Investigation on chlorine-based sanitization under stabilized conditions in the presence of organic load

Authors: TENG, ZI - University Of Maryland; Luo, Yaguang - Sunny; ALBORZI, SOLMAZ - University Of Maryland; Zhou, Bin; CHEN, LIN - University Of Maryland; ZHANG, JINGLIN - University Of Maryland; ZHANG, BOCE - Orise Fellow; Millner, Patricia; WANG, QIN - University Of Maryland

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2017
Publication Date: 11/30/2017
Citation: Teng, Z., Luo, Y., Alborzi, S., Zhou, B., Chen, L., Zhang, J., Zhang, B., Millner, P.D., Wang, Q. 2017. Investigation on chlorine-based sanitization under stabilized conditions in the presence of organic load. International Journal of Food Microbiology. 67:150-157.

Interpretive Summary: Washing is essential to remove the debris, soil, and organic matter from fresh and fresh-cut produce and to maintain quality and shelf life of the final products. The wash water needs to have an appropriate amount of sanitizer such as chlorine to rapidly inactivate bacteria that are washed off of the produce to prevent their spread to other clean produce. Chlorine-based sanitizers currently are the most widely used sanitizer in the fresh produce industry due to their low cost and rapid bacterial inactivation at relatively low doses. However, the sanitizing efficacy of chlorine is reduced significantly as increasing amounts of cut produce, which release organic matter, are placed into the wash water. This report describes a new methodology that was developed and used to evaluate the sanitizing efficacy of chlorine under well-controlled conditions. The method and results from this study are anticipated to facilitate researchers and industry in the development of science-based food safety practices and standards to reduce bacteria contamination and spread.

Technical Abstract: Chlorine is commonly used for preventing water-mediated cross contamination during fresh produce washing. The sanitization efficacy (SE) is constantly compromised by the organic load (OL), which has been attributed to rapid chlorine depletion and unsuccessful maintenance of residual free chlorine (FC). However, little is known on whether chlorine performs equally effectively with or without OL at a same, well-maintained residual level. Hereby, a sustained chlorine decay approach was employed to study the inactivation of E. coli O157:H7 at stabilized FC, chloramine, and chemical oxygen demand (COD) levels. Chlorine solution was first prepared and mixed with OL, and then left at room temperature for a period of up to 3 hr, modeling the effect of residual FC after its reaction with OL in produce wash system. The decline in FC was monitored and the targeted FC solution was obtained at different stage of the chlorine and OL reaction. Our study showed a clear decrease in SE as the OL increased. At 5 s residence time and pH 6.5, a minimum of 0.5 and 7.5 mg/L FC were needed to achieve a 5 log reduction at 0 and 900 mg/L COD, respectively. The decrease was more pronounced at lower FC, higher COD, higher pH, and shorter residence time values. The OL-associated interference with FC measurement and disruption of chlorine/bacteria interaction, together with the chlorine demand of concentrated inoculum per se, collectively resulted in inadequate FC level and SE. Finally, our results were compared with existing studies conducted under dynamic experimental settings in the context of different experimental settings. This study provided a method for studying the sanitization under stable conditions, and it evidenced the negative impact of organic load under well-controlled conditions. However, to fully account for these chemical interactions in actual industry-scale produce wash water under operational conditions further confirmation and adjustments are needed.