Inactivation of Escherichia coli O157:H7 on Orange Fruit Surfaces and in Juice Using Photocatalysis and High Hydrostatic Pressure

Preparation of modified chitosan-based nano-TiO2-nisin composite packaging film and preservation mechanism applied to chilled pork

Here, we developed a nano-TiO2-nisin-modified chitosan composite packaging film and investigated its properties and antibacterial activity, as well as its effect on chilled pork preservation time. The results indicated that the preservation time of chilled pork coated with a nano-TiO2-nisin-modified chitosan film (including 0.7 g/L nano-TiO2, irradiated with ultraviolet light for 40 min, and dried for 6 h) followed by modified atmosphere packaging (50% CO2 + 50% N2) increased from 7 to 20 days at 4 °C. Both nano-TiO2 and nisin enhanced the mechanical strength of the chitosan film, and nisin promoted nano-TiO2 dispersion and compatibility in chitosan. Treatment with 0.4 g/L nano-TiO2 for 60 min considerably inhibited spoilage bacteria, particularly Acinetobacter johnnii XBB1 (A. johnnii XBB1). As nano-TiO2 concentration and photocatalytic time increased, K+, Ca2+, and Mg2+ leakage in A. johnnii XBB1 increased but Na+/K+-ATPase and Ca2+/Mg2+-ATPase activities decreased. In A. johnnii XBB1, TiO2 significantly downregulated the expression of putrefaction-related genes such as cysM and inhibited cell self-regulation and membrane wall system repair. Therefore, our nano-TiO2-nisin-modified chitosan film could extend the shelf life without the addition of any chemical preservatives, demonstrating great potential for application in food preservation.

High pressure processing plus technologies: Enhancing the inactivation of vegetative microorganisms

High pressure processing (HPP) is a non-thermal technology that can ensure microbial safety without compromising food quality. However, the presence of pressure-resistant sub-populations, the revival of sub-lethally injured (SLI) cells, and the resuscitation of viable but non-culturable (VBNC) cells pose challenges for its further development. The combination of HPP with other methods such as moderate temperatures, low pH, and natural antimicrobials (e.g., bacteriocins, lactate, reuterin, endolysin, lactoferrin, lactoperoxidase system, chitosan, essential oils) or other non-thermal processes (e.g., CO2, UV-TiO2 photocatalysis, ultrasound, pulsed electric fields, ultrafiltration) offers feasible alternatives to enhance microbial inactivation, termed as "HPP plus" technologies. These combinations can effectively eliminate pressure-resistant sub-populations, reduce SLI or VBNC cell populations, and inhibit their revival or resuscitation. This review provides an updated overview of microbial inactivation by "HPP plus" technologies and elucidates possible inactivation mechanisms.

Effect of the High Hydrostatic Pressure Process on the Microbial and Physicochemical Quality of Shalgam

The processing of shalgam requires the use of an appropriate processing technique due to yeast overgrowth. With advancements in processing technology, high hydrostatic pressure (HHP) as nonthermal and nonchemical preservation has gained attention for its potential. Response surface methodology with the Box-Behnken experimental design was used to make sense of the effects of HHP parameters, namely, pressure (100-500 MPa), temperature (20-40 °C), and time (5-15 min), on microbial and physicochemical factors (pH, total soluble solids, titratable acidity, bioactive compounds, color values). The reduction in the counts of total mesophilic aerobic bacteria, lactic acid bacteria, and yeast-mold increased proportionally with the increase of all pressure levels, application temperatures, and pressurization times (p < 0.05). Stability was maintained in pH, total solubility, and some color parameters such as L*, a*, ΔE, yellow color tone, and red color tone. All findings of the bioactive components (phenolic content, flavonoid content, antioxidant activity, and monomeric anthocyanin content) in the RSM design showed a significant change only in proportion to the square of time (p < 0.05). The optimum pressurization parameter combination of shalgam was determined as a pressure of 367 MPa, temperature of 31.9 °C, and process time of 10.5 min. Under these conditions, values of yeast and mold (Y&M) reduction, total flavonoid content (TFC), total monomeric anthocyanin contents (TMACs), titratable acidity (TA), and reducing sugar content (RSC) were obtained as 4.30 log cfu/mL, 192.89 mg QE/100 mL, 11.88 mg/100 mL, 2.41 glactic acid/L, and 6.78 mg/100 mL, respectively. In particular, the findings in the basic color parameters proved that there was no significant change in the saturated red color of the shalgam. Gallic acid, caffeic acid, chlorogenic acid, catechin, cyanidin-3-O-glucoside, malvidin-3-O-glucoside, and peonidin-3-O-glucoside derivatives are dominant phenolic and anthocyanin compounds, which are frequently found in turnip plants. No important losses in bioactive components were observed, despite changes in pressure and temperature parameters. The HHP method can be suggested to have great potential in the processing of shalgam (fermented turnip beverage) in terms of its ability to maintain the flavors, colors, and nutrients, in addition to ensuring microbiological safety when compared to other preservation methods.

