Microbiological evaluation of fresh-cut organic vegetables produced in Zambia

This study was undertaken to assess the microbiological quality of fresh-cut organic vegetables produced in Zambia. Fresh-cut organic mixed vegetables and green beans produced in Zambia were analysed for aerobic plate counts, coliforms, Enterobacteriaceae, Escherichia coli, Bacillus cereus, Clostridium perfringens, Listeria monocytogenes, Salmonella spp., Staphylococcus aureus, and yeast and mould counts. The study included 160 samples for most of the parameters. The vegetables were grown on farms meant primarily for the export market. The vegetables were treated/washed with 150 μg ml⁻¹ chlorine solution at the processing plant prior to sampling. The aerobic plate count ranged between 3 log₁₀ and 9.7 log₁₀ CFU/g, with the highest count recorded for green beans. The largest grouping (26.1%) of vegetable samples fell between 3 and 4 log₁₀ CFU/g. Coliform counts were between 1.0 log₁₀ and 7.7 log₁₀ CFU/g. The highest incidence level was 31.4% for total coliform counts between 3 log₁₀ and 4 log₁₀ CFU/g. E. coli was only detected on mixed vegetables in the range of 0.6 log₁₀ to 3 log₁₀ CFU/g, while Enterobacteriaceae counts ranged between 1.6 log₁₀ and 9.8 log₁₀ CFU/g with the highest counts being found on green beans. The highest incidence level was of 25.8% for counts within the same range as the aerobic plate counts. Yeast and mould counts showed the highest incidence level between 5 log₁₀ and 6 log₁₀ CFU/g with an overall range between 1.5 log₁₀ and 5.6 log₁₀ CFU/g. L. monocytogenes, Salmonella spp. and S. aureus were detected in 20%, 23.1% and 83.9% of samples, respectively . C. perfringens and B. cereus were not detected in any of the samples analysed.     

Disinfection efficacy of slightly acidic electrolyzed water on fresh cut cabbage

A chlorine sanitizer that gives high disinfection efficacy with minimal available chlorine has a potential to be an environmentally-friendly method for disinfection of vegetables. In the present study, disinfection efficacy of slightly acidic electrolyzed water (SlAEW: pH 6.1, 20 mg/L available chlorine) produced by electrolysis for fresh cut cabbage was compared to that of sodium hypochlorite solution (NaOCl solution: pH 9.6, about 150 mg/L available chlorine). SlAEW reduced about by 1.5 log CFU/g for total aerobic bacteria and 1.3 log CFU/g for moulds and yeasts, compared to fresh cut cabbage before dipping. Statistical analysis of the results showed that the disinfectant efficacy of SlAEW was equivalent to or higher than that of NaOCl solution. Results also indicated that SlAEW under shaded and sealed conditions could keep its available chlorine during storage.     

Inhibition of Staphylococcus aureus on beef by nisin-containing modified alginate films and beads

Nisin, a bacteriocin, was immobilized into palmitoylated alginate-based films or in activated alginate beads. Sterile beef muscle slices or ground beef were inoculated with Staphylococcus aureus at a level of 10⁴ CFU/g. Sliced beef was then coated with palmitoylated alginate-based films containing 0, 500 or 1000 IU/mL of nisin. Also, ground beef was mixed with 0, 500 or 1000 IU/mL of nisin covalently linked to activated alginate beads in order to evaluate the effect of nisin concentration on S. aureus level. The content of S. aureus in beef was determined during storage at 4 °C. Results demonstrated that after 7 days of storage, a reduction of 0.91 and 1.86 log CFU/cm² was observed on sliced beef covered with film containing 500 or 1000 IU/mL of nisin, respectively. After 14 days of storage, when nisin solution (500 or 1000 IU/g) was mixed with ground beef, 2.2 and 2.81 log CFU/g reductions of S. aureus counts were respectively observed. However, when nisin (500 or 1000 IU/g) was linked into activated alginate beads, 1.77 and 1.93 log CFU/g reductions of S. aureus counts were respectively observed (P ⩽ 0.05). These results suggest that sterile, hydrophobic and biodegradable films or beads incorporating various amounts of nisin could be used efficiently to control the growth of pathogens or microorganisms responsible of spoilage at the surface of round beef or other meat products.     

