Extraction And Characterization Of Pectin From Premna Microphylla Turcz Leaves

Pectin is a macromolecule polysaccharide widely distributed in plants.It is generally composed of homogalacturonan(HG),rhamnogalacturonan I(RG-I)and rhamnogalacturonan II(RG-II).The major sources of commercial pectins are citrus peels and apple pomace.With the increasing application and demand of pectin,the development of new raw materials and the improvement of pectin production technology have become a research hotspot in recent years.Premna microphylla turcz is a kind of natural plant,which leaves are rich in pectin.In addition,Premna microphylla turcz leaves(PMTL)are traditionally used as raw material for production of "green tofu" with high acceptance,which is essentially a kind of pectin-gel food.However,there are few studies on the extraction,characterization and gelling properties of pectin from PMTL,which would restrict the industrial production and application of PMTL pectin.In this paper,pectin was extracted from PMTL by hydrochloric acid and ammonium oxalate,respectially.The pectin extraction process was optimized,physicochemical properties of pectin were determined,pectin gel properties were studied and applied in gelatin soft sweets.The main contents and results are as follows:(1)The extraction method and process of pectin was studied.pectin was extracted by hydrochloric acid and ammonium oxalate,and the extraction conditions of pectin from PMTL were optimized by orthogonal design.The optimized extraction conditions of hydrochloric acid pectin(HAP)were determined:pH was 1.5,ratio of material to liquid was 1:30(w/v),temperature was 90 ? and time was 120 min.Under these conditions,the yield of pectin was 20.53 ± 0.27%,the galacturonic acid content was 85.83 ± 0.53%.Besides,the optimized extraction conditions of ammonium oxalate pectin(AOP)were determined:the ammonium oxalate concentration was 4 g/L,ratio of material to liquid was 1:50(w/v),temperature was 70?,time was 120 min.Under these conditions,the yield of pectin was 19.72 ± 0.21%,and the galacturonic acid content was 84.72 ± 0.39%.The HAP and AOP were both classified as high methoxyl pectin.(2)The molecular weight,monosaccharide composition,rheological properties and apparent particle morphology of hydrochloric acid pectin(HAP)and ammonium oxalate pectin(AOP)were characterized by liquid chromatography,rheometer and scanning electron microscopy.The results showed that the average molecular weight(Mw)of HAP was 522.27 KDa,while the average Mw of AOP was 648.99 KDa.According to monosaccharide composition analysis,galacturonic acid,rhamnose,glucose,galactose and arabinose were existed both in HAP and AOP;additionally,HAP contained glucuronic acid while AOP contained mannose.Both HAP and AOP exhibited shear thinning flow behavior,compared with HAP,AOP has higher apparent viscosity.The apparent particle morphology of HAP and AOP were different,the surface of HAP particles were massive while the surface of AOP particles were in shape of "twig".(3)The effects of pectin concentration,sucrose addition,temperature,pH and type of metal ions on the gel properties of pectin were studied by using gel strength and water holding capacity as indexes.The results showed that the gel strength and water holding capacity of HAP and AOP increased with the increase of pectin concentration.Besides,the gel strength and water-holding capacity of HAP increased with the increase of sucrose addition(50?65%,w/v),and AOP could form strong gel with 10?20%(w/v)of sucrose concentration.The influence of pH on gel strength of HAP and AOP gels were showed that AOP has a maximum gel strength at pH 3.0 while HAP has a maximum gel strength at pH 3.3.In addition,the gel strength of HAP and AOP could be significantly increased by adding Cu2+ and Ca2+(P<0.05).(4)The effects of pectin addition on the quality of gelatin soft sweet were studied by texture analysis and sensory evaluation.The results showed that the addition of pectin(0.2%?1%)in gelatin soft sweet could improve the thermal stability of gelatin soft sweet,reduce the toughness of gelatin,improve the taste of the soft sweet,and make the gelatin fudge with high elasticity and chewiness easier to break.Besides,the texture properties of soft sweets could effectively reflect the sensory index,in which hardness,elasticity and chewiness were significantly correlated with the corresponding sensory indicators(p<0.05).When the hardness was between 3500 to 3900 g(sensory index was 6.76?8.00),the soft sweets have good hardness and suitable taste,and the tester has high acceptance.In summary,the structure and properties of the pectin extracted from the PMTL by hydrochloric acid method and ammonium oxalate method were significant different.Compared with AOP,HAP had higher yiled and esterification degree.Compared with HAP,AOP had larger molecular weight and stronger gel strength.Besides,both HAP and AOP could reduce the stickiness of gelatin soft sweet and improve the hard taste of gelatin soft sweet.