Investigating the role of the different molar mass fractions of a pectin rich extract from onion towards its emulsifying and emulsion stabilizing potential

摘要

A pectin rich nitric acid extract produced from onion flesh (NA) showed promising emulsion stabilizing potential. At both pH 2.5 and pH 6.0, emulsions produced with the NA sample as sole emulsifying and emulsion stabilizing compound displayed stable oil droplet size distributions. Moreover, the emulsions showed good stability against creaming. Interestingly, the pectin rich acid extract was characterized by a bimodal molar mass distribution which led to the research objective to investigate the possible role of both polymer fractions in the promising emulsion stabilizing potential. To investigate this, both fractions were separated using centrifugal ultrafiltration. Structural characterization revealed the presence of mainly short chain galactans in the low molar mass fraction (NA-LMM) while the high molar mass fraction (NA-HMM) consisted mainly of pectin. Rheological analysis clearly demonstrated the viscosity increasing effect of NA-HMM in solution while the viscosity of a NALMM solution at equal concentration was comparable to pure water. Emulsions produced with NA-LMM destabilized quickly during refrigerated storage by extensive coalescence and creaming at pH 2.5. Despite presenting a somewhat better stability at pH 6, also in this case fast destabilization was observed. Contrarily, NAHMM showed promising emulsion stabilizing potential. Oil droplet size distributions remained stable during storage at both pH 2.5 and pH 6.0. Creaming was observed for NA-HMM at pH 6.0 although to a lesser extent as for NA-LMM stabilized emulsions. Based on these results, it can be concluded that NA-LMM does not contribute to the emulsion stabilizing functionality of NA. Promising functionality is mainly attributed to the high molar mass polymers.