ULTRAVIOLET-C LIGHT PROCESSING OF GRAPE, CRANBERRY AND GRAPEFRUIT JUICES TO INACTIVATE SACCHAROMYCES CEREVISIAE

Two "Infinity" liquid disinfection systems were coupled in a serial arrangement to assemble one Ultraviolet-C disinfection unit. Two inner mercury lamps (intensity, 25 mW/cm2) were used as germicidal sources. Pasteurized grape, cranberry and grapefruit juices, inoculate with Saccharomyces cerevisiae, were processed by Ultraviolet (UV) light at six flow rates (0.073-1.02 L/min) and six UV light doses (75-450 kJ/m2). The first order kinetics modeling for S. cerevisiae inactivation proved that D(uv)values (i.e., ultraviolet decimal reduction time) ranged from 61.7 to 113.7 (R2 > 0.900), 12.2 to 40.7 (R2 > 0.930) and 12.5 to 20.7 (R2 > 0.860) min for grape, cranberry and grapefruit juices, respectively. The maximum log reduction (cfu/mL) was 0.53, 2.51 and 2.42 for yeast count in grape, cranberry and grapefruit juices, respectively, after 30 min of UV light treatment at the maximum flow rate (1.02 L/min). The total color difference (Delta E*) in the three fruit juices tested increased as UV light treatment time increased. PRACTICAL APPLICATIONS Ultraviolet (UV) light processing of liquid food products is an emerging nonthermal technology that can be used to treat liquid food products. Fruit juices and nectars used to be thermally treated to deliver microbiologically safe fruit products. However, thermal treatment can produce some sensory changes in fruit products. Changes such as caramelization of sugar may darken the food and consequently give a light bitter flavor to the product. Liquid fruit products can be UV light treated to obtain a commercially sterile product that is ready to drink. UV light processing equipment can be built in a serial arrangement to apply the dosage needed to obtain a microbiologically safe liquid fruit product with adequate sensory characteristics. An added advantage to UV processing is that compared to thermal treatment, less energy is required to obtain liquid food products similar to fresh products.