Ppm Nisin Research Articles

Optimizing insect repellence in open sun drying of fish through the combined influence of salt, turmeric, pepper and the bacteriocin nisin under tropical conditions

AbstractBackgroundSun drying of fish in open air is an age‐old traditional practice in Asia and some other parts of the world. This study aims to suggest optimal field doses of turmeric, pepper, salt and the bacteriocin nisin (food additive, E234) for open‐sun‐dried silver jewfish (Johnius argentatus) under a tropical environment. Investigations were carried out on the blowfly infestation, proximate composition, water reconstitution properties and organoleptic and microbial quality of open‐air‐dried fish samples.ResultsA direct relationship between moisture reduction and drying period was observed with salt‐treated samples demonstrating accelerated moisture reduction, reaching as low as 14.1% after 34 h. Turmeric and pepper treatments provided some protection against weight loss but ultimately extended the drying time to 38 h. Botanical pesticides like turmeric or pepper exhibited significant efficacy against blowfly adult and larval infestation with similar efficacy observed in 15% and 25% salt‐treated samples. Proximate composition analysis revealed that salt‐treated samples had lower moisture ranging from 14.1% to 16.0% but higher protein of 58.2%–62.1%, while the lipid and ash content did not vary significantly (p > 0.05). The water reconstitution properties of salt‐treated samples exhibited superior rehydration rates, with the highest in nisin (Niseen S) + 15% salt‐treated samples at 60°C, while organoleptic evaluations revealed salt‐treated samples to possess favourable attributes with minimal insect infestation and broken pieces. Finally, microbial analysis demonstrated the lowest aerobic plate count in dried fish samples treated with nisin (Niseen S) alone or in combination with 15% salt and/or 3% turmeric ranging from 3.97 ± 0.20 to 4.33 ± 0.07 log cfu/g.ConclusionIt is concluded that 200 ppm nisin (Niseen S)‐treated samples in combination with 3% turmeric and/or 15% salt are a viable option for producing high‐quality dried fish in traditional open‐air sun‐drying practices.

Virulence properties of nisin-resistant bacteria isolated from raw milk and cheese samples

AbstractNisin is a bacteriocin produced by Lactococcus lactis and it is generally recognised as safe by the U.S. Food and Drug Administration. The study aimed to determine the presence of nisin-resistant Staphylococcus, Enterococcus, and Listeria spp. in 157 raw milk and 125 cheese samples. As a result of the isolation procedure, a total of 282 bacterial strains were isolated. 83/282 strains showed resistance to 300 ppm nisin concentration and they were identified by 16S rRNA sequencing. The two most common species were Enterococcus faecalis and Staphylococcus aureus. In both raw milk and cheese samples, nisin-resistant Listeria could not be detected. Generally, enterococci (59/65) showed higher biofilm formation ability than staphylococci (13/18). 38% (25/65) of enterococci and 88% (16/18) of staphylococci were determined to have protease activity in at least one of Skim Milk Agar, Casein Agar, or Milk Agar. In addition, the most common antibiotic resistance in nisin-resistant enterococci was against chloramphenicol. This study revealed that nisin-resistant staphylococci and enterococci are present in raw milk and cheese. In addition, the presence of some virulence factors such as biofilm production, protease activity, and antibiotic resistance in resistant isolates needs to be drawn attention to. Consumption of nisin-resistant microorganisms with virulence factors through food is a food safety risk.

Bactericidal Effect of Combination of Atmospheric Pressure Plasma and Nisin on Meat Products Inoculated with Escherichia coli O157:H7.

