A new method to improve olfactory responses to GC effluents.

Biological detectors such as the human nose or an insect antenna represent extremely attractive detectors for gas chromatography (GC) since they are specifically tuned to perceive biologically relevant compounds. However, these detectors are nonlinear, noisy and often perform poorly under standard GC conditions since they are adapted to detect transient rather than long-lasting stimuli. These drawbacks can be overcome if the chemical stimulus, delivered by the gas chromatograph, is re-shaped (modulated) before reaching the biological detector. We describe a pulsing system that improves the performance of an insect olfactory system when stimulated with the effluent from a GC capillary column. Chemicals eluted from the GC column are trapped and rapidly desorbed within a thermal modulator in order to transform the continuous effluent into a succession of short-pulsed stimuli. The output from this modulator was directed to an insect antenna, from which electrophysiological responses were recorded. The system was evaluated with adult male Spodoptera littoralis (Lepidoptera: Noctuidae) stimulated with the conspecific female sex pheromone. Results obtained with this new approach indicate that both sensitivity and reliability of the biological detector are improved compared with the classical technique. Possible developments of this new technique are discussed.

Nitrogen movements in the upper jejunum lumen in humans fed low amounts of casein or beta-lactoglobulin.

OBJECTIVES AND METHODS: To compare the progression of milk proteins in the upper part of the digestive tract, gastro-jejunal nitrogen movements were studied in 6 healthy human volunteers after beta-lactoglobulin and casein ingestion. 400 mL of water (control), purified beta-lactoglobulin (20 g/L) or casein (20 g/L), each adjusted to 25 microCi with 14C-polyethylene glycol, were given per os. Samples were collected in the stomach and 20 cm below the Treitz ligament every 20 min for 2 hours and measured for volume, osmolarity, ions and nitrogen content. RESULTS: The jejunal flow rate peaked in the 0-20 min period following water and beta-lactoglobulin ingestion, and in the 20-40 min period after casein ingestion. The gastric half-emptying time (T1/2 min) of the liquid phase was significantly different (P < 0.05) for water (12.1 +/- 0.8), beta-lactoglobulin (14.5 +/- 3.3) and casein (26.5 +/- 9.3). Before ingestion of the test meals, the basal rate of nitrogen was 9.14 +/- 4.09 mmol/h in the jejunum. The total nitrogen content in the jejunum peaked significantly in the 0-20 min period after beta-lactoglobulin ingestion and the 20-40 min period after casein ingestion. The apparent gastro-jejunal protein absorption values were 63% for casein and 66% for beta-lactoglobulin in the 120 min period. CONCLUSIONS: These results show that beta-lactoglobulin and casein behave differently in the upper part of the digestive tract due to different gastric emptying rates.