Dominique Langlois

Chemical and behavioural characterization of the rabbit mammary pheromone

Mammals owe part of their evolutionary success to the harmonious exchanges of information, energy and immunity between females and their offspring. This functional reciprocity is vital for the survival and normal development of infants, and for the inclusive fitness of parents. It is best seen in the intense exchanges taking place around the mothers offering of, and the infants quest for, milk. All mammalian females have evolved behavioural and sensory methods of stimulating and guiding their inexperienced newborns to their mammae, whereas newborns have coevolved means to respond to them efficiently. Among these cues, maternal odours have repeatedly been shown to be involved, but the chemical identity and pheromonal nature of these cues have not been definitively characterized until now. Here we focus on the nature of an odour signal emitted by the female rabbit to which newborn pups respond by attraction and oral grasping, and provide a complete chemical and behavioural description of a pheromone of mammary origin in a mammalian species.

Influence of culture conditions on production of flavour compounds by 29 ligninolytic Basidiomycetes

The odorous volatile metabolites produced by 29 ligninolytic Basidiomycete strains (identified by gas chromatography coupled to mass spectroscopy — GC-MS) and the flavour quality of their cultures were investigated on 6 different liquid media tested with and without agitation. 113 compounds were identified, the most numerous being alcohols (2-methyl 1-propanol, 2-methyl 1-butanol, 3 methyl 1-butanol, 2 phenyl ethanol, 3,4, dimethoxy phenyl methanol, 4 vinyl phenol), aldehydes (3, 4 dimethoxybenzaldehyde) and ketones (4-hydroxy 3-methyl 2-phenyl 2-cyclopentene 1-one). One third of these compounds possessed an aromatic skeleton. The influences of medium composition and agitation conditions on the odorous profile are discussed. A strain specificity within several species was also observed.

Detection of powerful odorants in heated milk by use of extract dilution sniffing analysis

The odour impact compounds of raw, pasteurized and UHT bovine milk were investigated using vacuum extraction and extract dilution sniffing analysis using CharmAnalysis™. Fifteen odour peaks with Charm values between 10 and 3443 were detected. Of these peaks, twelve were identified as hexanal, ethyl butanoate, 2-heptanone, heptanal, dimethyl sulphone, l-octen-3-ol, ethyl hexanoate, 2-nonanone, nonanal, benzothiazole, 2-undecanone, indole and one as a mixture of 2-tridecanone and δ-decalactone. Dimethyl sulphone, indole and one unknown compound (retention index 1154) were the only ones detected as odour impact compounds in all three types of milk. Ethyl butanoate and ethyl hexanoate were found as powerful odorants only in raw milk. A further predominant odorant for this milk was dimethyl sulphone, which was the most important odorant in pasteurized milk. 2-Hexanone and 2-nonanone were identified as the most intense volatile flavour compounds of UHT milk. The powerful odorants described can be used as indicators of the aroma quality of heated milk.

Powerful odorants in bovine, ovine, caprine and water buffalo milk determined by means of gas chromatography–olfactometry

The main compounds responsible for the aroma of bovine, ovine, caprine and water buffalo freshly secreted milk have been identified by means of a gas chromatography–olfactometry technique. Of the fourteen odour-active volatile compounds detected, eight were present in all milks studied. Ethylbutanoate and ethylhexanoate (fruit-like aroma), among the neutral odorants, were the major contributors to the odour of bovine, ovine and caprine milk. The aroma of water buffalo milk was less dependent on ethylhexanoate and was also due to l-octen-3-ol (aroma of raw mushrooms), nonanal (freshly cut grass), indole (stable, animals) and an unidentified constituent, characterized by a retention index of 828, with a typical odour of warm milk and/or smoked cheese. Other aroma components were specific for some types of milk, contributing to the complexity and richness of flavour.

Sensory and instrumental characterisation of commercial tomato varieties

Ten tomato varieties, i.e. Cencara, Daniella, Elena, Ibiza, Lemon Boy, Lucy, Melody, Perfecto, Raf and Rondello, were studied over two consecutive years by GC and GC-sniffing for their differences in flavour composition. Precautions were taken to avoid differences due to the growth conditions and stage of matu-rity. The aroma profiles obtained from dilutions of the extracts confirm the importance of most compounds previously reported as being key flavour compounds in tomatoes. Moreover, they outline a greater number of other key compounds which had not been identified or reported as such in the literature. Among them, 2-methoxyphenol, eugenol, decanal and geranylacetone were identified. Among 39 compounds quantified, 27 were found to permit discrimination between varieties both in 1992 and 1993. Six varieties were characterised in both years by specific flavour compositions. The differences between varieties is due to particular relative amounts of volatile compounds arising from the metabolism of aliphatic amino acids and carotenoids. Volatile compounds arising from each metabolic processes were found to be highly correlated with each other.

