Simultaneous decontamination and drying of rough rice using combined pulsed light and holding treatment

Recent developments in applications of physical fields for microbial decontamination and enhancing nutritional properties of germinated edible seeds and sprouts: a review

Germinated edible seeds and sprouts have attracted consumers because of their nutritional values and health benefits. To ensure the microbial safety of the seed and sprout, emerging processing methods involving physical fields (PFs), having the characteristics of high efficiency and environmental safety, are increasingly proposed as effective decontamination processing technologies. This review summarizes recent progress on the application of PFs to germinating edible seeds, including their impact on microbial decontamination and nutritional quality and the associated influencing mechanisms in germination. The effectiveness, application scope, and limitation of the various physical techniques, including ultrasound, microwave, radio frequency, infrared heating, irradiation, pulsed light, plasma, and high-pressure processing, are symmetrically reviewed. Good application potential for improving seed germination and sprout growth is also described for promoting the accumulation of bioactive compounds in sprouts, and subsequently enhancing the antioxidant capacity under favorable PFs processing conditions. Moreover, the challenges and future directions of PFs in the application to germinated edible seeds are finally proposed. This review also attempts to provide an in-depth understanding of the effects of PFs on microbial safety and changes in nutritional properties of germinating edible seeds and a theoretical reference for the future development of PFs in processing safe sprouted seeds.

Inhibition of Aspergillus oryzae Mycelium Growth and Conidium Production by Irradiation with Light at Different Wavelengths and Intensities

Aspergillus oryzae is a safe filamentous fungus widely used in the food, medicine, and feed industries, but there is currently not enough research on the light response of A. oryzae. In this study, 12 different light conditions were set and A. oryzae GDMCC 3.31 was continuously irradiated for 72 h to investigate the effect of light on mycelial growth and conidium production. Specifically, each light condition was the combination of one light wavelength (475, 520, or 630 nm) and one light intensity (20, 40, 60, or 80 μmol photon m-2 s-1). The results show that mycelium growth was inhibited significantly by green light (wavelength of 520 nm and intensities of 20 and 60 μmol photon m-2 s-1) and blue light (wavelength of 475 nm and intensity of 80 μmol photon m-2 s-1). The production of conidia was suppressed only by blue light (wavelength of 475 nm and intensities of 40, 60, and 80 μmol photon m-2 s-1), and those levels of inhibition increased when the intensity of blue light increased. When the strain was irradiated by blue light (80 μmol photon m-2 s-1), the number of conidia was 57.4% less than that of the darkness group. However, within our set range of light intensities, A. oryzae GDMCC 3.31 was insensitive to red light (wavelength of 630 nm) in terms of mycelium growth and conidium production. Moreover, interaction effects between light wavelength and intensity were found to exist in terms of colony diameter and the number of conidia. This research investigated the light response of A. oryzae, which may provide a new method to regulate mixed strains in fermented foods by light. IMPORTANCE Studies on the monochromatic light response of Aspergillus nidulans and Neurospora crassa have gone deep into the molecular mechanism. However, research methods for the light response of A. oryzae remain in the use of white light sources. In this study, we first demonstrated that A. oryzae GDMCC 3.31 was sensitive to light wavelength and intensity. We have observed that blue light inhibited its growth and sporulation and the inhibitory effect increased with intensity. This research not only adds new content to the study of the photoreaction of Aspergillus but also brings new possibilities for the use of light to regulate mixed strains and ultimately improve the flavor quality of fermented foods.

Pulsed-Light Treatment of Dried Parsley: Reduction of Artificially Inoculated Salmonella and Impact in Given Quality Parameters

ABSTRACT

Dried parsley is regularly contaminated with foodborne pathogens, especially Salmonella. Application of contaminated ingredients in ready-to-eat dishes without further thermal treatment represents a considerable health risk. This study examined the suitability of pulsed light as a novel decontamination method of Salmonella in dried parsley, along with the impact on selected quality parameters (chlorophyll content, phenolic compounds, color, and odor) and product characters (temperature and water activity value). Samples were inoculated with one of three Salmonella isolates (Salmonella Cerro or one of two isolates of Salmonella Agona) at two contamination levels of 103 or 107 CFU/g and treated under various experimental factors, including distance to the light source and exposure time, resulting in fluences in the range of 1.8 to 19.9 J/cm2. At selected parameter settings (9.8 and 13.3 J/cm2), the effect of prolonged storage time (48 h) of inoculated samples before treatment on the reduction of Salmonella Cerro was examined. Samples treated at the same fluences were also stored for 35 days at 22 to 25°C. The three Salmonella isolates were significantly reduced by pulsed light (P < 0.05). Reduction factors ranged between 0.3 and 5.2 log CFU with varying sensitivities of the isolates. In general, increasing fluences (depending on exposure time and distance to the light source) resulted in increasing reductions of Salmonella. However, on closer examination, exposure time and distance to the light source had a varying influence on the reduction of the different Salmonella isolates. Decreasing reduction factors were observed by increasing the contamination level and prolonging the storage time of inoculated samples before treatment. No undesirable changes in quality parameters and sensory analysis were detectable at fluences of 9.8 and 13.3 J/cm2, indicating that pulsed light may be a suitable alternative for the decontamination of dried parsley.

