| Pectin is a kind of natural multifunctional hydrophilic colloid,which has been widely used in food,cosmetics,and medicine industry.It is mainly used as gel thickener,stabilizer,and functional transport carrier.LM pectin gel is not limited by sugar and acid and is used to produce low sugar products,so it is more popular.At present,the industrial production of LM pectin is mainly through acid/base/enzyme deesterification of high ester pectin,while the development of natural LM pectin resources is another effective way.Nicandra physaloides(Linn.)Gaertn seeds(NPGS)pectin is a kind of"food and medicine"resource,which can be scrubbed in water to obtain thick pectin to make"shiliangfen".However,the structure,gel properties and emulsifying properties of NPGS pectin need to be studied.In this study,the water method was used to extract pectin from NPGS,characterize its composition,reveal its spontaneous gelation mechanism,preliminatively explore the mechanism of monovalent cation,acid and sugar inducing its gelation,clarify its emulsifying and emulsion stabilization mechanism,and provide theoretical reference for the commercial application of NPGS.Firstly,the water extraction mechanism of NPGS pectin was studied,and the pectin components were characterized.The results showed that the seeds were composed of external pectin layer which was soluble in water and internal hard core.This explained the scientific reason why the traditional process could prepare"shiliangfen"by simple water washing.In addition,the yield of water extraction of the pectin was 10.56%,the content of galacturonic acid was 65.80%,the esterification degree was 46.93%,the molecular weight was 631.15 k Da,the water content was 14.32%,the total ash was 2.24%,the acid insoluble ash was 0.23%,the protein was undetectable.Therefore,the purity meets the national standard.The above results suggest that the seeds are probably a good source of natural LM pectin,and the pectin could be easily extracted by water.Secondly,the spontaneous gelation was destroyed by three dissociating agents respectively.EDTA was used to bind the divalent cation to destroy the electrostatic interaction;Urea was used to break hydrogen bond interaction;SDS was used to destroy the hydrophobic interaction.Finally,the mineral contents in the pectin were determined to explain the spontaneous gelation mechanism.The results showed that1.5%(w/w)of the pectin could spontaneously gel at room temperature,and the endogenous mineral content of pectin were K(48.7 mg/g),Mg(9.5 mg/g),Ca(3.6mg/g),and Na(0.49 mg/g).The endogenous divalent cations of pectin were insufficient to induce gelation.Hydrogen bond interaction caused by K~+and hydrophobic interaction caused by methyl group played major role in the process of spontaneous gelation,and the three forces worked together to cause the spontaneous gelation.Furthermore,a rheometer was used to further study the properties of the gelation induced by monovalent cation,acid,and sugar,and the mechanism of the unique gelation properties(wide range of gelation conditions)was preliminarily analyzed.The results showed that Na~+and K~+could induce the gelation of the 1%(w/w)pectin to be weak-gel state.GDL could induce the gelation of the pectin solution by adjusting the p H value,when the p H value was 3.71,the gel was in solution state,and when the p H value was between 2.19 and 3.5,the gel was in true-gel state,and the gelation speed of pectin was faster as the higher concentration of GDL.In addition,sucrose and glucose could hardly induce the gelation of 1%(w/w)pectin to be gel state alone,and only had a certain thickening effect,but had synergistic enhancing effect on acid-induced gel.These results indicated that the gelation conditions of NPGS pectin were very wide.Both Na~+/K~+and GDL could induce gelation,while glucose and sucrose could significantly enhance the gel strength induced by GDL.It was noteworthy that the pectin was very sensitive to p H value,which might be related to the fine structure of the pectin.Finally,the emulsifying and emulsion stabilization mechanism of three kinds of pectin(NPGS pectin-NP,apple pectin-AP,and citrus pectin-CP)were compared in terms of emulsions system,interface layer and pectin structure.The results showed the emulsifying properties of NP was superior to AP and CP,which attributed to lower interfacial tension(～15.57 m N/m)and better long-term stability to prepared emulsion.The long-term stability of NP emulsion ascribed to the higher emulsion viscosity,more uniform droplet size distribution,stronger electrostatic repulsion,and thicker interfacial layer.Structurally,the emulsifying activity of NP was mainly provided by acetyl and methyl groups,and the emulsifying stabilization was provided by the neutral monosaccharide side chains and ionized carboxyl groups.Therefore,the protein in pectin was not essential for the stabilization of oil-water interface,and the carbohydrate components played a crucial role in when especially lack of protein. |
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