Biotransformation of phenylpropanoid intermediates-ferulic acid, coniferyl aldehyde and p-coumaric acid was studied in free and immobilized cell cultures of Haematococcus pluvialis. H. pluvialis cultures accumulated vanilla flavor metabolites-vanillin, vanillic acid, vanillyl alcohol, protocatechuic acid, p-hydroxybenzoic acid, p-hydroxybenzaldehyde and p-coumaric acid when treated with these precursors. The accumulation of these metabolites increased gradually and reached a maximum on the third day in 1.0 mM ferulic acid fed immobilized Haematococcus cultures. The immobilized H. pluvialis cultures showed maximum vanillin (10.6 mg l(-1)), vanillic acid (5.4 mg l(-1)), vanillyl alcohol (3.3 mg l(-1)), protocatechuic acid (1.6 mg l(-1)),p-hydroxybenzoic acid (1.4 mg l(-1)) and p-coumaric acid (1.1 mg l(-1)) on the third day of the experimental period and these were 2.1, 1.8, 1.3, 1.14, 1.1 and 1.1 folds higher over free cell cultures of Haematococcus fed with 1.0 mM ferulic acid. Coniferyl aldehyde fed H. pluvialis cultures showed 2.3 and 2.2 folds higher vanillin and vanillyl alcohol accumulation when compared with 0.5 mM fed cultures. p-Coumaric acid fed Haematococcus cultures showed accumulation of p-hydroxybenzoic acid, p-hydoxybenzaldehyde and protocatechuic acid. These results demonstrated that cultures of Haematococcus can bioconvert externally fed phenylpropanoid precursors to a range of vanilla flavor metabolites. (C) 2002 Elsevier Science Ltd. All rights reserved.