Amino acid composition and in vitro digestibility of protein isolates from Silybum marianum

To assess the protein quality and the nutritive value of Silybum marianum protein (SMP), amino acid composition, differential scanning calorimetry (DSC) and the in vitro digestibility were determined and compared with those of soy protein isolate (SPI). The results showed that SMP had an excellent balance of all essential amino acids, with a relatively high level of glutamic acid, arginine, leucine and valine. Except lysine, the essential amino acids of SMP met the suggested requirements of FAO/WHO for 2-5 year old infants. The proportion of essential amino acids to the total amino acids (E/T) for SMP was higher than that of SPI. All the estimated nutritional quality parameters based on amino acid composition showed that SMP had good nutritional quality. SMP had a single denaturation temperature (97.8 degrees C). In an in vitro digestion model, SMP was easily digested by pepsin plus trypsin. In contrast, SMP was much more easily digested by trypsin than SPI. After pepsin plus trypsin digestion, SMP and SPI were all digested to release oligo-peptides and amino acids. These results about SMP are important for its potential application as functional food ingredients.