Study On Extraction And Properties Of Pectic Polysaccharides Obtained By Subcritical Water From Jackfruit Peel

Jackfruit(Artocarpus heterophyllus Lam.)has a long planting history and a good development prospect in Hainan province.With large planting area and yield,it has become a major economic crop in the local agricultural sector.In the production and marketing of jackfruit,the peel,weighing 40-45%of the fruit quality,is often discarded as waste,thereby causing environmental pollution.Besides,the abundant biological resources in the peel are also underutilized.An eco-friendly extraction technology,subcritical water extraction,was established in this study for extracting pectic polysaccharides from jackfruit peel by single factor experiment and response surface methodology.The extract(JFP-S)was compared with the product(JFP-C)extracted by the currently commmon organic acid(citric acid)extraction in physicochemical properties,spectral characteristics,functional properties and in vitro bioactivity.The present work provided reference for the improvement of production efficiency in the jackfruit and other similar industries.The main research contents and results are as follows:(1)Optimizing subcritical water extraction process of pectic polysaccharides of jackfruit peel,the effects of extraction temperature,extraction time and liquid-solid ratio on the extraction rate were investigated.The subcritical water extraction process of pectic polysaccharides was optimized through single factor experiment and response surface methodology.The optimal process conditions were obtained as follows:extraction temperature 138℃,extraction time 9.15 min,and liquid-solid ratio 17.03:1.In these conditions,the extraction rate of pectic polysaccharides(JFP-S)was 14.96%,which was lower than that by the citric acid extraction(16.83%).Nevertheless,the subcritical water extraction could significantly shorten the extraction time.Besides,it was more suitable for the food industry and was more environmentally friendly as it used green and safe solvents(pure water)only.(2)The properties and spectral characteristics of JFP-S and JFP-C were analyzed by liquid chromatography,fourier transform infrared spectroscopy(FTIR),scanning electron microscope(SEM)and differential scanning calorimetry(DSC).The results showed that,the conditions of subcritical water extraction could result in the higher neutral sugar and ash contents in JFP-S,along with comparatively lower galacturonic acid,molecular weight and degree of esterification.However,the subcritical water extraction contributed to obtaining higher contents of protein and amino acids.In terms of spectral characteristics,JFP-S and JFP-C not only showed similar infrared spectrum characteristics but also possessed typical absorption peaks of pectic polysaccharides.SEM observation of the microstructure revealed rougher surface morphology of JFP-S than JFP-C.As shown by the DSC thermodynamic characteristic curves,both of the pectic polysaccharides had relatively high thermal stability.However,the fusion heat of JFP-S was lower than that of JFP-C.It could be speculated based on the above detection results that there were some differences between JFP-S and JFP-C in properties.(3)The rheological,gel and emulsifying properties of JFP-S and JFP-C were evaluated with rheometer,texture analyzer,laser diffraction apparatus and Zeta potentiometer.With regard to rheological properties,JFP-S and JFP-C solutions belonged to non-Newtonian fluids with significant shear thinning characteristics.According to dynamic frequency scanning,elasticity dominated the viscoelasticity of the fluids.Additionally,JFP-S exhibited lower storage modulus(G’)and loss modulus(G")probably due to the weaker polymer chain interactions,which was also reflected in the gel properties.Both of the pectic polysaccharides could achieve rapid gelation relying on high DE value,and the viscosity index of the two samples was obviously lower than consistency.The gel prepared by JFP-S was lower than JFP-C in firmness,cohesiveness,consistency and viscosity index.The emulsifying properties results indicated that the surface weighted mean diameter(d3.2)and volume weighted mean diameter(d4.3)of the JFP-C emulsions were smaller than JFP-S,suggesting better emulsifying activities and stability of JFP-C.The Zeta-potential results also indicated that the emulsion stability of JFP-C was higher.Furthermore,the phase separation profiles of emulsions found out the favorable storage stability of pectic polysaccharides emulsions.Some differences were exhibited in the functional properties between JFP-S and JFP-C.(4)The in vitro biological activities of JFP-S and JFP-C were preliminarily determined through antioxidant experiment and in vitro enzymatic activity screening platform.This research indicated that the stronger in vitro bioactivities detected in JFP-S.As revealed by results of antioxidant experiment,stronger DPPH and hydroxyl radical scavenging activities as well as reducing power were found in JFP-S compared with JFP-C.The experiment demonstrated that both of the pectic polysaccharides were capable of inhibiting the activity of a-glucosidase,a key enzyme that affected blood glucose concentration.JFP-S showed notably higher a-glucosidase inhibitory activity.Overall,the pectic polysaccharide from jackfruit peel was a potential natural a-glucosidase inhibitor.