Protein digestibility determination

Apparent ileal amino acid and protein digestibilities determined in weaned and fattening pigs are presented in table 6. 

Figure 2.4. Peptide fingerprinting by MALDI-TOF mass Spectrometry. Proteins are extracted and separated on by 2D gel electrophoresis. A spot of interest is excised from the gel, digested with trypsin, and ionized by MALDI. The precise mass of proteolytic fragments is determined by time-of- flight mass spectrometry. The identity of the protein is determined by comparing the peptide masses with a list of peptide masses generated by a simulated digestion of all of the open reading frames of the organism.

Alternate Protocol 2 In Vivo or True Protein Digestibility to Determine... 

However, since the PER is an in vivo test, protein digestibility and amino acid bioavailability are encompassed to some extent within the assay. Despite these advantages, it is difficult to determine the individual contribution of digestibility and bioavailability of individual amino acids, or of individual proteins in a complex mixture, on overall protein quality. There are indications that the assay can be shortened from 4 weeks to 2 weeks with little loss in accuracy (Hackler, 1977). 

IN VIVO OR TRUE PROTEIN DIGESTIBILITY TO DETERMINE PROTEIN QUALITY... 

PDCAAS (%) is calculated as the product of the true protein digestibility and the amino acid score (or lowest amino acid ratio) relative to reference protein. Amino acid composition of protein is determined by hydrolyzing the protein into its component amino acids and then separating the amino acids chromatographically as described below. True protein digestibility is determined according to Alternate Protocol 2. 

The lab correction factor compensates for differences in proteolytic enzyme preparations and other experimental variables. Multiply the experimentally determined test protein digestibility by the correction factor to determine digestibility. 

In vitro protein digestibility requires preparation of a treated sodium caseinate standard. Because of the empirical nature of these determinations, it is critical that results for the so-... 

Reversed-phase HPLC is widely utilized to generate a peptide map from digested protein, and the MS online method provides rapid identification of the molecular mass of peptides. The HPLC-MS-FAB online system is a sensitive and precise method for low-MW peptides (<3000 Da) even picomol quantities can be detected. However, as the MW of the analytes increases, the ionization of peptides becomes more difficult and decreases the sensibility of the FAB-MS (112). Electrospray ionization (ESI-MS) was found to be an efficient method for the determination of molecular masses up to 200,000 Da of labile biomolecules, with a precision of better than 0.1%. Molecular weights of peptide standards and an extensive hydrolysate of whey protein were determined by the HPLC-MS-FAB online system and supported by MALDI-TOF (112). Furthermore, HPLC-MS-FAB results were compared with those of Fast Performance Liquid Chro-motography (FPLC) analysis. Mass spectrometry coupled with multidimensional automated chromatography for peptide mapping has also been developed (9f,l 12a). 

Acidic pH conditions caused the removal of dtraconyl groups from the citraconylated yeast proteins, so the environmental conditions of the stomach, i.e., pH and temperature, may cause the deacylation to occur following consumption of citraconylated proteins. This then would make lysine nutritionally available. The peptic digestibility of the citraconylated and decitraconylated yeast proteins was determined soy proteins and egg albumin were studied also for comparison. In a typical experi-... 

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