Influence of water activity on inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in peanut butter by microwave heating

Microbiological Assessment of Groundnut (Arachis hypogaea L.) Sold for Consumption in Ghana

The postharvest processes of groundnuts often become sources of microbial contamination leading to infections and intoxication. Hence, this study examined the microbial pathogens contaminating groundnuts after harvesting. About 50 samples were randomly collected from four major groundnut-producing towns: Bolgatanga, Chiana, Navrongo, and Bongo, all in the Upper East Region of Northern Ghana, and microbiologically examined using Analytical Profile Index (API® 20E). The results revealed that samples from Bolgatanga were the most contaminated, while Chiana has the least contaminated samples. Several species of bacterial genera such as Staphylococcus, Proteus, Escherichia, Bacillus, and Micrococcus, and fungal genera including Aspergillus, Fusarium, Rhizopus, Mucor, Saccharomyces, and Eurotium were isolated as the main microbial pathogens contaminating the produce. Navrongo and Bolgatanga recorded the highest rate of bacterial species for unshelled (29.5%) and shelled (30.4%) groundnuts, respectively, while Bongo and Bolgatanga registered the highest rate of fungal species under unshelled (32.8%) and shelled (32.6%) groundnuts, respectively. Due to the high levels of microbial contamination of most of the samples and the kind of microbial species involved, proper hygiene standards must be adopted during the postharvest handling of the shelled and unshelled groundnuts.

Synergistic effect of microwave heating and thermosonication on the physicochemical and nutritional quality of muskmelon and sugarcane juice blend

Melons (Cucumis melo L.) are highly popular due to its delicate and delightful flavor in the worldwide. However, the flavor of the melon juice was easily affected by thermal treatments and unpleasant cooking smell during production process. Sugarcane (Saccharum officinarum) juice is a proven nutritious beverage with high levels of antioxidants, polyphenols, and other beneficial nutrients. Due to its low sugar content, combined with sugarcane, muskmelon-sugarcane blend juice gives an appealing and exotic drink. The research was planned to evaluate the effect of thermo-sonication (20 kHz, 70% amplitude, 5, 10 and 15 min) and microwave (90 °C, 400 W, 120 sec) on physicochemical parameters including pH, titratable acidity, total soluble solids (TSS), total phenolic contents (TPC), total flavonoid contents (TFC) and antioxidant capacity of muskmelon and sugarcane juice blend, during storage of 90 days at refrigeration (4±1 °C). The statistical results showed that synergism of sonication and microwave treatments had a significant (p ≤ 0.05) influence on pH, TSS, titratable acidity, TPC, TFC and antioxidant capacity. T₃ (15 min of sonication and 120 s of microwave) showed the maximum TSS (12.00±0.40 °B), pH (5.07±0.02), TPC (484.33±10.41 mg GAE/100 mL), TFC (261.73±11.32 mg CE/100 mL), and antioxidant activity (381.62±17.72 µg AAE/100 mL), as compared to untreated samples. Thermosonication for 15 min caused maximum retention of TPC, TFC and antioxidant capacity of blend juice during 90 days of storage, whereas in untreated samples these parameters were found highly decreased during storage. Thus, sonication and microwave can be recommended as an alternative to both conventional pasteurization processes and chemical preservatives.

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.

Microwaves, a potential treatment for bacteria: A review

Bacteria have brought great harm to the public, especially after the emergence of multidrug-resistant bacteria. This has rendered traditional antibiotic therapy ineffective. In recent years, hyperthermia has offered new treatments to remove bacteria. Microwaves (MW) are a component of the electromagnetic spectrum and can rapidly heat materials. Taking advantage of this characteristic of MW, related studies have shown that both thermal and non-thermal effects of MW can inactivate various bacteria. Even though the understanding of MW in the field of bacteria is not sufficient for widespread use at present, MW has performed well in dealing with microorganisms and controlling infection. This review will focus on the application of MW in bacteria and discuss the advantages, prospects and challenges of using MW in the bacterial field.

