Inactivation of Staphylococcus aureus and Escherichia coli in milk by different processing sequences of ultrasound and heat

Abstract

Different processing sequences of ultrasound and heat were applied for the inactivation of Staphylococcus aureus and Escherichia coli in milk. The changes in whey protein content, particle size, zeta potential, pH, viscosity, and color values were studied to evaluate the effects on the quality of milk. Results indicated ultrasound treatment (600 W, 5 min) with postheating (63 °C 5 min) reduced S. aureus and E. coli by 1.58 and 2.02 log cfu/ml, respectively, but yielded 0.26 and 0.19 log cfu/ml sublethal S. aureus and E. coli. Milk preheated to 63 °C (5 min) followed by ultrasound (600 W, 5 min) showed 1.17 and 1.68 log reductions for S. aureus and E. coli, respectively, and the sublethal S. aureus and E. coli were reduced to 0.16 and 0.09 log cfu/ml. The increased cavitation effects make the simultaneous treatment (600 W, 63 °C, 5 min) the most effective approach in killing S. aureus and E. coli, causing 1.67 and 2.16 log reductions, respectively, and producing negligible sublethal bacteria. The simultaneous treatment was also able to improve some physical–chemical properties of milk; smaller particle size and whiter color were achieved. However, whey protein and stability indices of milk were slightly deteriorated by this approach. Practical applications In food processing fields, thermosonication can serve as an alternative processing technique to thermal pasteurization. Especially, the simultaneous treatment of ultrasound and heat showed best inactivation effect for viable and sublethal cells, while maintaining the overall milk quality in the meantime. The results of this research may be useful for the treatment of various bacterial contamination and give the guidance for milk processing.

Effect of sonication conditions: Time, temperature and amplitude on physicochemical, textural and sensory properties of yoghurt

“…Colour is the key quality characteristic of dairy products, which is related to the dispersion of casein micelles and fat globules in the visible spectrum (Li et al . 2019). The results of the colour values of the yoghurt samples and the colour difference are presented in Table 4.…”

“…The colour improvement of sonicated dairy products attributed to the improvement of homogenisation and light reflection which modified by the reduction of fat globules size and denaturation of soluble proteins (Li et al . 2019). Heat treatment at 65 and 90 ºC resulted in a Maillard reaction, but ultrasound had a discolouration effect on samples and decreased the yellowness value of samples and their colour scores.…”

Application of a 360-Degree Radiation Thermosonication Technology for the Inactivation of Staphylococcus aureus in Milk

“…Most of the commonly used ultrasonic horns have only one transmitter on the tip, which transfers nearly all the energy through one direction. In our previous study, it was found that the TS, combined with single-direction ultrasonic radiation (600 W) and 63 • C, resulted in less than 99% reduction of S. aureus for 5 min (Li et al, 2019). Individual heat exposure has been reported to activate protective systems in bacteria cells, which could compromise the microbial inactivation level (Liu et al, 2020;Wu et al, 2021).…”

Two Nonthermal Technologies for Food Safety and Quality—Ultrasound and High Pressure Homogenization: Effects on Microorganisms, Advances, and Possibilities: A Review

“…Other authors reported a partial or complete inactivation for other enzymes, such as proteases from P. fluorescens (110), pectin methyl-esterase (29,77,139), papain (86), trypsin (85), alkaline phosphatase (42), lactoperoxidase (42,66,81), lipase (42), and polyphenoloxidase (108). Few enzymes were found resistant or not affected by HPH, such as trypsin (82,83) and a protease from Rhizomucor miehei (81).…”