Guava seed storage protein: Fractionation and characterization

Abstract

In the present work, guava seed storage proteins have been fractionated and characterized. Glutelins (86–90 g/100 g) and globulins (≈10 g/100 g) are the main components of the protein extract. Albumins and prolamins are minor components (≈2 g/100 g). Guava seed glutelin extracts, like rice and amaranth glutelins, are legumine-like proteins that, due to their solubility properties, have to be extracted using extreme pH (borate buffer, pH 10, Gt-Bo; NaOH pH 12 Gt-Na), denaturing (borate buffer plus sodium dodecyl sulfate, Gt-BoSDS) or reducing conditions (borate buffer plus 2-mercaptoethanol, Gt-BoME; borate buffer plus sodium dodecyl sulfate and 2-mercaptoethanol, Gt-BoSDSME). The highest yield was obtained with SDS extraction, suggesting that proteins in the seeds form aggregates stabilized mainly by non-covalent interactions. Glutelins are mainly composed of 65 and 67 kD subunits, with a lower proportion of 55 kD subunits. These subunits are formed by disulfide bond-linked polypeptides with molecular masses 40–45 kD, 22–27 kD and 23–25 kD, respectively. The guava seeds protein isolate (GSI) exhibited a polypeptide profile very similar to that of the glutelin fraction. The guava seed could be an alternative source of protein for human and animal consume, additional to this to solve at least in part the pollution problem that fruit processing industry has for discarding this material.