Comparison of pulsed light inactivation kinetics and modeling of Escherichia coli (ATCC-29055), Clostridium sporogenes (ATCC-7955) and Geobacillus stearothermophilus (ATCC-10149)

Effect of UV LED and Pulsed Light Treatments on Polyphenol Oxidase Activity and Escherichia coli Inactivation in Apple Juice

Enzymatic browning in fruits and vegetables, driven by polyphenol oxidase (PPO) activity, results in color changes and loss of bioactive compounds. Emerging technologies are being explored to prevent this browning and ensure microbial safety in foods. This study assessed the effectiveness of pulsed light (PL) and ultraviolet light-emitting diodes (UV-LED) in inhibiting PPO and inactivating Escherichia coli ATTC 25922 in fresh apple juice (Malus domestica var. Red Delicious). Both treatments' effects on juice quality, including bioactive compounds, color changes, and microbial inactivation, were examined. At similar doses, PL-treated samples (126 J/cm2) showed higher 2,2- diphenyl-1-picrylhydrazyl inhibition (9.5%) compared to UV-LED-treated samples (132 J/cm2), which showed 1.06%. For microbial inactivation, UV-LED achieved greater E. coli reduction (>3 log cycles) and less ascorbic acid degradation (9.4% ± 0.05) than PL. However, increasing PL doses to 176 J/cm2 resulted in more than 5 log cycles reduction of E. coli, showing a synergistic effect with the final temperature reached (55 °C). The Weibull model analyzed survival curves to evaluate inactivation kinetics. UV-LED was superior in preserving thermosensitive compounds, while PL excelled in deactivating more PPO and achieving maximal microbial inactivation more quickly.

Combined treatment of pulsed light and nisin-organic acid based antimicrobial wash for inactivation of Escherichia coli O157:H7 in Romaine lettuce, reduction of microbial loads, and retention of quality

Microbial safety of fresh produce continues to be a major concern. Novel antimicrobial methods are needed to minimize the risk of contamination. This study investigated the antimicrobial efficacy of pulsed light (PL), a novel nisin-organic acid based antimicrobial wash (AW) and the synergy thereof in inactivating E. coli O157:H7 on Romaine lettuce. Treatment effects on background microbiota and produce quality during storage at 4 °C for 7 days was also investigated. A bacterial cocktail containing three outbreak strains of E. coli O157:H7 was used as inoculum. Lettuce leaves were spot inoculated on the surface before treating with PL (1-60 s), AW (2 min) or combinations of PL with AW. PL treatment for 10 s, equivalent to fluence dose of 10.5 J/cm2, was optimal and resulted in 2.3 log CFU/g reduction of E. coli O157:H7, while a 2 min AW treatment, provided a comparable pathogen reduction of 2.2 log CFU/g. Two possible treatment sequences of PL and AW combinations were investigated. For PL-AW combination, inoculated lettuce leaves were initially exposed to optimum PL dose followed by 2 min AW treatment, whereas for AW-PL combination, inoculated lettuce were subjected to 2 min AW treatment prior to 10 s PL treatment. Both combination treatments (PL-AW and AW-PL) resulted in synergistic inactivation as E. coli cells were not detectable after treatment, indicating >5 log pathogen reductions. Combination treatments significantly (P < 0.05) reduced spoilage microbial populations on Romaine lettuce and also hindered their growth in storage for 7 days. The firmness and visual quality appearance of lettuce were not significantly (P > 0.05) influenced due to combination treatments. Overall, the results reveal that PL and AW combination treatments can be implemented as a novel approach to enhance microbial safety, quality and shelf life of Romaine lettuce.

High-pressure pulses for Aspergillus niger spore inactivation in a model pharmaceutical lipid emulsion

High hydrostatic pressure (HHP) is a non-thermal process widely used in the food industry to reduce microbial populations. However, rarely its effect has been assessed in products with high oil content. This study evaluated the efficacy of HHP (200, 250, and 300 MPa) at different temperatures (25, 35, and 45 °C) by cycles (1, 2, or 3) of 10 min in the inactivation of Aspergillus niger spores in a lipid emulsion. After treatments at 300 MPa for 1 cycle at 35 or 45 °C, no surviving spores were recovered. All treatments were modeled by the linear and Weibull models. The presence of shoulders and tails in the treatments at 300 MPa at 35 or 45 °C resulted in sigmoidal curves which cannot be described by the linear model, hence the Weibull + Tail, Shoulder + Log-lin + Tail, and double Weibull models were evaluated to elucidate the inactivation kinetics. The tailing formation could be related to the presence of resistance subpopulations. The double Weibull model showed better goodness of fit (RMSE <0.2) to describe the inactivation kinetics of the treatments with the higher spore reductions. HHP at 200-300 MPa and 25 °C did not reduce the Aspergillus niger spores. The combined HHP and mild temperatures (35-45 °C) favored fungal spore inactivation. Spore inactivation in lipid emulsions by HHP did not follow a linear inactivation. HHP at mild temperatures is an alternative to the thermal process in lipid emulsions.

