Development and characterization of silver-based antimicrobial ethylene-vinyl alcohol copolymer (EVOH) films for food-packaging applications

The use of silver as an antimicrobial in the food area has raised wide interest in recent years. In the present work, 0.001-10 wt % silver ions was satisfactorily incorporated into an ethylene-vinyl alcohol (EVOH) copolymer matrix by a solvent casting technique. The antibacterial efficacy of the composite was evaluated under laboratory conditions and in contact with some foods. The ionic compound did not affect the crystallinity or the water-induced plasticization of the materials and was homogeneously distributed across the surface and thickness of the films. When immersed in water, sorption-induced release of 50-100% of the silver ions took place in <30 min. In the bacterial minimal growth medium M9, the minimal inhibitory concentration (MIC) of the film was in the range of 0.01-0.1 ppm. High protein content food samples displayed low susceptibility to the films (<1 log reduction in any case), whereas low protein content food samples exhibited no detectable bacterial counts for films with 1 and 10 wt % silver and about 2 log reduction for films with 0.1 wt % silver. These results represent a step forward in the understanding of silver antimicrobial efficacy and its possible application in the food-packaging industry, most likely as food coatings.     

Development of new antioxidant active packaging films based on ethylene vinyl alcohol copolymer (EVOH) and green tea extract

Ethylene vinyl alcohol copolymer (EVOH) films containing green tea extract were successfully produced by extrusion. The films were brown and translucent, and the addition of the extract increased the water and oxygen barrier at low relative humidity but increased the water sensitivity, the glass transition temperature, and the crystallinity of the films and improved their thermal resistance. An analysis by HPLC revealed that the antioxidant components of the extract suffered partial degradation during extrusion, reducing the content of catechin gallates and increasing the concentration of free gallic acid. Exposure of the films to various food simulants showed that the liquid simulants increased their capacity to reduce DPPH(?) and ABTS(?+) radicals. The release of green tea extract components into the simulant monitored by HPLC showed that all compounds present in the green tea extract were partially released, although the extent and kinetics of release were dependent on the type of food. In aqueous food simulants, gallic acid was the main antioxidant component released with partition coefficient values ca. 200. In 95% ethanol (fatty food simulant) the K value for gallic acid decreased to 8 and there was a substantial contribution of catechins (K in the 1000 range) to a greatly increased antioxidant efficiency. Kinetically, gallic acid was released more quickly than catechins, owing to its faster diffusivity in the polymer matrix as a consequence of its smaller molecular size, although the most relevant effect is the plasticization of the matrix by alcohol, increasing the diffusion coefficient >10-fold. Therefore, the materials here developed with the combination of antioxidant substances that constitute the green tea extract could be used in the design of antioxidant active packaging for all type of foods, from aqueous to fatty products, the compounds responsible for the protection being those with the higher compatibility with the packaged product.     

Characterization of (E,E,Z)-2,4,6-nonatrienal as a character impact aroma compound of oat flakes

To identify the compounds evoking the characteristic cereal-like, sweet aroma of oat flakes, an aroma extract dilution analysis (AEDA) was applied to a distillate prepared by solvent extraction/vacuum distillation from commercial oat flakes. Among the nine aroma-active compounds detected by gas chromatography-olfactometry and AEDA in the flavor dilution (FD) factor range of 4-1024, eight odorants, for example, (E)-beta-damascenone, (Z)-3-hexenal, and butanoic acid, showed only low FD factors. However, one odorant eliciting the typical cereal, sweet aroma of the flakes was detected with the highest FD factor of 1024. By mass spectrometry and nuclear magnetic resonance measurements followed by a synthesis, (E,E,Z)-2,4,6-nonatrienal, exhibiting an intense oat flake-like odor at the extremely low odor threshold of 0.0002 ng/L in air, was identified as the key odorant of the flakes. By means of a newly developed stable isotope dilution analysis using synthesized, carbon-13-labeled nonatrienal as the internal standard, a concentration of 13 mug of (E,E,Z)-2,4,6-nonatrienal per kilogram of the flakes was measured. Model studies suggested linolenic acid as the precursor of nonatrienal in oats.     

Formation of aroma compounds during long-term frozen storage of unblanched leek (Allium ampeloprasum Var. Bulga) as affected by packaging atmosphere and slice thickness

Content of aroma compounds and catalytic activity of lipoxygenase (LOX), hydroperoxide lyase (HPL), and alcohol dehydrogenase (ADH) were analyzed in 4- and 15-mm unblanched leek slices packed in atmospheric air (4- and 15-mm) or 100% nitrogen (N) (only 15-mm) seven times during 12 months of frozen storage (12M). Total amount of sulfur compounds was influenced by storage time, slice thickness, and atmosphere (concentration in fresh 4-mm slices = 17.8 mg/L, 4-mm 12M = 3.48 mg/L, fresh 15-mm slices = 2.48 mg/L, 15-mm 12M = 0.418 mg/L and 15-mm N 12M = 1.81 mg/L). The 4-mm slices significantly developed the most aldehydes after 12M (total amount = 9.28 mg/L) compared to 15-mm 12M (6.49 mg/L) and 15-mm N 12M (4.33 mg/L). LOX activity is positively influenced by nitrogen packaging, and HPL activity is influenced by slice thickness, whereas ADH is unaffected by both parameters.     

