Category Archives: Food Technology

Research – Application of ultra-fine bubble technology to reduce Listeria monocytogenes contamination of fresh produce

Center for Produce Safety

Summary

Water used for washing or hydrocooling can act as a source of produce contamination with Listeria monocytogenes. Since this could lead to human infections, controlling L. monocytogenes in hydrocooling water and produce is critical for food safety. Commercial disinfectants (chlorine, quaternary ammonium compounds) are not completely effective in killing L. monocytogenes in wash water or on produce, especially in presence of organic load.

This proposal aims to investigate the potential of a new technology that employs water containing ultra-fine gas bubbles (size ~ 1 micrometer or less) for washing produce (celery, gala apples, romaine lettuce). We will generate ultra-fine ozone (UFO) bubbles in water using a high energy shear method and test the potential of resulting solution to rapidly kill (in 30 to 60 sec) L. monocytogenes in wash water and on produce surface. In addition, the efficacy of UFO bubble water to synergistically improve the Listeria killing potential of aforementioned commercial disinfectants will be tested. The anti-listerial efficacy of UFO bubble water will also be tested in presence of organic load. Successful completion of this project will provide the produce industry with novel antimicrobial treatment for disinfecting wash water and produce in single pass or re- circulated hydrocooling systems.

Technical Abstract

The widespread distribution of Listeria monocytogenes in agricultural environments such as soil, manure and water results in frequent contamination of food processing areas. Although good agricultural practices partially reduce contamination, however, due to the open nature of farming, it is extremely difficult to completely prevent pathogen influx. Water used for washing or hydrocooling can act as a source of equipment and produce contamination with L. monocytogenes. Since this could lead to human infections, controlling L. monocytogenes in hydrocooling water and on the surface of fresh produce is critical for food safety. Currently used commercial disinfectants (chlorine, peracetic acid, quaternary ammonium compounds) are not completely effective in killing L. monocytogenes in wash water or on the surface of produce, especially in presence of organic load. Moreover, the presence of chemical residues and the formation of harmful organochlorine compounds is an occupational concern due to associated health risks, including cancer. Therefore, there is a need for developing novel strategies that could be employed (either alone or in combination with currently used commercial disinfectants) to control L. monocytogenes in wash water and on surface of fresh produce, vegetables and fruits.

This proposal aims to investigate the potential of a new technology that employs water containing ultra-fine gas bubbles (size ~ 1 micrometer or less) for washing produce (celery, gala apples, romaine lettuce). We will generate ultra-fine ozone (UFO) bubbles in water using a high energy shear method and test the potential of resulting solution to rapidly kill (in 30 to 60 sec) L. monocytogenes in wash water and on produce surface. In addition, the efficacy of UFO bubble water to synergistically improve the Listeria killing potential of aforementioned commercial disinfectants will be tested. The anti-listerial efficacy of UFO bubble water will also be tested in presence of organic load.

Potential impact from anticipated outcomes: Successful completion of this project will provide the produce industry with novel antimicrobial treatment for disinfecting wash water and produce in dump tanks, and single pass or re-circulated hydrocooling systems. This intervention will translate into increased microbiological safety of fresh produce.

Research – Microbial Safety and Sensory Analyses of Cold-Smoked Salmon Produced with Sodium-Reduced Mineral Salts and Organic Acid Salts

