Growth, biogenic amine production and tyrDC transcription of Enterococcus faecalis in synthetic medium containing defined amino acid concentrations.

AIMS: The tyraminogenic potential of the strains Enterococcus faecalis EF37 and ATCC 29212 was investigated in a synthetic medium containing defined amounts of tyrosine and phenylalanine at different temperatures. METHODS AND RESULTS: Enterococci growth and the production of biogenic amines (BA) were evaluated in relation to their pre-growth in medium containing tyrosine. Significant differences between the two strains were evidenced at metabolic level. Both the pre-adapted strains grew faster in all the tested conditions, independently of the presence of the precursor. Temperatures of 30 and 40°C positively affected the growth parameters. The tyrosine decarboxylase (tyrDC) activity of the strain EF37 was positively affected by pre-adaptation, while ATCC 29212 showed a faster and higher tyramine accumulation with not-adapted cells. The expression analysis of the gene tyrDC confirmed the influence of the growth conditions on gene transcription. CONCLUSIONS: The small differences found between the two strains in the maximum transcript level reached rapidly after the inoculum and the different behaviour in the tyramine accumulation suggested the possible involvement of complex regulation mechanisms on the tyrDC or on the membrane transport systems, which could affect the different BA accumulation trend. SIGNIFICANCE AND IMPACT OF THE STUDY: This study gives deeper insight into the metabolic regulation of tyrDC activity of enterococci.

Tween 80 and respiratory growth affect metabolite production and membrane fatty acids in Lactobacillus casei N87.

AIMS: To evaluate the effect of cultivation (anaerobiosis vs respiration) and Tween 80 supplementation on the production of metabolites and on the composition of membrane fatty acids (FAs) in Lactobacillus casei N87. METHODS AND RESULTS: Anaerobic and respiratory growth, with or without Tween 80 supplementation, was carried out in a chemically defined medium. Production of biomass, organic acids, volatile organic compounds (VOCs), consumption of amino acids and changes in membrane FAs were investigated. Respiration altered the central metabolism rerouting pyruvate away from lactate accumulation, while Tween 80 had a minor effect on metabolic pathways. VOCs were mainly affected by growth conditions and significant amounts of diacetyl were produced by respiratory cultures. Respiration increased desaturation of membrane lipids and Tween 80 improved the production of essential polyunsaturated FAs. Palmitic acid decreased in Tween-supplemented aerated cultures. CONCLUSIONS: Combination of Tween 80 and respiratory growth promoted production of biomass and aroma compounds and affected the composition of membrane FAs in Lact. casei N87. SIGNIFICANCE AND IMPACT OF THE STUDY: Respiration might be exploited in Lact. casei as a natural strategy for the enhanced production of aroma compounds.

Plants of the genus Allium as antibacterial agents: From tradition to pharmacy.

Plants belonging to the genus Allium are widely cultivated and used all over the world as food and medicinal plants. Since ancient times, these plants, particularly garlic (Allium sativum L.) and onion (Allium cepa L.), have represented important components of typical recipes and traditional healing systems. Not the least of which, their use as food biopreservatives is well documented, due to the relevant antibacterial activity of their extracts and essential oils. In addition to garlic and onion, this review article deals with the main members of the genus Allium, including A. ampeloprasum (Leek), A. schoenoprasum (Chive) and A. ascalonicum (Shallot), focusing both on their ethnonutritional uses and potential as promising food biopreservative agents. Noteworthy, recent research has demonstrated Allium derivatives to be novel components in active edible coatings as well as nanoformulates.

Survival of the functional yeast Kluyveromyces marxianus B0399 in fermented milk with added sorbic acid.

In this study, the survival of the functional yeast Kluyveromyces marxianus B0399 in an industrially produced fermented milk was evaluated. In particular, the yeast viability was assessed throughout the entire shelf-life of the product (30 d) to ensure the presence of the effective yeast dose (20 million viable cells for each serving of 125 g) while avoiding, by sorbic acid addition, yeast growth, which could affect product quality and stability. To find the best combination of yeast and sorbic acid concentration, 13 different combinations were tested, and then 2 of them were chosen for industrial production. In production at lower concentrations (30 million viable cells, 150 mg/kg of sorbic acid) the effective dose was maintained only at 4 and 6°C, whereas at higher dosages (70 million viable cells, 250 mg/kg of sorbic acid) the effect of temperature was less evident. In all the trials, the concentration of sorbic acid was not affected by microbial metabolism and remained stable throughout the entire shelf-life.

Effect of a sublethal high-pressure homogenization treatment on the fatty acid membrane composition of probiotic lactobacilli.

UNLABELLED: High-pressure homogenization (HPH) has been proposed to be applied directly to lactic acid bacterial cells at sublethal levels to enhance some functional properties. As the principal target of HPH are the cell surface envelope structures, the aim of this work was to study the effect of a HPH treatment, applied at 50 MPa, on cell membrane stress responses of already-known functional strains, isolated from Argentinean products. Specifically, the membrane fatty acid composition of cells before and after the sublethal treatment was investigated, and the results showed that plasma membranes, their level of unsaturation and their composition are involved in response mechanisms adopted by microbial cells when subjected to a sublethal HPH stress. In fact, the data obtained demonstrated that the treatment was able to modify the fatty acid profile of the different strains, although a uniform response was not observed. Further studies are necessary both to elucidate the role of each fatty acid in the cell response mechanisms and to clarify the changes in membrane compositions induced by HPH treatment also in relation to the applicative potential of this technique. SIGNIFICANCE AND IMPACT OF THE STUDY: This study contributed to understand the response mechanisms activated in cells exposed to pressure stress. It has been demonstrated that high-pressure homogenization (HPH) treatments, conducted at sublethal levels, could increase some important functional and technological characteristics of nonintestinal probiotic strains. The findings of this paper can contribute to elucidate the mechanisms through which these treatments can modify these strain probiotic properties that are related to outermost cell structures, also principal target of HPH.

