FUNCTIONAL AND MICROSTRUCTURAL PROPERTIES OF LOW FAT MOZZARELLA CHEESE AS AFFECTED BY EXOPOLYSACCHARIDES-PRODUCING S. THERMOPHILUS AND STORAGE CONDITIONS

This study was carried out to improve the functional properties of low fat mozzarella cheese and to extend its shelf-life via the use of exopolysaccharides (EPS) producing starter  cultures and different freezing conditions. Conventional starter culture consisting of both non EPS producing S. thermophilus St CH-1 in association with L. helveticus  Lh CH-5 with or without fat replacer (Simplesse.S-100), and two EPS-producing strains of S. thermophilus SFi-12 and SFi-39, each in combination with non-EPS L. helveticus  Lh CH-5 were used in manufacture of low fat Mozzarella cheese. The resultant cheeses were ripened at 4ºC for 28 days (refrigerated cheese). The results obtained indicated that cheeses made with EPS-producing S. thermophilus  had significantly(p < 0.05) higher level of moisture and moisture in non fat substances (MNFS) as compared with non-EPS cheeses with or without  simpelesse when fresh or during the refrigerated storage period. In addition, the meltability and fat leakage values of EPS-cheeses were the highest among all experimented cheeses. However, the cheese made with EPS (SFi-39) exhibited the lowest  apparent viscosity (AV). Statistical analysis showed that meltability, fat leakage and AV were significantly affected by type of EPS culture (p < 0.001), ripening period (p < 0.001) and their interactions (p < 0.001 for meltability, p < 0.05 for fat leakage and AV). As Mozzarella cheese is considered short storage lives, a freezing  scheme was designed to study its effect on the functional properties and shelf-life of the resultant cheese. The freezing schemes for the above experimental EPS and non EPS cheeses were as follows: a) Cheese ripening for 14d at 4ºC before freezing at -20ºC for 60 days, then again ripening at 4ºC for 14d., and b) Cheese freezing immediately after manufacturing at -20ºC for 60 days then ripening at 4ºC for 28d. The results obtained indicated that frozen EPS cheeses retained the highest MNFS and TA at the end of frozen schemes (88d). Meltability and fat leakage of experimented frozen cheeses have  increased upon ripening at two stages (before and after freezing) or one stage (after freezing). AV of frozen Mozzarella cheeses was fluctuated during freezing and ripening schemes. Regarding the microstructural properties of non EPS and EPS experimented cheeses, Scanning electron micrographs   (SEM) of the refrigerated cheeses (28d) showed that, the EPS-cheese was porous and had an open texture with numerous voids, whereas the non EPS cheeses had a closed and compact protein matrix. There were no  marked differences between the microstructure of all refrigerated  and frozen cheeses, which had a large voids in the cheese matrix. The obtained results confirmed that EPS-producing S. thermophilus  can be utilized to significantly increase  cheese moisture content and  to improve the texture and microstructure characteristics of resultant low fat Mozzarella cheese. In addition , freezing is a suitable alterative to prolong stability and shelf-life of low fat Mozzarella cheese without modifying  its functional properties