Sorbitol is a polyol widely used as a food additive. Containing one-third fewer calories than sucrose, it is often used as a texturing agent or sweetener in foods such as chewing gum, candies, cookies, cakes and ice cream. It is also found naturally in fruit. While side effects associated with sorbitol consumption are generally mild, excessive intake can cause gastrointestinal disturbances in some people. In the European Union (EU), the application of food additives is controlled by EU Regulation 1129/2011, which establishes quality standards to protect consumer safety. To enforce the safe use of sorbitol in accordance with these regulations, laboratories require rapid and reliable methods for determining polyol concentrations in food products.
Determination of sorbitol in food using ion chromatography
High-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) is a valuable technique for food analysis applications, providing rapid results without the need for sample derivatization. However, traditional HPAE-PAD methods for sorbitol analysis are associated with a number of limitations. When working with complex food sample matrices, sorbitol quantification can be confounded by poor peak resolution due to co-elution with structurally similar carbohydrates. This can lead to inaccurate measurements, especially using conventional column chemistries. Additionally, many chromatography applications require manually prepared eluents – a time-intensive task that can be a source of measurement inconsistencies between runs and laboratories.
Advances in high-performance ion chromatography
Ongoing improvements in high-performance ion chromatography (HPIC) technologies are delivering more accurate and convenient polyol determinations. In recent years, high-capacity columns, such as the Thermo Scientific™ Dionex™ CarboPac™ PA300-4μm column, have been developed specifically for the analysis of complex oligosaccharides in heterogeneous food samples. Incorporating a high-capacity supermacroporous resin, the column provides improved peak resolution when working with challenging sample matrices.
Other advances have sought to improve consistency in eluent generation. Modern HPIC systems, such as the Thermo Scientific™ Dionex™ ICS-6000™ HPIC™ system, support the use of automated electrolytic eluent generation, eliminating the need for manual eluent preparation steps. In addition to ensuring more accurate and precise eluent concentrations between runs, they also provide a faster and more convenient approach for HPAE-PAD analysis.
Using HPAE-PAD to determine sorbitol in fruit and juice samples
To evaluate the effectiveness of modern HPAE-PAD systems for polyol analysis, we used a Dionex ICS-6000 HPIC system equipped with a Dionex CarboPac PA300-4μm column to determine sorbitol concentrations in fruit and beverage samples.
The Dionex CarboPac PA300-4μm column achieved efficient separation of a mixed solution of sorbitol, myo-inositol and mannitol standards, resulting in a well-defined sorbitol peak that could be easily integrated. A calibration curve established using eight concentrations of sorbitol showed linearity in the range 0.0333 to 33.3 parts per million (ppm), with a coefficient of determination (r2) of 0.9999 and relative standard deviation of 1.66%, highlighting the suitability of this approach.
We then used this method to determine sorbitol levels in samples of mashed lychees, mixed fruit juice and prune juice. Before injection, the mashed lychees and mixed fruit juice samples were diluted by a factor of 500, and the prune juice sample diluted by a factor of 50.
Efficient separation of the samples was achieved in less than seven minutes (Figure 1), then a wash step was added to increase method reproducibility. Baseline resolution of sorbitol from other peaks was observed for all three samples. Sorbitol was present at a concentration of 162 mg/L in the mashed lychees sample, 721 mg/L in the mixed fruit juice sample and 179 mg/L in the prune juice sample. Prune juice is a calibrated reference material, and the value determined by this method is comparable with the sample calibrated value of 180 mg/L, reflecting the accuracy of this method.
Finally, to evaluate the robustness of the method, peak areas for sorbitol were measured for 21 consecutive injections of prune juice. The peak area measurements showed excellent stability, with a relative standard deviation of 0.87%. This impressive consistency reflects the improved performance achieved using automated electrolytic eluent generation.
HPAE-PAD: Upholding the highest standards of food quality and safety
Advances in HPIC technologies are supporting more accurate, sensitive and convenient methods for the analysis of carbohydrates in complex matrices. By applying these technologies for the determination of sorbitol in food, testing laboratories can better protect the quality and safety of the products consumers love to eat.
Read this application note for more information about this ion chromatography method for determining sorbitol in food.
Figure 1. Chromatograms demonstrating efficient separation of sorbitol in a 400 nL injection of A) mashed lychees, B) mixed fruit juice and C) prune juice.