Racemization Kinetics of Aspartic Acid in Fish Material under Different Conditions of Moisture, pH, and Oxygen Pressure

Abstract

The racemization kinetics of aspartic acid in heat-treated whole herring have been studied under conditions of treatment comparable to those that may occur in processing of fish meal. D-Aspartic acid content in the samples has been measured by RP-HPLC with precolumn automatic derivatization. The major parameters affecting the rate of racemization of aspartic acid k(Asp) have been demonstrated to be temperature (elevation of temperature from 95 to 120 degrees C resulted in an increase of k(Asp) from 0.46 to 3.39x10(-3) min(-1)), moisture of the raw material (reduction of the moisture content of the raw material from 80 to 15% lowered k(Asp) measured at 95 degrees C from 0.46 to 0.06x10(-3) min(-1)), and to a lesser extent, pH (k(Asp) at 95 degrees C was lowered from 0.46 to 0.37x10(-3) min(-1) following a decrease of pH from 7.0 to 4.0). No significant effects on the racemization rate of aspartic acid was observed for reducing the oxygen pressure to 0.8%. The results from the present study show that the content of D-aspartic acid in fish material is a function of heat exposure and may be used to predict the thermal history of fish meal.

The Impact of Processing on Amino Acid Racemization and Protein Quality in Processed Animal Proteins of Poultry Origin

“…After prolonged or severe heat treatments, a degree of racemization rate was reported (Liardonn and Hurrell, 1983;Bada, 1984;Friedman and Liardon, 1985;Luzzana et al 1999). In our results, the prolonged heat treatment (115°C, 180 min) revealed a D-Asp content of 28.1%, that reasonably agree with previously reported D-Asp racemization rates on heated (121°C) chicken muscle protein, 22.4% and 26.3%, after 4 h and 8 h, respectively (Liardon and Hurrell, 1983).…”

“…ently from other amino acids, the behaviour of bound aspartic acid of different proteins is very reproducible with a progressive complete liberation of this amino acid after the applied hydrolysis conditions (Luzzana et al, 1996(Luzzana et al, , 1999; iv) under chromatographic conditions described above aspartic acids enantiomers separation and elution are completed after 16 min (Figure 4). Moreover, aiming to moderate the hydrolysis-induced racemization but to guarantee the breakage of peptide bond aspartic acid, the time of hydrolysis and temperature were reduced to 6 h and 100°C for analysis of samples from industrial rendering plan, maintaining the same acid condition (6 N HCl) (Luzzana et al, 1999). The D-aspartic content of sampling is reported in Table 6.…”

“…Percentages of Denantiomers identified in bovine serum albumin and lysozyme resulted higher than Damino acids percentages reported by Kaiser and Benner (2005) Table 4. Literature data and previous experiments (Liardon and Ledermann, 1981;Bada, 1984;Luzzana et al, 1996Luzzana et al, , 1999 established that the lower limit for a correct determination of D/L (%) was 0.2-0.4 %, especially when the analyses concern a mixture of amino acids or proteins. Below this limit, a correct determination failed because of the residual interference of hydrolysis-induced recemization.…”

“…Aspartic acid is the amino acid more prone to racemization, whose rate appeared strictly related to heat exposure. The racemization kinetics of aspartic acid under different temperature, moisture and pH conditions revealed that the content of D-aspartic acid is a function of heat exposure and may be considered a useful biomarker to predict the thermal processing undergone samples (Luzzana et al, 1996(Luzzana et al, , 1999. Kinetics studies of racemization in peptide or protein treated even under controlled conditions, are very complex mainly because of the inductive strength of the side chain influences interactions between neighbouring amino acids, however in some cases it could not be considered as the main driving force of amino acids racemization.…”

“…Therefore, to evaluate the reliability of D-amino acids content as an indicator of the severity of thermal treatments during PAP manufacturing and its significance to evaluate processing conditions applied, racem-ization data should be obtained on whole material subjected to physical conditions similar to those which may occur in PAPs production. In a previous work (Luzzana et al, 1999), it was demonstrated that thermal treatment and different rendering conditions affect aspartic acid racemization in fish meal. Processing temperature, pH and moisture content of the raw material are the major factors affecting the rate of racemization of aspartic acid.…”