Process Wash Water Research Articles

Human intestinal enteroids and predictive models validate the operational limits of sanitizers used for viral disinfection of vegetable process wash water

Vegetables are globally associated with a considerable number of foodborne outbreaks caused by viral infections, specifically human norovirus. In fresh produce industry, washing represents a critical step for food safety as process wash water (PWW) needs to be maintained at appropriate microbial quality to prevent water-mediated cross-contamination. This study aimed to explore the disinfection efficacy of chlorine (free chlorine, FC), chlorine dioxide (ClO2) and peracetic acid (PAA) in PWW against infectious human norovirus and Tulane virus (TV). First, we tested the extent of TV inactivation in baby leaf, bell pepper, and vegetables mix PWW and monitored the viral decay by cell culture. Then, inactivation kinetics were defined for infectious human norovirus exposed to FC, ClO2 and PAA in baby leaves PWW using the human intestinal enteroids (HIE) system. Finally, kinetic inactivation models were fitted to TV reduction and decay of sanitizers to aid the implementation of disinfection strategies. Results showed that >8 log10 human norovirus and 3.9 log10 TV were inactivated by 20 ppm FC within 1 min; and by 3 ppm ClO2 in 1 min (TV) or 5 min (norovirus). PAA treatment at 80 ppm reduced ca. 2 log10 TV but not completely inactivated the virus even after 20 min exposure, while 5 min treatment prevented norovirus replication in HIE. TV inactivation in PWWs was described using an exponential decay model.Taking these data together, we demonstrated the value of applying the HIE model to validate current operational limits for the most commonly used sanitizers. The inactivation kinetics for human norovirus and TV, along with the predictive model described in this study expand the current knowledge to implement post-harvest produce safety procedures in industry settings.

Peroxyacetic acid and chlorine dioxide unlike chlorine induce viable but non-culturable (VBNC) stage of Listeria monocytogenes and Escherichia coli O157:H7 in wash water

The elaboration of guidelines for the industry to establish minimum concentration to prevent cross-contamination during washing practices based on operational limits is the core of the recommended criteria for the use of sanitizers. Several studies have evidenced that sanitizers reduced the levels of foodborne pathogens. However, they might lead to the progress into a viable but non-culturable (VBNC) state of the cells. This evidence has raised concerns regarding the effectiveness of the recommended washing practices for the inactivation of microbial cells present in the process wash water (PWW). The present study evaluated if the most commonly used sanitizers, including sodium hypochlorite (chlorine), peroxyacetic acid (PAA) and chlorine dioxide (ClO2) at established operational limits induced the VBNC stage of Listeria monocytogenes and Escherichia coli O157:H7. Prevention of cross-contamination was examined in four different types of PWW from washing shredded lettuce and cabbage, diced onions, and baby spinach under simulated commercial conditions of high organic matter and 1 min contact time. The results obtained for chlorine showed that recommended operational limits (20–25 mg/L free chlorine) were effective in inactivating L. monocytogenes and E. coli O157:H7 in the different PWWs. However, the operational limits established for PAA (80 mg/L) and ClO2 (3 mg/L) reduced the levels of culturable pathogenic bacteria but induced the VBNC state of the remaining cells. Consequently, the operational limits for chlorine are satisfactory to inactivate foodborne pathogens present in PWW and prevent cross-contamination but higher concentrations or longer contact times should be needed for PAA and ClO2 to reduce the likelihood of the induction of VBNC bacteria cells, as it represents a hazard.

Bacterial cell recovery after hollow fiber microfiltration sample concentration: Most probable bacterial composition in frozen vegetables

A commercial “concentrating pipette” was scrutinized from the perspective of sample volume reduction to augment native bacterial quantitation and identification within food samples. Aspects related to the elution protocol were evaluated for their impact on bacteria recovery. The results demonstrated there was no significant effect from different diluents/eluents on the relative recovery rate. Further, results from a complementary technique, dynamic light scattering, imply that recoveries less than unity are likely due to an inability to completely elute the bacterial cells from the capillary filter as opposed to bacterial injury caused by sample processing. When concentrating PBS washes from thawed frozen vegetables and enumerating after culturing at either 30 or 37 °C, the recovery rates were only slightly lower than the simplified experimental conditions. However, in food wash samples, significantly more mass-normalized bacteria were recovered at the lower culture temperature. Nevertheless, the vegetable wash concentration process did not change the most probable isolate composition relative to that of the controls at either culture temperature. The study demonstrates the potential for the system to serve as an effective tool for bacterial recovery and concentration within water-based food systems such as equipment rinses, process wash water, and other samples coming from food processing plants.

