Strategies to reduce microbial risk and improve quality of fresh and processed strawberries: A review

Strawberries are one of the most important fruits in the Mediterranean diet and have been widely investigatedfor their nutritional and nutraceutical properties. Concern about the safety of fresh and processed strawberrieshas increased in recent years due to the emergence of several outbreaks of foodborne pathogens linked to theirconsumption. The use of chlorine as a disinfectant has been identified as a concern due to public health issuesand limited efficacy at removing contamination, and preventing cross-contamination. This has led to the de-velopment of novel alternatives to chlorine disinfection and thermal treatments, which include, among others,the use of organic acids, high pressure processing, intense pulsed light, or pulsed electricfields. These tech-nologies do not generally affect the nutritional and organoleptic properties of the product and some of these havebeen reported to stimulate the production of valuable compounds in strawberries and to improve their overallquality.This work forms part of the FRESAFE Research Project (Mitigation Strategies to Reduce the Microbial Risks and Improve the Quality and Safety of Frozen and Ready-to-Eat Strawberries), funded by the Spanish Ministry of Economy, Industry and Competitiveness (AGL2016-78086-R). This work was also supported by the CERCA Programme of Generalitat de Catalunya. T. Lafarga is in receipt of Juan de la Cierva contract awarded by the Spanish Ministry of Economy, Industry, and Competitiveness (FJCI-2016-29541). I. Aguiló-Aguayo thanks the Spanish Ministry of Economy, Industry and Competitiveness and the European Social Fund for the Postdoctoral Senior Grant Ramon y Cajal (RYC-2016-19949)

Effect of ultrasound pre-treatment on the physical, microbiological, and antioxidant properties of calçots

The effect of ultrasound (US) treatment (40 kHz, 250 W) for 0, 10,25 and 45 min on the physical and microbiological quality, total antioxidant capacity (TAC) and total phenolic content (TPC) of calçots (Allium cepaL.) was evaluated. Moreover, the effect of roasting (270 °C, 8 min) and in vitro simulated digestion on the antioxidant properties was studied. Overall, US treatment had no effect of the physical quality and antioxidant properties of calçots regardless the treatment time, while thermal processing produced an increase on the TAC and maintenance in TPC. Furthermore, the digestion process caused a remarkable decrease on the TAC and TPC, but that decrease was higher in roasted than in fresh samples. The microbial load of all US-treated fresh samples was below 6 log (cfu g−1) and a decrease of 1-log reduction was observed after treating for 45 min. Those results indicated that US pre-treatment had no negative effects on the quality of calçot while produced a decrease on the microbial load at high processing times.This work was supported by ACCIÓ (Generalitat of Catalonia, RD14-1-004), Sociedad Agrícola i Secció de Crèdit de Valls S.C.C.L., Cooperativa of Cambrils, and PGI ‘Calçot de Valls’. This work was also supported by the ‘Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement’ (FI-2017-B2-00164, L. Zudaire) and CERCA Programme of Generalitat de Catalunya. T. Lafarga is in receipt of a ‘Juan de la Cierva’ contract awarded by the Spanish Ministry of Economy, Industry, and Competitiveness (FJCI-2016-29541). I. Aguiló-Aguayo thanks the National Programme for the promotion of talent and its employability of the ‘Ministerio de Economía,Industria y Competitividad’ of the Spanish Government and to the European Social Fund for the Postdoctoral Senior Grant ‘Ramon y Cajal’ (RYC-2016-19949)

Decontamination of Listeria innocua from fresh-cut broccoli using UV-C applied in water or peroxyacetic acid, and dry-pulsed light

The efficacy of two irradiation technologies: Ultraviolet-C light (UV-C), applied in water or in diluted peroxyacetic acid, and dry-pulsed light (PL) for the inactivation and growth inhibition of Listeria innocua in fresh-cut broccoli were evaluated. Water-assisted UV-C (WUV) (0.3 and 0.5 kJ/m2) reduced L. innocua initial populations by 1.7 and 2.4 log10 CFU/g, respectively; the latter dose also inhibited their growth for 8 d at 5 °C. Replacing water with 40 or 80 mg/L peroxyacetic acid did not improve this efficacy. Pulsed light (5, 10, 15, and 20 kJ/m2) showed no effect on native microbiota. Neither did 15 kJ/m2 PL inactivate L. innocua or inhibit its growth. Nonetheless, 24-h post-processing, PL (15 kJ/m2) increased total phenolic content by 25% in respect of chlorine-sanitation, and enhanced total antioxidant capacity by 12 and 18% compared to water and chlorine controls, respectively. Unlike dry-PL, WUV appears to be a suitable technology for controlling L. monocytogenes populations in fresh-cut broccoli.This work has been supported by the CERCA Programme / Generalitat de Catalunya, the Secretaria d'Universitats i Recerca / Departament d'Economia i Coneixement / Generalitat de Catalunya, and the European Social Fund (grant FI-DGR-2015-0004); the University of Lleida (Ref.127/2016); the Spanish Ministry of Economy, Industry, and Competitiveness (grant FJCI-2016-29541); and the European Social Fund (grant RYC-2016-19949).The authors thank INRA (UMR SQPOV, Avignon), in particular Veronique Broussole and Fréderic Carlin, for providing access to the facilities. Thanks are also given to CLARANOR s.a. for allowing the use of the PL equipment, and in particular to Alain Berberian, for his technical assistance

