Effect of single or combined chemical and natural antimicrobial interventions on Escherichia coli O157:H7, total microbiota and color of packaged spinach and lettuce.

Aqueous extract of Origanum vulgare (oregano), sodium hypochlorite (60 and 300 ppm of free chlorine), Citrox® (containing citric acid and phenolic compounds [bioflavonoids] as active ingredients), vinegar, lactic acid, and double combinations of Citrox, lactic acid and oregano were evaluated against Escherichia coli O157:H7 and total mesophilic microbiota on fresh-cut spinach and lettuce and for their impact on color of treated vegetables. Spinach and lettuce leaves were inoculated with E. coli O157:H7 to a level of 5-6 log CFU/g and immersed in washing solutions for 2 or 5 min at 20 °C, followed by rinsing with ice water (30s). Bacterial populations on vegetables were enumerated immediately after washing and after storage of the samples at 5 °C for 7 days under 20% CO2: 80% N2. No significant post-washing microbial reductions were achieved by chlorinated water, whereas after storage total microbiota was increased by 2.4 log CFU/g on lettuce. Vinegar wash was the most effective treatment causing E. coli O157:H7 reductions of 1.8-4.3 log CFU/g. During storage, pathogen was further decreased to below the detection limit level (<2 log CFU/g) and total microbiota exhibited the highest reductions compared to other treatments. Lactic acid reduced pathogen by 1.6-3.7 log CFU/g after washing; however levels of total microbiota increased by up to 2 log CFU/g on packaged lettuce during storage. Washing lettuce samples with oregano for 2 min resulted in 2.1 log CFU/g reduction of E. coli O157:H7. When Citrox was combined with oregano, 3.7-4.0 log CFU/g reduction was achieved on spinach and lettuce samples, with no significant effect on color parameters. Additionally, rinsing with ice water after decontamination treatments contributed to maintenance of color of the treated vegetables. In conclusion, the results indicated that vinegar, lactic acid or oregano aqueous extract alone or in combination, as alternative washing solutions to chlorine, may be effectively used to control E. coli O157:H7 and sustain acceptable appearance of fresh cut spinach and lettuce.

Quality of fresh-cut baby spinach grown under a floating trays system as affected by nitrogen fertilisation and innovative packaging treatments.

BACKGROUND: Alternative techniques for cultivation of leafy vegetables such as a floating tray system and unconventional gas mixtures for post-harvest active modified atmosphere packaging (MAP) could be of interest in the minimally processed vegetable industry. RESULTS: The combined effect of three pre-harvest fertilisation doses (8, 12 or 16 mmol N L(-1)) and three post-harvest MAP conditions (passive, super-atmospheric or N2O-enriched) on the main quality attributes of fresh-cut baby spinach leaves throughout 10 days at 5 degrees C was studied. After 8 days of shelf life, spinach leaves fertilised with 8 and 16 mmol N L(-1) and stored under N2O-enriched MAP showed the lowest microbial growth, with good sensory quality. Such combined treatments also preserved the total antioxidant capacity sampled at harvest (8 g ascorbic acid equivalent antioxidant capacity kg(-1) f.w.). A decrease of 10-20% in total vitamin C content regardless of N fertilisation and packaging treatment was found during shelf life. Total phenolics content at harvest was 2 g gallic acid equivalents kg(-1) f.w., which was slightly decreased or preserved during shelf life while total chlorophylls were preserved for all treatments assayed around 550 mg kg(-1) f.w. CONCLUSION: No clear effect of fertilisation doses was observed during post-harvest storage on overall quality of fresh-cut baby spinach leaves, while N2O-enriched atmospheres seems to be a promising alternative to passive MAP for extending shelf life.

Fate of Escherichia coli O157:H7 in the presence of indigenous microorganisms on commercially packaged baby spinach, as impacted by storage temperature and time.

