1.1 Problem definition
Fonterra companies make more than 30,000 tonnes of processed cheese and 300,000 tonnes of natural cheese per annum. In addition, they make more than 200,000 tonnes of raw materials for processing in the form of cheese, butter, anhydrous milkfat (AMF) and powders. Thus, both processed cheese and natural cheese are a very important part of the business, with significant research and development effort devoted to gaining a better understanding and therefore control of their manufacture.
Cheese can be regarded as a complex emulsion comprising water, protein, fat and minerals. As protein is often the most expensive major component in cheese, a reduction in the protein content of cheese can offer economic benefit to the manufacture, as well as potentially lower cost to the consumer. However, as protein provides the structural backbone of cheese, reducing the protein content can seriously compromise the product quality through softening and loss of some functional properties. The protein and moisture contents of cheese are important in terms of flavour delivery and textural attributes (such as hardness) and other attributes including spreadability and meltability. Thus, removing protein must be offset by adding another agent that is capable of contributing to the structure of the product. Polysaccharides (and exopolysaccharide-secreting cultures) can be used in this capacity.
2
1.2 Proposed solution
The application of microbial polysaccharides, such as xanthan gum, gellan gum and lactic acid bacteria (LAB) exopolysaccharide (EPS) produced from waste dairy stream media, is a recent area of research in the New Zealand dairy industry. Processed cheese and natural cheese have recently been identified as potential areas of application for such polysaccharides, and the research has been more focused on gellan gum. To date, only limited research has focused on the use of such polysaccharides in New Zealand dairy products. Moreover, many technological and functional problems related to the use of such polysaccharides in cheese have yet to be resolved.
Therefore, the aim of this project was to contribute to the understanding of the behaviour of polysaccharides such as xanthan gum and gellan gum in processed cheese formulations and of LAB EPS in Mozzarella cheese. This project investigated the use of commercially available polysaccharides in processed cheese and in-house-produced LAB microbial polysaccharides in Mozzarella cheese. Because of their unique moisture retention properties and their effects on cheese rheology, these polysaccharides have the potential to improve some functional properties of lower protein cheese and dairy products, including their textural and slicing properties.
1.3 Commercial significance
Polysaccharides have the potential to reduce syneresis in the cheese manufacturing process by retaining more moisture. Another focus in this manufacturing process is reducing the cost of a formulation. Fat and protein are the most expensive ingredients (protein being more expensive than fat) and moisture is the cheapest ingredient in cheese. Incorporation of more water has the potential to increase yield (reduce the
3
protein concentration). Thus polysaccharides may offer significant benefits in terms of reductions in the processing time and the formulation cost. In some cases, improved functionality may be obtained by the addition of polysaccharide to cheese with no significant reduction in the protein content, e.g. the common practice of adding polysaccharide to cream cheese to reduce syneresis.
1.4 Thesis objectives
The first goal was to study selected commercially available polysaccharides for their potential use in a model processed cheese. This included microstructural analysis (confocal laser microscopy and transmission electron microscopy) to characterise structural changes. Rheological and fracture properties related to functional properties were analysed to characterise functional changes (textural, spreading and melting properties). The analysis helped to establish an understanding of the behaviour of polysaccharides in making processed cheese.
The second phase aimed to study the effect of LAB EPS on model Mozzarella cheese. This involved producing a functional EPS ingredient for application in Mozzarella cheese and investigating the effect of the addition of LAB EPS on the textural and functional characteristics of a targeted model Mozzarella cheese.
The specific objectives of this research were as follows.
1. Establish a model processed cheese formulation for the study.
2. Using the model cheese system, analyse the specific interactions between the
4
polysaccharides, to determine the associations of the individual components: polysaccharide, fat, protein and water.
3. Include in this analysis the relative water affinities of polysaccharides and proteins
and the basic concepts of phase separation. To limit the scope to be appropriate for this size of work, exclude the large area of protein−polysaccharide bonding chemistry.
4. Develop a LAB EPS ingredient for application in a model Mozzarella cheese.
5. Determine the influence of the developed LAB EPS ingredient on the texture of
Mozzarella cheese.
1.5 Thesis structure
The thesis is structured in the traditional manner, with a literature review, followed by a series of chapters to address each of the above objectives. Each chapter also contains literature relevant to the area of investigation; some of this literature may not be addressed in the initial literature review. Each chapter is outlined briefly below.
Chapter 1 introduces the topic of study, by defining the problem and explaining the thesis objectives, as well as the economic benefit, and provides a brief outline of the thesis.
Chapter 2 gives a general review of the literature and discusses processed cheese, xanthan gum, gellan gum and LAB EPS.
Chapter 3 outlines the common materials and methods used in the individual chapters. Each chapter also contains materials and methods relevant to the area of work done.
5
Chapter 4 establishes a model processed cheese for further experimental work. It defines the experimental and analytical limits of the developed model cheese containing polysaccharides.
Chapter 5 uses the model cheese developed in Chapter 4 to study the relevant functional properties of a model processed cheese containing a blend of xanthan gum and locus bean gum (LBG). It compares xanthan gum and a blend of xanthan gum and LBG and measures the synergistic effect of the blend.
Chapter 6 studies the effect of two forms of gellan gum on the functional properties of the model processed cheese. It quantifies the effects of high acyl gellan gum (Gellan-H) and low acyl gellan gum (Gellan-L) on the emulsion, microstructural and rheological properties of the model processed cheese.
Chapter 7 describes the effects of Gellan-L and Gellan-H on the rheological properties related to spreadability, including elongational viscosity, and also the water mobility and the microstructure of the model processed cheese.
Chapter 8 describes the development of a bioingredient with a high level of functional EPS for inclusion in cheese, using dairy protein sources and a high EPS-yielding Streptococcus thermophilus strain. It optimises the yield of EPS by manipulating the medium composition and process control, with the medium subsequently being freeze dried to convert it into the ingredient.
Chapter 9 describes a pilot-scale study on the manufacture of Mozzarella cheese containing the developed bioingredient. It also studies the effect of such bioingredients on the functionality of Mozzarella cheeses.
6
Chapter 10 summarises the key conclusions of the thesis. It also discusses practical findings that have application to industry and includes recommendations for further work.
7