High Hydrostatic Pressure-Based Combination Strategies for Microbial Inactivation of Food Products: The Cases of Emerging Combination Patterns

The high demand for fresh-like characteristics of vegetables and fruits (V&amp;F) boosts the industrial implementation of high hydrostatic pressure (HHP), due to its capability to simultaneously maintain original organoleptic characteristics and to achieve preservative effect of the food. However, there remains great challenges for assuring complete microbial inactivation only relying on individual HHP treatments, including pressure-resistant strains and regrowth of injured microbes during the storage process. Traditional HHP-assisted thermal processing may compromise the nutrition and functionalities due to accelerated chemical kinetics under high pressure conditions. This work summarizes the recent advances in HHP-based combination strategies for microbial safety, as exemplified by several emerging non-thermally combined patterns with high inactivation efficiencies. Considerations and requirements about future process design and development of HHP-based combination technologies are also given.

Advances, Applications, and Comparison of Thermal (Pasteurization, Sterilization, and Aseptic Packaging) against Non-Thermal (Ultrasounds, UV Radiation, Ozonation, High Hydrostatic Pressure) Technologies in Food Processing

Nowadays, food treatment technologies are constantly evolving due to an increasing demand for healthier and tastier food with longer shelf lives. In this review, our aim is to highlight the advantages and disadvantages of some of the most exploited industrial techniques for food processing and microorganism deactivation, dividing them into those that exploit high temperatures (pasteurization, sterilization, aseptic packaging) and those that operate thanks to their inherent chemical–physical principles (ultrasound, ultraviolet radiation, ozonation, high hydrostatic pressure). The traditional thermal methods can reduce the number of pathogenic microorganisms to safe levels, but non-thermal technologies can also reduce or remove the adverse effects that occur using high temperatures. In the case of ultrasound, which inactivates pathogens, recent advances in food treatment are reported. Throughout the text, novel discoveries of the last decade are presented, and non-thermal methods have been demonstrated to be more attractive for processing a huge variety of foods. Preserving the quality and nutritional values of the product itself and at the same time reducing bacteria and extending shelf life are the primary targets of conscious producers, and with non-thermal technologies, they are increasingly possible.

Salt, glucose, glycine, and sucrose protect Escherichia coli O157:H7 against acid treatment in laboratory media

This study investigated the effects of combinations of acetic or malic acid and various solutes (salt, glucose, glycine, or sucrose) on the survival of Escherichia coli O157:H7 in laboratory broth. Additionally, the effectiveness of combining organic acids and various concentrations of salt (0-18%) or sucrose (0-100%) with different water activity values against E. coli O157:H7 were evaluated. For treatment of 1% malic acid, the addition of 3% salt showed synergistic effect. Whereas, when 3% salt, glucose, glycine, or sucrose was added to 1% acetic acid, the solutes antagonized the action of the acid against E. coli O157:H7. Acetic, lactic, or propionic acid combined with salt at either 7 or 9% or sucrose at 60, 80, or 100% resulted in the highest resistance of E. coli O157:H7. From a result of evaluating the membrane fatty acid (MFA) composition of cells, salt or sucrose significantly increased levels of saturated fatty acids (SFAs) or SFAs and cyclopropane fatty acids, respectively. From the results of this study, the addition of solutes and organic compounds may increase the tolerance of E. coli O157:H7 to acetic, lactic, and propionic acid treatments and that the salt or sucrose significantly affects cell MFA composition.