This study was conducted to investigate the bactericidal effect of nisin (Nisin) only, atmospheric pressure plasma (APP) only, and a combination of APP and nisin (APP+Nisin) on beef jerky and sliced ham inoculated with Escherichia coli O157:H7, gram-negative bacteria. The bactericidal effect against E. coli O157:H7 and Listeria monocytogenes was confirmed using a nisin solution at a concentration of 0-100 ppm, and APP+Nisin was tested on beef jerky and sliced ham using 100 ppm nisin. Beef jerky and sliced ham were treated with APP for 5 min and 9 min, respectively. In the bacterial solution, 100 ppm nisin out of 0-100 ppm nisin exhibited the highest bactericidal activity against L. monocytogenes (gram-positive bacteria; p<0.05); however, it did not exhibit bactericidal effects against E. coli O157:H7 (gram-negative bacteria). The APP+Nisin exhibited a 100% reduction rate in both E. coli O157:H7 and L. monocytogenes compared to the control group, and was more effective than the Nisin. The APP+Nisin decreased the number of colonies formed by 0.80 and 1.96 Log CFU/g for beef jerky and sliced ham, respectively, compared to the control, and exhibited a higher bactericidal effect compared to the Nisin (p<0.05). These results demonstrate the synergistic bactericidal effect of APP and nisin, providing a possible method to improve the limitations of nisin against gram-negative bacteria. In addition, this technology has the potential to be applied to various meats and meat products to control surface microorganisms.

Ready-to-Eat Egg Products Formulated with Nisin and Organic Acids to Control Listeria monocytogenes

Formulating ready-to-eat (RTE) products with growth inhibitors minimizes the risk of listeriosis. In part I, RTE egg products formulated with 6.25 ppm nisin were evaluated to control Listeria monocytogenes. Individual experimental units were surface inoculated with 2.5-log CFU/g of L. monocytogenes, packaged in pouches with a headspace gas of 20:80 CO2:NO2, and stored at 4.4°C for 8 weeks. Formulations with finished product pH of 6.29 ± 0.07 limited growth to <2-log for 4 weeks. Products at pH values of 7.42 ± 0.12 and 7.84 ± 0.11 were not different (p > 0.05) from the control without nisin at pH 7.34 ± 0.13, all supported 4-log growth by 4 weeks. In part II, a nisin bioassay test was performed to evaluate the stability of nisin in eggs as affected by the product pH (6.00 ± 0.03, 7.00 ± 0.00, 7.50 ± 0.03, and 8.00 ± 0.02) and cooking to an internal temperature of 73.9 or 85°C for 90 s. The nisin activity loss increased as the product pH or the cooking temperature increased (p < 0.05). Part III evaluated the effectiveness of 6.25 ppm nisin in combination with either an acetate-based antimicrobial used at 1.0% (w/w) in egg formulation (A1.0), propionate at 0.3% (P0.3), acetate-diacetate at 1.0% (AD1.0), acetate-diacetate at 0.6% (AD0.6), and lactate at 2.0% (L2.0) as a positive control. These formulations had a finished product pH, moisture, and salt contents of 5.97 ± 0.21, 72.4 ± 0.9%, and 0.67 ± 0.05%, respectively. L. monocytogenes did not grow in formulations A1.0 and AD1.0, whereas L2.0 and P0.3 supported 2-log growth by weeks 6 and 15, respectively and AD0.6 supported <1-log growth over 20 weeks at 4.4°C. Evaluation of uninoculated control units in parts I and III showed no changes (p > 0.05) in the CO2 and O2 headspace gas composition, generally no detection or growth of background microbes, and no changes (p > 0.05) in the pH of the formulations during storage, all assuring absence of uncontrolled interferences for the growth of L. monocytogenes.

Equivalent processing for pasteurization of a pineapple juice-coconut milk blend by selected nonthermal technologies.

Identifying equivalent processing conditions is critical for the relevant comparison of food quality attributes. This study investigates equivalent processes for at least 5-log reduction of Escherichia coli and Listeria innocua in pineapple juice-coconut milk (PC) blends by high-pressure processing (HPP), pulsed electric fields (PEF), and ultrasound (US) either alone or combined with other preservation factors (pH, nisin, and/or heat). The two blends (pH 4 and 5) and coconut milk (pH 7) as a reference were subjected to HPP at 300-600MPa, 20°C for 0.5-30min; PEF at an electric field strength of 10-21kV/cm, 40°C for 24µs; and US at 120µm amplitude, 25 or 45°C for 6 or 10min. At least a 5-log reduction of E. coli was achieved at pH 4 by HPP at 400MPa, 20°C for 1min; PEF at 21kV/cm, 235Hz, 40°C for 24µs; and US at 120µm, 45°C for 6min. As L. innocua showed greater resistance, a synergistic lethal effect was provided at pH 4 by HPP with 75ppm nisin at 600MPa, 20°C for 5min; PEF with 50ppm nisin at 18kV/cm, 588Hz, 40°C for 24µs; and US at 45°C, 120µm for 10min. The total soluble solids (11.2-12.4°Bx), acidity (0.47%-0.51% citric acid), pH (3.91-4.16), and viscosity (3.55×10-3 -4.0×10-3 Pas) were not significantly affected under the identified equivalent conditions. HPP was superior to PEF and US, achieving higher ascorbic acid retention and lower color difference in PC blend compared to the untreated sample.

