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End of Project Report The rheology of yogurts or fresh fermented products generally describes and measures the texture of the product and includes such terms as viscosity and firmness of the gel while syneresis refers to the tendency of the yogurt to whey-off during storage. The importance of rheology and susceptibility to syneresis of fermented milk products is that they both have major impacts on consumer perceptions of the final product quality. Indeed, variation in the quality of yogurt products can lead the consumer to experience either an over-thin watery or an over-thick stodgy texture or a product which has a high level of free whey. It is obvious that the seasonal milk supply in Ireland compounds the particular difficulties associated with achieving a consistency in the quality of yogurts or other fresh fermented products. Importantly, both the rheology and syneresis of yogurts are markedly influenced by milk composition, processing treatments and the addition of hydrocolloids. Therefore, this project was undertaken so as to develop a laboratory fermented milks model system which allows the evaluation of the effects of variation of milk components, individually or in combination, on the rheological and syneretic properties of fermented milk products such as yogurt. In particular, the effects of varying total protein, casein-to-whey protein ratio, and fat content were studied as these variations reflect both the differences in milk composition due to lactational/seasonal effects and those due to process variations such as milk heat treatment. Department of Agriculture, Food and the Marine

End of Project Report The aims of this study were to elucidate the contribution of fat to cheese biochemistry and texture and to improve the texture and flavour of half-fat Cheddar cheese by modifications in make procedure, the addition of a fat mimetic, and/or the use of novel starter cultures/bacterial culture adjuncts. The main conclusions were as follows: A 'Moorepark Process' has been established for the production of half-fat Cheddar cheese with improved sensory acceptability. The flavour and texture of half-fat (17% w/w) Cheddar was improved by modification of the cheesemaking procedure and/or ripening conditions and through the use of novel starter cultures and/or bacterial culture adjuncts. Extensive databases have been compiled on: the effects of fat on the compositional, microbiological, biochemical, rheological and sensory properties of, and the yield of, Cheddar cheese. the compositional, biochemical and sensory characteristics of commercial Cheddar cheeses of different fat levels, available on the Irish and UK markets. Reduction in the fat level of Cheddar cheese resulted in a marked deterioration both in texture and flavour due to: increases in cheese hardness and fracture stress, indicating that the cheese became more elastic, tough and less amenable to mastication. a higher ratio of secondary-to-primary proteolysis a reduction in the level of primary proteolysis and an increase in the concentration of hydrophobic peptides which are conducive to bitterness. Department of Agriculture, Food and the Marine

Milk protein concentrate (MPC) powders have numerous commercial applications and are integral ingredients in high quality functional dairy products and beverages. However, such high protein dairy powders pose significant technical challenges during processing and rehydration, due to high viscosity and poor powder particle dissolution, respectively. Previous work has shown that the use of calcium chelating salts is effective in improving dissolution of MPC powders; however, the use of such salts results in considerable increases in viscosity and reduction in casein micelle integrity. The objective of this research was to investigate the impact of depleting calcium in micellar casein systems after either enzymatic dephosphorylation or enzymatic crosslinking and to examine viscosity, particle size; ζ-potential and colour of the protein solutions and subsequent rehydration properties of these spray dried systems. Calcium depletion was achieved through either addition of a chelating salt (sodium hexametaphosphate; SHMP) or through ion exchange. MPC dispersions containing enzymatically dephosphorylated casein proteins exhibited lower viscosity than phosphorylated MPC dispersions; however, the former resulted in a loss of casein micelle integrity in the presence of SHMP. Phosphate nuclear magnetic resonance spectroscopy proved useful for quantifying the depletion of calcium phosphate from casein micelles and confirmed dephosphorylation. Enzymatic crosslinking of casein proteins using transglutaminase helped maintain a lower solution viscosity after calcium chelation by SHMP, and the resultant dispersions retained a higher degree of casein micelle integrity compared to non-crosslinked MPC dispersions. Co-dried crosslinked casein and SHMP powders had improved rehydration properties. As an alternative to the addition of calcium chelating salts, a strong cation exchange resin was investigated for its ability to deplete calcium to varying extents in the production of novel MPC powders with improved dissolution properties at low levels of calcium depletion. However, similar to with direct use of calcium chelating salts, concomitant increases in viscosity and decreases in micelle integrity were observed in MPC dispersions, with the effects increasing with extent of calcium removal. Solubility and dissolution properties of calcium depleted MPC powders exhibited improved rehydration ability and caused a shift in their heat stability towards lower pH values. MPC dispersions containing crosslinked proteins were observed to be more resistant to calcium depletion compared to their respective control samples. MPC dispersions containing crosslinked MPC proteins retained greater micelle integrity; however, extensive calcium reduction resulted in significantly higher viscosity than corresponding controls. This thesis provides new insights into the functionality of novel MPC powders generated using enzymatic modification of casein and chemical modification of the calcium content and distribution between colloidal and serum phases, resulting in MPC powders with enhanced functionality. The outcomes of this research have application in the formulation of MPC powders with improved dissolution properties and reduced viscosity.

