Ultrasound-Assisted Encapsulation of Phytochemicals for Food Applications: A Review

Abstract

The use of phytochemicals as natural food additives is a topic of interest for both academic and food industry communities. However, many of these substances are sensitive to environmental conditions. For this reason, encapsulation is usually performed prior to incorporation into food products. In this sense, ultrasound-assisted encapsulation is an emerging technique that has been gaining attention in this field, bringing important advantages for the production of functional food products. This review article covered applications published in the last five years (from 2019 to 2023) on the use of ultrasound to encapsulate phytochemicals for further incorporation into food. The ultrasound mechanisms for encapsulation, its parameters, such as reactor configuration, frequency, and power, and the use of ultrasound technology, along with conventional encapsulation techniques, were all discussed. Additionally, the main challenges of existing methods and future possibilities were discussed. In general, ultrasound-assisted encapsulation has been considered a great tool for the production of smaller capsules with a lower polydispersity index. Encapsulated materials also present a higher bioavailability. However, there is still room for further developments regarding process scale-up for industrial applications. Future studies should also focus on incorporating produced capsules in model food products to further assess their stability and sensory properties.

Keywords: bioactive compounds; encapsulation; food technology; functional food; phytochemicals; process intensification; ultrasound.

Figure 1

Examples of capsule morphologies that can be obtained through different encapsulation techniques, and particle types that can be produced with these morphologies. Adapted from the studies published by the authors of [28,34,35].

Figure 2

Picture of a spray dry system and a schematic representation of the spray dry encapsulation process. The liquid core and shell materials are homogenized and introduced into a drying chamber, where the droplets undergo atomization and drying to form solid capsules. Reproduced from the study published by the authors of [41].

Figure 3

Proposed mechanism for ultrasound-assisted oil-in-water emulsification. (1–5) The collapse of cavitation bubbles causes water droplets to disperse into the oil phase, forming a water-in-oil emulsion. (6–9) Due to Rayleigh–Taylor instability, some of the oil phase disperses into the aqueous phase, and the droplets are broken down to smaller particles through continued sonication. These steps are repeated until a true oil-in-water emulsion is formed. W/O: water-in-oil; R-T: Rayleigh–Taylor; O/W: oil-in-water. Reproduced from the study published by the authors of [48].

Figure 4

Representation of (A) bath and (B) probe reactor configurations for ultrasound-assisted encapsulation applications. In bath reactors, US is indirectly applied to the reaction medium, being transmitted from the transducers through a water bath. For probe reactors, US energy is directly transmitted into the medium via the probe tip.

Figure 5

A schematic illustration of a glycogen-based shell being formed during the ultrasound-assisted encapsulation of soybean oil/vitamin D. First, sonication induces the generation of an oil-in-water emulsion. Glycogen molecules then agglomerate at the interface of the oil droplets, encapsulating them. Reproduced from the study published by the authors of [58].

Figure 6

Instrumental setup for the scale-up application of the ultrasound-assisted nanoemulsification process using a single pass flow-through approach. The aqueous and oil phases are mixed in the premix tank, and then pumped through the reactor chamber (where emulsification occurs) into the product tank. HBH: half-wave Barbell horn. Reproduced from the study published by the authors of [70].