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detection of amino acids, hydrolysate of collagen-containing meat [90]. In this case, OPA does not react
with secondary amino acids. Before the reaction with OPA reagent, oxidation with sodium hypochlorite
(NaOCl) of secondary amino acid is required for the first step. The drawback of NaOCl oxidation is the
decomposition of tryptophan.

Recently developed on-column fluorescence derivatization is applied to the analysis of amino acids [91]
and taurine [92]. Derivatizing reagents for on-column methods are used in pairs such as OPA and an
active thiol, N-acetyl-L-cysteine(NAC), Thiofluor and 2-ME. The analysis of taurine [92] employs SPE
(Bond Elut SCX) clean-up as sample pretreatment was used for infant formula and milk products, eggs,
honey, fish powder, shellfish and so on. High sensitivity of OPA derivatives and improvement of clean-
up, enabled trace analysis, and taurine in egg yolk and honey to be detected for the first time (Fig.
1.2.3).

On-column methods use OPA mixed with mobile phase, thus simultaneous analysis of
multicomponents with gradient elution is difficult. Combining the column-switching technique and
step-gradient elution, the simultaneous analysis of polyamines and their precursors, amino acids, was
carried out. This method was applied to the investigation of the arginine degradation pathway of
Photobacterium phosphreum, a putrefactive bacteria [93] and the measurement of citrulline, which is
produced stoichiometrically from arginine when nitric oxide (NO) is produced, in order to study the
effect of food stuffs on the NO productivity of macrophage cultured cell [94].

The use of CE with derivatization of amino acids for the analysis of foods is hardly reported. For
derivatization with CE, the pre-column method is the most common, and the reaction system is
fundamentally similar to the HPLC method. A recent report shows that free amino acids in fish and
lysine, tyrosine, histidine, and ornithine in soya flour hydrolysates, are derivatized to di-dansyl amino
acids followed by separation and detection with micellar electrokinetic chromatography (MEKC) [95].

Fig. 1.2.3.
Typical chromatograms of taurine from: (A) clam; (B) Yolk; (C)
salmon reo; and (D) honey. (Reproduced from ref. 92: J Food
Hyg. Soc. Japan, (1997) 38, 403, Fig. 2.).
Peptides

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