Abstract
Age gelation is a main defect in Ultra-high temperature (UHT) processed milk. It is a process with two stages which distinguished by loss of viscosity. It can be followed by measuring the apparent viscosity of the milk. A control (T0) and four whole milk (fat 3.85%) samples fortified with Zinc (T1), Ferrous (T2) and Magnesium (T3) individually and collectively (T4) was processed by indirect heating UHT system at 145 ºC for six seconds. The UHT-processed milk samples were filled aseptically into Gamma ray pre-sterilized PET containers in a laminar flow cabinet sterilized shortly before filling by UV. The samples stored at 30 ºC for 60 days to investigate at 15 days intervals the effect of processing on apparent viscosity and appearance of the fortified milk and compared to control UHT milk (T0). Results recorded during 60 days of storage showed a slight rise in viscosity in all samples. No changes in appearance have been observed during the storage period. UHT Zinc-milk has shown at all intervals insignificant increase. Only after 30 days of storage, milk-fortified with ferrous showed a significant increase in viscosity measured by spindle speed of 30 rpm (SS30). Significant increases (p≤0.05) in viscosity were recorded within the fortified UHT-milk samples. Appearance and apparent viscosity can be adopted to follow gel forming in fortified milk with some minerals.