HIGHLIGHTS

Disrupting Irreversible Bacterial Adhesion and Biofilm Formation with an Engineered Enzyme

Biofilm formation is often attributed to postharvest bacterial persistence on fresh produce and food handling surfaces. In this study, a predicted glycosyl hydrolase enzyme was expressed, purified, and validated for the removal of microbial biofilms from biotic and abiotic surfaces under conditions used for chemical cleaning agents. Crystal violet biofilm staining assays revealed that 0.1 mg/ml of enzyme inhibited up to 41% of biofilm formation by Escherichia coli O157:H7, E. coli 25922, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes. Furthermore, the enzyme was effective at removing mature biofilms, providing a 35% improvement over rinsing with a saline solution alone. Additionally, a parallel-plate flow cell was used to directly observe and quantify the impact of enzyme rinses on E. coli O157:H7 cells adhering to spinach leaf surfaces. The presence of 1 mg/liter enzyme resulted in nearly 6-times-higher detachment rate coefficients than a deionized (DI) water rinse, while the total cells removed from the surface increased from 10% to 25% over the 30-min rinse time, reversing the initial phases of biofilm formation. Enzyme treatment of all 4 cell types resulted in significantly reduced cell surface hydrophobicity and collapse of negatively stained E. coli 25922 cells imaged by electron microscopy, suggesting potential polysaccharide surface modification of enzyme-treated bacteria. Collectively, these results point to the broad substrate specificity and robustness of the enzyme for different types of biofilm stages, solution conditions, and pathogen biofilm types and may be useful as a method for the removal or inhibition of bacterial biofilm formation. IMPORTANCE In this study, the ability of an engineered enzyme to reduce bacterial adhesion and biofilm formation of several foodborne pathogens was demonstrated, representing a promising option for enhancing or replacing chlorine and other chemical sanitizers in food processing applications. Specifically, significant reductions of biofilms of the pathogens Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes are observed, as are reductions in initial adhesion. Enzymes have the added benefits of being green, sustainable alternatives to chemical sanitizers, as well as having a minimal impact on food properties, in contrast to many alternative antimicrobial options such as bleach that aim to minimize food safety risks.

Degradation kinetics of aflatoxin B1 and B2 in solid medium by using pulsed light irradiation

BACKGROUND

Pulsed light (PL) is a new potential technology to degrade aflatoxin. The objective of this study was to investigate the degradation characters of aflatoxin B₁ (AFB₁ ) and B₂ (AFB₂ ) treated under PL irradiation. A kinetic degradation study of AFB₁ and AFB₂ in solid medium was performed under PL irradiation at different initial concentrations of AFB₁ (229.9, 30.7 and 17.8 μg kg^-1 ) and AFB₂ (248.2, 32.2 and 19.5 μg kg^-1 ) and irradiation intensities (2.86, 1.60 and 0.93 W cm^-2 ) of PL. A second-order reaction model was applied to describe degradation of AFB₁ and AFB₂ .

RESULTS

The results showed that the degradation of AFB₁ and AFB₂ followed the second-order reaction kinetic model well (R²  > 0.97). The degradation rate was proportional to the intensities of PL irradiation and the initial concentrations of aflatoxins.

CONCLUSION

It is concluded that the degradation of AFB₁ and AFB₂ with the use of PL could be accurately described using the second-order reaction kinetic model. © 2018 Society of Chemical Industry.

Recent findings in pulsed light disinfection

Nonthermal disinfection technologies are gaining increasing interest in the field of minimally processed food in order to improve the microbial safety or to extend the shelf life. Especially fresh-cut produce or meat and fish products are vulnerable to microbial spoilage, but, due to their sensitivity, they require gentle preservation measures. The application of intense light pulses of a broad spectral range comprising ultraviolet, visible and near infrared irradiation is currently investigated as a potentially suitable technology to reduce microbial loads on different food surfaces or in beverages. Considerable research has been performed within the last two decades, in which the impact of various process parameters or microbial responses as well as the suitability of pulsed light (PL) for food applications has been examined. This review summarizes the outcome of the latest studies dealing with the treatment of various foods including the impact of PL on food properties as well as recent findings about the microbicidal action and relevant process parameters.