The efficacy of nisin against Listeria monocytogenes on cold-smoked salmon at natural contamination levels is concentration-dependent and varies by serotype.

Cold-smoked salmon is a ready-to-eat food product capable of supporting Listeria monocytogenes growth at refrigeration temperatures. While the FDA-approved antimicrobial nisin can be used to mitigate L. monocytogenes contamination, stresses associated with cold-smoked salmon and the associated processing environments may reduce nisin efficacy. A previous study in our laboratory showed that, at high inoculation levels, pre-exposure of L. monocytogenes to sublethal concentrations of quaternary ammonium compounds had an overall detrimental effect on nisin efficacy. The objective of this study was to investigate the impact of nisin concentration and storage temperature on nisin efficacy against L. monocytogenes inoculated on salmon at natural contamination levels. Three L. monocytogenes strains were pre-grown in the presence of sublethal levels of benzalkonium chloride prior to inoculation at ~102 CFU/g on salmon slices that were pre-treated with either 0, 25, or 250 ppm nisin, followed by vacuum-packing and incubation at 4 or 7°C for up to 30 days. L. monocytogenes was enumerated on days 1, 15, and 30 using direct plating and/or most probable number methods. A hurdle model was constructed to describe the odds of complete elimination of L. monocytogenes on salmon and the level of L. monocytogenes when complete elimination was not achieved. Our data showed that (i) nisin efficacy (defined as L. monocytogenes reduction relative to the untreated control) was concentration-dependent with increased efficacy at 250 ppm nisin, and that (ii) 250 ppm nisin treatments led to a reduction in L. monocytogenes prevalence, independent of storage temperature and serotype; this effect of nisin could only be identified since low inoculation levels were used. While lower storage temperatures (i.e., 4°C) yielded lowered absolute L. monocytogenes counts on days 15 and 30 (as compared to 7°C), nisin efficacy did not differ between these two temperatures. Finally, the serotype 1/2b strain was found to be more susceptible to nisin compared with serotype 1/2a and 4b strains on samples incubated at 7°C or treated with 25 ppm nisin. This variation of nisin susceptibility across serotypes, which is affected by both the storage temperature and nisin concentration, needs to be considered while evaluating the efficacy of nisin.

Impact of Nisin in Combination with Sodium Benzoate and Calcium Carbonate on the Bacterial and Yeast Population of Coconut Neera (Coconut Inflorescence sap)

A natural sap from mature coconut palm known as coconut neera is enriched with essential minerals and vitamins. Rapid microbial fermentation affects neera processing industries because it spoils the physicochemical properties. There are various methods in preservation that extend the shelf life of coconut neera. The addition of nisin is one of the methods which protect neera against fermentation. Therefore, the study is focused to identify the effective combination of nisin (50 ppm) with preservatives like sodium benzoate (500, and 1000 ppm), and calcium carbonate (2500, and 3000 ppm) at two different combinations in neera. At the end of 21 d, 3000 ppm calcium carbonate with 50 ppm nisin in N4 treatment had an effective reduction of 120 × 105 CFU/ml and 143 × 102 CFU/ml for total bacteria and total yeast count. The reduced microbial survival resulted in the pH of 10.45 ± 0.05, total soluble solids of 15.43 ± 0.12 °Brix, and total acidity of 1.11 ± 0.04 mg/ L, at this combination. The treatment of nisin with 3000 ppm calcium carbonate demonstrated the high red fluorescence bacterial cells than the treatment of nisin with 1000 ppm sodium benzoate. Additionally, the microorganisms in N4 treatment precipitated 65.34% Ca2+ from 79.96% in XRF intensity analysis. The synergistic effect of nisin and calcium carbonate explored their antimicrobial activity against the heterogeneous microbial population in coconut neera. The concentration of 3000 ppm calcium carbonate and nisin 50 ppm preserves the physicochemical and sensory qualities, up to 21 d at 4°C, and offer hope for the industrial-scale implementation.