MDPI

Cold-smoked (CS) salmon contains high levels of sodium salts, and excess dietary sodium intake is associated with an array of health complications. CS salmon may also represent a food safety risk due to possible presence and growth of the foodborne pathogen Listeria monocytogenes which may cause fatal human infections. Here we determine how reformulated CS salmon using commercial sodium-reduced salt replacers containing KCl (e.g., Nutek, Smart Salt, SOLO-LITE) and acetate-based preservative salts (Provian K, proviant NDV) affect sensory properties, quality, and microbial safety. Initial sensory screening of sodium-reduced CS salmon was followed by L. monocytogenes growth analyses in selected variants of reformulated CS salmon, and finally by analyses of CS salmon variants produced in an industrial smokehouse. Projective mapping indicated overall minor sensory changes in sodium-replaced samples compared with a conventional product with NaCl. Growth of L. monocytogenes was temperature-dependent (4 °C vs. 8 °C storage) with similar growth in sodium-reduced and conventional CS salmon. The addition of 0.9% of the preservative salts Provian K or Provian NDV gave up to 4 log lower L. monocytogenes counts in both sodium-reduced and conventional cold-smoked salmon after 29 days of chilled storage. No changes in pH (range 6.20–6.33), aw levels (range 0.960–0.973), or weight yield (96.8 ± 0.2%) were evident in CS salmon with salt replacers or Provian preservative salts. Analyses of CS salmon produced with selected mineral salt and preservative salt combinations in an industrial salmon smokery indicated marginal differences in sensory properties. Samples with the preservative salt Provian NDV provided L. monocytogenes growth inhibition and low-level total viable counts (<2.8 log/g) dominated by Photobacterium and Carnobacterium during storage. Production of sodium-reduced CS salmon with inhibiting salts provides a simple method to achieve a healthier food product with increased food safety.

Research – Removal of Ochratoxin A from Grape Juice by Clarification: A Response Surface Methodology Study

MDPI

This study achieved maximum removal of ochratoxin A (OTA) during the grape juice clarification process with minimal reduction in antioxidant compounds (phenolic acid, flavonoids, and antioxidant capacity by FRAP) by the RSM method. Independent variables included three types of clarifiers—gelatin, bentonite, and diatomite (diatomaceous earth)—at a concentration level of 0.25–0.75% and clarification time of 1–3 h. OTA was measured by high-performance liquid chromatography with fluorescence detection. Clarifying agent concentration and clarification time affected the reduction amount of OTA and antioxidant compounds in grape juice. There was a direct linear correlation between the reduction amounts of OTA and antioxidant compounds and capacity with the concentration of bentonite, gelatin, and diatomite, and the clarification time. The reduction amount of OTA and antioxidant capacity followed the linear mode. However, the decreased phenolic acid and flavonoid values followed the quadratic model. The study results showed that if the concentrations of bentonite, gelatin, and diatomite and clarification time were 0.45, 0.62, 0.25%, and 1 h, respectively, the maximum amount of OTA reduction (41.67%) occurred. Furthermore, the phenolic acid, flavonoid, and antioxidant activity decrease amounts were at their lowest levels, i.e., 23.86, 7.20, and 17.27%, respectively. View Full-Text

Research – Inactivation of Foodborne Pathogens on Inshell Walnuts by UV-C Radiation

Journal of Food Protection

Inshell walnuts could be contaminated with pathogens through direct contact or cross-contamination during harvesting and postharvest hulling, drying, or storage. This study aimed to assess the efficacy of ultraviolet–C (UV–C) radiation in inactivating foodborne pathogens on inshell walnut surfaces. Intact inshell walnut surfaces were inoculated separately with Salmonella spp., Escherichia coli O157:H7, Listeria monocytogenes , and Staphylococcus aureus , and then subjected to UV–C radiation at doses of 29.4, 147.0, 294.0, 588.0, and 882.0 mJ/cm 2 . UV–C radiation inactivated the inoculated pathogens in a dose-dependent manner, and a tailing effect was observed for the inactivation of pathogens. UV–C radiation at 29.4 mJ/cm 2 and 882.0 mJ/cm 2 reduced the populations of  S . Enteritidis PT 30, S . Typhimurium, E. coli O157:H7, L. monocytogenes , and S. aureus on inshell walnut surfaces by 0.82–1.25 and 1.76–2.41 log CFU/walnut, respectively. Scanning electron photomicrographs showed pathogenic bacterial cells in the cracks and crevices of the inshell walnut surface, and the shielding of microorganisms by the cracks and crevices may have contributed to the tailing effect observed during UV–C inactivation. No significant changes ( p  > 0.05) were found in walnut lipid oxidation following UV–C radiation at doses up to 882.0 mJ/cm 2 . Together, the results indicate that UV–C radiation could be a potential technology for reducing the populations of various foodborne pathogens on inshell walnut surfaces while maintaining the quality of walnuts.

