Study On The Color Mechanism And Decolorization Process Of Sugar Beet Pectin

Pectin is an acid polysaccharide macromolecule,which has the functions of emulsification,gelation,stability and thickening,and widely used in food,chemical industry,medicine,textile and other industries.Sugar beet pectin?SBP?is a kind of polysaccharide extracted from sugar beet pulp.The traditional extraction method of SBP is hot acid maceration,and the pectin extracted by this method often present high value of color,which limits the application.This paper investigated the source of SBP pigment,SBP coloring mechanism,and put forward a kind of low color value of SBP production methods.Providing the theoretical reference to improve its added value.1.Explored the source of pigment in SBP.Compared the decoloration effect of SBP between using alcohol washing,dialysis and H₂O₂ bleaching,and the effect of H₂O₂ bleaching was found to be obvious.Because the physical washing and filtration could not decrease the color value of pectin,it was suggested that the pigment of pectin was not caused by the small molecules,but might caused by the endogenous pigment of pectin.When the concentration of H₂O₂ was 3%and the decolorization time was 1h,the decolorizing effect was the best.However,the content of galacturonic acid in pectin was significantly lower than that in untreated pectin,which were 50.1%and 75.5%respectively.The content of neutral sugar decreased from 23.3%to 11.6%,besides the molecular weight and emulsification activity was also decreased.It suggesting that H₂O₂ bleaching process significantly modified the molecular structure of pectin.It was also indicated that pectin molecules were not easy to adsorb on the surface of emulsified particles,resulted in lower emulsification activity as the molecular weight of pectin decreases and the branch chain decreases.Therefore,the next step is to look for a gentle and effective decolorization method.2.Study on the degradation rule of SBP.The side chains of SBP was removed by trifluoroacetic acid,and it was found that trifluoroacetic acid could effectively remove the pectin side chain,but had no obvious effect on the main chain of pectin.Compared the color value of the hydrolyzed pectin and the original sample,it was found that the pectin side chain had a chromogenic substance.And the solution was extracted and separated by liquid solution.HPLC and HRMS were used to identify pectin acid excision materials containing a large amount of ferulic acid.Using the Arrhenius equation,the activation energy of SBP demethylation reaction was 50.6 KJ/mol,and the activation energy of pectin molecular degradation was 27.7 KJ/mol.3.Determination the color group of SBP.Using three methods?acid treatment,alkali treatment and alkali plus hydrogen peroxide?to process SBP,in order to destroy the main chain and side chain of pectin.Investigated the small molecular substance effect of color of pectin.The chemical constituents of pectin samples were analyzed and the morphological characteristics of pectin molecules were observed by AFM.Acid treatment can remove the side chains of pectin,resulting in a decrease in neutral sugar content and a corresponding increase in galacturonic acid content.Alkali treatment causes the main chain of pectin to take place?-eliminate reaction,reduce the molecular weight of pectin,and can destroy the ferulic acid ester bond,so that ferulic acid dissociates.H₂O₂ treatment destroyed the conjugated structure of ferulic acid and protein,and gives the pectin a good color.By the determination of the content of ferulic acid and aromatic amino acids in pectin,the color difference of the samples obtained by different methods were compared and analyzed,and the chromophore group of pectin was determined.The decolorization process and color mechanism of pectin are described visually through schematic diagram,which provides theoretical basis for the production of low color beet pectin.4.The extraction process parameters of SBP were optimized by full-factor test.The effects of temperature,time and pH on the extraction rate,color value and chemical structure of SBP were investigated.The results showed that the extraction yield of SBP was4.0%¹4.1%,the color value was 0.32².02,and the SBP was rich in galacturonic acid?58.1%⁶3.8%?,neutral sugar?15.2%¹9.8%?and a small amount of protein remained?0.39%¹.54%?.The methylation degree and acetylation degree of SBP were 33.2%⁴6.8%and 18.0%²6.5%respectively.The molecular weight of SBP was determined by HPSEC.The results showed that the molecular weight of SBP obtained from different process parameters were from 322 to 488 kg/mol,and the difference was obvious.The results showed that the extraction temperature had significant effects on the GalA,NS and protein content of SBP,and the pH had a significant effect on the extraction yield and color difference.Considering the extraction yield,color value and emulsification of SBP,the extraction conditions were suggested as:extraction time of 2 h,extraction temperature of 80?,and pH=1.5.