Sugar Estimation as an Alternative and Rapid Approach to Predicting Chemical Oxygen Demand (COD) in Produce Wash Water

Monitoring chemical oxygen demand (COD) during washing of fresh produce is critical to maintaining the antimicrobial efficacy of sanitizers. However, traditional COD analysis is time-consuming (2-3 h) and costly. Since sugars released from fresh produce contribute to the overall COD, we investigated whether sugar estimation using the colorimetric sulfuric acid-UV spectrometry method (SA-UV method) can be a rapid, low-cost, and field-deployable method to predict the COD. The method relies on measurement of furfurals (absorbance at 315 nm, A₃₁₅) formed by sulfuric acid-induced oxidation of sugars (∼5 min). The correlation between A₃₁₅ and measured COD was assessed using the coefficient of determination (R²) for a linear regression model. A linear prediction model was subsequently developed. We first demonstrated this method with glucose, fructose, and sucrose (0-100 mg/L) solutions. Actual produce (grape, cantaloupe, and pineapple) wash water samples (> 15 samples per commodity) from a facility were then tested to validate this method. Strong positive associations were observed between A₃₅₀ versus measured COD in all three sugar solutions (R²> 0.91) as well as for grape (R² = 0.82) and cantaloupe (R² = 0.85) wash samples; while a relatively weaker correlation was observed for pineapple (R² = 0.62). Similar trends were observed between the measured and predicted COD of all three sugar solutions (R²> 0.95) and produce commodities (grape: R² = 0.82; cantaloupe: R² = 0.87; pineapple: R² = 0.65). Compared to turbidity measurements (R² range 0.17-0.59), this method was more accurate (R² range 0.65-0.82) as a predictor of COD. PRACTICAL APPLICATIONS: It is critical to monitor chemical oxygen demand (COD) levels in fresh produce wash water because elevated levels are associated with decreased antimicrobial efficacy of applied sanitizing agents. However, traditional COD measurements are time-consuming (2-3 h), which creates a burden for wash operations, especially under extreme wash water conditions (high COD). The results from this study offer an alternative approach for estimating the COD present in wash water and can be useful for produce wash operations because of the minimal time required, low cost of reagents and supplies, and minimal exposure to toxic chemicals.