The development of processes for the preparation of prebiotic compounds, namely inulin from tubers of Jerusalem artichoke (JA-Helianthus tuberosus L.), and lactulose from milk concentration permeate (MCP) was examined. Inulin was extracted from the whole JA tubers using hydrothermal extraction process, followed by clarification and concentration. The concentrate was fractionated using two different procedures i.e. ethanol fractionation and cold precipitation (+4 and/or -24C) into high- and low-molecular-weight components. The most satisfactory method was cold fractionation wherein the insoluble heavier inulin fractions were found to settle to the bottom and were separated and spray-dried to obtain inulin powder. Lactose in MCP was isomerised into lactulose using carbonate-based catalysts (oyster shell and egg shell powders) followed by clarification and concentration. The high-performance liquid chromatography with refractive index detector (HPLC-RID) chr omatograms and changes in pH and colour values confirmed the conversion of lactose into lactulose and decomposition of lactulose into by-products. The results obtained showed the suitability of oyster shell powder for lactose isomerisation in lieu of egg shell powder. For preparing lactulose-enriched MCP with acceptable lactulose yield of 22%, the optimum reaction conditions were found to be catalyst loading of 12 mg per mL of MCP and isomerisation time of 120 min at 96C. The resulting products i.e. JAI concentrate and powder and lactulose-enriched MCP syrup (40B) were tested for their prebiotic power in media broth and in fermented milk models. Prebiotic properties of these compounds were observed as supplementation levels increased from 0-2% to 3-4%. Based on the growth and acidification abilities of the probiotic strains tested, the combination of Lactobacillus casei LC-01 with JAI, and Lactobacillus acidophilus LA-5 with lactulose-enriched MCP syrup were found to be the best for development of synbiotic yoghurt. The prebiotic effect of JAIP was then compared with the two commercial chicory inulin products (Raftiline GR and Raftilose P95). Probiotic yoghurts supplemented with 4% inulin powders were prepared from reconstituted skim milk using mixed cultures of Lactobacillus casei LC-01, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (1:0.5:0.5, w/w). The survival and acidifying activity of probiotic and lactic acid cultures were investiga ted during the shelf life of 28 days at 4C. Incorporation of JAIP and chicory inulins resulted in a significant improvement in viability of LC-01 compared with non-supplemented yoghurt, maintaining more than 107 CFU g-1 throughout storage time. Additionally, the suitability of JAIP as fat replacer was determined in a set of fat-free yoghurt in comparison to three commercial chicory inulin products. Results of large deformation tests revealed that the firmness of JAIP-supplemented yoghurt was reduced to a similar level as the full-fat control yoghurt. However, small deformation results showed that the JAIP could not fully mimic milk fat to the same extent as Raftiline HP with an average DP of 23. The rheological effects of JAIP addition were comparable to those of short-chain (Raftilose P95 with an average DP of 4) and medium-chain inulins (Raftiline® GR with an average DP of 12).

The thermal processing of milk changes the composition and surface properties of the colloidal particles present and alters the physical properties of the milk. Whilst some changes such as those used to improve the texture of products such as yoghurt and are desirable, others such as gel formation during the manufacture of Ultra-High Temperature milk are highly undesirable. This work aims to characterize the effects of milk composition and pH on the chemical and physical changes that occur when milk is heated in order to understand and control the effect of thermal processing on the functional properties of the milk. Particularly important are: (i) the changes to the integrity of the casein micelles and the extent to which they are reversible on cooling of the heated milk, (ii) the changes to the speciation of the components of the serum as they re-equilibrate in response to the changed environment during heating and on cooling, (iii) the heat-induced denaturation of the whey proteins, (iv) the interaction between the components of the micelles and those in the milk serum, particularly those interactions that lead to aggregation or other changes that affect the functional properties of the milk on heating. This project includes thermal treatment (90°C/10 min) of control skim milk solutions (9% Milk Solids Non Fat) with or without addition of calcium chelating agents (orthophosphate (Pin) & Ethylenediaminetetraacetic acid (EDTA)) and concentrated skim milk solutions (up to 21% MSNF). The pH range chosen was 6.2 to 7.2. Almost all of the studies on heat stability to date have been carried out by heating the milk and determining the changes that have occurred after the milk is cooled. This project is focussed on the direct measurements in real time of the changes that occur at the exact temperature. The experimental techniques included pH, calcium activity and 31P NMR measurements at high temperatures to investigate the consequences to the change in mineral speciation, Size Exclusion Chromatography in combination with SDS-PAGE analysis for protein speciation during heating and Diffusing Wave Spectroscopy and viscosity measurements to determine the heat stability of milk systems. pH and calcium activity decreased with increase in temperature for all the milk systems studied. These changes were largely reversible as enough time was given for equilibration. pH and calcium activity changes during heating are a function of milk composition. The quantity, size and the composition of the protein aggregates present in the serum phase after mild centrifugation (~33,000g) of heated (90°C/10min) milk solutions were found to be a function of pH and milk composition (including the consequent differences in speciation of the components of milk). DWS and the viscosity measurements showed that pH at the temperature of heating is one of the primary determinants in influencing the aggregation of the proteins, which led to thermal stability of milk systems. Hence, changing the milk composition resulted in differences in pH at the temperature of heating, which led to different behaviours of heat stability of milk systems. Careful control of the composition of milk and thereby the pH at the temperature of heating allows a greater control of thermal stability of milk systems.