Ultrasonic washing as an abiotic elicitor to increase the phenolic content in fruits and vegetables: A review

Abstract

Ultrasonic washing has been widely applied to the postharvest storage of fruits and vegetables as a residue‐free physical washing technology, which plays an important role in improving shelf‐life, safety, and nutritional value. Phenolics are a large group of phytochemicals widespread in fruits and vegetables, and they have been considered potential protective factors against some diseases because of potent antioxidative properties. Previous studies have shown that ultrasonic washing can increase the phenolic content of fruits and vegetables immediately or during storage through the induction of plant stress responses, which is of great significance for improving the functional and nutritional value of fruits and vegetables. However, the mechanisms of ultrasound as an elicitor to improve the phenolic content remain controversial. Therefore, this review summarizes the applications of ultrasonic washing to increase the phenolic content in fruits and vegetables. Meanwhile, the corresponding physiological stress response mechanisms of the phenolic accumulation in terms of immediate stress responses (i.e., higher extractability of phenolics) and late stress responses (i.e., metabolism of phenolics) are expounded. Moreover, a hypothetical model is proposed to explain phenolic biosynthesis triggered by signaling molecules produced under ultrasound stress, including primary signal (i.e., extracellular adenosine triphosphate) and secondary signals (e.g., reactive oxygen species, Ca2+, NO, jasmonates, and ethylene). Additionally, the techno‐economic feasibility of ultrasonic washing technology is also discussed. Further, challenges and trends for further development of ultrasonic washing as an abiotic elicitor applied to the postharvest storage of fruits and vegetables are presented.

Ultrasound Treatment Improves Fruit Quality of Postharvest Blood Oranges (Citrus sinensis L. Osbeck): Anthocyanin Enrichment and Its Biosynthesis

“…US treatments generated numerous cavitation bubbles around the fruits, and the collapsing cavities will cause high-concentration reactive oxygen species (ROS) in blood oranges, leading to an imbalance in the redox state. The occurrence of oxidative burst can activate the antioxidant defense systems in blood oranges to eliminate the excessive ROS by inducing the accumulation of antioxidative anthocyanins . However, excessive cavitation effects of US will generate instantaneous high temperature and high pressure, which lead to undesirable consequences such as cell disintegration, enzyme inactivation, and protein denaturation, ultimately resulting in anthocyanin degradation.…”

“…The occurrence of oxidative burst can activate the antioxidant defense systems in blood oranges to eliminate the excessive ROS by inducing the accumulation of antioxidative anthocyanins. 28 However, excessive cavitation effects of US will generate instantaneous high temperature and high pressure, which lead to undesirable consequences such as cell disintegration, enzyme inactivation, and protein denaturation, ultimately resulting in anthocyanin degradation. Similar results were also observed in strawberries treated by US treatment (33 kHz and 60 w) with different durations.…”