Bactericidal Activities Of Electrolyzed Water In Cleaning And Sanitizing Of Shrimp

Shrimp farming has become an important pillar of aquaculture industry in China; however, during the course from being harvested to being consumed, the shrimp are often subject to pathogenic microorganisms including Vibrio parahaemolyticus (VP) and Listeria monocytogenes (LM) contamination, to kill pathogens contamination on shrimp efficiently and fastly is an important topic of improving the food safety of shrimp. Electrolyzed water can not only kill a variety of pure culture of bacteria fastly and efficiently, but also effectively reduce bacterial contamination on fruits and vegetables, meat, seafood and food contact surfaces.This study investigated the bactericidal activity of electrolyzed water, from a pure culture of bacteria, artificially contaminated shrimp and natural shrimp three levels; applied traditional plate count and PCR-DGGE technology to monitor the bactericidal activity of electrolyzed water on shrimp; and examined the physicochemical properties of electrolyzed water stored before/after or used before/after.The purpose of this study was to provide applied basic research for pratical application of electrolyzed water in cleaning and sanitizing of shrimp surface, and to accumulate the basic data of bactericidal activity of electrolyzed water on shrimp. Therefore to provide a new, efficient, environmentally friendly, and low-cost technical support for the quality and safety control of shrimp. The main results were as follows:1. In order to investigate the killing effect of acidic electrolyzed water (AEW) on common foodborne pathogens– VP in seafood. AEW made from different NaCl concentrations and electrolyte were used to evaluate the bactericidal acitity on VP, AEW and basic electrolyzed water (BEW), mixed electrolyzed water (MEW) and different dilution of AEW were compared. MEW, NaCl concentrations of above 0.05% and NaCl, KCl, CaCl2 and MgCl2 solution from AEW [available chlorine concentration (ACC) of more than or equal to (16±1) mg / L] resulted in VP cells reduction of 7.81 ~ 8.70 log10CFU/ml in 2 min; AEW diluted 10 times (ACC of (2±1) mg / L) reduced 5.62 log10CFU/ml cells, AEW diluted 50 or 100 times (ACC <1 mg / L) only reduced <1 log10CFU/ml cells. Scanning electron microscopy showed that, after AEW treatment for 2 min, the cell membrane of VP is damaged, part of the cell contents overflow. AEW can kill the VP, and can be used in the disinfection of seafood processing.2. To seek a safe and environmentally friendly disinfectant in cleaning and sanitizing of shrimp surface for the prevention and control of VP and LM on shrimp. Comparison between the bactericidal activity of two types of AEW (AEW1, AEW2) and organic acids [2% acetic acid (2% AA), 2% lactic acid (2% LA)] in inactivating VP or LM on shrimp in the different immersion mode (standing or oscillating immersion) made. Impact of three different temperatures (4,20 and 50℃) and BEW (50℃) pretreatment for 1 or 5min on the bactericidal activity of AEW was investigated. The results showed that when standing soaking for 1 or 5min, AEW reduced the cell number of VP or LM on shrimp surface <1 log CFU / g; when oscillating soaking for 5min, AEW reduced the cell number of VP or LM on shrimp surface > 1 log CFU / g. The bactericidal activity of AEW in killing of VP or LM on shrimp, 50℃was better than 20℃or 4℃. When oscillating soaking for 5 min, AEW(50℃) killed VP on shrimp by 1.96 log CFU/g, killed LM on shrimp by 3.11 log CFU/g. BEW (50℃) pretreatment greatly increased the bactericidal activity of AEW (50℃) in killing of VP on shrimp, the cell number of VP on shrimp reduced by 2.7-5.4 log CFU / g. However, BEW (50℃) pretreatment did not increase the bactericidal activity of AEW (50℃) in killing of LM on shrimp. Physicochemical properties [pH, oxidation reduction potential (ORP) and the ACC] of AEW before and after used had undergone significant changes (P <0.05), ORP and ACC of AEW significantly decreased after used. AEW can be used for prevention and control of VP or LM contamination on shrimp surface.3. In order to investigate the bactericidal activity of electrolyzed water, organic acids and TW in cleaning and sanitizing of raw shrimp surface. Comparison between the bactericidal acitivity of four types of electrolyzed water, 2% LA and 2% AA on shrimp in the different immersion mode (standing or oscillating immersion) in the three different treatment time of 1, 5 and 10 min was made; sterile TW was used as treated control. The residual bacteria in the soaking solution after 10min of immersion were detected, and the sensory evaluation of raw shrimp was carried out after 10min of standing immersion. The results showed that TW resulted in the least reduction of the number of bacteria on shrimp when both standing and oscillating soaking. The surviving bacteria were not detected in the electrolyzed water and organic acids soaking solution. When standing soaking using AEW2 (102ppm) for 5 min, 2%AA for 5 or 10min, bacteria on shrimp were reduced by > =1 log CFU/g. When oscillating soaking using AEW1 (45ppm), AEW2 (102ppm) for 5min, 2%AA for 5 or 10min, bacteria on shrimp were reduced by > =1 log CFU/g. Sensory evaluation results showed that, the electrolyzed water immersion did not affect the sensory quality of raw shrimp, 2% LA soaking had a slight impact on the color, odor and overall acceptability of raw shrimp, 2% AA soaking affected the smell of raw shrimp greatly, and had a slight impact on the muscle tissue and overall acceptability of raw shrimp. Electrolyzed water can be used in cleaning and sanitizing of raw shrimp to replace TW.4. In order to monitor the bactericidal activity of AEW on raw shrimp. Different treatment time (1 or 5 min), different temperatures [50℃or room temperature (20℃)] of AEW or different treatment solution (AEW or 2% AA) in the treatment time of 5min were used to soak raw shrimp. Plate culture was combined with PCR-DGGE technique to monitor the bactericidal activity of AEW on raw shrimp. The results showed that, the number of bacteria on raw shrimp reduced by 1.44 log CFU / g after AEW (50℃) treatment. PCR-DGGE fingerprinting and clustering or similarity coefficient analysis showed that the average similarity coefficient between AEW(50℃) and control was the lowest-0.45. AEW (50℃) showed good bactericidal activity, PCR-DGGE technology can be used to monitor the bactericidal activity of AEW on raw shrimp.5. To evaluate the physicochemical properties and bactericidal activities of electrolyzed water before and after storage. Four types of electrolyzed water were stored in low temperature(-18±2)℃and room temperature(23±2)℃, respectively. The main physicochemical properties (pH, ORP and ACC) of them were measured in the storage time of 7, 14, 21 and 30 days. The bactericidal activity of them on raw shrimp was evaluated before storage and after storage for 30 d, and the surviving bacteria in the soaking solution were detected. pH value of electrolyzed water was on the rise during storage, ORP and ACC had a downward trend. pH and ACC of electrolyzed water stored in low temperature were higher than that of electrolyzed water stored in room temperature, ORP (MEW1, MEW2) was lower than that of room temperature, and ORP (AEW1) was higher than that of room temperature. When stored for 30 d, the bactericidal activity of electrolyzed water was worse than that of electrolyzed water before storage. The bactericidal activity of electrolyzed water stored in low temperature was better than that of room temperature. Electrolyzed water stored in low temperature of (-18±2)℃is better than that stored in room temperature of (23±2)℃to keep the content of ACC and the bactericidal activity on raw shrimp.