María C. Manca de Nadra

A comparative survey of two analytical methods for identification and quantification of biogenic amines

Recent trends in food security are promoting an increasing search for trace compounds that can affect human health such as biogenic amines. The present paper describes a comparative study between two modified quick and simple HPLC methods for evaluating biogenic amines. In both methods biogenic amines were separated by reversed-phase chromatography. In the method with pre-column derivatization with o-phthaldialdehyde after modifications we obtained excellent results to separate and to quantify both biogenic amines and amino acids in a single run.

Antimicrobial effect of polyphenols from apple skins on human bacterial pathogens

Apples possess many beneficial properties for the human health related with their high content in phenolic compounds. The antimicrobial effect of these compounds from the skin of two apple varieties, Royal Gala and Granny Smith, against human pathogens was examined. The phenolic compounds were extracted with the following solvents: A, acetone: water: acetic acid; B, ethyl acetate: methanol: water and C, ethanol: water. Total phenolic, flavonoid and non-flavonoid contents were analyzed in the extracts. The antimicrobial effect was determined using the agar diffusion method. The highest inhibitory effect of both apple varieties corresponded to extract A, which contained a high phenolic content. The Granny Smith extracts with higher phenolic content presented a superior antimicrobial effect against the selected microorganisms: Escherichia coli, Escherichia coli ATCC 25922, Escherichia coli ATCC 35218, Staphylococcus aureus ATCC 25923, Staphylococcus aureus ATCC 29213, Pseudomonas aeruginosa ATCC 27853, Enterococcus faecalis ATCC 29212 and Listeria monocytogenes. The most sensitive microorganisms

Kinetics and metabolic behavior of a composite culture of Kloeckera apiculata and Saccharomyces cerevisiae wine related strains

The kinetics and metabolic behavior of Kloeckera apiculata mc1 and Saccharomyces cerevisiae mc2 in composite culture was investigated. K. apiculata showed a higher viability through the fermentation; however the maximum cell density of both yeasts decreased. This behavior was not due to ethanol concentration, killer toxins production or competition for assimilable nitrogenous compounds between both yeasts. Despite the consistent production of secondary products by single culture of K. apiculata, an increase of these compounds was not observed in mixed culture. These results contribute to a better understanding of the behavior of non-Saccharomyces yeasts and their potential application in the wine industry.

Polysaccharide production by Pediococcus pentosaceus from wine.

Abstract Two polymer-forming strains of Pediococcus pentosaceus from Argentinian wines were grown under different conditions. Polysaccharides were produced independently of carbon source at the early logarithmic phase of growth. With the presence of ethanol and SO2, the specific polymers production was greater. The polysaccharides comprised of glucose, fructose and galactose, with predominant linkages of α-1,4- and α-1,6-glucosidic with a ratio 1:1. They contained approximately 5500 hexose molecules.

Phenolic compound combinations on Escherichia coli viability in a meat system.

The aim of this work was to investigate the antibacterial activity of flavonoid and nonflavonoid phenolic compound combinations and the synergistic antibacterial effects against Escherichia coli ATCC 35218. In nutrient medium, the combinations of gallic and protocatechuic acids, gallic and caffeic acids, and rutin and quercetin were the best antibacterial agents, with synergistic effects, and were selected to test their activity in a meat model system. All combinations diminished the bacterial growth, without cellular death at 20 degrees C. The combinations of gallic and caffeic acids and rutin and quercetin were the most effective at 4 degrees C; no viable cells were detected with 100 or 200 mg/L at 21 or 14 days of incubations, respectively. The lowest decimal reduction times were found with the rutin-quercetin combination. These results demonstrate a synergistic effect of the selected combination of flavonoid or nonflavonoid compounds with an important antibacterial effect in meat, using low concentrations.

Acetaldehyde Production by Strains Used as Probiotics in Fermented Milk

Lactic acid bacteria have diverse shunts for the metabolism of acetaldehyde, which is involved in the metabolism of carbohydrates, proteins and nucleic acids. In Lactobacillus acidophilus and Lactobacillus casei , strains isolated from feces of healthy children, acetaldehyde can be formed from different sources. Phosphotransacetilase, acetate kinase, aldehyde dehydrogenase and 2-deoxiriboaldolase activities were found in both strains. α-Carboxilase and threonine aldolase activities only occurred in L. acidophilus . In contrast, phosphoketolase activity was present in L. casei , but absent in the other strain studied. The accumulation of acetaldehyde in the growth medium is possible because the enzymes specific activities to form it are higher than those able to convert it to ethanol.

