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Effect of milk pH at heating on protein complex formation and ultimate gel properties of free-fat yoghurt

Abstract

The effect of milk pH before heating on casein–whey protein interactions and ultimate gel properties of the free-fat yoghurt was investigated. Reconstituted skim milk at different pH values (6.4, 6.8 and 7.2) was heated at 80 °C for 30 min. The type of protein and size of casein micelle in milk were determined. The storage modulus (G′), loss tangent (tan δ), flow behaviour as well as microstructure, firmness and water holding capacity of the yoghurt samples were measured. Heating milk at pH 7.2 formed mostly soluble protein complexes whereas at pH 6.4 micelle bound complexes was dominant. However, heating milk at pH 6.8 resulted in a relatively compact protein network due to a balanced contribution from both soluble protein/κ-casein complexes and whey protein-casein micelle associated complexes. Yoghurt prepared with milk heated at pH 6.8 showed significantly higher G′ values, shorter gelation times, higher water holding capacity, firmness and more compact protein network compared to those at pH 6.4, 7.2 and unheated milk. The obtained results demonstrated that milk pH adjustment before heating could be an important factor governing uniform quality yoghurt production.

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Acknowledgements

The authors gratefully acknowledge the financial support of Japanese Government through the MEXT fellowship for the PhD program of first author. We are thankful to Prof. Takahisa Nishizu at the Department of Applied Life Science in Gifu University for his support in using the rheometer, zeta sizer and confocal microscopy. This research did not receive any specific Grants from funding agencies in the public, commercial, or not-for-profit sectors.

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Correspondence to Md Asaduzzaman.

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Mahomud, M.S., Haque, M.A., Akhter, N. et al. Effect of milk pH at heating on protein complex formation and ultimate gel properties of free-fat yoghurt. J Food Sci Technol 58, 1969–1978 (2021). https://doi.org/10.1007/s13197-020-04708-8

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  • DOI: https://doi.org/10.1007/s13197-020-04708-8

Keywords

  • Milk pH
  • Protein complexes
  • Rheology
  • Microstructure
  • Yoghurt texture