Sensory, rheological, physical, chemical and microbiological properties of different types of yoghurt.

Abstract

This study was designed to evaluate the quality of yoghurt sold in Assiut city, Egypt, in which a total of 60 samples of Baladi, pasteurized plain and pasteurized flavored (20 each) were collected randomly. The sensory evaluation was based on visual, texture and flavor. Syneresis was applied for rheological properties and pH for physical properties. Chemical analysis was applied through moisture, TS, fat and SNF%. Also, titratable acidity% and starch were detected. The microbiological examination for coliforms, fecal coliforms, E. coli , anaerobes and yeasts & molds were counted. The achieved results showed that the sensory evaluation of the pasteurized plain and pasteurized flavored samples was of higher scores than the Baladi samples, however on contrast, syneresis was higher in the Baladi samples. The average values of pH were 4.9, 4.89 and 4.83 for the Baladi, pasteurized plain and pasteurized flavored samples, respectively. For the fat content, the Baladi samples had higher fat%, followed by the pasteurized plain then the pasteurized flavored types. All the examined Baladi samples were starch free, while 70 & 65% of the pasteurized plain and pasteurized flavored types were positive, respectively. The average values of titratable acidity% were 0.91, 0.82 and 0.75, respectively. The microbiological examination cleared that the Baladi samples were more contaminated for coliforms, fecal coliforms and E. coli , while, the pasteurized plain and pasteurized flavored samples were more contaminated for anaerobes. It was found that 85% of the total examined samples were unacceptable according to the Egyptian Standards for their content of yeasts and molds.