Amino Acid Digestibility in Dairy Proteins Compared with Plant Proteins

Abstract Text:

An experiment was conducted to determine the standardized ileal digestibility (SID) of AA in whey protein isolate (WPI), whey protein concentrate (WPC), milk protein concentrate (MPC), skim milk powder (SMP), pea protein isolate (PPI), soy protein isolate (SPI), soy flour (SF), and wheat. Nine ileal-cannulated barrows (initial BW: 26.25 ± 1.57 kg) were allotted to a 9 × 9 Latin square design with 9 diets and 9 periods. A N-free diet was formulated to determine basal endogenous losses of AA and CP and to enable the calculation of SID of AA. The remaining diets were formulated with each test ingredient as the sole source of AA, with the exception that wheat was included in a diet that also contained SF to compensate for the low CP in wheat. The AID and SID values were calculated using the difference procedure for the wheat diet. The direct procedure was used for all other ingredients. The SID of Lys was greater (P < 0.05) in WPI and SPI than in SF and wheat (Table 1). The SID of Met was greater (P < 0.05) in WPI than in SMP, SPI, SF, PPI, and wheat. The SID of Trp was greater (P < 0.05) in WPI, WPC, and MPC than in SF, SMP, PPI, and wheat (P < 0.05). These data indicate that the SID of AA in most indispensable AA is greater in dairy proteins compared with plant proteins.

Table 1. Standardized ileal digestibility (%) of indispensable AA in dairy and plant proteins

	Protein source								P - value
Item	WPI	WPC	MPC	SMP	PPI	SPI	SF	Wheat
Arg	103.9a	101.5ab	101.9ab	97.9d	98.6cd	100.7bc	98.9cd	86.5e	<0.05
His	99.5a	96.7ab	98.5a	93.6bc	94.6bc	96.8ab	92.0c	85.0d	<0.05
Ile	98.4a	96.5ab	93.1cd	88.8e	91.3d	95.3bc	92.1d	85.5f	<0.05
Leu	99.3a	97.7a	98.3a	94.4b	92.00c	95.1b	91.2c	86.5d	<0.05
Lys	98.3a	96.1ab	95.7ab	95.2ab	95.7ab	97.4a	93.3b	76.7c	<0.05
Met	98.0a	97.0ab	97.2ab	95.8bc	90.4e	95.5c	93.0d	87.7f	<0.05
Phe	97.6a	95.6ab	97.5a	94.5b	91.8c	95.8ab	92.0c	87.3d	<0.05
Thr	94.0a	91.1abc	93.2a	81.9d	87.9bc	92.2ab	87.1c	79.6d	<0.05
Trp	99.7a	97.7ab	97.2ab	90.6d	86.9e	95.8bc	92.4cd	74.2f	<0.05
Val	96.9a	94.7ab	94.0bc	89.6d	89.0d	94.3b	91.3cd	82.5e	<0.05

^a-fMeans within a row lacking a common superscript letter differ (P < 0.05).

 

Keywords: amino acid digestibility, dairy protein, pigs