Khanh Dang Vu

In vitro evaluation of antimicrobial activities of various commercial essential oils, oleoresin and pure compounds against food pathogens and application in ham

The purpose of this research was to evaluate the application of commercially available essential oils (EOs) and oleoresins to control bacterial pathogens for ready to eat food. In this study, sixty seven commercial EOs, oleoresins (ORs) and pure compounds were used to evaluate in vitro their antimicrobial activity against six food pathogens. These products were first screened for their antimicrobial activity using disk diffusion assay. Forty one products were then chosen for further analysis to determine their minimum inhibitory concentration against 6 different bacteria. There were 5 different products (allyl isothiocyanate, cinnamon Chinese cassia, cinnamon OR, oregano and red thyme) that showed high antimicrobial activity against all tested bacteria. Further analysis examined the effect of four selected EOs on controlling the growth rate of mixed cultures of Listeria monocytogenes in ham. A reduction of the growth rate by 19 and 10% was observed when oregano and cinnamon cassia EOs were respectively added in ham at a concentration of 500 ppm.

Antibacterial and physical effects of modified chitosan based-coating containing nanoemulsion of mandarin essential oil and three non-thermal treatments against Listeria innocua in green beans

The antimicrobial activity against Listeria innocua of three different combined non-thermal treatments, along with the impact on color and texture on green bean samples, was evaluated. In this study a bioactive coating formulation based on modified chitosan containing 0.05% nanoemulsion of mandarin essential oil was tested in combination with γ-irradiation, UV-C and ozonated water treatments, and the results in terms of antimicrobial activity, color and texture changes, were evaluated during 14 days storage. The combined coating and γ-irradiation treatment gave promising results, showing 3.3 log CFU/g initial microbial reduction, and exhibiting a strong synergistic antimicrobial effect. The treatment based on UV-C and coating formulation allowed a 3 log CFU/g reduction of initial L. innocua population on samples, showing a good residual antimicrobial activity and preventing loss of firmness and color changes during storage. The combined treatment of coating and ozonated water did not show any synergistic or additive antimicrobial effect, but they showed an impact on firmness and color. In conclusion UV-C and γ-irradiation treatments, in combination with the bioactive coating, represent an effective approach to control the growth of L. innocua on vegetable foods.

Synergistic effect of gamma (γ)-irradiation and microencapsulated antimicrobials against Listeria monocytogenes on ready-to-eat (RTE) meat

Oregano essential oil (Origanum compactum; 250 μg/ml), cinnamon essential oil (Cinnamomum cassia; 250 μg/ml) and nisin (16 μg/ml) were used alone or in combination to evaluate their efficiency to inhibit the growth of Listeria monocytogenes on RTE ham. Microencapsulation of the antimicrobial formulations was done to verify the potential effect of the polymer to protect the antimicrobial efficiency during storage. Combined treatments of antimicrobial formulation with γ-irradiation were done to verify the synergistic effect against L. monocytogenes. Microencapsulation of essential oils-nisin and γ-irradiation treatment in combination showed synergistic antimicrobial effect during storage on RTE meat products. Microencapsulated cinnamon and nisin in combination with γ-irradiation (at 1.5 kGy) showed 0.03 ln CFU/g/day growth rate of L. monocytogenes whereas the growth rate of non-microencapsulated cinnamon and nisin in combination with γ-irradiation was 0.17 ln CFU/g/day. Microencapsulation significantly (P ≤ 0.05) improved the radiosensitivity of L. monocytogenes. Microencapsulated oregano and cinnamon essential oil in combination with nisin showed the highest bacterial radiosensitization 2.89 and 5, respectively, compared to the control.

Edible Coating and Film Materials: Proteins

Edible coatings can be applied on food surfaces as a thin layer edible film. Edible coatings can potentially extend the shelf life and improve the quality of food by the control of mass transfer, moisture and oil diffusion, gas permeability (O2, CO2), and flavor and aroma losses and by maintaining mechanical, rheological characteristics, color and appearance of foods. Edible film as a solid sheet can be applied between food components or on the surface of the food system in order to inhibit migration moisture, oxygen, CO2, aromas and lipids. Edible films with adequate mechanical properties could also serve as edible packaging for selected foods. In this chapter, the methods to produce protein-based films and coating, the properties of protein-based films and coatings and their applications in food systems are presented. The selected proteins are originated from animal and plant sources consisting of caseins, whey proteins, collagen and gelatin, plasma proteins, myofibrillar proteins, egg white proteins, soy protein, wheat gluten and zein. Further, the current development and the potentials of application of protein-based nanocomposites for food preservation are also presented.

