Comparison of Chromatographic and Titrimetric Methods for the Determination of the a-amino Nitrogen in Standard Solution and Fish Protein Hydrolysates

Haiyan Wang,Jin Cao,Qingsheng Zhang,Fenglan Zhang,Zhirong Chen

doi:10.5539/jfr.v1n4p174

Abstract

<p>Two analytical methods, reverse phase high-performance liquid chromatography (RP-HPLC) and formol titration, were compared for their accuracy and precision for the determination of a-amino nitrogen (a-AN) concentration in fish protein hydrolysates. The result showed that, when tested with pure amino acid solutions, RP-HPLC method had a better standard deviation (S. D.), coefficient of variation (C. V.), and standard error (S. E.) but a poorer recovery rate compared with formol titration technique. The observed a-AN value by RP-HPLC has good coincidence with the actual a-AN value and their correlation coefficient (r) is 0.9981, which was close to the r value (0.9995) between the a-AN by formol titration and the actual a-AN. However, when tested with protein hydrolysates, the a-AN obtained from RP-HPLC technique were significantly (p&lt;0.05) lower than that from formol titration for the same sample. Therefore, the formol titration method can be used as a quick screening method to assess the quality fish hydrolystaes.</p><p> </p>

Highlights

Enzymatic hydrolysis is widely used to improve functional or nutritional properties of food proteins (Mahmoud, 1994; Kim & Wijesekara, 2010)
Our research group have done a lot of work on fish protein hydrolysates (Ren et al, 2008a & 2008b), and during our routine assay, we have found that the α-amino nitrogen (α-AN) molar concentration obtained by reverse phase high-performance liquid chromatography (RP-HPLC) was far less than that by formol titration for the same sample
Taking into account the arithmetic mean of the five measurements obtained for each concentration (Table 2), the formol titration method gave a better recovery rate compared with the RP-HPLC technique

Summary

Introduction

Enzymatic hydrolysis is widely used to improve functional or nutritional properties of food proteins (Mahmoud, 1994; Kim & Wijesekara, 2010). Protein hydrolysates with different degree of hydrolysis values (DH) can be used as flavourings having unique flavors and aromas (Su, Ren, Yang, Cui, & Zhao, 2011). A traditional seasoning popular in the Orient, is the hydrolysate of fish protein by fungal proteases and amylases (Chou & Ling, 1998). During the processing of fish sauce, soluble nitrogenous compounds such as amino acids and peptides are formed (Kiesvaara, 1975). The amount of new amino acids formed is very important to the flavor of the sauce. The concentration of α-amino nitrogen (α-AN) is often used as the quality indicator for fish sauce products according to both the national standard of China and the Japanese Agricultural Standard (JAS) (Chinese National Standard, 1994; Yokotsuka, 1986). Fish sauce can be graded by α-AN concentration and the higher the α-AN concentration, the better the quality

Methods

Results

Conclusion