Searching potential candidates for development of protective cultures: Evaluation of two Lactobacillus strains to reduce Listeria monocytogenes in artificially contaminated milk

The aims of this work were (a) to select the minimum concentrations of two bacteriocin-producing lactobacilli strains to reduce Listeria monocytogenes growth in whole milk, (b) to evaluate the individual and combined application of these chosen lactobacilli concentrations as protective culture in this food and, (c) to estimate if lactobacilli growth caused undesirable changes in the visible characteristics of milk. The selected minimum lactobacilli concentration with antilisterial activity was 10⁶ CFU ml⁻¹ for both lactobacilli. Although a high initial concentration of L. monocytogenes (10⁴ CFU ml⁻¹) was added to milk, a notable reduction on listerial counts (2–4 log CFU ml⁻¹) was achieved in comparison to the control. These lactobacilli showed a good adaptability in milk reaching optimal counts and not causing undesirable visible changes. In conclusion, the use of these lactobacilli could be considered as a bio-strategy potentially effective to limit the contamination by L. monocytogenes in certain milk-derived products.     

Hyperbaric storage at and above room temperature of a highly perishable food

Hyperbaric storage at naturally variable room temperature (RT) conditions (18–21 °C) and above (30 °C) was evaluated as a possible new food preservation method, regardless of temperature. Preservation of watermelon juice (used as a case study of a highly perishable food) at RT and 5 °C at atmospheric pressure was compared to preservation under 100 MPa at RT. After 8 h of hyperbaric storage at 100 MPa, the initial microbial loads of the watermelon juice were reduced by 1 log unit for total aerobic mesophiles, and 1–2 log units for Enterobacteriaceae and yeasts and moulds, to levels of about 3 log units for the former and below the detection limit for the latter, and remained thereafter unchanged up to 60 h. Similar results were obtained at 30 °C at 100 MPa after 8 h. At atmospheric pressure at RT (24 h) and 30 °C (8 h), microbial levels were already above quantification limits and unacceptable for consumption. Furthermore, pressure attenuated the increase in titratable acidity verified at atmospheric pressure, but caused higher colour changes, especially a higher lightness and a lower browning degree. Post-hyperbaric storage at 5 °C revealed an extended shelf life, as an additional benefit of hyperbaric storage. These results show that hyperbaric storage is a very promising food preservation methodology.     

Screening of mycotoxin multicontamination in medicinal and aromatic herbs sampled in Spain

BACKGROUND: The aim of this study was to screen the multicontamination by mycotoxins in a wide variety of aromatic and/or medicinal herb samples collected in Spain. Mycotoxins studied were aflatoxins (AFs), ochratoxin A (OTA), zearalenone (ZEA), deoxynivalenol (DON), T‐2 toxin (T‐2), citrinin and fumonisins (FBs). Mycotoxins were analysed by ELISA after a clean‐up step with multifunctional columns (AFs, ZEA, DON, FBs and T‐2) or polyamide column (citrinin). RESULTS: Of the 84 samples analysed 99% were contaminated with T‐2, 98% with ZEA, 96% with AFs, 63% with OTA, 62% with DON, 61% with citrinin and 13% with FBs. Nearly 87% of samples contained four or more mycotoxins simultaneously, being AFs, T‐2 and ZEA the mycotoxins co‐existing in almost every sample. 100% of the samples in our study were multicontaminated. CONCLUSION: This study shows that this kind of commodity could be an important source of mycotoxin contamination and, in general, this contamination is not limited to only one group of mycotoxins. Mycotoxin contamination on artichoke immature florets, boldus leaves, burdock leaves, dandelion plant, frangula bark, ginkgo leaves, lemon verbena leaves, olive leaves, red tea leaves, ribgrass leaves, St Mary's thistle seeds, spearmint leaves, star anise fruit, vervain and white tea leaves has been described for the first time. Finally, this is the first report on DON and T‐2 presence in herbs. No study of this kind has been previously developed in Spain. Copyright © 2009 Society of Chemical Industry     

Impact of Debaryomyces hansenii strains inoculation on the quality of slow dry-cured fermented sausages

Debaryomyces hansenii strains, M4 and P2, isolated from natural fermented sausages were inoculated in slow fermented sausages to study their effect on processing parameters, microbial population, volatile compound and sensory characteristics. The inoculation of D. hansenii strains, M4 and P2, did not affect the ripening process as no differences in pH and Aw were detected. The dominance of the inoculated yeast strains along the process was followed by RAPDs of M13 minisatellite. The inoculated yeasts, P2 and M4, were recovered at the end of the ripening process although P2 appeared in higher counts than M4. The sausages inoculated with P2 resulted in a decrease in lipid oxidation values (TBARS) and a reduction of lipid-oxidation derived aldehydes in addition to a highest acid compound abundance. M4 inoculated sausages resulted in highest sulphur containing compound abundance. However, no differences in consumer acceptance were detected. Moreover, both yeast strains were responsible for the generation of ethyl methyl-branched ester compounds in the dry-cured sausages.     

