Agave syrup is growing in popularity as an alternative to traditional sweeteners such as table sugar and honey. But as its use grows, so does the incentive for adulteration. High-performance anion chromatography with pulsed amperometric detection (HPAE-PAD) is recommended in the official guidelines for the characterization of agave syrup to determine product authenticity. Now, this can be performed in dual eluent generation cartridge (Dual EGC) mode for faster, more economical analysis.
Agave syrup: A sweeter choice
Over the past few years, agave syrup, produced from the sap of the agave plant in Mexico, has been widely adopted as a sweetener. The syrup boasts a low glycemic index (GI) (17-27) compared to honey (55) and sucrose (68),[i] meaning that its carbohydrates are more slowly digested, absorbed, and metabolized. Agave nectar therefore causes a smaller rise in blood sugar and, consequently, insulin levels. In addition, it can provide the same level of sweetness as other glucose and sucrose-based syrups, but with fewer calories thanks to its high fructose content.
The increased popularity of agave syrup means that inauthentic variations are entering circulation. As the syrup is mostly composed of carbohydrates, it is easy and cheap to adulterate using less expensive sweeteners, including high fructose corn syrup (HFCS). Knowing the composition of agave syrup using analytical techniques is therefore essential to ensuring authenticity and protecting human health through better consumer knowledge.
Improving determination of sugars with Dual EGC
The Mexican government has created official guidelines for characterizing agave syrup, known as Norma Oficial Mexicana (NOM)-003-SAGARPA-2016.[ii] HPAE-PAD is the recommended NOM method for determination of sugars and detection of adulterants in agave syrup, as it enables direct detection of analytes — thereby eliminating errors that can be caused by analyte derivatization.
However, Dual EGC mode can improve the recommended HPAE-PAD method by reducing eluent consumption and eliminating manual eluent preparation. The Dual EGC mode uses a methanesulfonic acid (MSA) EGC and potassium hydroxide (KOH) EGC sequentially to electrolytically produce a KOH/KMSA eluent. The eluent gradient is highly reproducible and accurate, and is perfect for separating complex carbohydrates such as those found in agave syrup.
HPAE-PAD with Dual EGC: Linear, precise, sensitive and accurate
In a recent application note, we performed carbohydrate analysis of agave syrup with HPAE-PAD using a Thermo Scientific™ Dionex™ CarboPac™ PA200-1 mm column (250 × 1 mm) in Dual EGC mode. We analyzed three different agave syrup samples, and determined the main sugars (fructose, glucose, and sucrose), polyols (sorbitol and mannitol), and 5-hydroxymethylfurfural (HMF). We also evaluated the presence of adulterants (HFCS or corn syrup) using HPAE-PAD and amyloglucosidase enzymatic hydrolysis.
The Dionex CarboPac PA200-1 mm column is the recommended column for separating charged and neutral oligosaccharides, as it can provide high-resolution separation.[iii] When tested on agave syrup, we found excellent resolution (>2.0) between all the components (Figure 1).
Figure 1: Separation of seven agave sugar standards using a Dionex CarboPac PA200-1 mm column set.
We investigated the key parameters of the HPAE-PAD method with Dual EGC mode for carbohydrate analysis of agave syrup, and found the method was:
Linear: A coefficient of determination of <0.999> was obtained for each sugar.
Precise: Calculated peak area precision was 0.85 – 1.66%, with retention time precision <0.28% (Table 1).
Sensitive: The limit of detection (LOD) and limit of quantitation (LOQ) for all seven sugars were below 11.56 μg/L and 48.6 μg/L, respectively.
Accurate: Recovery of sorbitol, glucose, and sucrose from spiked samples was 97.2 – 105%.
Table 1: Retention time and peak area precision. RSD: relative standard deviation.
Importantly, the results were comparable to those obtained using manually prepared sodium hydroxide and sodium acetate eluent in NOM, but with superior precision.[iii]
Fighting adulterated agave syrup with Dual EGC
Overall, HPAE-PAD in Dual EGC mode is an excellent tool for agave syrup carbohydrate analysis, with excellent linearity, precision, sensitivity, and accuracy. The method delivers resolution of agave carbohydrates similar to that achieved with standard HPAE-PAD, but with improved retention time precision. The quality of results and simplified operation makes the method a valuable tool in agave syrup adulteration detection.
[i] a) Wolever, T.; Vuksan, V.; Jenkins, A. L.; Campbell, J. Determination of glycemic index of: Organic 100% blue agave syrup and prebiotic 100% blue agave syrup; Final report for Glycemic Index Laboratories: Toronto, ON, November 2011. b) Foster-Powell, K.; Holt, S.H.A.; Brand-Miller, J.C. International table of glycemic index and glycemic load values: Am. J. Clin Nutr. 2002, 76, 5–56.