María V. Selma

Interaction between Phenolics and Gut Microbiota: Role in Human Health

Dietary phenolic compounds are often transformed before absorption. This transformation modulates their biological activity. Different studies have been carried out to understand gut microbiota transformations of particular polyphenol types and identify the responsible microorganisms. Although there are potentially thousands of different phenolic compounds in the diet, they are typically transformed to a much smaller number of metabolites. The aim of this review was to discuss the current information about the microbial degradation metabolites obtained from different phenolics and their formation pathways, identifying their differences and similarities. The modulation of gut microbial population by phenolics was also reviewed in order to understand the two-way phenolic-microbiota interaction. Clostridium and Eubacterium genera, which are phylogenetically associated, are other common elements involved in the metabolism of many phenolics. The health benefits from phenolic consumption should be attributed to their bioactive metabolites and also to the modulation of the intestinal bacterial population.

Fresh-cut product sanitation and wash water disinfection: Problems and solutions

It is well known that fresh-cut processors usually rely on wash water sanitizers to reduce microbial counts in order to maintain quality and extend shelf-life of the end product. Water is a useful tool for reducing potential contamination but it can also transfer pathogenic microorganisms. Washing with sanitizers is important in fresh-cut produce hygiene, particularly removing soil and debris, but especially in water disinfection to avoid cross-contamination between clean and contaminated product. Most of the sanitizing solutions induce higher microbial reduction after washing when compared to water washing, but after storage, epiphytic microorganisms grow rapidly, reaching similar levels. In fact, despite the general idea that sanitizers are used to reduce the microbial population on the produce, their main effect is maintaining the microbial quality of the water. The use of potable water instead of water containing chemical disinfection agents for washing fresh-cut vegetables is being advocated in some European countries. However, the problems of using an inadequate sanitizer or even none are considered in this manuscript. The need for a standardized approach to evaluate and compare the efficiency of sanitizing agents is also presented. Most new alternative techniques accentuate the problems with chlorine suggesting that the industry should move away from this traditional disinfection agent. However, the use of chlorine based sanitizers are presented as belonging to the most effective and efficient sanitizers when adequate doses are used. In this review improvements in water disinfection and sanitation strategies, including a shower pre-washing step and a final rinse of the produce, are suggested.

Anti-inflammatory properties of a pomegranate extract and its metabolite urolithin-A in a colitis rat model and the effect of colon inflammation on phenolic metabolism.

Whether the beneficial effects of pomegranate are due to the ellagitannins or to their microbiota-derived urolithins is not known. Our objectives were to evaluate the effects of pomegranate intake and its main microbiota-derived metabolite urolithin-A (UROA) on colon inflammation and to assess whether UROA is the main anti-inflammatory compound. In addition, the effect of the inflammation on the phenolic metabolism was also explored. Male Fisher rats were fed with 250 mg kg(-1) day(-1) pomegranate extract (PE) or 15 mg kg(-1) day(-1) UROA for 25 days. Dextran sodium sulfate (5%) (DSS) was administered for the five last days and then rats were euthanized. DSS is a well-known model of inflammatory bowel disease. Colon tissue damage, microbiota changes, antioxidant status, prostaglandin E(2) (PGE(2)), nitric oxide production, inducible nitric oxide synthase (iNOS), prostaglandin E synthase (PTGES), gene expression (microarrays and RT-PCR) and polyphenol metabolism (LC-MS-MS) were evaluated. Both PE and UROA decreased inflammation markers (iNOS, cycloxygenase-2, PTGES and PGE(2) in colonic mucosa) and modulated favorably the gut microbiota. The G(1) to S cell cycle pathway was up-regulated in both groups. UROA group showed various down-regulated pathways, including that of the inflammatory response. PE, but not UROA, decreased oxidative stress in plasma and colon mucosa. Only UROA preserved colonic architecture. The normal formation of urolithins in PE-fed rats was prevented during inflammation. Our results suggest that UROA could be the most active anti-inflammatory compound derived from pomegranate ingestion in healthy subjects, whereas in colon inflammation, the effects could be due to the nonmetabolized ellagitannin-related fraction.

Effect of a low dose of dietary resveratrol on colon microbiota, inflammation and tissue damage in a DSS-induced colitis rat model.

The naturally occurring polyphenol resveratrol has been acknowledged with health-beneficial properties. Most of the studies dealing with its in vivo effects assay huge doses, not representative from a dietary point of view. Our aim was to ascertain whether resveratrol can exert anti-inflammatory activity in vivo at an attainable dietary dose. Rats were fed with 1 mg of resveratrol/kg/day (a human equivalent dose) for 25 days, and in the last 5 days, 5% dextran sulfate sodium (DSS) was administered to induce colitis. Effects on colon tissue damage, gut microbiota, reactive oxygen species, inflammatory markers and nitric oxide production as well as gene expression profile with microarrays were evaluated. Resveratrol increased lactobacilli and bifidobacteria as well as diminished the increase of enterobacteria upon DSS treatment. Resveratrol significantly protected the colonic mucosa architecture, reduced body weight loss, diminished the induced anemia and reduced systemic inflammation markers, colonic mucosa prostaglandin E(2), cycloxygenase-2, prostaglandin E synthase and nitric oxide levels. In addition, the expression of 2,655 genes in distal colon mucosa related to important pathways was varied. These results reinforce the concept of resveratrol as a dietary beneficial compound in intestinal inflammation at doses possibly attainable with resveratrol-enriched nutraceuticals.

