Preparation Of Coix Seed Oil Nanoemulsion And Its Application In Beverage

Coix seed oil is a kind of functional oil with a variety of physiological activities,but Coix seed oil has low water solubility,poor environmental adaptability,low bioavailability and easy to be oxidized,which is limited in applying in food,medicine and other fields.Therefore,it is a very meaningful to improve the bioavailability,antioxidant ability,water solubility and environmental adaptability of Coix seed oil by constructing an appropriate food delivery system.At present,using protein-polysaccharide mixed emulsifier for preparing Coix seed oil nanoemulsion system（CSO-NEs）is rarely reported.In this paper,protein and polysaccharide were used as emulsifiers to prepare CSO-NEs.The main results are as follows:（1）Whey protein（WPI）was combined with konjac glucomannan（KGM）,Yam polysaccharide（YP）,Ganoderma lucidum polysaccharide（GLP）and Lentinan（LNT）as emulsifier to prepare CSO-NEs,respectively.The optimal formulation of CSO-NEs were obtained through single factor test:The concentration of WPI was 3.5%,the concentration of LNT was 0.15%.The prepared CSO-NEs particle size was 285.6 nm,PDI was 0.264,and Zeta potential was-32.4m V.Under the observation of optical microscope and transmission electron microscope,the particle size distribution of CSO-NEs was uniform,and agglomeration and flocculation had not been found.（2）The influence of environmental factors（p H,ionic strength,heating-cooling cycle,storage）on CSO-NEs was studied.The results showed that the addition of LNT changed the isoelectric point of WPI,and the stability of CSO-NEs under acidic condition（p H 2-5）was stronger than alkaline condition（p H 8-10）.When the ionic strength is 20-100 m M,there is no significant influence on the emulsion stability.After five heating and cooling cycles,CSO-NEs still had smaller particle size and larger absolute Zeta-potential,indicating that CSO-NEs had good thermodynamic stability.After storing at 4℃,25℃and 40℃for 30 days,the particle size of CSO-NEs was slightly increased and the absolute Zeta-potential of CSO-NEs was not significantly changed at 4℃and 25℃,while the particle size of CSO-NEs was significantly increased and the absolute Zeta-potential of CSO-NEs was decreased significantly at40℃.Therefore,CSO-NEs is suitable to store at low and normal temperature,but not at high temperature.（3）Fluorescence spectroscopy,Circular dichroism spectrum（CD）,Fourier transform infrared spectroscopy（FT-IR）,molecular simulation docking and other techniques were used to explore the interaction between WPI and LNT.It was found that the quenching type of WPI by LNT was static quenching,and the number of binding sites was 1.The thermodynamic parameters of the interaction between WPI and LNT indicate that the bonding process between them is spontaneous,the bonding process is entropy driven,and the main binding force is hydrogen bond and van der Waals force.CD determination showed that WPI and LNT interacted to form a complex,which destroyed the original secondary structure of the protein and significantly changed the secondary structure of the protein.FT-IR measurement showed that the peak intensity of the characteristic peak of WPI decreased at 3279 cm^-1,indicating that the bond between WPI and LNT was non-covalent and shifted from3279 cm^-1 to 3275 cm^-1.The change of peak value may be due to the hydrogen bond interaction between WPI and LNT.The WPI-LNT complex also shifted in the vibration bands of amide I and amide II bands,indicating that LNT has a significant effect on the secondary structure of WPI.Through molecular simulation docking of four major globulins in WPI and LNT,hydrogen bond is the main binding force between these four proteins and LNT,indicating that the main interaction between WPI and LNT is hydrogen bond.（4）The results of in vitro digestion experiment showed that the particle size of CSO-NEs did not change significantly in the simulated oral and gastric digestion stage,but significantly increased in the simulated intestinal digestion stage,which was consistent with the observation result of inverted fluorescence microscope.The absolute potential value increased first and then decreased in the simulated oral and gastric digestion,and increased again in the simulated intestinal digestion.The free fatty acid release of WPI-stabilized CSO-NEs was higher than that of WPI-LNT-stabilized CSO-NEs,indicating that WPI-LNT-stabilized CSO-NEs could delay the release of free fatty acids.The fitting results of CSO-NEs release kinetics model show that in Simulated gastric fluid（SGF）,Retger-Peppas equation and Higuchi equation have the highest fitting degree,R² is 0.8787 and 0.8756,respectively,release index n is 0.5379,0.43<n<0.85,Therefore,the release behavior of CSO-NEs in SGF may be a combination of dissolution and diffusion.In Simulated intestinal fluid（SIF）,Retger-Peppas equation and Higuchi equation have the highest fitting degree,R² is 0.9740 and0.9427,respectively.The release index n is 0.6357,0.43<n<0.85.Therefore,the release behavior of CSO-NEs in SIF is a combination of dissolution and diffusion.（5）The optimal formula of CSO-NEs beverage was studied through single factor and orthogonal test,the results are as follows:The content of CSO-NEs is 4%（v/v）,xylitol is 8%（w/v）,essence is 0.16%（w/v）,β-cyclodextrin is 0.70%（w/v）,pectin is0.14%（w/v）,CMC is 0.16%（w/v）and Xanthan gum is 0.20%（w/v）.The CSO-NEs beverage prepared under this formula tastes fine and smooth with moderate sweetness,it also has Coix seed flavor and good stability.The determination of physicochemical and microbial indexes showed that soluble solid content≥9%,lead and total arsenic were not detected,total number of colonies,coliform,mold and yeast were all less than1 CFU/m L,and pathogenic bacteria were not detected.