Vanilla Flavour Production Through Biotransformation Using Capsicum frutescens Root Cultures

Normal roots of Capsicum frutescens were excised from
tissue-cultured plants into half strength Murashige and
Skoog’s medium with 2.23 mM naphthalene acetic acid.
Maximum growth of cultured roots was 6.5 g fresh
weight 40 ml-1, as recorded on day 20. Even though
normal roots were unable to accumulate capsaicin, they
contained other phenylpropanoid intermediates and
vanillylamine, as detected by HPLC analysis. Normal
roots of Capsicum frutescens were treated with ferulic
acid and protocatechuic aldehyde in order to study their
biotransformation ability. Ferulic acid, which is the
nearest precursor to vanillin, when fed at concentrations
of 1 and 2 mM led to the accumulation of vanilla flavour
metabolites, vanillin being the major one. In cultures
treated with 1 and 2 mM ferulic acid, maximum vanillin
accumulation of 12.3 and 16.4 mM was observed, on day 6
after precursor addition, respectively. Feeding of ferulic
acid and b-cyclodextrin complex (2 mM each) enhanced
the accumulation of biotransformed products. Moreover,
vanillin accumulation was recorded as 24.7 mM on day 6
after precursor addition, which was 1.5 times higher than
in cultures fed with ferulic acid (2 mM) alone. When
ferulic acid was fed along with b-cyclodextrin (1 mM
each) to cultures growing in a three-litre bubble column
bioreactor, the maximum vanillin production of 10.7 mM
was obtained; other vanilla flavour metabolites were also
formed after 9 days of precursor addition. Root cultures
could also biotransform protocatechuic aldehyde
wherein a maximum vanillin production of 7.9 mM was
recorded on day 6 after precursor addition. The bioconversion
efficiency was observed to be 5
/7% in case of
ferulic acid fed cultures and 3.2% in case of protocatechuic
aldehyde fed cultures suggesting the possible
channelling of precursors to alternate biosynthetic pathways
such as lignin.