Effects of pulsed electric fields and ultraviolet processing on quality characteristics, microbial inactivation and shelf life of licorice sherbet

Licorice sherbet as one of the most common traditional beverage in Turkey has been produced and consumed in very small amounts due to its very short shelf life. Processing of licorice drink by heat processing provides shelf life extension but cause adverse effects on some physical, chamical and sensory properties. Thus, processing of licorice drink by pulsed electric fields (PEF) and ultraviolet light (UV) prompted in this study. Licorice drink samples were processed by various treatment time (108, 432 and 756 µs), temperature (6, 18, and 30 °C), electric field strength (2, 4 and 7 kV) for PEF treatment and processing temperature (4, 17 and 30 °C), cycle (1, 3 ve 5) and number of lamps (1, 6 ve 11) for UV treatment according to Box-Behnken design.Treated samples were analyzed for turbidity, titratable acidity, pH, conductivitycolor (L*, a*, b*), color intensity, color tone, total antioxidant capacity, total phenolic substance content, and total reducing sugar. Results revealed that PEF and UV processing did not adversly affect the physical, chemical and sensory properties of licorice drink with ca. of 3 log cfu/mL inactivation on both the mean initial total mold and yeast and total mesophilic aerobic bacteria. The result was modeled using the response surface design and optimum conditions were determinated for PEF and UV process parameters. The response variables modeled for the pulsed electric field process were found to be conductivity. For the ultraviolet process pH, turbidity, red color composition, particle value, sweetness value was found. The optimum conditions for the pulsed electric field process were determined 2 kV, the duration of 756 µs and the temperature value of 7.5 °C, while the optimum conditions for the ultraviolet process were determined as 29 °C, the number of cycles 2 and the number of lamps 4. After the optimum conditions were determined, licorice sherbet samples were stored at 4 and 22 °C for each process. Starting from day 0 physicochemical sensory and microbiological analyzes were performed at 5 days intervals. During the storage process, the PEF and UV samples stored at 4 °C began to deteriote from the 40th day and the samples stored at 22 °C from the 30th day. Results revealed that PEF and UV can succesfully be applied to process licorice drink.