Study On The Application Of Nisin, Citric Acid And Sodium Acetate In The Washing Process Of Fresh-cut Lettuce

Leafy lettuceis considered one of the most popular fresh-cut vegetables, however, the process of cutting could change lettuce’s original tissue and lead to shortening the shelf life, at the same time, fresh-cut lettuce is also prone to infection by pathogensand cause the outbreak of foodborne disease. The washing process is one of the most important processing steps to eliminate or reduce the population of microorganisms in fruit-cut production. This article takes leafy lettuce as the experimental material.Nisin, citric acid and sodium acetatewere chosed as the sanitizers, and then, the optimumconcentration of the compound antibacterial agents was determined.The compound antibacterial agents were used in the washing solution of fresh-cut lettuce, and investigate the effectiveness of compound antibacterial agents in controlling the quality and reducing bacteria on fresh-cut lettuce. This paper also studied the cross contamination caused by pathogens as the sanitizers repeat used, and pathogentic bacteria transfer model was established. The main research results are as follows:1. Using Nisin, citric acid and sodium acetate as single factor, and the result ofthe experiment showed that with the increase of antibacterial substance concentration, bacteriostatic action also gradually enhanced.0.5% citric acid has significant inhibitory effect to Escherichia coli, Salmonellaenteritidis, Staphylococcus aureus. The bacteriostatic effect of Nisin on Staphylococcus aureuswas better than Escherichia coli and Salmonellaenteritidis, and the bacteriostatic effect of Nisin and sodium acetate were significant when they were used in large concentration. The combination of nisin and citric acid have synergistic antimicrobial effect.2. The multiple proportion dilution of the compound antibacterial agents consists of Nisin, citric acid and sodium acetate were selected in vitro experiment, and the minimum inhibitory concentration for Escherichia coli, Salmonellaenteritidis, Staphylococcus aureus is 250IU/mlNisin,0.15%citric acid,0.05% sodium acetate.3. The shredded lettuce were treated bydistilled water, 100mg/L NaCIO, the compound antibacterial agents, and the compound antibacterial agents+distilled water (distilled water was used to rinse the lettucefor 15 second after the treatment of compound antibacterial agents). For all the treatments, the pH values of lettuces were slightly increased and basically maintain unchanged. Respiratory intensity and the activity of PPO were increased before they were reduced, and chlorophyll content, Vc content, sensory quality were gradually reduced during the storage at 4℃. Compared with other sanitizers, the compound antibacterial agents could delay the corruption of lettuce. Therefore, compound antibacterial agents as the sanitizer of fresh-cut lettuce is feasible in terms of maintain the quality, and extended the shelf life to 4 days, but in the same circumstances, the treatment of distilled water could onlyextend the shelf life to 3 days.4. This study showed that the compound antibacterial agents could significantlyreduce the counts of pathogenic bacteria and general bacteria on lettuce, and could control the growth of bacteria during the storage. The results also show that the bacteriostatic effect of the compound antibacterial agents was better than NaCIO which was commonly used in fresh-cut industrial.5. The compound antibacterial agents and NaCIO were used to washing fresh-cut lettuce inoculated with Salmonella enteritidis, the result showed that both of those two sanitizers could not totally inhibit the transfer of Salmonella enteritidiswhile washing if the first batch of lettuces were contaminated. However, the use of compound antibacterial agents helped to reduce cross contamination of Salmonella enteritidis.6. This paper established the pathogentic bacteria transfer model, and and found that exponential functionwas better used to describethe transfer of Salmonella enteritidisas didistilled water repeated using. And for the compound antibacterial agents and NaCIO, Power function was better. However, this result also need more test verification.