Titrimetric studies on milk and milk products

Abstract

Potentiometric acid-base titration is a simple method that can be used successfully in the investigation of the protein system of milk and other proteincontaining products. Its applications include the examination of conventional heating procedures, cheese ripening, the investigation of processed cheese and the effect of melting salts. The principle depends on the performance of pH-dependent phase transitions which are recorded by a single titration cycle and evaluated quantitatively by means of hysteresis loops.An unusual feature of some proteins and nucleic acids is the existence of hysteresis phenomena in their pH titrations in the acid range. The proton-binding vs. pH data lie on one curve when the pH is lowered by addition of acid, and on a different curve when the pH is raised by addition of base. One thus obtains a closed loop. The loop exists between definite pH limits, while above and below these limits only a single reversible curve is observed. Hysteresis loops for milk reflect non-equilibrium transitions within the system. RESULTSThe succession of buffering capacities (Kirchmeier, 1976(Kirchmeier, , 1977a shown by milk and by acid casein during acidification from pH 8-6 to 3-6 differed from those exhibited during subsequent back-titration with alkali, the latter being characterized by the occurrence of marked hysteresis between pH 5-0 and 6-5. The degree of hysteresis was greater in heated than in unheated milk and increased with increasing heat treatment. It is apparently due to conformational changes in the casein complex induced by acidification and heat treatment. Hysteresis in a milk system can thus furnish information about its thermal history. Fig. 1 shows acid titration curves of raw milk and milk after different heating procedures in a sealed tube. The maxima of the titration curves are shifted towards lower pH values for longer heating times. This means that higher energy barriers have to be overcome for the protonation process. At higher temperatures the surface of the micelles are covered progressively with serum proteins. Due to this coating additional diffusion barriers are constructed and the diffusion rate of the protons into the interior of the micelles is measurably retarded. The resulting expansion of the hysteresis loop can be determined quantitatively.

Making Kareish Cheese With High With Added Sesame Hulls

“…The acid base titration of cheese samples and measurement of hysteresis loop was carried out the modified method of Kirchmeier (1979). Total phenols in kareish samples from different treatments were determined by folin-ciocalteauʼs reagent as described by Amous et al, (2001).…”

Effect of Cardamom, Thyme and Clove Powder on the Composition and Quality of White Soft Cheese Made From Goat's Milk

“…Total volatile fatty acids (TVFA) were determined by the direct distillation method as described by Kosikowski, (1978), and values are expressed as ml 0.1 NaOH/100gm cheese. The acidbase titration of cheese samples and measurement of hysteresis loop was carried out the modified method of Kirchmeier (1979). The quantitative measurement of hysteresis is performed with the closed integration of (  αdpH) which represent the hysteresis area.…”

Advanced Dairy Chemistry Volume 3

“…There are many reports on the buffering of milk (Buchanan and Peterson, 1927;Whittier, 1933;Wiley, 1935a,b;Jenness and Patton, 1959;Kirchmeier, 1979Kirchmeier, , 1980Unnikrishnan and Doss, 1982;Miyagawa and Namba, 1988;Sherban, 1988;Srilaorkul et a/., 1989;Lucey, 1992;Lucey et al, 1993a) and of cheese (Ollikainen, 1990;Lucey and Fox, 1993;Lucey eta/., 1993c), calculated from titration curves. However, the titration curve obtained depends on the methodology used, e.g.…”