High heat treatment

The properties of many dairy products, in fact their very existence, depend on the properties of milk proteins, although the fat, lactose and especially the salts, exert very significant modifying influences. Casein products are almost exclusively milk protein while the production of most cheese varieties is initiated through the specific modification of proteins by proteolytic enzymes or isoelectric precipitation. The high heat treatments to which many milk products are subjected are possible only because of the exceptionally high heat stability of the principal milk proteins, the caseins. 

However, an inhibitory effect of high heat treatment on the oxidative deterioration of milk and milk products has been reported by many investigators who have attributed this effect to the activation of thiol groups (Josephson and Doan, 1939 Tamsma et al., 1962 Wilson and Herreid, 1969 Schwartz and Parks, 1974 Baldwin and Ackland, 1991 Saidi and Warthesen, 1995 Tong et al., 2000). The principal sources of thiols in milk are the fat globule membrane (McPherson and Kitchen, 1983) and the serum proteins, particularly (3-lactoglobulin (Larsson and Jenness, 1950 Schwartz and Parks, 1974). 

The char precursors were carbonized at 823 K for 90 minutes under a nitrogen pressure of 0.68 MPa in tubing bomb reactors. The carbonaceous residues were subsequently heat treated at 1273 K for 1 hour under argon in a tube furnace to drive off residual volatile matter. The carbonization was conducted to increase char yield direct heat treatment of the precursors would result in very low char yeilds. The high heat treatment temperature was chosen to ensure that at the lower temperature used in the oxidation experiments, there would be no volatile material, thus ensuring that the reaction was heterogeneous. 

Bulca, S., Leder, J., and Kulozik, U. (2004). Impact of UHT or high heat treatment on the rennet gel formation of skim milk with various whey protein contents. Milchwissenschaft 59, 590-593. 

The strength of renneted milk gels (curd tension, CT) is very important, especially from the viewpoint of cheese yield. This subject has been reviewed (Fox, 1984 Green and Grandison, 1993). Suffice it to say here that curd tension is positively affected by protein concentration, [Ca +], and reduced pH to —5.9 and adversely by high heat treatments. Thus, CT is affected by the same variables that affect rennet coagulability. 

The addition of milk protein coprecipitates (produced by high heat treatment of milk followed by acidification and calcium addition), at levels up to 5% of the blend, to processed Cheddar yielded products with increased firmness and sliceability and lower meltability and a reduced propensity to nonenzymatic browning (Thomas, 1970). However, the level at which meltability became noticeably impaired varied from 0.25 to 3.0% and varied with the source of the coprecipitate. 

In the case of FDA-derived Co catalysts (Fig. 8.18b), the EXAFS of not heat-treated sample shows the presence of one major peak around the R values of ca. 1.2 A. That peak can be assigned the Co-N interactions. The Co-N peak weakens and the Co-Co peak becomes more apparent with an increase in the heat-treatment temperature. The CoN chelate complexes decompose at high heat-treatment temperatures, 800 °C and higher, which results in the formation of metallic Co species. As a consequence, the Co-N structure is no longer dominant in both heat-treated PANI- and EDA-derived Co catalysts. 

High heat treatment of milk exposes free thiol groups that autoxidize to form diiyl radicals, Oj and HjOj. Thiols may exert an indirect prooxidmit effect through this mechanism (4). The thiols are mainly derived from modification of the milk flit globule membrane and the serum proteins, particularly P-lactoglobulin. In freeze-dried milk proteins, radicals were detected by ESR spectroscopy, and spectral characteristics were consistent with carbon-centered radicals (7). 

Biodegradable plastics based on soy protein were prepared with glycerol as a plasticizer and compounded wi different additives such as polycaprolactone and zinc stearate as well as heat treated at various temperatures after the injection molding process in order to characterize base material strength and the effect of water absorption. The results indicated that the polycaprolactone and, respectively a medium to high heat treatment enhanced the tensile strength and decreased the water absorption significantly. 

---