Research – Attachment and survival of Salmonella enterica and Listeria monocytogenes on tomatoes (Solanum lycopersicum) as affected by relative humidity, temperature and time of storage 

Journal of Food Protection

Tomatoes (Solanum lycopersicum) are one of the most consumed fruits worldwide. The fruit can become contaminated with Salmonella and Listeria monocytogenes at different stages of the production and supply chain, and these pathogens may survive under different storage conditions. The effect of relative humidity, temperature and time of storage on the attachment and survival characteristics of both pathogens on the surface of tomatoes was investigated. Fresh whole Roma tomatoes were inoculated with a cocktail of Salmonella or L. monocytogenes and stored at 5, 12, 25, 30, or 35 ºC for 10 days. Every day during storage, relative humidity and temperature were measured and tomatoes were removed to enumerate cells of these pathogens that were loosely attached (LA, cells detached from the tomato surface by simple rinse) and strongly attached (SA, cells that required sonication to detach. Enumeration was achieved by spread-plate method. Surviving populations of LA and SA cells were obtained and the attachment strength (SR) was calculated to express the proportion of SA cells on the tomato surface. The LA initial counts of Salmonella and L. monocytogenes on the surface of the fruit after inoculation were 6.6 and 6.5 log CFU/tomato, and for SA were 5.1 and 5.6 log CFU/tomato, respectively. For both pathogens, the LA counts were higher (p < 0.05) than the SA counts. Also, the LA and SA counts varied significantly as a function of temperature, relative humidity and time of storage. The S R for Salmonella was affected by the time but not the temperature of storage, while the S R for L. monocytogenes was affected by the temperature, relative humidity and time of storage (p < 0.05). Understanding the attachment and survival of Salmonella and L. monocytogenes on tomatoes stored at different temperature conditions may be useful in determining ways to prevent/reduce the establishment of pathogens and designing improved decontamination methods for tomatoes.

Research – The effectiveness and safety of high pressure food treatment

asca

Definition and applicable regulations

Type of food treated and processing conditions

Intrinsic and extrinsic factors of food that influence the effectiveness of high pressure treatment

Possible chemical and microbiological hazards associated with high pressure treatment

High pressure treatment as an alternative to pasteurization of milk

Efficacy of high pressure treatment for the control of Listeria monocytogenes in ready-to-eat foods

Research – Possible explanation for limited reduction of pathogens on radish microgreens after spray application of chlorinated water during growth with disperse contamination spread of abiotic surrogate on leaves

Wiley Online

The purpose of this study was to determine the efficacy of spray application of chlorinated water before harvest on the population of Salmonella enterica Typhimurium and Escherichia coli O157:H7 on radish microgreens. The transfer of abiotic surrogate to radish microgreens was also evaluated to track possible pathogen contamination spread by inoculating seed and growth media. During growth, microgreens inoculated with strains of pathogens were sprayed with chlorinated water at three different concentrations (0.50, 1.00, and 2.00 ± 0.05 ppm free chlorine). Spray application of chlorinated water was performed on microgreens once (day 9), twice (day 8 and 9), three (day 7, 8, and 9), and four times (day 6, 7, 8, and 9). Microgreens were harvested 12 hr after the last application of chlorinated water. Salmonella and E. coli O157:H7 populations were reduced with the increase in chlorine concentration. Chlorinated water reduced Salmonella and E. coli O157:H7 populations up to 1.1 log CFU/g (p < .05) and 0.9 log CFU/g (p > .05), respectively. Images taken under UV illumination provided the visualization of abiotic surrogate spread on cotyledon and upper hypocotyl (all edible parts) of radish microgreen plants regardless of seed or growth media inoculation. Scanning Electron Microscopy showed the presence of abiotic surrogate and generic E. coli on microgreen leaves. Spray application of chlorinated water during microgreen growth may help to reduce microbial load but cannot be used as the only control measure.

