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Effects of preheat treatment of milk powder on the properties of reconstituted set skim yogurts
International Dairy Journal 9 (1999) 415}416
E!ects of preheat treatment of milk powder on the properties of reconstituted set skim yogurts M.A. Augustin*, L.J. Cheng, P.T. Clarke CSIRO Division of Food Science and Technology, Melbourne Laboratory Highett, Vic. 3190, Australia
Abstract Yogurts were prepared on three occasions during a lactation period from reconstituted milk powders which had been subjected to heat treatments of varying severity prior to powder manufacture. A linear relationship was found between whey drainage and extent of whey protein denaturation. A similar trend was found for gel strength and denaturation level but seasonal e!ects confounded this relationship. 1999 Elsevier Science Ltd. All rights reserved. Keywords: Yogurt; Preheat treatment; Milk powders
1. Introduction The gel structure of a set yogurt is in#uenced by many factors including milk composition, season of milk production and the processing conditions during yogurt manufacture, in particular the heat treatment of yogurt milk. It is well established that heat treatment of milk which causes whey protein denaturation is necessary for production of yogurt with "rm texture and resistance to syneresis. Systematic studies on the quantitative e!ects of heat treatment and whey protein denaturation on yogurt characteristics appear to be lacking apart from that by Dannenberg and Kessler (1988a, b) where a clear relationship between heat-induced denaturation of b-lacto-globulin and yogurt characteristics was observed. The aim of this work was to examine the e!ects of preheat treatment of milk on gel strength and syneresis of reconstituted set yogurts made from milk powders produced at di!erent times during the dairying season (February, July and October).
2. Materials and methods Skim milks were subjected to a range of preheat treatments (803C/30 s, 803C/1 min, 803C/2 min, 803C/5 min, * Corresponding author. Tel.: #61-3-9252-6451; fax: #61-3-92526555. E-mail address: [email protected] (M.A. Augustin)
853C/2 min, 853C/5 min, 903C/2 min or 853C/30 min) prior to concentration and drying on three occasions during a dairying season. Milks (12% milk solids non-fat) were reconstituted from these powders, pasteurised at 603C/30 min, inoculated with yogurt cultures (S. thermophilus and L. bulgaricus), fermented at 433C to pH 4.6 and transferred to 43C. Gel strength and syneresis of yogurts were measured on the next day.
3. Results and discussion Yogurts made from February powders (12}77% whey protein denaturation), July powders (13}80% whey protein denaturation) and October powders (10}83% whey protein denaturation) had gel strengths between 5}9, 4.5}11 and 8}11 g, respectively. In yogurts made from powders produced from the same batch of milk, the gel strength increased when the extent of whey protein denaturation was increased from 10 to 40% but whey protein denaturation beyond 40% generally had less of an e!ect on gel strength (Table 1). Increasing whey protein denaturation in powders produced from the same batch of milk reduced syneresis. Whey drainage values from 50 g yogurts after 2 h were 27}20.5, 24.5}18.5 and 27.5}21 ml for February, July and October powders with varying extents of whey protein denaturation (Table 1). These results showed that there were di!erent factors
0958-6946/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 8 - 6 9 4 6 ( 9 9 ) 0 0 1 1 3 - 2
416
M.A. Augustin et al. / International Dairy Journal 9 (1999) 415}416
Table 1 In#uence of milk powder characteristics on the properties of reconstituted set skim yogurts Powder series
Preheat treatment of milk during powder manufacture 803C/30 s
803C/1 min
803C/2 min
% of denatured whey in milk powder (% of total whey protein) 1 12.2 17.3 29.5 2 13.1 16.0 25.0 3 10.3 19.6 26.8
803C/5 min
853C/2 min
903C/2 min
853C/30 min
31.7 41.0 *
38.8 47.1 42.3
55.0 64.1 61.9
76.5 80.1 82.9
Amount of denatured whey protein in 12% MSNF yogurt (g/100 g yogurt) 1 0.092 0.130 0.222 0.238 2 0.100 0.122 0.198 0.314 3 0.076 0.146 0.198 *
0.292 0.360 0.314
0.412 0.490 0.460
0.574 0.614 0.616
Gel strength of 12% MSNF set yogurt (g) 1 5.0 6.0 2 4.7 5.8 3 7.9 9.2
7.3 5.3 10.8
8.0 8.6 *
8.8 9.0 10.8
9.1 9.3 11.4
9.0 10.9 11.2
Whey drained from 50 g yogurt after 2 h (ml) 1 27.1 26.9 2 24.7 24.6 3 27.5 27.4
26.0 23.6 25.9
23.3 22.3 *
23.5 24.2 24.6
22.4 21.3 22.7
20.6 18.5 20.8
Powder series 1*Powders manufactured on 6/2/96; total protein 35.4%, casein 29.4%, total whey protein 6.0%, non-protein N 0.29%. Powder series 2*Powders manufactured on 23/7/96; total protein 35.8%, casein 29.6%, total whey protein 6.1%, non-protein N 0.37%. Powder series 3*Powders manufactured on 25/10/96; total protein 34.5%, casein 28.5%, total whey protein 5.9%, non-protein N 0.37%.
