteins and these proteins could be retained and separated during the posterior centrifugation (Fauquant et al., 1985). These proteins could be the compounds responsible for the good emulsifying properties of aggregates (Díaz et al., 2004). Rosenberg (1995) also indicated that these aggregates had potential as an emulsification agent for their high content of phospholipids. However, the proportion of phospholipids of caprine aggregates was similar to CWP and UWP (Sanmartín et al., 2012). The emulsifying capacity of caprine aggregates were not affected by the pH. Caprine aggregates showed higher amounts of caseinomacropeptide, immunoglobulin G and serum albumin than caprine and bovine WPCs (Sanmartín et al., 2012). Their similar emulsifying properties at both pH values could be due to that the properties of these proteins are independent of the pH (Klemaszewski et al., 1992). 4. Conclusions Caprine whey protein concentrates produced by ultrafiltration and diafiltration showed higher solubility and emulsifying stability than commercial bovine WPC. Thermocalcic precipitation increased the emulsifying capacity at pH 7. Other functional properties (solubility, foaming properties and emulsion stability) were not improved by this clarification procedure. The clarified caprine WPC also showed better emulsifying capacity than commercial bovine WPC. Caprine and bovine WPCs did not show foaming capacity. The aggregates could also be useful in food manufacturing due to their functionality (solubility and emulsifying properties). References Borderías, A.J., Montero, P., 1988. Fundamentos de la funcionalidad de las proteínas en alimentos. Rev. Agroquim. Tecnol. Aliment. 28, 159–169.

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Casper, J.L., Wendorff, W.L., Thomas, D.L., 1999. Functional properties of whey protein concentrates from caprine and ovine specialty cheese wheys. J. Dairy Sci. 82, 265–271. Damodaran, S., 1996. Functional properties. In: Nakai, S., Modler, H.W. (Eds.), Food proteins, properties and characterization. VCH Publishers Inc., New York, pp. 167–234. Damodaran, S., 2005. Protein stabilization of emulsions and foams. J. Food Sci. 70, 54–66. De Wit, J.N., Hontelez-Backx, E., Adamse, M., 1988. Evaluation of functional properties of whey protein concentrates and whey protein isolates, 3. Functional properties in aqueous solution. Nether. Milk Dairy J. 42, 155–172. De Wit, J.N., 1998. Nutritional and functional characteristics of whey proteins in food products. J. Dairy Sci. 81, 597–608. Díaz, O., Pereira, C.D., Cobos, A., 2004. Functional properties of ovine whey protein concentrates produced by membrane technology after clarification of cheese manufacture by-products. Food Hydrocoll. 18, 601–610. Fauquant, J., Vieco, E., Brulé, G., Maubois, J.L., 1985. Clarification des lactosérums doux par agrégation thermocalcique de la matière grasse résiduelle. Le Lait. 65, 1–20. Hanson, S.W.F., Olley, J., 1963. Application of the Bligh and Dyer method of lipid extraction to tissue homogenates. Biochem. J. 89, 101–102. Heino, A., Uusi-Rauva, J.O., Rantamäki, P.R., Tossavainen, O., 2007. Functional properties of native and cheese whey protein concentrate powders. Int. J. Dairy Technol. 60, 277–285. Karleskind, D., Laye, I., Mei, F.I., Morr, C.V., 1995. Foaming properties of lipid-reduced and calcium-reduced whey protein concentrates. J. Food Sci. 60, 738–741. Kim, S.H., Morr, C.V., Seo, A., Surak, J.G., 1989. Effect of whey pretreatment on composition and functional properties of whey protein concentrate. J. Food Sci. 54, 25–29. Klemaszewski, J.L., Das, K.P., Kinsella, J.E., 1992. Formation and coalescence stability of emulsions stabilized by different milk proteins. J. Food Sci. 57, 366–371. Kruger, N.J., 1996. The Bradford method for protein quantification. In: Walker, J.M. (Ed.), The Protein Protocols. Humana Press Inc, Totowa, New Jersey Handbook, pp. 15–20. Lara-Villoslada, F., Olivares, M., Xaus, J., 2005. The balance between caseins and whey proteins in cow’s milk determines its allergenicity. J. Dairy Sci. 88, 1654–1660. McClements, D.J., 2008. Whey protein-stabilized emulsions. In: Onwulata, C.I., Huth, P.J. (Eds.), Whey Processing, Functionality and Health Benefits. Wiley-Blackwell IFT press, Iowa, pp. 63–97. Morr, C.V., Foegeding, E.A., 1990. Composition and functionality of commercial whey and milk protein concentrates and isolates: a status report. Food Technol. 44, 100–112.

