amino acids production from fish proteins hydrolysis

8/7/2019 Amino Acids Production from Fish Proteins Hydrolysis

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for 28 h in 20% (by mass) HCl solution. The totalamino acid yield in hydrolysate was taken as the theo-retical total amino acids yield after entirely hydrolyzed.

2.4 Amino acid analysis

The quantitative determination of the amino acidswas determined by BioLC (Amino Acid Analyzer,DIONEX, USA). Comparison of amino acid chroma-togram between 18 kinds of amino acid standard sam-ples and hydrolysate sample of fish proteins wasshown in Fig. 2.

3 RESULTS AND DISCUSSION

3.1 Reaction temperature

Figure 3 shows that the relationship of amino acidyield with reaction temperature is different for differentkinds of amino acid under the same reaction time andpressure. The yield of amino acid in hydrolysate riseswith increasing temperature at first, then decreases,except cystine whose yield seems very low and inde-

pendent with temperature. This is perhaps because ofdecomposition of amino acid in high temperature [9].There is a maximum yield for each amino acid, but thecorresponding temperature is different from each other.

3.2 Reaction time

Figure 4 shows that the yield of amino acids in

Figure 1 Flow chart of sub-critical water hydrolysis experimental apparatus1,2feeding vessel; 3reaction atmosphere bottle; 4,5pump; 6,7water tank; 8pressure reactor; 9feeding funnel;10sampling device; 11cooling device; 12collector

Figure 2 Compare of amino acid chromatogram between standard and sample hydrolysate of fish proteinsaarginine; blysine; calanine; dthreonine; eglycine; fvaline; gproline; hserine; iisoleucine; jleucine;kmethionine; lhistidine; mphenylalanine; nglutamic acid; oaspartate; pcystine; qtyrosine; rtryptophan

Figure 3 Effect of reaction temperature on amino acidyield (5 MPa, 30 min) tyrosine; arginine;alanine; cystine;isoleucine;leucine;histidine;phenylalanine


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Chin. J. Chem. Eng., Vol. 16, No. 3, June 2008458

hydrolysate rises with increasing reaction time at first,then decreases a little, except cystine which is likeindependent with reaction time.

3.3 Reaction pressure

Figure 5 shows that the effect of pressure onyield of amino acids in hydrolysate is not very markedas compared with temperature and time.

3.4 Contrast of different atmosphere results

Figure 6 shows that the effect of different reac-tion atmosphere on different amino acid yield in hy-drolysate is different. No matter whatever atmosphere

is used, there is a given temperature for maximumyield of amino acid in hydrolysate. Fig. 6 suggest thatleucine, histidine and isoleucine should be hydrolyzedin atmosphere of nitrogen or carbon dioxide, while

tyrosine and phenylalanine may be in air.It is found that amino acids could be produced in

air, nitrogen or carbon dioxide, and it is much cheaper

than other methods of hydrolysis for breaking downbiomass which require expensive argon gas. This im-provement can help in industrial conversion of bio-mass into a useful resource.

4 HYDROLYSIS KINETICS

Biomass hydrolysis kinetics in super(sub)-critical water have been studied [10-12]. Hy-drolysis kinetics of fish proteins in sub-critical waterwas researched in this article.

4.1 Kinetics formula of fish proteins hydrolysis

It is very difficult to analyze the fish protein, butvery easy to determine the total yield of amino acids

Figure 4 Effect of reaction time on amino acid yield inhydrolysate (5 MPa, 260C) tyrosine; arginine;alanine; cystine;isoleucine;leucine;histidine;phenylalanine

(a) Leucine (b) Tyrosine (c) Histidine

(d) Isoleucine (e) Phenylalanine

Figure 6 The amino acid yield in hydrolysate of fish proteins versus temperature under nitrogen (), air (), carbon dioxide() atmosphererespectively

Figure 5 Effect of pressure on amino acid yield in hydro-lysate (260C, 30 min) tyrosine; arginine;alanine; cystine;isoleucine;leucine;histidine;phenylalanine


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Chin. J. Chem. Eng., Vol. 16, No. 3, June 2008 459

in hydrolysate at different reaction time by usingAAA-Direct. The amino acid yield rate Xat any timecan be defined as:

( )0(a) / atX M M= (1)

where M(a)t is the total amount of amino acids in hy-drolysate at different reaction time, M(a)0 the totalamount of amino acids in hydrolysate of fish proteinsentire hydrolysis by using hydrochloric acid. So, thefraction of remainder fish proteins at any time is 1 X .

The hydrolysis of fish proteins is as follows:

fish proteins + waterK amino acid+other products

(2)

So, the hydrolysis kinetic equation may be expressed as

( ) ( ) [ ]2d / d H O1 1bat KX X= (3)

in which t is the reaction time (s), K the hydrolysis

rate constant, and a, b are the reaction order.In this experiment, the water is much more ex-cessive, so [H2O]

bcan be set as a constant to be in-

corporated into K. So Eq. (3) can be turned into Eq. (4):

( ) ( )d / d1 1at kX X= (4)

Integrating Eq. (4) leads to Eq. (5):

[ ]1/(1 )

1 1 (1 )a

X k a t

= (5)

According to the Arrhenius equation :

aln / lnk E RT A= + (6)

where k is the hydrolysis rate constant, Ea the active

energy, and A the pre-exponential factor.The values ofa and kcan be obtained by non-linearnumerical fitting of experimental data to Eq. (5). Ea andA may be obtained from linear plot of lnkversus 1/T.

4.2 Kinetics parameters

(1 X ) values changing with reaction time underdifferent temperature are showed in Table 1. The ef-fect of reaction time on (1 )X at different tempera-tures is showed in Fig. 7.

Table 1 ( 1 X ) values changing with reaction time underdifferent temperatures1 X

t/min220 C 240 C 260 C

1 0.933 0.848 0.728

3 0.888 0.798 0.548

5 0.812 0.701 0.383

10 0.809 0.677 0.348

15 0.729 0.650 0.251

20 0.712 0.623 0.239

25 0.706 0.549 0.150

It is found that the hydrolysis reaction order is1.615, and the reaction rate constant k, lnkand 1/RT

values under different temperature are in Table 2. Therelationship between lnkand 1/ RT is shown in Fig. 8.Ea is 145.1 kJmol

1and the pre-exponential factor is

9.476109

(mgg1

)0.615s1

.

Figure 8 lnkversus ( 1/ ) RT

5 CONCLUSIONS

(1) Different amino acid shows different rela-tionship between reaction temperature and amino acidyield, even under the same reaction time and pressure.There is a maximum yield for each amino acid, but thecorresponding temperature is different from each other.

(2) Reaction atmosphere may be carbon dioxide,nitrogen and air. Leucine, histidine and isoleucineshould be hydrolyzed in atmosphere of nitrogen orcarbon dioxide. The others can be hydrolyzed in at-mosphere of air.

(3) The experimental results show that the hy-drolysis reaction order is 1.615 and the velocity con-

stants are 0.00170.0045 and 0.0097 min1 at 220,240 and 260 respectively. The activation energyis 145.1 kJmol

1and the Arrhenius pre-exponential

factor is 9.476109(mgg

1)0.615s1

.

Figure 7 ( 1 X ) changing with reaction time under dif-ferent temperatures220C;240C;260C

Table 2 The values ofk, lnk and 1/RT underdifferent temperatures

T k/min1 lnk 1/ RT

220C 0.0017 6.37713 0.000202

240C 0.0045 5.40368 0.000196

260C 0.0097 4.63563 0.000190


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amino acids production from fish proteins hydrolysis

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