Adding Value to Crop Biorefineries: Efficient Extraction of Ferulic Acid from Wheat Bran

Abstract

Wheat bran can be considered as a feedstock for future biorefineries, due to the enormous quantities arising in the milling industry and its specific properties. It has a high content of nutritionally valuable and technologically desirable compounds. Development of efficient processes for the isolation of such high-value compounds could represent a real cost effectiveness to the whole process. Ferulic acid (FA) is the most abundant hydroxycinnamic acid found in wheat bran and is of considerable interest due to its antioxidant properties. Its extraction from wheat bran represents a great opportunity to add value. The main inconvenient is that the major part of the FA is in an insoluble bound form, esterified to the arabinoxylans (AX) and other cell wall structural components (≈92%). Hence, new processes are required to break these bonds in order to recover it in high quantities. In this study, different strategies have been tested for ferulic acid recovery, i) extraction with pressurized aqueous ethanol mixtures, ii) microwave-assisted extractions and iii) ultrafast supercritical water extraction. Operational conditions have been studied and optimized for these three extraction processes to maximize the FA extraction yield. The studied variables were: the ethanol:water content in the mixture (20-50-80%), temperature (130-145-160ºC) and extraction time (20-40-60min) in the pressurized solvent extraction process, extraction time (1-10 min) in the microwave-assisted extraction and time (0.15-0.3 s) in the ultrafast supercritical water extraction process. The analysis of the FA profile in the wheat bran use as raw material consists in the quantification of its free, soluble bound and insoluble bound forms. An alkaline hydrolysis is performed in order to release the bound forms, and finally, they are quantified as free ferulic acid by HPLC analysis. In the samples obtained in each experiment, the FA content and the total phenolic content (TPC) are analysed. The TPC analysis is performed by the Folin-Ciocalteu method.