Effect of Gaseous Ozone on Foodborne Pathogens and Their Surrogates on Fresh and Frozen Strawberries

Introduction:  Ozone technology has been widely applied in water disinfection and is used in food industry to extend the shelf life of fresh produce with well-documented bactericidal effects. With the increasing number of outbreaks related to berry products, alternative technologies need to be investigated to improve the safety of berries. However, information on the application of gaseous ozone on fresh produce is limited and not comparable due to various expressions of ozone dose.

Purpose:  Our study investigated the inactivation effect of gaseous ozone on foodborne pathogens on fresh and frozen strawberries and the sensorial impact of gaseous ozone on strawberries.

Methods: Fresh strawberries (25 g) were inoculated with MS2, MNV-1, Salmonella, and E. faecium and treated with gaseous ozone at 1% (ca. 15g/m³) and 6% (ca. 80g/m³) for five and 30 minutes or pure oxygen for 40 minutes. Frozen strawberries were treated with 6% ozone for five minutes. After treatment, samples were transferred into a filter-stomacher bag containing either 50 ml virus elution buffer or 225 ml buffered peptone water to recover and enumerate viruses and bacteria, respectively. All experiments were done in triplicates.

Results: For frozen strawberries, treatment with ozone resulted in log reductions of 1.60, 0.72, 0.67, and 1.77 on Salmonella, E. faecium, MNV-1, and MS2, respectively, which were higher compared to fresh samples treated in parallel. Treatments of 6% for 30 min provided the highest reduction on fresh strawberries; 2.06-, 1.52-, 1.76-, and 3.30-log reductions were reached on Salmonella, E. faecium, MNV-1, and MS2, respectively, which were significantly higher than oxygen treated samples (P<0.05). No sensorial differences were detected on strawberry flesh but green leaves were decolorized by ozone.

Significance: This study proved the inactivation effect of gaseous ozone against pathogens without altering the taste of strawberries and showed more efficiency on the frozen strawberry matrix compared to fresh strawberries.