Application of slightly acidic electrolyzed water as a potential non-thermal food sanitizer for decontamination of fresh ready-to-eat vegetables and sprouts

The sanitization efficacy of slightly acidic electrolyzed water (SAEW) against food pathogens on selected fresh ready-to-eat (RTE) vegetables and sprouts was evaluated and compared to sodium hypochlorite (NaOCl) solution. RTE vegetables and sprouts were dip-inoculated with Escherichia coli (E. coli) and Salmonella spp. and dip-treated with SAEW, NaOCl solution for 5 min. SAEW treatment significantly (p < 0.05) reduced the total aerobic mesophilic bacteria from Chinese celery, lettuce and daikon sprouts by 2.7, 2.5 and 2.45 log₁₀CFU/g, respectively relative to un-treated. Pathogens were significantly (p < 0.05) reduced from Chinese celery, lettuce and daikon sprouts by 2.7, 2.8 and 2.8 log₁₀CFU/g (E. coli) and 2.87, 2.91 and 2.91 log₁₀CFU/g (Salmonella spp.), respectively following a SAEW treatment. SAEW and NaOCl solution showed no significant sanitization difference (p > 0.05). Results demonstrate that SAEW at low chlorine concentration and a near neutral pH is a potential non-thermal food sanitizer that could represent an alternative to NaOCl solution and would reduce the amount of free chlorine used in fresh-cut vegetables industry, since the same microbial reduction as NaOCl solution is obtained.     

Effect of isothiocyanates from horseradish (Armoracia rusticana) on the quality and shelf life of tofu

The effects of isothiocyanates (ITCs) on microbiological, physicochemical, and sensory properties were investigated in tofu on days 0, 2, 4, 6, 8, and 10 of storage at 10 °C. When compared to the control (8.14 log CFU/g), the 200 ppm of ITCs (4.40 log CFU/g) effectively retarded the growth of microflora in tofu after 10 days of storage. The initial pH slightly declined after 10 days of storage, ranging between 5.81 and 6.14. The control showed significantly higher acid values over storage. Compared to the control, the preference to sensory attributes (color, taste, odor, chewiness, and over acceptance) of ITC-treated samples was highly rated after 10 days of storage. The ITCs can be used as an alternative for extending the shelf life and improving the safety of tofu.     

Microorganisms associated with the spoilage of Pupuru

This study involved evaluation of physicochemical and microbiological changes in dried Pupuru (fermented, smoke dried cassava) balls under storage conditions simulating those currently used by the traditional processors. The aim was to understand the process of spoilage with a view to reducing the rate. pH ranged from 3 to 4, reducing significantly in cabinet-dried samples from 4.24 to 3.27 after 6 days of storage. Viable counts were in the range of 6–8 log cfu/g. Spoilage microorganisms included aerobic spore-forming and non-sporing bacteria as well as potentially toxigenic moulds like Aspergillus flavus and Penicillium species, which could constitute a health hazard to consumers.     

Histamine contents and histamine-forming bacteria in sufu products in Taiwan

Twelve white and ten brown sufu products sold in the supermarkets in southern Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, and aerobic plate count (APC) in all samples ranged from 4.6 to 6.6, 6.2% to 12.0%, and 3.0 to 7.9 log CFU/g, respectively. None of these samples contained total coliform and Escherichia coli. Although the average content for each of the nine biogenic amines in all samples was less than 5 mg/100 g, only one brown sufu sample had histamine content (15.8 mg/100 g) greater than the 5.0 mg/100 g allowable limit suggested by the US Food and Drug Administration. Two histamine-producing bacterial strains capable of producing 1.33 mg/100 ml and 1.34 mg/100 ml of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH) were identified as Bacillus subtilis by 16S rDNA sequencing with PCR amplification.     

