Ultrasound-Microwave Assisted Acid Extraction And Emulsifying Properties Of Pectin From Potato Pulp

In China,potato is mainly used in starch processing industry and after processing starch,a large quantity of waste pulp is produced.The pectin content in the pulp can reach to 17%in dry basis.At present,pulp has not been exploited in a reasonable way,which results in environmental pollution and resource wasting.In this study,the potato pectin was extracted from potato pulp with five kinds of acid extractants?HCl,H₂SO₄,HNO₃,citric acid and acetic acid?and the most suitable extractant was selected according to the differences of yields,structure characteristics and emulsifying properties of the pectin.Afterwards,extraction conditions of ultrasound-microwave assisted acid extraction with the selected acid were optimized,in addition,the composition and structural characteristics of the pectin extracted under the optimal conditions were analyzed.The effects of pectin concentration,oil phase volume fraction and pH values on emulsifying properties of this pectin were also evaluated.The purpose of this research work is to provide a theoretical basis for the comprehensive utilization of potato pulp and the use of the potato pectin in the food processing industry.The types of acid extarctants have effects on the yields,structural characteristics and emulsifying properties of the potato pectin.The highest yield?14.34%?was obtained by citric acid and the lowest yield?4.08%?was from acetic acid extraction.The yields of the pectin extracted by three mineral acids were at the range of 8.38%-9.83%.The pectin was mainly composed of galacturonic acid?31.90%-39.99%?and galactose?49.96%-55.92%?.Rhamnogalacturonan-I?RG-I?was the main domain?60.77mol%-65.54mol%?of the potato pectin and the branching extent??Gal+Ara?/Rha?was23.95-33.34)of RG-I was different for the pectin extracted by different kinds of acids.The pectin from acetic acid extraction had the highest branched RG-I domain followed by the RG-I domain of pectin exracted by HCl?28.45?.The potato pectin extracted by acids can be classified as low methoxyl pectin?DM,21.51%-37.45%?with high degree of acetylation?DA,9.21%-15.38%?.The pectin extracted by acetic acid had the highest degree of methylation and acetylation followed by the degree of methylation?DM,28.61%?and acetylation?DA,11.92%?of pectin from HCl extraction.The protein content of the pectin was at the range of 1.85%-6.97%?dry basis?.The weight-average molecular weight?3.207×10⁵g/mol?of pectin extracted by acetic acid was the highest,while the weight-average molecular weight?2.319×10⁵g/mol?of pectin from citric acid extraction was the lowest.The pectin obtained from HCl extraction enjoyed the highest emulsifying activity?47.71%?and emulsion stability?46.00%?.Considering the results of all the experiments,HCl was the suitable extractant for potato pectin extraction.Ultrasound-microwave assisted acid extraction method was applied for pectin extraction.According to the results of the single factor experiment,the effects of extraction temperature,pH values,and extraction time on pectin yield were investigated by Box-Behnken design experiment when the solid to liquid ratio was fixed at 1:20?g/mL?.The optimal extraction conditions were as follows,temperature was at 93?,pH was at 2.00 and extraction time was at 50 min.The yield reached to 22.86%when it was extracted under the optimal conditions.The monosaccharide composition of pectin extracted with the optimal conditions mainly included galacturonic acid?41.78%?and galactose?49.38%?and the RG-?was the main domain?61.54mol%?in pectin.The potato pectin was the low methoxyl pectin?DM,32.58%?with high degree of acetylation?DA,17.84%?and protein content?4.14%,dry basis?and the weight-average molecular weight of pectin was 1.537×10⁵g/mol.The surface structural features of potato pectin mainly presented as the irregular lamella structure and the topographical features of pectin presented as chains.When increasing the pectin concentrations?0.5%-3%?,the particle size(D_4,3)of fresh emulsions and the creaming index decreased,and the emulsifying activity,emulsion stability and the absolute values of zeta potential of emulsions increased.The emulsifying properties of emulsion were good when the pectin concentrations were higher than 2.5%.The particle size values(D_4,3)of fresh emulsions increased as the oil phase volume fraction increased from 10%to 50%,however,the emulsifying properties and emulsion stability of emulsions increased significantly.The emulsions whose oil phase volume fraction was higher than 40%obtained good emulsifying properties.The particle size(D_4,3)of fresh emulsions was almost independent of pH from 3.0 to 7.0.The emulsifying activity,emulsion stability and the absolute values of zeta potential increased at first and then decreased,while the creaming index decreased at first and then increased.The emulsion with pH 5 obtained better emulsifying properties than emulsions with other pH values.