“Quality changes of semi-preserved Mugil cephalus ovaries (avgotaracho), during storage at 3.0 ± 1.0 ºC” V.J. Sinanoglou , M. Voulgarelis , P. Androutsaki , I.F. Strati , V. Oreopoulou , V.R. Kyrana , V.P. Lougovois 1
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Instrumental Food Analysis Laboratory, Department of Food Technology, Technological Educational Institution of Athens, e-mail:
[email protected] 2 Fisheries Laboratory, Department of Food Technology, Technological Educational Institution of Athens, e-mail:
[email protected] 3 Laboratory of Food Chemistry and Technology, School of Chemical Engineering, National Technical University of Athens, e-mail:
[email protected]. 1
Abstract Quality changes of Greek avgotaracho were assessed over a 4-month storage period at 3.0 ± 1.0 ºC, by lipid, fatty acid and carotenoid profile analysis, assays of thiobarbituric acid-reactive substances (TBA-RS), colour measurements (CIE L*a*b*) and determinations of total volatile bases (TVB). The major lipid classes in freshly prepared avgotaracho were neutral lipids (NL), mainly triglycerides (TG), followed by cholesterol. Polar lipids (PL) consisted mainly of phosphatidylcholine (PC), followed by sphingomyelin (Sphm) and phosphatidylethanolamine (PE). Cold storage did not significantly affect the individual lipid classes’ content. The minor amounts of free fatty acids and monoglycerides released over the storage period suggested slow TG and PhL hydrolysis. GC-FID analysis of the lipid revealed the presence of 37 fatty acids (FA). Heptadecanoic acid (C17:0) was the main saturated fatty acid (SFA), followed by palmitic acid (C16:0), while palmitoleic (C16:1 ω-7), oleic (C18:1ω-9) and vaccenic (C18:1ω7) were the major monounsaturated fatty acids (MUFA). Polyunsaturated fatty acids (PUFA) occurred in the lowest concentration and consisted mainly of DHA (C22:6ω-3) and EPA (C20:5ω-3). An increase in SFA content and a decrease in PUFA, especially ω-3 fatty acids, was observed during storage. PUFA/SFA, MUFA/SFA and ω-3/ω-6 ratios gradually decreased in the stored product. However, oxidative changes were rather limited, as judged by the slow increase in TBA-RS levels. HPLC-DAD analysis of the carotenoids showed that β-cryptoxanthin predominated, followed by all-trans lutein, all-trans canthaxanthin, α-cryptoxanthin and all-trans zeaxanthin. Carotenoid profile was not affected by storage. Nevertheless, a significant decrease in individual carotenoid compounds was observed in the stored product. CIE L*a*b* coordinates varied considerably between samples, probably reflecting differences in roe maturation. The high levels of volatile basic nitrogen (up to 133.98 mg/100 g) observed after 4 months of storage are in accordance with previous results in this field of study and appear to be associated with autolytic and microbial activities during the ripening process.
Materials and Methods Total lipid was determined by the chloroform-methanol extraction procedure (Hanson & Olley, 1963). Thiobarbituric acid-reactive substances (TBA-RS) were monitored by the method of Witte et al. (1970). Colour measurements were conducted on both sides of thin slices of the product, using a ColorTecTM-PCM analyzer (ColorTec Associates, Clinton, N.J.). Data were expressed as CIE L*a*b* coordinates. TLC–FID analysis of neutral and polar lipids was performed by an Iatroscan thin-layer chromatograph (MK-6 TLC/FID - FPD Analyser, Iatron Laboratories, Japan) (Sinanoglou et al., 2013). Analyses of fatty acids methyl esters of total lipids were performed on an Agilent 6890 Series Gas Chromatograph (Sinanoglou et al., 2013). Carotenoids analysis was performed by HPLC (Hewlett Packard Series 1100, Waldbronn, Germany) according to the method of Strati et al. (2012). All statistical calculations were performed with the SPSS package (IBM SPSS Statistics, version 19.0, Chicago, IL, USA) statistical software for Windows.
PL consisted mainly of phosphatidylcholine (PC), followed by sphingomyelin (Sphm) and phosphatidylethanolamine (PE) (Fig. 1). Greek avgotaracho is an excellent source of dietary PC, providing ≈1910 mg of PC per 100 g of dry matter, which apparently exceeds the recommended daily intake (RDI) in the human diet (550 mg for men and 450 mg for women) (Fig. 2). Cold storage did not seem to cause any significant (P0.05) at 0.8 g per 100 g of dry matter.
Results and Discussion The sum of moisture and total extractable lipid contents averaged 61.54% (s.d. 0.63) and did not change (P93.6%), mainly triglycerides (TG). In the course of the trial, FFA and MG levels increased significantly (P