Practical applications of sensor-based methodologies for monitoring peracetic acid (PAA) as a disinfectant of fresh produce wash water

An accurate sensor for peracetic acid (PAA) is needed to monitor and control the disinfection of fresh produce wash water. Inaccurate measurements can result in underdosing and unsafe produce or overdosing with huge cost implications. In this study, five methods were compared for measuring PAA in process water from washing apples, tomatoes, red sweet peppers, and lemons. A reversed phase HPLC-DAD method for the determination of PAA in water was adapted for process wash water and used as a reference method. The results showed that HPLC offered high selectivity for PAA and precise and reproducible measurement for its quantification. However, as HPLC is not suitable for in-line applications in processing plants and requires highly skilled technicians, installation and maintenance costs, other analytical methods were examined including a redox titration, a reflectometric method and two electrochemical methods (an amperometric in-line probe and a chronoamperometric method with disposable single-use electrode sensor). The drop titration kit overestimated PAA because of the interferences from other oxidizing agents such as hydrogen peroxide (HP) apart from it required substantial time to perform the measurements plus the extensive training of the technical personnel to ensure confidence in the results. The reflectometric method with disposable test strips, although fast and objective, overestimated PAA due to the wash water with a high content of suspended organic matter that needed the addition of high concentrations of PAA, coexisting with HP. From the two electrochemical methods studied, the in-line amperometric sensor underestimated the PAA concentration in lemon wash water as the PAA could not freely diffuse through the membrane through the active electrode because of the organic matter present in the wash water released from the lemon peel. In contrast, the chronoamperometric sensor showed good selectivity for PAA without interferences, with reliable results across all the wash water types and PAA concentrations.

Evaluation of a sanitizing washing step with different chemical disinfectants for the strawberry processing industry

Strawberries are often consumed fresh or only receive minimal processing, inducing a significant health risk to the consumer if contamination occurs anywhere from farm to fork. Outbreaks of foodborne illness associated with strawberries often involve a broad range of microbiological agents, from viruses (human norovirus) to bacteria (Salmonella spp. and Listeria monocytogenes). The addition of sanitizers to water washes is one of the most commonly studied strategies to remove or inactivate pathogens on berries as well as avoid cross contamination due to reuse of process wash water. The risk posed with the safety issues of by-products from chlorine disinfection in the fruit industry has led to a search for alternative sanitizers. We evaluated the applicability of different chemical sanitizers (peracetic acid (PA), hydrogen peroxide (H2O2), citric acid (CA), lactic acid (LA) and acetic acid (AA)) for the inactivation of S. enterica, L. monocytogenes and murine norovirus (MNV-1) on strawberries. A control treatment with chlorine (NaClO) (100 ppm) was included. For each sanitizer, different doses (40, 80 and 120 ppm for PA and 1, 2.5 and 5% for H2O2, LA, AA and CA) and time (2 and 5 min) were studied in order to optimize the decontamination washing step. The best concentrations were 80 ppm for PA, 5% for H2O2 and 2.5% for organic acids (LA, AA and CA) after 2 min treatment. Results indicate that the sanitizers selected may be a feasible alternative to chlorine (100 ppm) for removing selected pathogenic microorganisms (P > 0.05), with reductions about ≥2 log for bacterial strains and ≥ 1.7 log for MNV-1. As the washing water may also increase the microbial counts by cross-contamination, we observed that no pathogenic bacteria were found in wash water after 5% H2O2 and 80 ppm PA after 2 min treatment. On the other hand, we also reported reductions about total aerobic mesophyll (TAM) (0.0–1.4 log CFU/g) and molds and yeasts (M&Y) (0.3–1.8 log CFU/g) with all alternative sanitizers tested. Strawberries treated did not shown significant differences about physio-chemical parameters compared to the untreated samples (initial). For this study, the optimal sanitizer selected was PA, due to the low concentration and cost needed and its microbiocidal effect in wash water and fruit. Notwithstanding the results obtained, the effect of PA in combination with other non-thermal technologies such as water-assisted ultraviolet (UV-C) light should be studied in future research to improve the disinfection of strawberries.

