RESUMO

Recently, the interest of consumers regarding artisan cheeses worldwide has increased. The ability of different autochthonous and characterized lactic acid bacteria (LAB) to produce aromas and the identification of the volatile organic compounds (VOCs) responsible for flavor in cheeses are important aspects to consider when selecting strains with optimal aromatic properties, resulting in the diversification of cheese products. The objective of this work is to determine the relationship between VOCs and microorganisms isolated (Lacticaseibacillus paracasei, Lactiplantibacillus plantarum, Leuconostoc mesenteroides and Lactococcus lactis subsp. hordniae) from raw sheep milk cheeses (matured and creamy natural) using accuracy and alternative methods. On combining Sanger sequencing for LAB identification with Gas Chromatography coupled to Ion Mobility Spectrometry (GC−IMS) to determinate VOCs, we describe cheeses and differentiate the potential role of each microorganism in their volatilome. The contribution of each LAB can be described according to their different VOC profile. Differences between LAB behavior in each cheese are shown, especially between LAB involved in creamy cheeses. Only L. lactis subsp. hordniae and L. mesenteroides show the same VOC profile in de Man Rogosa and Sharpe (MRS) cultures, but for different cheeses, and show two differences in VOC production in skim milk cultures. The occurrence of Lactococcus lactis subsp. hordniae from cheese is reported for first time.

RESUMO

The purpose of this work was to study the potential of gas chromatography-ion mobility spectrometry (GC-IMS) to differentiate lactic acid bacteria (LAB) through target identification and fingerprints of volatile metabolites. The LAB selected were used as reference strains for their influence in the flavour of cheese. The four strains of LAB can be distinguished by the fingerprints generated by the volatile organic compounds (VOCs) emitted. 2-butanone, 2-pentanone, 2-heptanone and 3-methyl-1-butanol were identified as relevant VOCs for Lactobacillus casei and Lactobacillus paracasei subsp. paracasei. 2-Butanone and 3-methyl-1-butanol were identified in Lactococcus lactis subsp. lactis and Lactococcus cremoris subsp. cremoris. The IMS signals monitoring during a 24-30h period showed the growth of the LAB in vitro. The results demonstrated that GC-IMS is a useful technology for bacteria recognition and also for screening the aromatic potential of new isolates of LAB.

Assuntos

RESUMO

Capillary electrophoresis (CE) is increasingly being used not only for research purposes but also for routine analyses. The latter, however, are especially difficult when the analytes are present at very low concentrations in complex food samples (e.g. penicillins in milk of animal origin). No study of the difficulties encountered in daily practice in sample treatments for the determination of penicillins (PENs) in milk by CE has to our knowledge been reported. Rather than reviewing the main uses of CE for determining PENs in different types of samples, this paper focuses on the weaknesses of available methods for this purpose, which originate in sample treatment rather than in a lack of robustness of the CE technique. Some problems which, based on our own experience, often confront sample treatment and method development in this context are discussed here. Clearly, the greatest source of error in this context is sample processing, which must provide optimal extraction and preconcentration of analytes, and extracts compatible with the separation technique to be used. In this respect, using time-consuming procedures can cause the loss of variable amounts of analytes in different steps. Interestingly, dramatically simplifying the sample preparation process can detract from sensitivity but lead to increased recoveries. As with any methodological development in routine analysis, acceptable results can only be obtained by considering all potentially influential factors.

Assuntos

RESUMO

An easy, selective, and sensitive method has been developed for the determination of enrofloxacin (ENR) and its main active metabolite, ciprofloxacin (CIP), in raw bovine milk using CE with UV detection at 268 nm. Milk samples were prepared by a clean-up/extraction procedure based on protein precipitation with hydrochloride acid followed by being defatted by centrifugation and SPE using a hydrophilic-lipophilic balance cartridge. Optimum separation was obtained using a 50 mM phosphoric acid at pH 8.4 and the total electrophoretic run time was 6 min. Sample preparation by this method yielded clean extracts with quantitative and consistent mean recoveries from 89 to 97% for CIP and from 93 to 98% for ENR. LODs obtained were lower to the maximum residue limits for these fluoroquinolones. The precision of the ensuing method is acceptable; thus, the RSD for peak area and migration time was less than 8.5 and 0.5% for CIP and 9.9 and 0.9% for ENR, respectively. The results showed that the proposed method was efficient showing good recoveries, sensitivity, and precision for the studied compounds and could be satisfactorily applied in routine analysis for the monitoring of ENR and CIP residues in milk, due to its ruggedness and feasibility demonstrated.

Assuntos

RESUMO

CE has generated considerable interest in the research community since instruments were introduced by different trading companies in the 1990s. Nowadays, CE is popular due to its simplicity, speed, highly efficient separations and minimal solvent and reagent consumption; it can also be included as a useful technique in the nanotechnology field and it covers a wide range of specific applications in different fields (chemical, pharmaceutical, genetic, clinical, food and environmental). CE has been very well evaluated in research laboratories for several years, and different new approaches to improve sensitivity (one of the main drawbacks of CE) and robustness have been proposed. However, this technique is still not well accepted in routine laboratories for food analysis. Researching in data bases, it is easy to find several electrophoretic methods to determine different groups of analytes and sometimes they are compared in terms of sensitivity, selectivity, precision and applicability with other separation techniques. Although these papers frequently prove the potential of this methodology in spiked samples, it is not common to find a discussion of the well-known complexity of the matrices to extract analytes from the sample and/or to study the interferences in the target analytes. Summarizing, the majority of CE scientific papers focus primarily on the effects upon the separation of the analytes while ignoring their behavior if these analytes are presented in real samples.

Assuntos

RESUMO

The interaction between Acacia and Pseudomyrmex is a textbook example of mutualism between ants and plants, nevertheless aspects of its evolutionary biology have not been formally explored. In this paper we analyze primarily the phylogenies of both New World Acacia and of their associated species of ants, and the geographic origin of this mutualism. Until now, there has been no molecular analysis of this relationship in terms of its origin and age. We analyzed three chloroplast markers (matK, psaB-rps14, and trnL-trnF) on a total of 70 taxa of legumes from the subfamily Mimosoideae, and two nuclear regions (long-wavelength rhodopsine and wingless) on a total of 43 taxa of ants from subfamily Pseudomyrmecinae. The monophyly of subgenus Acacia and within the New World lineages that of the myrmecophilous Acacia group was established. In addition, our results supported the monophyly of the genus Pseudomyrmex and of the associated acacia-ants P. ferrugineus group. Using Bayesian methods and calibration data, the estimated divergence times for the groups involved in the mutualism are: 5.44+/-1.93 My for the myrmecophilous acacias and 4.58+/-0.82 My for their associated ant species, implying that their relationship originated in Mesoamerica between the late Miocene to the middle Pliocene, with eventual diversification of both groups in Mexico.

Assuntos