This study investigated the effect of storage temperature and time on the survival and growth of Escherichia coli O157:H7, the growth of indigenous microorganisms, and the changes in product quality of packaged baby spinach. Commercial packages of spinach within 2 days of processing were cut open at one end, sprayed with fine mists of E. coli O157:H7 inoculum, resealed, and then stored at 1, 5, 8, and 12 degrees C for 12 days until their labeled best-if-used-by dates. Microbial enumeration and product quality evaluation were conducted on day(s) 0, 3, 6, 9, and 12 postinoculation. Spinach held at 12 degrees C supported significant (P < 0.001) E. coli O157:H7 growth, with a 1.0-log CFU/g increase within 3 days postinoculation, which was followed by additional growth during continued storage. E. coli O157:H7 grew slowly when held at 8 degrees C, with a significant (P < 0.01) level of growth reached after 6 days of storage. However, on products held at 1 and 5 degrees C, E. coli O157:H7 populations declined significantly (P < 0.01 and P < 0.001, respectively) within 3 days of storage. Aerobic mesophilic bacteria, psychrotrophic bacteria, and yeast and mold populations increased significantly at all storage temperatures, with more growth on products held at elevated temperatures. Product quality scores remained high within the first 6 days of storage, with a sharp decline noted on samples held at 12 degrees C on day 9. Results suggest that E. coli O157:H7 can grow significantly on commercially packaged spinach held at 8 degrees C or above before significant product quality deterioration occurs.

The oral bioavailability of nitrate from nitrate-rich vegetables in humans.

High dietary nitrate intake may pose a risk to human health. Since up to 80-85% of dietary nitrate intake comes from vegetables, the aim of this study was to determine the absolute bioavailability of nitrate from three nitrate-rich vegetables. In an open, four-way cross-over, single dose study, 12 human subjects underwent the following treatments: (1) intravenous infusion of 500mg sodium nitrate, (2) oral administration of 300g cooked spinach, (3) oral administration of 300g raw lettuce, and (4) oral administration of 300g cooked beetroot. The wash-out period between treatments was at least 6 days. Plasma samples were analysed to assess the nitrate and nitrite concentrations, and pharmacokinetic parameters were calculated. The bioavailability of nitrate was 98+/-12% from cooked spinach, 114+/-14% from raw lettuce and 106+/-15% from cooked beetroot. There was no significant increase in plasma nitrite concentrations. This study shows that nitrate from vegetables, whether cooked or uncooked, is absorbed very effectively, resulting in an absolute nitrate bioavailability of around 100%. Thus, reducing the amount of nitrate in vegetables can be an effective measure to lower the systemic nitrate exposure of the general population. However, other aspects, such as the costs to produce vegetables with a low nitrate content and the possible beneficial effects of nitrate in vegetables, need to be considered when evaluating the usefulness of such a measure.

The use of bacterial alkaline phosphatase assay for rapid monitoring of bacterial counts on spinach.

This study was undertaken to evaluate the applicability of bacterial alkaline phosphatase (ALP) activity for rapid monitoring of total mesophilic bacteria counts in spinach. A set of fresh and decayed spinach mixtures were tested to rapidly (10 min) monitor spinach bacterial counts. To assay ALP activity, Lumigen APS-5 was used as a substrate. Bovine ALP was reduced after heat treatment at 75 degrees C for 1 min; in contrast, bacterial ALP activity increased. To differentiate bacterial ALP from other ALP, heat treatment (75 degrees C, 1 min) was applied before measurement. As a result, a regression equation was established between the actual mesophilic aerobic bacteria count and ALP activity of spinach mixtures (r= 0.90). The predicted total mesophilic aerobic bacterial count calculated from the fitted regression line (predicted log(10) CFU/g = 0.00056 x ALP values + 1.4002) showed a high correlation with the actual observed total bacterial count (r= 0.93). The ALP assay is a simple and rapid method to utilize for estimation of existing or contaminating microorganism levels on spinach.

E-Beam irradiation of bagged, ready-to-eat spinach leaves (Spinacea oleracea): an engineering approach.

