A potential of ultrasound on minerals, micro-organisms, phenolic compounds and colouring pigments of grapefruit juice

Effect of ultrasound and chemical treatment on total phenol, flavonoids and antioxidant properties on carrot-grape juice blend during storage

Ultrasonics is one of the developing technologies which is being studied extensively on different food commodities. Our aim was to study the effect of sonication and chemical (Potassium metabisulfite, K₂S₂O₅,) preservation method on grape-carrot juice blend. Sonication/ultrasound treatments (20 kHz frequency, 70% amplitude level (525 W power), and pulse duration 5 s on and 5 s off, 5 min at 15 °C) of all the samples (250 mL) were performed by using an ultrasonic processor with 0.5 in. probe at 2 in. depth of the sample. Additionally, impact of sonication on 90 days of storage period at refrigerated temperature was also measured. It was observed that sonication had a positive effect on nutritional status of juice blend as it enhanced the total phenolic, flavonoid, reducing power and antioxidant properties of juice significantly (p < 0.05) with increase in sonication time. Sonication can be employed successfully for treatment of juice with better nutritional attributes from consumers' point of view.

Effect of Pulsed Electric Field on Membrane Lipids and Oxidative Injury of Salmonella typhimurium

Salmonella typhimurium cells were subjected to pulsed electric field (PEF) treatment at 25 kV/cm for 0–4 ms to investigate the effect of PEF on the cytoplasmic membrane lipids and oxidative injury of cells. Results indicated that PEF treatment induced a decrease of membrane fluidity of Salmonella typhimurium (S. typhimuriumi), possibly due to the alterations of fatty acid biosynthesis-associated gene expressions (down-regulation of cfa and fabA gene expressions and the up-regulation of fabD gene expression), which, in turn, modified the composition of membrane lipid (decrease in the content ratio of unsaturated fatty acids to saturated fatty acids). In addition, oxidative injury induced by PEF treatment was associated with an increase in the content of malondialdehyde. The up-regulation of cytochrome bo oxidase gene expressions (cyoA, cyoB, and cyoC) indicated that membrane damage was induced by PEF treatment, which was related to the repairing mechanism of alleviating the oxidative injury caused by PEF treatment. Based on these results, we achieved better understanding of microbial injury induced by PEF, suggesting that micro-organisms tend to decrease membrane fluidity in response to PEF treatment and, thus, a greater membrane fluidity might improve the efficiency of PEF treatment to inactivate micro-organisms.

Using homogenization, sonication and thermo-sonication to inactivate fungi

Ultrasound (US), Thermo-sonication (TS) and High Pressure Homogenization (HPH) were studied as tools to inactivate the spores of Penicillium spp. and Mucor spp. inoculated in distilled water. For US, the power ranged from 40% to 100%, pulse from 2 to 10 s, and duration of the treatment from 2 to 10 min. TS was performed combining US (40-80% of power, for 8 min and pulse of 2 s) with a thermal treatment (50, 55 and 60°C at 4, 8 and 12 min). Homogenization was done at 30-150 MPa for 1, 2 and 3 times. Power was the most important factors to determine the antifungal effect of US and TS towards the conidia of Penicillium spp.; on the other hand, in US treatments Mucor spp. was also affected by pulse and time. HPH exerted a significant antifungal effect only if the highest pressures were applied for 2-3 times.