Comparative analysis of maple syrups and natural sweeteners: Carbohydrates composition and classification (differentiation) by HPAEC-PAD and FTIR spectroscopy-chemometrics

Highlights

• Carbohydrate fingerprinting of maple syrup differs from natural sweeteners.

• HPAEC-PAD investigations revealed new oligosaccharides in maple syrup.

• FTIR and 2nd-derivative spectra of maple syrup were compared to natural sweeteners.

• Maple syrup displays strong absorption at 997 cm⁻¹ in agreement with sucrose abundance.

• FTIR-PCA allowed discrimination of maple syrup from other natural sweeteners.

Abstract

Maple syrup is a natural sweetener obtained from the sap of maple trees (Acer saccharum), highly rich in bioactive molecules placing it among the most desirable and natural sweeteners for human consumption (agave, sugarcane, corn and honey). Carbohydrate profiles (amounts and composition) as well as FTIR-PCA classification of maple syrup were performed and compared to other natural sweeteners. TLC and HPAEC-PAD revealed that maple syrup exhibits unique carbohydrate profiles dominated by high sucrose content (511–688 mg/g) followed by glucose and fructose traces. Alternately and highly relevant, it was possible to identify three oligosaccharides, not previously reported in maple syrup, with potential to be used as authenticity markers. The FTIR spectra displayed the most characteristic differences in the carbohydrate region (1185–950 cm⁻¹), particularly, maple syrup exhibited strong absorption bands at 997 and 1054 cm⁻¹ wavelengths in agreement with their high sucrose content. Principal component analysis of the FTIR carbohydrates region allowed maple syrup to be distinguished from other natural sweeteners based on botanical source. The above information would be helpful for the authentication, characterization, and subsequent detection of intentional adulteration of this natural sweetener.

Introduction

Maple syrup is the natural sweetener obtained from the sap of several species of Acer trees but is predominantly derived from sugar maple (Acer saccharum), boiled to evaporate water and concentrated to a 67° brix sugar content (Perkins and Van den Berg, 2009). When compared to other natural sweeteners, maple syrup is considered by many to be a superior option due to its unique flavor compounds, high mineral nutrient content, high antioxidant capacity, antiradical, antimutagenic and antiproliferative (anticancer effects) activities with many potential putative health benefits (Thériault et al., 2006, González-Sarrías et al., 2012, Perkins and Van den Berg, 2009, Phillips et al., 2009, Singh et al., 2014).

The chemical composition of maple syrup is dominated by carbohydrates, mainly sucrose (>80%) followed by variable detectable traces of glucose and fructose; minerals (potassium, magnesium and calcium), vitamins (riboflavin) and organic acids such as fumaric and malic (Stuckel and Low, 1995, Stuckel and Low, 1996, Perkins and Van den Berg, 2009). Additionally, maple syrup exhibits a wide diversity of phytochemicals, among which phenolic compounds predominate with strong antioxidant activities, responsible for the known potential health benefits of this natural sweetener (Li and Seeram, 2010, Li and Seeram, 2011a, Li and Seeram, 2011b). Also, many phenolic derivatives are associated with the color and aroma of the syrup; therefore, the darkness of syrups is often associated with stronger flavor and functionality (Stuckel and Low, 1996, Perkins and Van den Berg, 2009).

In maple syrup, a carbohydrate profile is mainly based on the qualitative and quantitative content of glucose, fructose and sucrose (Stuckel and Low, 1995); however, nowadays oligosaccharides are useful molecular markers of authenticity, adulterant detection, and quality of natural sweeteners. The most common technique used to generate high resolution, sensitivity and reproducibility of oligosaccharides profiles is an anion exchange chromatography coupled to pulsed amperometric detection (HPAEC-PAD). This type of chromatography has been used for the identification of adulterants in food products like honeybee and fruit juices; as well as for the characterization of the carbohydrate profile of agave syrups and natural sweeteners (Martens and Frankenberger, 1990, Morales et al., 2008, Megherbi et al., 2009, Willems and Low, 2014, Mellado-Mojica and López, 2015).

The infrared region (IR) measures the vibrations of molecules, the functional group vibrations have very specific vibration frequencies that have been key in molecular identification (Rodriguez-Saona and Allendor, 2011). Fourier transform infrared (FTIR) spectroscopy has been widely used in the food and drug industries because it is simple (little sample preparation), rapid, low-cost and non-destructive. The use of attenuated total reflectance (ATR) with FTIR improves the potency for spectral collection from solids, liquids, semi-solids and thin films (Rodriguez-Saona and Allendor, 2011, Cozzolino, 2012).

Chemometrics is the science of extracting molecular relevant information from complex multidimensional data, generated during chemical experiments, by using multivariate analysis techniques. Multivariate data analyses have the ability to determine more than one component at a single or specific time point in a sample, to group, recognize or classify a sample(s) in order to establish geographic origin, or process modification, adulteration, etc. (Rodriguez-Saona and Allendor, 2011, Cozzolino et al., 2011a, Cozzolino et al., 2011b, Cozzolino, 2012, Santos et al., 2013). Principal component analysis (PCA) is one of many chemometric methods employed to extract the classifier features (defined as principal components; PCs) from spectroscopic data to visualize the data and exhibit the clustering pattern of different groups of samples (Javidnia et al., 2013). PCs are uncorrelated with each other, hierarchical and sequentially calculated and express the main information contained within a group of samples (Mellado-Mojica and López, 2015).

The powerful combination of FTIR and chemometrics has been successfully applied in many research areas, for example, the differentiation of fruit varieties and their geographic origin (Rodriguez-Saona and Allendor, 2011, Cozzolino et al., 2011a, Cozzolino et al., 2011b), the classification and discrimination of organic and non-organic wines (Cozzolino et al., 2009), the determination of extra virgin olive oils origin (Hennesey et al., 2009) and honey quality and authenticity based on botanical and geographical origin (Ruoff et al., 2006, Cozzolino et al., 2011a, Cozzolino et al., 2011b). Recently, a study on agave syrups discrimination from natural sweeteners and classification according to their natural source was reported by our group (Mellado-Mojica and López, 2015).

The maple syrup unique flavor and the richness of bioactive molecules such as carbohydrates, amino acids, vitamins, minerals, and phenolic compounds with many potential health benefits makes this sweetener highly desirable for human consumption. Hence, new knowledge generation or confirmation on maple syrup properties such as identification of oligosaccharides as chemical markers would be helpful for the authentication, characterization, and subsequent detection of intentional adulteration of this natural sweetener, which are the goals of the current work. Simultaneously, the potential of FTIR spectroscopy in the discrimination between maple syrup and other common natural sweeteners is evaluated herein.