The effects of composition and some processing treatments on the rennet coagulation properties of milk

Abstract

The effects of various processing parameters on the rennet coagulation properties of milk were assessed. Using low amplitude oscillation rheometry, the coagulation properties were monitored by measurement of the elastic shear modulus, G', as a function of time, t, from rennet addition; Gapos; was taken as a measure of curd firmness. The Scott‐Blair time dependency model was fitted to the experimental G' It curves for the determination of the following coagulation parameters: gel time, maximum curd firming rate, the set‐to‐cut time at 20 Pa (ie, time to reach 20 Pa) and the curd firmness after a renneting time of 2400 s. The renneting properties were enhanced by increasing the levels of milk protein and fat in the ranges 0.3–7.0% (w/w) and 0.1–10% (w/w) respectively and by two stage homogenization pressure where the first stage pressure, P1, was varied from 0 to 25 MPa and the second stage pressure, P2, was held constant at 5 MP a. The influence of these parameters, within the range investigated, in complementing the gel forming properties decreased in the following order: protein > fat > homogenization pressure. In contrast, the coagulation properties of milk were impaired by high heat treatment, the addition of a commercial microparticulated whey protein based fat substitute and by partial replacement of protein with fat.

Acid coagulation behavior of homogenized milk: effect of interacting and non-interacting droplets observed by rheology and diffusing wave spectroscopy

“…Even though the fat globule is not entirely covered with caseins (there are still some non-interacting material such as fat globule membrane and whey proteins), the presence of the caseins is enough to cause these droplets to become an active interacting particle in the formation of the milk gel. These results have been observed previously by other authors (Guinee et al 1997;Lucey et al 1998b;van Vliet and Dentener-Kikkert 1982). It has been in fact reported that unheated skim milk containing 3.5% fat had a higher, albeit small, modulus compared to milk gels made with skim milk (Lucey and Singh 1998).…”

Pre-treatment of cheese milk: principles and developments

“…Lucey and Gorry [89] reported that a commercial microparticulated milk protein had little effect on rennet coagulation; however, Fenelon and Guinee [34] and Guinee et al [49] reported impaired rennet coagulation properties, with lower curd-firming rates and curd firmness after a fixed renneting time, possibly due to the denatured protein content or dilution of the casein, i.e., the active gel forming component. Addition of microparticulated whey protein resulted in reduced-fat Cheddar with increased moisture and MNFS contents, higher yields, probably due to hydrated whey proteins, lower firmness, but had little effect on or slightly reduced levels of proteolysis and flavour grades [34,89].…”

Formation of heat-induced protein aggregates in milk as a means to recover the whey protein fraction in cheese manufacture, and potential of heat-treating milk at alkaline pH values in order to keep its rennet coagulation properties. A review

“…The heat-treatment of cheese milk for reasons of food safety or for the recovery of the whey proteins generally induces an increase in the rennet coagulation time (RCT); this is also true when a mixture of already denatured and aggregated whey protein and milk is heated [60]. The formation of heat-induced aggregates of denatured whey proteins and κ-casein on the surface of the casein micelles seems responsible for the inhibition of the renneting process in heated cheese milk [114,120,164].…”

“…The curds of Cheddar cheeses made with heated milk are generally crumbly, and can be difficult to process mechanically [10,12,102]. The firmness of fresh curds, obtained by renneting heated milk at pH 6.6, was reported to be inversely correlated to the rate of whey protein denaturation [60], although increased heating temperature from 80 to 130°C prior to the manufacture of Mozzarella cheese (renneting pH 5.6) resulted in greater firmness of the cheeses, possibly as a result of a bias with the solid-not-fat content [132]. The firmness of ripened Cheddar cheeses made with heated milk generally compared with cheeses made with pasteurised milk [10,12,13].…”