Influence of electroporation, high pressure and thermal pasteurization on sensory properties of fruit juices

Namen magistrske naloge je bil proučiti možnosti uporabe alternativnih metod pasterizacije, elektroporacije (PEF) in visokih tlakov (HHP) v primerjavi s klasično termično pasterizacijo. S termično pasterizacijo sicer podaljšamo rok trajanja sokov, vendar pride do negativnih senzoričnih sprememb (sprememba barve, okusa, vonja) ter razgradnje fenolnih spojin in drugih antioksidantov. Pripravili smo sadne sokove iz jabolk, pomaranč ter nektar iz jagod. Sokove smo pasterizirali s klasično termično pasterizacijo ter z elektroporacijo in visokimi tlaki. Opravili smo kemijske analize skupnih fenolov, antioksidativnega potenciala (AOP) in skupnih flavonoidov, mikrobiološke analize ter senzorične analize vzorcev pred pasterizacijo ter 7 dni po pasterizaciji. Ugotovili smo primerne parametre elektroporacije za zmanjšanje skupnega števila mikroorganizmov za logaritem 2. Po pasterizaciji jagodnega soka je imel po 7 dneh najvišji AOP, vsebnost skupnih fenolov in skupnih flavonoidov termično pasteriziran sok. Pri pomarančnem soku po pasterizaciji po 7 dneh ni bilo razlik v vrednosti AOP, največ skupnih fenolov je imel sok pasteriziran z visokimi tlaki, največ skupnih flavonoidov pa svež sok. 7 dni po pasterizaciji je imel termično pasteriziran jabolčni sok največji AOP in največjo vsebnost skupnih fenolov, največ skupnih flavonoidov pa sta vsebovala termično in z visokimi tlaki pasterizirana sokova. Najbolje senzorično ocenjena jagodna sokova sta bila elektroporiran in pasteriziran z visokimi tlaki, pri pomarančnem je bil najbolje ocenjen elektroporiran pri jabolčnem pa termično pasteriziran.The purpose of this master\u27s thesis was to study the possibility of using alternative methods of pasteurization by pulsed electric field (PEF) and high hydrostatic pressure (HHP) in comparison to conventional thermal pasteurization. Conventional thermal pasteurization protects juices against microbiological spoilage, but negative effects like sensory changes (change in color, taste, and odour) and the degradation of phenolic compounds and other antioxidants might occur. In our experiment, fruit juices from strawberries, oranges and apples were prepared. The juices were pasteurized applying conventional thermal pasteurization, PEF and HHP. Chemical analyses were performed before and after 7 days after pasteurization and include total phenols, antioxidant potential (AOP) and flavonoids, microbiological analysis as well as sensory analysis. Through preliminary experiments we determined the appropriate parameters of electroporation to reduce the total number of microorganisms for log 2. 7 days after pasteurization strawberry juice, had the highest AOP, the content of total phenols and flavonoids was determined in thermally pasteurized juice. No differences between treatments were found in orange juice 7 days after pasteurization in AOP, while HHP juice had the highest total phenols and fresh juice had the highest content of flavonoids. Seven days after pasteurisation, thermally pasteurized apple juice had the highest AOP and the highest content of total phenols, while the highest content of flavonoids were determined in HHP juice. Regarding strawberry juice PEF and HHP pasteurisation gave the best sensory score, for orange juice PEF pasteurisation and for apple juice thermal pasteurisation gave the best sensory score