49 Alex. J. Fd. Sci. & Technol. Vol. 15, No. 1, pp. 51-64, 2018 Effect of Milk Quality and Stabilizers on Some Physicochemical Properties of UHT-Milk El-Sayed 1 , M. I., Amel A. Ibrahim 2 , & Awad 2* , S. 1 Department of Dairy Technology Research, Food Technology Research Institute, ARC, Egypt. 2 Department of Dairy Science and Technology, Faculty of Agriculture, Alexandria University, Egypt. Received: 21 March, 2018 Revised: 8 May, 2018 Accepted: 15 May, 2018 ABSTRACT Milk quality and stabilizers were investigated to revere their effects on undesirable changes in sensory of UHT milk as infuenced by storage at 25°C or 37°C. The obtained results showed that the total microbial count, psychro- philic bacteria, mesophilic & thermophilic spore forming bacteria were higher in grade B (GB) milk than in grade A (GA) milk. Seven treatments were carried out with GA, GB, reconstituted full cream milk powder (FCMP), FCMP mix with GA and GB milk, meanwhile, two commercial stabilizers were separately evaluated. Mesophilic and ther- mophilic spore forming bacteria exhibited high scores and were found in standardized pasteurized GB milk comparing with GA milk. The type of stabilizer has no any effect on the UHT milk quality. The treatments of UHT milk made using GB milk received low levels of sensory properties (color & favor), as well as, fat separation and sedimentation could be noted during storage when compared to that made from GA milk or FCMP. The fat separation and sedimenta- tion were more pronounced in treatments stored at 37 °C when compared to that stored at 25°C. Results of SDS-PAGE and RP-HPLC did not show any signifcant differences among all treatments in proteolysis during storage period. Accordingly’ the fat separation and sedimentation were not related only to proteolysis but were related to quality of milk used in processing. Key words: UHT milk, sedimentation, fat separation, milk stabilizers. INTRODUCTION The manufacture of almost all types of milk and its products involves one or more heat treat- ments. The aim of heat treatments is to kill micro- organisms and inactivate enzymes “partially or fully” dependent on type of heat treatment. This is done to secure safety of consumer along with extension of shelf life of the dairy product. Heat treatment can, however, also cause certain undesir- able changes like production of brown pigments, development of cooked favour and loss of nutri- ents (Walstra et al., 1999, Kessler 2002). UHT treatment is a technological process used to pro- duce drinking milk that is microbiologically safe and its shelf life ranges between 6-12 months at room temperature and stability of casein micelles during their storage (Deeth, 2010, Baglinière et al., 2012). Normally, UHT treatment is carried out at a range of 135–150°C for 1–10 s as a holding time required to achieve ‘commercial sterility’ (Chen et al., 2015). UTH milk is stable for long-term storage at ambient temperatures if microbiological sterility has been achieved by the UHT treatment and main- tained by aseptic packaging (Kelly & Fox 2012). The UHT milk processed by indirect systems show low sediment formation than its counterpart from direct systems, but sedimentation increased with elevating heat treatment and temperature of stor- age in direct UHT-milk (Datta, et al., 2002). Age gelation is a main factor reduces the shelf-life of UHT milk. It can be explained by a two-stage pro- cess involving formation of a β-lactoglobulin–k- casein complex during heating which cross-links after partial or complete release from the micelle of casein to forming a protein network gel. Prote- olysis, by native milk proteinase (plasmin) or bac- terial proteinases, increase gelation as a result of facilitating release of the complex from the micelle of casein-. Plasmin is suffciently heat-stable en- zyme to play a key role in term of age gelation of UHT milk, especially with direct UHT processing * Corresponding author: Sameh Awad Department of Dairy Science & Technology, Faculty of Agriculture (El-Shatby), Alexandria University, Egypt Tel & Fax: 002035903915 e.mail: sameh111eg@yahoo.com