Nélio José de Andrade

Zinc Oxide Nanoparticles: Synthesis, Antimicrobial Activity and Food Packaging Applications

Zinc oxide (ZnO) is an inorganic compound widely used in everyday applications. ZnO is currently listed as a generally recognized as safe (GRAS) material by the Food and Drug Administration and is used as food additive. The advent of nanotechnology has led the development of materials with new properties for use as antimicrobial agents. Thus, ZnO in nanoscale has shown antimicrobial properties and potential applications in food preservation. ZnO nanoparticles have been incorporated in polymeric matrices in order to provide antimicrobial activity to the packaging material and improve packaging properties. This review presents the main synthesis methods of ZnO nanoparticles, principal characteristics and mechanisms of antimicrobial action as well as the effect of their incorporation in polymeric matrices. Safety issues such as exposure routes and migration studies are also discussed.

Physical–mechanical and antimicrobial properties of nanocomposite films with pediocin and ZnO nanoparticles

This work aimed to develop nanocomposite films of methyl cellulose (MC) incorporated with pediocin and zinc oxide nanoparticles (nanoZnO) using the central composite design and response surface methodology. This study evaluated film physical-mechanical properties, including crystallography by X-ray diffraction, mechanical resistance, swelling and color properties, microscopy characterization, thermal stability, as well as antimicrobial activity against Staphylococcus aureus and Listeria monocytogenes. NanoZnO and pediocin affected the crystallinity of MC. Load at break and tensile strength at break did not differ among films. NanoZnO and pediocin significantly affected the elongation at break. Pediocin produced yellowish films, but nano ZnO balanced this effect, resulting in a whitish coloration. Nano ZnO exhibited good intercalation in MC and the addition of pediocin in high concentrations resulted crater-like pits in the film surfaces. Swelling of films diminished significantly compared to control. Higher concentrations of Nano ZnO resulted in enhanced thermal stability. Nanocomposite films presented antimicrobial activity against tested microorganisms.

Chemical composition and antibacterial activities from the essential oils of myrtaceae species planted in Brazil

The essential oils of seven Myrtaceae species were investigated for its chemical composition and antibacterial activity. The volatile oils were characterized by a high content of monoterpenoids of which 1,8-cineole (88.0, 65.0 and 77.0% for Melaleuca hypericifolia, Callistemon viminalis and Callistemon citrinus respectively), terpinen-4-ol (47.0 and 49.8% for Melaleuca thymifolia and Callistemon polandii respectively) and α-pinene (54.5% for Kunzea ericoides) were the major components. The oil from M. linariifolia was characterized by a high concentration of methyleugenol (87.2%). The oil from Melaleuca thymifolia was the most active, exhibiting high antimicrobial activity against all tested bacteria.

Bacterial adherence to different inert surfaces evaluated by epifluorescence microscopy and plate count method

The adherence of Listeria inoccua L6a and Staphylococcus aureus ATCC6538 was evaluated on stainless steel (SS), polycarbonate (PC) and polypropylene (PP) chips. The EP results showed a significant difference (p<0.05) among the microorganism species interactions, the surfaces and the contact time. The number of adhered cells on the chip surfaces increased as contact time increased and the number of L. innocua or S. aureus on the surface of SS, PC and PP chips reached 1.0x105 CFU/cm2 after 12 h of contact, in both methods. The CP method showed a better sensitivity to detect low number of adhered cells. The EP was better when the average number of adhered cells was between 10 and 100 per microscopy field.