Optimization of microfluidization for the homogeneous distribution of cellulose nanocrystals (CNCs) in biopolymeric matrix

Abstract Microfluidization, which is a high-pressure homogenization technique, was used to develop highly dispersed cellulose nanocrystal (CNC) reinforced chitosan based nanocomposite films. A three factor central composite design with five levels was designed to systematically optimize the microfluidization process. The three factors were the CNC content, the microfluidization pressure and the number of microfluidization cycles. Response surface methodology was used to obtain relationship between the mechanical properties of the nanocomposite films and the factors. Polynomial equations were generated based on the regression analysis of the factors and the predicted properties of the nanocomposite films were in good agreement with the experimental results. Microfluidization effectively reduced the CNC–chitosan aggregates and improved the mechanical properties of the nanocomposite films. Microscopic analysis of the microfluidized nanocomposite films revealed a 10–15 times reduction in the size of the aggregates compared to the non-microfluidized CNC/chitosan films and an increase in the root mean square surface roughness (Rq).

Induced production of chitinase to enhance entomotoxicity of Bacillus thuringiensis employing starch industry wastewater as a substrate

Induced production of chitinase during bioconversion of starch industry wastewater (SIW) to Bacillus thuringiensis var. kurstaki HD-1 (Btk) based biopesticides was studied in shake flask as well as in computer-controlled fermentors. SIW was fortified with different concentrations (0%; 0.05%; 0.1%; 0.2%; 0.3% w/v) of colloidal chitin and its consequences were ascertained in terms of Btk growth (total cell count and viable spore count), chitinase, protease and amylase activities and entomotoxicity. At optimum concentration of 0.2% w/v colloidal chitin, the entomotoxicity of fermented broth and suspended pellet was enhanced from 12.4x10(9) (without chitin) to 14.4x10(9) SBU/L and from 18.2x10(9) (without chitin) to 25.1x10(9) SBU/L, respectively. Further, experiments were conducted for Btk growth in a computer-controlled 15 L bioreactor using SIW as a raw material with (0.2% w/v chitin, to induce chitinase) and without fortification of colloidal chitin. It was found that the total cell count, spore count, delta-endotoxin concentration (alkaline solubilised insecticidal crystal proteins), amylase and protease activities were reduced whereas the entomotoxicity and chitinase activity was increased with chitin fortification. The chitinase activity attained a maximum value at 24 h (15 mU/ml) and entomotoxicity of suspended pellet reached highest (26.7x10(9) SBU/L) at 36 h of fermentation with chitin supplementation of SIW. In control (without chitin), the highest value of entomotoxicity of suspended pellet (20.5x10(9) SBU/L) reached at 48 h of fermentation. A quantitative synergistic action of delta-endotoxin concentration, spore concentration and chitinase activity on the entomotoxicity against spruce budworm larvae was observed.

Antimicrobial effects of marine algal extracts and cyanobacterial pure compounds against five foodborne pathogens

The marine environment is a proven source of structurally complex and biologically active compounds. In this study, the antimicrobial effects of a small collection of marine-derived extracts and isolates, were evaluated against 5 foodborne pathogens using a broth dilution assay. Results demonstrated that algal extracts from Padina and Ulva species and cyanobacterial compounds antillatoxin B, laxaphycins A, B and B3, isomalyngamide A, and malyngamides C, I and J showed antimicrobial activity against Gram positive foodborne pathogens (Listeria monocytogenes, Bacillus cereus and Staphylococcus aureus) at low concentrations (⩽ 500 μg/ml). None of the algal extracts or cyanobacterial isolates had antibacterial activity against Gram negative bacteria (Escherichia coli and Salmonella enterica serovar Typhimurium).

