博士 / 國立臺灣海洋大學 / 食品科學系 / 92 / he levels and compositions of free amino acids (FAAs) and low-molecular-
weight peptides of eleven commercial meat essences were determined. Their
antioxidant activities were also studied. The total FAAs in seven chicken
essences varied from 150 to 725 mg/100g. Taurine was the dominant FAA
accounted for 16~37% of the total FAA. Beef essence had the highest level
of total FAAs among the eleven products, its taurine contributed only about
2%. Taurine in freshwater clam essence was very low, but a high level of
ornithine was found. Anserine was higher than carnosine in seven chicken
essences, while anserine was far less than carnosine in beef essence. These
dipeptides in both clam essences were not detectable. Only a small amount
of carnosine was present in eel essence. Another dipeptide, balenine, was
found in two chicken essences. The amount of small peptides in chicken
essences was more than FAAs in each product. Both clam essences contained
much lower amount of small peptides than other products.
Including the inhibition of linoleic acid autoxidation, scavenging effect
on a,a-diphenyl-b-picrylhydrazyl free radical, reducing power, and
chelating ability of Cu2+ were used to evaluate the antioxidant activities
of dipeptides and some FAAs. Results showed that carnosine and anserine
were antioxidants preventing lipid peroxidation in linoleic acid systems.
They also possessed effective abilities as free radical scavengers,
reducing agents, and copper ion chelators. The activities increased with
increasing concentration. However, the constituent amino acids of
dipeptides, b-alanine, histidine and 1-methylhistidine, were not as
effective in inhibiting oxidation regardless of individual or combined
usage. Taurine, glycine, alanine and b-alanine showed much weaker
antioxidant activities than carnosine, anserine, histidine and 1-
methylhistidine. No synergistic effects on antioxidation were found among
compounds used in combination.
The extracts of chicken, beef and eel essence had noticeable antioxidant
properties. The activity was concentration dependent. Freshwater clam and
hard clam essences, however, showed much lower activities than other
products. The low-molecular-weight peptides were present in chicken essence
in a large quantity. The peptide contents had a good correlation with
antioxidant activity. However, no correlation was found between total FAAs
and antioxidant activity. The meat essence possessed antioxidant activity
might be associated with its high levels of carnosine, anserine and small
peptides. Three peptide fractions of chicken essence were separated by size
exclusion chromatography. The peptide with molecular weight of
approximately 1400 Da possessed the strongest in vitro antioxidant
activity, followed by peptides with 900 and 500 Da. Two antioxidant
peptides were further isolated using size exclusion chromatography and
reversed-phase HPLC, and their amino acid sequences were His-Val-Thr-Glu-
Glu and Pro-Val-Pro-Ala-Glu-Gly-Val, respectively.
The antioxidant properties associated with FAAs and peptides in protein
hydrolysates of mackerel (Scomber austriasicus) were also investigated. The
raw and cooked meat were hydrolyzed by autolytic process and accelerated
hydrolysis with commercial enzymes including Protease N, papain, and
Prozyme 6. The levels of FAAs and small peptides during hydrolysis were
significantly increased during hydrolysis. Increased levels of FAA,
anserine, carnosine and other peptides of the hydrolysates obtained with
commercial enzymes were much higher than those by autolysis. The Prozyme 6
hydrolysate had the highest amount of FAAs among the hydrolysates. Raw meat
hydrolysates had more FAAs than cooked meat hydrolysates. Anserine and
carnosine were not found in the muscle of mackerel and autolysis
hydrolysates; however, they were found in considerable levels in the
protease hydrolysates. The peptides of the enzyme hydrolysates increased
dramatically in the first 10 h of hydrolysis and thereafter decreased with
the increase of FAAs. Different antioxidant measurements showed that
mackerel hydrolysates possessed noticeable antioxidant activities, and the
activities increased with increasing concentration. Enzyme hydrolysates had
much higher activities than that of autolysis. There existed a good
correlation between the amount of peptides and antioxidant activity.
Three and/or five peptide fractions were separated from the hydrolysates by
size exclusion chromatography on Sephadex G-25. The absorbances of the
fractions isolated from enzyme hydrolysates were much higher than that of
autolysis. The molecular weights of Fraction I, II, III of papain and
Protease N hydrolysates were estimated to be about 1,400, 900, and 200 Da.
All fractions displayed noticeable antioxidant activities, and the
activities increased with increasing concentration. Four and five
antioxidant peptides were further isolated and purified from the
hydrolysates by reversed-phase HPLC. These peptides were composed of 4-6
amino acid residues in the sequences, being Val-Trp-Trp-Trp, His-Gly-Ala-
Tyr-Val and His-Ala-Gly-Ile-Ile possessed stronger antioxidant activitie
| Identifer | oai:union.ndltd.org:TW/092NTOU5253003 |
| Creators | Hui-Chun Wu, 吳蕙君 |
| Contributors | 蕭泉源 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 180 |
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