Fermentation of currant and raspberry leaves and effect on flavonols

Abstract

The aim of this thesis was to gain knowledge on solid state fermentation on raspberry and black currant leaves. The focus was on the possible increase in polyphenol content and in particular flavonols. The knowledge is then used to further the development of a supplement meant for human consumption. Raspberry leaf was investigated to see if fruit bearing, and insect infestation affected flavonols and polyphenol content. Flavonols have been found to have health benefits. These include antioxidant activity, anti-hypertension, anti-obesity, anti-carcinogenic, anti inflammatory properties, which may have therapeutic effects on cardiovascular diseases, diabetes, and gastrointestinal pains. The use of yeasts and filamentous fungi have been found to increase polyphenols and antioxidant activity. In this thesis yeasts Saccharomyces cerevisiae and Torulaspora delbrueckii and filamentous fungi Monascus anka were used to increase beneficial properties of raspberry and black currant leaves. There were found subtle signs that the fermentation with the three different microorganisms did increase antioxidant activity and polyphenol content. No accurate measurements were found on which flavonols increased during fermentation due to fermentation proceeding to overfermentation stage. At that stage all of the identified flavonols decreased. Fruit bearing and insect infested raspberry leaves were found to have the highest antioxidant activity but not the highest flavonol content. The highest flavonol content was found in the fruit bearing leaves.