Biological Production from ferulic acid obtained from wheat bran hydrolyzates

Wheat bran contains about 5 g/kg of dry matter of ferulic acid, which can be released from cell wall polysaccharides through chemical or enzymatic hydrolysis. Ferulic acid is a precursor of vanillin, one of the most used flavouring compound in the food industry. It has previously been shown that ferulic acid occurring in wheat bran can be successfully bioconverted into vanillin by resting cells of Escherichia coli JM109/pBB1. In this work the role of ferulic acid concentration in wheat bran hydrolyzates is explored in order to evidence possible inhibitory effect on the bioconversion process by high substrate concentration. Moreover, different ferulic acid purification methods are compared in terms of vanillin molar yields obtained by the bioconversion of the recovered ferulic acid. In addition, the possibility of exploiting the carbohydrate rich water phase obtained after ferulic acid recovery as the growth substrate for the microorganism operating the bioconversion is explored. The results obtained have demonstrated that the high carbohydrate concentration present in crude bran hydrolyzates contribute to the low vanillin yields rather than the high concentration of ferulic acid. Purification of ferulic acid allowed in fact to increase the yields of the bioconversion process. The best ferulic acid recovery method was solid-liquid extraction with ISOLUTE ENV+® cartridges as it allowed the maximum ferulic acid recovery (95%) and good bioconversion yields (up to 75%); moreover the water phase rich in reducing carbohydrates resulting from this extraction is a good growth substrate for E.coli JM109/pBB1.