Ethanol Precipitation Properties Of Sugar Beet Pectins Combined With Bovine Serum Albumin

Ethanol precipitation method is widely used to separate and precipitate pectins as a main technique in the pectin industrial production.The method operates simply,and the nontoxic precipitant is not volatile,has less residues and impurity substance.However,the property of this method determines it may consume a lot of ethanol in ethanol precipitation process inevitably.Besides,due to the technique and cost limits,it is very difficult to recover and recycle the used ethanol.Therefore the precipitant,ethanol,determines the cost of pectin production to a large extent.Based on that,improving the pectin precipitation rate to save ethanol has become a common goal of the researchers.The effects of p H and ethanol concentration on the alcohol extraction rate and physicochemical properties of sugar beet pectin(SBP)were explored firstly,and a binding phase diagram based on the electrostatic interaction between SBP and bovine serum albumin(BSA)was established then.At last,eligible SBP/BSA complex solutions were prepared with the help of the phase diagram.On this basis,the SBP/BSA co-precipitation process and mechanism under different precipitation conditions(ethanol concentration,pH,BSA ratios)were studied.The main conclusions are as follows:Ethanol precipitation experiments of cation resin purified SBP and non-purified SBP were carried out.The molecular structure of SBP was analyzed by various chromatographic techniques.It indicated that the endogenous cations had promoted the ethanol precipitation rate of SBP during the process.The SBP precipitation rate promoted as the ethanol concentration increasing from 31.67% to 71.25%,and increased from 42.61% to 57.23% when the initial pH(I-pH)reduced from 4.5 to 2.5 with a system ethanol concentration of 71.25%.The above results showed that the ethanol concentration and I-pH of SBP solution had a significant effect on the precipitation rate of pectin.The galacturonic acid content in SBP ranged from 64.81% to 68.37%.Neutral sugars could be found in all the samples in varying degrees,mainly included rhamnose(Rha),arabinose(Ara),galactose(Gal),glucose(Glc)and xylose(Xyl),among which Rha,Ara and Gal were three main neutral sugars.The methylation degree(DM)of SBP ranged from 45.36% to 51.49%,and the acetylation degree(DA)from 19.32% to 23.97%.All the samples turned out to be low-methoxyl pectins.The molecular weight of SBP ranged from 145.07 kg/mol to 404.27 kg/mol,and the protein content ranged from 8.81% to 9.27%.The I-pH and the system ethanol concentration had effects on SBP structures in varying degrees.Zeta potential of SBP/BSA complex systems in varies pH and BSA ratios were measured.By measuring the scattering intensity and hydrodynamic radius in different conditions,the SBP/BSA complex phase diagram was established by studying the changing process of SBP/BSA complex structures.The results showed that it was necessary to ensure the system pH value less than 4.9 to form SBP/BSA complex.The scattering intensity of SBP/BSA complex system was related to its hydrodynamic radius.In general,the larger the scattered light intensity was,the smaller the hydrodynamic radius was,and then the size of the dispersed phase was smaller,the complex solution became more clear and transparent.The scattering intensity of SBP/BSA composite system reflected the phase transition process when SBP and BSA interacted with each other.And the lower system pH value was,the less BSA required to achieve the maximum scattered light intensity.According to the phase diagram,the complex pH value range was confirmed from 2.5 to 4.5 and the BSA ratio range was confirmed from 0 to 0.25 to ensure the following experiment.The co-precipitation process of SBP/BSA in ethanol system was studied,and the obtained complexes were analyzed through various chromatographic techniques.The results showed that the ethanol precipitation rate was influenced by system initial pH,system ethanol concentration and BSA ratios of the mixture.In general,a smaller I-p H value,a higher ethanol concentration and a higher BSA proportion jointly resulted in the promotion of SBP precipitation rate.The Fourier Transform infrared spectroscopy indicated that the electrostatic interaction mainly formed between negatively charged carboxyl groups of SBP and positively charged amino groups of BSA.BSA was able to precipitate in accompany with SBP in ethanol system.The precipitated complexes contained three types of proteins: original conjugated protein,BSA and free small molecule protein in SBP.The co-precipitation study showed that BSA had reduced the hydration of SBP significantly and made SBP more unstable in the ethanol system,thus improved the ethanol precipitation rate of SBP markedly.The emulsions were produced by the precipitated SBP/BSA mixtures at a low pH value(pH 3.5).The particle size and particle distribution of the emulsion were measured and the stability of the obtained emulsion was compared with that prepared by pure SBP.Then the emulsion stability was evaluated by CLSM images and emulsion stratification.The results showed that SBP had a good emulsifying activity,and the particle size of the prepared emulsion was about 1?m.The presence of BSA let the emulsion droplets more dense,and also more difficult to deform and agglomerate,thereby improved the stability of SBP emulsion to a great degree.