Exploring the physicochemical basis of cheese texture, rheology and functionality, with emphasis on cation-casein interactions

The physicochemical properties of cheese and milk gels are greatly influenced by molecular interactions between the casein proteins involving calcium. Novel experiments were designed to investigate the relationship between insoluble caseinbound cations and rheological properties of Cheddar cheese and rennet-induced milk gels. Cheddar cheese and rennet-induced milk gels were supplemented with Mg2+ or Sr2+ to compare their effects on their rheological properties to those previously reported in literature for Ca2+ supplementation. Sr2+ displayed behaviour similar to Ca2+ as observed by its ability to increase the rigidity of cheese and rennet milk gels and also decrease cheese meltability. Mg+2 had no influence on cheese rheological properties and was greatly inferior to Ca2+ and Sr2+ in its ability to increase rennet milk gel elasticity. Cheddar cheese was supplemented with the calcium-chelating salts trisodium citrate, disodium hydrogen phosphate or disodium EDTA, in an attempt to reduce the CCP content of cheese and thereby modify its rheological and functional properties. TSC and EDTA were successful in decreasing cheese CCP, whereas DSP caused an initial increase in CCP content. Cheddar cheese was supplemented with chlorides of iron, copper and zinc at salting to investigate the effects of concentrations of these elements in excess of those found innately or commonly in fortification studies, with emphasis on mineral equilibria changes and resultant alteration of rheological properties. Zinc addition was the only added metal that significantly influenced cheese rheological properties, leading to an increase in cheese rigidity and decreased cheese melt at elevated temperatures. Gum tragacanth was used as a fat-replacer in the manufacture of reduced-fat Cheddar cheese, in an attempt to improve the rheological, functional and sensory properties of reduced-fat Cheddar. Overall, the experimental work reported in this thesis generated new knowledge and theories about how casein-mineral interactions influence rheological properties of casein systems.

Immune and stress factors in the pathophysiology of the mdx mouse model of Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a fatal multi-system neuromuscular disease caused by loss of dystrophin. The loss of dystrophin from membranes of contractile muscle cells and the dysregulation of the DAPC, induces chronic inflammation due to tissue necrosis and eventual replacement with collagen which weakens muscular force and strength. Dystrophin deficiency may cause under-diagnosed features of DMD include mood disorders such as depression and anxiety and dysfunction of the gastrointestinal tract. The first study in the thesis examined mood in the dystrophin-deficient mdx mouse model of DMD and examined the effects of the tri-cyclic antidepressant, amitriptyline on behaviours. Amitriptyline had anti-depressant and anxiolytic effects in the mdx mice possibly through effects on stress factors such as corticotrophin-releasing factor (CRF). This antidepressant also reduced skeletal muscle inflammation and caused a reduction in circulating interleukin (IL)-6 levels. In the second and third studies, we specifically blocked IL-6 signalling and used Urocortin 2, CRFR2 agonist to investigate their potential as therapeutic targets in mdx mice pathophysiology. Isometric and isotonic contractile properties of the diaphragm, were compared in mdx mice treated with anti IL-6 receptor antibodies (anti IL-6R) and/or Urocortin 2. Deficits in force production, work and power detected in mdx mice were improved with treatment. In study three I investigated contractile properties in gastrointestinal smooth muscle. As compared to wild type mice, mdx mice had slower faecal transit times, shorter colons with thickened muscle layers and increased contractile activity in response to recombinant IL-6. Blocking IL-6 signalling resulted in an increase in colon length, normalised faecal output times and a reduction in IL-6-evoked contractile activity. The findings from these studies indicate that for both diaphragm and gastrointestinal function in a dystrophin-deficient model, targeting of IL-6 and CRFR2 signalling has beneficial therapeutic effects.

Studies on quinoa (Chenopodium quinoa) for novel food and beverage applications

Quinoa (Chenopodium quinoa) is a seed crop native to the Andes, that can be used in a variety of food product in a similar manner to cereals. Unlike most plants, quinoa contains protein with a balanced amino acid profile. This makes it an interesting raw material for e.g. dairy product substitutes, a growing market in Europe and U.S. Quinoa can however have unpleasant off-flavours when processed into formulated products. One means of improving the palatability is seed germination. Also, the increased activities of hydrolytic enzymes can have a beneficial influence in food processing. In this thesis, the germination pattern of quinoa was studied, and the influence of quinoa malt was evaluated in a model product. Additionally, to explore its potential for dairy-type products, quinoa protein was isolated from an embryo-enriched milling fraction of non-germinated quinoa and tested for functional and gelation properties. Quinoa seeds imbibed water very rapidly, and most seeds showed radicle protrusion after 8-9 h. The α-amylase activity was very low, and started to increase only after 24 hours of germination in the starchy perisperm. Proteolytic activity was very high in dry ungerminated seeds, and increased slightly over 24 h. A significant fraction of this activity was located in the micropylar endosperm. The incorporation of germinated quinoa in gluten-free bread had no significant effect on the baking properties due to low α-amylase activity. Upon acidification with glucono-δ-lactone, quinoa milk formed a structured gel. The gelation behaviour was further studied using a quinoa protein isolate (QPI) extracted from an embryoenriched milling fraction. QPI required a heat-denaturation step to form gel structures. The heating pH influenced the properties drastically: heating at pH 10.5 led to a dramatic increase in solubility, emulsifying properties, and a formation of a fine-structured gel with a high storage modulus (G') when acidified. Heating at pH 8.5 varied very little from the unheated protein in terms of functional properties, and only formed a randomly aggregated coagulum with a low G'. Further study of changes over the course of heating showed that the mechanism of heat-denaturation and aggregation indeed varied largely depending on pH. The large difference in gelation behaviour may be related to the nature of aggregates formed during heating. To conclude, germination for increased enzyme activities may not be feasible, but the structure-forming properties of quinoa protein could possibly be exploited in dairy-type products.