Antimicrobial Polyamide-Alginate Casing Incorporated with Nisin and ε-Polylysine Nanoparticles Combined with Plant Extract for Inactivation of Selected Bacteria in Nitrite-Free Frankfurter-Type Sausage.

The effects of combining a polyamide-alginate casing incorporated with nisin (100 ppm and 200 ppm) and ε-polylysine (500 ppm and 1000 ppm) nanoparticles and a mixed plant extract as ingredient in sausage formulation (500 ppm; composed of olive leaves (OLE), green tea (GTE) and stinging nettle extracts (SNE) in equal rates) were studied to improve the shelf life and safety of frankfurter-type sausage. The film characteristics and microbiological properties of sausage samples were evaluated. Sausage samples were packaged in polyethylene bags (vacuum condition) and analysed during 45 days of storage at 4 °C. Control sausages were also treated with 120 ppm sodium nitrite. Polyamide-alginate films containing 100 ppm nisin and 500 ε-PL nanoparticles had the highest ultimate tensile strength compared to other films. However, 100 ppm nisin and 500 ε-PL nanoparticles decreased water vapour permeability of films. The results also revealed that nisin nanoparticles had significantly (p < 0.05) low inhibitory effects against Escherichia coli, Staphylococcus aureus, molds and yeasts and total viable counts compared to control and ε-PL nanoparticles. Furthermore, 1000 ppm ε-PL nanoparticles displayed the highest antimicrobial activity. Based on the obtained results, the films containing ε-PL nanoparticle could be considered as a promising packaging for frankfurter-type sausages.

Effect of High-Pressure Processing and Nisin on Microbial Inactivation and Quality of Avocado Dressing

HighlightsA =7-log reduction of E. coli and L. innocua was accomplished using HPP at 600 MPa for 3 min.There was a synergy between HPP and nisin in all treatments to inactivate both E. coli and L. innocua.HPP and nisin did not affect the color, pH, and total soluble solids content of avocado dressing.Viscosity measurements of avocado dressing samples after HPP showed a good fit to a power-law model.Abstract. The effect of high-pressure processing (HPP) (200, 300, 400, 500, and 600 MPa) and nisin (0, 100, and 200 ppm) on L. innocua and E. coli inactivation and on the color, pH, TSS, and viscosity of avocado dressing was investigated. HPP at 600 MPa for 3 min resulted in 7 log CFU mL-1 reductions of both L. innocua and E. coli in avocado dressing. Combining HPP at =500 MPa with 100 ppm nisin exhibited significant additional L. innocua and E. coli inactivation, indicating high synergy between HPP and nisin. Pressure levels up to 600 MPa did not affect the color, pH, and total soluble solids of avocado dressing. The avocado dressing followed pseudoplastic flow behavior, and the viscosity of the samples decreased with increasing pressure and temperature. HPP was effective in controlling E. coli and L. innocua in avocado dressing without significant quality loss. Keywords: Color, Escherichia coli, High-pressure processing, Listeria innocua, Nisin, Viscosity.

Precise management of chronic wound by nisin with antibacterial selectivity

Traditional broad-spectrum antibacterial agents are limited by high toxicity and the destruction to the bacterial flora balance in the wound site. Herein, we propose an opinion that one or several especial antibacterial peptides are adopted to kill the target bacteria in order to precisely manage the bacteria infected chronic wound under the premise of biobalance, and specially employ nisin to treat S. aureus infected chronic wound as model with positive effects. The results showed that without cytotoxicity to the normal cells, only 25 ppm nisin could contrapuntally kill S. aureus and have little inhibitory to other bacteria. Mechanism of antibacterial selectivity indicated the superior biomolecular interaction between nisin and S. aureus compared with E. coli and normal cells. Furthermore, nisin significantly accelerated the healing process of S. aureus-infected rabbit full thickness burn wound, but had no effect on the E. coli-infected wound as a comparison. Therefore, it has been demonstrated that special peptides with antibacterial selectivity can be adopted to precise management for bacteria infected chronic wound under good biobalance.