Prevention of Escherichia coli cross-contamination by different commercial sanitizers during washing of fresh-cut lettuce.

The efficacy of fresh-cut produce sanitizers has mainly been evaluated by measuring microbial reductions on produce. However, its suitability to ensure that pathogens are rapidly killed avoiding cross-contamination of subsequent product also needs to be considered. The efficacy of chlorine, Tsunami, Citrox and Purac on non pathogenic Escherichia coli reductions in processing water and on fresh-cut lettuce were studied. Selection of minimum effective doses was carried out in processing water, which contained a chemical oxygen demand (COD) within the range of 700-1000 mg/l and a total mesophilic load of about 7 log CFU/ml. The processing water was inoculated with two inoculum levels (3 and 5 log CFU/ml). It was observed that 40 mg/l of chlorine and 500 mg/l of Tsunami were effective in reducing the inoculum levels in the processing water to the detection limit (5 and 4 log units). However, Citrox and Purac were not effective in reducing E. coli population even at the highest manufacturers recommended doses. Evaluation of cross-contamination in fresh-cut lettuce was carried out by measuring E. coli transfer from inoculated (~5 log CFU/g) to uninoculated lettuce after washing the contaminated product in the water containing different sanitizing agents. Chlorine and Tsunami were able to inactivate E. coli in wash water, avoiding cross-contamination between contaminated and non-contaminated product. However, Citrox and Purac at the recommended doses did not prevent transfer of E. coli cells between inoculated and uninoculated fresh-cut lettuce and therefore indicating cross-contamination. The results obtained show that chlorine and Tsunami are recommended as water disinfection agents preventing E. coli cross-contamination of produce during processing.

Disinfection potential of ozone, ultraviolet-C and their combination in wash water for the fresh-cut vegetable industry

The purpose of this research was to investigate the disinfection efficacy of ozone (O(3)) and UV-C illumination (UV), and their combination (O(3)-UV) for reducing microbial flora of fresh-cut onion, escarole, carrot, and spinach wash waters collected from the industry. Furthermore, the influence of water physicochemical parameters on the decontamination efficacy and the effect of these technologies on physicochemical quality of wash water were analyzed. O(3), UV, and O(3)-UV were effective disinfection treatments on vegetable wash water, with a maximum microbial reduction of 6.6 log CFU mL(-1) after 60 min treatment with O(3)-UV. However, maximum total microbial reductions achieved by UV and O(3) treatments after 60 min were 4.0 and 5.9 log CFU mL(-1), lower than by O(3)-UV treatment. Furthermore, turbidity of wash water was reduced significantly by O(3) and O(3)-UV treatments, while UV treatment did not affect the physicochemical quality of the water. Conclusions derived from this study illustrate that O(3) and O(3)-UV are alternatives to other sanitizers used in the fresh-cut washing processes. The use of these technologies would allow less frequent changing of spent water and the use of much lower sanitizer doses. Nevertheless, in specific applications such as carrot wash water, where levels of undesirable microbial and chemical constituents are lower than other vegetable wash water, UV treatment could be an appropriate treatment considering cost-effectiveness criteria.

Cross-contamination of fresh-cut lettuce after a short-term exposure during pre-washing cannot be controlled after subsequent washing with chlorine dioxide or sodium hypochlorite

Chlorine dioxide (ClO(2)) has been postulated as an alternative to sodium hypochlorite (NaClO) for fresh-cut produce sanitization to avoid risks associated with chlorination by-products. Experiments were performed to determine the prevention of cross-contamination of fresh-cut lettuce by Escherichia coli using chlorine dioxide (3 mg/L) or sodium hypochlorite (100 mg/L) as sanitation agents. The efficacy of these sanitation solutions was evaluated simulating as much as possible the conditions of a fresh-cut processing line. Thus, to evaluate the potential risk of cross-contamination during pre-washing, inoculated fresh-cut lettuce was pre-washed and after that non-inoculated lettuce was then pre-washed in the same water. After this pre-washing, non-inoculated lettuce was cross-contaminated, changing from 0 to 3.4 log units of E. coli cells. During washing with sanitizers, none of the tested sanitation agents significantly reduced E. coli counts in both inoculated and cross-contaminated lettuce. These results suggest that when cross-contamination occurs, even if the event is recent, subsequent sanitation steps are inefficient for inactivating E. coli cells on the vegetable tissue. However, chlorine dioxide and sodium hypochlorite solutions were able to inactivate most E. coli cells that passed from inoculated product to wash water. Therefore, they might be able to avoid cross-contamination between clean and contaminated product during the washing step. Scanning electron microscopy micrographs indicated that bacterial cells were mainly located in clusters or tissue stomata where they might be protected, which explains the low efficacy of sodium hypochlorite and chlorine dioxide solutions observed in this study.

