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

Inactivation of Vibrio parahaemolyticus and retardation of quality loss in oyster (Crassostrea gigas) by ultrasound processing during storage

The health problems caused by foodborne pathogens of raw oysters have been widely concerned. Traditional heating methods tend to lead the loss of the original nutrients and flavors, in this study, the nonthermal ultrasound technology was applied to inactivate Vibrio parahaemolyticus on raw oysters, and the retardation effects on microbial growth and quality loss of oysters stored at 4 ℃ after ultrasonic treatment were also investigated. After treated by 7.5 W/mL ultrasound for 12.5 min, the Vibrio parahaemolyticus in oysters was reduced by 3.13 log CFU/g. By measuring total aerobic bacteria and total volatile base nitrogen, the growth trend after ultrasonic treatment was delayed compared with heat treatment, and the shelf life of oysters was prolonged. At the same time, ultrasonic treatment delayed the changes of color difference and lipid oxidation of oysters during cold storage. Texture analysis showed that ultrasonic treatment helped maintain the good textural structure of oysters. Histological section analysis also demonstrated that muscle fibers were still tightly packed after ultrasonic treatment. Low-field nuclear magnetic resonance (LF-NMR) illustrated that the water in the oysters was well maintained after ultrasonic treatment. In addition, gas chromatograph - ion mobility spectrometer (GC-IMS) showed that ultrasound treatment could better preserve the flavor of oysters during cold storage. Therefore, it is believed that ultrasound can inactivate foodborne pathogens of raw oysters and keep its freshness and original taste better during storage.

Combined Effect of Ultrasound and Microwave Power in Tangerine Juice Processing: Bioactive Compounds, Amino Acids, Minerals, and Pathogens

The inhibition of Escherichia coli ATCC 25922 (E. coli), Staphylococcus aureus ATCC6538 (S. aureus), Salmonella Enteritidis ATCC 13076 (S. Enteritidis), and Listeria monocytogenes DSM12464 (L. monocytogenes) is one of the main aims of the food industry. This study was the first in which the use of ultrasound and microwave power were applied to optimize the values of the bioactive components, amino acids, and mineral compositions of tangerine juice and to inhibit Escherichia coli, Staphylococcus aureus, Salmonella Enteritidis, and Listeria monocytogenes. The response surface methodology (RSM) was used to describe the inactivation kinetics, and the effects of ultrasound treatment time (X1: 12–20 min), ultrasound amplitude (X2:60–100%), microwave treatment time (X3: 30–40 s), and microwave power (X4:200–700 W). The optimum parameters applied to a 5-log reduction in E. coli were determined as ultrasound (12 min, 60%) and microwave (34 s, 700 W). The optimum condition ultrasound–microwave treatment was highly effective in tangerine juice, achieving up to 5.27, 5.12, and 7.19 log reductions for S. aureus, S. Enteritidis, and L. monocytogenes, respectively. Ultrasound–microwave treatment increased the total phenolic compounds and total amino acids. While Cu, K, Mg, and Na contents were increased, Fe and Ca contents were lower in the UM-TJ (ultrasound–microwave-treated tangerine juice) sample. In this case, significant differences were detected in the color values of ultrasound–microwave-treated tangerine juice (UM-TJ) (p < 0.05). The results of this study showed that ultrasound–microwave treatment is a potential alternative processing and preservation technique for tangerine juice, resulting in no significant quality depreciation.

Microbial inactivation of milk by low intensity direct current electric field: Inactivation kinetics model and milk characterization