Nature inspired approach to mimic design for increased specific capacitance as supercapacitor electrodes

In this study, the experiment was conducted assuming that the citrus fruits were contaminated with bacteria. Herein, orange peels (OP) and lemon peels (LP) can be used as a carbon source and have the advantage of using discarded materials and heteroatoms. Also, the nitrogen heteroatom is introduced by naturally doping the materials with bacteria (Escherichia Coli, E. coli). The as-prepared bacteria doped activated carbon showed an increase in nitrogen content and surface properties which led to an improvement in electrochemical properties. The specific capacitance of bacteria doped OP and LP was 92.4 and 139 Fg^-1 compared to the bare samples with a specific capacitance of 60.9 and 49.6 Fg^-1 at a current density of 0.2Ag^-1 and capacity retention of 129% after 10,000 cycles for the bacteria-doped samples. This process which is simple, cheap, and environmentally friendly can be applied to discarded fruit peels for the fabrication of supercapacitor materials.

Bacterial Spore Inactivation in Orange Juice and Orange Peel by Ultraviolet-C Light

Spore-forming bacteria are a great concern for fruit juice processors as they can resist the thermal pasteurization and the high hydrostatic pressure treatments that fruit juices receive during their processing, thus reducing their microbiological quality and safety. In this context, our objective was to evaluate the efficacy of Ultraviolet-C (UV-C) light at 254 nm on reducing bacterial spores of Alicyclobacillus acidoterrestris, Bacillus coagulans and Bacillus cereus at two stages of orange juice production. To simulate fruit disinfection before processing, the orange peel was artificially inoculated with each of the bacterial spores and submitted to UV-C light (97.8-100.1 W/m²) with treatment times between 3 s and 10 min. The obtained product, the orange juice, was also tested by exposing the artificially inoculated juice to UV-C light (100.9-107.9 W/m²) between 5 and 60 min. A three-minute treatment (18.0 kJ/m²) reduced spore numbers on orange peel around 2 log units, while more than 45 min (278.8 kJ/m²) were needed to achieve the same reduction in orange juice for all evaluated bacterial spores. As raw fruits are the main source of bacterial spores in fruit juices, reducing bacterial spores on fruit peels could help fruit juice processors to enhance the microbiological quality and safety of fruit juices.

High pressure processing combined with selected hurdles: Enhancement in the inactivation of vegetative microorganisms

High pressure processing (HPP) as a nonthermal processing (NTP) technology can ensure microbial safety to some extent without compromising food quality. However, for vegetative microorganisms, the existence of pressure-resistant subpopulations, the revival of sublethal injury (SLI) state cells, and the resuscitation of viable but nonculturable (VBNC) state cells may constitute potential food safety risks and pose challenges for the further development of HPP application. HPP combined with selected hurdles, such as moderately elevated or low temperature, low pH, natural antimicrobials (bacteriocin, lactate, reuterin, endolysin, lactoferrin, lactoperoxidase system, chitosan, essential oils), or other NTP (CO₂ , UV-TiO₂ photocatalysis, ultrasound, pulsed electric field, ultrafiltration), have been highlighted as feasible alternatives to enhance microbial inactivation (synergistic or additive effect). These combinations can effectively eliminate the pressure-resistant subpopulation, reduce the population of SLI or VBNC state cells and inhibit their revival or resuscitation. This review provides an updated overview of the microbial inactivation by the combination of HPP and selected hurdles and restructures the possible inactivation mechanisms.

Recent Trends in Pretreatment of Food before Freeze-Drying

Drying is among the most important processes and the most energy-consuming techniques in the food industry. Dried food has many applications and extended shelf life. Unlike the majority of conventional drying methods, lyophilization, also known as freeze-drying (FD), involves freezing the food, usually under low pressure, and removing water by ice sublimation. Freeze-dried materials are especially recommended for the production of spices, coffee, dried snacks from fruits and vegetables and food for military or space shuttles, as well as for the preparation of food powders and microencapsulation of food ingredients. Although the FD process allows obtaining dried products of the highest quality, it is very energy- and time consuming. Thus, different methods of pretreatment are used for not only accelerating the drying process but also retaining the physical properties and bioactive compounds in the lyophilized food. This article reviews the influence of various pretreatment methods such as size reduction, blanching, osmotic dehydration and application of pulsed electric field, high hydrostatic pressure or ultrasound on the physicochemical properties of freeze-dried food and drying rate.

