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The present study aims at comparing the performances of three Lactobacillus reuteri strains (DSM 20016, DSM 17938, and ATCC 53608) in producing 3-hydroxypropionic acid (3-HP) from glycerol and at exploring inhibition phenomena during this bioconversion. Differences were highlighted between the three strains in terms of 3-HP production yield, kinetics of substrate consumption, and metabolite production. With a maximal productivity in non-optimal conditions (free pH) around 2 g.L⁻¹.h⁻¹ of 3-HP and 4 g.L⁻¹.h⁻¹ of 3-hydroxypropionaldehyde (3-HPA) depending on the strain, this study confirmed the potential of L. reuteri for the biotechnological production of 3-HP. Moreover, the molar ratios of 3-HP to 1,3-propanediol (1,3-PDO) obtained for the three strains (comprised between 1.25 and 1.65) showed systematically a higher 3-HP production. From these results, the DSM 17938 strain appeared to be the most promising strain. The impact of glycerol bioconversion on the bacteria’s physiological state (a decrease of around 40 % in DSM 17938 cells showing an enzymatic activity after 3 h) and survival (total loss of cultivability after 2 or 3 h depending on the strains) was revealed and discussed. The effect of each metabolite on L. reuteri DSM 17938 was further investigated, displaying a drastic inhibition caused by 3-HPA, while 3-HP induced lower impact and only at acidic pH.

The color of smear cheeses (Muenster) is traditionally thought to be due to the bacterial flora, e.g., Brevibacterium linens. This study was carried out to evaluate indirect effects of yeast on the color of B. linens. A 60% cheese medium was desacidified with Debaryomyces hansenii or Kluyveromyces marxianus until pH 5.8 was reached. After inactivation of the yeast and addition of agar-NaCl, B. linens was inoculated on the medium surface and incubated at 12°C from d 2 to 28. For each bacterial biofilm, color was evaluated by L*C*h° (brightness, chroma, hue angle) spectrocolorimetry. After d 14 (D. hansenii deacidification) and d 21 (K. marxianus desacidification), the color level (as a function of all 3 factors) of B. linens biofilms became maximal and remained so until d 28. Debaryomyces hansenii 304 (LGMPA) was less efficient for deacidification than K. marxianus Laf5. However, color intensity (function of chroma only) was higher when D. hansenii was used. The yeast used had an effect on the composition of the cheese medium in relation to production and consumption of metabolites during deacidification. The results concerning color are discussed with respect to this cheese medium composition.

Five cheese-ripening yeasts (Geotrichum candidum, Saccharomyces cerevisiae, Kluyveromyces lactis, Yarrowia lipolytica and Debaryomyces hansenii) were compared with respect to their ability to generate volatile aroma compounds. K. lactis produced a variety of esters - ethylacetate (EA) being the major one - and relatively limited amounts of volatile sulphur compounds (VSCs). Conversely, G. candidum produced significant amounts of VSCs [with the thioester S-methyl thioacetate (MTA) being the most prevalent] and lower quantities of non-sulphur volatile compounds than K. lactis. We suspect that K. lactis is able to produce and/or accumulate acetyl CoA - a common precursor of MTA and EA - but that it produces limited amounts of methanethiol (MTL); both acetyl CoA and MTL are precursors for MTA synthesis. When supplemented with exogenous MTL, MTA production greatly increased in K. lactis cultures whereas it was unchanged in G. candidum cultures, suggesting that MTL is a limiting factor for MTA synthesis in K. lactis but not in G. candidum. Our results are discussed with respect to L-methionine catabolism.

The aroma of a deacidified cheese medium is the result of the overall perception of a large number of molecules belonging to different classes. The volatile compound composition of (60%) cheese medium (pH 5.8) deacidified by Debaryomyces hansenii (DCMDh) was compared with the one deacidified by Kluyveromyces marxianus (DCMKm). It was determined by dynamic headspace extraction, followed by gas chromatography separation and quantification as well as by mass spectrometry identification. Whatever the media tested, a first class of volatile compounds can be represented by the ones not produced by any of the yeasts, but some of them are affected by K. marxianus or by D. hansenii. A second class of volatile compounds can be represented by the ones produced by K. marxianus, which were essentially esters. Their concentrations were generally higher than their thresholds, explaining the DCMKm global fruity odor. A third class can be represented by the ones generated by D. hansenii, which were essentially methyl ketones with fruity, floral (rose), moldy, cheesy, or wine odor plus 2-phenylethanol with a faded-rose odor. The impact of methyl ketones on the DCMDh global flavor was lower than the impact of 2-phenylethanol and even negligible. Therefore, the global faded-rose odor of D. hansenii DCM can be explained by a high concentration of 2-phenylethanol.

