The Research On Polyphenols And Red Pigments In Jujube Skin

This paper reports polyphenol extraction and the stability and separation of red pigments in jujube skin, and mainly discusses the extraction and separation of the red pigments. The optimum extraction conditions and separation methods of polyphenols and red pigments were established, and the red pigments were identified preliminarily. The main findings are as follows:It was showed that jujube skin contained polyphenols. The method of measuring the polyphenols content in jujube skin was established gallic acid as reference standard.Acetone - water was used as solvent in polyphenols extraction from the jujube skin. Following five extraction conditions were studied: extraction time, times, temperature, acetone concentration, and ratio of solid skin to solvent. The result showed that the optimum extraction conditions obtained was as follows: 45% acetone concentration, ratio of solid skin to solvent at 1:25, temperature at 70℃, extraction for 2 hours. The extraction yield obtained was 0.8388% with this method. The descending order of above factors was: A (acetone concentration)> B (temperature)> D (ratio)> C (time).Absorbance at 540nm was selected for measuring the red pigments in jujube skin. Acidic ethanol solution was mainly used in red pigment extraction. Five extraction conditions were studied: pH, temperature, time, and ratio of solid skin to solvent. The result showed that the optimum extraction conditions obtained was as follows: temperature at 85℃, extraction for 2 hours, pH 0.5 acidic ethanol solution, and ratio of solid skin to solvent at 1:30. Under these conditions, the extraction yield of red pigment obtained was the highest. The descending order of above factors was: A (pH)> C (temperature)> B (time) > D (ratio).Studies on the stability of red pigments in jujube skin showed that the red pigments were stable under avoid light, K⁺, Ca²⁺, and Mg²⁺ in the acidic solution, and were instable under heat, strong oxidants, citric acid, Fe³⁺, and Zn²⁺. Sweeteners had no significant effect on the pigment stability, but reducing agents had stable effect on the red pigments in jujube skin.Red pigments were separated through the pH gradient of sodium bicarbonate, sodium carbonate, sodium hydroxide solution, then red pigments of the crude and refined by thin-layer chromatography were analyzed preliminarily by UV and IR spectral. The results suggest that the main components of red pigments in jujube skin may be anthraquinones.