Evaluation of Protein in Foods: Iii. A Study of Bacteriological Methods

Abstract

Bacteriological methods for the determination of protein quality were evaluated by comparison with protein efficiency ratio (P.E.R.) values determined by a standardized rat growth assay. Enzyme or acid hydrolyzates of foods were used as the source of amino acids with hydrolyzed whole egg powder as the reference standard. With Streptococcus faecalis A.T.C.C. 9790 autolysis occurred in media containing hydrolyzates of proteins deficient in lysine, and was largely responsible for results which did not agree with P.E.R. values. In methods employing Leuconostoc mesenteroides P-60 A.T.C.C. 8042, growth was influenced only by the most limiting amino acid relative to the requirements of the test organism.Results with enzyme hydrolyzates correlated poorly with P.E.R. values, whereas, with acid hydrolyzates, a good correlation was obtained for cereal proteins. A difference in amino acid requirements was largely responsible for the lack of agreement between the P.E.R. assay and methods employing L. mesenteroides, particularly for legumes and foods of animal origin. It was concluded that bacteriological assay methods which have been proposed for protein evaluation are unsatisfactory as screening procedures for the evaluation of protein in foods.

Two‐dimensional mapping as a tool for classification of green coffee bean species

“…The strings of spots characterizing the a and b arms, at 33 kDa and 22 kDa, respectively, are clearly visible, as well as their precursor at 55 kDa. The string of spots around 80 kDa could be oligomers (tetramers) of the b arm, as suggested by Rogers et al [6]. Figure 2 shows three 2-D maps obtained by extracting the grains with the three different methods reported in section 2 (conventional method, method from Damerval et al [11] and the AUC variant).…”

“…Our approach was also used by Rogers et al [6]; however, their 2-D maps were only shown to highlight some differences between C. arabica and C. canephora, but no differential analysis with dedicated software was attempted. Interestingly, a completely different approach was attempted by Procida et al [22] for obtaining fingerprints of native proteins from C. arabica and C. canephora, for differentiation of these two species as well as for characterizing differences among samples of the same variety from various plantations.…”

“…First of all, Procida et al [22] might also be looking at rather small peptides, which are in general not visible in 2-D maps, unless one uses special buffers in the SDS-PAGE dimension, as performed by Ludwig et al [7]. Secondly, we a) Calculated pI value according to [6] b) For possible 11S fragments we reported the calculated M r and pI of the entire legumin c) Calculated considering the amino acid sequence corresponding to the acid chain 28-300 aa of the entire precursor (giu2979526) d) Calculated considering the amino acid sequence corresponding to the acid chain 27-306 aa of the entire precursor (giu4127631) e) Calculated considering the amino acid sequence corresponding to the basic chain 301-487 aa of the entire precursor (giu2979526) The comparison is performed between the matched spots in C. canephora (var. Indiano Robusta) and C. arabica (var.…”

“…However, very few studies have investigated the protein content of coffee beans, especially in regard to the use of 2-D maps, although it is well known that free amino acids, peptides and proteins are essential aroma precursors [5]. In this respect, perhaps the cornerstone study is the one by Rogers et al [6], who reported the first detailed investigation of proteins in the C. arabica endosperm by 2-D map analysis, coupled to MS characterization of the most abundant polypeptide chains and mRNA amplification. In their study, the most abundant polypeptide spots observed on mature coffee grain 2-D profiles were found to be subunits of the same protein, which exist as multiple isoforms with varying pI values.…”