Determining the shelf life of carrot juice treated by cold plasma

Abstract

Introduction: Carrot juice is one of the perishable foods with a short shelf life. Cold plasma is one

of the new non-thermal methods for food treatment. Cold plasma treatment on carrot juice increases its shelf life by maintaining more nutrients. In this study, the physicochemical, microbial, and sensory properties of carrot juice treated with different treatments of dielecteric barrier discharge cold plasma with air, heat-treated, and untreated during shelf life were investigated, and the best test for predicting the shelf life of carrot juice was selected by calculating kinetic parameters.

Materials and methods: The obtained carrot juice was exposed to different times of plasma treatment (3, 4 and 5 minutes) at a constant voltage, then according to the change in the appearance and microbial characteristics of the carrot juice, the treatment was selected in 3 minutes. Next, carrot juice was subjected to 8 kV, 10 kV, 12 kV and 15 kV for 3 minutes. The 15 kV treatment was abandoned due to its phase separation. Cold plasma treatment samples physicochemical, microbial and sensory properties during storage at 4 °C were compared with thermally pasteurized samples (80 °C for 7 minutes) and control. The best plasma treatment was selected in terms of maintaining the main physicochemical, sensory properties and inhibiting microbial growth. Degradation of carotenoid content and total number of mesophilic bacteria (TMB) during storage of carrot juice at isothermal temperatures (-18 °C, 4 °C, 15 °C and 25 °C) to calculate kinetic parameters and determine the amount of Q10 using A combination of primary and secondary models was used.

Results: There was no significant difference in titratable acidity values between samples treated with cold plasma and control samples however heat-treated sample showd significantly decrease in titratable acidity. All samples showed a decrease in titratable acidity over time. Viscosity showed a significant increase during storage that the highest level was for heat-treated sample then control sample and the least was for plasma treatments. The phenolic content showed a general decreasing trend in all test samples until the end of the storage days, however, the carrot juice treated with cold plasma at 12 kV showed the highest and heat-treated sample showed the

lowest phenolic content in all the evaluation days. 8 kV plasma-treated sample had no significant difference with control sample in the beginning. The content of ascorbic acid after 21 days of storage was reduced by 52, 63 and 73% for control, 8 kV cold plasma treatment and other treatments, respectively. Plasma treatment decresed the carotenoid content of the carrot juice significantly but heat-treated sample maintained the carotenoid content better at day 1. During storage, the carotenoid content significantly decreased, and the largest decrease was observed in samples treated with cold plasma. A significant decrease in DPPH free radical scavenging activity of samples treated with heat treatment was observed compared to the control sample. However, plasma treatment led to the preservation of antioxidant activity. Plasma treatment of carrot juice at 8 kV reduced the number of TMB by 2-logCFU/mL, which turned out to be the most effective method in eliminating the natural microbial flora of carrot juice. The sample treated with cold plasma at 8 kV showed the highest mean sensory scores compared to other treatments during storage. Thermal treatment and cold plasma treatments at high voltage obtained the lowest sensory scores. However, in the case of all samples, a trend of decreasing acceptability was observed during the storage time. Better color retention of samples treated with cold plasma at 8 kV was consistent with Hunter lab data, resulting in lower ΔE values compared to other treatments. The correlation coefficient (R2) of first order kinetics for all temperatures was higher than zero-order; Therefore, the first-order model best described carotenoid degradation in carrot juice treated with cold plasma. Great changes in k values were observed with increasing temperature from -18°C to 25°C. The values of t1.2 varied from 1.55 days for 25°C to 63.01 days for -18°C. The values of Q10 decreased significantly from the temperature of 255.15 K (2.5829 ± 0.0059) to 298.15 K (2.0106±0.0034). Comparison of Q10 values obtained from TMB and carotenoid degradation showed significantly higher values for microbial growth. This result shows that the use of microbial indicators to predict shelf-life in carrot