Preparation Of Nisin-loaded Pectin Microcapsule And Its Effect On Mango Preservation

Nisin is cationic polypeptide composed of 34 amino acid residues,with good antibacterial activity,safety and no side effects,widely used in meat products,fruits and vegetables and dairy products.However,in practical application,the stability and persistence of Nisin antibacterial activity will be affected by enzymes,lipids and other substances in food matrix,and the stability of Nisin can be effectively improved and the application range of Nisin can be expanded after microencapsulation.Mango is very vigorous in postharvest physiological activities,and it is easy to suffer from pathogen infection during postharvest storage,which leads to fruit decay and loss.Microencapsulated Nisin has strong application potential in delaying mango rot.In this experiment,Nisin-loaded pectin microcapsule was constructed with pectin as wall material and Ca Cl₂as crosslinking agent.The microcapsule has the advantages of safety and good slow-release effect,overcomes the disadvantage of Nisin instability in food matrix,and effectively maintains the quality of mango during storage.The main research contents and conclusions are as follows:（1）Taking Nisin encapsulation rate as the reference index,the preparation process parameters of Nisin-loaded pectin microcapsule were optimized by single factor experiment and orthogonal experiment.The results showed that the optimal preparation parameters of microcapsule were Ca²⁺concentration 7%,stirring temperature 25℃,stirring time 0.5 h,pectin:Nisin mass ratio 4:4,wall material concentration 2 mg/m L,p H4.4,the Nisin encapsulation rate of Nisin-loaded pectin microcapsule was 79.1±1.3%.（2）On the basis of process optimization,the structural properties,bacteriostatic performance,biological toxicity and sustained-release effect of Nisin-loaded pectin microcapsule were investigated.It showed that the"egg-box structure"was formed between pectin molecules through calcium ion crosslinking,so Nisin was encapsulated in the"egg-box structure",and there was no chemical reaction between Nisin and pectin,forming a new chemical bond.Biotoxicity experiments showed that the microcapsules had no side effects on human body.When the concentration of microcapsules reached500μg/m L,the relative viability rate of cells was still 94.53±2.8%.The antibacterial activity analysis showed that microcapsule could inhibit the growth of Colletotrichum Gloeosporioides,which is the main postharvest mango disease and when the concentration of microcapsule reached 10mg/m L,the mycelial growth inhibition rate of Colletotrichum Gloeosporioides reached 47%.Sustained release experiment and release model fitting results showed that microcapsule had good sustained release effect,the cumulative release rate of microcapsule reached 74.0±4.3%at 96h,and the release process of microcapsule was the most consistent with Higuchi model,the goodness of fit R²reached 0.9833,indicating that Nisin release was mainly diffusion.（3）The mango was coated with Nisin-loaded pectin microcapsule solution and then stored.The results showed that the coating film on mango peel was smooth and compact in the early storage stage.At the end of the storage period,the treatment mango reduced the decay rate by 15%compared with the control group,and the degree of decay and shrinkage was lower in appearance,and the weight loss rate was as low as 3.4±0.03%.The firmness,soluble solid content and titratable acid content remained at20.5±3.3 N,6.4±0.1%and 2.2±0.4%,respectively.In addition,the peak of mango respiration in treatment group was 4 days later than that in control group.The activities of defense enzymes（Peroxidase,Polyphenol oxidase,Superoxide dismutase,Catalase）of mango fruits in treatment group showed an increasing trend at the early stage of storage and were significantly higher than those in control group.Compared with the control group,the activities of softening enzymes（Polygalacturonase,β-galactosidase,Pectinlyase,Cellulase）of mango fruits in the treatment group were at a lower level during storage.In conclusion,Nisin-loaded pectin microcapsule can effectively maintain the storage quality of mango,and improve the enzyme activity level of mango defense enzyme system at the early stage of infection by Colletotrichum Gloeosporioides,delaying fruit aging.In addition,it can inhibit the activity of mango softening enzyme system,and then delay fruit softening.