| Pectin is a polysaccharide compound with complex structure,which can be widely used in food industry,pharmaceutical industry and some cosmetic industry,etc.At present,the main raw materials for the production of commercial pectin are by-products of fruit processing,such as citrus peels and apple pomace.In China,pectin is abundant,but its utilization rate is very low,because most of the raw materials that can be used to produce pectin are directly discarded.If the potential raw materials for pectin production can be exploited,it will bring great economic effects.Celery is a potential raw material for the production of pectin.China is the world’s largest producer and consumer of celery,with 20 million tons planted annually,and the rich pectin is the main source of high value-added products in celery,however,the immature processing technology has led to a low utilization of resources and a low conversion rate of active ingredients.Recently,it has been shown that organic acids such as oxalic acid can be used to assist in the extraction of pectin fractions from plant materials,but the consequent problems are the low extraction efficiency of organic acids,high extraction costs and complex reuse processes.In addition,the structure of pectin is mainly a galacturonic acid(Gal A)skeleton and various monosaccharide branching chains.The complexity of the structure makes it difficult to accurately quantify the pectin components,and the traditional method of acid hydrolysis of pectin has the problem of product re-degradation due to harsh conditions.Therefore,in this paper,the technical conditions and product characterization of the sulfuric acid-assisted extraction of celery pectin were explored and studied with reference to the techniques and principles of bioengineering,and the quantitative determination of the main components in pectin was also investigated.The main results of the study are as follows:1.In response to the problem of imprecise analysis of the main components of pectin,an accurate method for the determination of galacturonic acid,the main component of pectin,was investigated,and a method combining pectinase hydrolysis(PH)and HPLC determination,named PH-HPLC method,was established.The enzymatic conditions were optimized for the enzymatic digestion of 4.0 g/L of substrate commercial pectin at 50 ℃ for 24 h under the pectinase addition of 2250 U/g pectin,and the enzymatic yield could reach 100%,and this process is for pectin is completely hydrolyzed,which can achieve complete degradation of non-destructive quantitative analysis.The reproducibility of the PH-HPLC method was verified,and the quantitative determination of Gal A in two common natural pectin raw materials,beet and citrus peel pectin,showed that the results of pectinase hydrolysis were 45.5～233.1% higher than those of acid hydrolysis.And the relative standard deviations(RSDs)of the results of pectin hydrolysis by pectinase enzymes from two different sources were 1.24 and 1.40%,respectively,both <5%,indicating that the stability and reproducibility of the method were good.2.To investigate the technology of sulfuric acid-assisted extraction for the preparation of celery pectin in response to the problems of high cost and difficult acid reuse caused by organic acid extraction of pectin.The results of the optimization of pectin production from celery stems using sulfuric acid catalytic extraction were as follows: the highest pectin yield of16.58% was achieved at 107 °C with 5% sulfuric acid adjusted to p H 2.2,solid-liquid ratio of1:20 and extraction time of 100 min.The celery pectin extracted by sulfuric acid catalytic method had higher product quality.By comparing the differences of neutral sugar fractions,it was determined that the structure of sulfuric acid-extracted celery pectin was mainly RG-I type,and the structure of commercial pectin was mainly HG and RG-II type.The molecular weight Mw of the sulfuric acid extracted pectin was 93.01 k Da and that of the commercial pectin was126.10 k Da,which is in accordance with the average Mw range(10-150 k Da)of pectins that can be used as food additives from different sources.The DE of the sulfuric acid extracted pectin sample was 16.02%(<50%),which is a low esterification pectin,and the DE of the commercial pectin was 59.08%(>50%),which is a high esterification pectin.3.This study compares the impact of three frequently used inorganic acids,namely sulfuric acid,hydrochloric acid,and nitric acid,on the yield and chemical fractions of extracted celery pectin.Under identical conditions,the yield of pectin extraction using sulfuric acid,hydrochloric acid,and nitric acid was 16.58%,15.91%,and 15.67%,respectively.Therefore,the sulfuric acid catalysis method increased the yield of celery pectin extraction by 4.21% and5.81%,compared to the hydrochloric and nitric acid methods,respectively.The analysis of the celery pectin products extracted by the three acid methods showed that the galacturonic acid content of the pectin products by sulfuric acid,hydrochloric acid and nitric acid methods were34.28%,34.92% and 26.38%,respectively,and the methoxylation(Me O)and esterification(DE)were 0.64%,0.69%,0.72% and 12.82%,16.02% and 17.51%,respectively.The overall analysis showed that the quality of the celery pectin products extracted by sulfuric acid catalysis was higher than those extracted by other acids.4.The rheological analysis showed that the stable value of pectin viscosity for sulfuric acid extraction was 4.0 m Pas,while the constant values of pectin viscosity for hydrochloric acid and nitric acid extraction were 3.0 m Pas and 1.67 m Pas,respectively,and the viscosity of pectin extracted by sulfuric acid was 1.33 and 1.46 times higher than that of pectin catalyzed by hydrochloric acid and nitric acid methods,respectively.The highest viscosity of sulfuric acid extracted pectin among the three inorganic acids was attributed to the higher molecular weight of sulfuric acid extracted pectin,which formed a more coherent 3D network structure.All three samples showed viscosity response(G’<G")in stress test and frequency test at the same concentration and the sulfuric acid extracted pectin exhibited the largest viscosity modulus,demonstrating that the sulfuric acid catalyzed extracted pectin has better viscosity properties than the hydrochloric acid and nitric acid extracted pectin.The antioxidant capacity of different acid-extracted celery pectin was compared by DPPH radical scavenging rate experiment,and the results showed that when the pectin concentration was 0.8 mg/m L,the sulfuric acid-extracted celery pectin showed 41.71% scavenging rate of DPPH,while the hydrochloric acid and nitric acid-extracted celery pectin showed 33.48% and 27.23% scavenging rate of DPPH,and the sulfuric acid-extracted pectin showed stronger DPPH scavenging rate,which was 1.24 and 1.53 times higher than that of hydrochloric acid and nitric acid extracted pectin,respectively. |
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