Antigenicity and nutritional value of selected milk proteins and their hydrolysate in growing rats

Ultra high temperature treatment, but not pasteurization, affects the postprandial kinetics of milk proteins in humans

Although the chemical and physical modifications to milk proteins induced by technological treatments have been characterized extensively, their nutritional consequences have rarely been assessed in humans. We measured the effect of 2 technological treatments on the postprandial utilization of milk nitrogen (N), pasteurization (PAST) and ultra high temperature (UHT), compared with microfiltration (MF), using a sensitive method based on the use of milk proteins intrinsically labeled with (15)N. Twenty-five subjects were studied after a 1-wk standardization of their diet. On the day of the investigation, they ingested a single test meal corresponding to 500 mL of either MF, PAST, or UHT defatted milk. Serum amino acid (AA) levels as well as the transfer of (15)N into serum protein and AA, body urea, and urinary urea were determined throughout the 8-h postprandial period. The kinetics of dietary N transfer to serum AA, proteins, and urea did not differ between the MF and PAST groups. The transfer of dietary N to serum AA and protein and to body urea was significantly higher in UHT than in either the PAST or MF group. Postprandial deamination losses from dietary AA represented 25.9 +/- 3.3% of ingested N in the UHT group, 18.5 +/- 3.0% in the MF group, and 18.6 +/- 3.7% in the PAST group (P < 0.0001). The higher anabolic use of dietary N in plasma proteins after UHT ingestion strongly suggests that these differences are due to modifications to digestive kinetics and the further metabolism of dietary proteins subsequent to this particular treatment of milk.

Effects of alimentary intact proteins and their oligopeptide hydrolysate on growth, nitrogen retention, and small bowel adaptation in inflammatory turpentine rat

The effects of dietary proteins given as whole proteins (WP) or as a peptide hydrolysate (PH) on growth, nitrogen retention, and small bowel adaptation were assessed using two groups of male Wistar rats. Measurements were made 18, 42, and 66 h after acute inflammation induced by subcutaneous injections of 0.125 mL turpentine and in two control groups (n = 12). The two diets had the same caloric, nitrogen, vitamin, and mineral content. The WP diet resulted in better weight gain, nitrogen retention, and small intestinal adaptation by control rats than did the PH diet. Loss of body weight after 18 h of acute inflammation was significantly lower and nitrogen retention significantly higher in animals on the WP diet than in those on the PH diet. Small intestine morphology was maintained with the WP diet, whereas villus height was significantly lower after 66 h, and there were fewer mitoses per crypt in the rats on the PH diet. Glucoamylase activity at all times, and N-aminopeptidase activity at 18 h, were significantly higher in rats on the WP diet. The putrescine (at 42 h) and spermidine (at 18 h) concentrations in the mucosa were higher in the rats on the WP diet. These data suggest that synthetic diets should be tested for their nutritional value during acute inflammation before they are used in human nutrition.