Textural properties of infra red dried apple slices as affected by high power ultrasound pre-treatment

Drying is a process frequently used in food industry, often based on the use of conventional methods using heat exchange by conduction or convection. This kind of method may lead to quality loss in structure, texture and  sensory characteristics of final products. Consequently, the need for research of new drying methods arises.  One of such methods is power ultrasound aided drying. The aim of this work was to investigate the impact of  high power ultrasound pre-treatment on drying rate and textural properties of the infra red dried apple slices.  Ultrasound device working at a frequency of 24 kHz with a power capacity of 200 W was used for ultrasound  pre-treatment. The amplitudes used for ultrasonic pre-treatment were 50 and 100%. The results showed that  the use of different amplitudes of ultrasound reduces the time of drying and allows elimination of more water  from the apple slices. Usage of 50 and 100% of ultrasonic amplitude in great extent shortened the duration of  drying (up to 40%). The results showed that hardness of samples gradually increases (50% amplitude –  97.260 N; 100% of amplitude – 217.90 N) with increase of ultrasound intensity. As a result, hardness of  untreated apple slices (41.037N) was significantly lower (p < 0.05).Key words: High power ultrasound, amplitude, drying, apple

Optimization of ultrasound assisted extraction of functional ingredients from Stevia rebaudiana Bertoni leaves

The aim of the present study was to reveal an effective extraction procedure for maximization of the yield of steviol glycosides and total phenolic compounds as well as antioxidant activity in stevia extracts. Ultrasound assisted extraction was compared with conventional solvent extraction. The exami-ned solvents were water (100ºC/24 h) and 70% ethanol (at 70°C for 30 min). Qualitative and quantitative analyses of steviol glycosides in the extracts obtained were performed using high performance liquid chromatography. Total phenolic compounds, flavonoids, and radical scavenging capacity by 2, 2-azino-di-3-ethylbenzothialozine-sulphonic acid) assay were also determined. The highest content of steviol glycosides, total phenolic compounds, and flavonoids in stevia extracts were obtained when ultrasound assisted extraction was used. The antioxidant activity of the extracts was correlated with the total amount of phenolic compounds. The results indicated that the examined sonication parameters represented as the probe diameter (7 and 22 mm) and treatment time (2, 4, 6, 8, and 10 min) significantly contributed to the yield of steviol glycosides, total phenolic compounds, and flavonoids. The optimum conditions for the maximum yield of steviol glycosides, total phenolic compounds, and flavonoids were as follows: extraction time 10 min, probe diameter 22 mm, and temperature 81.2oC