Amino Acid Digestibility of Whey and Zein Proteins

True ileal amino acid digestibility of whey protein isolate (WPI) and zein proteins will be determined in healthy subjects. The endogenous losses of proteins and amino acids will be determined by collecting digesta samples after a protein-free test-meal in a different group of subjects.

24 volunteers will be included in the study (men and women; aged 18-65 y; BMI 18-30 kg/m2) and tested at AgroParisTech (Human Nutrition Research Centre of Avicenne Hospital). Due to the invasive procedure of intubation, each volunteer will test only one test-meal (n=8 / test-meal).

One week before the experiment, the volunteers will follow a standard diet adapted to their body weight to control their protein intake (1.3 g protein/kg body weight). The volunteers will arrive at the hospital the morning before the day of the experiment and will be equipped with a double lumen intestinal tube that will be allowed to progress through the intestinal tract for 24h. On the day of the experiment, the position of the tube will be checked by radiography to verify its location at the terminal ileum. A catheter will be inserted in the forearm vein for blood sampling. A perfusion of the non-absorbable marker polyethylene glycol -4000 will start to estimate the intestinal flow and the basal ileal sample will be collected during 30 min. Basal plasma sample will be collected. Then, at t=0, the volunteer will drink the test-meal. Until t=9h, intestinal content will be continuously collected by aspiration and pooled every 30 minutes. Blood will be sampled every 30 minutes during 4h and hourly thereafter.

The test meal will consist of a protein-free biscuit (160 g) and a drink (500 ml) with the test protein as the sole source of protein or no protein for the protein-free group. Celite will be added to the protein-free biscuit and inulin labelled with carbon 13 will be added to the drink as indigestible markers of the meal to allow correction for incomplete collection of digesta. The test proteins will be WPI or zein.

The total nitrogen will be measured in meal and digesta samples by the coupling of Elemental Analysis with stable Isotope Ratio Mass Spectrometry (EA-IRMS) and the amino acid concentration in meal, digesta and plasma samples will be measured by High Performance Liquid Chromatography (HPLC) in order to determine the ileal bioavailability of amino acid of zein and whey protein. Plasma hormonal profile will also be determined to evaluate the effect of each protein sources on metabolic hormones such as insulin, glucagon, leptin, etc.

Inclusion criteria

• Normal body weight (18 < BMI < 30 kg.m-2)
• Women or men
• 18 - 65 y
• Healthy
• Insured under the French social security system
• Signed informed consent
• For women: use of birth control

Exclusion criteria

• People under trusteeship
• Latex, cow milk or corn allergy A
• HIV, hepatite C virus antibodies, hepatite B virus surface antigen and core antibodies positive
• Pregnant women
• Excessive alcohol drinking or drugs intake
• Hypertension, diabetes, digestive tract, liver or renal diseases, severe heart disease
• High sport practicing (> 7h/week)
• Blood donation in the 3 months prior to the study
• Participation in a clinical study in the 3 months prior to the study
• No signed informed consent