Non-enzymatic depolymerization of carrot pectin: Toward a better understanding of carrot texture during thermal processing

Pretreated carrot discs were thermally processed (90 degrees C to 110 degrees C) in closed containers and the resulting textural characteristics were analyzed. The pretreatment conditions used include conventional high-temperature blanching (90 degrees C, 4 min), low-temperature blanching (LTB = 60 degrees C, 40 min), LTB combined with 0.5% calcium chloride soaking, LTB combined with 2% sodium chloride soaking, high pressure pretreatment (HP = 400 MPa, 60 degrees C, 15 min), HP combined with 0.5% calcium chloride soaking, and control (non-pretreated sample). Alcohol insoluble residues (AIR) from the pretreated carrot discs were characterized in terms of degree of methoxylation (DM). The AIR samples were further subjected to fractionation into water-soluble pectin (WSP), chelator-soluble pectin (CSP), and sodium carbonate-soluble pectin (NSP). Heat depolymerization patterns and beta-elimination kinetics were investigated on the different pectin fractions. Thermal texture degradation was strongly influenced by the pretreatment condition used and the processing temperature during subsequent thermal treatment. Pretreatment conditions that showed a significant reduction in DM exhibited decreased WSP content, reduced beta-elimination, and consequently superior textural characteristics. beta-elimination was markedly pronounced in the highly methoxylated WSP fractions. CSP and NSP fractions were insensitive to beta-elimination. A strong correlation (r > 0.95) between thermal texture loss of carrots and beta-elimination kinetics exists. Overall, the benefits of controlled pectinmethylesterase activity in carrot processing were pointed out.