Basil conservation affected by cropping season, harvest time and storage period

O manjericao (Ocimum basilicum L.) e empregado tanto na industria culinaria quanto fitoterapica e na medicina tradicional, devido ao teor e composicao de seu oleo essencial. No entanto, o manjericao nao pode ser conservado por longo periodo apos a colheita e sua qualidade pode ser prejudicada. O objetivo deste trabalho foi verificar a influencia da epoca e do horario de colheita sobre a conservacao de manjericao armazenado por diferentes periodos. O manjericao foi colhido as 8h e as 16h em agosto/1999 e em janeiro/2000. Os ramos foram acondicionados em filmes de PVC e armazenados por 3, 6 e 9 dias. Durante o armazenamento, o teor de clorofila, e o teor e a composicao do oleo essencial foram determinados e foram conduzidas analises microbiologicas. A epoca de colheita e os dias de armazenamento influenciaram o teor final de oleo essencial. Houve decrescimo linear dos teores de oleo essencial e de clorofila e do numero de colonias de fungos e bacterias ao longo do armazenamento. Nao houve efeito da epoca de colheita ou do horario de colheita sobre a composicao do oleo essencial, mas os teores de eugenol e linalol aumentaram durante o armazenamento. O numero de coliformes ficou abaixo de 0,3 NMP g-1 e o numero de Staphylococcus aureus, abaixo de 1,0x102 UFC g-1.

Hazards in non-pasteurized milk on retail sale in Brazil: prevalence of Salmonella spp, Listeria monocytogenes and chemical residues

A instabilidade do mercado de leite no Brasil forca pequenos produtores de leite a procurar alternativas de comercio de sua producao, o que inclui a venda de leite cru para individuos que dao preferencia a esse tipo de leite. Considerando a importância desse mercado e os conhecidos riscos a saude que o consumo de leite cru pode representar, este estudo avaliou a qualidade microbiologica e a presenca de Listeria monocytogenes, Salmonella spp., residuos de cloretos, antimicrobianos e inseticidas (organofosforados e carbamatos) em leite cru produzido em 210 propriedades leiteiras localizadas em quatro importantes estados produtores de leite no Brasil (Parana, Sao Paulo, Minas Gerais e Rio Grande do Sul). Em 66% das propriedades selecionadas, a ordenha era manual. Em 33% a ordenha era semi-automatica (ordenha mecânica balde ao pe) e em apenas 1% o sistema de ordenha e armazenamento era totalmente mecânico (sistema fechado). Todas as amostras de leite cru foram negativas para L. monocytogenes, Salmonella spp e residuos de cloretos. As contagens de aerobios mesofilos foram superiores a 105 UFC/mL em 75,7% das amostras. Em 80,4%, as contagens de coliformes foram superiores a 102 UFC/mL. Escherichia coli foi detectada em 36,8% das amostras. Inseticidas e residuos de antibioticos foram observados em 74,4% e 11,5% das amostras, respectivamente. Niveis inaceitaveis de microrganismos indicadores de higiene, inseticidas e residuos de antibioticos foram considerados fatores de risco mais importantes que os dois patogenos estudados.

Thermodynamic study of colorimetric transitions in polydiacetylene vesicles induced by the solvent effect.

We report the synthesis of 10,12-pentacosadyinoic acid (PCDA) and PCDA + cholesterol (CHO) + sphingomyelin (SPH) vesicles dispersed in water and the determination of their colorimetric response induced by small amount of organic solvents. In the absence of solvent, PCDA and PCDA/CHO/SPH vesicles showed an intense blue color. The addition of CHCl(3), CH(2)Cl(2), and CCl(4) caused a colorimetric transition (CT) in both structures with the following efficiency: CHCl(3) > CH(2)Cl(2) ≅ CCl(4). However, CH(3)OH did not cause a blue-to-red transition. By microcalorimetric technique we also determined, for the first time, the enthalpy change associated with the CT process and the energy of interaction between solvent molecules and vesicle self-assembly. We observed that the chloride solvents induced a colorimetric transition, but the thermodynamic mechanism was different for each of them. CT induced by CHCl(3) was enthalpically driven, while that caused by CH(2)Cl(2) or CCl(4) was entropically driven.

Toxigenic status of Staphylococcus aureus isolated from bovine raw milk and minas frescal cheese in Brazil.

