Preparation Of W/O/W Double Emulsion And Its Loading Effect On Grape Seed Proanthocyanidins

Grape seed proanthocyanidins(GSP)is a kind of natural polyphenols with a broad spectrum of biological activity.However,due to the numerous unstable phenolic hydroxyl groups in its structure,GSP is susceptible to degradation affected by external factors such as high temperature,alkaline pH,metal ions,light,etc.In this study,the conjugate of sugar beet alkaline soluble polysaccharide(ASP)and whey protein isolate(WPI)was prepared and utilized to stabilize a W/O/W emulsion,which was used to encapsulate GSP for improving its stability and bioaccessibility.The main research work is as follows:(1)The genipin-crosslinked ASP-WPI conjugate(G-AWC)was successfully fabricated.Compared with ASP and WPI,the molecular weight and hydrodynamic radius of G-AWC were larger,and there was a new absorption peak at 596 nm.The total sugar content decreased from84.2%to 70.9%,and the protein content increased significantly from 4.5%to 18.1%after the cross-linking of ASP and WPI.Besides,the G-AWC had lower potential than that of ASP,and exhibited better colloid stability in a wide pH range from 3 to 12.The surface hydrophobicity of G-AWC was significantly lower than ASP-WPI-Blend.In addition,the reduction degree of G-AWC on the oil-water interfacial tension was higher than that of ASP,indicating that the emulsifying property of ASP was improved after crosslinking.The results of atomic force microscopy showed that the spherical protein molecules were linked to one or more long chains of polysaccharides after the crosslinking of ASP and WPI,and the molecular conformation was more compact than that before crosslinking.(2)W₁/O/W₂ emulsion was prepared using polyglycerol polyricinoleate(PGPR)and G-AWC as emulsifiers via a two-step method.The optimal preparation parameters of the double emulsion were confirmed by analysis of visual appearance,microscopic structure,droplet size,and rheological property.The optimal conditions were PGPR concentration of 5%(w/v),the W₁:O ratio of 2:8,the G-AWC concentration(c)of 0.5%(w/v),and the W₁/O volume fraction((37))of 80%(v/v).Gel-like high internal phase double emulsion could be fabricated at(37)of75%-90%when the c was 2%.The droplet size of the emulsion showed a decreasing trend as the(37)increased.Gel-like emulsion could also be formed at c of 0.5%with(37)of 80%.Under this condition,the encapsulation efficiency(EE)and the loading efficiency(LE)of GSP were 95.86%and 0.192%,respectively.The EE value decreased by about 10%during storage of 7 days at room temperature.(3)The effect of pH,ionic strength,in vitro digestion,temperature,and UV irradiation on the stability and antioxidant activity of GSP-loaded double emulsion were investigated.The emulsion showed good stability when the pH of external aqueous phase was 7-11,but demulsified at pH 3.The emulsion provided effective protection for GSP at pH of 7-9,and the retention rate of GSP after 7 days of storage was between 83%and 85%.Moreover,the addition of Na Cl has an electrostatic shielding effect on G-AWC.The droplet size of the emulsion increased with the increase of ionic strength.When the Na Cl concentration was 10 m M,the stability of the emulsion and its protective effect on GSP could be effectively improved.Besides,in vitro digestion experiments showed that the bioaccessibility of GSP in the W/O/W emulsion(40.72%)was remarkably higher than that of free GSP(13.11%)and encapsulated GSP in W/O emulsion(27.15%).Additionally,the retention rate of GSP in the emulsion was significantly higher than that of free GSP at different storage temperatures(4?,25?,60?)during 7 days.The protective effect of 4? on GSP was the most significant.Under UV irradiation,the free GSP degraded rapidly.However,the encapsulation of W/O/W emulsion could effectively protect GSP,significantly improve the retention rate and delay the decline of antioxidant activity of GSP.