Radio frequency inactivation kinetics of Bacillus cereus spores in red pepper powder with different initial water activity

A review of food safety in low-moisture foods with current and potential dry-cleaning methods

Food is one of the basic needs of human life. With the increasing population, the production and supply of safe and quality foods are critical. Foods can be classified into different categories including low moisture, intermediate moisture, and high moisture content. Historically, low-moisture foods have been considered safe for human consumption due to the limited amount of moisture for microbial activity. Recalls of these foods due to pathogens such as Salmonella and undeclared allergens have brought attention to the need for improved cleaning and sanitization in dry food manufacturing facilities. In the food industry, cleaning and sanitation activities are the most efficient methods to prevent microbial contamination; however, water is most often required to deliver cleaning and sanitation agents. A well-written and properly implemented sanitation standard operating procedure can take care of microbial and allergen cross-contamination. Nevertheless, there are unique challenges to cleaning and sanitation processes for low-moisture food manufacturing facilities. The introduction of moisture into a low-moisture food environment increases the likelihood of cross-contamination by microbial pathogens. Hence, the use of water during cleaning and sanitation of dry food manufacturing facilities should be limited. However, much less research has been done on these dry methods compared to wet sanitation methods. This review discusses recent foodborne outbreaks and recalls associated with low-moisture foods the accepted methods for cleaning and sanitation in dry food manufacturing facilities and the limitations of these methods. The potential for air impingement as a dry-cleaning method is also detailed.

Pasteurization of Salmonella spp. in black fungus (Auricularia auricula) powder by radio frequency heating

Radio frequency (RF) heating has been studied to inactivate bacteria in some powder foods. In this study, a 6 kW, 27.12 MHz RF system was used to pasteurize Salmonella in black fungus (Auricularia auricula) powder. The effects of different conditions (initial aw, electrodes gaps, particle sizes) on RF heating rate and uniformity were investigated. The results showed that RF heating rate was significantly (p < 0.05) improved with decreasing electrodes gap and increasing initial aw, and the heating rate was the slowest when the particle size was 120-160 mesh. However, these factors had no significant (p > 0.05) influence on heating uniformity. RF pasteurization of Salmonella in black fungus powder was also studied. The results showed that, to inactivate Salmonella for 5 log reductions in the cold spot (the center of surface layer), the time needed and bacteria heat resistance at designated temperature (65, 75, 85 °C) decreased with increasing aw, and the first order kinetics and Weibull model could be used to fit inactivation curves of Salmonella with well goodness. Quality analysis results showed that although RF pasteurization had no significant (p > 0.05) effect on Auricularia auricula polysaccharide (AAP) and total polyphenols, obvious changes were found on color. Results suggested that RF pasteurization can be considered as an effective pasteurization method for black fungus powder.

Trends in Food Pathogens Risk Attenuation

Foodborne pathogens represent one of the most dangerous threats to public health along the food chain all over the world. Over time, many methods were studied for pathogen inhibition in food, such as the development of novel packaging materials with enhanced properties for microorganisms' growth inhibition (coatings, films) and the use of emerging technologies, like ultrasound, radio frequency or microwave. The aim of this study was to evaluate the current trends in the food industry for pathogenic microorganisms' inhibition and food preservation in two directions, namely technology used for food processing and novel packaging materials development. Five technologies were discussed in this study, namely high-voltage atmospheric cold plasma (HVACP), High-Pressure Processing (HPP), microwaves, radio frequency (RF) heating and ultrasound. These technologies proved to be efficient in the reduction of pathogenic microbial loads in different food products. Further, a series of studies were performed, related to novel packaging material development, by using a series of antimicrobial agents such as natural extracts, bacteriocins or antimicrobial nanoparticles. These materials proved to be efficient in the inhibition of a wide range of microorganisms, including Gram-negative and Gram-positive bacteria, fungi and yeasts.

Dry surface biofilms in the food processing industry: An overview on surface characteristics, adhesion and biofilm formation, detection of biofilms, and dry sanitization methods

Bacterial biofilm formation in low moisture food processing (LMF) plants is related to matters of food safety, production efficiency, economic loss, and reduced consumer trust. Dry surfaces may appear dry to the naked eye, however, it is common to find a coverage of thin liquid films and microdroplets, known as microscopic surface wetness (MSW). The MSW may favor dry surface biofilm (DSB) formation. DSB formation is similar in other industries, it occurs through the processes of adhesion, production of extracellular polymeric substances, development of microcolonies and maturation, it is mediated by a quorum sensing (QS) system and is followed by dispersal, leading to disaggregation. Species that survive on dry surfaces develop tolerance to different stresses. DSB are recalcitrant and contribute to higher resistance to sanitation, becoming potential sources of contamination, related to the spoilage of processed products and foodborne disease outbreaks. In LMF industries, sanitization is performed using physical methods without the presence of water. Although alternative dry sanitizing methods can be efficiently used, additional studies are still required to develop and assess the effect of emerging technologies, and to propose possible combinations with traditional methods to enhance their effects on the sanitization process. Overall, more information about the different technologies can help to find the most appropriate method/s, contributing to the development of new sanitization protocols. Thus, this review aimed to identify the main characteristics and challenges of biofilm management in low moisture food industries, and summarizes the mechanisms of action of different dry sanitizing methods (alcohol, hot air, UV-C light, pulsed light, gaseous ozone, and cold plasma) and their effects on microbial metabolism.