Detection and Quantification Methods for Viable but Non-culturable (VBNC) Cells in Process Wash Water of Fresh-Cut Produce: Industrial Validation.

The significance of viable but non-culturable (VBNC) cells in the food industry is not well known, mainly because of the lack of suitable detection methodologies to distinguish them from dead cells. The study aimed at the selection of the method to differentiate dead and VBNC cells of Listeria monocytogenes in process wash water (PWW) from the fruit and vegetable industry. Different methodologies were examined including (i) flow cytometry, (ii) viability quantitative polymerase chain reaction (v-qPCR) using an improved version of the propidium monoazide (PMAxx) dye as DNA amplificatory inhibitor, and (iii) v-qPCR combining ethidium monoazide (EMA) and PMAxx. The results showed that the flow cytometry, although previously recommended, was not a suitable methodology to differentiate between dead and VBNC cells in PWW, probably because of the complex composition of the water, causing interferences and leading to an overestimation of the dead cells. Based on results obtained, the v-qPCR combined with EMA and PMAxx was the most suitable technique for the detection and quantification of VBNC cells in PWW. Concentrations of 10 μM EMA and 75 μM PMAxx incubated at 40°C for 40 min followed by a 15-min light exposure inhibited most of the qPCR amplification from dead cells. For the first time, this methodology was validated in an industrial processing line for shredded lettuce washed with chlorine (10 mg/L). The analysis of PWW samples allowed the differentiation of dead and VBNC cells. Therefore, this method can be considered as a rapid and reliable one recommended for the detection of VBNC cells in complex water matrixes such as those of the food industry. However, the complete discrimination of dead and VBNC cells was not achieved, which led to a slight overestimation of the percentage of VBNC cells in PWW, mostly, due to the complex composition of this type of water. More studies are needed to determine the significance of VBNC cells in case of potential cross-contamination of fresh produce during washing.

Use of Chlorine Dioxide to Treat Recirculated Process Water in a Commercial Tomato Packinghouse: Microbiological and Chemical Risks

Antimicrobial treatment of fresh produce wash water can enable water reuse by avoiding microbial cross-contamination. In this study, the efficacy of chlorine dioxide (ClO2; 2-3 mg/L) to maintain the microbiological quality of process wash water in a tomato packinghouse was assessed. Different parameters were measured, including the physicochemical characteristics of the wash water (pH, oxidation-reduction potential (ORP), chemical oxygen demand (COD), absorbance at 254 nm (UVA254), temperature, electrical conductivity (EC)), the levels of different microorganisms present in water and in the product (aerobic mesophilic bacteria (AMB), total coliforms, yeasts and molds, E. coli), and the presence of chlorate as disinfection by-product. The treatment with ClO2 had a significant effect on the microbial populations present in the recirculated wash water and the tomatoes compared with the use of untreated recirculated water. The microbial load in tomatoes washed with tap water, and ClO2-treated recirculated water was similar. The transfer of chlorate from wash water to the fruits was very low under the conditions tested. The results obtained indicate that ClO2 could be a suitable option for the reuse of wash water in commercial packinghouses, as it reduces the microbial populations in wash water while not leading to the presence of disinfection by-products, such as chlorate, in the final product. This study shows that the monitorization and control of the microbiological quality of process wash water should be managed together with good practices able to guarantee hygienic conditions of the equipment by implementing efficient cleaning and disinfection systems.

Chlorination management in commercial fresh produce processing lines

Despite all the information available and the fact that the fresh produce industry has been active for more than 30 years, chlorination management of process wash water (PWW) still needs to be further optimized. It is necessary to adjust the chlorination management to the demanding goals of avoiding microbial cross-contamination and the presence of disinfection by-products (DBPs). In the present study, two commercial processing plants were examined, and the impact of chlorination management was studied by comparing two chlorine sources (chlorine gas and liquid chlorine) under manual and automatic control procedures. The effect of the reduction of water replenishment rates, product type and cut size, as well as product rinse, were also evaluated. Results showed that there was no presence of chlorate in PWW (<0.001 mg/L) and in the product (<0.001 mg/kg) when chlorine gas alone was used, while chlorate accumulation occurred in water (up to 16 mg/L) and product (>2 mg/kg) when liquid chlorine was combined to cope with the chlorine demand. Chlorination management using the automatic control system led to better free chlorine and pH regulation. pH levels using the automatic control were in the range 5.5–6.5, while pH was in the range 6.5–8.5 when using manual control systems. Fluctuations in the physicochemical and microbiological characteristics of PWW were linked to changes in product type and cut size. Chemical oxygen demand (COD) of PWW was twice as high when shredded lettuce was washed (1000–1800 mg/L) compared with chopped lettuce (500–900 mg/L). The microbial load in PWW was higher when washing baby leaves (≈4.0 log cfu/100 mL) compared with cut lettuce (≈2.5 log cfu/100 mL), and higher when washing shredded lettuce compared with chopped lettuce. Product type and cut size significantly affected chlorate residues removal by produce rinse. Tap water rinsing led to significant reductions (p < 0.05) in chlorate concentration in the case of chopped lettuce, but not in the case of shredded lettuce and baby leaves. This study highlights the importance of adequate chlorination management for chlorate residue mitigation, including the selection of chlorine source, control system, and proper water rinse. The concept that ‘one size does not fit all’ should be present when establishing the operational procedures for different commodities and product formats.

