Screening of glucan and pectin contents in broad bean (Vicia faba L.) pods during maturation

Abstract

This study was performed to investigate broad bean pods (BBPs), a food waste by-product material, for their glucan and pectin contents, at three different stages of maturation, in order to provide basic support for the functional uses of BBPs and for the development of a potential market for bioactive ingredients from residual sources. In the first instance, the isolation of glucans was performed by carrying out an alkaline extraction on the dry BBP flour, at each stage of maturation. The isolated glucans were dialyzed and the crude and soluble samples were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy analyses. Afterwards, the colorimetric method for the enzymatic measurement of glucans was used. This procedure involved partial acid hydrolysis combined with an enzyme complex for the quantitative determination of α- and β-glucans. The results showed that, regardless of the used method, the glucan content increased with maturation. The maximum total glucan yield was recovered from BBPs at third stage of maturation (45 mg/g). The kit-based procedure revealed the variability of the β-glucan amount with maturation whose percentage, compared to total glucans, increased from 47.6 at the first stage up to 61.9 at the third stage. On the contrary, the pectin content in BBPs decreased with maturation. The yields ranged from 8.7% at the third stage to 17.2% at the first stage of maturation. The degree of esterification was determined by the classical titrimetric method and confirmed by the instrumental FT-IR method. The samples showed an average titrimetric value of 43.4% and the typical fingerprint in IR spectra with an average value of 50.5%. The degree of methoxylation remained almost unchanged during maturation, regardless of the method used.