Effect of Nisin on Microbial, Physical and Sensory Qualities of Micro-Filtered Coconut Water (Cocos Nucifera L.) During Refrigerated Storage

The efficacy of nisin (25-75 ppm) and effect of storage time on quality attributes of micro-filtered coconut water during refrigerated storage (4°C) for 8 days was investigated in terms of total viable counts, colour, turbidity and overall sensory acceptance. All treatments significantly retarded the bacterial growth in coconut water during storage when compared to the control sample (p &lt; 0.05). The samples treated with 50 and 75 ppm nisin had significantly lower aerobic microbial counts than the control (p &lt; 0.05) without affecting colour, turbidity and sensory acceptability. The treated samples also had the significantly higher scores in overall acceptance than the control sample after 7 days of storage.50 ppm Nisin was suggested to be applied in micro-filtered coconut water without effects on colour, turbidity, and sensory acceptability by a reduction in changes of the microbial growth during the refrigerated storage.

Energy and Nutrient intake and Dietary Diversity among Female Residential Students of Bangladesh

The efficacy of nisin (25-75 ppm) and effect of storage time on quality attributes of micro-filtered coconut water during refrigerated storage (4°C) for 8 days was investigated in terms of total viable counts, colour, turbidity and overall sensory acceptance. All treatments significantly retarded the bacterial growth in coconut water during storage when compared to the control sample (p &lt; 0.05). The samples treated with 50 and 75 ppm nisin had significantly lower aerobic microbial counts than the control (p &lt; 0.05) without affecting colour, turbidity and sensory acceptability. The treated samples also had the significantly higher scores in overall acceptance than the control sample after 7 days of storage.50 ppm Nisin was suggested to be applied in micro-filtered coconut water without effects on colour, turbidity, and sensory acceptability by a reduction in changes of the microbial growth during the refrigerated storage.

The effect of nisin and storage temperature on the quality parameters of processed cheese

The aim of this study was to evaluate the effect of nisin and storage temperature on the microbiological, physico-chemical and sensory properties of processed cheese. Processed cheese samples were prepared without and with 12.5 ppm nisin, stored at different temperatures (4, 8 and 20 degrees C). Research covered microbiological, physico-chemical and sensorial analysis of the samples. In processed cheese samples prepared without nisin, aerobic colony count (ACC) significantly increased over the experimental period, while in nisin supplemented samples no significant increase was determined. At lower storage temperature (4 degrees C), the effectiveness of nisin was more pronounced. Yeast and moulds (YM) and psychrotrophic colony count (PCC) were below the limit of quantification over the entire experimental period. Also, no significant changes in pH values and textural characteristics (firmness and stickiness) were determined. Sensory analyses confirmed that processed cheese samples became whiter and less yellow, compared to fresh samples. The viscosity of all samples decreased over the experimental period, which was in line with the results of baking stability. The obtained results confirmed the potential of using this type of processed cheese in baking industry.

Antimicrobial activity optimization of nisin, ascorbic acid and ethylenediamine tetraacetic acid disodium salt (EDTA) against Salmonella Enteritidis ATCC 13076 using response surface methodology