Effective household disinfection methods of kitchen sponges

Several household disinfecting treatments to reduce bacteria, yeasts and molds on kitchen sponges were evaluated. Sponges were soaked in 10% bleach solution for 3 min, lemon juice (pH 2.9) for 1 min, or deionized water for 1 min, placed in a microwave oven for 1 min at full power, or placed in a dishwasher for full wash and drying cycles, or left untreated (control). Microwaving and dishwashing treatments significantly lowered (P < 0.05) aerobic bacterial counts (<0.4 log and 1.6 log CFU/sponge, respectively) more than any chemical treatment or control (7.5 CFU/sponge). Counts of yeasts and molds recovered from sponges receiving microwave (<0.4 log CFU/sponge) or dishwashing (0.4 log CFU/sponge) treatments were significantly lower than those recovered from sponges immersed in chemical treatments. Our study shows that microwaving and dishwashing treatments may kill foodborne pathogens in a household kitchen environment.     

Radiation sensitivity of selected pathogens in ice cream

Microbial contamination was investigated using ice creams with a vanilla, chocolate, and strawberry flavor commercially available in Korea. Radiation sensitivity of the food-borne pathogens was also determined by an inoculation test. Food-borne pathogens used were Listeria ivanovii, Escherichia coli, and Salmonella typhimurium. Total aerobic bacteria, moulds and yeasts, and coliforms in the ice creams ranged from 2 to 3 log CFU/g. Irradiation of 3 kGy was enough to inactivate the total aerobic bacteria for the vanilla ice cream but that of 5 kGy was needed for the chocolate or strawberry ice creams at a frozen condition (−20 °C). To inactivate (>log 6.5) the inoculated L. ivanovii, E. coli, and S. typhimurium into ice cream irradiation of 3, 1, and 0.1 kGy was needed, respectively. The D₁₀ value of L. ivanovii and E. coli was calculated as 0.71–0.77 and 0.28–0.38 kGy range for the ice cream with different flavors at −72 °C, respectively. The D₁₀ value of S. typhimurium could not be calculated in this study because even 0.1 kGy of irradiation reduced the number of S. typhimurium to undetected level. Results suggest that a low dose irradiation can improve the microbial quality and reduce the risk by the food-borne pathogens of ice cream, which has limited alternative sterilization methods due to the temperature characteristics of the products.     

Emerging sanitizers and Clean Room packaging for improving the microbial quality of fresh-cut ‘Galia’ melon

This study evaluated how traditional or new sanitizers, alone, or in combination with the use of a Clean Room (CR), affected the respiration rate, microbial, nutritional and sensorial quality of fresh-cut ‘Galia’ melon. Melon pieces were packed in polypropylene trays under passive modified atmosphere (7.4 kPa O₂ + 7.4 kPa CO₂) and stored up to 10 days at 5 °C. The following treatments were performed: 150 mg/l chlorine (control) for 1 min; 80 mg/l peracetic acid (PAA) for 1 min; ozonated water (0.4 mg/l) for 3 and 5 min. The combinations of: ozonated water and PAA; 150 mg/l chlorine and packaging in CR; ozonated water for 3 min and package in CR; ozonated water for 3 min + PAA and packaging in CR were also studied. Throughout the shelf-life psychrotrophic, mesophilic, Enterobactericeae, lactic acid bacteria, moulds and yeast growth were determined. The use of PAA provided the lowest microbial load, but this sanitizer decreased the total vitamin C and the antioxidant activity. Nevertheless, the combination of PAA with 0.4 mg/l of ozonated water (3 min) could be a good substitute of use of chlorine. This treatment was effective in reducing the microbial counts, maintaining the antioxidant compounds and respiration rate and maintained the sensorial quality of the product during the 10 days at 5 °C. Treated product packaged in a CR did not show increased treatment effect, probably due to air quality in the laboratory. The use of CR just for the packaging of the melon pieces did not offer any additional advantage. However, the utilization of CR in an industrial environment during all processing steps (from washing to packaging) should be investigated for potential benefits.     

