Seaweed samples of 20 g were placed in a beaker and 80ml of distilled water was added at ambient temperature conditions. A 750W ultrasonic processor (VC 750, Sonics and Materials Inc., Newtown, USA) with a 13 mm diameter probe operating at 20kHz was used for sonication pretreatments.
The schematic diagram of the equipment used is shown in Fig. 1.
The energy input was controlled by setting the amplitude of the sonicator probe.
The ultrasound probe was submerged to a depth of 25 mm in the sample.
Ultrasound power applied to the sample was calculated at a particular amplitude level, with temperature T recorded as a function of time under adiabatic conditions using a digital thermometer (VWR, Ireland).
From temperature versus time data, the initial temperature rise dT/dt was determined by polynomial curve fitting.
The ultrasound power P was determined using Eq