Martin Palmer

Hot topic: sonication increases the heat stability of whey proteins.

The thickening or gelling of protein-based dairy streams and ingredients upon exposure to heat has been an ongoing problem in dairy processing for many decades. This phenomenon can restrict the range of dairy product options and reduce manufacturing efficiencies by limiting the type and extent of heat treatment that can be used. In this report, we outline a novel approach to overcoming this problem. The use of preheating treatments to induce whey protein aggregate formation in whey products is well known in the field. However, we show that the application of ultrasound for a very short duration after such a heating step breaks down these aggregates and prevents their reformation on subsequent heating, thereby reducing the viscosity increase that is usually associated with this process. This novel technique has the potential to provide significant economic benefit to the dairy manufacturing industry.

Effects of emulsion droplet sizes on the crystallisation of milk fat.

The crystallisation properties of milk fat emulsions containing dairy-based ingredients as functions of emulsion droplet size, cooling rate, and emulsifier type were investigated using a differential scanning calorimeter (DSC). Anhydrous milk fat and its fractions (stearin and olein) were emulsified with whey protein concentrate, sodium caseinate, and Tween80 by homogenisation to produce emulsions in various size ranges (0.13-3.10 μm). Particle size, cooling rate, and types of emulsifier all had an influence on the crystallisation properties of fat in the emulsions. In general, the crystallisation temperature of emulsified fats decreased with decreasing average droplet size and was of an exponent function of size, indicating that the influence of particle size on crystallisation temperature is more pronounced in the sub-micron range. This particle size effect was also verified by electron microscopy.

Properties of acid whey as a function of pH and temperature

Compositional differences of acid whey (AW) in comparison with other whey types limit its processability and application of conventional membrane processing. Hence, the present study aimed to identify chemical and physical properties of AW solutions as a function of pH (3 to 10.5) at 4 different temperatures (15, 25, 40, or 90°C) to propose appropriate membrane-processing conditions for efficient use of AW streams. The concentration of minerals, mainly calcium and phosphate, and proteins in centrifuged supernatants was significantly lowered with increase in either pH or temperature. Lactic acid content decreased with pH decline and rose at higher temperatures. Calcium appeared to form complexes with phosphates and lactates mainly, which in turn may have induced molecular attractions with the proteins. An increase in pH led to more soluble protein aggregates with large particle sizes. Surface hydrophobicity of these particles increased significantly with temperature up to 40°C and decreased with further heating to 90°C. Surface charge was clearly pH dependent. High lactic acid concentrations appeared to hinder protein aggregation by hydrophobic interactions and may also indirectly influence protein denaturation. Processing conditions such as pH and temperature need to be optimized to manipulate composition, state, and surface characteristics of components of AW systems to achieve an efficient separation and concentration of lactic acid and lactose.

Effect of solubilised carbon dioxide at low partial pressure on crystallisation behaviour, microstructure and texture of anhydrous milk fat

The crystallisation and melting behaviour, fat polymorphs, microstructure and texture of anhydrous milk fat (AMF) was investigated in the presence of dissolved CO2 (0-2000ppm) under two crystallising conditions (non-isothermal versus isothermal). CO2 was found to induce higher onset crystallisation temperature during cooling from 35 to 5°C at 0.5°Cmin-1. X-ray scattering analysis showed that, in the presence of dissolved CO2, this rapid crystallisation caused the formation of unstable, α polymorph fat crystals. For milk fat crystallised under isothermal condition at 25°C for 48h, dissolved CO2 improved solid fat content, slightly depressed melting temperature and exhibited a sharper melting peak. Microstructure of AMF visualised by Polarised light microscopy of crystallised AMF showed that increasing dissolved CO2 concentration was associated with smaller crystal size and greater crystal number. The bulk properties of the fat appeared to mirror the microstructural differences, in that the texture of CO2-treated AMF was harder under isothermal condition but became softer than untreated AMF under cooling condition. The results of this study are of significance in understanding how CO2 treatment might be used to modulate the crystallisation behaviour of milkfat and thereby the structural development and physical functionality of fat-containing dairy products.

Effect of Milk Fat Globule Size on the Physical Functionality of Dairy Products

Effect of Milk Fat Globule Size on the Physical Functionality of Dairy Products provides a comprehensive overview of techniques utilized to vary milk fat globule size in fat-structured dairy products. The text aims to highlight the importance of both native and emulsified milk fat globule size in the processing and functionality of these products. Both herd managements strategies and fractionation techniques utilized to vary milk fat globule size are covered thoroughly, as are the effects of mechanical sheer processing. The influence of different size fat globules on aspects such as TAG composition, physical stability, viscosity, crystallization properties and electric conductivity are studied, as are the influences on processability and function. This Brief aims to highlight the importance of milk fat as a determinant of the microstructural, rheological and sensorial properties of fat-containing dairy products such as milk, cream, yogurt, ice cream, cheese, butter and milk chocolate. Since milk fat globules have a widely varied size distribution, controlling their size is of major importance in processing. In comprehensively covering the various methods used to vary milk fat globule size, this text serves as an important resource for those involved in dairy product processing.