There are numerous review papers discussing liquid nanoemulsions and how they compare to other emulsion systems. Little research is available on dried nanoemulsions. The objectives of this research were to (i) study the effect of varying the continuous phase of nanoemulsions with different carbohydrate/protein ratios on subsequent emulsion stability, and (ii) compare the physicochemical properties, lactose crystallisation properties, microstructure, and lipid oxidation of spray dried nanoemulsions compared to spray dried conventional emulsions having different water and sugar contents. Nanoemulsions containing sunflower oil (10% w/w), β-casein (2.5–10% w/w) and lactose or trehalose (10–17.5%) were produced following optimisation of the continuous phase by maximising and minimising viscosity and glass transition temperature (Tg’) using mixture design software. Increasing levels of β-casein from caused a significant increase in viscosity, particle size, and nanoemulsion stability, while resulting in a decrease in Tg’. Powders were made from spray drying emulsions/nanoemulsions consisting of lactose or a 70:30 mixture of lactose:sucrose (23.9%), sodium caseinate (5.1%) and sunflower oil (11.5%) in water. Nanoemulsions, produced by microfluidisation (100 MPa), had higher stability and lower viscosity than control emulsions (homogenization at 17 MPa) with lower solvent extractable free fat in the resulting powder. Partial replacement of lactose with sucrose decreased Tg and delayed Tcr. DVS and PLM showed that in powdered nanoemulsions, lactose crystallises faster than in powdered conventional emulsions. Microstructure of both powders (CLSM and cryo-SEM) showed different FGS in powders and different structure post lactose crystallisation. Powdered nanoemulsions had lower pentanal and hexanal (indicators of lipid oxidation) after 24 months storage due to their lower free fat and porosity, measured using a validated GC HS-SPME method, This research has shown the effect of altering the continuous phase of nanoemulsions on microstructure of spray dried nanoemulsions, which affects physical properties, sugar crystallisation, and lipid oxidation.

Starches are a source of digestible carbohydrate and are frequently used in formulated food products in the presence of other carbohydrates, proteins and fat. This thesis explored the effect of addition of neutral (Konjac glucomannan) or charged (milk proteins) polymers on the physical characteristics and digestion kinetics of waxy maize starch. The aim was to identify mechanisms to modulate the pasting properties and subsequent susceptibility to amylolytic digestion. Addition of αs- or β-caseinate protein fractions to waxy maize starch restricted granular swelling during gelatinisation, increasing granule integrity. It was shown that, while β-caseinate can adsorb to starch granules during pasting, αscaseinate can be absorbed into maize starch granules. The resultant effect was a reduction in granule size after heating, more intact granules and a subsequent decrease in starch digestion in vitro as determined by analysis of reducing sugars. The ability of αs-caseinate to reduce the level of amylolytic digestion was confirmed through in vivo pig (Teagasc, Moorepark) and human (University of Surrey, UK) trials. The scope of the thesis extended to the development of a new automated cell for attachment to a rheometer to measure digestion kinetics of starch-protein mixtures. In conclusion, the thesis offers new approaches to modulation of the physical characteristics of unmodified starch during gelatinisation and suggests that the type of protein and/or polysaccharide used in starch-based food systems may influence the ability of the food to modulate glycemia. This is an important consideration in the design of foods with positive health benefits.