IMPROVEMENT THE KEEPING QUALITY AND EXTENSION OF SHELF LIFE OF LOW SALT WHITE SOFT CHEESE USING TREATED MILK WITH NISIN

Abstract

White soft cheese was made from reconstituted partially skim milk powder (2% fat) with two salt concentrations (2% and 4%) and then (50, 100, 200 IU/ml) nisin were added. Control groups of both salted white soft cheeses were manufactured without addition of nisin. Furthermore, the two types of white soft cheese samples were kept in their whey at refrigerator temperature (2-4°C) till signs of spoilage were observed. Periodically, the control and preserved samples were examined chemically (pH and titratable acidity) and bacteriologically (aerobic plate, psychrotrophic, coliform and aerobic sporeformer counts) to determine the influence of nisin on prolongation of their shelf life. Nisin extended the shelflife of low salt cheese (2% salt) up to 9 days at concentration 100 IU/ml and up to 11 days for 200 IU/ml, while, nisin-free cheese samples were spoiled after the 5th day of refrigeration storage. On the other hand, the shelf life of 4% salt cheese was extended up to 21 days of cold storage by addition of nisin at conc. 100 and 200 IU/ml. In contrast, the cheese samples of control group were deteriorated after the 9th day of refrigerated storage. There were significant differences (p < 0.05) between the chemical and bacteriological profiles of low salt soft cheese as a result of storage time. Actually, the nisin had a significant destructive action on contaminating coliforms and aerobic spore forming bacteria of white soft cheese and lead to increase its validity period.