Effect of Sonication on the Functional Properties of Different Fruit Juices

Pineapple Juice

Sonication is an upcoming technology that can enhance food quality and reduce nutrient loss. It has been explored for Kasturi lime, cantaloupe melon, apple and orange juice. Sonication retained most of the nutrients in juices and reduced microbial load of the treated samples. Epidemiological studies have confirmed that a diet comprising fruits in larger portion may exert numerous health benefits to the consumers. The health benefits have been linked with the different classes of phytochemicals present in fruits like, flavonoids, phenolic acids, and carotenoids. Currently, the consumer's expectation on food products with reasonable shelf-life and high levels of nutrients had been increased immensely.

Ultrasonic’s has emerged to an unconditional extent in the last decade. It has found its application in fruit juice and beverage industry due to its multifunctional desired effects. The technology is inexpensive, simple, reliable, and environmentally friendly and highly effective in the preservation of juices with enhanced quality attributes. Practical applications Ultrasound processing is an emerging nonthermal technique which can be utilized in the processing of liquid food products. In general, fruit juices are processed through thermal treatments to keep the safe microbial levels. However, thermal processing adversely affects the quality of food products.

In recent years, for purpose of meeting consumer demand of more safe, healthy, and nutritious foodstuff, many studies of food processing field have moved from the conventional thermal processing technology to the innovative non-thermal treatment technologies (Zou & Jiang, 2016). Thermal processing of food product can lead to some adverse organoleptic and nutritional losses (Gómez  et  al., 2011). However, innovative emerging non-thermal treatment approaches can be used to enhance food quality and ensure its security without any damage or adverse impact to food nutrients (Caminiti et al., 2011). Sonication is one of non-thermal treatment approaches, which may observably enhance food quality and avoid nutrient damage.

In the last few years, impact of sonication on raw juices from fruits and vegetables such as kasturi lime, cantaloupe melon, apple, orange, and carrot. It has been investigated and proved to an appropriate processing method of the juice. Sonication can effectively retain the most beneficial nutrients and decrease microbial load in the juice. Moreover, sonication can shorten processing time and reduce energy consumption. However, until now there is still little report available in literatures about impact of sonication on the processing of blueberry juice. This research explored impact of sonication on physicochemical parameters of blueberry juices by evaluating the pH, viscosity, electric conductivity, color, total sugars, soluble solids, polyphenol, and anthocyanidin. Moreover, the scavenging activities of sonicated blueberry juice on DPPH, superoxide, and hydroxyl radicals were investigated.

However, high temperature may change the biochemical, physicochemical, organoleptic (taste, aroma, flavor), and physical properties (color, viscosity) and nutritional values (vitamins, phenolic, etc.) of juices.

Juice is presently one of the most popular beverages in food technology. It is a product of vegetables and fruits that retains properties with very similar characteristics to the raw materials. Juice is easy to consume, delicious, and refreshing, and it is rich in vitamins, phytochemicals, and sometimes fiber, depending on the raw materials used. Juices can be more preferable for consumption than vegetables and fruits because a given amount of juice includes more nutrition than the same amount of fruits and vegetables, as long as nutritional losses are minimized during processing. The digestion of fruits and vegetables is also more complex and difficult than digestion of juices, so more of the nutritional value of fruit and vegetables is realized by drinking juice. Juice production consists of many processes, including thermal treatments necessary for food safety and preservation of quality. High-temperature treatment denatures proteins, thereby inactivating microorganisms and enzymes that cause undesirable changes in juice and shorten its shelf life. Incomplete inactivation of enzymes will result in unwanted changes, such as enzymatic browning and cloudiness.

The enzymes polyphenol oxidase (PPO), pectin methyl esterase (PME), and peroxidase (POD) are generally found in fruit juices, with PME being the 2 M. Başlar et al. predominant enzyme in various fruits. However, high temperature may change the biochemical, physicochemical, organoleptic (taste, aroma, flavor), and physical properties (color, viscosity) and nutritional values (vitamins, phenolic, etc.) of juices. For example, application of thermal treatments to fresh watermelon juice changed its color and dynamic viscosity and destroyed its lycopene content. More unwanted color changes occurred in apple juice following a thermal process than with a pulsed electrical field process (a nonthermal process).

The current trend toward consumption of fresh, organic, or minimally processed foods with the highest product quality now demands that new processing methods be developed and applied by the food industry by determining juice acceptability to the consumer. When fruits and vegetables are first processed, their nutritional values are the highest, but once thermal treatments are applied to increase shelf life, the nutritional values start to decrease. However; if no treatments are applied, the food deteriorates because of harmful microorganisms and enzymes. Therefore, the search continues for nonthermal treatments that can prolong shelf life and minimize quality loss. The nonthermal treatments used in fruit juice processing have included ultrasound, UV light, high-intensity light pulses, pulsed electric fields, high hydrostatic pressure, supercritical carbon dioxide, dense-phase carbon dioxide, radiofrequency electric fields, γ-irradiation, ozonation, and flash-vacuum expansion. Other alternatives include dielectric heating, ohmic heating, microwave heating, and radio frequency heating, used in combinations or as pretreatments. The ultrasound process may minimize the effects on other quality parameters of fruit juices – for example, the content of heat-sensitive vitamins – because it is a nonthermal process. The application of ultrasound to orange juice was reported to diminish its ascorbic acid content by only 5 % during processing, and the subsequent stability of ascorbic acid was enhanced during the storage period.

