Summary:
In the present research work chemical composition (fat, moisture, ash and
proteins), lipid composition (of total lipid, polar lipids and neutral lipids
including cholesterol and triglycerides) as well as fatty acid composition (of
total lipids, polar lipids and of individual classes PE, PC) of the muscle and
cephalothorax of shrimp Peneaeus kerathurus were studied. The objective of this
work was the determination and the study of molecular structures of
phospholipids (PC, PE, Sph and LPC) and arsenolipids as well as the
determination of carotenoids which are known for their important biological
activity. Moreover, metals and metalloids such as: Fe, Cu, Zn, Mn, Se, Mg, Ni,
Cr, Cd, As, Pb and Hg were analysed. In order to achieve the experimental
research work as above mentioned, the combination of methodology was applied
including HPLC, LC-ESI-MS/MS, NMR, spectroscopy techniques etc.
P. kerathurus is the most popular shrimp among the other species of
shrimps and represent a substantial part of the Mediterranean diet, is consumed
in larger quantities than other edible decapod crustaceans such as prawn,
lobster or crab and is subject of aquaculture.
The percentage of fat, humidity, ash and protein of the muscle tissue of
P. kerathurus was 0.6% of wet tissue, 77.4%, 1.93% and 19.2% respectively while
that of cephalothorax tissue was 1.4% of wet tissue 39.0% and 12.0%
respectively (protein was not determined).
The polar lipids proportion in muscle and cephalothorax total lipids was found
to be 68.0% and 46.5% respectively.
According to the study of composition of individual classes of muscle and
cephalothorax phospholipids was found that PC was the major phospholipids
(55.6% and 46.4% respectively) followed by PE (29.3% and 25.7% respectively),
while Sph, CL, LPC, PS and PI were determined as minor components.
Sterols were the major component of muscle neutral lipids (84,9 % of total
neutral lipids) while triacylglycerols were the dominant component of
cephalothorax neutral lipids (67.2 % of total neutral lipids).
The fatty acids profile of muscle and cephalothorax total lipids did not differ
significantly. So, C16:0, C18:0, C16:1 ω-9 cis and C18:1 ω-9 cis were the main
fatty acids. The contents of PUFA, the essential fatty acids were C20:5 ω-3 cis
(EPA) and C22:6 ω-3 cis (DHA). The ratio ω-3/ω-6 of polar lipids, PC and PE was
higher in muscle (2.49, 1.66 and 1.76) in comparison with that of
cephalothorax. The ratio EPA/DHA of PC (3.52) and PE (2.74) was higher of unit
in muscle as well as cephalothorax.
In order to study and identify the molecular structures of phospholipids and
arsenolipids, total lipids of muscle and cephalothorax were separated into
neutral and polar lipids by SPE (solid phase extraction). After that, molecular
species of muscle and cephalothorax phospholipids of shrimp were isolated by
preparative TLC in order to analyze and identify:the molecular structure
(diacyl, alkyl-acyl and alkyl-enyl-acyl derivates) of intact phospholipids in
positive ion mode LC- ESI-MS/MS (electrospray ionization tandem Mass
Spectrometry). the molecular structure of individual phospholipids after their
hydrolisation (mild alkaline and acid hydrolisation). LC-ESI-MS/MS in the
selected reaction monitoring (SRM) mode was used for the detection of
organoarsenic species such as: DMA, AC (arsenocholine), oxo- arsenosugars.In
order to identify and determine the molecular structure of polar lipids
(phospholipids), their main compounds, phosphatidylcholine (PC) and
phosphatidylethanolamine (PE), as well as Sph and LPC, High Resolution NMR
spectroscopy was used. 1H and 31P NMR was used for the identification of
specific lipid classes. 2D COSY and HSQC techniques as well as 1H spectra of
standards (PC and PE) were used to elucidate the characteristic peaks of
individual phospholipids. Two dimensional NMR spectroscopy (COSY, HSQC, HMBC)
was applied for the identification of plasmalogens (alk-1-enyl glyceryl ethers)
in polar lipids. Distinctive signals corresponding to the protons of double
bond (Ο-CH=CH-) near the vinyl ether group were shown to be the most useful in
the qualitative analysis of plasmalogens . The qualitative and quantitative
analysis of carotenoid pigments was performed by high-performance liquid
chromatography (HPLC). Carotenoid content of P. kerathurus muscle (3.33 g/ 100
g of total lipids) were lower than in cephalothorax (9.30 g/ 100 g of total
lipids). The major carotenoid was found canthaxanthin in both muscle and
cephalothorax. Lesser amount mono ester and diester of astaxanthin were also
determined in both tissues, while cryptoxanthin was detected only in
cephalothorax.Finally, concentrations of metals and metalloids in samples of
muscle and cephalothorax of shrimp were measured Fe, Cu, Zn, Mn, Mg, Ni, Cd, Pb
and metalloids (Se and Αs) by Atomic Absorption Spectrometry. Cr was not
detected in both tissues, while Hg was found only in cephalothorax.