Isolation and identification of histamine-forming bacteria in tuna sandwiches

Forty-three tuna sandwiches sold in diners and convenience store in southern Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, water content, ash content, salt content, total volatile basic nitrogen (TVBN), aerobic plate count (APC), total coliform (TC), and Escherichia coli in all samples ranged from 4.5 to 6.9, 36.8% to 62.8%, 1.11% to 6.55%, 0.10% to 3.90%, 11.2 to 78.0 mg/100 g, <1.0 to 9.7 log CFU/g, <3 to 70,000 MPN/g and <3 to 1000 MPN/g, respectively. The average content of each of the eight biogenic amines in all samples was less than 3 mg/100 g, and only one tuna sandwich sample had histamine content (5.21 mg/100 g) greater than the 5.0 mg/100 g allowable limit suggested by the U.S. Food and Drug Administration. Five histamine-producing bacterial strains, capable of producing 42.1–595.4 ppm of histamine in trypticase soy broth supplemented with 1.0% L-histidine (TSBH), were identified as Hafnia alvei (one strain), Raoultella ornithinolytica (three strains) and Raoultella planticola (one strain), by 16S rDNA sequencing with PCR amplification.     

Disinfecting efficacy of a plastic container covered with photocatalyst for postharvest

The simplification of the cleaning process of plastic containers used in the storage and/or distribution of fruits or vegetables is important. We coated a plastic container with an apatite-coated titanium dioxide photocatalyst (TiO₂–Ap container), and examined its disinfecting efficacy under UV irradiation from black light. The disinfecting efficacy of the TiO₂–Ap container on diluted drops evaporated from spinach (suspension) was examined. Changes in the microbial populations of the total aerobic bacteria, coliform bacteria, and moulds and yeasts in the TiO₂–Ap container were assayed at 25 °C for 24 h (UV-A intensity of 0.2 and 0.4 mW cm⁻²). The results showed that all of the microbial populations in the TiO₂–Ap container decreased with irradiation time and then reduced to uncountable levels. It was found that the increase in UV-A intensity enhanced the disinfecting efficacy.     

Reduction of coliforms in rice treated with sanitizers and disinfectants

The efficacy of commercial sanitizers and disinfectants to minimize the contamination of total mesophilic bacteria and coliforms in rice was investigated. Water treated rice showed 0.7 log CFU/g reduction of both total mesophilic bacteria and coliforms. Reduction in sanitizer-treated rice was even greater. Coliforms in rice treated with the sanitizers 24,000 ppm hydrogen peroxide, 250 ppm chlorine, 180 ppm quaternary ammonium compound (QAC), 350,000 ppm ethanol, and 2000 ppm calcium oxide were eliminated. The sensory properties of 250 ppm chlorine treated cooked rice did not differ significantly from the same properties of water treated cooked rice.     

Prevalence of foodborne pathogens in Turkish Van otlu (Herb) cheese

The survey was conducted on 50 unripened Van otlu cheese samples obtained in Van and Hakkari markets at retail level to determine the microbial characteristics with special emphasis on Staphylococcus aureus, Escherichia coli, E. coli O157:H7 and Salmonella spp. The results revealed that S. aureus and E. coli were present in extremely high numbers, with a mean 6.10 and 3.68 log CFU/g, respectively. S. aureus was found in all samples ranging from 2.48 to 7.15 log CFU/g and was present in more than 5.0 × 10⁵ CFU/g in 54% of the samples whereas E. coli was found in 62% of the samples. None of the samples contained E. coli O157:H7; but 3 of the 50 samples had Salmonella spp. The results indicate that Van otlu cheese presents a potential hazard for public health; and the necessary precaution will have to be taken to improve the sanitary practices and cheese manufacturing technique.     

