Microbial Safety and Quality Evaluation of Ultraviolet Treated, Cold-pressed, Colored and Turbid, Fruit and Vegetable Beverages

Introduction: The growing demand for health-promoting fruit and vegetable juice blends, with improved nutritional and sensory attributes, has prompted the adoption of nonthermal technologies, including ultraviolet (UV) light. Due to safety concerns, FDA mandates that wholesale juice processors shall ensure a five-log reduction of pathogens. Limited studies have explored alternative conditions to overcome the well known limitations of UV when treating colored liquids with high insoluble solids contents.

Purpose: This study addressed the effectiveness of UV light application by a commercial juice-processing unit at a reduced flow rate, to inactivate Salmonella spp., Listeria monocytogenes, Escherichia coli O157:H7, and spoilage microorganisms in turbid and colored beverages.

Methods: Inactivation of five strains/serotypes cocktails of pathogenic E. coli O157:H7, Salmonella spp. and L. monocytogenes, isolated from fruit and vegetable-derived products linked to outbreaks, was determined in seven turbid and colored cold-pressed beverages (apple-lemon, carrot-cucumber-apple-orange, cucumber-apple-lemon, cucumber-spinach-celery-apple-kale-ginger-lemon-parsley, cucumber-fennel-kale-spinach-lime, celery-apple-beet-parsley-ginger, and almond milk). Beverages were inoculated to a targeted initial population of 10⁷ CFU/ml and treated with a CiderSure 3500 UV reactor at 150 L/h constant flow rate through multiple consecutive passes. Reduction of molds and yeasts, aerobic mesophilic, and lactic acid bacteria was, also, assessed at the cumulative dose that guaranteed a five-log reduction of the most UV-tolerant pathogen in each product. Beverages were physicochemically characterized. Trials were performed in triplicate.

Results: A five-log reduction of the three pathogens was achieved in all beverages at a maximum cumulative UV dose of 12.0±0.6 mJ/cm². The dose required to ensure the targeted reduction significantly varied (P<0.05) depending on the formulation, physicochemical properties (pH, soluble solids, acidity, color, and turbidity), and pathogen inoculated. The reduction of aerobic mesophiles, molds and yeasts, and lactic bacteria varied from 0.5 to 3.6, 0.2 to 2.0, and 0.5 to 3.6 log CFU/ml, respectively.

Significance: The proposed nonthermal treatment represents a suitable processing alternative to ensure the safety and extend the shelf life of colored and turbid cold-pressed beverages.