Influence of pH and NaCl on rheological properties of rennet-induced casein gels made from UF concentrated skim milk |
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Affiliation: | 1. Agrosup Dijon, UMR PAM 02.102, Equipe PAPC (Procédés Alimentaires et Physico Chimie), 1 Esplanade Erasme, 21000 Dijon, France;2. GIP AgroSup Tech Est, ENILBIO Poligny, Rue de Versailles, 39801 Poligny Cedex 1, France;1. The ARC Dairy Innovation Hub, The University of Melbourne, Parkville, Victoria 3010, Australia;2. School of Chemistry, The University of Melbourne, Parkville, Victoria 3010, Australia;3. Department of Chemical Engineering, The University of Melbourne, Parkville, Victoria 3010, Australia;1. INRA, UMR1253, Science et Technologie du Lait et de l''?uf, 65 rue de St Brieuc, F-35 042 Rennes Cedex, France;2. AGROCAMPUS OUEST, UMR 1253, Science et Technologie du Lait et de l''?uf, 65 rue de St Brieuc, F-35 042 Rennes Cedex, France;3. Faculty of Agriculture Industrial Technology, Padjadjaran University, Indonesia;1. Riddet Institute, Massey University, Private Bag 11222, Palmerston North, New Zealand;2. Fonterra Research and Development Centre, Palmerston North, New Zealand;3. Dairy Technology Division, National Dairy Research Institute, Karnal 132001, Haryana, India |
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Abstract: | Milk concentrates are used in the production of cast cheese. The effects of pH (5.19–6.21) and NaCl concentration (0, 1.75% and 3.50%, w/w) on the rheological and microstructural properties of rennet-induced casein gels made from ultra filtered skim milk (19.8%, w/w casein) were investigated. Low pH and high NaCl concentration reduced the development rate of the gel elasticity after coagulation of the ultra filtrated skim milk. Strain at fracture and stress at fracture from uniaxial compression of casein gels 48 h after coagulation showed maximum and minimum values at pH ~5.8 and 5.29, respectively. Young's modulus from uniaxial compression of the same gels was almost constant between pH 5.52 and 6.21 but much lower at pH 5.28. Addition of NaCl resulted in increased Young's modulus in the interval pH 6.21–5.52. As pH decreased, the level of colloidal calcium phosphate decreased concomitantly, giving less cross-links in the casein network and partly explaining the changes in the rheological properties. Increased ionic strength by adjusting pH and addition of NaCl also influenced rheological results. The microstructure examined with confocal laser-scanning microscopy was unaffected by the changes in pH and concentrations of NaCl in the range studied as revealed by image analysis and calculations of two- and three-dimensional data from micrographs. |
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