| Potato pulp is a byproduct in potato starch production, and the fresh potato pulp containing high water content not only occupies a large space, but also results in environmental pollution. Since potato pulp is rich in pectin, but its utilization efficiency is low, and only a few investigations on potato pulp pectin and no study PPP's structure and properties have been reported, PPP has been prepared to study its structure and properties, and the feasibility of PPP application in yoghurt as thickener has been investigated in this paper.On the basis of single factor experiment, water, acidic and acidic assisted microwave procedure were used to extract PPP from potato pulp respectively, and saturated aluminum sulfate was used to precipitate PPP. The optimal conditions for extractions are as follow: for water extraction, the ratio of material and liquid was 1:15, the extracting temperature was 90℃, and the extracting time was 60 min; for acidic extraction, the ratio of material and liquid was 1:15, pH was 2.0, the extracting temperature was 90℃, and the extracting time was 60 min; for acidic assisted microwave extraction, the ratio of material and liquid was 1:15, pH was 2.0, the power was 600 W, and the extracting time was 6 min. The optimal condition for precipitation was 4 mL saturated aluminum sulfate per 5 g potato pulp, pH5.0, 50℃and 45 min. The yield of PPP extracted by water, acidic and acidic assisted microwave procedure were 14.8%, 17.7% and 17.9%, respectively.The differences between CPP and PPP extracted by the three different extracting procedures were studied by testing their apparent, pH, viscosity, drying loss weight, ashes, insoluble hydrochloric acidic compound, degree of esterification, content of total galacturonic acid and gelling strength. The results showed that PPP extracted by acidic method and acidic assisted microwave method was LMP, and PPP extracted by water method and CPP were HMP. The peak molecular weight of PPP determined by HPGPC was about 41,000 Da. Besides, acidic procedure was founded to be the best extracting method for PPP.DEAE-Sepharose Fast Flow was used to isolate and purify PPP and the results showed that PPP was composed of a neutral polysaccharide and an acidic polysaccharide with a yield ratio of 1:195, indicating APPP was the main component of PPP. The monosaccharides constitution analysis showed that APPP contained Ara, Rha, Xyl, GalA, Glc, Gal and Man, besides a large amount of galacturonic acid. Analyzing by gel chromatography of Sephadex G-100, HPGPC, ultraviolet spectra and infrared spectra, APPP was found to be an anionic polysaccharide with high purity and a 41,161 Da peak molecular weight, containingα- andβ-glycosidic linkages, but no protein, peptide or nucleic acid. 1%~5% (w/w) of APPP all exhibited as pseudoplastic liquid at the shearing rates between 1s-1~100s-1. Because PPP was mostly composed of APPP, and its rheological property was also related to APPP, a preliminary study was focused on the primary structure of APPP.The results of periodic acid oxidation and Smith degradation suggested that APPP's main structure had seldom branches and composed of GalA and Gal, and the core structure of the main chain wasα-(1→4) GalA. Besides, galacturonic acid could be esterified to a certain extent with one branch composing of (1→6) Gal and (1→3,6) Gal in every 12 hexose residues, and having Rha,Ara and Gal as the terminal residues.Comparison study was done to investigate the differences in the viscosity, acidity and sensory evaluation of the self-made yoghurts adding PPP, CPP, CMC-Na), PGA, GEL and AGAR as thickeners. Besides, comparing with CPP production in the same technology conditions, the cost of PPP was lowered by about 20% per ton. Thus, PPP is a good thickener with low cost and high performance, and it can be used in yoghurt production.
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