Extraction,Purification And Steady-state Complex Of Anthocyanins From Purple Corn Cob

Purple corn(Zea mays L.)belongs to the genus Zea of Gramineae.This plant is dark purple to black in color,so it is also called black corn.Studies have shown that anthocyanins in purple corn cob(PCC)are abundant and have many physiological activities,such as antioxidant,hypoglycemic,anti-obesity,anti-inflammatory and so on.PCC is a by-product of processing.Because of its wide range of sources and low price,it is an ideal raw material for extracting anthocyanins in the food industry.However,anthocyanins are unstable during gastrointestinal digestion,thereby reducing their bioavailability.In this study,we optimized the procedure of extraction by ultrasonic and purification of anthocyanins from PCC,and carried out qualitative and quantitative analysis.On this basis,four steady-state complexes were prepared: pectin purple corn cob anthocyanin(PC-PCCA),isolated whey protein purple corn cob anthocyanin(WPI-PCCA),isolated whey protein pectin purple corn cob anthocyanin(WPI-PC-PCCA)and chitosan purple corn cob anthocyanin pectin(CS-PC-PCCA).The physical properties,antioxidant activity,hypoglycemic activity and in vitro digestibility of the steady-state complexes were compared.In addition,in order to explore its steady-state mechanism,the structure of steady-state complexes was studied.The purpose of this study was to optimize the process parameters for the extraction and purification of purple corn cob anthocyanins(PCCA),and to screen out PCCA stabilized complexes with good stability.And clarify the mechanism of its stabilization,provide theoretical basis for its development and application in the field of food and functional food.The main results are as follows:(1)On the basis of single factor experiment,response surface methodology was used to optimize the process of ultrasonic extraction of PCCA.The effects of extraction solvent,solid-liquid ratio,ultrasonic temperature,ultrasonic power and ultrasonic time on the extraction rate of PCCA were investigated.The optimal process parameters obtained by response surface method are: absolute ethanol:0.2mol/L citric acid solution(7:3)as the extraction solvent,solid-to-liquid ratio of 1:63(g/m L),ultrasonic temperature of 58 °C,ultrasonic power of 240 W,and ultrasonic time of 41 min.The extraction yield of anthocyanins was 118.89±1.148 mg/100 g.(2)PCCA was purified by D-101 macroporous resin,and the best purification process was determined by single factor test.Among them,the loading concentration is 0.03 mg/m L,the p H of the loading solution is 4,and the loading volume is 11 BV.70% ethanol solution is the best for isocratic elution,and for gradient elution,it is best to remove impurities with water and 10% ethanol,and then elute with 30% ethanol solution.The purity of anthocyanins obtained by gradient elution(21.74%)was higher than that by isocratic elution(11.13%),which was 14 times higher than that before purification(1.54%).(3)A total of 23 anthocyanins were identified by HPLC-Q-TOF-MS.The results of quantitative analysis showed that the anthocyanins of PCC were mainly Pelargonidin-3-O-(6’’-malonylglucoside)、 Peonidin-3-O-(6″-malonylglucoside)、 Cyanidin-3-O-(6’’-malonylglucoside)、 Pelargonidin-3-O-(dimalonylglucoside)、 Peonidin-3-O-(dimalonylglucoside)、 Cyanidin-3-O-(dimalonylglucoside)and Cyanidin-3-O-glucoside.The contents are 999.26±5.71、808.11±7.80、383.14±0.17、686.35±10.84、395.82±2.31、110.43±0.06 and 291.84±2.14 μg/g.(4)The encapsulation efficiency and average particle size of PC-PCCA、WPI-PCCA、WPI-PC-PCCA and CS-PC-PCCA were in the range of 41.80 ± 0.05% ～ 58.84 ± 2.82% and100～400 nm,respectively.The encapsulation rate of CS-PC-PCCA is good(48.13%±2.73),second only to WPI-PC-PCCA.CS-PC-PCCA has the weakest hygroscopicity,the lowest solubility and the highest absolute value of zeta potential,indicating that its sustained-release property and solution stability are the best.SEM analysis shows that PC-PCCA、WPI-PCCA and WPI-PC-PCCA are spherical or oval,but they are relatively aggregated.However,CS-PC-PCCA is multi-granular and irregular in shape,and the aggregation degree of CS-PC-PCCA is lower than the other three complexes.XRD analysis showed that the four steady-state complexes were amorphous.FT-IR analysis showed that PC-PCCA and WPI-PC-PCCA are combined by hydrogen bond,WPI-PCCA is combined by hydrogen bond and hydrophobic interaction,and CS-PC-PCCA is combined by hydrogen bond and electrostatic interaction.(5)DPPH·,ABTS+ free radical scavenging capacity and α-glucosidase inhibition of PC-PCCA、WPI-PCCA、WPI-PC-PCCA and CS-PC-PCCA were studied.The results showed that the DPPH·,ABTS+ radical scavenging ability of the four steady-state complexes was slightly lower than that of PCCA due to the interaction between hydroxyl groups of PCCA and wall material.But the inhibitory ability of α-glucosidase was increased except for WPI-PC-PCCA,and the order from strong to weak is CS-PC-PCCA >PC-PCCA >WPI-PCCA > PCCA > WPI-PC-PCCA.The simulated in vitro digestion results of four steady-state complexes showed that PCCA and its steady-state complexes were relatively stable in the mouth and stomach.After intestinal digestion,the content of anthocyanin monomer decreased significantly.Among them,the retention rates of total anthocyanins and monomers of the steady-state complex were significantly higher than those of PCCA,indicating that the steady-state complex was more stable in gastrointestinal digestion.The order of in vitro gastrointestinal digestive stability of the four compounds from strong to weak was CS-PC-PCCA > PC-PCCA > WPI-PCCA >WPI-PC-PCCA.