Modeling the combined resistance to microwave treatments and salt conditions of Escherichia coli and Staphylococcus aureus.

In the present study, the efficiency of the combined effect of microwave irradiation treatments together with salt concentration was assessed against Escherichia coli and Staphylococcus aureus. Microbial survival has been modeled through a one-step Weibull equation considering the non-isothermal profiles during the heating treatments. Three sodium chloride concentrations 0.5%, 3.5%, and 8.5% (w/v) treated under three microwave power levels (450, 600, and 800 W) were studied. Predictive models were validated using the determination coefficient (R2), root mean squared error and the acceptable prediction zone with external data obtained from ultra high temperature milk. The results obtained suggested that increasing microwave power levels and decreasing salt concentrations led to a higher microbial inactivation, being the δ values (time for achieving a first decimal reduction) for E coli of 19.57 s at 800 W and 0.5% NaCl. In contrast, experimental data of S aureus showed a higher variability since it presented more resistance to the microwave treatments. The results obtained and generated models can be used as decision-making tools to set specific guidelines on microwave treatments for assuring food safety.

Application of Rosmarinic Acid with Its Derivatives in the Treatment of Microbial Pathogens.

The emergence of the antimicrobial resistance phenomena on and the harmful consequences of the use of antibiotics motivate the necessity of innovative antimicrobial therapies, while natural substances are considered a promising alternative. Rosmarin is an original plant compound listed among the hydroxycinnamic acids. This substance has been widely used to fight microbial pathology and chronic infections from microorganisms like bacteria, fungi and viruses. Also, various derivatives of rosmarinic acid, such as the propyl ester of rosmarinic acid, rosmarinic acid methyl ester or the hexyl ester of rosmarinic acid, have been synthesized chemically, which have been isolated as natural antimicrobial agents. Rosmarinic acid and its derivatives were combined with antibiotics to obtain a synergistic effect. This review reports on the antimicrobial effects of rosmarinic acid and its associated derivatives, both in their free form and in combination with other microbial pathogens, and mechanisms of action.

Inactivation of Escherichia coli in an Orange Juice Beverage by Combined Ultrasonic and Microwave Treatment.

The inactivation of Escherichia coli is one of the major issues in the food industry. The present study focuses on the application of a combined microwave-ultrasound system for the optimization of the inactivation of Escherichia coli ATCC 25922 in an orange juice drink. Using response surface methodology (RSM), trials were planned with a Box-Behnken Design (BBD) to maximize the impact of microwave power (A: 300-900 W), microwave treatment time (B: 15-35 s), and time of ultrasound (C: 10-30 min) on E. coli inactivation. Analysis of variance (ANOVA) was carried out and E. coli inactivation was expressed with a mathematical equation depending on the factors. The results showed that both the microwave treatment time and the time of ultrasound were effective as independent variables in eliminating the E. coli strain. However, the effect of these two variables, ultrasound and microwave exposure time, in combination was significantly greater than when examined separately. RSM modeling determined that optimal treatment conditions include 900 W microwave power, 33 s microwave treatment time, and 20 min time of ultrasound to achieve an 8-log reduction of E. coli, constituting total inactivation. The results of this study showed that ultrasound-microwave treatment is a potential alternative processing method for an orange juice beverage.

Effect of Sonication on Microwave Inactivation Kinetics of Enterococcus faecalis in Dairy Effluent.

The aim of this study is to inactivate Enterococcus faecalis ATCC 29212 present in dairy wastewater effluent using microwave (MW) waves and/or ultrasound waves (US). The ultrasonic bath treatment (35 kHz) had no significant effect on the reduction of the survival rate (predominant declumping effect). At 650 W of microwave treatment, the total destruction was completed at 75 s, while at 350 W a 3 log reduction was achieved. The Weibull model was fitted to the survival curves to describe the inactivation kinetics, and the effect of the combined microwave-ultrasound treatments was evaluated. The scaling parameter α that was estimated from the inactivation kinetics for the microwaves combined with the ultrasound waves in pre-treatment was found to be lower than the scaling parameters obtained in post-treatment, which were in turn lower than those estimated for microwaves or ultrasound waves alone. The use of the ultrasound waves in pre-treatment was more effective than in post-treatment; a total reduction was achieved using a combination of US (30 min) followed by MW (650 W) with α = 28.3 s, while 4.0 log was obtained by reversing all processes with α = 34.5 s. The results from the protein assays indicate that the bacterial wall was damaged and that holes were formed from which protein leakage occurred.