Extraction and physicochemical characterization of pectin from tomato processing waste

The pectins extracted from tomato processing waste (TW) by the acid method using hydrochloric acid (ATP) and by water (WTP) were analyzed for their chemical composition, galacturonic acid (GalA) content, degree of methylation (DM), solubility (%S), intrinsic viscosity ([eta]), molecular weight-viscosity average (Mw(v)), flow and gelling properties as well as gel texture and color, and were compared against commercial high-methoxyl pectin from citrus (HMC). The maximum yields were: 280 g kg(-1) dry TW, obtained at 85 degrees C, 60 min, pH 2.0 for ATP, and 87 g kg(-1) dry TW at 95 degrees C, 180 min for WTP. The GalA content and DM of pectin extracted from TW were higher than that of HMC. The [eta] and Mw(v) of ATP were in the same order as that of HMC and higher than that of WTP. All the pectin solutions presented a pseudoplastic flow behavior. The consistency coefficient (K) of ATP was significantly was the highest at all pH values studied. The initial (IST) and critical structure temperature (CST) values of WTP (92-85 degrees C) were higher than in ATP (74-52 degrees C). The elastic modulus (G') values of the ATP gels showed weaker gels than that of HMC but higher than WTP ones. The hardness of ATP gels was similar to that of HMC and higher than that of WTP. Tomato pectin gels presented reddish color compared to the HMC gel. The acid method extraction was the best method to reach the maximum yield extraction of TW pectin and provided pectin with physicochemical properties similar to that of HMC.