Nisin is a commercial bacteriocin produced by Lactococcus lactis subsp. lactis and widely used as a natural preservative in the food industry. However, while nisin alone cannot inhibit the growth of Gram-negative bacteria, it can in combination with a chelating agent or organic acid. This study combined nisin with some chelating agents, weak organic acids and their salts to inhibit Salmonella Enteritidis ATCC 13076. The combinations of nisin (2000 parts per million; ppm) and ascorbic acid (2000 ppm) or ethylenediamine tetraacetic acid disodium salt (EDTA; 7400 ppm) showed significant inhibitory effects on the target strain. Due to regulatory limits, the second part of the study reduced the concentrations of nisin, ascorbic acid and EDTA to 500 ppm, 2000 ppm and 250 ppm, respectively. The mixture of nisin, ascorbic acid and EDTA showed the highest inhibitory effect with a reduction number of 3.41 log colony forming units (p < 0.05). To minimize the growth of S. Enteritidis ATCC 13076, central composite design and response surface methodology were applied to investigate the combined effect of nisin (0–500 ppm), ascorbic acid (0–2000 ppm), and EDTA (0–250 ppm) on the target strain growth. Among the three factors, nisin had a higher antimicrobial effect than ascorbic acid or EDTA, while an increase in nisin resulted in a decrease in S. Enteritidis ATCC 13076 growth. The optimum concentration was 500 ppm nisin with 1515 ppm ascorbic acid and 250 ppm EDTA. Under these conditions, the growth of S. Enteritidis ATCC 13076 predicted by the model was 24.99%.

Characterization of Enterococcus durans 152 bacteriocins and their inhibition of Listeria monocytogenes in ham

Listeria monocytogenes is a nonfastidious, widely occurring foodborne pathogen that is a major challenge to the food industry. Enterococcus durans 152, a confirmed L. monocytogenes-control microorganism, was isolated from floor drain samples from a food processing facility. In this study, the two bacteriocins produced by E. durans 152 were characterized and identified as Dur 152A (an enterocin L50A derivative with two amino acid substitutions of I→M) and enterocin L50B. The bacteriocins were then partially purified and evaluated for inhibitory activity to L. monocytogenes in deli ham. Results revealed that at 400 AU/ml, the bacteriocins prevented growth of listeria in deli ham for at least 10 weeks at 8 °C and at least 30 days at 15 °C. For comparison, 500 ppm Nisin controlled listeria growth for up to 6 weeks at 8 °C and up to 18 days at 15 °C. These findings reveal the potential for the bacteriocins of E. durans 152 to serve as anti-listerial agents in deli meat.

Antimicrobial activity of collagen casing impregnated with nisin against foodborne microorganisms associated with ready-to-eat sausage

Antimicrobial collagen casing incorporated with nisin was developed to inhibit foodborne pathogens and spoilage bacteria associated with ready-to-eat (RTE) sausage. Collagen casing was impregnated with 10,000 ppm of nisin solution at vacuum pressure (-680 mmHg) under various conditions of a vacuum time range from 150 to 600 s and an atmospheric time range from 30 to 90 s. The antimicrobial activity of the collagen casing impregnated with nisin was screened using the survival cell count method against Listeria monocytogenes strain Scott A. After that, the most active antimicrobial casing was examined both in vitro and in Vienna sausage. In vitro, the antimicrobial casing decreased L. monocytogenes by 2.8 log CFU/mL, Staphylococcus aureus by 2.1 log CFU/mL and Lactobacillus plantarum by 2.4 log CFU/mL (>99% reduction) when compared with a pre-treated collagen casing (CTRL). After applied to the sausage, the antimicrobial casing extended shelf-life of the sausage at least 90 days at 4 °C and 49 days at 10 °C, respectively. Furthermore, it reduced artificially inoculated L. monocytogenes by 1.1 log CFU/g (>90% reduction) during storage at 4 °C. The concentration of nisin released from the casing was evaluated using the agar well diffusion method. An amount of 852 ppm nisin was released from the antimicrobial casing which was higher than the minimum inhibitory concentration (MIC) values of tested bacteria (25–250 ppm). The FTIR spectral band of the antimicrobial casing showed interaction between nisin and collagen casing at 1800-800 cm−1. Furthermore, physical properties of the antimicrobial casing and CTRL were not significantly different in color, thickness and percent elongation (%E) but the tensile strength of IMP was higher than CTRL. Therefore, it can be concluded that the antimicrobial collagen casing impregnated with nisin has the potential to control foodborne microorganisms in order to enhance the microbial food safety and shelf life of RTE sausage.

