There are several types of probe shape, including uniform cylinder,
exponential, taper, linear taper, or cone and stepped. Volume
of the sample and type are two critical factors governing the selection
of probe {for details, see [37]}. High-power ultrasonic probes
are generally preferred for their extraction efficiency and can enhance
yields in short extraction time. Temperature sensitivity of the target
compound and flammability of solvents should be considered when
selecting a high-intensity probe for extraction. High-intensity ultrasonic
probes that can raise the temperature of the medium to
50–85°C can lead to degradation of the target compound, depending
on the temperature sensitivity. A probe-type system for UAE
allows better extraction yields than an ultrasonic bath system.With
an ultrasonic probe, ultrasonic energy is applied directly to the
sample and energy losses are minimal. In a study, Bajerová, Adam
[34] carried out ultrasonic extraction of antioxidants from various
plants in ultrasonic bath and by ultrasonic probe. In the majority
of cases, they observed significantly higher antioxidant capacity and
levels of antioxidant extraction using the probe system, compared
to the ultrasonic bath system. However, Adam, Dobiáš [32] observed
higher values for antioxidant compounds using an ultrasonic
bath and no significant differences in the antioxidant capacity of
antioxidants extracted from various plant samples under comparable
extraction conditions. Both studies employed similar ultrasonic
frequencies and power levels. The obvious differences are mainly
attributed to the matrix and other extrinsic and intrinsic factors.