Comparative Study of Natural Vinegars and Sodium Hypochlorite on Microbial Load Reduction, Antioxidant Activity, and Phenolic Content in Fresh Spinach

This study evaluates the effectiveness of four culinary vinegars—white wine vinegar, apple cider vinegar, sherry vinegar, and balsamic vinegar—as natural disinfectants for fresh spinach, compared to sodium hypochlorite. Microbial analysis was performed using standard culturing and plate count techniques to quantify molds, yeasts, and psychrophilic microorganisms and detect Listeria monocytogenes. Antioxidant activity was assessed using the DPPH method, while total polyphenolic content was determined using Folin–Ciocalteu reagent.

The results showed a significant reduction in microbial load for all vinegar-treated samples compared to the untreated control (p < 0.05), with a reduction in molds and yeasts from 6.45 log CFU/10 g in the untreated sample to below the detection limit (<1.0 log CFU/10 g) at the first vinegar concentration applied. Although differences between the four vinegar types were not statistically significant (p > 0.05), vinegar-treated samples consistently showed lower counts of psychrophilic microorganisms and Listeria monocytogenes than those treated with sodium hypochlorite (p < 0.05).

In terms of antioxidant properties, vinegar treatments led to a significant increase in radical scavenging activity. The highest activity was observed with 50% (v/v) balsamic vinegar (14.60 µM Trolox/10 g sample), compared to 5.51 µM Trolox/10 g in the untreated control and only 2.74 µM Trolox/10 g in sodium hypochlorite-treated samples. Moreover, total polyphenolic content increased significantly following vinegar treatment, with white wine vinegar at 50% (v/v) reaching 10.05 mg GAE, compared to 5.46 mg GAE in the untreated sample and a reduced level of 2.54 mg GAE after sodium hypochlorite treatment. These results indicate an enhancement of nutritional value with vinegar treatments, while sodium hypochlorite led to a marked decrease in both antioxidant activity and phenolic content.