controlling gel strength and resistance of yogurts to syneresis. Although the relationship between gel strength and denatured whey protein content was similar within a batch of powder, the relationship was not absolute when yogurts were made from di!erent powders. The results suggested that milk components other than protein also in#uenced the strength of the gel network. There was a linear relationship (P(0.001) between whey drainage and denatured whey protein for yogurts made with all powders showing that the denatured whey protein content had the major in#uence on resistance of yogurts to syneresis.
Acknowledgements This work was supported by the Dairy Research and Development Corporation. References Dannenberg, F., & Kessler, H. G. (1988a). E!ect of denaturation of b-lactoglobulin on texture properties of set-style nonfat yoghurt. 1. Syneresis. Milchwissenschaft, 43(10), 632}635. Dannenberg, F., & Kessler, H. G. (1988b). E!ect of denaturation of b-lactoglobulin on texture properties of set-style nonfat yoghurt. 1. Firmness and #ow properties Syneresis. Milchwissenschaft, 43(11), 700}730.
E!ects of preheat treatment of milk powder on the properties of reconstituted set skim yogurts M.A. Augustin*, L.J. Cheng, P.T. Clarke CSIRO Division of Food Science and Technology, Melbourne Laboratory Highett, Vic. 3190, Australia
Abstract Yogurts were prepared on three occasions during a lactation period from reconstituted milk powders which had been subjected to heat treatments of varying severity prior to powder manufacture. A linear relationship was found between whey drainage and extent of whey protein denaturation. A similar trend was found for gel strength and denaturation level but seasonal e!ects confounded this relationship. 1999 Elsevier Science Ltd. All rights reserved. Keywords: Yogurt; Preheat treatment; Milk powders
1. Introduction The gel structure of a set yogurt is in#uenced by many factors including milk composition, season of milk production and the processing conditions during yogurt manufacture, in particular the heat treatment of yogurt milk. It is well established that heat treatment of milk which causes whey protein denaturation is necessary for production of yogurt with "rm texture and resistance to syneresis. Systematic studies on the quantitative e!ects of heat treatment and whey protein denaturation on yogurt characteristics appear to be lacking apart from that by Dannenberg and Kessler (1988a, b) where a clear relationship between heat-induced denaturation of b-lacto-globulin and yogurt characteristics was observed. The aim of this work was to examine the e!ects of preheat treatment of milk on gel strength and syneresis of reconstituted set yogurts made from milk powders produced at di!erent times during the dairying season (February, July and October).
2. Materials and methods Skim milks were subjected to a range of preheat treatments (803C/30 s, 803C/1 min, 803C/2 min, 803C/5 min, * Corresponding author. Tel.: #61-3-9252-6451; fax: #61-3-92526555. E-mail address: [email protected] (M.A. Augustin)
853C/2 min, 853C/5 min, 903C/2 min or 853C/30 min) prior to concentration and drying on three occasions during a dairying season. Milks (12% milk solids non-fat) were reconstituted from these powders, pasteurised at 603C/30 min, inoculated with yogurt cultures (S. thermophilus and L. bulgaricus), fermented at 433C to pH 4.6 and transferred to 43C. Gel strength and syneresis of yogurts were measured on the next day.