Investigation of Virulence and Antibiotic-Resistance of Bacillus cereus Isolated from Various Spices

Spices and herbs are potential vectors for virulent and pathogenic micro-organisms, which cause illness in consumers, contribute to spoilage, and reduce the durability of foodstuffs. The present study aims to provide relevant data about virulence and antibiotic resistance of Bacillus cereus isolated from various spices. A total of 200 samples of 8 types of spices (black pepper, chilli, white pepper, cumin, cinnamon, turmeric, curry powder, and sumac) were collected from various markets, retail shops, and sucuk production premises located in the Isfahan province of Iran. Presumptive B. cereus strains were obtained using Bacara Agar plates after enrichment in saline peptone water and final colonies were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Enterotoxin (HBL) and nonhaemolytic enterotoxin (NHE) production were assessed using the Duopath® Cereus Enterotoxins Test kit. The Kirby-Bauer disc diffusion method was applied as antibiotics susceptibility test. PCR was used to detect Emetic toxin gene (CES and CER) and enterotoxigenic toxin gene (cytK, nheA, hblC, and entFM). Results show a significant prevalence of B. cereus (42%) in spices. However, the spices meet food safety recommendations (<10⁴ cfu/g). Antibiotics susceptibility test show alarming rate of resistance to beta-lactam antibiotics specially ampicillin (83.33%) and penicillin (82.14%). Concerning the toxin producing capacity more than half of the isolates (51.19%) produce NHE toxin and 27.38% produce HBL toxin. The most abundant gene were nheA, nheB, and nheC and a combination of 4 genes (entFM, nheA, hblC, and cytK) was detected in many isolates. In conclusion, the presence of multidrug resistant B. cereus strains carrying diarrhoeal toxin-encoding genes in spices intended for human consumption represents a serious health hazard. These results indicate the need for regular surveillance of the occurrence of B. cereus strains in spices and food products in Iran.

Salmonella spp. in low water activity food: Occurrence, survival mechanisms, and thermoresistance

The occurrence of disease outbreaks involving low-water-activity (a_w ) foods has gained increased prominence due in part to the fact that reducing free water in these foods is normally a measure that controls the growth and multiplication of pathogenic microorganisms. Salmonella, one of the main bacteria involved in these outbreaks, represents a major public health problem worldwide and in Brazil, which highlights the importance of good manufacturing and handling practices for food quality. The virulence of this pathogen, associated with its high ability to persist in the environment, makes Salmonella one of the main challenges for the food industry. The objectives of this article are to present the general characteristics, virulence, thermoresistance, control, and relevance of Salmonella in foodborne diseases, and describe the so-called low-water-activity foods and the salmonellosis outbreaks involving them.

Recent developments in low-moisture foods: microbial validation studies of thermal pasteurization processes

Outbreaks associated with low-moisture foods (e.g., wheat flour, nuts, and cereals) have urged the development of novel technologies and re-validation of legacy pasteurization process. For various thermal pasteurization processes, they share same scientific facts (e.g., bacterial heat resistance increased at reduced water activity) and guidelines. However, they also face specific challenges because of their different heat transfer mechanisms, processing conditions, or associated low-moisture foods' formulations. In this article, we first introduced the general structural for validating a thermal process and the shared basic information that would support our understanding of the key elements of each thermal process. Then, we reviewed the current progress of validation studies of 7 individual heating technologies (drying roasting, radiofrequency-assisted pasteurization, superheated steam, etc.) and the combined treatments (e.g., infrared and hot air). Last, we discussed knowledge gaps that require more scientific data in the future studies. We aimed to provide a process-centric view point of thermal pasteurization studies of low-moisture foods. The information could provide detailed protocol for process developers, operators, and managers to enhance low-moisture foods safety.

