Određivanje trans masnih kiselina u prehrambenim proizvodima gasnom hromatografijom-masenom spektrometrijom

Abstract

U okviru doktorske disertacije optimizovani su uslovi određivanja metilestara masnih kiselina, uključujući i trans izomere, primenom kapilarne gasne hromatografije–masene spektrometrije, na kapilarnoj koloni SP-2560 (dužina x unutrašnji prečnik: 100 m x 0,25 mm, debljina sloja stacionarne likvidne faze 0,20 μm, biscijanopropil polisiloksan). Korišćenjem standarnih rastvora metilestara masnih kiselina optimizovani su temperaturni program, odnos razdeljivanja i uslovi akvizicije podataka SCAN tehnikom. Razvijena je metoda za pripremu uzoraka u cilju određivanja sastava masnih kiselina u prehrambenim proizvodima gasnom hromatografijom–masenom spektrometrijom zasnovana na istovremenoj mikrotalasnoj ekstrakciji i esterifikaciji (SMEE). Validacija metode je izvedena poređenjem sa rezultatima dobijenim gasnom hromatografijom–masenom spektrometrijom nakon ekstracije po Soxhlet-u i derivatizacije masnih kiselina u metilestre masnih kiselina. Rezultati dobijeni primenom razvijene i referentne metode bili su statistički isti, kako u pogledu sastava masnih kiselina, tako i efikasnosti ekstrakcije. Rezultati su pokazali da su prednosti SMEE u odnosu na konvencionalnu metodu: kratko vreme pripreme uzoraka i samim tim manja potrošnja energije, kao i upotreba malih količina skupih organskih rastvarača. Dobro slaganje rezultata dobijenih primenom referentne i metode zasnovane na istovremenoj mikrotalasnoj ekstrakciji i esterifikaciji pokazuje da bi se SMEE mogla primeniti kao rutinska metoda za pripremu uzoraka prehrambenih proizvoda u cilju određivanja trans masnih kiselina (TFA). Određen je sastav masnih kiselina, sa posebnim akcentom na trans masne kiseline, u 273 uzoraka prikupljenih sa našeg tržišta u periodu od juna 2006. do juna 2009. godine. Sadržaj trans masnih kiselina u analiziranim uzorcima prehrambenih proizvoda, sirovina i međuproizvoda koji se koriste u pekarskoj i konditorskoj industriji, kretao se u veoma širokom intervalu, od 0,0% do čak 48,7%. Prosečan sadržaj trans masnih kiselina iznosio je 0,2% u uljima, 6,5% u jestivim margarinima, 19,9% u margarinima za domaćinstvo, 9,8% u industrijskim margarinima, 24,3% u namenskim mastima, 10,8% u masnim punjenjima, 1,6% u mlečnim proizvodima, 10,9% u slanom trajnom pecivu, 10,2% u čajnom pecivu, 6,3% u tvrdom keksu, 11,0% u vafel proizvodima, 10,6% u čokoladnim proizvodima i 9,2% u karamelama. Od ukupno 124 analizirana uzorka, koja se ne koriste za direktnu upotrebu u ishrani (namenske masti, masna punjenja, industrijski i margarini za domaćinstvo) 86 uzoraka (69,3%) sadrži više od 5% trans masnih kiselina, 25 (20,2%) sadrži manje od 5% TFA, dok u 13 uzoraka (10,5%) nije detektovano prisustvo trans izomera. Od ukupno 140 analiziranih uzoraka, koji se koriste za direktnu upotrebu u ishrani 74 uzoraka (52,8%) sadrži više od 2% trans masnih kiselina, 20 (14,3%) sadrži manje od 2% TFA, dok u 46 uzoraka (32,9%) nije detektovano prisustvo trans izomera.

In this thesis, operating conditions for fatty acids determination, including trans isomers, by capillary gas chromatography–mass spectrometry, on capillary column SP-2560 (100 m x 0.25 mm, with a 0.20 μm film thickness of biscyanopropyl polysiloxane liquid phase) were optimized. Temperature program, split ratio and condition of data acquisition by SCAN technique were optimized using standard solutions of fatty acid methyl esters. A sample preparation method based on simultaneous microwave assisted extraction–esterification (SMEE) was developed for the determination of the fatty acid composition of foodstuffs by gas chromatography–mass spectrometry. The proposed sample preparation method was validated by comparison with the reference Soxhlet extraction method followed by derivatisation by methyl ester formation and the same determination step. The fatty acid compositions, as well as extraction efficiencies obtained by the use of the proposed SMEE method and reference method were statistically similar. The results showed that compared to the conventional method, SMEE method offer the advantages of short sample preparation time, low consumption of expensive organic solvents and less energy consumption. This good agreement between results provided, both by the SMEE and reference method, demonstrates the usefulness of the former as the routine method for the treatment of food samples prior to trans fatty acid analysis. The fatty acid composition, and trans fatty acid content of 273 samples collected from June 2006 to June 2009 year were determined. Trans fatty acid content in the analysed samples of food products, raw materials and intermediate products used in bakery and confectionery industry was ranged in a very wide interval, from 0.0% to 48.7%. The average contents of trans fatty acids were 0.2% in oils, 6.5% in the edible margarines, 19.9% in cooking margarines, 9.8% in industrial margarines, 24.3% in shortenings, 10.8 % in fat fillings, 1.6% in dairy products, 10.9% in crackers, 10.2% in tea cookies, 6.3% in biscuits, 11.0% in wafer products, 10.6% in chocolate products and 9.2% in the caramels. From the total of 124 analysed samples, which are not used for direct human consumption (shortenings, fat fillings, industrial and cooking margarines) 86 samples (69.3%) contained more than 5% trans fatty acids, 25 (20.2 %) contained less than 5% TFA, while 13 samples (10.5%) had an undetectable levels of trans isomers. From a total of 140 analysed samples, which are used for direct human consumption 74 food samples (52.8%) contained more than 2% trans fatty acids, 20 (14.3%) contained less than 2% TFA, while 46 samples (32.9%) had an undetectable levels of trans isomers.