Avaliação da multiplicação de Listeria monocytogenes e da atividade antimicrobiana do Biomax D® em nata

The proliferation of Listeria monocytogenes in cream, a milk derivative with high fat content, was evaluated as well as the anti-listerial activity of Biomax D® in this type of food. Antilisterial activity of Biomax was compared with nisin. Six treatments were used: T1: Cream + 102 CFU.g-1 of L. monocytogenes; T2: Cream + 102 CFU.g-1L. monocytogenes + 2,5ppm nisin; T3: Cream + 102 CFU.g-1 L. monocytogenes + 1.5% Biomax; T4: Cream + 105 CFU.g-1 of L. monocytogenes; T5: Cream + 105 CFU.g-1 L. monocytogenes + 2,5ppm nisin; T6: Cream + 105 CFU.g-1 L. monocytogenes + 1.5% Biomax. L. monocytogenes counts were performed on three days storage at 8 °C (zero, 6, 14 and 20th day), with averages ranging between 2 and 10 log CFU.g-1 in treatments without the addition of nisin or Biomax®. However, there was elimination of the microorganism when the antimicrobials were added. It was found that L. monocytogenes is able to grow in cream, reaching high levels of contamination, even when it presents low initial counts. In this dairy derivative, Biomax D® presents antilisterial activity similar to nisin and might be used as a natural antibiotic for the control of L. monocytogenes in fatty foods.

Effect of heat, nisin and ethylene diamine tetra‐acetate treatments on shelf life extension of liquid whole egg

SummaryThis study examined the effect of nisin alone or in combination with pasteurisation or ethylene diamine tetra‐acetate (EDTA), on the shelf life of unpasteurised liquid whole egg (LWE) stored at refrigerator temperature for a period of 21 days. The shelf life of samples was determined by counting total mesophilic bacteria, yeast and mould and also pH changes. It was observed that addition of 3 ppm nisin to pasteurised LWE was effective enough to extend the shelf life of this product from about 7 days to at least 21 days. However, for unpasteurised LWE nisin alone had no significant effect on shelf life while treatment of LWE with nisin in combination with EDTA showed a significant antibacterial and antifungal activity leading to extended shelf life of unpasteurised LWE from 1 to 4 days to at least 21 days.

Influences of malic acid and nisin supplementations on the decimal reduction times of Escherichia coli O157:H7 in mildly-heated young coconut liquid endosperm

This study was conducted to determine the effects of malic acid (800–1500 ppm) and nisin (0–150 ppm) on the heat resistance of Escherichia coli O157:H7 in young coconut liquid endosperm. The Central Composite Rotatable Design was applied to determine the various combinations of the two supplements to be added to young coconut liquid endosperm. The lowest D55 value was observed in the combination of 1500 ppm malic acid and 75 ppm nisin at 14.89 ± 4.17 min, while highest was 27.04 ± 4.98 min in the combination of 1150 ppm malic acid and 75 ppm nisin. The D55 values established from the combinations tested did not significantly vary, indicating that within the ranges of supplementation tested, significant influences of both additives and their interaction on the heat resistance of the pathogen did not exist. It was however emphasized that all supplementation combinations resulted in D55 values significantly lower than that in the unsupplemented medium, reducing the heat resistance of the cells by as much as 3-folds. Therefore, thermal processes to be established in the supplemented liquid endosperm shall be less severe, and may be applied to preserve sensory attributes.

Listeria monocytogenes develops no resistance to ferulic acid after exposure to low concentrations

Antimicrobial agents have been used as additives to control the growth of Listeria monocytogenes. Although nisin has been used to inhibit the growth of L. monocytogenes in food products, exposure to this agent also poses a risk for the development of nisin resistance. Ferulic acid has also been extensively used for growth inhibition of L. monocytogenes, although no previous investigations on the development of ferulic acid resistance have been conducted. In the present study, we inoculated culture media containing one of these two antimicrobial agents with bacteria that had been previously exposed to these agents and assessed for any changes in resistance. The resistance of L. monocytogenes to nisin increased after exposure to 5 ppm nisin, and its survival rate against 20 ppm nisin improved. On the other hand, exposure to 1000 ppm ferulic acid did not increase ferulic acid resistance. The present study demonstrated that the concentration of added nisin must be considered carefully to achieve a sufficient effect. Ferulic acid, on the other hand, showed a minimal risk of producing resistant bacteria, thus allowing it to impart a stable effect.