Research on the qualities of the set type plain and fruit-aroma yogurts produced from cowis and goats milk and stured for 15 days

124 SUMMARY In this research set type plain and fruit-aroma yogurts were made in 3 repetitions from cow's and goat's milk and stored at +4±1 °C for 15 days. Samples from the raw and pasteurised (heat treated) milks and from the yogurts at 1st 5th 10th and 15th days of storage were taken and physical, chemical, microbiological and organoleptical qualities changes were analysed. The effects of the different types of milk and of fruit-aroma and the storage period on the quality changes of the yogurts were also found to be statistically significant. Variance analyses to determine the difference between the cow's and the goat's milk used in the production of the plain yogurts indicated that the difference between the acidity, fat, protein, lactose and ash contents were statistically significant (p<0.05). Similarly there was also a statistically significant difference (p<0.05) between the fat, protein, lactose and ash contents of the cow's and goat's milks used for the production of fruit-aroma yogurts. From the microbiological point of view, both of the milks were of a similar quality. As a result the statistical analyses also indicated the differences as "not significant" (p>0.05). There were no coliform group bacteria or yeast and mould in the milks used. Type of the milk were found to have statistically significant effects (p<0.05) on the chemical (pH, acidity, dry matter, fat, protein, lactose and ash), physical (penetrometer reading, viscosity and whey separation) and organoleptical (colour and appearance, body and texture, flavor and the total points) qualities of the plain yogurts (p<0.05). Organoleptical evaluations of the expert panel members showed that the plain yogurts made from the cow's milk were preferred over the yogurts made from the goat's milk. Effects of the storage period of plain yogurts on pH, acidity, penetrometer reading and viscosity were found to be statistically significant (p<0.05). Similar results were also obtained with the pH, acidity, penetrometer125 reading and viscosity values of plain yogurts made from the goat's milk (p<0.05). Colour and appearance, flavour and total points of the plain yogurts from the cow's and goat's milk declined towards the end of the storage period howewer these changes were found to be statistically insignificant (p>0.05). The number of lactic acid bacteria and total microorganisms in plane set yogurts produced from cow's and goat's milk fluctuated during storage. There were not any coliform group bacteria or any yeast and mould in the plain yogurts. Effects of the type of milk and fruit-aroma on the chemical qualities (pH, acidity, dry matter "only for peach yogurt", fat in dry matter, protein in dry matter, total sugar, invert sugar, saccharose and ash), physical qualities (penetrometer reading, viscosity and whey separation) and organoleptical qualities (colour and appearance "only for nescafe yogurts", body and texture, flavor and the total points) were found to be statistically significant (p<0.05). Expert panel evaluations indicated as in the plain yogurts that the fruit- aroma yogurts made from cow's milk were superior over the goat's milk samples. Storage period had statistically significant effects (p<0.05) on the qualities of pH, acidity, invert sugar, saccharose and penetrometer reading of the fruit-aroma yogurts made from the cow's milk. Similar statistically significant effects were also observed with the fruit-aroma yogurts made from the goat's milk, in connection with the pH, acidity, protein in dry matter, invert sugar (except for the cherry yogurts), saccharose, penetrometer readings and viscosity values. Microbiological analyses showed that number of yeast and mould in fruit-aroma yogurts made from goat's and cow's milk constantly increased. Number of lactic acid bacteria and total microorganisms increased until the 10th day of storage, thenafter decreased. No coliform bacteria were detected during storage as in plain set yogurts produced from cow's and goat's milk.126 All the effects of the fruit-aroma types on the chemical, physycal and organoleptical qualities of yogurts made from the cow's and goat's milk were found to be statistically significant (p<0.05). Organoleptical evaluations of the expert panel group on the fruit-aroma yogurts made from the cow's and the goat's milk placed the strawberry yogurts in the first place which was followed by the peach, cherry and the nescafe yogurt varieties.