Improved Detection of Sugar Addition to Maple Syrup Using Malic Acid as Internal Standard and in 13C Isotope Ratio Mass Spectrometry (IRMS)

Stable carbon isotope ratio mass spectrometry (δ13C IRMS) was used to detect maple syrup adulteration by exogenous sugar addition (beet and cane sugar). Malic acid present in maple syrup is proposed as an isotopic internal standard to improve actual adulteration detection levels. A lead precipitation method has been modified to isolate quantitatively malic acid from maple syrup using preparative reversed-phase liquid chromatography. The stable carbon isotopic ratio of malic acid isolated from this procedure shows an excellent accuracy and repeatability of 0.01 and 0.1‰ respectively, confirming that the modified lead precipitation method is an isotopic fractionation-free process. A new approach is proposed to detect adulteration based on the correlation existing between the δ13Cmalic acid and the δ13Csugars − δ13Cmalic acid (r = 0.704). This technique has been tested on a set of 56 authentic maple syrup samples. Additionally, authentic samples were spiked with exogeneous sugars. The mean theoretical detection level was statistically lowered using this technique in comparison with the usual two-standard deviation approach, especially when maple syrup is adulterated with beet sugar : 24 ± 12% of adulteration detection versus 48 ± 20% (t-test, p = 7.3 × 10-15). The method was also applied to published data for pineapple juices and honey with the same improvement. Keywords: Maple syrup; sugars and malic acid; internal standard; authentification; stable isotope analysis; 13C IRMS; pineapple juices; honey