Nonstarter lactic acid bacteria volatilomes produced using cheese components.

In long-ripened cheese, flavor formation occurs during ripening. The metabolism of lactic acid bacteria (LAB) leads to the production of different compounds that contribute to the flavor of cheese. The contribution of LAB to the formation of cheese flavor has previously been studied. However, the specific nonstarter LAB (NSLAB) metabolic reactions in ripened cheese that lead to the formation of flavor compounds remain unclear. In ripened cheese, the nutrient sources available include small peptides or amino acids, citrate, lactate, free fatty acids, and starter LAB cell lysis products. Thus, the aim of this study was to evaluate the ability of NSLAB to produce volatile flavor compounds by using an in vitro system that used only the nutrients available in ripened cheese as the energy source. Moreover, the potential contribution of the NSLAB volatilome on total cheese flavor is discussed. For this purpose, the production of volatile compounds on cheese-based medium (CBM) and on starter LAB lysed cell medium (LCM) by 2 Lactobacillus casei and 2 Lactobacillus rhamnosus strains, previously isolated from ripened Parmigiano Reggiano cheese, was investigated. The generated volatile compounds were analyzed with head-space gas chromatography mass spectrometry. Overall, ketones, aldehydes, alcohols, and acids were the most abundant compounds produced. Differences in volatilome production were found between NSLAB grown in LCM and CBM. The catabolic metabolism of amino acids and fatty acids were required for NSLAB growth on LCM. Conversely, pyruvate metabolism was the main catabolic pathway that supported growth of NSLAB in CBM. This study can be considered a first step toward a better understanding of how microbiota involved in the long ripening of cheese may contribute to the development of cheese flavor.

Does milk treatment before cheesemaking affect microbial and chemical traits of ripened cheese? Grana Trentino as a case study.

The aim of this study was to evaluate the influence of different storage temperatures and delivery system of the milk on the microbiological and physicochemical characteristics of Grana Trentino, a long-ripened hard-cooked Italian cheese. In particular, 3 kinds of milk storage and delivery were studied: milk delivered to the dairy in the traditional manner without temperature control, milk delivered at 18°C, and milk stored at the farm and delivered at 12°C. Milk, natural whey starter, and cheeses after 18 mo of ripening were sampled for microbiological profiles, physicochemical analysis, and proteolysis evaluation, and a study of cheese volatile compounds through a solid-phase microextraction gas chromatography-mass spectrometry technique was performed. Milk microbiota was not affected by any of the treatments. At the end of ripening, free fatty acid and ester contents were significantly higher in cheeses from milk without temperature control. This was probably due to the milk delivery to the dairy in churns causing the fat globule membrane break during transport and, consequently, a greater release of fat and deeper lipolysis. Milk refrigeration at 12°C for 12h before delivery affected the distribution of nitrogen fractions in cheeses. Lower temperatures of milk storage favored a larger soluble nitrogen fraction and greater cheese proteolysis, probably caused by an enhanced plasmin activity. From this work, it is concluded that both milk temperature storage and transport system could affect cheese ripening, leading to significant differences in chemical compounds: if milk was delivered by churns, higher free fatty acid and ester content in cheeses was observed; if milk was stored at 12°C for 12h before delivery, greater cheese proteolysis was induced with consequent faster ripening.

5-Aminosalicylic acid in patients with ulcerative colitis in remission: plasma levels after administration of a new rectal enema.

Plasma levels of total 5-aminosalicylic acid (5-ASA) were determined after a single administration of 2 g and 4 g 5-ASA enemas to 6 patients with ulcerative colitis. The mean plasma levels and AUC values confirmed that the active substance is poorly absorbed by rectal route.

5-Aminosalicylic acid as enemas or suppositories in distal ulcerative colitis?

Thirty-nine patients with documented active distal proctitis (less than 20 cm) received either 5-aminosalicylic acid (5-ASA) enemas (2 g in 100 ml) or suppositories 1 g b.i.d., in a controlled study. Twenty patients received enemas, while 19 patients received suppositories, for 30 days. No difference could be observed in terms of efficacy; however, it was the patients' opinion that treatment with suppositories was easier than that with enemas (p less than 0.01).

Efficacy of 5-aminosalicylic acid enemas versus hydrocortisone enemas in ulcerative colitis.

A controlled trial has been carried out in order to compare the efficacy of enemas containing a high dosage of 5-ASA (4 g) versus enemas containing hydrocortisone 100 mg. The trial was conducted on 86 patients, 44 of whom received 5-ASA and 42 received hydrocortisone. The results were favorable in terms of clinical, sigmoidoscopic, and histologic criteria for 5-ASA treatment. Other aspects have been investigated, such as retrograde spread of enemas which have been shown to reach the left colon. No nephrotoxicity was detected. The long term experience confirmed the preliminary positive results.

Cholinesterase patterns in the cerebellum of reptiles.

In the cerebellum of four species belonging to the three main reptilian orders the histochemical localization of cholinesterases has been studied. The use of different substrate-inhibitor combinations permits to record the distribution patterns of acetylcholinesterase and pseudocholinesterase, mainly revealed as butyrylcholinesterase activity. From the neurological point of view it is interesting to note that acetylcholinesterase activity shows three different distribution patterns in reptilian cerebellum, thus confirming the characteristic variability previously noticed in the cerebellar cortex of other vertebrates.