A group of 291 Staphylococcus aureus isolates from mastitic cows milk (n = 125), bulk tank milk (n = 96), and Minas frescal cheese (n = 70) were screened for staphylococcal enterotoxin (SE) genes (sea, seb, sec, sed, see, seg, seh, sei, selj, and sell) and for the tst-1 gene encoding staphylococcal toxic shock syndrome toxin 1 by PCR assay. A total of 109 (37.5%) of the isolates were positive for at least one of these 11 genes, and 23 distinct genotypes of toxin genes were observed. Of the S. aureus isolates bearing SE genes, 17 (13.6%) were from mastitic cows milk, 41 (41.7%) were from bulk tank milk, and 51 (72.9%) were from Minas frescal cheese. The occurrence of exclusively more recently described SE genes (seg through sell) was considerably higher (87 of 109 PCR-positive strains) than that of classical SE genes (sea through see, 15 strains). The SE genes most commonly detected were seg and sei; they were found alone or in different combinations with other toxin genes, but in 60.8% of the cases they were codetected. No strain possessed see. The tst-1 gene was found in eight isolates but none from mastitic cows milk. Macrorestriction analysis of chromosomal DNA from 89 S. aureus isolates positive for SE gene(s) was conducted with the enzyme SmaI. Fifty-five distinct pulsed-field gel electrophoresis patterns were found, demonstrating a lack of predominance of any specific clone. A second enzyme, Apa I, used for some isolates was less discriminating than Sma I. The high genotype diversity of potential toxigenic S. aureus strains found in this study, especially from Minas frescal cheese, suggests various sources of contamination. Efforts from the entire production chain are required to improve consumer safety.

Assessment of hydrophobicity and roughness of stainless steel adhered by an isolate of Bacillus cereus from a dairy plant

The interaction between the surface of stainless steel and Bacillus cereus was studied in terms of the characteristics of interfacial interaction determined from the measurement of the contact angle of the surface of B. cereus and stainless steel in the presence or absence of B. cereus adherence. The microtopographies and the roughness of the surface of stainless steel and stainless steel adhered by B. cereus were evaluated with the help of atomic force microscopy and perfilometry. The strain of B. cereus studied was considered hydrophilic, whereas the stainless steel was considered hydrophobic. The adhesion was not thermodynamically favorable (ΔGadhesion > 0) between the stainless steel and the strain of B. cereus studied. Thus, the interaction between them was not favored by the thermodynamic aspect of adhesion. There was no difference (p > 0.05) in the roughness of the surfaces of stainless steel adhered by B. cereus when analyzed by atomic force microscope and perfilometry.

Increased presevation of sliced mozzarella cheese by antimibrobial sachet incorporated with allyl isothiocyanate

There is an increasing tendency to add natural antimicrobials of plant origin into food. The objective of this work was to develop a microbial sachet incorporated with allyl isothiocyanate (AIT), a volatile compound of plant origin, and to test its efficiency against growth of yeasts and molds, Staphylococcus sp. and psychrotrophic bacteria on sliced mozzarella cheese. Another objective was to quantify the concentration of AIT in the headspace of cheese packaging. A reduction of 3.6 log cycles was observed in yeasts and molds counts in the mozzarella packed with the antimicrobial sachet over 15-day storage time. The sachet also showed an antibacterial effect on Staphylococcus sp., reducing 2.4 log cycles after 12-day storage. Psychrotrophic bacteria species were the most resistant to the antimicrobial action. The highest concentration of AIT (0.08µg.mL(-1)) inside the active packaging system was observed at the 6(-)day of storage at 12 oC ± 2 oC. At the end of the storage time, AIT concentration decreased to only 10% of the initial concentration. Active packaging containing antimicrobial sachet has a potential use for sliced mozzarella, with molds and yeasts being the most sensitive to the antimicrobial effects.