Decontamination of fresh-cut broccoli with a water–assisted UV-C technology and its combination with peroxyacetic acid

Predicting the impact of temperature and relative humidity on Salmonella growth and survival in sliced chard, broccoli and red cabbage

This study assessed the fate of a Salmonella enterica cocktail (S. Typhimurium, S. Enteritidis, S. Newport, S. Agona and S. Anatum; initial counts 3.5 log CFU/g) in minimally processed sliced chard, broccoli and red cabbage at 16 conditions of different temperature (7, 14, 21 and 37 °C) and relative humidity (RH; 15, 35, 65 and 95%) over six days (144 h). Linear regression was used to estimate the rate change of Salmonella in cut vegetables as a function of temperature and relative humidity (RH). R2 value of 0.85, 0.87, and 0.78 were observed for the rates of change in chard, broccoli, and red cabbage, respectively. The interaction between temperature and RH was significant in all sliced vegetables. Higher temperatures and RH values favored Salmonella growth. As temperature or RH decreased, the rate of S. enterica change varied by vegetable. The models developed here can improve risk management of Salmonella in fresh cut vegetables.

Inactivation of Escherichia coli, Salmonella enterica and Listeria monocytogenes on apple peel and apple juice by ultraviolet C light treatments with two irradiation devices

Following the market trends, the consumption of fresh and cold-pressed juice in Europe is increasing. However, a primary concern - particularly in apple juice - is the related outbreaks caused by food-borne pathogens. One of the challenges is to find methods able to reduce pathogenic loads while avoiding deterioration of nutritional properties and bioactive compounds that occur in thermal pasteurization processes. In this study, the inactivation of Escherichia coli, Salmonella enterica and Listeria monocytogenes was evaluated under different ultraviolet C (UVC_254nm) light treatments (up to 10,665.9 ± 28.1 mJ/cm²), in two different steps of the production chain (before and after juice processing): on apple peel discs and in apple juice. The systems proposed were a horizontal chamber with UVC_254nm emitting lamps treating the product disposed at a distance of 12 cm, and a tank containing UVC_254nm lamps and in which the product is immersed and agitated. Final reductions ranged from 3.3 ± 0.5 to 5.3 ± 0.4 logarithmic units, depending on the microorganism, matrix and used device. The survival curves were adjusted to Weibull and biphasic models (R²-adj ≥ 0.852), and UVC doses needed for the first decimal reduction were calculated, being lower for the apple peel discs (0.20 to 83.83 mJ/cm²) than they were for apple juice (174.60 to 1273.31 mJ/cm²), probably for the low transmittance of the apple juice compared to the surface treatment occurring on the peels. Within the treatments evaluated, the UVC_254nm irradiation of apple peels immersed in water was the best option as it resulted in a reduction of the tested microorganisms of ca. 2-3 log units at lower UVC_254nm doses (< 500 mJ/cm²) when compared to those occurring in apple peel treated with the UVC chamber and in juice. As contamination can proceed from apples, the sanitization of these fruit prior to juice production may be helpful in reducing the safety risks of the final product, reducing the drawbacks related to the poor transmittance of the fruit juices.

Water UV-C treatment alone or in combination with peracetic acid: A technology to maintain safety and quality of strawberries

Disinfection of fruits is one of the most important steps since they are going to be eaten fresh-or minimally-processed. This step affects quality, safety, and shelf-life of the product. Despite being a common sanitizer in the fruit industry, chlorine may react with organic matter leading to the formation of toxic by-products. Alternative sustainable disinfection strategies to chlorine are under study to minimize environmental and human health impact. Water-assisted UV-C light (WUV-C) is proposed here as an alternative sanitizing method for strawberries. In this study, strawberries were washed for 1 or 5 min in a tank with 2 or 4 lamps on, each emitting UV-C light at 17.2 W/cm², or in a chlorine solution (200 ppm, pH 6.5). Moreover, trials with 4 lamps on, together with a washing solution consisting on peracetic acid at 40 or 80 ppm, were carried out. Overall, quality and nutritional parameters of strawberries after treatments were maintained. Changes in color were not noticeable and fruits did not lose firmness. No major changes were observed in antioxidant activity, organic acid, anthocyanin, vitamin C, and total phenolic content. Yeasts and molds were not affected by the WUV-C treatment, and 5 min were needed to significantly reduce total aerobic mesophylls population. However, reductions of artificially inoculated Listeria innocua and Salmonella Typhimurium after WUV-C treatments were comparable to those obtained with chlorine-wash, which were 3.0 log CFU / g. Moreover, WUV-C light was effective to minimize microorganisms remaining in washing water, avoiding cross-contamination and thus, allowing water recirculation. This effect was improved when combining the action of UV-C light with peracetic acid, showing the suitability of this combined treatment, understood as an alternative to chlorine sanitation, for sanitizing strawberries and keeping the populations of pathogenic bacteria in washing water lower than 0.6 ± 0.1 log CFU / mL.