Microbial inactivation by pulsed electric field (PEF) has been studied widely although with high operational risk, while few studies on the potential of low intensity electric fields for microbial inactivation have been reported. In this study, the feasibility of inactivating microorganisms in milk by low intensity direct current (DC) electric field was investigated. Then a kinetics model was proposed based on the inactivation curves. Finally, the effect of electric field on the microflora and physicochemical properties of milk was analyzed. Results showed that the bacterial reduction >5 log CFU/mL could be achieved at 50–55°C, 0.3 A–0.6 A, and with 5 min starting intensity of 5 V/cm-9 V/cm. The inactivation kinetics consisted of three stages, therein, the middle stage, main part of the inactivation curve, followed 1st-order reaction kinetics, and the effect of temperature on it was consistent with the Arrhenius Law, which implied that the electric field itself can inactivate bacteria without thermal inactivating effect. The microflora analysis showed that naturally occurring bacteria in the milk contained typical potential pathogenic bacteria (e.g., 56.9% of Acinetobacter spp.) and spoilage bacteria (e.g., 27.5% of Pseudomonas spp.), and the electric field can inactivate them. Moreover, the inactivation chemically preserved the milk's fresh-like characteristics (according to indexes of whey protein denaturation rate, furosine content), and physical stability (turbidity, zeta potential, particle size, color and so on). Therefore, a promising approach is provided for microbial inactivation in dairy industry.

•

Microbial inactivation of milk in low intensity direct current electric field was verified.

•

The bacteria (7.5 log CFU/mL) in milk were completely inactivated.

•

The main part, middle stage, of inactivation followed 1st-order reaction kinetics.

•

For Acinetobacter spp. and Pseudomonas spp., inactivation of the electric field was non-selective.

•

Inactivation on the physicochemical properties of milk was at an acceptable level.

Degradation mechanism and toxicity assessment of chlorpyrifos in milk by combined ultrasound and ultraviolet treatment

The aim of this study was to compare the degradation kinetics of chlorpyrifos by treatment with ultrasound (US), ultraviolet radiation (UV) and a combination of both (US/UV), to evaluate the toxicity of the degradation products and the effect of the treatments on milk quality. US/UV markedly accelerated the degradation of chlorpyrifos. The half-life of chlorpyrifos by US/UV was 6.4 min, which was greatly shortened compared to the treatment with US or UV alone. Five degradation products were identified by GC-MS, and a degradation pathway for chlorpyrifos was proposed, based on density functional theory calculations. According to the luminescent bacteria test and predictions from a structure/activity relationship model, the toxicity of the degradation products was lower than that of chlorpyrifos. In addition, US/UV treatment had little effect on the quality of the treated milk. Therefore, US/UV can be used as a potential non-thermal processing method to degrade pesticide residues in milk.

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

Milk is easy to be contaminated by microorganisms due to its abundant nutrients. In this study, a 360-degree radiation thermosonication (TS) system was developed and utilized for the inactivation of Staphylococcus aureus in milk. The 360-degree radiation TS system-induced inactivation kinetics of S. aureus was fitted best by the Weibull model compared with biphasic and linear models. The treatment time, the exposure temperature, and the applied ultrasound power was found to affect the bactericidal efficacy of the 360-degree radiation TS system. Additionally, the TS condition of 200 W and 63°C for 7.5 min was successfully applied to achieve complete microbial inactivation (under the limit of detection value) in raw milk. The treatment of 360-degree radiation TS can enhance the zeta potential and decrease the average particle size of milk. It also exhibited better retainment of the proteins in milk compared with the ultrahigh temperature and conventional pasteurization processing. Therefore, the 360-degree radiation TS system developed in this study can be used as an alternative technology to assure the microbiological safety and retain the quality of milk, and the Weibull model could be applied for the prediction of the inactivation levels after exposure to this technology.

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

Some nonthermal technologies have gained special interest as alternative approaches to thermal treatments. High pressure homogenization (HPH) and ultrasound (US) are two of the most promising approaches. They rely upon two different modes of action, although they share some mechanisms or ways of actions (mechanic burden against cells, cavitation and micronization, primary targets being the cell wall and the membrane, temperature and pressure playing important roles for their antimicrobial potential, and their effect on cells can be either positive or negative). HPH is generally used in milk and dairy products to break lipid micelles, whereas US is used for mixing and/or to obtain active compounds of food. HPH and US have been tested on pathogens and spoilers with different effects; thus, the main goal of this article is to describe how US and HPH act on biological systems, with a focus on antimicrobial activity, mode of action, positive effects, and equipment. The article is composed of three main parts: (i) an overview of US and HPH, with a focus on some results covered by other reviews (mode of action toward microorganisms and effect on enzymes) and some new data (positive effect and modulation of metabolism); (ii) a tentative approach for a comparative resistance of microorganisms; and (iii) future perspectives.