Operational limits of sodium hypochlorite for different fresh produce wash water based on microbial inactivation and disinfection by-products (DBPs)

The goal of the present study was to establish free chlorine operational limits for the disinfection of different types of fresh-cut produce wash water using sodium hypochlorite (NaClO). The proposed operational limits in the wash water are based on both the effectiveness of microbial inactivation and the occurrence of disinfection by-products (DBPs). For this purpose, lab-scale dynamic experiments were performed simulating the conditions of commercial fresh-cut processing lines. Different free chlorine (FC) concentrations (≈0, ≈10, ≈20, and ≈30 mg/L) were maintained in process wash water (PWW) of shredded iceberg lettuce, baby leaves (rocket, red oak leaf, and red swiss chard), shredded red cabbage and diced onions by means of the constant addition of the different doses of NaClO. Physicochemical characteristics of PWWs were monitored during the experiments including FC, total chlorine (TC), pH, temperature, oxidation-reduction potential (ORP), electrical conductivity (EC), chemical oxygen demand (COD), absorbance at 254 nm (UV254), and the presence of DBPs such as trihalomethanes (THMs), haloacetic acids (HAAs) and chlorate. The antimicrobial capacity of FC doses was evaluated by the inactivation of indigenous total aerobic bacteria (TAB). In all cases, FC had a significant antimicrobial effect (p < 0.05), but the operation limit differed depending on the type of PWW. A lower FC operational limit based on TAB counts of 10 mg/L was effective for onion PWW, while levels up to 20–25 mg/L were established for lettuce and cabbage PWWs. However, the levels of TAB in PWW of baby leaves were not controlled even at the highest FC concentration of 30 mg/L. The establishment of a maximum operational limit for FC based on the concentration of DBPs in PWW was not possible as even the lowest FC concentration (10 mg/L) would potentially lead to unacceptable levels of chlorate in the different types of product washed including lettuce, baby leaves, red cabbage and onion.

Disinfection by-products generated by sodium hypochlorite and electrochemical disinfection in different process wash water and fresh-cut products and their reduction by activated carbon

Antimicrobial treatment of fresh produce process wash water (PWW) needs to be optimized to improve the microbiological safety while minimizing the presence of disinfection by-products (DBPs) that can be adsorbed by the washed produce. In this study, the occurrence of DBPs including trihalomethanes (THMs) and chlorate in the PWW of shredded lettuce, baby spinach and shredded carrots treated with sodium hypochlorite (NaClO), and electrochemical disinfection (ED) was assessed. The potential of activated carbon (AC) filtration treatment for the reduction of DBPs was also evaluated. Results showed that both antimicrobial treatments caused the accumulation of DBPs in PWW, reaching concentrations above the legal limits for potable water. However, there were significant differences in the concentration of DBPs due to the type of washed product and antimicrobial treatment. There was a lower accumulation of THMs in spinach PWW compared with lettuce and carrot PWWs. Electrochemical disinfection generated higher concentrations of DBPs in the PWW, but a significant reduction was observed when using AC. Such reduction led to a lower accumulation of chlorate in the washed produce. The presence of THMs in PWW was not relevant when using these chlorine-based antimicrobial treatments as there was a limited transfer of THMs to the washed produce. On the contrary, a significant migration of chlorate from the PWW to the washed product occurred, even when the AC was used as a mitigation treatment.

