Figure 6.5 Probable biosynthetic pathway of vanillin from protocatechuic aldehyde in C. frutescens cell cultures.
Ferulic acid administered Capsicum cultures are biotransformed to vanilla flavour metabolites -vanillin, vanillic acid, vanillyl alcohol, />-hydroxybenzoic acid, /'-coumaric acid and protocatechuic acid. Additionally, an increase in the capsaicin accumulation is observed in free cells and immobilized cell cultures. Immobilized Capsicum cells show a 4.0 and 5.23 times increase in vanillin and vanillyl alcohol accumulation on the 10th day over its freely suspended cultures in 2.5 mM ferulic acid supplementation whereas vanillic acid, protocatechuic acid and /'-hydroxy-benzoic acid accumulation were 3.14-, 7.4-, and 1.27-fold over freely suspended cultures (Ramachandra Rao, 1998; Ramachandra Rao and Ravishankar, 2000b).
/3-cyclodextrin (Figure 6.7) was used to effectively biotransform the phenylpropanoid precursor to capsaicin and vanillin. The precursor moiety fills the lumen of /3-cyclodextrin molecule and renders it soluble. This results in higher biotransformation efficiency. /3-cyclodextrin (BCD) used as a BCD—ferulic acid mixture treatment reveals that there is a 1.8-fold increase in vanillin accumulation (18.0 mg/L) in four days of incubation in immobilized Capsicum cell cultures. The addition of BCD favours increase in the vanillin accumulation in a shorter duration. The effect of reducing agent, dithiothreitol (DTT) at a 1:1 ratio (2.5 mM each) on ferulic acid biotransformation shows that a 4.35-fold higher vanillin accumulation (23.0 mg/L) over only ferulic acid-fed freely suspended Capsicum cell cultures. At a higher concentration of DTT (5.0 mM) treatment shows significant reduction in vanillin accumulation (Ramachandra Rao, 1998).
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