Effect of combination of essential oils and bacteriocins on the efficacy of gamma radiation against Salmonella Typhimurium and Listeria monocytogenes

Abstract Purpose: Using essential oils (EO) alone or combined EO with nisin to enhance the lethality of Salmonella Typhimurium and Listeria monocytogenes to γ-irradiation treatment. Materials and methods: Cell suspension or inoculated carrots (106 colony forming unit (CFU)/ml) of L. monocytogenes or Salmonella Typhimurium were treated with carvacrol and mountain savory EO alone or treated by the combined EO plus nisin and were irradiated at different doses. The radiation dose required to reduce bacterial population by 90% (D10 value) and the relative sensitivity (RS) of treated bacteria to irradiation were calculated. Results: The RS of L. monocytogenes cell suspension to irradiation was increased by 4.19 and 6.31 times when treated by carvacrol plus nisin and mountain savory plus nisin, respectively, as compared to the control. The RS of Salmonella Typhimurium cell suspension to irradiation was increased by 1.84-fold when treated with carvacrol plus nisin. Coated carrots by nisin plus carvacrol increased the RS of L. monocytogenes to irradiation by 2.74 times while coated carrots by nisin and nisin plus carvacrol increased the RS of Salmonella Typhimurium to irradiation by 2.46 and 2.52, respectively. Conclusions: The combined EO with nisin and irradiation could increase the RS of L. monocytogenes and Salmonella Typhimurium.

Effect of Antimicrobial Coatings on the Radiosensitization of Escherichia coli, Salmonella Typhimurium, and Listeria monocytogenes in Fresh Broccoli

Radiosensitization of Listeria monocytogenes, Escherichia coli, Salmonella Typhimurium, and aerobic microflora was evaluated in broccoli florets coated by antimicrobial coatings and treated with different doses of γ-radiation. Broccoli florets were inoculated with aerobic microflora isolated from broccoli and with pathogenic bacteria (L. monocytogenes, E. coli, and Salmonella Typhimurium) at 10(6) CFU/ml. Inoculated florets were then coated with methylcellulose-based coating containing various mixtures of antimicrobial agents: organic acids plus lactic acid bacteria (LAB metabolites), organic acids plus citrus extract, organic acids plus citrus extract plus spice mixture, and organic acids plus rosemary extract. Coated florets were irradiated with various doses (0 to 3.3 kGy), and microbial analyses were conducted to calculate the D(10)-value and relative sensitivity. All antimicrobial coatings had almost the same effect of increasing the radiosensitivity of L. monocytogenes (from 1.31 to 1.45 times) to γ-irradiation. The coating containing organic acid plus citrus extract was the most efficient formulation for increasing the radiosensitization of E. coli and aerobic microflora, by 2.40 and 1.76 times, respectively, compared with the control without the antimicrobial coating. The coating containing organic acids plus LAB metabolites was the most effective formulation for increasing the radiosensitization (by 2.4 times) of Salmonella Typhimurium. Results suggest that the spice extract, when mixed with organic acids and citrus extract, might protect E. coli and aerobic microflora from the effects of γ-irradiation.

Starch industry wastewater for production of biopesticides--ramifications of solids concentrations.

Total solids (TS) concentrations ranging from 15 to 66 g L−1 of starch industry wastewater (SIW) were tested as raw material for the production of Bacillus thuringiensis var. kurstaki HD‐1 (Btk) biopesticide in shake flasks and a 15 L bench‐scale fermenter. Shake flask studies revealed a higher delta‐endotoxin concentration of Btk at 30 g L−1 TS concentration and 2.5% (v v−1) volume of pre‐culture. The fermenter experiments conducted using SIW at 30 g L−1 TS concentration under controlled conditions of temperature, pH and dissolved oxygen showed higher spore count, enzyme production (protease and amylase) and delta‐endotoxin concentration as compared with those of SIW at 15 g L−1 TS concentration. The entomotoxicity, at the end of fermentation, with SIW at 30 g L−1 solids concentration (17.8 × 109 SBU L−1, measured against spruce budworm) was considerably higher as compared with entomotoxicity at 15 g L−1 solids concentration (15.3 × 109 SBU L−1) and semi‐synthetic medium (11.7 × 109 SBU L−1). The pellet, comprising spores and delta‐endotoxin complex obtained after centrifugation and followed by resuspension (in supernatant) in one‐tenth of the original volume, of SIW at 30 g L−1 solids concentration media registered the highest potential for application (to protect forests against spruce budworm) than other media in term of entomotoxicity.