(177j) Effect of Ultrasound in Bioactive Compounds of Acerola Juice

Many fruits and their products are sensitive to heat preservation, such as pasteurization and sterilization. Thermal preservation can result in the loss of antioxidant compounds naturally present in the food, resulting in the formation of residual taste and degradation of color, vitamins and aromatic compounds. The introduction of new technologies can reduce processing time and improve industrial operating conditions, resulting in high-quality products that preserve their initial characteristics. Ultrasound, among the technologies, has been used in many recent applications and often as a complementary technology to classic thermal processes, being particularly useful in the sterilization process, where it has a lethal effect on microorganisms, contributing to food quality and safety, and in the extraction, freezing and filtration processes, reducing processing times and increasing efficiency. Ultrasound produces acoustic cavitation, repetitive cycles of compression and decompression, which is nothing more than the process of nucleation, growth, and collapse of bubbles in liquids exposed to ultrasonic waves at low frequency (20-100 kHz) and high power (10-1000 W/cm²). Bubble collapse generates high local temperatures, around 5000K, and high pressures, around 1000 atm, resulting in high shear rates and strong micro-currents that can contribute to enzymatic and microbial inactivation. Therefore, ultrasound can be considered an effective non-thermal technology in the inactivation of microorganisms and enzymes related to the degradation of fruit juices. The use of ultrasound is considered as an alternative to thermal processing and there are reports in the literature of minimal effects caused in the quality of fruit juices, such as orange, blackberry, strawberry. However, studies on the influence of ultrasound on bioactive compounds of acerola juice are scarce. Therefore, the objective of this work was to evaluate the influence of ultrasound (intensity and time of application) on total phenolic and ascorbic acid contents of acerola juice. The juice was obtained from fruit pulps, these being free of the addition of water and additives. The juice was obtained by diluting the pulp in water in a ratio of 1: 1 and stored at 4 °C prior to processing. A 500 W ultrasonic processor with 1.3 cm diameter probe was used for the sonication of acerola juice. The samples were processed at a constant frequency of ultrasound (19 kHz). The pulp samples were placed in 250 mL beakers and the probe was submerged to a depth of 25 mm. The applied power was controlled through the amplitude conversion and power levels were adjusted between 20 and 100% of the input power (500 W). The calculated intensities were between 75 and 373 W/cm². In order to study the effects of power intensity and time of application of the ultrasound on acerola juice, a rotatable central composite design was used. The ranges of variation between the lower and upper limits of each variable were established based on the literature. The results of the statistical analysis, applied to the experimental data of the ascorbic acid content in acerola juice, showed that only the regression coefficients of linear factors of power intensity and quadratic time and power intensity were significant at 95% confidence (p≤0.05). The power intensity was the parameter that most influenced this response. The obtained regression model was considered predictive and the response surface was generated. The highest values of the ascorbic acid content were obtained using low power values (close to 75 W/cm²), independent of the time of application of the ultrasound. Regarding the total phenolic compounds content, the value of the regression coefficient obtained was below 0.50. Thus, the response surface methodology was not applied to analyze the experimental data of this analysis. However, it can be observed that, among the eleven treatments, four presented an increase in the total phenolic content when compared to the value of the control juice, and the largest increases were observed when the time of application of the 9 minutes was used. This increase can be attributed to the reaction between the aromatic ring of the polyphenols and the free radicals generated in the sonication, which contributes to the increase of the antioxidant capacity. Furthermore, sonication removes oxygen dissolved in the juice, contributing to the greater bioavailability of the phenolic compounds. The use of non-thermal ultrasound technology significantly influenced the acerola juice quality parameters and the response surface methodology can be used to optimize critical process parameters.