Advanced Analysis of Carbohydrates in Foods

Abstract

In this chapter, modern analytical procedures used to study carbohydrates in foods and beverages are discussed. The main advanced analytical methodologies applied to determine the different carbohydrate families (monosaccharides, oligosaccharides, polysaccharides and macromolecules including different glycosilated compounds) are reviewed considering the sample preparation required and the type of technique (separation or spectroscopic) used, including their different couplings, multidimensional-approaches, modern glycomics strategies, etc. The goal of this contribution is, therefore, to provide the reader with a broad and critical view on the different analytical methods nowadays employed to analyze carbohydrates in foods and their foreseeable trends. Introduction.Carbohydrates are the most abundant and diverse class of organic compounds occurring in nature. Chemically they are composed of carbon, hydrogen, and oxygen in the ratio C n :H 2n :O n . Food carbohydrates include a wide range of macromolecules that can be classified according to their chemical structure into three major groups: low molecular weight monoand disaccharides, intermediate molecular weight oligosaccharides and high molecular weight polysaccharides. They can also be classified as simple or complex carbohydrates. Simple carbohydrates are monosaccharides and disaccharides while complex carbohydrates are made up of many monosaccharides such as starches and fiber (polysaccharides).Carbohydrates are a major source of energy in the human diet with intakes ranging from 40 to 80% of total energy requirements (Muir et al. 2009). Carbohydrates constitute the main source of energy for all body functions, particularly brain functions, and are necessary for the metabolism of other nutrients. Other important effects of carbohydrates on human physiology are satiety and gastric emptying, control of blood glucose, insulin metabolism and serum cholesterol, and influencing colonic microflora and gastrointestinal processes such laxation and fermentation (Muir et al. 2009). Cereals, vegetables, fruits, rice, potatoes, legumes, and flour products are the major sources of carbohydrates. Thus, naturally occurring sugars are consumed as part of a healthy diet.Monosaccharides, sucrose, and polysaccharides are present in all vegetables (Hounsome et al. 2008).Carbohydrates are synthesized by all green plants and in the body are either absorbed immediately or stored in the form of glycogen. They can also be manufactured in the body from some amino acids and the glycerol component of fats. Moreover, sugars can be added to foods during processing or preparation, mainly to enhance food sensorial quality (Murphy et al. 2003).

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“…58 Also, carbohydrates have low volatility, possess similar polarities, and lack a chromophore which complicates their analysis by gas chromatography (GC), chromatographic separation based on polarity, and ultraviolet (UV) detection, respectively. 55 Multiple analytical techniques are generally required to obtain complete structural information.…”

“…Polysaccharides have differing susceptibility to hydrolysis allowing for partial degradation and selectivity in the substrate to be hydrolysed. 55 Carbohydrate susceptibility to hydrolysis depends on the position and configuration of the glycosidic linkage (α or β), the identity of the atom involved in the glycosidic linkage (O-, C-, S-, or N-), the identity of the residues at and near the site of hydrolysis, and the reaction conditions including pH, temperature, duration, and the structure and strength of the acid/base. 56 Due to the diversity of natural polysaccharides, the conditions of the hydrolysis reaction need to be carefully controlled and optimised to ensure complete hydrolysis of the polysaccharides while avoiding degradation of the liberated monosaccharides.…”