Oolong tea extract (OTE) and the purified polymeric polyphenols from OTE have been found to inhibit glucosyltransferase (GTase) of mutans streptococci. In view of the partial fermentation characteristic of oolong tea, we describe here an in vitro model reaction system to produce partially fermented products of D-(+)-catechin or green tea extract (GTE) using horseradish peroxidase. A dimeric catechin molecule was identified as dehydro-dicatechin A by instrumental analyses. The molecular size of some oligomeric catechins was estimated by the elution profile with HPLC. These catechin oligomers markedly inhibited GTase from Streptococcus sobrinus 6715. As the degree of polymerization of catechin or GTE increased, GTase was inhibited more effectively. These results suggest that polymeric polyphenols found in OTE are synthesized by partial fermentation due to oxidases/peroxidases present in tea leaves.

The uptake mechanism of liquid hydrocarbons of low solubility in water was investigated, using microorganisms with different affinities for liquid hydrocarbon. Microorganisms which could utilize hydrocarbon were much more adherent to hydrocarbon than those which could not. The adhesive force between Candida intermedia IFO 0761 and hydrocarbon was higher than that of Candida tropicalis ATCC 20336, though both could utilize hydrocarbon; The total hydrocarbon uptake from the drop and accommodation forms of hydrocarbons was much higher than that from dissolved hydrocarbon. The uptake rate of drop-form hydrocarbon was nearly equal to that of accommodation-form hydrocarbon for C. intermedia, but was lower for C. tropicalis which shows lower adhesion to hydrocarbon.

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The growth kinetics of a microorganism with high affinity for liquid hydrocarbon which has a low solubility in water was investigated for Candida intermedia IFO 0761 in our previous work. The microorganism contained a hydrocarbon pool in and/or on the cell. The transfer of water-soluble substrates to the cell was not the rate-limiting step in the growth of C. intermedia accompanied by clump formation with liquid hydrocarbon. The operating conditions necessary for the oxygen supply for the growth were adequate for the growth of C. intermedia on n-tetradecane. The saturation kinetics was valid for the specific growth rate of C. intermedia and specific concentration of hydrocarbon per unit cell mass; the specific growth rate was expressed by the following equation: (formula: see text).