|Title||Electrometrisch onderzoek der thee-fermentatie in verband met de kwaliteit|
|Source||University. Promotor(en): H.J.C. Tendeloo; E.C. Wassink. - Wageningen : Verweij - 130|
|Publication type||Dissertation, internally prepared|
|Keyword(s)||camellia sinensis - thee - fermentatie - kwaliteit - tea - fermentation - quality|
|Abstract||Fermentation of tea-leaf was compared with different leaf ages, grades of leaf withering, temperatures and aerations. Fermentation was known to be very important for the final quality of tea. Careful estimation of redox potential proved suitable for study of fermentation in a single leaf. Potentiometric titration under aerated water (so not as normally in factories) showed that 'Buds' ('Pecco': best quality leaves) contained more ascorbid acid (AA) and fermented more rapidly than older leaves. More withered leaves fermented more actively and completely. Optimum temperature for fermentation was found to be about 26°C. Aeration to a certain point encouraged fermentation strongly. Thorough grinding promoted fermentation most. AA had to be oxidized to allow reddish brown discoloration of fermenting tea-leaves. 'Buds' oxidized AA much quicker than older leaves.
It was assumed that 'potential quality' of a fresh leaf was correlated with active fermentation. So in practice leaves had to be rolled often but briefly, while the rolling and fermenting rooms should be thoroughly aerated, although the leaves should not be allowed to dry. Ascorbic dehydrogenase, polyphenol oxidase and peroxidase were involved in the oxidation of AA. Traces of CU2 +(occurring in the prosthetic groups of ascorbic dehydrogenase and polyphenol oxidase) accelerated oxidation of AA in leaf extracts. Fe3 +less so. By rectilinear adjustment fermentation activity could be calculated. It was higher for 'Buds' than for older leaves.