The Clarifying Reagent, or how to make the analysis of milk and dairy products easier
Difficulties with the analysis of opaque milk and dairy products can be resolved by rendering the sample transparent. This allows direct photometric measurements of the reaction mixtures, and all sample pre-treatment steps become unnecessary. For this, several reagents have been reported in literature. Among them, the ‘Clarifying Reagent’ is mainly described here: its composition is given because it is now released from patenting restrictions. Its main property is a low absorbance between 340 and 800 nm. So it can be used in many chemical and enzymatic colorimetric measurements for estimating the quality of milk and dairy products.
Effect of Lenient Steam Injection (LSI) heat treatment of bovine milk on the activities of some enzymes, the milk fat globule and pH
This study investigated the effects of Lenient Steam Injection (LSI) treatment at temperatures 70–150 °C on the enzymatic activities of the indigenous milk enzymes alkaline phosphatase, lactoperoxidase (LPO), xanthine oxidase (XO), lipoprotein lipase (LPL) and plasmin in comparison with two reference heat treatments of 63 °C for 30 s and of 72 °C for 15 s by indirect heating. Milk fat globule (MFG) size distributions and pH were also monitored. Alkaline phosphatase, LPO, XO and LPL activities decreased with increasing LSI temperature. Plasmin activity was increased at temperatures <80 °C and decreased at temperatures above 90 °C. Milk fat globule homogenisation was observed at temperatures above 110–130 °C.
Enzymes of psychrotrophic bacteria and their effects on milk and milk products
The widespread adoption of refrigerated storage of bulk raw milk at the farm, and its subsequent delivery to the processing creamery in large insulated road tankers, has largely eliminated spoilage associated with the growth of lactic acid bacteria and most pathogens. This handling system also has direct economic advantages such as reduced unit costs for transport and uniformity of supply (reviewed recently by Sinclair, 1979; Ellemor, 1979). However, despite these advantages, the storage and handling of milk at refrigeration temperatures is selective for psychrotrophic bacteria which have considerable spoilage potential. The organisms can multiply at or below 7 °C, irrespective of their optimum growth temperature, and the increase in total counts observed during prolonged storage of raw milk < 7 °C is caused by multiplication of its psychrotrophic flora (Thomas, 1974; Cousins, Sharpe & Law, 1977). Although most raw milk psychrotrophs are heat-sensitive Gram-negative rods, some heat-resistant Gram-positive species have also been isolated (Shehata & Collins, 1971; Bhadsavle, Shehata & Collins, 1972; Washam, Olson & Vedamuthu, 1977). These latter organisms may cause spoilage of stored heat-treated milk or milk products by their growth, but the involvement of specific enzymes has not been reported. The psychrotrophic Gram-negative bacteria in raw milk are not present in heat-treated milk or milk products and do not themselves cause spoilage (other than as postpasteurization contaminants) but many species produce heat-resistant extracellular enzymes capable of degrading important milk constituents. This review describes the production and properties of these enzymes and considers their effects both in raw milk itself, and in products made from the milk after it has been heat treated.