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Changes in selected local fruits during freezing.
Matějková, Markéta ; Melounová, Jitka (referee) ; Márová, Ivana (advisor)
This diploma thesis was focused on study of low-molecular antioxidants present in various kinds of fruits, namely berries. In theoretical part detailed characterization of antioxidants studied in presented work and their biological effects are introduced. Further, principals of processing and storage of specified species of fruits are discussed. Changes observed during storage of specific fruits are described too. In practical part changes in content of selected antioxidants in berries were followed. As studied material strawberries, raspberries, blueberries, red and black currants were used. All kind of these fruits was stored in fridge for six months using several different kind of processing. Berries were stored as whole fruits, whole osmotically processed fruits by sucrose, raw pulp and sweetened pulp. At first, starting values of selected antioxidant parameters were measured in fresh fruits (ascorbate, total antioxidant activity, total phenolics, catechins and individual flavonoids). After freezing the same parameters were measured regularly in two month periods. As the most suitable method of fruit processing, with regard to antioxidant content, storage of the whole fruits or pulp can be recommended. Content of ascorbate decreased in all forms and species of the processed fruits during all the time of storage. Oppositely, the content of other studied antioxidants exhibited fluctuations or increasing trend. Sensory analysis was proved for the whole fruits and also for whole sweetened fruits.
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Changes of antioxidants in selected fruits during long-term freezing
Štindlová, Jitka ; Lichnová, Andrea (referee) ; Márová, Ivana (advisor)
In this bachelor thesis some low molecular weight antioxidants contained in strawberries, raspberries, blueberries and cranberries are described. In the theoretical part also general characteristics of these fruits are introduced. Experimental part was focused on analysis of the changes of selected antioxidant content in the fruits. These changes were monitored during storage in two different conditions – in refrigerator and in freezer. In refrigerator whole fruits were stored for 8 days. The experiment in the freezer was performed for 2 months and the fruits were stored in four different processed forms – as a whole fruit, whole fruit impregnated by sucrose solution, as a pulp and pulp mixed with sucrose. Antioxidant content in fruits was analyzed by HPLC and spectrophotometry. The highest total content of antioxidants was found in strawberries, while the lowest values were found in raspberries. During storage some part of original antioxidant content stayed conserved, the highest content was preserved in blueberries processed as a whole fruits and impregnated whole fruits.
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