Electrochemical disinfection of process wash water for the fresh-cut industry

Electrochemical disinfection of process wash water for the fresh-cut industry

Microbial and chemical characterization of commercial washing lines of fresh produce highlights the need for process water control

Abstract Process wash water and washed products from three different fresh produce processing lines were characterized at commercial scale. Different physicochemical and microbiological characteristics of wash water were measured. Great variability between processing lines on the physicochemical quality of process wash water was observed, caused in part by the type of produce washed. The relationship between lower aerobic mesophilic bacteria and higher free chlorine (FC) concentrations in wash water was detected (Pearson's correlation coefficient (PCC) = −0.53). Independently of the FC concentration, most of the water samples (>80%) showed presence of cultivable (limit of detection 1 CFU/100 mL), probably caused by the uncontrolled pH conditions. Higher values of FC and oxidation-reduction potential (ORP) in wash water were related to lower microbial load in washed produce (PCC = −0.82, and − 0.79, respectively). Higher concentration of chlorine was linked to a higher presence of disinfection by-products (DBPs) in the wash water, and washing in chlorinated water led to a significant increase in the concentration of DBPs in produce. However, the accumulation of trihalomethanes (THMs) in process wash water was not correlated with higher concentrations of these DBPs in produce. Industrial relevance The washing step of fresh produce processing lines is a critical process. The dose of disinfectants needs to be adequately optimized to avoid microbial contamination without generating the accumulation of disinfection by-products (DBPs). In this study, critical parameters that influence the efficacy of water disinfection and the occurrence of DBPs in fresh produce processing lines were identified under commercial conditions. The results evidenced that monitoring and control of pH play a critical role by maximizing the concentration of the most active form of chlorine in the water. The parameter UV254 measured on-line in the washing tank, can be suggested as a suitable indicator of the presence of organic matter in fresh produce wash water.

Efficacy of chlorine dioxide on Escherichia coli inactivation during pilot-scale fresh-cut lettuce processing

Controlling water quality is critical in preventing cross-contamination during fresh produce washing. Process wash water (PWW) quality can be controlled by implementing chemical disinfection strategies. The aim of this study was to evaluate the pilot-scale efficacy of chlorine dioxide (ClO2) during processing on the reduction of Escherichia coli in the PWW and on processed fresh-cut ‘Lollo Rossa’ lettuce. The objective was to have a residual target concentration of either 5 or 3 mg/L ClO2 in the washing tank (3.5 m3) before and during 800 kg of lettuce processing (90 min). After 90 min., a nonpathogenic, non-Extended Spectrum Beta-Lactamase (ESBL) E. coli inoculum from an overnight culture broth (37 °C) was added to the tank resulting in an approximate final level of 106 CFU/mL. PWW and lettuce samples for microbiological and chemical analyses were taken before and after the input and supply halted. ClO2 concentrations quickly decreased after ClO2 input halted, yet a residual concentration of ≥2.5 mg/L and ≥2.1 mg/L ClO2, respectively for 5 and 3 mg/L pilots, was present 12 min after the supply halted. No detectable levels of E. coli (limit of detection 5 log) were determined in the water within 1 min after E. coli was added to the ClO2 containing wash water. Results demonstrated that ClO2 use at the semi-commercial pilot scale was able to reduce the E. coli peak contamination in the PWW. After storage (5 days, 4 °C), background microbial communities (i.e., fluorescent Pseudomonads and total heterotrophic bacteria) grew out on lettuce. Overall, ClO2 decreased the potential for cross-contamination between batches compared to when no sanitizer was used. Chlorate levels of the lettuce sampled before entering the wash water ranged from 7.3–11.6 μg/kg. The chlorate levels of the lettuce sampled after being washed in the ClO2 containing wash water, as well as after rinsing and centrifugation, ranged from 22.8–60.4 μg/kg; chlorite levels ranged from 1.3–1.6 mg/kg, while perchlorate levels were below the limit of quantification (LOQ, <5 ng/g). In this study, we report the semi-commercial pilot-scale evaluation of ClO2, for its ability to maintain the PWW quality and to prevent cross-contamination in the washing tank during fresh-cut lettuce processing. Furthermore, we provide quantitative values of ClO2 disinfection by-products chlorate and chlorite as well as of perchlorate from PWW and/or lettuce samples.