However, the viscosity of the juice affects the numbers of ultrasound-induced cavitation, so the juice composition may protect microbes and enzymes against the effects of cavitation. Ultrasonication may also cause changes in the aroma profile and sensory attributes. Simunek et al. examined the use of high-power ultrasound treatment for the pasteurization of apple juice and nectar and found that ultrasonic treatment caused the formation of new substances and/or the disappearance of existing ones when compared with untreated samples of juices and nectars. Ultrasound processing, also called sonication, is used for extraction, homogenization, emulsification, drying, crystallization, cutting, and inactivation of microorganisms and enzymes.

Microbial and enzymatic inactivation is essential for pasteurization of juices, and ultrasound, one of the nonthermal processes, has important potential in this respect. It does not have the common side effects of conventional thermal treatments on food nutritional and quality parameters, such as degradation of some vitamins, color, and proteins, and it has been approved by FDA since 2000, providing a potential 5 log reduction in juice microbial content. High-power ultrasound applications have also been used for extraction of bioactive compounds (e.g., phenolics, flavonoids, ascorbic acid, and anthocyanins) found in fruits and vegetables because ultrasound improved yield, productivity, and selectivity and decreased the required extraction time. Vilkhu et al. reported that extraction yield was increased from 6 % to 35 % by ultrasound processing. A further benefit of decreased thermal effects and increased yield/ productivity was that ultrasound technology improved the rheological and cloudy properties of the final juice product.

Effect of Ultrasound on Juice Quality

Shelf Life: Ultrasound treatment of juice has been reported to be effective for the inactivation of enterobacteria, total yeasts and molds, aerobic plate count, coliform count, total yeast and mold count, and Escherichia coli. Abid et al. observed that total plate count was considerably decreased in samples sonicated for 60 and 90 min when compared to samples treated for 30 min and control samples. A significant decrease was also observed in yeasts and molds in all sonicated samples

Yield and Extraction:  Ultrasonic treatments provide high yields and effective extractions by increasing the cutting power and generating microbubbles that increase the surface area and mass transfer based on the cavitation effect.

Sensory properties: One important reason for the use of alternatives to thermal processing is that nonthermal treatments prevent the loss of sensory properties that occurs during heat treatment of juice. Ertugay and Başlar reported that apple juice treated at an ultrasound amplitude of 50 μm and a temperature of 50 C for 10 min had the most acceptable aroma and flavor as determined by panelists.

Bioactive compounds: Some studies indicate that ultrasonic treatment increases the levels of bioactive compounds by improving the release of these components from the cells. For example, the bioactive components of apple juice were significantly increased after ultrasound application: The total phenolic values were higher in juice samples treated for 30, 60, and 90 min (768, 815 and 829 μg/g) than in nontreated apple juice (757 μg/g). Similar increases were also observed in flavonoid and flavonol content and in the total antioxidant capacity of the sonicated samples. The ascorbic acid value of the apple juice was improved by increasing the ultrasound treatment time, with the highest value observed in juice treated for 90 min.

Rheological Properties: The rheological properties are identifying characteristics of fluid foods such as juice. The properties of juice can change during conventional heat treatments because of changes in the structural properties of the juice. Similarly, ultrasound treatment can usually induce some changes in juice rheological properties.

Cloudiness:  Cloudiness is an important quality parameter that affects the appearance and flavor of the juice. It is determinative for consumer approval for some juices. It is related to the presence of particles composed of pectin, protein, cellulose, and lipids. The concepts of cloud value and cloud stability value are generally used for interpretation. The cloud value indicates the current turbidity levels, while cloud stability refers to the cloud value of the juice over time. Centrifugation at 4200  g for 15 min is equivalent to 1 year of storage.

Conclusions and Future Directions:  Alone ultrasonic treatment is not sufficient for extending the shelf life of juices; therefore, it is commonly used in combination with a thermal process referred to as thermosonication. Various combinations of heat and sonication have been tested to extend the shelf life, but no method has yet been developed for application in the industrialization stage. Further research is needed for optimization of new processing combinations that incorporate ultrasonication. At the same time, it seems that some nonthermal process (UV and PEF) in commercialization stage is present.


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Uzma Gulzar, Mahital Jamwal, Mehvish Mushtaq, and  Prabhdeep Singh

Email: gulzaruzma1@gmail.com

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