i THERMAL PROCESSING EFFECTS ON TOTAL ... - McGill University

lentils do not contain any traces of isoflavone content. Therefore, simple phenols and
flavonoids are mostly low molecular weight compounds which can be solubilized in
alkaline conditions or be retained in the fiber matrix, based on their ester linkages (Bravo,
1998).
Figure 2.4 Basic structure and numbering system of flavonoids (Adapted from
Bravo, 1998)
Another group of basic phenolics, tannins, contain at least two phenol rings.
Tannins are highly hydroxylated compounds of high molecular weight, which form
insoluble complexes with proteins and carbohydrates. They are divided into two groups:
condensed and hydrolysable (Bravo, 1998; Kim et al., 2003). Tannic acid, one of the best
known hydrolysable tannins (Fig 2.5) consists of a pentagalloyl glucose molecule that
can be further esterified into five Gallic acid subunits (Bravo, 1998). Additionally,
phenolic compounds act as radical scavengers and chelators of metals ions (Lopes et al.,
1999, Bravo, 1998).
Figure 2.5: Basic Structure of tannic acid (Adapted from Bravo, 1998)
28