Physicochemical and rheological properties of gelling pectin from Sosnowskyi's hogweed (Heracleum sosnowskyi) obtained using different pretreatment conditions

Abstract

Using extraction with 0.7% aqueous ammonium oxalate, Sosnowskyi's hogweed pectins (yield 5–10%) with high molecular weight (200–700 kDa) and galacturonic acid content (70–85%), low degree of methylation (17–28%) and neutral sugar content (7–15%) were isolated from fresh, previously air-dried and frozen plant materials. All plant raw materials were pretreated with aqueous formaldehyde at 25 °C and dilute hydrochloric acid (pH 1.0 or 4.0, 50 °C). The different pretreatments of plant raw material slightly affected yield, chemical composition and molecular weight (average value and distribution) of hogweed pectin. The 13C-NMR spectroscopy indicated the similar structure of the pectins isolated from fresh and air-dried hogweed raw materials. The pectins were differed slightly in thermal degradation depending on the type of hogweed raw material. The aqueous solutions of hogweed pectins had a pseudoplastic flow behavior. Dynamic oscillatory shear tests showed that the pectin hydrogels in the presence Ca2+ (R∼0.6) represent true gels. The pectins from fresh plant material (pH 4.0) formed stronger gel networks (G' ∼2400 Pa) then compared to pectins from air-dried (G' ∼1400 Pa) and frozen (G' ∼900 Pa) plant raw materials. The pectin gelispheres of different size, particle shape, density and textural parameters were prepared by ionotropic gelation. The gelispheres derived from hogweed pectins (fresh and air-dried raw materials) were more stiffness compared to the gelispheres from the commercial low methoxyl apple pectin.