Novel pulsed infrared radiation: Effect on microbial, chemical, and sensory properties of saffron (Crocus sativus L.)

AIM

In this study, the effect of pulsed infrared (PIR) irradiation on saffron microbial, chemical, and sensory properties were evaluated.

METHODS AND RESULTS

The PIR power (250, 350, and 450W), the distance of sample with irradiation source (10, 20, and 30cm), irradiation time (0-20min), and PIR pulse (1, 2, and 3pulse/s) were investigated. Decontamination of total bacteria and total mold and yeast flora and microbial inactivation kinetics were determined. Saffron quality by FTIR and HPLC and sensory attributes were also measured. The highest reduction of the total bacterial count (2.203 Log₁₀ CFU/g) and total mold and yeast counts (2.194 Log₁₀ CFU/g) were obtained in Sargol Negin saffron at 350 W PIR power, 10 cm distance, 1.5 min treatment time, and 3 pulse/s. The Double Weibull model is the best-fit model for the prediction of the microbial population.

CONCLUSION

Until now, there have been no reports of application for PIR in food processing and decontamination. According to the results, it can be concluded that PIR can be used as a safe method of saffron processing.

SIGNIFICANCE AND IMPACT OF THE STUDY

Utilization of a proper decontamination method for spices especially saffron as the most expensive agricultural product is challengeable. It is recommended to use the PIR method for food processing because due to the reduction of microbial population, it can maintain foodstuff quality at an acceptable level.

Pasteurization of fruit juices by pulsed light treatment: A review on the microbial safety, enzymatic stability, and kinetic approach to process design

Pulsed light (PL) is a polychromatic radiation-based technology, among many other non-thermal processing techniques. The microbiological lethality of the PL technique has been explored in different food matrices along with their associated mechanisms. Pasteurization of fruit juice requires a 5-log cycle reduction in the resistant pathogen in the product. The manufacturers look toward achieving the microbial safety and stability of the juice, while consumers demand high-quality juice. Enzymatic spoilage in fruit juice is also a crucial factor that needs attention. The retailers want the processed juice to be stable, which can be achieved by inactivating the spoilage enzymes and native microflora inside it. The present review argued about the potential of PL technology to produce a microbiologically safe and enzymatically stable fruit juice with a minimal loss in bioactive compounds in the product. Concise information of factors affecting the PL treatment (PLT), primary inactivation mechanism associated with microorganisms, enzymes, the effect of PLT on various quality attributes (microorganisms, spoilage enzymes, bioactive components, sensory properties, color), and shelf life of fruit juices has been put forward. The potential of PL integrated with other non-thermal and mild thermal technologies on the microbial safety and stability of fruit juices has been corroborated. The review also provides suggestions to the readers for designing, modeling, and optimizing the PLT and discusses the use of various primary, secondary kinetic models in detail that have been utilized for different quality parameters in juices. Finally, the challenges and future need associated with PL technology has been summarized.

Evaluation of Pulsed Light to Inactivate Brettanomyces bruxellensis in White Wine and Assessment of Its Effects on Color and Aromatic Profile

Brettanomyces bruxellensis is a wine spoilage yeast that could be inactivated by pulsed light (PL); however, this technology may induce changes in the quality of this alcoholic drink. The present research aimed to determine the potential of PL to inactivate B. bruxellensis inoculated in white wine and to assess the effect of this technology on the color and aromatic profile of the wine. For this, a cocktail of B. bruxellensis strains was inoculated into the wine and its inactivation by PL was determined and fitted to a microbial inactivation model. Along with this, the effect of PL on instrument-measured color, and the volatile compounds of the wine were evaluated by GC/MS and descriptive sensory analysis, respectively. B. bruxellensis was inactivated according to the Geeraerd model including the tail effect, with a maximum inactivation of 2.10 log reduction at 10.7 J/cm²; this fluence was selected for further studies. PL affected wine color but the total color difference was below the just noticeable difference at 10.7 J/cm². The concentration of 13 out of 15 volatile compounds decreased due to the PL, which was noticeable by the panel. It is not clear if these compounds were photolyzed or volatilized in the open reactor during treatment. In conclusion, PL is able to inactivate B. bruxellensis in white wine but the treatment impairs the volatile profile. The use of a closed reactor under turbulent flow is recommended for disaggregating yeast clumps that may cause the tailing of the inactivation curve, and to avoid the possible escape of volatile compounds during treatment.