Does the nose know? : Physiological and behavioural responses upon food odours

Abstract

The food that we choose and eat consists mainly of a mix of macronutrients. Macronutrients -carbohydrates, protein, and fats -are fundamental to preserve the structure and functions of the body, providing it with the needed energy (Hofheins, 2007). Each macronutrient has exclusive chemical and physical properties, nutritional value, and function, and are present in specific foods (Hofheins, 2007;Velíšek, 2014).Carbohydrates are based on monosaccharides connected to each other by glycosidic linkages to form di-, oligo-, and polysaccharides. Its conformation depends on the type of linkages and number of monosaccharides bonded together, offering a large variety of chemical and physical properties (Belitz, Grosch, & Schieberle, 2009; Damodaran, Parkin, & Fennema, 2007). They are the energy fuel of the body, essential to the brain. The main sources of carbohydrates are fruits, vegetables, and grains (Hofheins, 2007). Digestion of carbohydrates starts in the oral cavity with the activity of the salivary α-amylase (Bender, 2014). The salivary α-amylase is an endoglycohydrolase secreted by the parotid gland that breaks the α1→4 glycosidic bonds of polysaccharides into maltose, dextrin, and oligosaccharides (Levine, 2010;Mattes, 2000;Robyt & French, 1970). Some studies have shown a higher release of α-amylase from the parotid gland after a sucrose solution compared to other taste solutions (starch > sodium chloride > citric acid) (Froehlich, Pangborn, & Whitaker, 1987) and after mastication of bread (high-in-starch food) compared to other products (non-food products as parafilm and low-in-starch food as celery) (Mackie & Pangborn, 1990). This suggests that salivary α-amylase may specifically facilitate the digestion of carbohydrates. Furthermore, pancreatic amylase is secreted into the small intestine to continue the digestion of the starch. Hydrolysis of the disaccharides occurs in the brush border of the intestinal mucosa by disaccharidases (Bender, 2014). Additionally, an increase of the hormone insulin has been shown upon modified sham feeding of food rich in carbohydrates compared to sweet-tasting solutions such as aspartame, saccharin, and sucrose (Teff, Devine, & Engelman, 1995), or to food rich in other macronutrients (Zhu, Hsu, & Hollis, 2014).The building blocks of proteins are amino acids bonded through amide linkages. Depending on the amino acid sequence and interactions, the structure of the proteins could vary (primary to quaternary) and this determines its functional properties (