Production of volatile sulphur compounds (VSC) was assessed in culture media supplemented with l-methionine or l-methionine/l-cysteine mixtures, using five cheese-ripening yeasts: Debaryomyces hansenii DH47(8), Kluyveromyces lactis KL640, Geotrichum candidum GC77, Yarrowia lipolytica YL200 and Saccharomyces cerevisiae SC45(3). All five yeasts produced VSC with l-methionine or l-methionine/l-cysteine, but different VSC profiles were found. GC77 and YL200 produced dimethyldisulphide and trace levels of dimethyltrisulphide while DH47(8), KL640 and SC45(3) produced mainly methionol and low levels of methional. S-methylthioacetate was produced by all the yeasts but at different concentrations. DH47(8), KL640 and SC45(3) also produced other minor VSC including 3-methylthiopropyl acetate, ethyl-3-methylthiopropanoate, a thiophenone, and an oxathiane. However, VSC production diminished in a strain-dependent behaviour when l-cysteine was supplemented, even at a low concentration (0.2 g l-¹). This effect was due mainly to a significant decrease in l-methionine consumption in all the yeasts except YL200. Hydrogen sulphide produced by l-cysteine catabolism did not seem to contribute to VSC generation at the acid pH of yeast cultures. The significance of such results in the cheese-ripening context is discussed.

The aim of this study was to develop and validate an iterative procedure based on odor assessment to select odor-active associations of microorganisms from a starting association of 82 strains (G1), which were chosen to be representative of Livarot cheese biodiversity. A 3-step dichotomous procedure was applied to reduce the starting association G1. At each step, 3 methods were used to evaluate the odor proximity between mother (n strains) and daughter (n/2 strains) associations: a direct assessment of odor dissimilarity using an original bidimensional scale system and 2 indirect methods based on comparisons of odor profile or hedonic scores. Odor dissimilarity ratings and odor profile gave reliable and sometimes complementary criteria to select G3 and G4 at the first iteration, G31 and G42 at the second iteration, and G312 and G421 at the final iteration. Principal component analysis of odor profile data permitted the interpretation at least in part, of the 2D multidimensional scaling representation of the similarity data. The second part of the study was dedicated to 1) validating the choice of the dichotomous procedure made at each iteration, and 2) evaluating together the magnitude of odor differences that may exist between G1 and its subsequent simplified associations. The strategy consisted of assessing odor similarity between the 13 cheese models by comparing the contents of their odor-active compounds. By using a purge-and-trap gas chromatography-olfactory/mass spectrometry device, 50 potent odorants were identified in models G312, G421, and in a typical Protected Denomination of Origin Livarot cheese. Their contributions to the odor profile of both selected model cheeses are discussed. These compounds were quantified by purge and trap-gas chromatography-mass spectrometry in the 13 products and the normalized data matrix was transformed to a between-product distance matrix. This instrumental assessment of odor similarities allowed validation of the choice of G312 as the best 10-strain ecosystem.

Objectives: The study aimed at addressing the issue of the precise nature of gait apraxia and the cerebral dysfunction responsible for it. Methods: The case of a patient, affected by a bilateral infarction limited to a portion of the anterior cerebral artery territory is reported. The patient's ability to walk was formally assessed by means of a new standardised test. Results: Due to an anomaly within the anterior cerebral artery system, the patient's lesion was centred on the supplementary motor regions of both hemispheres. He presented with clear signs of gait apraxia that could not be accounted for by paresis or other neurological deficits. No signs of any other form of apraxia were detected. Conclusions: The clinical profile of the patient and the analysis of 49 cases from previous literature suggest that gait apraxia should be considered a clinical entity in its own right and lesions to the supplementary motor areas are responsible for it.

This detailed clinical report of a typical Capgras delusion (CD) in a demented patient is presented in order to foster future descriptions in neurological cases. In the framework of a recently developed model of familiar person processing, it is suggested that CD might be due to a dysfunction at the level of Person Identity Nodes. Prefrontal impairment is held to represent a critical factor leading to a failure of belief evaluation.

Objectives: To investigate whether gait apraxia is a possible cause for some of the walking abnormalities shown by patients with Alzheimer’s disease. Methods: 60 patients with Alzheimer’s disease, selected as being free from overt extrapyramidal impairment or other potential causes of walking deficits, were assessed with a new test evaluating aspects of walking and related movements. Norms for this test were collected from a sample of 182 healthy volunteers. Results: 40% of the Alzheimer group performed below the cut off score on this test, and half performed poorly. Performance of the Alzheimer group in the walking skills test correlated highly with scores in a test assessing limb apraxia and with dementia severity. Conclusions: Gait apraxia may be the cause of walking disorders found in a subgroup of patients with Alzheimer’s disease. Its detection is made easier by the use of a standardised test, but still relies heavily on the exclusion of other causes of walking deficits. It is a recognisable and independent form of apraxia.