Preparation And Properties Of Cellulose Nanocrystals By Jujube Cores And Their Pickering Emulsion Antibacterial Films

About 200 thousand tons of processing waste is generated each year during the processing of jujubes in Xinjiang: jujube cores,which are rich in a large amount of fiber components and can be used to extract cellulose nanocrystals(CNCs).CNCs can be used as solid particles to stabilize Pickering emulsion to realize the embedding and delivery of essential oils,thus overcoming the problems of volatile and poor hydrophilicity of essential oils during use,so that they can be better loaded into composite films and exert their antibacterial effects.Based on this,in this study,cellulose nanocrystals were extracted from jujube cores and used as solid particles to stabilize thyme essential oil to prepare Pickering emulsion composite films.The main contents and results of the study are as follows:(1)CNCs were extracted from red jujube cores by Soxhlet dewaxing,alkali treatment,bleaching and sulfuric acid hydrolysis.Scanning electron microscope(SEM),Fourier transform infrared spectroscopy(FTIR)and chemical composition analysis of fibers showed that the fractional purification effectively removed lignin and hemicellulose from jujube cores.The results of transmission electron microscopy(TEM)and atomic force microscopy(AFM)showed that the CNCs presented rod-like shapes with a length of 205.7 ± 52.4 nm and a high aspect ratio(20.5).The properties of the fibers were analyzed by X-ray diffraction(XRD),thermogravimetric analysis(TGA)and water contact angle(WAC).With the progress of fractional purification,the crystallinity of the fibers increased,the crystallinity of CNCs was(72.36%),the thermal stability was good(>200 °C),and the Iβ crystal structure of cellulose was not destroyed by acid hydrolysis.The zeta(ζ)potential of the aqueous suspension of CNCs was-23.72 ± 1.7 m V,slightly agglomerated,and the CNCs powder had high hydrophilicity,indicating that the CNCs can be used as reinforcements for nanocomposites.(2)CNCs as solid particles to stabilize thyme essential oil for preparing Pickering emulsions,and the emulsions were loaded into modified tapioca starch/polyvinyl alcohol(PVA)based films.The particle size and potential of the emulsion as well as the structure and properties of the film were studied.The results showed that the particle size of the emulsion decreased with the increasing concentration of the CNCs and increased with the increasing proportion of thyme essential oil.At the concentration of 1% CNCs,when thyme essential oil accounted for 15%(1-15%),the emulsion had a relatively low particle size(1154.7 ±16.5 nm)and the lowest potential(-43.2 ± 1.1 m V),indicating that the emulsion under the condition has good stability.The emulsion films prepared under the condition of 1-15% have relatively good mechanical properties and relatively dense microstructure.The addition of the emulsion significantly decreased the water vapor transmission rate(WVP)of the film(p<0.05),the crystallinity of the film decreased,and the thermal stability slightly decreased,but the composite film showed relatively excellent UV blocking ability.(3)The effects of different addition amounts of thyme essential oil Pickering emulsion on the structure and properties of the modified tapioca starch/PVA composite film were studied,and the antibacterial properties of the film during storage of Esox lucius were verified.The results showed that the tensile strength of the composite films decreased significantly from 17.59 MPa to 12.71 MPa(p<0.05)as the emulsion addition increased to 20%,but the films still showed better elongation at break and WVP.The composite film has a rough surface and a dense structure,showing thermal stability like that of the blank film and excellent UV blocking ability.With the increase of the amount of emulsion added in the composite film,the antibacterial effect on Esox lucius during storage was more obvious.The film added with 20% Pickering emulsion kept the total number of colonies of Esox lucius stored at 4°C within an acceptable range(< 6 log CFU/g)at 10 d,indicating that the composite film can reduce the vitiligo of Esox lucius stored at 4°C.The shelf life of Esox lucius was extended to 10 d.In conclusion,the modified tapioca/PVA film loaded with thyme essential oil Pickering emulsion has great potential as an antibacterial packaging for fish meat.