Study On Extraction And Purification,Preparation Of Emulsion,and Simulated Digestion In Vitro Of Zeaxanthin Dipalmitate From The Fruits Of Lycium Barbarum L.

As a well-known edible and medicinal substance,the fruit of Lycium barbarum L.contains a variety of biologically active ingredients that are beneficial to human health.Carotenoids are one important active ingredients of the fruit of L.barbarum.Carotenoid esters are the main form of carotenoids in the mature fruits of L.barbarum.However,little information on carotenoid esters is available due to the widespread use of saponification.More research on carotenoids esters could be done to better develop the industry of the fruit of L.barbarum.In this paper,therefore,the first aim was to develop an accurate and sensitive HPLC method to analyze the carotenoids in the fruits of L.barbarum,determine the optimal extraction conditions for carotenoids extraction,and develop a promising method for the separation of zeaxanthin dipalmitate.The second aim was to develop a suitable oil in water emulsion.The third aim was to evaluate the effects of different food matrices(the emulsion,L.barbarum powder,and L.barbarum-emulsion mixure)on the digestive properties of zeaxanthin dipalmitate by in vitro digestion.This research might provide theoretical support for the production of carotenoid esters and lay the foundation for the improving bioavailability of carotenoids.Main results are listed as follows:1.Extraction and purification of zeaxanthin dipalmitate from the fruits of L.barbarumThe analysis of lutein,zeaxanthin,?-carotene,and zeaxanthin dipalmitate was carried out by using the HPLC.The column was a C30 reversed-phase column.The mobile phase consisted of methanol/water(80/20 in v/v,eluent A)and methanol/methyl tert-butyl ether/water(20/78/2 in v/v/v,eluent B).The HPLC gradient elution condition allowed good separation of the main carotenoids.The carotenoids were extracted by using ultrasonicassisted extraction.The optimized extraction conditions by response surface methodology were determined as:ultrasonic power ratio of 360 W,ultrasonic time of 40 min,and ratio of extraction solvent to sample of 30 mL/g.The actual extraction yield of zeaxanthin dipalmitate was 5.40 mg/g.High-speed counter-current chromatography(HSCCC)was used for the purification of zeaxanthin dipalmitate from the fruits of L.barbarum.The solvent system composed of n-hexane/dichloromethane/acetonitrile(10/3/7,v/v/v)was selected for HSCCC at 35 ?.The purity of zeaxanthin dipalmitate([M+H]+ was 1045.258)obtained was higher than 92%.2.Preparation and characterization of zeaxanthin dipalmitate emulsionThe mixtures of zeaxanthin dipalmitate-enriched oil phase(5 wt%)and aqueous phase(95 wt%)containing lecithin(1.5 wt%)and xanthan gum(0.0?0.4 wt%,respectively)were homogenized by a digital Ultra-Turrax at 13,000 rpm for 3 min to prepare oil-in-water emulsion.The effects of xanthan gum addition and oil type on the physicochemical properties of the emulsion were studied.The results showed that the viscosity and stability of the emulsion without xanthan gum or with low concentration xanthan gum(0.1?0.2 wt%)was poor,while the viscosity and stability of the emulsion could be significantly improved with high concentration xanthan gum(0.3?0.4 wt%).The oil types showed limited effect on the viscosity.The particle size distribution of the emulsion prepared in this chapter is not uniform.The particle size of emulsion increased with the concentration of xanthan gum increased.The monounsaturated fatty acid-rich olive oil emulsion showed the largest average particle size of 39.1 ?m at the same xanthan gum concentration.All the emulsions were negatively charged,and the absolute values of the potentials were about 12 mV.No significant difference was observed between emulsions with different xanthan gum concentrations and oil types.3.The in vitro simulated digestive properties of zeaxanthin dipalmitate in different food matricesThe emulsion,L.barbarum powder,and L.barbarum-emulsion mixture were chosen as the food matrices in this chapter.A general standardized and practical static digestion method was applied to evaluate the digestive properties of zeaxanthin dipalmitate in different food matrices.The results showed that after the simulated gastric digestion,the emulsion droplets decomposed more than coalesced,and the absolute value of the ?-potential decreased significantly for the emulsion rich in unsaturated fatty acids.After the simulated intestinal digestion,all the emulsions were more negatively charged,and the emulsion particle size was significantly decreased.In particularly,the particle size of monounsaturated fatty acid-rich olive oil emulsion decreased significantly from 39.1 ?m to 10.4 ?m.As for the L.barbarum powder and L.barbarum-emulsion mixture,the cell wall hindered the release of zeaxanthin dipalmitate.Mixing the emulsion and powder was beneficial to the release of carotenoids after intestinal digestion.The bioaccessibility results showed that zeaxanthin dipalmitate in the emulsion was higher than that of other food matrices.The monounsaturated fatty acidrich olive oil emulsion showed the highest bioaccessibility of 25.67%.The bioaccessibility of zeaxanthin dipalmitate in L.barbarum and L.barbarum-emulsion mixture was 2.63%and 3.02%,respectively.