Investigation of solubility of carbon dioxide in anhydrous milk fat by lab-scale manometric method

This study aims to examine the solubility of CO2 in anhydrous milk fat (AMF) as functions of partial pressure, temperature, chemical composition and physical state of AMF. AMF was fractionated at 21°C to obtain stearin and olein fractions. The CO2 solubility was measured using a home-made experimental apparatus based on changes of CO2 partial pressures. The apparatus was found to be reliable as the measured and theoretical values based on the ideal gas law were comparable. The dissolved CO2 concentration in AMF increased with an increase in CO2 partial pressure (0-101kPa). The apparent CO2 solubility coefficients (molkg-1Pa-1) in the AMF were 5.75±0.16×10-7, 3.9±0.19×10-7 and 1.19±0.14×10-7 at 35, 24 and 4°C, respectively. Higher liquid oil proportions resulted in higher CO2 solubility in the AMF. There was insignificant difference in the dissolved CO2 concentration among the AMF, stearin and olein fractions in their liquid state at 40°C.

Effect of Milk Fat Globule Size on Physical Properties of Milk

Within the wide size range of MFG, the smallest globules are approximately 100-fold smaller in diameter compared to the largest ones. For the same bulk volume of fat, milk, with smaller MFG will have a higher total number of MFG. Within these milks, the smaller MFG will tend to have greater surface curvature, and a larger surface area/volume ratio, compared to larger MFG. These differences can give rise to marked differences in the physical properties of MFG size-differentiated milk and milk fat as summarised in Fig. 6.1.

An Overview of Milk Fat Globules

Assembly, growth and secretion of MFG takes place in the milk-secreting cells of the mammary gland of mammals. In the original state, tiny intracellular lipid droplets (<0.5 μm) are formed at the endoplasmic reticulum membranes, which is the site of origin of TAGs. These discrete small droplets have a TAG core coated by a single layer of polar lipids and proteins. They migrate from the endoplasmic reticulum to the cytosol, fuse together and form bigger droplets (Heid and Keenan 2005; Deeney et al. 1985). The formation of these cytoplasmic lipid droplets by droplet-droplet fusion is assumed to be governed by calcium and protein complexes originating from the cytosol and fusion-promoting agents, gangliosides (Valivullah et al. 1988). However, the coalescence of cytoplasmic lipid droplets to form larger droplets is not facilitated. It is assumed that the regulation of droplet size might be associated with the difference in composition of surface coat between the micro-lipid and cytoplasmic lipid droplets (Deeney et al. 1985). The lipid droplets are then transported to the apical plasma membrane in which they are discharged from the epithelial cell and secreted. At this point the lipid droplets are progressively coated by the plasma membrane to form the outer bilayer milk fat globule membrane (MFGM), rendering the final trilayer structure of intact MFGM upon secretion (Heid and Keenan 2005) (Fig. 2.1). With its dense protein coat (10–50 nm thick) and complex molecular organization, the MFGM is considered to be a true biological membrane (Keenan and Mather 2006) (Fig. 2.1). The MFGM is enriched in polar lipids and also possesses size-related biochemical and structural differences (Lopez 2011).

Techniques to Measure Milk Fat Globule size

The first micrograph of MFGs was captured by Van Leeuwenhoek in 1674 using primitive microscopy (Kernohan and Lepherd 1969). Microscopy is a useful technique as it not only provides measurements of individual MFG size but also visualises shape, distribution and microstructure of MFG, MFGM and fat crystals (Truong et al. 2015; Ong et al. 2010; Precht 1988). Along with microscopy numerous techniques such as Coulter counting (Cornell and Pallansc 1966; Walstra and Oortwijn 1969), laser diffraction, static and dynamic light scattering (Michalski et al. 2001; Robin and Paquin 1991; McCrae and Lepoetre 1996), spectroscopy, ultrasound (Miles et al. 1990), scanning flow cytometry (Konokhova et al. 2014) and electroacoustics (Wade and Beattie 1997) have been employed to estimate the size and size distribution of MFG. These techniques yield complex primary data, which need to be processed mathematically to obtain MFG size data (Huppertz and Kelly 2006). Among these techniques, particle size analysis by small angle light scattering is now widely used to measure MFG size and its distribution.

Effect of Milk Fat Globule Size on Functionalities and Sensory Qualities of Dairy Products

Milk fat globules, along with casein micelles and whey protein, are three main supramolecular constituents of bovine milk. The characteristic physical and chemical properties of the wide variety of dairy products that can be made from milk can, to a large extent, be related back to the fundamental properties of each of these constituents in the product mix (Fig. 7.1). Thus the chemical composition and physical properties of milk fat globules, many of which are size-dependent, can be expected to impact on the physical functionality, texture and flavour of a range of fat-containing dairy products, such as liquid milk, cheese, yoghurt, ice cream and butter (Fig. 7.2). Depending on their size and native state along with their interaction with other components of milk (mainly casein), utilisation of differentiated-size MFG can be exploited to improve the quality of dairy products. The following section describes the impact of MFG size on the physical functionality and sensory quality of selected fat-structured dairy products.