The efficacy of chemical sanitizers on the reduction of Salmonella Typhimurium and Escherichia coli affected by bacterial cell history and water quality

Washing fresh produce with potable water helps to remove microorganisms, providing about a 1- to 2-log reduction, but this process can also pose an opportunity for cross-contamination of bacteria in the washing tank. The objective of this study was to evaluate the efficacy of three chemical sanitizers, sodium hypochlorite, chlorine dioxide, and a silver-copper solution on the reduction of S. Typhimurium and extended-spectrum beta-lactamase (ESBL) E. coli as well as to evaluate the impact bacterial cell history and water quality had on sanitizer efficacy. This was investigated with three scenarios representing different contamination routes and history of cells: (i) on starved and non-starved cells in potable water, (ii) on starved and non-starved cells in lettuce wash water and on lettuce leaf punches, and (iii) on non-starved cells in organically loaded process wash water (PWW). Sodium hypochlorite (NaClO) and chlorine dioxide (ClO2) were more effective in preventing cross-contamination in the potable water than the silver-copper solution. Starved and non-starved bacterial cells displayed minor differences in their susceptibility to sanitizing agents in the (i) potable water and (ii) lettuce wash water demonstrating that other conditions greater influenced sanitizer efficacy. Particularly, the organic load of the water, wash water temperature, and pathogen attachment and release from the produce were shown to affect a sanitizer's efficacy during washing. Furthermore, results emphasize that chemical sanitizer use should focus more on wash water disinfection, rather than produce decontamination, to prevent pathogenic cross-contamination during processing. Future research should investigate the feasibility of ClO2 application during pilot-scale processing.

A novel electrochemical device as a disinfection system to maintain water quality during washing of ready to eat fresh produce

Electrolyzed water (EW) is known by its bactericidal efficacy and capability to oxidize organic matter. The present research evaluated the efficacy of recently developed electrolytic cells able to generate higher concentration of reactive oxygen species using lower power and salt concentration than conventional cells. This study tested the inactivation of Escherichia coli O157:H7, the organic matter depletion and trihalomethane (THM) generation by EW in process wash water under dynamic conditions. To achieve this, clean tap water was continuously added up to 60 min with artificial process water with high chemical oxygen demand (COD) inoculated with E. coli O157:H7, in experiments performed in a pilot plant that recirculated water through one electrolytic cell. Plate counts of E. coli O157:H7, COD, THMs, free, combined and total chlorine, pH, temperature and oxidation-reduction potential were determined. Results indicate that the novel electrolysis system combined with minimal addition of NaCl (0.05%) was able to suppress E. coli O157:H7 population build-up and decreased the COD accumulation in the process wash water. THM levels in the water were relatively high but its concentration in the washed product was marginal. Highly effective electrolysis has been proven to reduce the occurrence of foodborne diseases associated to cross-contamination in produce washers without having an accumulation of THMs in the washed product.

Water and detergent recovery from rinsing water in an industrial environment

Wash water streams coming from rinsing of equipment in a detergent production site is in many cases considered as waste. On site treatment in waste water plants is possible but typically requires advanced oxidation process (AOP) technology which uses chemicals and creates a waste sludge. A new treatment approach, based on nanofiltration, has been demonstrated at industrial scale in a detergent production site in China. Wash water could be split into a concentrate stream and water fraction. The concentrate stream contains most of the valuable surfactants and has a value to recycle. The water fraction can easily be polished by MBR to feed cooling towers. As such, this production site does not discharge any process wash water and recovers all resources out of the rinsing water: both chemicals (as surfactants) as the water.

Superhydrophilic anti-fouling electrospun cellulose acetate membranes coated with chitin nanocrystals for water filtration

Electrospun cellulose acetate (CA) random mats were prepared and surface coated with chitin nanocrystals (ChNC) to obtain water filtration membranes with tailored surface characteristics. Chitin nanocrystals self-assembled on the surface of CA fibers into homogenous nanostructured networks during drying that stabilized via hydrogen bonding and formed webbed film-structures at the junctions of the electrospun fibers. Coating of CA random mats using 5% chitin nanocrystals increased the strength by 131% and stiffness by 340% accompanied by a decrease in strain. The flux through these membranes was as high as 14217Lm−2h−1 at 0.5bar. The chitin nanocrystal surface coating significantly impacted the surface properties of the membranes, producing a superhydrophilic membrane (contact angle 0°) from the original hydrophobic CA mats (contact angle 132°). The coated membranes also showed significant reduction in biofouling and biofilm formation as well as demonstrated improved resistance to fouling with bovine serum albumin and humic acid fouling solutions. The current approach opens up an easy, environmental friendly and efficient route to produce highly hydrophilic membranes with high water flux and low fouling for microfiltration water purification process wash water from food industry for biological contaminants.