Application of an innovative water-assisted ultraviolet C light technology for the inactivation of microorganisms in tomato processing industries

We aimed to study the efficacy of a water-assisted UVC light device (WUVC) as an innovative clean technology for the disinfection of fresh sound tomatoes and processing wash water and water turbidity was evaluated as a critical parameter. First, wash waters with different turbidities (from 0.4 to 828 NTU) were inoculated with Listeria innocua and treated in the WUVC device at different dosages. Secondly, fresh tomatoes, inoculated with L. innocua and non-inoculated ones, were treated using the WUVC device containing wash water of different turbidities for different times. The reduction of L. innocua populations on wash water and on the surface of tomato was influenced by turbidity; lower reduction values were observed at higher turbidities. Washing tomatoes with tap water with UVC lamps off (control treatment, TW) decreased L. innocua population on the surface of tomatoes but did not eliminate those bacteria that went into the water. Contrarily, when UVC lights were on, L. innocua population in wash water after treatment significantly decreased, those in clean water being the lowest populations. Reductions of native microbiota on the clean water treated with the highest UV-C radiation dose were lower than those obtained when tomatoes were artificially inoculated. We demonstrated that high reductions of L. innocua population on fresh tomatoes could be achieved using the WUVC system but some drawbacks related to the increase of turbidity should be solved for its implementation in real conditions.

Assessing water-assisted UV-C light and its combination with peroxyacetic acid and Pseudomonas graminis CPA-7 for the inactivation and inhibition of Listeria monocytogenes and Salmonella enterica in fresh-cut 'Iceberg' lettuce and baby spinach leaves

The effectiveness of ultraviolet C light (UV-C) delivered in water (WUV) or in peroxyacetic acid (PAA) for the inactivation and inhibition of L. monocytogenes and S. enterica in ready-to-eat 'Iceberg lettuce' and baby spinach leaves, was evaluated throughout chilled storage in modified atmosphere packaging (MAP). The inhibition of pathogen's growth by sequential pretreatments with UV-C in PAA and then biocontrol using Pseudomonas graminis CPA-7 was assessed during MAP storage at 5 °C and upon a breakage of the cold-storage chain. In fresh-cut lettuce, 0 1 kJ/m2 UV-C, in water or in 40 mg/L PAA, inactivated both pathogens by up to 2.1 ± 0.7 log10, which improved the efficacy of water-washing by up to 1.9 log10 and showed bacteriostatic effects on both pathogens. In baby spinach leaves, the combination of 0 3 kJ/m2 UV-C and 40 mg/L PAA reduced S. enterica and L. monocytogenes populations by 1.4 ± 0.2 and 2.2 ± 0.3 log10 respectively, which improved water-washing by 0.8 ± 0.2 log10. Combined treatments (0.1 or 0 3 kJ/m2 WUV and 40 mg/L PAA) inactivated both pathogens in the process solution from lettuce or spinach single sanitation, respectively. Pretreating lettuce with UV-C in PAA reduced L. monocytogenes and S. enterica's growth by up to 0.9 ± 0.1 log10 with respect to the PAA-pretreated control after 6 d at 5 °C in MAP. Upon a cold-chain breakage, CPA-7 prevented S. enterica growth in PAA-pretreated lettuce, whereas showed no effect on L. monocytogenes in any of both matrices. Low-dose UV-C in PAA is a suitable preservation strategy for improving the safety of ready-to-eat leafy greens and reducing the risk of cross contamination.