3. Results and discussion Yogurts made from February powders (12}77% whey protein denaturation), July powders (13}80% whey protein denaturation) and October powders (10}83% whey protein denaturation) had gel strengths between 5}9, 4.5}11 and 8}11 g, respectively. In yogurts made from powders produced from the same batch of milk, the gel strength increased when the extent of whey protein denaturation was increased from 10 to 40% but whey protein denaturation beyond 40% generally had less of an e!ect on gel strength (Table 1). Increasing whey protein denaturation in powders produced from the same batch of milk reduced syneresis. Whey drainage values from 50 g yogurts after 2 h were 27}20.5, 24.5}18.5 and 27.5}21 ml for February, July and October powders with varying extents of whey protein denaturation (Table 1). These results showed that there were di!erent factors
0958-6946/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 8 - 6 9 4 6 ( 9 9 ) 0 0 1 1 3 - 2
416
M.A. Augustin et al. / International Dairy Journal 9 (1999) 415}416
Table 1 In#uence of milk powder characteristics on the properties of reconstituted set skim yogurts Powder series
Preheat treatment of milk during powder manufacture 803C/30 s
803C/1 min
803C/2 min
% of denatured whey in milk powder (% of total whey protein) 1 12.2 17.3 29.5 2 13.1 16.0 25.0 3 10.3 19.6 26.8
803C/5 min
853C/2 min
903C/2 min
853C/30 min
31.7 41.0 *
38.8 47.1 42.3
55.0 64.1 61.9
76.5 80.1 82.9
Amount of denatured whey protein in 12% MSNF yogurt (g/100 g yogurt) 1 0.092 0.130 0.222 0.238 2 0.100 0.122 0.198 0.314 3 0.076 0.146 0.198 *
0.292 0.360 0.314
0.412 0.490 0.460
0.574 0.614 0.616
Gel strength of 12% MSNF set yogurt (g) 1 5.0 6.0 2 4.7 5.8 3 7.9 9.2
7.3 5.3 10.8
8.0 8.6 *
8.8 9.0 10.8
9.1 9.3 11.4
9.0 10.9 11.2
Whey drained from 50 g yogurt after 2 h (ml) 1 27.1 26.9 2 24.7 24.6 3 27.5 27.4
26.0 23.6 25.9
23.3 22.3 *
23.5 24.2 24.6
22.4 21.3 22.7
20.6 18.5 20.8
Powder series 1*Powders manufactured on 6/2/96; total protein 35.4%, casein 29.4%, total whey protein 6.0%, non-protein N 0.29%. Powder series 2*Powders manufactured on 23/7/96; total protein 35.8%, casein 29.6%, total whey protein 6.1%, non-protein N 0.37%. Powder series 3*Powders manufactured on 25/10/96; total protein 34.5%, casein 28.5%, total whey protein 5.9%, non-protein N 0.37%.
controlling gel strength and resistance of yogurts to syneresis. Although the relationship between gel strength and denatured whey protein content was similar within a batch of powder, the relationship was not absolute when yogurts were made from di!erent powders. The results suggested that milk components other than protein also in#uenced the strength of the gel network. There was a linear relationship (P(0.001) between whey drainage and denatured whey protein for yogurts made with all powders showing that the denatured whey protein content had the major in#uence on resistance of yogurts to syneresis.
Acknowledgements This work was supported by the Dairy Research and Development Corporation. References Dannenberg, F., & Kessler, H. G. (1988a). E!ect of denaturation of b-lactoglobulin on texture properties of set-style nonfat yoghurt. 1. Syneresis. Milchwissenschaft, 43(10), 632}635. Dannenberg, F., & Kessler, H. G. (1988b). E!ect of denaturation of b-lactoglobulin on texture properties of set-style nonfat yoghurt. 1. Firmness and #ow properties Syneresis. Milchwissenschaft, 43(11), 700}730.