Human Taste Perception of Starch Hydrolysis Products : Target Substrates, Potential Mechanism, Quality, and Factors of Influence

Graduation date: 2016When it comes to carbohydrate, it has been assumed that only mono- and disaccharides, but not oligo- and polysaccharides, can be tasted. However, because of its importance in the human diet, oral detection of starch or its hydrolysis products would be beneficial. The main goal of this study was to investigate whether humans can detect starch or its hydrolysis products through the gustatory system. In the first study, the taste responsiveness to sugars and maltodextrins were measured. Results showed that maltodextrins could be tasted and that the responsiveness to maltodextrins were highly correlated to one another (r = 0.69 – 0.82, P < 0.001) but not to sugars (r = 0.07 – 0.27, P > 0.05). These results were suggestive of a gustatory detection of glucose oligomer and polymer mixtures independent of that to sugars. Nevertheless, maltodextrins contain a broad mixture of glucose oligomers and polymers of varying chain lengths. Thus, it was unclear what target substrates can facilitate the detection of glucose oligomers and/or polymers. The second study thus further elucidated the specific chain length ranges that can be tasted. Results showed that the taste of glucose oligomers (degree of polymerization, DP, 7 and 14) (P < 0.05) but not glucose polymers (DP 44) (P > 0.05) can be discriminated from water blanks without the confounding effects of other sensory\ud cues (i.e., odor and texture). Further, when hT1R2/hT1R3 sweet taste receptors were blocked by lactisole, a known sweet inhibitor, the sweet substances could not be discriminated from blanks (P > 0.05) while glucose oligomers (DP 7 and 14) still could be (P < 0.05). This suggests that glucose oligomer detection was independent of the sweet taste receptor mechanism. Accordingly, during a focus group, subjects described the taste of glucose oligomers as 'starchy' while they described sweet substances as ‘sweet’. While these data suggest that humans may have an independent taste receptor that is activated by glucose oligomers, they also raise a question regarding the availability of glucose oligomers in the human diet. Glucose oligomers can be produced in the mouth during oral digestion of starch by way of salivary α-amylase hydrolysis. Thus, the third study investigated whether starch or its hydrolysis products can be tasted and if at all, what factors influence its perception. Results showed that cooking was effective in aiding salivary α-amylase hydrolysis and the amounts of glucose oligomers produced increased with increasing reaction time. Further, subjects with high amylase activity had higher total amounts of glucose oligomers produced than those with low activity. Accordingly, salivary α-amylase activity was found to modulate taste responsiveness. Overall, these studies were the first to demonstrate that humans can taste glucose oligomers. The 'starchy' taste may represent the 'sixth' taste category. A novel taste receptor for complex glucose-based saccharides has been previously proposed in animal models but is yet to be identified. If such exists, its main function is presumably to identify and signal the body of incoming starch, a substance that is an important source of energy