Research – Researchers study use of blue light technology for foodborne outbreaks

National Hog Farmer

Researchers from the University of Georgia Center for Food Safety are beginning a new study to investigate the effectiveness of antimicrobial blue light technology to reduce the foodborne pathogens that cause food poisoning.

When used as a means of disinfecting surfaces in a hospital setting, antimicrobial blue light technology has shown promising results, but little research has yet been done to explore its potential efficacy to control foodborne pathogens.

Through a three-year, $599,900 grant awarded by the U.S. Department of Agriculture’s National Institute of Food and Agriculture, UGA College of Agricultural and Environmental Sciences researchers will test the technology to uncover possible applications in the food production process.

Despite industry efforts, the number of foodborne infections has remained steady and, in some cases, has increased in recent years according to the Centers for Disease Control and Prevention (CDC).

Large-scale outbreaks and recalls still occur, particularly due to environmental contamination — like food preparation and processing surfaces — with Salmonella enterica and Listeria monocytogenes, both of which can cause illness and even death.

Most food manufacturers use chemical sanitizers on food preparation surfaces to help control the spread of foodborne pathogens.

This is typically effective in easy-to-reach areas, but areas that are hard to reach may not receive the same degree of sanitation.

These hard-to-reach places sometimes harbor biofilms, which are clusters of microorganisms such as bacteria that are hard to eliminate. The inadvertent spread of these microorganisms can occur during food production both by humans and machinery. Viruses pose a further challenge as many, such as norovirus, can survive on a variety of surfaces for long periods of time.

Research – Unraveling the Antimicrobial Effectiveness of Coridothymus capitatus Hydrolate against Listeria monocytogenes in Environmental Conditions Encountered in Foods: An In Vitro Study

MDPI

The increased resistance of bacteria to antimicrobials, as well as the growing interest in innovative and sustainable alternatives to traditional food additives, are driving research towards the use of natural food preservatives. Among these, hydrolates (HYs) have gained attention as “mild” alternatives to conventional antimicrobial compounds. In this study, the response of L. monocytogenes ATCC 7644 exposed to increasing concentrations of Coridothymus capitatus HY (CHY) for 1 h at 37 °C was evaluated by means of Phenotype Microarray, modelling the kinetic data obtained by inoculating control and treated cells into GEN III microplates, after CHY removal. The results revealed differences concerning the growth dynamics in environmental conditions commonly encountered in food processing environments (different carbon sources, pH 6.0, pH 5.0, 1–8% NaCl). More specifically, for treated cells, the lag phase was extended, the growth rate was slowed down and, in most cases, the maximum concentration was diminished, suggesting the persistence of stress even after CHY removal. Confocal Laser Scanner Microscopy evidenced a diffuse aggregation and suffering of the treated cells, as a response to the stress encountered. In conclusion, the treatment with HY caused a stressing effect that persisted after its removal. The results suggest the potential of CHY application to control L. monocytogenes in food environments.

Research – Effect of Pulsed Light on Quality of Shelled Walnuts

MDPI

Shelled walnuts are considered a microbiologically low-risk food but have been linked to some outbreaks, and a treatment aiming to decrease this risk is desirable. Pulsed light (PL) may be an alternative, providing it does not seriously impair their quality. This work assessed the impact of PL on some quality attributes of walnuts. To do this, measurements of rancidity, volatiles, total phenols, antioxidant activity, and descriptive sensory analysis were carried out on untreated and PL (43 J/cm2)-treated kernels. PL had no statistically significant (p > 0.05) effects on TBARS, peroxide value, total phenols, and antioxidant activity but significantly increased the concentration of volatiles related to green/herbaceous odors and decreased compounds related to fruity and citrus odors. The descriptors nut overall, walnut odor and flavor, and aftertaste were given statistically significantly (p < 0.05) higher scores, while descriptors woody odor and sweet received lower scores; 16 other traits such as all those related to color, texture, and rancidity were unaffected. No significant (p > 0.05) effects on total phenols and antioxidant activity in general were observed during the course of PL treatment. It can be concluded that PL technology may be used in shelled walnuts with only mild effects on their quality; a storage study must be carried out in order to determine the effect of PL treatment on its shelf-life. View Full-Text