Effects of organic load, sanitizer pH and initial chlorine concentration of chlorine-based sanitizers on chlorine demand of fresh produce wash waters

- Chlorine demand increased with decreasing organic load and chlorine concentration.
- Increased NaOCl pH led to decrease in chlorine demand except for pH 6 to 8.
- Demand prediction models for various produce and wash conditions were developed.

Chlorine-based sanitizers are widely used in fresh produce industry. However, maintaining sufficient free chlorine residual in wash solution in the presence of organic matter is a challenge. The purpose of this study was to evaluate the effects of organic load, sanitizer pH and initial chlorine concentration on chlorine demand of fresh produce wash water. A full factorial design was used to study the chlorine demand of romaine lettuce wash water with different organic load when reacting with NaOCl solution at different pH (2.5, 4.0, 6.0, 8.0 and 9.5) and initial chlorine concentration (50, 75 and 100 mg L−1 free chlorine residual). The results showed that the chlorine demand of lettuce wash water significantly increased (P ≤ 0.05) with increasing organic load. The significant effect (P ≤ 0.05) of initial chlorine concentration on chlorine demand was only detected at high organic load. Increasing the pH of NaOCl from 2.5 to 9.5 led to decrease in the chlorine demand except slight increase from 6.0 to 8.0. Equations for predicting chlorine demand of various fresh produce wash waters at different organic load for different sanitizer pH and initial chlorine concentration were developed, and verified using four types of produce (romaine lettuce, iceberg lettuce, strawberry and grape) and two types of chlorine-based sanitizers (NaOCl and electrolyzed water). Our study demonstrated that organic load, sanitizer pH and initial chlorine concentration all affected the chlorine demand of produce wash water, and chlorine demand prediction equations developed can be used for different types of fresh produce and chlorine-based sanitizers.