Ultra-high temperature (UHT) stability of ready to drink (RTD) high milk protein beverages is mainly governed by their protein concentration, the relative abundance of the type of milk proteins present in their formulation and heat induced interaction of milk proteins among themselves and other beverage ingredients. The present PhD project was focused on addressing these issues in order to improve the UHT stability of high protein beverages.The UHT (145 dC for 5 s) stability and fouling behaviour of reconstituted low heat skimmed milk powder (RSMP) and milk protein concentrate powder (RMPC) was compared to study the effect of type of milk protein ingredient and protein concentration on UHT stability of high protein beverages. RMPC at 10 and 14% protein content was more UHT stable as compared to lower protein content RSMP (3.25 to 8%). Matching the total solids and mineral composition of 7.5% protein RMPC with 7.5% protein RSMP by addition of minerals and lactose markedly reduced its UHT stability (UHT run-time reduced to 66 min from g120 min). The RP-HPLC analysis showed increased casein dissociation but similar whey protein aggregation in 7.5-RSMP as compared to 14-RMPC. UHT processing led to formation of larger particles in case of 7.5-RSMP (1.84 mm D(0.9)) as compared to 14-RMPC (0.23 mm D(0.9)). It was observed that mineral environment affected protein interactions leading to the differences in UHT behaviour of RSMP and RMPC.The role of major minerals content in high heat stability of RMPC as compared to RSMP was further studied by matching Ca, Mg, Na and K contents of 7.5-RMPC with 7.5-RSMP using mineral salts. CaCl2 added RMPC sample could not be UHT processed due to its low heat stability. Addition of NaCl to RMPC did not adversely affect their UHT stability (UHT run-time g120 min). KCl caused a decrease in UHT stability (run-time 15 min) and a drop in overall heat transfer co-efficient (OHTC) values. High apparent viscosity and formation of larger particles were observed in KCl added RMPC as compared to control RMPC. Overall mineral balance with reduced amount of minerals per protein unit were found to be responsible for high heat stability for RMPC compared to RSMP.Effect of relative concentrations of caseins and whey proteins on UHT stability of high protein dispersions was also studied. RMPC, reconstituted whey protein concentrate (RWPC) and samples with various casein to whey protein ratios (C:W) (80:20 to 40:60) were UHT processed. A 2% protein RWPC showed severe fouling suggesting its poor UHT stability. Inclusion of caseins caused stabilization of whey proteins to UHT processing and 10% protein C:W-50:50 was successfully processed for g120 min suggesting the chaperone protein like activity of caseins protecting whey proteins against thermal stresses. Further increase in whey proteins proportion caused a drop in run-times (l120 min) and OHTC, corresponding to an increase in particle size and apparent viscosity. Presence of higher amounts of casein in the serum phase of samples caused the formation of smaller protein aggregates (D(4,3) was 0.23 and 0.16 mm for supernatants of C:W-40:60 and RMPC, respectively) after heating.The knowledge gained from above mentioned studies was applied to formulate an RTD beverage. The effect of two 10% milk protein formulation bases: i) RMPC base (RMPC-Choco) and ii) RMPC and RWPC base (C:W-Choco) and different k-carrageenan concentrations (0, 0.01, 0.03 and 0.05%) on UHT stability of chocolate flavoured high protein beverages were studied. Samples without the addition of k-carrageenan showed severe fouling and very short UHT run-times due to settlement of cocoa powder particles in the processing line. It was found that addition of 0.03 and 0.01% k-carrageenan to RMPC-Choco and C:W-Choco, respectively,n made them UHT stable (UHT run-times g120 min) due to formation of a weak gel by milk protein- k-carrageenan interactions entrapping cocoa particles. High UHT stability of C:W-Choco at low levels of k-carrageenan was linked to additional gelation of higher amounts of whey proteins present in the formulation. However, a loss of fluidity in C:W-Choco samples with 0.03 and 0.05% k-carrageenan was observed.n During a sensory evaluation no significant difference for overall preference among three selected samples (RMPC-Choco with 0.03 and 0.05% k-carrageenan and C:W-Choco with 0.01% k-carrageenan) was found.nThe objective of the last study in this thesis was to investigate the effect of the addition of soy protein hydrolysates on UHT stability of high protein milk beverages. UHT stability of 8% protein RMPC (8-RMPC), 8% protein soy protein hydrolysate (8-RSPH) and 8-RMPC with added 1, 2 and 3% protein RSPH (e.g. 8-RMPC+1-RSPH) was studied. Both 8-RMPC and 8-RSPH had high UHT stability (UHT run-time g120 min). Inclusion of 1-RSPH in 8-RMPC did not affect UHT run-time (g120 min) and OHTC. Significant drops in OHTC was observed in 8-RMPC+2-RSPH without reducing the UHT run-time (g120 min). 8-RMPC+3-RSPH showed markedly reduced UHT stability (UHT run-time 61 min and low OHTC values) due to the formation of larger protein aggregates and increase in apparent viscosity.