Factors Affecting Microbial Inactivation during High Pressure Processing in Juices and Beverages: A Review

ABSTRACT

The purpose of this article is to review and discuss the factors affecting high pressure processing (HPP) in juices and beverages. The inactivation of microorganisms by HPP depends on numerous factors, including the magnitude of the pressure and the holding time, process temperature, compression and decompression rates, the microbiota, and the intrinsic properties of juices and beverages. Although extensive HPP research has been performed to characterize many of these factors, a number of issues, such as the rates of compression and decompression, still remain unresolved and need further investigation. In addition, some published results are conflicting and do not provide enough evidence to develop juice HPP "safe-harbor" parameters to achieve a minimum 5-log reduction of the pertinent microorganism and produce safe fruit juices and beverages.

HIGHLIGHTS

Development of ginseng powder using high hydrostatic pressure treatment combined with UV-TiO2 photocatalysis

Background

Korean ginseng (Panax ginseng Meyer) powder is in rising demand because powder forms of foods are convenient to handle and are highly preservable. However, ginseng powder (GP) manufactured using the conventional process of air drying and dry milling suffers nutrient destruction and a lack of microbiological safety. The objective of this study was to prepare GP using a novel process comprised of UV-TiO₂ photocatalysis (UVTP) as a prewashing step, wet grinding, high hydrostatic pressure (HHP), and freeze-drying treatments.

Methods

The effects of UVTP and HHP treatments on the microbial population, ginsenoside concentration, and physiological characteristics of GP were evaluated.

Results

When UVTP for 10 min and HHP at 600 MPa for 5 min were combined, initial 4.95 log CFU/g-fw counts of total aerobes in fresh ginseng were reduced to lower than the detection limit. The levels of 7 major ginsenosides in UVTP-HHP–treated GP were significantly higher than in untreated control samples. Stronger inhibitory effects against inflammatory mediator production and antioxidant activity were observed in UVTP-HHP–treated GP than in untreated samples. There were also no significant differences in CIELAB color values of UVTP-HHP–treated GP compared with untreated control samples.

Conclusion

Combined processing of UVTP and HHP increased ginsenoside levels and enhanced the microbiological safety and physiological activity of GP.

Portable Nanofiber-Light Addressable Potentiometric Sensor for Rapid Escherichia coli Detection in Orange Juice

The growing need to prevent pathogen outbreaks is irrefutable in the case of the food industry. Early detection in products, especially beverages, contaminated with bacterial strains is vital to avoid infected foods from reaching the consumer. If E. coli is pesent in such foods, it can cause infections. It can also be an indicator of the existence of other harmful coliforms. In this study, we have investigated the detection of Escherichia coli ( E. coli) in orange juice using a portable nanofiber-light addressable potentiometric sensor (NF-LAPS). We have chosen electrospun pH-sensitive poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) hydrogel NFs as the sensitive layer. The successful detection of E. coli was reported with the NF-LAPS in less than 1 h. The limit of detection (LOD) measured in the sensor is found to be10² CFU/mL. We have confirmed the selectivity of the biosensor toward E. coli by examining the response of the NF-LAPS against Salmonella typhimurium ( S. typhi), also commonly found in orange juice. Despite the complex nature of orange juice, the response of the biosensor is in no way affected while orange juice is tested as is.

Inactivation of Salmonella Typhimurium in fresh cherry tomatoes using combined treatment of UV-TiO2 photocatalysis and high hydrostatic pressure

The antibacterial efficacy of UV-TiO₂ photocatalysis pre-washing in a water-assisted system (UVT, 4.5 mW/cm², 5-15 min) and high hydrostatic pressure (HHP, 300-500 MPa, 1 min at 25 °C) post-package combined treatment was evaluated against Salmonella Typhimurium inoculated onto whole cherry tomato surfaces and compared with chlorine disinfection (200 ppm). An air pump was fitted at the bottom of UVT reactor to create turbulent flow for rotation of fruits for uniform disinfection. UVT-HHP combined treatment at 500 MPa achieved bacterial reduction of more than 5 log via a synergistic effect, compared with chlorine disinfection. Lycopene and total phenolic contents and antioxidant activities were not significantly changed in tomatoes after any treatment. UVT-HHP combined treatment did not affect the surface color but caused softness in tomatoes. UVT pre-washing followed by HHP post-package treatment can be the effective intervention strategy alternative to conventional chlorine disinfection for production of ready-to-eat (RTE) fresh cherry tomatoes.