We experimentally assessed the efficacy of electron beam irradiation to ensure the safety and quality of ready-to-eat spinach leaves using a 2-MeV Van de Graff accelerator. Spinach leaves (approximately 8 g) inside petri dishes were irradiated up to 1 kGy and stored at 4 degrees C for 15 d. Nonirradiated samples served as controls. Color, texture, vitamin C, total carotenoids, and chlorophyll content were measured using standard methods. Sensory analysis was performed by 15 untrained panelists using a 9-point hedonic scale. Color of control and irradiated samples showed slight variation throughout storage. Firmness of all samples changed significantly (P < 0.05) by half the storage time; however, exposure to radiation did not cause significant differences by the end of shelf life. Irradiation did not affect the chlorophyll and total carotenoid content, though it produced samples with significantly lower (P < 0.05) vitamin C content. For all treatments, chlorophyll content decreased by day 15 while total carotenoids remained constant. Although, by the end of refrigerated storage, all the irradiated samples received slightly lower odor scores, sensory analysis revealed that irradiation had little or no effect on the overall quality of spinach leaves. We also simulated the dose distribution within a bag of spinach leaves irradiated using a 10-MeV linear accelerator (0.3 to 1 kGy) to quantify the problem of nonuniform dose absorbed at different parts of the bag and predict death of a pathogen such as Escherichia coli O157:H7. The simulation results confirmed that it is feasible to irradiate baby spinach leaves (up to 1 kGy) to eliminate E. coli 0157:H7 while maintaining the overall quality of the produce.

Postprandial parathyroid hormone response to four calcium-rich foodstuffs.

We studied the effects of four calcium-rich foodstuffs on postprandial parathyroid hormone secretion. Four hundred milligrams calcium from either Emmental cheese, milk, sesame seeds, spinach, or calcium salt (calcium lactate gluconate + calcium carbonate) or no additional calcium (control session) were given to nine female volunteers immediately after a first blood sample (at 0900) in random order with a light standardized meal containing 37 mg Ca. Blood samples were taken at 0900 (before the calcium load), 1000, 1100, 1300, and 1500 at every study session. Urine was collected during the sessions. Serum ionized calcium, phosphate, magnesium, intact parathyroid hormone, and urinary calcium excretion were measured. The serum ionized calcium concentration increased significantly after ingesting cheese (P = 0.004, contrast analysis) or calcium salt (P = 0.05, contrast analysis) compared with the control session. Compared with the control session, the serum phosphate concentration increased after the cheese session (P = 0.004, contrast analysis) and after the milk session (P = 0.02, contrast analysis). Calcium salt (P = 0.007, contrast analysis) and cheese (P = 0.002, contrast analysis) caused a significant decline in serum intact parathyroid hormone compared with the control session. The urinary calcium excretion with cheese was 141% (P = 0.001), with milk was 107% (P = 0.004), and with calcium salt was 75% (P = 0.02) above that of the control session. Our results show that calcium from sesame seeds and spinach does not cause an acute response in calcium metabolism. Our results indicate that fermented cheese could be a better dietary source of calcium than milk when the metabolic effects of the foodstuffs are considered.

Bone composition and histological analysis of young and aged rats fed diets of varied calcium bioavailability.

OBJECTIVE: The effects of varied calcium bioavailability on bone development (young animal) and bone maintenance (aged animal) were evaluated by the application of bone composition and histologic/histomorphometric techniques. METHODS: Groups of male young (3-4 weeks old) and aged (24-month-old) rats were fed nutritionally-complete but calcium-restricted (0.15%) diets in which calcium was derived from spinach or nonfat dry milk (NFDM). A 0.5% calcium casein-based diet group was included as a comparison at the National Research Council's requirement level. All animals were pair-fed to the spinach-fed group. At the end of 60 days, lumbar vertebrae, tibia and femurs were harvested for bone histomorphometric and bone composition analyses. RESULTS: Histological analysis of the fifth lumbar vertebral body of the young spinach-fed group showed retarded development and mineralization of trabecular bone. Histomorphometry revealed that the spinach-fed group seemed to respond to the lower bioavailable calcium source by reducing the mineralization of bone matrix and stimulating bone resorption with a resultant decrease in bone volume (0.027, 0.059, 0.068 mm3 in spinach, NFDM and 0.5% calcium casein-based diet groups, respectively). The aged animals, however, appeared to respond to the reduction in available dietary calcium by mobilizing skeletal reserves, with a subsequent decrease in bone volume (0.057, 0.060, 0.073 mm3 in spinach, NFDM and 0.5% calcium casein-based diet groups, respectively). CONCLUSION: This study demonstrates that a low bioavailable calcium source, spinach, suppresses calcium deposition in bones of young animals resulting in a reduction in both quality and quantity of bone. Moreover, despite the stable structure of the mature bone, a low bioavailable calcium source may also compromise the skeletal integrity of the aged animal.