Mango (Mangifera indica) and ambarella (Spondias cytherea) peel extracted pectins improve viscoelastic properties of derived jams
Food industries in developing countries are faced with the problem of inadequate supply of additives which can be met by proper utilization of local pectin sources. Mango (Mangifera indica) and ambarella (Spondias cytherea) peels are most of the time thrown into nature or used for animal feeding. They have been reported to be a potential source of pectins which could be used to process the fruits into various products. In order to assess their feasibility to be used in jam processing, ambarella and mango (Mango variety) peel pectins were extracted using three different extraction conditions: HCl at 85 °C/1h, water at 70 °C/1h and oxalic acid/ammonium oxalate (OAAO) at 85 °C/1h. Compare to commercial lime pectin with degree of methoxylation (DM) 70%, phase diagrams presenting sol-gel transition of purified pectins established as sucrose concentration (40-75 %, weight/weight) versus reduced pectin concentration (0.1-1.8 %, weight/weight) were studied at pH 3. Mango and ambarella jams were prepared with and without highly methoxylated peels pectins (0.4 %; DM 60-75%) and the effect of pectins on jam firmness was studied. Prepared hot jams, with 64 % of dry matter, 60 % of sucrose and/or 0.4 % of pectin, were characterized for their gelation kinetics and mechanical spectra at 20 °C. Phase diagrams showed that at pH 3, the minimal sucrose concentration used to obtain the gel is 40 % for OAAO mango pectin, 45 % for HCl mango and OAAO ambarella pectin, and 50 % for HCl ambarella and commercial pectin. Only gelation of OAAO extracted pectins was possible at low polymer (0.2 %) and standard sucrose (60 %) concentrations. Jams prepared without pectins exhibited a week gel behaviour (G' = 500-1000 Pa at 10 Hz) with those of ambarella being stronger than those of mango. Because of its good physicochemical characteristics, ambarella pulp was more suitable than mango pulp for jam processing. Mango and ambarella jams exhibited very strong gels (G'=2000-5000 Pa at 10 Hz) behaviour while using OAAO extracted pectins; the viscoelastic strength of the processing fruits increases 3-6 folds. Accordingly, OAAO extracted mango and ambarella peel pectins allow to obtain jams with excellent gelling properties.