Inactivation of Salmonella spp., Escherichia coli O157:H7 and Listeria monocytogenes in Tahini by Microwave Heating

Tahini (sesame paste) is a traditional food. Numerous foodborne outbreaks have been associated with it. This study aimed to (i) explore the efficiency of 2450 MHz microwave heating at 220, 330, 440, 550, and 660 W on the inactivation of Salmonella spp, Escherichia coli O157:H7, and Listeria monocytogenes in tahini; (ii) determine the impact of desiccation and starvation stresses on pathogen survival; (iii) assess the impact of microwave heating on the physicochemical characteristics of tahini. The inoculated microorganisms in tahini were reduced with higher microwave power levels (p < 0.05) and longer exposure times. The D-values of unstressed Salmonella spp., Escherichia coli O157:H7, and L. monocytogenes ranged from 6.18 to 0.50 min, 6.08 to 0.50 min, and 4.69 to 0.48 min, respectively, at power levels of 220 to 660 W, with z-values of 410, 440, and 460 W, respectively. Generally, desiccation and starvation stress levels prior to heating increased microbial resistance to heat treatment. Microwave heating did not affect acid, peroxide, p-anisidine, or color values of tahini up to 90 °C. These findings reveal microwave heating as a potential method for lowering the risk of Salmonella spp., E. coli O157:H7 and L. monocytogenes in tahini with no compromise on quality.

Inactivation of Escherichia coli O157:H7 and Salmonella Typhimurium in black and red pepper by vacuumed hydrogen peroxide vapour

AIMS

In this study, the efficacy of using vacuumed hydrogen peroxide vapour (VHPV) to inactivate foodborne pathogens in whole dried black pepper (Piper nigrum) and powdered dried red pepper (Capsicum annuum) was evaluated.

METHODS AND RESULTS

Black and red pepper inoculated with Escherichia coli O157:H7 and Salmonella Typhimurium were subjected to 3.81, 7.93, 12.33, 17.04 and 21.67 mg l^-1 VHPV for 1 min, and the change in pepper colour was evaluated after treatment. Pathogen quantities decreased with increasing hydrogen peroxide concentration. For black pepper, the 21.67 mg l^-1 VHPV treatment decreased E. coli O157:H7 and S. Typhimurium quantities by >6.12 and 4.52 log CFU per gram, respectively, without causing colour change. In addition, the 21.67 mg l^-1 VHPV treatment caused 4.35 and 2.36 log CFU per gram reductions in these two pathogen quantities in red pepper, respectively. During the VHPV treatment, colour values of peppers did not significantly change.

CONCLUSIONS

VHPV effectively reduced the levels of foodborne pathogens in black and red pepper while inducing minimal colour changes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Hydrogen peroxide vapour (HPV) is typically used as a sterilization method for medical devices, and many studies have confirmed the effectiveness of HPV or the gaseous phase of hydrogen peroxide on the inactivation of micro-organisms. However, using HPV for food pasteurization has rarely been studied. In the present study, we confirmed that VHPV effectively reduced the levels of pathogens in black and red pepper without colour changes.

Recent trends in bacterial decontamination of food products by hurdle technology: A synergistic approach using thermal and non-thermal processing techniques

Researchers are continuously discovering varied technologies for microbial control to ensure worldwide food safety from farm-to-fork. The microbial load and virulence of spoilage causing microorganisms, including bacteria, fungi, yeasts, virus, and protozoa, determines the extent of microbial contamination in a food product. Certain pathogenic microbes can cause food poisoning and foodborne diseases, and adversely affect consumers' health. To erade such food safety-related problems, various traditional and novel food processing methods have been adopted for decades. However, some decontamination techniques bring undesirable changes in food products by affecting their organoleptic and nutritional properties. Combining various thermal and non-thermal food processing methods is an effective way to impart a synergistic effect against food spoilage microorganisms and can be used as an alternative way to combat certain limitations of food processing technologies. The combination of different techniques as hurdles put the microorganisms in a hostile environment and disturbs the homeostasis of microorganisms in food temporarily or permanently. Optimization and globalization of these hurdle combinations is an emerging field in the food processing sector. This review gives an overview of recent inventions in hurdle technology for bacterial decontamination, combining different thermal and non-thermal processing techniques in various food products.

Thermal Decontamination Technologies for Microorganisms and Mycotoxins in Low-Moisture Foods

The contamination risks of microorganisms and mycotoxins in low-moisture foods have heightened public concern. Developing novel decontamination technologies to improve the safety of low-moisture foods is of great interest in both economics and public health. This review summarizes the working principles and applications of novel thermal decontamination technologies such as superheated steam, infrared, microwave, and radio-frequency heating as well as extrusion cooking. These methods of decontamination can effectively reduce the microbial load on products andmoderately destruct the mycotoxins. Meanwhile, several integrated technologies have been developed that take advantage of synergistic effects to achieve the maximum destruction of contaminants and minimize the deterioration of products.