Characterization, antimicrobial activity, and mechanism of a high-performance (-)-epigallocatechin-3-gallate (EGCG)-CuII/polyvinyl alcohol (PVA) nanofibrous membrane

(-)-Epigallocatechin-3-gallate (EGCG) exhibited strong antimicrobial activity. However, the easy oxidation of EGCG has limited its application. To increase the antimicrobial activity and stability of EGCG, the EGCG-Cu(II) complex was formed by chelating copper ions and then electronspun into polyvinyl alcohol (PVA) nanofibers. Electronspun nanofibrous membranes were investigated by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), which showed that the average fiber diameter was 210 nm. Minimal inhibitory concentrations (MICs) of EGCG-Cu(II)/PVA membranes were tested against the tested strains. The bactericidal activity of EGCG-Cu(II) was suppressed by ethylenediaminetetraacetic acid (EDTA). Cell killing was accompanied by the leakage of intracellular proteins, indicating that the cytoplasmic membrane was badly damaged after exposure to the EGCG-Cu(II)/PVA membrane. We observed the process of cell damage by SEM. On the basis of experimental evidence and theoretical analyses, the mechanism proposed that copper ions played a cooperative role in the bactericidal process of EGCG. To evaluate the antimicrobial activity of the EGCG-Cu(II)/PVA membrane, we developed a rapid detection method by labeling cells with water-soluble CdTe quantum dots.     

Nutritional status of Amerindian children from the Beni River (lowland Bolivia) as related to environmental, maternal and dietary factors

OBJECTIVES: To report the nutritional status of children aged up to 15 years and their mothers living in a remote Amazonian area of Bolivia, and to study its main social, familial and maternal determinants.SETTING: Fifteen Beni River communities located at the foot of the Andes.DESIGN: Cross-sectional survey of riverside populations. All childbearing mothers and their children in the 15 communities were examined.METHODS: Information on household production, dietary habits and demography was collected. Individual clinical, anthropometric and parasitological examinations were carried out.SUBJECTS: A total of 631 persons were examined: 171 mothers and 460 children and adolescents aged 0 to 15 years.Results: There were no cases of severe wasting, but 41% of 0-5-year-olds and 36% of 5-10-year-olds were stunted. Among 346 stool specimens examined, 75% were positive for at least one helminth. Diversity of food and quality of diet were satisfactory in 54% of households, but 27% had low diversity scores. Mothers were lighter and shorter than those observed at the national level: 20% had height below 145 cm. Prevalence of anaemia (42%) was also higher. In pre-school children, multivariate analysis indicated a relationship between growth retardation and household factors such as dietary quality, ethnic group and clinical state, but not maternal anthropometry. In contrast, in school-age children and adolescents, growth retardation was related to maternal characteristics.CONCLUSIONS: Growth retardation appeared mainly during the weaning period and did not seem to improve thereafter. To ameliorate this situation, an effort should be made to prevent common parasitic and infectious diseases in young children. Follow-up of pregnant mothers during pregnancy and delivery also needs to be reinforced.     

Effects of ergot alkaloids on food preference and satiety in rabbits, as assessed with gene-knockout endophytes in perennial ryegrass (Lolium perenne)

Neotyphodium species are fungal endophytes best known for their protection of grass hosts and production of bioactive metabolites including ergot alkaloids. Perennial ryegrass-Neotyphodium sp. Lp1 symbiota that have altered ergot alkaloid profiles (resulting from knockouts in two different endophyte genes) were fed, along with controls, to rabbits to test the effects of ergot alkaloids on food preference and satiety. Interestingly, rabbits dramatically preferred plants that were endophyte-infected but free of ergot alkaloids over endophyte-free plants (P = 0.01). Accumulation of ergot alkaloids of the clavine class counteracted the added appeal of endophyte-infected plants. In satiety tests, consumption of ergovaline (the ultimate ergot pathway product in wild-type endophyte), but not of several other ergot alkaloids, during an initial meal had a negative effect on subsequent rabbit chow consumption (P < 0.05). The data indicate that clavines were sufficient to reduce the appeal of endophyte-infected grasses, whereas only ergovaline reduced appetite.     

Bioaccumulation potential of dietary arsenic, cadmium, lead, mercury, and selenium in organs and tissues of rainbow trout (Oncorhyncus mykiss) as a function of fish growth

The distribution and potential bioaccumulation of dietary arsenic, cadmium, lead, mercury, and selenium in organs and tissues of rainbow trout (Oncorhyncus mykiss Walbaum, 1792), a major aquaculture species, was studied in relation to fish growth over a period of >3 years. Fish were reared under normal farming conditions, that is, fed a standard fish food and exposed to negligible levels of waterborne trace elements. The age-related variations in the content of each trace element in gills, kidney, liver, muscle, and skin were studied through nonparametric regression analysis. A buildup of all elements in all tissues and organs was observed, but due to dilution with growth, the concentrations did not increase, except in a few cases such as cadmium and mercury in liver and kidney. In muscle tissue, the concentrations of mercury, lead, and selenium did not alter significantly with growth, whereas cadmium increased but remained at exceedingly low levels. The concentration of arsenic in muscle tissue peaked at 14 months and then decreased in adult specimens. Arsenic speciation by high-performance liquid chromatography--inductively coupled plasma mass spectrometry revealed that arsenic in muscle was almost exclusively present in the form of nontoxic arsenobetaine. Application of a mercury mass balance model gave predicted concentrations in agreement with measured ones and showed that in farmed rainbow trout the ratio of mercury concentrations in feed and in fish is about 1:1. Therefore, rainbow trout does not approach the limits established for human consumption even when reared with feed at the maximum permitted levels. These findings highlight the low bioaccumulation potential of toxic trace elements such as cadmium, lead, and mercury in rainbow trout following dietary exposure. On the other hand, selenium concentrations in muscle (about 0.2 microg g (-1) of fresh weight) show that rainbow trout may be a good source of this essential element.