15N and 2H Intrinsic Labeling Demonstrate That Real Digestibility in Rats of Proteins and Amino Acids from Sunflower Protein Isolate Is Almost as High as That of Goat Whey

Abstract

Background In the context of developing plant protein sources for humans, sunflower is a good candidate in its form as an oilseed coproduct. Objectives We aimed to compare the real digestibility in rats of a sunflower isolate to that of goat whey protein. We also studied the efficiency of 15N and 2H intrinsic labeling in this assessment. Methods Sunflower seeds and goat milk were labeled with 15N and 2H. Male Wistar rats (10 wk old) were fed a meal containing 12% of either sunflower isolate (n = 8) or whey (n = 8). Six hours after meal ingestion, protein and amino acid digestibility were assessed by measuring nitrogen, hydrogen, and amino acids in the digesta, as well as isotope enrichments in the bulk and individual amino acids. The differences between groups and isotopes were respectively tested with an unpaired and a paired t test. Results Protein isolate purity was 87% for whey and 94% for sunflower. 2H and 15N enrichments were, respectively, 0.12 atom % (AP) and 1.06 AP in sunflower isolate and 0.18 AP and 0.95 AP in whey. Fecal 15N protein digestibility was 97.2 ± 0.2% for whey and 95.1 ± 0.5% for sunflower isolate. The use of 2H resulted in a lower digestibility estimate than 15N for whey (96.9 ± 0.2%, P < 0.05) and sunflower (94.2 ± 0.5%, P < 0.01). For both isotopes, protein digestibility was about 2% higher for whey than for sunflower isolate. Mean 15N amino acid caecal digestibility was 97.5 ± 0.2% for whey and 96.3 ± 0.2% for sunflower isolate. The values obtained with 15N and 2H resulted in significant differences ranging from −0.1% to 3.5%. The DIAAS was >1.0 for whey and 0.84 for sunflower (lysine). Conclusions The protein and amino acid digestibility of sunflower isolate was high but its DIAAS reflected a moderate lysine imbalance. Despite slight differences with 15N, deuterium produced comparable results, making it suitable for in vivo digestion studies.

Multi-criteria assessment of pea protein quality in rats: a comparison between casein, gluten and pea protein alone or supplemented with methionine

“…We determined caecal digestibility because of the low amount of ileal content that can be sampled at a unique time point in rats and the difficulty of finding a reliable indigestible marker, which leads to uncertainties (34,35) . The method we used was developed previously (16) and consists of collecting gastrointestinal contents from all segments of the gastrointestinal tract 6 h after meal intake. It facilitates a compromise between complete digestion and minimal duration of fermentation of digesta in the caecum.…”

“…The rats were housed on a reversed light cycle (dark period from 07.00 to 19.00 hours) in cages with wire bottoms to prevent coprophagia. They were trained to eat a calibrated meal containing 4 g (dry weight) of their usual diet in a short time by providing the meal at 09.00 hours for 30 min, only, and before commencing a 2-h fast, as described previously (16) . They were subsequently fed ad libitum from 11.00 to 17.00 and fasted until the next calibrated meal.…”

Caecal digestibility as an approximation of ileal protein digestibility evaluation in rats

“…It can therefore be assumed that a large part of the losses of dietary nitrogen and amino acids can be collected in the caecum after an appropriate digestion time, which may dispense with the use of an indigestible marker. Indeed, in several studies, most of the dietary nitrogen is found in the caecum 5–6 h after ingestion, which appeared to be an optimal time to collect the digesta ( 6 , 7 ) . This method has been used in previous studies and yielded close digestibility values when compared to studies using ileal sampling.…”

Evaluation of Protein Quality in Humans and Insights on Stable Isotope Approaches to Measure Digestibility – A Review

“…Goat milk protein has been previously labeled with 2 H by administering 2 H 2 O to a lactating goat ( 38 ). In this method, labeling occurs by the exchange between the hydrogen atoms at the α-H position of AAs with 2 H from enriched body water during the transamination reaction, with a small quantity of 2 H labeled AAs being synthesized de novo ( 39–42 ).…”