Morr, C.V., German, B., Kinsella, J.E., Regenstein, J.M., Van Buren, J.P., Kilara, A., Lewis, B.A., Mangino, M.E., 1985. A collaborative study to develop a standardized food protein solubility procedure. J. Food Sci. 50, 1715–1728. Morr, C.V., Ha, E.Y.W., 1993. Whey protein concentrates and isolates: processing and functional properties. Crit. Rev. Food Sci. Nutr. 33, 431–476. Pandya, A.J., Ghodke, K.M., 2007. Goat and sheep milk products other than cheeses and yoghurt. Small Rumin. Res. 68, 193–206. Patel, M.T., Kilara, A., 1990. Studies on whey protein concentrates, 2. Foaming and emulsifying properties and their relationships with physicochemical properties. J. Dairy Sci. 73, 2731–2740. Patel, P.D., Stripp, A.M., Fry, J.C., 1988. Whipping test for the determination of foaming capacity of protein: a collaborative study. Int. J. Food Sci. Technol. 23, 57–63. Pearce, K.N., Kinsella, J.E., 1978. Emulsifying properties of proteins: evaluation of a turbidimetric technique. J. Agric. Food Chem. 26, 716–723. Pearce, R.J., 1992. Whey processing. In: Zadow, J.G. (Ed.), Whey and Lactose Processing. Elsevier Science Publishers, Barking, pp. 73–89. Pelegrine, D.H.G., Gasparetto, C.A., 2005. Whey proteins solubility as function of temperature and pH. Lebensm. -Wiss. u. -Technol. 38, 77–80. Phillips, L.G., German, J.B., Oneill, T.E., Foegeding, E.A., Harwalkar, V.R., Kilara, A., Lewis, B.A., Mangino, M.E., Morr, C.V., Regenstein, J.M., Smith, D.M., Kinsella, J.E., 1990. Standardized procedure for measuring foaming properties of three proteins, a collaborative study. J. Food Sci. 55, 1441–1453. Rinn, J.C., Morr, C.V., Seo, A., Surak, J.G., 1990. Evaluation of nine semi-pilot scale whey pretreatment modifications for producing whey protein concentrate. J. Food Sci. 55, 510–515. Rosenberg, M., 1995. Current and future applications for membrane processes in the dairy industry. Trends Food Sci. Technol. 6, 12–19. Sanmartín, B., Díaz, O., Rodríguez-Turienzo, L., Cobos, A., 2012. Composition of caprine whey protein concentrates produced by membrane technology after clarification of cheese whey. Small Rumin. Res. 105, 186–192. Shimizu, M., Saito, M., Yamauchi, K., 1985. Emulsifying and structural properties of ␤-lactoglobulin at different pHs. Agric. Biol. Chem. 49, 189–194. Tornberg, E., Hermansson, A.M., 1977. Functional characterization of protein stabilized emulsions: effect of processing. J. Food Sci. 42, 468–472. Vaghela, M.N., Kilara, A., 1996. Foaming and emulsifying properties of whey protein concentrates as affected by lipid composition. J. Food Sci. 61, 275–280. Vojdani, F., 1996. Solubility. In: Hall, G.M. (Ed.), Methods of Testing Protein Functionality. Chapman and Hall, London, pp. 11–60. Zayas, J.F., 1997. Functionality of Proteins in Food. Springer-Verlag, Berlin.