Preparation Of Nisin-loaded γ-PGA/chitosan Nanoparticles-embedded Gelatin Nanofiber Film And Its Application On Cheese During Storage

Nisin is one kind of food additive with nature,safety and high efficiency.It has excellent antibacterial activity against a wide range of Gram-positive bacteria.However,the stability and bioactivity of nisin are reduced when directly used in foods,due to its binding to food components and proteolytic degradation.In order to circumvent this problem,this paper encapsulated nisin in ?-PGA/chitosan nanoparticles,and then embedded nisin-loaded ?-PGA/chitosan nanoparticles(NGC nanoparticles)on gelatin nanofibers by using electrospinning technique.Thus,the antibacterial activity of nisin was improved during the storage of cheese.Initially,this study prepared NGC nanoparticles by using nisin,?-PGA and chitosan as raw materials and polyelectrolytes self-assembly principle.The physicochemical properties,including particle size,PDI,Zeta potential,entrapment efficiency and loading content,of NGC nanoparticles were analyzed to obtain the nanoparticles with the best performance.Quartz crystal microbalance was introduced to verify the encapsulation of nisin into ?-PGA/chitosan nanoparticles.The influences of temperature and time for the stability of NGC nanoparticles and the cumulative release of nisin were investigated.The antibacterial activity of NGC nanoparticles against Listeria monocytogenes in model cheese system was also evaluated.Subsequently,NGC nanoparticles were embedded into gelatin nanofiber film by using gelatin as raw materials and electrospinning technique.The surface morphology of NGC nanoparticles-embedded gelatin nanofiber film was observed by using scanning electron microscopy.The cumulative release of nisin from the gelatin nanofiber film and its antibacterial activity in model cheese system were investigated.Eventually,the fresh-keeping effect of NGC nanoparticles-embedded gelatin nanofiber film on cheese during the storage and its influence for surface-color,texture and sensory property were evaluated.The main results were as follows:(1)The optimal particle size(384.8 nm),PDI(0.187),Zeta potential(46.1 mV),encapsulation efficiency(49.3%)and loading content(16.4%)of NGC nanoparticles were obtained at the concentration of nisin to 5 mg/mL.The analysis of quartz crystal microbalance showed that NGC nanoparticles had the larger mass compare to control groups.It indicated that nisin was successfully loaded into ?-PGA/chitosan nanoparticles.After stored 60 d,NGC nanoparticles still had good stabilities.(2)The cumulative release test showed that nisin in NGC nanoparticles had a good release property.The results for the antibacterial experiment indicated that NGC nanoparticles in model cheese system had desired antimicrobial activity against Listeria monocytogenes.Compared with control groups,the numbers of Listeria monocytogenes in NGC nanoparticles groups were inhibited by 3.42 log CFU/m L at 25 °C and 3.60 log CFU/m L at 4 °C.(3)The surface morphology of NGC nanoparticles-embedded gelatin nanofibers was observed by using scanning electron microscopy.The gelatin nanofibers were uniform and smooth,and the diameters of the nanofibers were larger compare to control groups.The results of agar-diffusion assay showed that the larger inhibition zones(30-33 mm in diameter)were observed in NGC nanoparticles-embedded gelatin nanofibers samples.The nisin release test displayed that nisin in the gelatin nanofibers had excellent release property.After 96 h,the cumulative release reached 44% at 25 °C and 29% at 4 °C.NGC nanoparticles-embedded gelatin nanofibers in model cheese system showed desired antibacterial activity.Compared with control groups,the numbers of Listeria monocytogenes in the gelatin nanofibers groups were inhibited by 3.38 log CFU/m L after 7 d at 25 °C and 3.42 log CFU/m L after 14 d at 4 °C.(4)NGC nanoparticles-embedded gelatin nanofibers could effectively prolong the shelf-life of cheese.The bacteria grew fast in control groups,while grew slower in the gelatin nanofibers samples.After 7 d stored at 25 °C,the number of the bacteria in control groups increased by 4.72 log CFU/g,and in the gelatin nanofibers samples only increased by 1.64 log CFU/g.After 14 d stored at 4 °C,the numbers of the bacteria in the gelatin nanofibers samples were inhibited by 3.32 log CFU/g.The results indicated that NGC nanoparticles-embedded gelatin nanofibers had desired antibacterial and fresh-keeping effect.(5)NGC nanoparticles-embedded gelatin nanofibers could maintain the lightness,redness,yellowness,hardness,springiness,cohesiveness,gumminess,appearance,color,taste,off-flavor,and overall acceptability of cheese,thus,NGC nanoparticles-embedded gelatin nanofibers have a broad prospect for cheese preservation.