Comparative rheology and antioxidant potential of high-methoxyl sugar acid gels of unrefined powder and acid-extracted pectin from two hawthorn (Crataegus pinnatifida) fruit cultivars

Abstract

Hawthorn fruits (Crataegus pinnatifida) present high content of high-methoxyl pectin, able to gel under high-sugar acidic conditions. In this work, the proximate and phytochemical composition of two cultivars of hawthorn fruit and the gelling ability of their unrefined (not further processed) dried powders and their extracted pectins were evaluated and systematically compared with citrus pectins (CP1 and CP2). Mianqiu (MI), a less known cultivar, showed two-fold higher pectin content and titratable acidity than Dajinxing (DA), one of the most common cultivars. DA showed higher starch, insoluble dietary fiber, pasting viscosity and total and extractable (EPP) phenolic compounds. EPP content was almost two-fold higher in DA than MI, resulting in stronger antioxidant properties. All high-methoxyl sugar acid gels exhibited a predominantly elastic response. MI resulted in hawthorn-powder gels with higher elastic modulus (G′) after gel-making (initially stronger gels), and lower G′ increase during storage (hardening) than DA. Citrus pectins (CP2 > CP1) showed higher gel-strength and faster gelling ability than hawthorn pectin gels (DA > MI) based on the lower G’ and lack of gel formation after 90 min of cooling in hawthorn pectin-based gels. The gelation results were closely linked to the starch-to-pectin ratio, purity, and degree of methyl esterification.