Low cost sample preparation method using ultrasound for the determination of environmentally critical elements in seaweed.

In this study, ultrasound (US) was evaluated for As, Cd, Pb, Mn, Sr and V extraction from seaweed samples. The following parameters of ultrasound-assisted extraction (UAE) using an US bath were: frequency (25 to 130 kHz), amplitude (30 to 100%), temperature (30 to 80 °C), sample mass (50 to 200 mg), extractant concentration (1 to 3 mol L-1 of HNO3) and treatment time (5 to 30 min). Acoustic density and power density distribution were calculated using the calorimetric method and mapping of the acoustic pressure distribution was also evaluated. The optimized UAE conditions were 200 mg of sample in 10 mL of 2 mol L-1 HNO3 and 30 min of sonication in a 25 kHz US bath (37.2 ± 4.0 W L-1) at 70% of amplitude and 70 °C. Analytes were quantified using inductively coupled plasma mass spectrometry and results were compared with values obtained using "silent" conditions (magnetic or mechanical stirring at 500 rpm, and without stirring), and a reference method based on microwave-assisted wet digestion (MAWD). The UAE method demonstrated the best extraction efficiency (higher than 95%) for all analytes, especially for As, Cd and V, with lower standard deviations (up to 5%) and lower blank values in comparison with the silent conditions. The proposed UAE method was more advantageous than the reference method, being faster, simpler, safer, more environmentally friendly, and with higher detectability (lower limits of quantification, from 0.0033 to 1.34 µg g-1). In addition, negligible blank values were obtained for UAE and no interference were observed in the determination step. Furthermore, the optimized UAE method was applied for Antarctic seaweed samples and comparison with results obtained by MAWD was satisfactory. In this sense, UAE is demonstrated to be a suitable option for sample preparation of seaweed samples and further determination of environmentally critical elements avoiding the use of concentrated reagents as in the MAWD reference method.

Thermosonication as a pretreatment of raw milk for Minas frescal cheese production.

Minas frescal cheese is extremely popular in Brazil, with high perishability and acceptability. Among emerging technologies, ultrasound stands out for its satisfactory results regarding microbiological safety and technological and sensory aspects. The combined mild temperature application, called thermosonication, can generate even more promising results. In this study, a high-intensity ultrasound system combined with thermal heating (TS, thermosonication) was applied for the treatment of raw milk to produce Minas Frescal cheese. US energy was delivered to raw milk samples using a probe operating at a 20 kHz of frequency and nominal power of 160, 400, and 640 W. The TS system was compared with conventional pasteurization (HTST, high-temperature short-time pasteurization) at 72 to 75 °C and 15 s. Soft cheeses were prepared with different samples: (a) raw milk (control), b)conventionally pasteurized milk (HTST), and c) TS treat milk in different nominal power (TS160, TS400, and TS640). The produced cheeses were evaluated for microbiological behavior, rheology, color parameters, and bioactive compounds. TS treatment in milk resulted in higher microbial inactivation and stability during storage, improved color parameters (higher lightness (L*), and whiteness index (WI). TS treatment also showed a higher generation of bioactive compounds (higher antioxidant, and inhibitory activities of α-amylase, α-glucosidase, and angiotensin-converting enzymes) than HTST. The impact of TS on rheological properties was similar to HTST, resulting in more brittle and less firm products than the cheese produced with raw milk. The positive effects were more prominent using a nominal power of 400 W (TS400). Therefore, TS proved to be a promising process for processing milk for Minas Frescal cheese production.

The physical, mechanical, thermal and barrier properties of starch nanoparticle (SNP)/polyurethane (PU) nanocomposite films synthesised by an ultrasound-assisted process.

This article reports on the ultrasound-assisted acid hydrolysis for the synthesis and evaluation of starch nanoparticles (SNP) as nanofillers to improve the physical, mechanical, thermal, and barrier properties of polyurethane (PU) films. During the ultrasonic irradiation, dropwise addition of 0.25 mol L-1 H2SO4 was carried out to the starch dispersion for the preparation of SNPs. The synthesized SNPs were blended uniformly within the PU matrix using ultrasonic irradiation (20 kHz, 220 W pulse mode). The temperature was kept constant during the synthesis (4 °C). The nanocomposite coating films were made with a regulated thickness using the casting method. The effect of SNP content (wt%) in nanocomposite coating films on various properties such as morphology, water vapour permeability (WVP), glass transition temperature (Tg), microbial barrier, and mechanical properties was studied. The addition of SNP to the PU matrix increased the roughness of the surface, and Tg by 7 °C, lowering WVP by 60% compared to the PU film without the addition of SNP. As the SNP concentration was increased, the opacity of the film increased. The reinforcement of the SNP in the PU matrix enhanced the microbial barrier of the film by 99.9%, with the optimal content of SNP being 5%. Improvement in the toughness and barrier properties was observed with an increase in the SNP content of the film.