Safe and shelf-stable natural casing using hurdle technology

Safe and shelf-stable natural casing were prepared using a combination of hurdles viz. reduced water activity, packaging and gamma irradiation. Washed lamb intestines were treated with common salt to reduce water activity to 0.80 ± 0.02, packed in polyethylene bags and subjected to gamma-irradiation (5 and 10 kGy). Control non-irradiated samples had high total viable counts (10⁶ CFU/g), aerobic spores (10³ CFU/g), spores of sulphite reducing clostridia (10³ CFU/g), potentially pathogenic bacteria such as staphylococci (10⁴ CFU/g) and coliforms (10² CFU/g). Treatment with gamma radiation resulted in a dose dependent reduction in counts of these microbes. A dose of 5 kGy was sufficient to reduce total viable counts by three log cycles; spore counts by two log cycles and completely eliminate staphylococci and coliforms. Samples subjected to a 10 kGy dose were devoid of any viable microbes. The reduced water activity of the product prevented growth of the microbes in natural casings during storage at room temperature. Sausages prepared using hurdle processed natural casing were examined for sensory and textural properties. It was observed that product acceptability and mechanical strength was not affected by radiation processing. Our studies indicated that shelf-stable and safe natural casing could be prepared using a combination of hurdles.     

Efficacy of aqueous chlorine dioxide and fumaric acid for inactivating pre-existing microorganisms and Escherichia coli O157:H7, Salmonella typhimurium,and Listeria monocytogenes on broccoli sprouts

The combined effect of aqueous chlorine dioxide (ClO₂) and fumaric acid as a chemical treatment to inactivate pre-existing microorganisms was evaluated using broccoli sprouts. Broccoli sprouts were treated with distilled water, 50 ppm ClO₂, 0.5% fumaric acid, and a combination of 0.5% fumaric acid and 50 ppm ClO₂. Treatment with 50 ppm ClO₂ and 0.5% fumaric acid reduced the initial populations of total aerobic bacteria, yeasts and molds, and coliforms in broccoli sprouts by 2.70, 2.46, and 1.71 log CFU/g, respectively. In addition, the combined treatment of 50 ppm ClO₂ and 0.5% fumaric acid reduced the initial populations of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes inoculated on broccoli sprouts by 2.39, 2.74, and 2.65 log CFU/g, respectively, compared to the control. These results suggest that the combination of aqueous ClO₂ and fumaric acid can be useful as a hurdle for extending the shelf life of broccoli sprouts during storage.     

Microbial ecology of a small-scale facility producing traditional dry sausage

The microbial ecology of a small-scale facility producing traditional dry sausage (without addition of starter cultures) was investigated at 17 control points (12 processing surfaces and equipments samples, 5 raw materials and products samples) and at different periods: winter and spring.Technological flora (lactic acid bacteria, staphylococci/Kocuria and yeast/moulds) populations were low in processing surfaces and equipments (below 10² c.f.u/cm²), but reached a level of about 10⁶–10⁷ c.f.u/g for lactic acid bacteria and staphylococci/Kocuria and about 10⁴ c.f.u/g for yeasts/moulds in the final product. Counts of enterococci were low in most of processing surfaces and equipments and increased in the batter and the sausage-1 week; but declined after 8 weeks of ripening.Differences in temperatures of the processing facility recorded in winter and in spring influenced the hygienic quality of raw materials. Pseudomonas and Coliforms populations enumerated from raw materials in spring were about 3 log₁₀ c.f.u/g superior compared to enumeration results recorded in winter. While Pseudomonas population declined remarkably in the final product, Coliforms population remained higher. Staphylococcus aureus was undetected in spring; however in winter, its population was about 2.5 log₁₀ c.f.u/g in the final product after 9 weeks ripening. One isolate originating from the stuffing machine was identified as Listeria monocytogenes. Finally, 9 presumptive Salmonella were identified as belonging to Hafnia alvei, Providencia alcalifaciens, Proteus vulgaris, P. penneri and Morganella morganii species.These results emphasize the necessity of improving the general hygienic conditions and also technological process of sausage production in this processing facility.     

