Browsing by Author "Nylund, Asta"

The aim of this work was to collect information about the effects of enzymatic lactose hydrolysis to the structure of yoghurt. The literature part of the study deals with the hydrolysed yoghurt components such as milk, lactic acid bacteria and lactases, lactose intolerance, yoghurt production and the concepts of defining a good structure of yoghurt. The factors influencing the structure of the fat-free and hydrolysed yoghurt is also mentioned. In the experimental part the influences of hydrolysis and the certain lactase to the structure of yoghurt was studied. Purpose of the experimental part of the work was to study on the influence of certain hydrolysis methods and certain lactases on the structure of yoghurt. First of all the optimum solid nonfat content of the hydrolysed and unhydrolysed yoghurt was defined. Three different solid non fat contents in yoghurt were studied and the one showing best viscosity differences between hydrolysed and unhydrolysed yoghurt was chosen for further tests. In the follow-up studies the lactose was hydrolysed using three different methods and four different lactases in a manner, that two methods was made with the same lactase and the third method was made using three different lactases. Both chemical and microbial souring agents were used in the yoghurt production. The samples were examined at the moment of fermenting the yoghurt to seven day old yoghurts. During the acidification of the yoghurts the amounts of lactic acid bacteria, acidification and the titrable acidification rate, tyrosine equivalent-, glucose-, galactose and lactose contents were measured and during the seven days viscosity and whey separation were defined. For the result there was differences in the structure of the hydrolysed and unhydro-lysed yoghurts which could occur because of the lactose hydrolysis. There was also differences in lactases used so both the lactose hydrolysis method and lactase used may affect significantly the structure of the yoghurt.