Effect of Wine Phenolic Compounds on Lactobacillus hilgardii 5w Viability

After 6 days of Lactobacillus hilgardii 5w incubation at 4 degrees C, the viable cell counts diminish 31.9, 45.6, and 89.0% when suspended in control wine (2,600 mg/liter gallic acid equivalents [GAE]), three-fold concentrated wine (6,150 mg/liter GAE), and six-fold concentrated wine (13,000 mg/liter GAE), respectively. At 20 degrees C in the same conditions, the cell viabilities decrease 74.2, 80.5, and 100.0%, respectively. In decolorized wines, which result in tannin losses, the viable cell counts increase. There is a relationship between L. hilgardii 5w tannin binding and its viability loss.

The role of two families of bacterial enzymes in putrescine synthesis from agmatine via agmatine deiminase.

Putrescine, one of the main biogenic amines associated to microbial food spoilage, can be formed by bacteria from arginine via ornithine decarboxylase (ODC), or from agmatine via agmatine deiminase (AgDI). This study aims to correlate putrescine production from agmatine to the pathway involving N-carbamoylputrescine formation via AdDI (the aguA product) and N-carbamoylputrescine amidohydrolase (the aguB product), or putrescine carbamoyltransferase (the ptcA product) in bacteria. PCR methods were developed to detect the two genes involved in putrescine production from agmatine. Putrescine production from agmatine could be linked to the aguA and ptcA genes in Lactobacillus hilgardii X1B, Enterococcus faecalis ATCC 11700, and Bacillus cereus ATCC 14579. By contrast Lactobacillus sakei 23K was unable to produce putrescine, and although a fragment of DNA corresponding to the gene aguA was amplified, no amplification was observed for the ptcA gene. Pseudomonas aeruginosa PAO1 produces putrescine and is reported to harbour aguA and aguB genes, responsible for agmatine deiminase and N-carbamoylputrescine amidohydrolase activities. The enzyme from P. aeruginosa PAO1 that converts N-carbamoylputrescine to putrescine (the aguB product) is different from other microorganisms studied (the ptcA product). Therefore, the aguB gene from P. aeruginosa PAO1 could not be amplified with ptcA-specific primers. The aguB and ptcA genes have frequently been erroneously annotated in the past, as in fact these two enzymes are neither homologous nor analogous. Furthermore, the aguA, aguB and ptcA sequences available from GenBank were subjected to phylogenetic analysis, revealing that gram-positive bacteria harboured ptcA, whereas gram-negative bacteria harbour aguB. This paper also discusses the role of the agmatine deiminase system (AgDS) in acid stress resistance.

Influence of wine-related physicochemical factors on the growth and metabolism of non-Saccharomyces and Saccharomyces yeasts in mixed culture

The influence of two physicochemical factors involved in winemaking, temperature and SO2, on the kinetics and metabolic behavior of Kloeckera apiculata and Saccharomyces cerevisiae was examined. Highest biomass was reached at 15 and 25°C for K. apiculata and S. cerevisiae, respectively. Pure cultures of K. apiculata died off early with increasing temperature, but in co-culture with S. cerevisiae it showed higher viability and a change in the death curve from exponential to linear. Statistical analysis revealed that metabolite production was significantly different for the three cultures and also at the different fermentation temperatures. Besides, the interaction between culture type and temperature was significant. At temperatures from 15 to 30°C the mixed culture showed similar ethanol and lower acetic acid production compared with a pure culture of K. apiculata. SO2 addition slightly increased survival of the non-Saccharomyces species in pure and mixed cultures. Statistical evaluation indicated that culture type and SO2 addition significantly affected metabolite production, but the interaction between culture and SO2 was not significant. These results contribute to current knowledge of enological factors and their effect on prevalence and fermentative activities of the composite yeast flora and the statistical significance emphasizes the importance of the combined influence of the culture type and physicochemical factors on the production of fermentation metabolites.

Arginine metabolism inLactobacillus leichmannii

Lactobacillus leichmannii ATCC 4797 metabolizes arginine via the arginine dihydrolase pathway producing ornithine, ammonia, carbon dioxide, and ATP. The specific activities of arginine deiminase and ornithine transcarbamylase were two-or threefold lower (stationary growth phase) in galactose-grown cells. The addition of arginine increased the specific activities of these two enzymes with all growth sugars. When glucose was virtually exhausted from the medium, maximum activities of both enzymes were achieved. The formation of two first enzymes of the arginine dihydrolase pathway inL. leichmannii ATCC 4797 seems to be under the control of two processes: induction by arginine and repression of the induced synthesis by glucose.