Investigation of the potential direct and cross protection effects of sublethal injured Salmonella Typhimurium induced by radio frequency heating stress

Many studies demonstrated that radio frequency (RF) was an effective pasteurization method for low-moisture foods (LMFs), and our previous study confirmed RF heating stress generated sublethal injured cells (SICs) of Salmonella enterica serovar Typhimurium (S. Typhimurium) in red pepper powder with initial a_w ≥ 0.53. So this study investigated the potential direct protection and cross protection effects of the SICs of S. Typhimurium to multiple stresses, and analyzed fatty acid composition and cell morphology. Results showed that the SICs were repaired after incubating for 5 h, and there were no obvious direct and cross protection effects by exposing to different external stresses (heat, 15% ethanol, pH 3.0 acid buffer solution, 10% salt). According to the fatty acid composition analysis, no significant difference (p > 0.05) between the ratio of unsaturated to saturated fatty acids (UFA/SFA) was observed for SICs of S. Typhimurium and control cells, indicating the same membrane fluidity which can support the experimental results. This study investigated and confirmed there are no direct and cross protection effects for the SICs of S. Typhimurium induced by RF heating stress, and it would be helpful for deeply understand the response of pathogens under RF heating stress.

Combination of supercritical CO2 and high-power ultrasound for the inactivation of fungal and bacterial spores in lipid emulsions

For the first time, this study addresses the intensification of supercritical carbon dioxide (SC-CO2) treatments using high-power ultrasound (HPU) for the inactivation of fungal (Aspergillus niger) and bacterial (Clostridium butyricum) spores in oil-in-water emulsions. The inactivation kinetics were analyzed at different pressures (100, 350 and 550 bar) and temperatures (50, 60, 70, 80, 85 °C), depending on the microorganism, and compared to the conventional thermal treatment. The inactivation kinetics were satisfactorily described using the Weibull model. Experimental results showed that SC-CO2 enhanced the inactivation level of both spores when compared to thermal treatments. Bacterial spores (C.butyricum) were found to be more resistant to SC-CO2 + HPU, than fungal (A.niger) ones, as also observed in the thermal and SC-CO2 treatments. The application of HPU intensified the SC-CO2 inactivation of C.butyricum spores, e.g. shortening the total inactivation time from 10 to 3 min at 85 °C. However, HPU did not affect the SC-CO2 inactivation of A.niger spores. The study into the effect of a combined SC-CO2 + HPU treatment has to be necessarily extended to other fungal and bacterial spores, and future studies should elucidate the impact of HPU application on the emulsion's stability.

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.

Effect of radiofrequency heating of vacuum-packed nitrite-free sausage on quality properties and microorganism inactivation

The effect of radiofrequency (RF) heating technology at 27 MHz and 8 kW on the quality properties of vacuum-packed nitrite-free sausages was investigated. One of the several advantages of RF heating technology is the use of less time compared to retort heating. RF heating at 125 °C for a holding time of 2 min and retort heating at 121 °C for 7 min reduced Bacillus subtilis to 7 log cfu/g. In addition, the textural properties of the RF-heated sausages were better than those of retort-heated samples. Furthermore, the growth of B. subtilis and general live bacteria at 25 °C were not detected after 42 days of shelf life in the sausages that underwent RF heating at 125 °C with a holding time of 2 min.

Thermal Reduction of Bacillus spp. in Naturally Contaminated Mesquite Flour with Two Different Water Activities

ABSTRACT

Mesquite flour with endogenous high sugar content is often contaminated with Bacillus cereus. The purpose of the present study was to evaluate the thermal resistance of Bacillus spp. in naturally contaminated mesquite flour. Flours with and without adjusted water activity (aw) were treated at various temperatures (100 to 140°C) and times (up to 2 h). Total mesophilic bacteria and Bacillus spp. were enumerated using tryptic soy agar and Brilliance Bacillus cereus Agar, respectively. Results revealed that naturally contaminated Bacillus spp. and other mesophilic bacteria in mesquite flour (aw = 0.34) were highly resistant to heat. To reduce the initial populations (4.75 log CFU/g) of Bacillus spp. to nondetectable levels (<1.18 log CFU/g), thermal treatments of 120°C for 2 h were required. D100°C-values for total mesophilic bacteria were 5.6-fold higher than those of Bacillus spp. With increasing treatment temperature, the difference in D-value between total mesophilic bacteria and Bacillus spp. became smaller. When the aw of flour was adjusted from 0.34 to 0.71, the D-values for Bacillus decreased significantly. Treatment at 100°C for 1 h reduced Bacillus spp. populations to nondetectable levels. Our results demonstrate that naturally present Bacillus spp. in flour are highly resistant to heat, whereas increasing the aw increased their heat sensitivity. The high thermal resistance of microbes in mesquite flour warrants further investigations.

