Effect of Thermo-sonication on Quality Properties of Barberry (Berberis vulgaris) Juice

Barberry (Berberis vulgaris) from the distant past has been used as one of the main medicinal plants in Iran and many other countries. Currently, it has been known for pharmaceutical active compounds such as berberine, which has wide application in pharmaceutical industry. Barberry fruits are used in preparing sauces, jellies, candies, marmalades and especially fruit juices. Also, the fruit contains health promoting compounds such as polyphenols and anthocyanins. Anthocyanins are bioactive compounds present in many fruits, vegetables and their products. They are responsible for the wide array of colors present in flowers, petals, leaves, fruits and vegetables and are a sub-group within the flavanoids characterized by a C6-C3-C6 skeleton. A substantial property of anthocyanin is their antioxidant activity, which plays an important role in prevention of neuronal and cardiovascular illnesses, cancer and diabetes, among others. Therefore, preservation of these compounds during processing of barberry juice is very important. Conventional thermal pasteurization is the common preservation technique used for fruit juice processing. Although this method inactivates microorganisms and enzymes causing spoilage and extends the shelf life of juices, but also it causes degradation of anthocyanins and loss of the nutritional quality of these products. Moreover, the increasing demand for natural and fresh fruit juice resulted in the development of various non-thermal technologies, such as radiation processing, osmotic dehydration, pulse electric field, sonication and high pressure. Power ultrasound has shown important advances in food processing and has a potential to meet the FDA requirement of a 5 log reduction in pertinent microorganisms found in fruit juice. Physical (cavitation, micromechanical shocks and mechanical effects) and chemical (formation of free radicals) mechanisms are responsible for the biocidal effect of sonication. Other advantages of this technology include low cost, reduced processing time and environmentally friendly technique. However, ultrasound by itself is not very effective for microbial inactivation and the use of other technologies during sonication such as temperature (thermo-sonication) and pressure (mano-sonication) has shown efficient results in inactivation of microorganisms. Thermosonication has been reported as an alternative to thermal pasteurization for processing of fruit juices such as strawberry juice, blackberry juice and orange juice. According to the negative effect of thermal processing on color and anthocyanins of barberry juice this study aimed to evaluate the effect of thermo-sonication as an emerging technology in two intensities 18.32 and 27.62 W/cm2 at 45°C for 5 and 10 minutes on the quality of barberry juice.
Material and Barberry (B. vulgaris) ripe fresh fruits were collected from gardens of Qaen. Fruits were crushed into pieces in an electric blender. The mixture was then filtered through a nylon filter and kept in dark condition at 4°C before subjecting to thermosonication. Barberry juice was sonicated at 200W capacity batch sonication system (Sonopuls HD 3200 BANDELIN, Germany) and a constant frequency of 20 kHz with a 13mm probe. Barberry juice samples of 60 mL were placed in a 100 mL double wall cylindrical vessel pyrex glass through which water at 4±1°C and a flow rate of 0.5 L/min was circulated to attain a constant temperature in the juice sample during sonication. The samples were sonicated at 70 and 100% amplitudes levels for 10 and 15 min at 45°C with pulse durations of 15s on and 5s off (US70-5, US70-10, US100-5 and US100-10). After the sonication treatment, juice samples were kept in sterilized bottles and were stored at 4°C until further analysis. Total anthocyanin content of barberry juice was determined by the pH differential method and the color of juice samples was determined using a Chroma Meter (Color Flux, USA). The color values were expressed as L* (lightness), a* (redness/greenness) and b* (yellowness/blueness). The total phenolic content and antioxidant activity was determined by modified Folin–Ciocalteu method and DPPH radical scavenging activity. The counting of microorganisms was made using standard techniques (AOAC 1984), and included total plate counts and yeasts and molds. All experiments were carried out in at least three replicates and the results were expressed as mean ± SD. The significant differences between mean values of juice samples were determined by analysis of variance (one way-ANOVA) using Dunkan’s test at a significance level of P The result showed that the processing in all treatments completely inactivated the microbial population. The reduction of total plate counts and yeast and mold counts after processing was equal to 3.68±0.1 and 3.34±0.48, respectively. Thermo-sonication, especially in low intensity (32/18 w/cm2) had little effect on total anthocyanin compounds of barberry juice. The losses in total anthocyanin content of juice samples were 0.03%, 1.14%, 1.56% and 10.79% in TS-70-5, TS-70-10, TS-100-5 and TS-100-10, respectively. Hydroxyl radicals produced by cavitation can be involved in the degradation of anthocyanins by opening of rings and formation of chalcone. Thermosonication had significant effect on color parameters of barberry juice. All the color values (L*, a*, b* and C*) of barberry juice treated with thermosonication treatment were decreased as compared to control. The color loss of barberry juice samples decreased with increasing the amplitude and time of thermosonication. Extreme physical conditions which occur within the bubbles during cavitational collapse at micro-scale reaction may be responsible for the degradation of color in fruit juices. A significant increase (p˂0.05) in both total phenolic content and antioxidant activity of samples treated at TS-70-5 and TS-70-10 was observed. However, higher amplitude significantly decreased the total phenolic content and antioxidant activity of barberry juice. It has been shown the enhancement of total phenolic content in juices after sonication might be attributed to the facilitation the release of bound phenolic present in the suspended particles. Since there is a correlation between total phenolic content and antioxidant activity, the extraction of bound polyphenols due to cavitation can be presumed the increase in antioxidant activity. The result of this study showed that thermo-sonication could be used as an alternative to thermal treatment.