Extraction, Antioxidant Activity And Gastrointestinal Accessibility Of Raspberry Polyphenols

Raspberry（Rubus chingii Hu）is a kind of medicinal and edible plant,which immature berries are astringent Chinese medicines with the functions of invigorating the kidney and strengthening the essence and anti-aging.The ripe berries can be eaten fresh and processed into jams and fruit wines.Modern studies have shown that R.chingii Hu is rich in polyphenol compounds which has significant antioxidant,anti-inflammatory and antitumor activities.It is widely used in food,medicine,health care products and cosmetics.However,at present,there are limited efficient green extraction methods for polyphenols of R.chingii Hu.The stability of its oral and gastrointestinal stability is also lacking.Therefore,this paper optimizes the ultrasonic-assisted deep eutectic solvents（DES）extraction process of polyphenols from R.chingii Hu,which also systematic analysis of the chemical and antioxidant activity differences between extractable free polyphenols and bound polyphenols of R.chingii Hu,and then to study the gastrointestinal stability and bioavailability of polyphenols from R.chingii Hu.It hopes to provide theoretical clues for the deep development of R.chingii Hu.The main conclusions of this study are as follows:1.Deep eutectic solvents with ultrasound-assisted extraction（DESUAE）process optimization of polyphenols from R.chingii Hu.Through single factor test and response surface design,the ultrasound assistance was optimized,and DES（choline chloride+lactic acid）was used as the extractant to extract polyphenol compounds of R.chingii Hu.The optimal extraction conditions for polyphenols by DES-UAE were established as follows:material-to-liquid ratio of 1:45（g/mL）,50%water content and 50 min extraction time.Under these conditions,the total polyphenol extraction content was 95.08 mg GAE/g DW,which were about twice that of water with ultrasound-assisted extraction（W-UAE）;the total flavonoid extraction content was 52.24 mg RE/g DW,which were higher than the extraction volume of organic reagents.The total tannin extract content was 8.04 mg CE/g DW,which were close to the predicted value.HPLC was used to identify the chemical composition of polyphenols from R.chingii Hu,and 10 standard products could be detected in the DES-UAE polyphenol extract.The main phenolic acid compounds were ferulic acid and gallic acid,rutin is the higher content of flavonoids,followed by epicatechin and epigallocatechin.2.Research on the chemical composition and antioxidant activity of polyphenols from R.chingii Hu.We compared and analyzed their respective polyphenols,flavonoids,tannin content and in vitro antioxidant capacity,which selected 40%ethanol solution with ultrasound-assisted extraction（EUAE）and acid with water-bath extraction（A-WBE）,alkaline with water-bath extraction（B-WBE）,complex enzymatic with water-bath extraction（C-WBE）to extract free polyphenols and bound polyphenols.Moreover,we used HPLC to qualitatively and quantitatively identify the composition and content of phenolic compounds from R.chingii Hu.The contents of polyphenols,flavonoids and tannins extracted by E-UAE were more than those extracted by water with ultrasound-assisted extraction（W-UAE）,indicating that the extraction efficiency of E-UAE for free polyphenols was much higher than that of W-UAE.The content of bound polyphenols obtained by A-WBE was more than that of B-WBE and C-WBE,which is almost 4 times that of CWBE.However,different extraction methods had little effect on the changes of flavonoids and tannins.It could be seen that for the release of bound polyphenols,A-WBE is more effective than B-WBE and C-WBE.In the free polyphenols,the higher content of phenolic acid were syringic acid and caffeic acid,and the higher content of flavonoids were rutin,epicatechin and p-hydroxybenzoic acid.The types and content of free polyphenols extracted by E-UAE were more than those of W-UAE.The composition and content of bound polyphenols extracted by B-WBE were more than those of A-WBE and C-WBE.Among them,syringic acid had a higher content of phenolic acids,and rutin was the higher content of flavonoids in A-WBE and B-WBE.The results of free polyphenols were consistent,and the higher content in CWBE was p-hydroxybenzoic acid.3.The gastrointestinal stability and bioavailability of polyphenols from R.chingii Hu.In vitro simulated digestion model was used to study the release of the powder,free polyphenols and bound polyphenols from R.chingii Hu in the oral,stomach,and intestinal digestion process and changes in antioxidant activity,through HPLC analyzing the composition and content.The order of phenolic compound content from high to low was powder>free polyphenols>bound polyphenols,and free polyphenols had the highest intestinal permeability.Meanwhile,the composition and content of phenols in each digestion stage were analyzed.Caffeic acid,syringic acid and phydroxybenzoic acid were the main polyphenols in the digestion process of powder from R.chingii Hu,and syringic acid and p-hydroxybenzoic acid were also the main polyphenols of free polyphenols and bound polyphenols.Except for the small intestine-SF stage of free polyphenols,Tiliroside was detected in other digestion processes.It could be seen that tiliroside could be stably released in all stages of in vitro digestion.Powder of R.chingii Hu showed strong antioxidant capacity after digestion,followed by free polyphenols,and bound polyphenols the weakest.The antioxidant activity was positively correlated with the content of polyphenols.