Purple Potato Physical And Chemical Quality Of The Pigment

Purple potato is a choicedness variation of potato(Solanlum tuberosum L.),which is rich in anthocyanin beside the nutrition compositions. Anthocyanin showed a good sensory with attractive color.Purple potato was mainly planted by farmyard manure without any chemical fertilizer and poisonous substances.Therefore,purple potato was regarded as a kind of health-care food with natural,pollution-free,nutritional and functional characteristic.The study included four parts such as physical and chemical properties of composition,distribution feature and optimal extraction of the pigment, and its functional properties.The results indicated that solid substances, especially carbohydrate of purple potato were significantly higher than that of general potato(P＜0.05 and 0.01).The contents of protein,fat and ash in purple potato was not significant difference compared to general potato. Moreover,the purple potato were rich in minerals including Se,Fe,Ca,P and so on.There was a high content of anthocyanins in cortex and pitch.The pigment content in cortex was the highest of all parts.So,the purple potato indicated higher nutrition value and more healthy function than general potato.Most of the starch granules in three kinds of purple potato were ellipse, smooth,and size different with hilum.The diameter of starch ranged from 39.468 to 46.038μm.DSC showed that△Hgel was 4.902～5.829 J/g and the temperature of To,Tp,Tc were 62.353～64.931℃,65.173～67.703℃, 70.437～72.890℃,respectively.The gelatinization temperatures of purple potato starch were higher than the favorita starch.The purple potato pigment was anthocyanin composition.Acid polar impregnant would be the appropriate solvent to extract the pigment.The response surface methodology was used to evaluate the factors affecting extracting pigment from purple potato based on single factor test.The optimum conditions were established as that the ratio of material-to-solution was 1:30(g/ml),the concentration of HC1 was 1.1%(v/v),the exacting temperature was at 54.8℃and time was 1 hour.Each exaction repeated two times,the rate of pigment extracted was around 93.78%. The purple potato pigment was good water-solubility and heat-resistant in acid environment,but was sensitive to the pH value of environment,light, oxidizer and high concentration of some reducers.The maximum absorption wavelength of this pigment is 528nm when the pH value is at pH1 and pH3. The influences of Cu²⁺,Fe²⁺,Fe³⁺,Al³⁺,Mg²⁺,Ca²⁺ on the pigment are not obvious,moreover Cu²⁺,Fe²⁺ can increase its chroma.The pigment had activity against Bacillus subtilis,Staphylococcus aureus,Salmonelle Dublin and Escheriehia coli.The minimum concentrations of inhibiting the bacterials was 41.75mg/L,25.05mg/L, 25.05mg/L and 300.58mg/L,respectively.And the pigment showed a good effect on scavenging DPPH·(1,1-diphenyl-2-picryl-hydrazyl).The amount of the pigment scavenging DPPH as half of orginal amount(EC₅₀) was 20.842mg/L.