Should chlorate residues be of concern in fresh-cut salads?

Chlorine remains the most popular method used by the fresh produce industry for decontamination. However, the occurrence of disinfection by-products (DBP) derived from chlorine-based disinfectants has been highlighted as a problem. After recent reports, chlorate residues in fresh produce are of concern in Europe. This study evaluated the chlorate accumulation in process wash water and the residues in fresh-cut lettuce when sodium hypochlorite was used as a wash aid. At a commercial processing facility, total chlorine was continually added to achieve a free chlorine level of 1–80 mg L−1 for water disinfection as the organic load measured as chemical oxygen demand (COD) increased over time (1000–1500 mg O2 L−1). This resulted in chlorate accumulation (19–45 mg L−1) in the process water. When fresh-cut lettuce was washed in that water, chlorate residues were detected in the lettuce and the concentrations increased linearly with the repeated use of the same process water, reaching concentrations of 4.5–5.0 mg kg−1. To understand the chlorate accumulation in the process wash water, several experiments were performed at a pilot plant scale with different levels of COD and free chlorine. There was a significant (p < 0.001) correlation (R = 0.91) between the total added chlorine and the chlorate accumulation in the process water. We demonstrated that the added chlorine needed to maintain a free chlorine level in the process water was the contributing factor to chlorate accumulation. Chlorate residues in the washed fresh-cut lettuce after rinsing for 1 min in tap water and in commercial bags were below the limit of quantification. This study contributes to the knowledge of chlorate accumulation in the process water when sodium hypochlorite was used as a sanitizer.

Effect of Disinfectants on Preventing the Cross-Contamination of Pathogens in Fresh Produce Washing Water.

The potential cross-contamination of pathogens between clean and contaminated produce in the washing tank is highly dependent on the water quality. Process wash water disinfectants are applied to maintain the water quality during processing. The review examines the efficacy of process wash water disinfectants during produce processing with the aim to prevent cross-contamination of pathogens. Process wash water disinfection requires short contact times so microorganisms are rapidly inactivated. Free chlorine, chlorine dioxide, ozone, and peracetic acid were considered suitable disinfectants. A disinfectant’s reactivity with the organic matter will determine the disinfectant residual, which is of paramount importance for microbial inactivation and should be monitored in situ. Furthermore, the chemical and worker safety, and the legislative framework will determine the suitability of a disinfection technique. Current research often focuses on produce decontamination and to a lesser extent on preventing cross-contamination. Further research on a sanitizer’s efficacy in the washing water is recommended at the laboratory scale, in particular with experimental designs reflecting industrial conditions. Validation on the industrial scale is warranted to better understand the overall effects of a sanitizer.

Methodology for modeling the disinfection efficiency of fresh-cut leafy vegetables wash water applied on peracetic acid combined with lactic acid

A methodology to i) assess the feasibility of water disinfection in fresh-cut leafy greens wash water and ii) to compare the disinfectant efficiency of water disinfectants was defined and applied for a combination of peracetic acid (PAA) and lactic acid (LA) and comparison with free chlorine was made. Standardized process water, a watery suspension of iceberg lettuce, was used for the experiments. First, the combination of PAA+LA was evaluated for water recycling. In this case disinfectant was added to standardized process water inoculated with Escherichia coli (E. coli) O157 (6logCFU/mL). Regression models were constructed based on the batch inactivation data and validated in industrial process water obtained from fresh-cut leafy green processing plants. The UV254(F) was the best indicator for PAA decay and as such for the E. coli O157 inactivation with PAA+LA. The disinfection efficiency of PAA+LA increased with decreasing pH. Furthermore, PAA+LA efficacy was assessed as a process water disinfectant to be used within the washing tank, using a dynamic washing process with continuous influx of E. coli O157 and organic matter in the washing tank. The process water contamination in the dynamic process was adequately estimated by the developed model that assumed that knowledge of the disinfectant residual was sufficient to estimate the microbial contamination, regardless the physicochemical load. Based on the obtained results, PAA+LA seems to be better suited than chlorine for disinfecting process wash water with a high organic load but a higher disinfectant residual is necessary due to the slower E. coli O157 inactivation kinetics when compared to chlorine.