Staphylococcus xylosus S03/1M/1/2, bacteriocin-producing meat starter culture or additive

The aim of this study was to use Staphylococcus xylosus SX S03/1M/1/2 in manufacturing of dry-fermented salami to monitor its survival in the product and to evaluate its protective ability. S. xylosus SX S03 1M/1/2 survived sufficiently in the salamis; on 4 weeks of ripening it was still enumerated in the amount 4.5 log cfu/g from the initial count 6.6 log cfu/g. The counts of lactic acid bacteria in salami were high. S. aureus was found under the detection limit (<1.7). The counts of enterobacteriae were decreased, although not significant difference was found; reduction in moulds was detected with difference of p < 0.01 to compare the samples on 2 weeks of ripening with the control samples. The counts of yeasts were significantly decreased in the samples on 1 day and on 1 week (p < 0.001). The pH and water activity were not influenced. The activity of bacteriocin produced by SX S03/1M/1/2 strain reached 800–1600 AU/ml in the pH range 5.0–7.0. This substance did not lost activity after the heat treatment. After the further additional tests, this strain seems to be promising new starter culture or meat additive.     

Validation studies on an online monitoring system for reducing faecal and microbial contamination on beef carcasses

The objective of this research was to establish the reduction in the incidence of carcass faecal contamination and microbial counts that could be achieved in a beef slaughter plant using a novel information technology based online monitoring system. On 18 separate visits over the course of 6 months, every carcass (approximately 500 per day) was examined at the final inspection stand for visible faecal contamination. Each incidence was attributed to dehiding or evisceration operations. On each visit, 10 carcasses were swabbed at the trimming stand, at the hock, rump, anus, brisket and flank to determine total viable counts (TVC), Escherichia coli counts (ECC), total enteric counts (TEC) and total coliform counts (TCC). Over the course of this study, faecal contamination rates for dehiding and evisceration were reduced from 54.2% to 28.2% and from 32.5% to 13.7%, respectively. TVC remained constant at approximately 3.0 log₁₀ cfu cm⁻² while ECC, TEC and TCC decreased by 0.56 log₁₀ cfu cm⁻², 0.83 log₁₀ cfu cm⁻² and 0.9 log₁₀ cfu cm⁻², respectively. Online monitoring is therefore an effective means of reducing the incidence of bovine carcass faecal and enteric counts.     

Histamine level and histamine-forming bacteria in dried fish products sold in Penghu Island of Taiwan

Forty-six dried fish products sold in retail markets in Penghu Islands, Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, water content, water activity (Aw), total volatile basic nitrogen (TVBN), aerobic plate count (APC), Escherichia coli and total coliform (TC) in all samples ranged from 5.60 to 7.57, 1.8% to 27.1%, 19.32% to 61.90%, 0.63 to 0.92, 10.41 to 168.56 mg/100 g, 3.18 to 9.28 log CFU/g, <3 to 210 MPN/g and <3 to >1100 MPN/g, respectively. There had 30.4% of the tested dried fish products to contain histamine level more than 5 mg/100 g of FDA guideline for scombroid fish and/or product. Among them, all of the nine samples of Selariodes leptolepis had the highest histamine content of 6.31–47.90 mg/100 g. Thirteen histamine-producing bacterial strains isolated from tested samples produced 8.7–531.2 ppm of histamine in trypticase soy broth supplemented with 1.0% l-histidine (TSBH). Among these histamine-producing bacteria, Enterobacter aerogenes (one strain) isolated from S. leptolepis sample was proven to be a prolific histamine-former.