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Study on the Constituents Correlating to Quality of Porphyra

Author: LiRuiXia
Tutor: ShenSongDong
School: Suzhou University
Course: Cell Biology
Keywords: Porphyra soluble protein Free amino acid Lipoxygenase
CLC: S968.431
Type: Master's thesis
Year: 2011
Downloads: 83
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Abstract


Porphyra are the main economic red algae, among which Porphyra yezoensis and P. haitanensis are the two extensively-cultivated Porphyra of China. This thesis is composed of three sections, in the first part Bradford was selected to investigate the content of soluble protein contents of Porphyra （including P. yezoensis and P. haitanensis） and their seasonal changes. The result indicated that the soluble protein contents of Porphyra were among 142.11-290.77mg/g, and significant variations among species and connected with the harvest season. So the soluble protein can be used as a reference indicator of the quality evaluation of Porphyra, this study also confirms the feasibility of Porphyra harvest for a highly valued product based on its chemical constituents.In order to elucidate the character of free amino acid compositions in Porphyra, extracts were prepared from 12 specimens which were cultivated in Nantong coastal areas in the second part.Free amino acids were derived with O-phthalaldehyde（OPA） and 9-fluorenylmethyl chloroforma（FMOC） in precolumn and separated by RP-HPLC. The results showed that 16 kinds of free amino acids were detected and the total free amino acids varied from 19.82 mg to 38.91 mg per gram. The contents of free Ala, Arg, Glu and Asp were predominant in all test samples, accounting for more than 80% of the total free amino acid.Meanwhile the contents of freely Ala and Glu were significantly and positively correlated with the total free amino acid （P<0.01）. Besides the contents of essential amino acids ranged from 9.48 to 13.06 mg per gram, accounting for 33.44-52.75% of the total free amino acids, the contents of taste amino acids in test samples differed from 10.23 to 25.86 mg per gram, accounting for 47.53-66.88% of the total free amino acids.It was suggested that LOX/HPL pathway might exist also in the algae, similar to high plants. Therefore, the third part was aimed to clarify the metabolic pathway of the volatile aldehydes in Porphyra. We identified Lipoxygenase activity using the spectrophotometric assay by incubating monounsaturated fatty acid （Oleic acid） and polyunsaturated fatty acid（Linoleic acid, Linolenic acid, Arachidonic acid, and Eicosapentaenoic Acid ） with partially purified crude enzyme of Porphyra. The results indicated that the Porphyra LOX showed the highest reactivity toward Linoleic acid （18:2）, followed by Arachidonic acid （20:4）, Linolenic acid（18:3） and Eicosapentaenoic Acid（20:5）, while little activity was observed against Oleic acid （18:0）. When with linoleic acid as substrate, the optimal pH of Porphyra LOX was 9.0, the optimal temperature was around 30°C, and the optimal substrate concentration of 2.5×10-4mol·L-1. The enzyme was stable at pH ranging from 6.0 to 9.0 and temperature below 40°C.

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CLC: > Agricultural Sciences > Aquaculture, fisheries > Aquaculture technology > A variety of seafood, animal and plant breeding > Algae farming > Red algae > Laver
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