Acid milk gels

Heertje, I., Visser, J., Smits, P. 1985. Structure formation in acid milk gels. Food Microstruct. 4, 267-277. 

Aichinger, P.A., Dillmann, M.L., Rami-Shojaei, S., Michel, M. and Home, D.S. (2006). Xan-than gum in skim milk designing stmcture into acid milk gels. In E. Dickinson and M.E. Leser. Food Colloids Self-Assembly and Material Science, Royal Society of Chemistry, Cambridge, pp. 283-296. 

Lucey, J.A., and Singh, H. (1997) Formation and physical properties of acid milk gels a review. Food Res. Ini. 30, 529 542. 

Figure 6. Effect of MTG treatment on water-holding capacity of the acid milk gel (set-type yogurt). MTG was added to reconstituted milk solution and incubated at 25 C for 2 hr. After enzyme reaction, the lactic starter was added, and the acid milk gel, set-type yogurt, was prepared after 4-6 hr fermentation.

The pH and the concentration of calcium in milk also vary, with consequential effects on the properties of renneted milk gels. The addition of CaCl2 to cheesemilk (0.02%) is widely practised and adjustment and standardization of milk pH by using the acidogen, gluconic acid-5-lactone (GDL), is recommended and commercially practised on a limited scale. 

Although the gelation properties of whey proteins are of great importance in many foods (Mulvihill, 1992) and it is possible to form a weak gel in creams by the formation of a continuous network of fat globules, most important milk gels are those involving casein micelles which can be made to form a gel matrix either by isoelectric precipitation (acid-induced gel) or by the action of a proteolytic enzyme (rennet-induced gel). Both gel types... 

Lucey, J.A., Tamehana, M., Singh, H., and Munro, P.A. 1998. A comparison of the formation, rheological properties and microstructure of acid skim milk gels made with a bacterial culture or glucono-delta-lactone. Food Res. Imernatl. 31 147-155. 

Despite experimental progress, the mechanisms and kinetics of acid milk gelation are still not fully understood. Theoretical approaches such as the adhesive sphere, percolation or fractal model applied to acid-induced milk gel formation can successfully explain specific aspects of the process (Tuinier and Kruif 1999), but all fail in rationalizing its kinetics (Home 1999). 

Milk gels can be made by the combined action of rennet and acid. With the combined action of acid and rennet, gels can be made over a broader pH and temperature range than by acidification alone, with both the pH and rermet action influencing the resulting gel properties (Roefs et al., 1990). 

Xiong, Y.L.L., Aguilera, J.M., and Kinsella, J.E. (1991). Emulsified milkfat effects rheology of acid-induced milk gels. J. Food Sci. 56,918-925. 

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