The Effects of Age and Adiposity on the Digestibility of Micellar Casein in Rats

Objectives The aim of this study was to evaluate the digestibility of casein and its amino acids (AA) in rats of different ages (2 months vs 11 months) and adiposity levels (normal vs high). Methods Wistar rats of 1 month (n = 15) and 10 months (n = 15) at their arrival were fed ad libitum for 28 days either with a standard diet (14% P/E, 75% C/E, 11% L/E) or a Western diet (14% P/E, 51% C/E, 35% L/E) in order to obtain respectively rats of normal and high adiposity levels. Four groups were constituted (n = 7/8): 2 months/normal adiposity (2 M/NA), 2 months/high adiposity (2 M/HA), 11 months/normal adiposity (11 M/NA) and 11 months/high adiposity (11 M/HA). After a week on the standard diet, the rats consumed a 4 g meal containing 15N labeled casein (Prodiet® 85B). Blood samples were taken at t = 0, t = 1 h, t = 3 h after meal consumption, and the rats were euthanized at t = 6 h. Digestive contents were collected and body composition was determined. Nitrogen quantity and 15N enrichment were analyzed in the meal and digestive contents by EA-IRMS, allowing for the estimation of casein digestibility. Concentrations in AA and their 15N enrichments were determined respectively by UHPLC and GC-C-IRMS to obtain the digestibility of individual AA. Results Weight did not differ between groups of the same age, but body composition analysis showed a significant difference in adiposity (P = 0.0008 between the 2 M groups; P = 0.0004 between the 11 M groups). Nitrogen fecal digestibility of casein increased significantly in rats with higher adiposity levels (2 M/NA = 94.1 ± 1.1%; 2 M/HA = 95.2 ± 1.7%; 11 M/NA = 94.5 ± 2.2% for 11 M/HA = 95.9 ± 0.7%; P = 0.0339). No difference was found in the digestibility of individual AA. 6 hours after meal ingestion, there was significantly more exogenous nitrogen in the stomach of rats aged 11 months compared to those of 2 months (3,9 ± 6,9% for the 2 M groups and 11,3 ± 9,2% for the 11 M groups P = 0.0188;). Except for methionine, there was no difference in plasma concentration levels of essential AA over time between the groups. Conclusions Our results suggest that age slows down digestion, in accordance with the literature. We showed that adiposity increased casein digestibility but without any effect at the level of individual AA digestibility. Funding Sources Ingredia.

Real Ileal Digestibility of Sunflower Protein and Amino Acids in Humans

Objectives Sunflower protein has a relatively well-balanced amino acid profile but it is little used in human food. Nutritional quality of sunflower protein isolate has never been directly measured in humans. This study aims to determine the ileal digestibility of protein and amino acid of a sunflower isolate incorporated in biscuits, in healthy humans. Methods Healthy volunteers (n = 7) were intubated with a naso-ileal tube. They ingested every 30 min for 4 h, sunflower biscuits for a total of 156 g of biscuits and 25 g of 15N intrinsically labeled sunflower protein isolate. A non-absorbable marker was perfused into the ileum. Ileal samples were continuously collected during 8 h after the first meal. Blood was sampled every 30 min for 4 h and every hour after and total urine was collected every 2 h. To measure nitrogen ileal digestibility, the percentage of nitrogen and 15N enrichment in ileal contents were assessed by an elemental analyzer coupled with and isotope ratio mass spectrometer (EA-IRMS). Indispensable amino acid (IAA) ileal digestibility was determined by measuring amino acid 15N enrichment by GC-C-IRMS and their quantification by UHPLC. Metabolic losses of dietary nitrogen were assessed by measuring 15N in urine and plasma. The digestible indispensable amino acid score (DIAAS) and the net post-prandial utilization (NPPU) were calculated. Results Exogenous nitrogen appeared in the ileum 1 h after the first meal, its flow was stable between 4 h and 7 h. Cumulated dietary nitrogen in the ileum was 14.0 ± 4.0% over 8 h. Sunflower nitrogen real ileal digestibility was 86.0 ± 4.0% of ingested nitrogen. Mean IAA ileal digestibility was 87.0 ± 6.1% with values ranging from 84.4% for lysine and threonine to 89.3 ± 7.8% for methionine. DIAAS was 0.93 for lysine. After 8 h, 4.0 ± 1.0% of dietary nitrogen was incorporated in plasma protein. Cumulated exogenous nitrogen in urinary urea was 4.0 ± 1.4% and exogenous nitrogen in body urea after 8 h was 9.8 ± 2.5%. The NPPU was 72.2 ± 3.7% at 8 h. Conclusions Sunflower isolate ileal digestibility is relatively low compared to other protein isolate assessed in similar conditions (ileal tube and 15N labeling of protein). Despite a moderate deficiency in lysine, sunflower protein isolate has a good post-prandial metabolic utilization. Funding Sources French Research National Agency (ANR), financial support of SOFIPROTEOL under the FASO Project PRODIA.

Isotopic partitioning of nitrogen in PM_2.5 at Beijing and a background site of China

Using isotope mixing model (IsoSource) and natural δ15N method, this study evaluated contributions of major sources to N of PM2.5 at Beijing (collected during a severe haze episode of January 22nd–30th, 2013) and a background site (Menyuan, Qinghai province; collected from September to October of 2013) of China. At Beijing, δ15N values of PM2.5 (−4.1 – +13.5 ‰; mean = +2.8 ± 6.4 ‰) distributed within the range reported for major anthropogenic sources (including NH3 and NO2 from coal combustion, vehicle exhausts and domestic wastes/sewage). However, δ15N values of PM2.5 at the background site (+8.0 – +27.9 ‰; mean = +18.5 ± 5.8 ‰) were significantly higher than that of potential sources (including NH3 and NO2 from biomass burning, animal wastes, soil N cycle, fertilizer application, and organic N of soil dust). Evidences from molecular ratios of NH4+ to NO3− and/or SO42− in PM2.5, NH3 to NO2 and/or SO2 in ambient atmosphere suggested that the equilibrium of NH3 ↔ NH4 + caused apparent 15N enrichment only in NH4 + of PM2.5 at the background site due to more abundant NH3 than SO2 and NO2. Therefore, a net 15N enrichment (33 ‰) was assumed for NH3 sources of background PM2.5 when fractional contributions were estimated by IsoSource model. Results showed that 41 %, 30 % and 14 % of N in PM2.5 of Beijing originated from coal combustion, vehicle exhausts and domestic wastes/sewage, respectively. Background PM2.5 derived N mainly from biomass burning (58 %), animal wastes (15 %) and fertilizer application (9 %). These results revealed the regulation of the stoichiometry between ammonia and acidic gases on δ15N signals in PM2.5. Emissions of NO2 from coal combustion and NH3 from urban transportation should be strictly controlled to advert the risk of haze episodes in Beijing.