Preparation Of Lysozyme-modified Liposomes Of Thyme Essential Oil And Its Application In Beef Preservation

Thyme essential oil is a natural antimicrobial agent of plant origin with good antibacterial and antioxidant properties,but low stability and poor water solubility limit its direct application in food.Liposomes are common encapsulating materials that can improve the unstable nature of natural substances.In this context,thyme essential oil liposomes have been extensively studied.Modification of polysaccharides or proteins can also further enhance liposome function.Lysozyme is a natural antimicrobial agent of animal origin with the advantage of being stable,safe and edible.It has been demonstrated that lysozyme has the potential to modify and improve the properties of liposomes.However,few studies use lysozyme to modify liposomes,and the specific effects of lysozyme on liposomes are not apparent.Therefore,this study prepared liposomes from thyme essential oil liposomes,modified with lysozyme,and the basic liposome process formulation was investigated.The effects of lysozyme modification on thyme essential oil liposomes regarding physicochemical stability,storage stability and antimicrobial properties,and beef preservation were further investigated.The results of the study can evaluate the modification potential of lysozyme on liposomes and provide a reference for their application,and also help to develop a new antibacterial liposome system of lysozyme-modified thyme essential oil liposomes and provide a basis for the application of this system in beef preservation.The main research contents and results are as follows:(1)Liposomes of thyme essential oil were successfully prepared by using the thin film hydration method.The optimal process and formulation of liposomes were determined by single-factor experiments using morphological parameters as stability criteria.The optimal parameters were phospholipid/cholesterol=8/1,ultrasonic power 260 W,and ultrasonic time 5min.The morphological stability and encapsulation rate were combined to determine the optimal concentration of thyme essential oil addition of 2.5 mg/m L and the optimal mass ratio(w/w)of lysozyme/soy lecithin S100 of 0.05%.Morphological characterization demonstrated that adding lysozyme increased the particle size and decreased the potential of thyme essential oil liposomes.Fourier transform infrared spectroscopy revealed that the binding of lysozyme to thyme essential oil liposomes was mainly electrostatic.It provided the basis for the subsequent experiments.(2)The effect of lysozyme on the physical and chemical stability of thyme essential oil liposomes was investigated.The lysozyme-modified thyme essential oil liposomes showed enhanced resistance to acid-base and ionic influences and were storage stable.The lysozyme modification for thyme essential oil liposomes slightly improved antioxidant properties and significantly enhanced resistance to phospholipid oxidation.The retention at high temperatures was 45.9 ± 2.06 % and 51.6 ± 1.87 %,and the release during storage was 43.2 ± 0.59 % and30.3 ± 0.94 %,respectively,for thyme essential oil liposomes with lysozyme modification.The results indicated that the modification of lysozyme could improve the stability of liposomes and enhance the controlled release of thyme essential oil.The theoretical role was probed for subsequent experiments.(3)The effect of lysozyme on the antibacterial properties of thyme essential oil liposomes was investigated.The growth curves and inhibition experiments showed that the lysozymemodified thyme essential oil liposomes were better than thyme essential oil liposomes and better than free thyme essential oil in determining the antibacterial properties of representative Gram-negative and Gram-positive bacteria.After 3 d of storage,the lysozyme-modified thyme essential oil liposomes eventually reduced Escherichia coli by 2.80 and Staphylococcus aureus by 2.10 orders of magnitude compared to the blank control.It provided a theoretical food preservation basis for the subsequent experiments.(4)The application of lysozyme-modified thyme essential oil liposomes in beef preservation was investigated.14 d of chilled beef in the lysozyme-modified thyme essential oil liposome group showed a non-significant decrease in sensory scores,the highest overall sensory score,and a minor change in color difference.The acidity and fat oxidation levels indicated that lysozyme-modified thyme essential oil liposomes might delay beef after ripening and fat oxidation.Also,the lysozyme-modified thyme essential oil liposomes could effectively slow the decrease of hardness,elasticity,chewiness,and recovery in beef;the lysozyme-thyme essential oil liposomes group ended up with the lowest TVB-N content.The total number of colonies proved that the encapsulation of liposomes could effectively retain the antimicrobial properties of thyme essential oil.The combined results showed that the lysozyme-modified thyme essential oil liposomes had the best preservation capacity.It provides a reference for applying the studied liposomes in beef preservation.