HIGHLIGHTS

Pasteurization of flavored shredded pork using Zno nanoparticles combined with radio frequency pasteurization technology

Effects of ZnO nanoparticles combined radio frequency (ZNCRF) pasteurization on the survival of microorganism, flavor and taste of Flavored shredded pork were compared with conventional high pressure steam (HPS) sterilization. The results showed that ZNCRF pasteurization was better than HPS sterilization in terms of flavor and taste parameters and at the same time met the pasteurization requirement. GC-MS and NMR measurements were performed to explore changes in volatile compounds and status and distribution of water within the sample. The ZNCRF pasteurization when carried out for 30 min and the HPS sterilization reduced the relative contents of aldehydes by 18.8% and 19.7%, respectively, while the ZNCRF pasteurization within 20 min had less effect on aldehydes. Both ZNCRF pasteurization and HPS sterilization destroyed the vacuolar membrane of the samples caused the loss of water from the cytoplasm (T₂₃). This work shows that ZNCRF when applied for 20 min is a mild pasteurization method that can be applied to improve the quality of Flavored shredded pork.

Microbial and quality improvement of boiled gansi dish using carbon dots combined with radio frequency treatment

Use of carbon dots (CDs) combined with radio frequency (RF) was applied to pasteurize and reduce the microorganism population in order to improve the quality of boiled gansi dish. CDs were prepared from banana using hydrothermal method, and characterized by using TEM, XRD and FTIR. The minimal inhibitory concentration (MIC) test showed CDs can efficiently inactivate Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis). This study also evaluated the effectiveness of five treatments, including CDs alone, CDs combined RF (CDRF) heating for different time (8 min, 12 min, and 16 min), and high pressure steam (HPS) sterilization of boiled gansi dish inoculated with B. subtilis. After CDRF treated for 8 min, 12 min, and 16 min, the center temperature of samples reached to 78.92, 87.77 and 93.82 °C, and the colony forming units (CFU) of B. subtilis reduced by 2.13, 3.62, and 4.63 log, respectively. Samples with CDRF12 treatment, exhibited better product quality as evidenced by reduced loss of texture, flavor, and sensory as compared with HPS sample. The results indicated that CDRF treatment has a great potential to produce packaged boiled gansi dish with high product quality.

Non-thermal pasteurization of lipid emulsions by combined supercritical carbon dioxide and high-power ultrasound treatment

Supercritical carbon dioxide (SC-CO₂) is a novel method for food pasteurization, but there is still room for improvement in terms of the process shortening and its use in products with high oil content. This study addressed the effect of high power ultrasound (HPU) on the intensification of the SC-CO₂ inactivation of E. coli and B. diminuta in soybean oil-in-water emulsions. Inactivation kinetics were obtained at different pressures (100 and 350 bar), temperatures (35 and 50 °C) and oil contents (0, 10, 20 and 30%) and were satisfactorily described using the Weibull model. The experimental results showed that for SC-CO₂ treatments, the higher the pressure or the temperature, the higher the level of inactivation. Ultrasound greatly intensified the inactivation capacity of SC-CO₂, shortening the process time by approximately 1 order of magnitude (from 50 to 90 min to 5-10 min depending on the microorganism and process conditions). Pressure and temperature also had a significant (p < 0.05) effect on SC-CO₂ + HPU inactivation for both bacteria, although the effect was less intense than in the SC-CO₂ treatments. E. coli was found to be more resistant than B. diminuta in SC-CO₂ treatments, while no differences were found when HPU was applied. HPU decreased the protective effect of oil in the inactivation and similar microbial reductions were obtained regardless of the oil content in the emulsion. Therefore, HPU intensification of SC-CO₂ treatments is a promising alternative to the thermal pasteurization of lipid emulsions with heat sensitive compounds.

A comprehensive review on recent developments of radio frequency treatment for pasteurizing agricultural products

Recent pathogen incidents have forced food industry to seek for alternative processes in postharvest pasteurization of agricultural commodities. Radio frequency (RF) heating has been used as one alternative treatment to replace chemical fumigation and other conventional thermal methods since it is relatively easy to apply and leaves no chemical residues. RF technology transfers electromagnetic energy into large bulk volume of the products to provide a fast and volumetric heating. There are two types of RF technology commonly applied in lab and industry to generate the heat energy: free running oscillator and 50-Ω systems. Several reviews have been published to introduce the application of RF heating in food processing. However, few reviews have a comprehensive summary of RF treatment for pasteurizing agricultural products. The objective of this review was to introduce the developments in the RF pasteurization of agricultural commodities and to present future directions of the RF heating applications. While the recent developments in the RF pasteurization were presented, thermal death kinetics of targeted pathogens as influenced by water activity, pathogen species and heating rates, non-thermal effects of RF heating, combining RF heating with other technologies for pasteurization, RF heating uniformity improvements using computer simulation and development of practical RF pasteurization processes were also focused. This review is expected to provide a comprehensive understanding of RF pasteurization for agricultural products and promote the industrial-scale applications of RF technology with possible process protocol optimization purposes.