UV-Visible Spectroscopy and Multivariate Classification as a Screening Tool for Determining the Adulteration of Sauces

A rapid, simple, and economic multivariate screening methodology based on UV-visible spectroscopy and multivariate classification is proposed to test for adulteration in sauces. Two classification strategies were evaluated to compare their ability to detect food fraud: untargeted modeling (class modeling) and targeted classification (discriminant analysis). As a case study, the possible adulteration of ketchups and barbecue sauces with the banned Sudan I dye was considered. The classification models were built with a new classification tool for class modeling (partial least squares-density modeling, PLS-DM) and with the classical discriminant partial least squares-discriminant analysis (PLS-DA). Very satisfactory classification results were obtained with both strategies: regarding untargeted modeling, only original samples (class 1) were modeled obtaining a 94.5 % of correct classification and regarding targeted classification, two classes were considered (class 1 original samples and class 2 adulterated samples) with an overall classification rate of 97.3 %. The two strategies are useful and adequate as screening tools for monitoring the quality of sauces especially in situations that require quick responses.     

Preservative Effect of a Previous High-Pressure Treatment on the Chemical Changes Related to Quality Loss in Frozen Hake (<Emphasis Type="Italic">Merluccius merluccius</Emphasis>)

The objective of this study was the quality loss inhibition of hake (Merluccius merluccius) during the frozen storage. For it, the effect of a previous high-pressure (HP) treatment (150–450 MPa for 2 min) was analysed throughout a 5-month storage at ? 10 °C. Quality changes were monitored by complementary chemical analyses. Inhibition (p < 0.05) of dimethylamine (DMA), free fatty acid (FFA), formaldehyde (FA), trimethylamine, total volatile amine and fluorescent compound (tertiary lipid oxidation compound) formation was concluded by previous pressure treatment according to the one-way ANOVA analysis. On the contrary, no effect (p > 0.05) on the K value, polyene index and formation of peroxides and thiobarbituric acid reactive substances was achieved. Additionally, a multifactor ANOVA test (pressure and frozen storage time effects; i.e. comparison among HP treatments) showed an inhibitory effect (p < 0.015) on DMA and FFA formation, this effect increasing with pressure level applied. This inhibitory effect on the formation of such molecules related to quality loss can be explained on the basis of the damage caused to different kinds of enzymes such as trimethylamine oxide demethylase, lipases and phospholipases, so that their activity during the subsequent frozen storage would decrease. The work here presented provides for the first time information concerning the employment of HP technology to inhibit the DMA, FA and FFA formation during the frozen storage of hake. Further research focussed on commercial frozen conditions (? 18 °C) and including sensory and nutritional aspects is foreseen.     

Gel mechanical properties of milk whey protein–dextran conjugates obtained by Maillard reaction

The effect of Maillard reaction on the mechanical properties of whey protein isolate (WPI) heat-induced gels was evaluated. WPI and dextran (15–25 kDa) conjugates were obtained by controlled dry heating during storage at 60 °C and 63% relative humidity for 2, 5 and 9 days. Changes in browning intensity and content of free amino groups were used to estimate the Maillard reaction. A decrease in free amino groups of WPI was observed when increasing polysaccharide concentration and reaction time. An increase in both a* and b* CIE Lab colour parameters indicated the development of a reddish-brown colour, typical of the Maillard reaction. Uniaxial compression and stress relaxation tests were performed to measure the mechanical properties of mixed and conjugate gels. Maillard reaction significantly modified the mechanical properties of WPI/DX gels, and even prevented fracture when conjugate gels were subjected to 80% deformation in uniaxial compression test.     

Review of the environmental policy instruments in the standardization of H2 for the decarbonization of Mexico

The objective of this work is to review the environmental and ecological policy instruments that Mexican legislation for existence of an Official Mexican Hydrogen Standard according to the premises motivates decarbonization. There is a worldwide interest in hydrogen (H₂) and its incorporation into legal systems. In Mexico there are large legal gaps that question the legality of H₂, because it is not recognized in a federal law and is only considered in technical standards of voluntary application. Also, Mexico has forest, agricultural, and livestock waste that, if properly used, can cover the energy demand of communities. The main findings of this study refer to the fact that, according to international standards for the management of H₂ and taking into account the regulatory limitations in Mexico, it is possible to promote, an Official Mexican Standard exclusively aimed at establishing the minimum requirements for the design, construction, operation and maintenance of H₂ storage, considering the areas of the opportunity offered by foreign experiences, according to the Mexican context. It is concluded that the parameters of legality exist in the instruments of environmental policy, to support the existence of an Official Mexican Standard of H₂.