Pre- and Postharvest Preventive Measures and Intervention Strategies to Control Microbial Food Safety Hazards of Fresh Leafy Vegetables

This review includes an overview of the most important preventive measures along the farm to fork chain to prevent microbial contamination of leafy greens. It also includes the technological and managerial interventions related to primary production, postharvest handling, processing practices, distribution, and consumer handling to eliminate pathogens in leafy greens. When the microbiological risk is already present, preventive measures to limit actual contamination events or pathogen survival are considered intervention strategies. In codes of practice the focus is mainly put on explaining preventive measures. However, it is also important to establish more focused intervention strategies. This review is centered mainly on leafy vegetables as the commodity identified as the highest priority in terms of fresh produce microbial safety from a global perspective. There is no unique preventive measure or intervention strategy that could be applied at one point of the food chain. We should encourage growers of leafy greens to establish procedures based on the HACCP principles at the level of primary production. The traceability of leafy vegetables along the chain is an essential element in ensuring food safety. Thus, in dealing with the food safety issues associated with fresh produce it is clear that a multidisciplinary farm to fork strategy is required.

Impact of Wash Water Quality on Sensory and Microbial Quality, Including Escherichia coli Cross-Contamination, of Fresh-Cut Escarole

The influence of wash water quality on the microbial load and sensory quality of fresh-cut escarole was evaluated. Additionally, the degree of Escherichia coli cross-contamination between inoculated and uninoculated products after washing was also studied. Three types of wash water, i.e., potable water, diluted recirculated water, and recirculated water, containing different microbial counts and organic loads, were used. Results showed that microbial load (P > or = 0.02) and sensory quality (P > 0.625) of the product were not influenced by the water quality after washing and storage. Cross-contamination between inoculated and uninoculated products was observed after washing, as there was significant transmission of E. coli cells from the product to the wash water (P < 0.001). When fresh-cut escarole was contaminated at a high inoculum level (5.1 log CFU/g), wash water quality influenced the level of cross-contamination, as the highest E. coli load (P < 0.001) was shown in uninoculated fresh-cut escarole washed with recirculated water. However, when fresh-cut escarole was contaminated at a low inoculum level (3.2 log CFU/g), the wash water quality did not influence the level of cross-contamination, as E. coli slightly increased, although not at a statistically significant level, after the uninoculated product was washed with recirculated water (P > 0.035). Therefore, the contamination level may impact the effectiveness of water quality to reduce pathogen concentrations. It was clearly observed that cross-contamination of fresh-cut escarole with E. coli occurs, thereby suggesting that small amounts of contamination could impact the overall product and indicating the necessity of using wash water sanitizers to eliminate pathogens.

Reduction by gaseous ozone of Salmonella and microbial flora associated with fresh-cut cantaloupe

This research investigates the efficacy of gaseous ozone, applied under partial vacuum in a controlled reaction chamber, for the elimination of Salmonella inoculated on melon rind. The performance of high dose, short duration treatment with gaseous ozone, in this pilot system, on the microbial and sensory quality of fresh-cut cantaloupes was also evaluated. Gaseous ozone (10,000 ppm for 30 min under vacuum) reduced viable, recoverable Salmonella from inoculated physiologically mature non-ripe and ripe melons with a maximum reduction of 4.2 and 2.8 log CFU/rind-disk (12.6 cm(2)), respectively. The efficacy of ozone exposure was influenced by carrier matrix. Salmonella adhering to cantaloupe was more resistant to ozone treatment when suspended in skim-milk powder before aqueous inoculation to the rind. This indicated that organic matter interferes with the contact efficiency and resultant antimicrobial activity of gaseous ozone applied as a surface disinfectant. Conversely, in the absence of an organic carrier, Salmonella viability loss was greater on dry exocarp surfaces than in the wetted surfaces, during ozone treatment, achieving reductions of 2.8 and 1.4 initial log CFU/rind-disk, respectively. Gaseous ozone treatment of 5000 and 20,000 ppm for 30 min reduced total coliforms, Pseudomonas fluorescens, yeast and lactic acid bacteria recovery from fresh-cut cantaloupe. A dose Ct-value (concentration x exposure time) of 600,000 ppm min achieved maximal log CFU/melon-cube reduction, under the test conditions. Finally, fresh-cut cantaloupe treated with gaseous ozone, maintained an acceptable visual quality, aroma and firmness during 7-day storage at 5 degrees C. Conclusions derived from this study illustrate that gaseous ozone is an effective option to risk reduction and spoilage control of fresh and fresh-cut melon. Moreover, depending on the timing of contamination and post-contamination conditions, rapid drying combined with gaseous ozone exposure may be successful as combined or sequential disinfection steps to minimize persistence of Salmonella on the surface of cantaloupe melons and transference during fresh-cut processing of home preparation. Based on these results, greater efficacy would be anticipated with mature but non-ripe melons while ripe tissues reduce the efficacy of these gaseous ozone treatments, potentially by oxidative reaction with soluble refractive solids.