Lipoprotein lipase and lipolysis in milk

Bovine milk contains a lipoprotein lipase that accounts for most, if not all, of its lipolytic activity. The total lipase activity in raw milk is sufficient to cause rapid hydrolysis of a large proportion of the fat. However, in reality this does not happen, because the lipase is prevented from accessing the fat by the milkfat globule membrane. Physical damage to this membrane in raw milk initiates lipolysis. Furthermore, simply cooling certain individual milks soon after secretion can initiate the so-called spontaneous lipolysis. The biochemical basis of spontaneous lipolysis is still poorly understood, but it appears to be related to a balance between activating and inhibiting factors in the milk. Lipolysis in milk and milk products causes rancid off-flavours and other problems, and is a constant concern in the dairy industry. A thorough understanding of the mechanism of lipolysis and constant vigilance by operatives is required to minimize lipase-related problems. (c) 2006 Elsevier Ltd. All rights reserved

Electrical heating using 'current passage tube' technology

Current passage tube technology is a heating technology in which a stainless steel tube carrying a pumpable food product is connected to low-voltage, high-amperage electrical power and heated due to the resistance of the tube. The heat is transferred to the product flowing in the tube by conduction and convection. A unique feature of the technology is the constant temperature differential between the wall of the tube and the product along the length of the tube. This causes less chemical change in the product than conventional heat exchangers which, in the case of UHT processing of milk, results in less burn-on, and hence reduced cleaning and better flavour of the final product

Methods for detecting lipase activity in milk and milk products

Methods for detecting lipase activity in milk and milk products are reviewed. They include titrimetric, colorimetric, fluorimetric, turbidometric, chromatographic, radiometric, enzymatic, physical and immunological procedures. Titrimetric methods using triacylglycerols, such as milkfat and triolein, as substrates provide reliable results but lack sensitivity and are time-consuming. Colorimetric methods using substrates such as B-naphthyl esters, fluorimetric methods using 4-methylumbelliferyl esters, and turbidity clearing methods based on tributyrin are rapid and suitable for screening purposes. However, differences in the specificities of the target lipases towards these substrates and the natural substrate, milkfat, and interference from fat and protein in the enzyme source, limit their usefulness for predicting lipolytic changes in milk and milk products. Assays involving triacylglycerols, such as milkfat, as substrates, and determination of the reaction products by chromatographic (GC or HPLC) means are the most reliable for predictive purposes. The suitability of several other reported methods for detecting low levels of lipase activity has not been established for milk and milk products; some of these warrant further investigation

Alternative technologies for producing sterile low acid food products

Four emerging high-energy non-thermal technologies may replace or augment heating for producing sterile low-acid food products. High pressure, high-voltage pulsed electric field, high-energy ultrasound and high-intensity pulsed light are all capable of reducing bacterial spore counts under certain conditions. However, only non-continuous high pressure treatments, at temperatures higher than ambient, are currently capable of completely inactivating spores and producing sterile food products. The first three technologies also reduce the resistance of spores to inactivation by heat

High pressure processing of milk and dairy products

The application of high-pressure processing to foods has attracted considerable research and commercial interest in recent years. High pressure disrupts non-covalent bonds in macromolecules, such as proteins and polysaccharides, causing denaturation, aggregation and gelling, but has little or no effect on small molecules responsible for the flavour, colour and nutritive value of foods. Vegetative micro-organisms and, under certain conditions, bacterial spores, are destroyed without accompanying detrimental chemical changes caused by heat. High-pressure treatment of milk at similar to 600 MPa destroys most vegetative micro-organisms and greatly increases its shelf-life. Through changes in the milk proteins, it also affects other characteristics of the milk, and the yield and nature of products such as cheese produced from it. The process has been in commercial use since 1990, with yogurt being the major dairy product treated. The unique physical and sensory properties of pressure-processed foods offers new opportunities for new product development in the dairy industry. This paper reviews the principles, equipment, effects and applications of high-pressure processing of foods, with particular emphasis on milk and dairy products

Age gelation of UHT milk - A review

Gelation of UHT milk during storage (age gelation) is a major factor limiting its shelf-life. The gel which forms is a three-dimensional protein matrix initiated by interactions between the whey protein beta -lactoglobulin and the kappa -casein of the casein micelle during the high heat treatment. These interactions lead to the formation of a beta -lactoglobulin-kappa -casein complex (beta kappa -complex). A feasible mechanism of age gelation is based on a two-step process; in the first step, the beta kappa -complexes dissociate from the casein micelles due to the breakdown of multiple anchor sites on kappa -casein, and in the second step, these complexes aggregate into a three-dimensional matrix. When a critical volume concentration of the beta kappa -complex is attained, a gel of custard-like consistency is formed. Significant factors which influence the onset of gelation include the nature of the heat treatment, proteolysis during storage, milk composition and quality, seasonal milk production factors and storage temperature. In this review, age gelation is discussed in terms of these factors, causative mechanisms and procedures for controlling it

Survival of probiotics encapsulated in chitosan-coated alginate beads in yoghurt from UHT- and conventionally treated milk during storage

Survival of the microencapsulated probiotics, Lactobacillus acidophilus 547, Bifidobacterium bifidum ATCC 1994, and Lactobacillus casei 01, in stirred yoghurt from UHT- and conventionally treated milk during low temperature storage was investigated. The probiotic cells both as free cells and microencapsulated cells (in alginate beads coated with chitosan) were added into 20 g/100 g total solids stirred yoghurt from UHT-treated milk and 16 g/100 g total solids yoghurt from conventionally treated milk after 3.5 h of fermentation. The products were kept at 4 degrees C for 4 weeks. The survival of encapsulated probiotic bacteria was higher than free cells by approximately 1 log cycle. The number of probiotic bacteria was maintained above the recommended therapeutic minimum (10(7) cfu g(-1)) throughout the storage except for R bifidum. The viabilities of probiotic bacteria in yoghurts from both UHT- and conventionally treated milks were not significantly (P > 0.05) different. (c) 2004 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved

Effect of storage time and conditions on the seed coat colour of Australian adzuki beans

Two varieties of adzuki beans (Vigna angularis), Bloodwood and Erimo, were stored at temperatures of 10, 20 or 30degreesC, and relative humidities (RH) 40 or 65%, and samples were analysed at 0, 1.5, 3 and 6 months. Storage at 30degreesC for > 1.5 months caused a significant decrease in the a(star) and b(star) colour values and darkening of the seed coat. Beans stored at 65% RH had lower L-star but higher a(star) and b(star) colour values than those stored at 40% RH. Bloodwood and Erimo samples showed similar trends in colour during storage. The best storage conditions for the preservation of the adzuki colour were 10degreesC and 65% RH. The Australian beans had lower L-star, a(star) and b(star) colour values than Japanese Erimo-shouzu beans and storage increased the difference