Innovative induction heating of grapefruit juice via induced electric field and its application in Escherichia coli O157:H7 inactivation

The proposed induction heating method was applied in the pasteurization of grapefruit juice. In this processing, an alternating magnetic field acted as the stimulus instead of conventional electrodes to create an induced electric field (IEF) for heat treatment of the continuous-flow juice sample, which excluded the possibility of electrochemical reaction and electrode corrosion that might occur in conventional electric field treatments. As a typical food pathogen, Escherichia coli O157:H7 was selected as a representative to investigate its inactivation by the heating process under different voltages and frequencies, initial temperatures, and flow rates (or retention time). The grapefruit juice was successfully heated up by IEF and the temperature curve was achieved when the juice exposed to IEF. The heating rate and terminal temperature increased with the increasing induced voltage, decreasing frequency and at higher initial temperature. A highest terminal temperature of 93.7 °C for grapefruit juice with an initial temperature of 20 °C was achieved under induced voltage of 2700 V, frequency of 300 Hz and residence time of 400 s. At the same time, E. coli O157:H7 in the grapefruit juice was thoroughly inactivated. There was a trend that the pathogen survival rate was reduced at higher induced voltage, lower frequency and higher initial temperature during the heating treatment. No significant changes in pH and °Brix was observed after this innovative induction heating, but the color of grapefruit juice was brightened. The proposed induction heating can be regarded as a sister technology of ohmic heating, and it provide a reference for the application of this heating method in liquid food pasteurization.

Innovative induction heating method is applied in the pasteurization of grapefruit juice.

Mathematical modeling of ohmic heating for inactivation of acid-adapted foodborne pathogens in tomato juice

The objective of the present study was to predict the inactivation trends of acid-adapted foodborne pathogens in tomato juice by ohmic heating through a numerical analysis method. The mathematical model based on finite element method (FEM) was used to simulate the multiphysics phenomena including electric heating, heat transfer, fluid dynamics, and pathogen inactivation. A cold spot was observed in the corner part of the ohmic heating chamber, where some pathogens survived even though all pathogens were inactivated elsewhere. Challenges of this study were how to reflect the increased resistance of pathogen by acid-adaptation. After simulation, we verified that inactivation level of acid-adapted foodborne pathogens by 25 Vrms/cm ohmic heating (1 kHz), predicted with the developed mathematical model, had no significant differences with experimental results (p > 0.05). Therefore, the mathematical approaches described in the present study will help juice processors determine the processing conditions necessary to ensure microbial safety at the cold point of a rectangular type batch ohmic heater.

Optimization of broth recovery for repair of heat-injured Salmonella enterica serovar Typhimurium and Escherichia coli O157:H7

AIMS

The purpose of this research was to determine optimum conditions for broth recovery of heat-injured Salmonella Typhimurium and Escherichia coli O157:H7.

METHODS AND RESULTS

Exposure to 55°C for 15 and 25 min, respectively, induced cellular injury to those pathogens. Comparison was made with the commonly used overlay method using selective medium for recovering sublethally injured cells of S. Typhimurium. For E. coli O157:H7, phenol red agar base with 1% sorbitol was used. After cell suspensions were heated at 55°C for selected time intervals, microbes were 10-fold diluted with brain heart infusion (BHI), tryptic soy broth (TSB) and TSB with 0·6% yeast extract (TSBYE) and incubated at 37°C for up to 3 h. At hourly intervals, diluents were plated onto selective medium for recovery. Simultaneously, diluents were plated onto tryptic soy agar (TSA) for recovery of sublethally injured cells. For overlays, diluents were plated onto TSA and overlaid with selective agar after a resuscitation interval. Broth recovery conditions for S. Typhimurium and E. coli O157:H7 were determined to be 1 h in any of the following broth media: BHI, TSB or TSBYE. When liquid resuscitation was applied to sublethally injured cells in food samples (milk), 1 h was also sufficient time for recovery.

CONCLUSIONS

The broth recovery method is a convenient alternative to conventional recovery methods.

SIGNIFICANCE AND IMPACT OF THE STUDY

Cells sublethally injured by control interventions might not grow on selective medium because they have no resistance to several selective compounds. However, injured cells can recuperate and multiply under conditions sufficient for recovery. To repair and detect heat-injured cells, the overlay method is commonly used but this method has some limitations. This study confirms the effectiveness of liquid resuscitation method on recovery of injured cells. The broth recovery can replace the overlay method due to greater convenience and timesaving.