Abstract:
The objective of this project was to determine the effect of emulsifying salt (ES) and their Ca chelating ability on milk samples made by reconstituting 10wt% skim milk powders. The rheological and physico-chemical properties of reconstituted skim milk system were measured in order to understand the function of ES in processed cheese manufacturing. Particularly, three main ES were investigated, and these were sodium pyrophosphate decadydrate (SPD), sodium tripolyphosphate (STPP), and sodium citrate tribasic dehydrates (Cit). Various concentrations (0.25%, 0.5%, 1% and 2% w/w) of selected emulsifying salts (SPD, STPP and Cit) were added to the milk which was then readjusted to pH 6.7. Viscosity values of both heated and unheated ES added milk samples were measured at a fixed shear rate (100 s-1). Different to STPP and Cit added samples, SPD added milk showed peculiar viscosity trends in both heated and unheated samples where a peak was when 0.5 or 2% (w/w) SPD was added. Temperature sweep from 25-95°C was also carried out and SPD again showed unique viscosity activities compared to other ES added samples with a peak viscosity value was at around 45°C. Rheological properties of the ES added milk samples were also studied at two different pHs (6.7 and 5.6). SPD added samples had the highest values for all three parameters (G’, G” and G* moduli) compared to STPP and Cit added samples. Moreover, turbidity measurement and Ca activity of the ES added samples were also performed. The results showed that SPD has the highest Ca chelating power followed by STPP and Cit is the weakest Ca chelating agent. Owing to the distinctive behavior of milk samples with added SPD, additional experimental work was done to demonstrate the importance of calcium in the increase in viscosity observed when SPD was added to milk. The findings of this study might have an importance in processed cheese manufacture were this different ES are generally used.
