Emulsifying properties of pectic polysaccharides obtained by sequential extraction from black tomato pomace

The polysaccharides in black tomato pomace (BTP) were extracted by water, cyclohexane-trans-1,2-diamine tetraacetic acid, Na2CO3 and KOH to obtain hemicellulose fraction (HF) and pectic fractions including water-soluble pectin (WEP), chelator-extractable pectin (CEP), sodium carbonate extractable pectin (NEP). Structural characterization indicated that WEP, CEP and NEP were high-methylated (68.02%, 61.58% and 59.70%, respectively). Percentage content of the major domain, linear homogalacturonan (HG), in WEP, CEP and NEP were 70.44%, 84.07% and 60.08%, respectively, while the percentage content of branched rhamnogalacturonan (RG-I) were 10.97%, 5.32% and 29.08%, respectively. The results were also confirmed by atomic force microscope (AFM) images. DSC results showed that the Tm of CEP and NEP was higher than WEP. Evaluation of emulsifying property suggested that the pectic fractions could stabilize emulsion containing 50% oil phase at a concentration as high as 1.5% (w/v) and pH 4.0–8.0. Pectin's ability to lower surface tension and increase viscosity, along with the repulsion in pectin molecules, facilitated emulsion formation. Protein residue (WEP) and structure difference (CEP and NEP) might be responsible to the distinction of emulsifying capacity.