Browsing by Author "Ahervo, Eeva"

The aim of this thesis was to find a suitable natural antifungal substituent to improve shelf life of quark based products. Antifungal properties were analysed with four different protective cultures: HOLDBAC™ YM-B Plus, HOLDBAC™ YM-C Plus, HOLDBAC™ YM-XPM and FreshQ® 1. Also two different plant based compounds Melinat® and Verdad® F95 were examined. Different dosages and adding methods were used to study the feasibility of these compounds to quark based products. Physical and microbiological factors affecting the shelf life of fresh cheeses, manufacturing processes of cream cheese and quark based products and antifungal properties of both lactic acid and propionic bacteria as well as plant based compounds were reviewed in the literature section. The mixture of milk and quark in elimination tests and cream cheese and quark based spread in following tests were used as samples. The samples were contaminated with two different yeasts, Rhodotorula mucilaginosa and Candida utilis and a mold Aspergillus brasiliensis. The concentration of yeasts and mold were analysed after 0, 7 and 14 days storage at 9 °C. The properties of antifungal compounds were analysed also with the help of chemical and sensory analysis as well as shelf life tests. Protective cultures with recommended dosage were able to inhibit the growth of yeasts in the mixture of milk and quark. A tenfold increase in dosage did not have effect on yeast concentration. HOLDBAC™ YM-B Plus and FreshQ® 1 -cultures added at the same time with fermentation when manufacturing cream cheese and spread samples were not as efficient as potassium sorbate. However, the results from spread samples prepared with post-addition were equal to the results of potassium sorbate. Heat treatment was shown to have a significant impact on the performance of protective cultures. The heat tolerance of protective cultures is needed to investigate in the future so that the adding methods and feasibility especially to heat-treated products would be evaluated more closely.