Abstract:

Objective: To establish a method for the determination of total conjugated linoleic acid (CLA) content
in cheeses by quantitative nuclear magnetic resonance (QNMR) and to compare its effectiveness with that of
ultraviolet spectrophotometry. Methods: The analysis employed 1,2,4,5-tetramethylbenzene as internal standard, and a
5-mm Bruker broadband observe (BBO) probe, working at 300 K with a pulse sequence of Noesyig1d, 128 scans and a
pulse delay time (D1) of 10 s. Results: The recovery rate was 93.33% with relative standard deviation (RSD) of 4.20%. The
precision RSD was 0.99%, the reproducibility RSD was 3.17% and the stability RSD was 1.81%. Conclusion: This method
enables direct determination of target and non-target compounds in foods without using standard reference. Compared with
ultraviolet spectrophotometry, it had a higher specificity.

Key words: quantitative nuclear magnetic resonance (QNMR), cheeses, conjugated linoleic acid (CLA), quantitation