GC sniffing analysis : olfactive intensity measurement by two methods

The intensity perceived by sniffing after GC elution of six volatile compounds was measured by ten judges using two pieces of apparatus: a PC mouse which is moved on a 60-cm length scale and a rheostat apparatus which measures the finger span. The choice of the components mixed was influenced by purity, elution time, presence in food and known Stevens slopes. The histograms obtained by summing the responses (determined by measuring the areas under the peaks) of ten people show no significant differences between the two pieces of apparatus. Histograms realised in parallel by Charm analysis with three other judges showed great differences between subjects. However, the mean of the three Charm analysis histograms was very similar to those histograms obtained with the two previously described pieces of apparatus. The same concentrations of ethyl butyrate, 3-methyl butanoic acid and 2,3,5-trimethyl pyrazine had the greatest odour intensity and thiophene, 2,6-dimethyl pyrazine and acetophenone had the lowest odour intensity.

A single key-odorant accounts for the pheromonal effect of rabbit milk: further test of the mammary pheromone's activity against a wide sample of volatiles from milk

Summary.In the rabbit, lactating females emit a volatile compound in milk, the mammary pheromone (MP), that triggers rooting for the nipple and its grasping in pups. Previous studies have shown that the MP seems to act selectively, in terms both of intensity and quality. Here, we aimed to add new evidence to these properties of the MP. Newborn rabbits (n=825) were submitted to an oral activation test allowing to measure their searching/grasping responses towards different stimuli. In Experiment 1 we assessed whether pups respond to the MP in an intensity-dependent manner. In Experiment 2 we assessed the activity of 20 volatiles previously identified in rabbit milk, other than the MP, which were never systematically tested for intensitydependence. The assays showed that a) neonatal responses are released by the MP only for a limited range of concentrations; b) the 20 other odorants from milk are inactive at any concentration. Thus, the MP appears to be the single volatile from rabbit milk that releases searching/grasping behaviour in pups.

Convergent changes in the maternal emission and pup reception of the rabbit mammary pheromone

Summary.Lactating rabbit females emit volatile odour cues that trigger specialized motor actions leading to sucking. But the activity of these cues may change with advancing lactation. Here, we tested this possibility in three experiments. In Exp. 1, we assessed whether 2-day-old pups respond differently to the odour of milk from females in early (day 2) as compared to late (day 23) lactation. In Exp. 2, a compound bearing pheromonal properties, the Mammary Pheromone (MP), was dosed in these milks to assess whether its concentration is correlated with behavioural activity. In Exp. 3, the responsiveness to a constant level of MP was compared in d2 versus d23-pups. Run on 240 pups, the assays showed that a) the milk activity declines between d2 and d23 of lactation; b) during this same period, the concentration of the MP decreases in milk; c) the MP itself becomes less active to elicit oral grasping in pre-weaning pups than in newborns. These results indicate that the MP is active during the period when pups are exclusively dependent on milk. The convergent changes in emission and reception of this pheromone may sequentially warrant that pups are first attracted to the mammae, and then that they progressively disinvest the mother as they begin to eat solid food and to be attracted by other conspecifics.

Volatile compounds produced by the ligninolytic fungus Phlebia radiata Fr. (Basidiomycetes) and influence of the strain specificity on the odorous profile

Abstract The odorous volatile compounds produced by 3 strains (out of 25 strains tested) of Phlebia radiata Fr. were investigated on six synthetic media and identified by GC-MS analysis. One of the 3 strains was odourless. Aromatic primary alcohols and a sesquiterpenic alcohol, α-bisabolol, were the most abundant metabolites for both of the other strains, which exhibited similar flavours and a similar gas chromatographic profile.

Nosespace with an ion trap mass spectrometer-quantitative aspects

Abstract A new APCI source and interface connected to an ion trap mass spectrometer have been designed in order to allow introduction and analysis of a gaseous flow within the source. In vitro detection limits, linear response ranges and repeatability (daily and day-to-day) have been determined for a set of flavour molecules of various chemical classes. Detection limits and linear response ranges have been found compatible with aroma compounds concentrations generally found in foodstuffs. Repeatabilities were found within the values already published for another interface connected to an ion trap mass spectrometer. During breath-by-breath data acquisition it appeared clearly that some competition between volatiles towards the chemical ionisation process occured. This point has been addressed specifically. Mixtures of 2-heptanone, ethyl hexanoate, 2,3,5-trimethylpyrazine and 2-heptanol in varying concentration ranges have been analysed and their responses compared to pure compound responses. In the case of 2-heptanol, it clearly appeared that its APCI-MS response decreased when ethyl hexanoate concentration increased in the mixture.