Occurrence of selected viral and bacterial pathogens and microbiological quality of fresh and frozen strawberries sold in Spain

Strawberry production and exports have been increasing in Spain in recent decades. However, little information is available about their microbiological quality. Due to the growing concern about the microbial safety of these fruits, the objective of this investigation was to study the microbiological quality and the prevalence of the main foodborne pathogens on strawberries sold in Spain. Fresh (n = 152) and frozen (n = 31) samples were obtained from marketplaces and fields in 2017 and 2018. The samples were assayed for total aerobic mesophilic microorganisms (TAM), moulds and yeasts (M&Y), total coliforms (TC), Escherichia coli, Salmonella spp., Listeria monocytogenes as well as Norovirus (NoV) GI and GII. The microbiological counts ranged from <1.70 (detection limit, dl) - 5.89 log10 CFU/g (mean 3.78 log10 CFU/g) for TAM; 2.10-5.86 log10 CFU/g (mean 3.80 log10 CFU/g) for M and <0.70 (dl) - 4.91 log10 CFU/g (mean 2.15 log10 CFU/g) for TC in fresh strawberries. In frozen strawberries, the counts were <1.70 (dl) - 3.66 log10 CFU/g (mean 2.30 log10 CFU/g) for TAM; <1.70 (dl) - 2.76 log10 CFU/g (mean 1.82 log10 CFU/g) for M and <0.70(dl) - 1.74 log10 CFU/g (mean 0.77 log10 CFU/g) for TC. All the samples in this study tested negative for Salmonella spp., L. monocytogenes. E. coli and NoV GI and GII genome. A global overview of all the data was executed using Principal Component Analysis (PCA), and the results showed that the scores and loadings according to principal components 1 (PC1) and 2 (PC2) accounted for 75.9% of the total variance, allowing a distinction between fresh and frozen samples. The presence of moulds was significantly higher in the supermarket samples whereas the presence of total coliforms was significantly higher in the field samples (p < 0.05). Although pathogenic microorganisms were not found, preventative measures and prerequisites in the strawberry production chain must be considered in order to avoid possible foodborne diseases related to the microbiological quality of the fruit.The authors are grateful to the Spanish Government (Ministerio de Economia y Competitividad, Spain, research project AGL2016-78086-R) and the CERCA Programme of ‘Generalitat de Catalunya’ for its financial support. J. Ortiz-Solà thanks the University of Lleida for its PhD grant (UdL 2018)

An innovative water-assisted UV-C disinfection system to improve the safety of strawberries frozen under cryogenic conditions

Strawberries inoculated with Salmonella enterica, Listeria monocytogenes (108 CFU/mL, 50 μL) and murine norovirus (MNV-1; 106 TCID50/mL, 50 μL), were washed for 2 min in a water-assisted UV-C light tank (WUVC) combined or not with 40 mg/L of peracetic acid (WUVC+PA), and 200 mg/L of free chlorine solution (NaClO) with the UV-C lamps switched off. Moreover, a ‘conventional’ dry UV-C treatment (DUVC) was also tested. After 2-min exposure, washing sanitization with chemical agents gave the highest reduction for both bacteria (ca. ≥ 3.3 log CFU/g) and MNV-1 (≥1.8 log TCID50/mL). DUVC treatment proved to be the least effective technology (≤0.6 log CFU/g for bacteria and 1.5 log TCID50/mL for MNV-1). Regarding wash water, no presence of L. monocytogenes and S. enterica were reported with WUVC+PA and NaClO sanitization. After disinfection, samples were frozen at − 70 ± 2 ◦C in a cryogenic freezing cabinet with liquid nitrogen (N2). For both pathogens, frozen storage after washing substantially enhanced their inactivation in the first 3 days (1.1–4.9 log UFC/g) compared to the reductions obtained the following sampling points (0.0–0.8 log UFC/g). After 90 days, L. monocytogenes and S. enterica were not detected on the samples treated with water-assisted methodologies (WUVC, WUVC+PA and NaClO treatments), whilst MNV-1 was little affected. Further studies are needed to improve norovirus inactivation on frozen strawberries. Industrial relevance: The present work provides relevant information to the frozen food industry regarding a suitable decontamination alternative to chlorine sanitation. Low-dose immersion-assisted UV-C allows inactivation and inhibition of pathogenic microbiota while generates non-toxic byproducts and allows reusing the process water, contributing to the so-called “smart green growth” attended to provide a more innovative and sustainable future for the food industry.FRESAFE AGL2016-78086-