Neurocognitive mechanisms of odor-induced taste enhancement: A systematic review

Abstract

Odor-induced taste enhancement (OITE) is a phenomenon derived from the integrative processing of odor and taste in the brain. In summarizing the published research articles on OITE, the current review discusses the effects of odor perceptual routes (orthonasal or retronasal), odor concentration, and odor-taste congruency on OITE. In addition, the review highlights the neural mechanisms of OITE by presenting human neuroimaging research results related to the brain processing of taste intensity, taste quality of odors, and taste-odor interactions. Finally, the paper discusses the implication of OITE on nutritional and clinical applications. The identification of odor molecules with potent taste enhancement effects and the application of OITE in the food industry and clinical populations are necessary for future research.

Introduction

We live in a multisensory world where sensory stimuli from one modality can affect the perception of stimuli from other sensory modalities, which is known as cross-modal sensory interaction. Food flavor perception involves complex cross-modal interactions between taste, odor, and chemesthesis (Verhagen and Engelen, 2006). Among them, odor-induced taste enhancement (OITE) refers to the increase of perceived taste intensity in the presence of certain odors. There is growing evidence that OITE is a stable phenomenon that the perception of all primary taste qualities can be enhanced by the presentation of certain odors. In addition, the rapid growth of research on brain processing of odor, taste, and their integration has suggested a neurocognitive basis for the OITE effect (Small and Prescott, 2005). However, it remains elusive whether OITE mainly originates from a top-down cognitive modulation mediated by high-order brain activation, or whether certain odors innately have “taste” qualities that can activate the primary gustatory cortex in the brain. Moreover, the effect of aroma on taste perception is also dependent on the specific aroma used. The elucidation of key factors that influence OITE is beneficial for screening odorants with taste-enhancing effects and maximizing enhancement levels. This review first examines and summarizes the sensory or psychophysical research findings related to OITE, and analyzes the key factors that influence the OITE effect, namely odor stimuli concentration, odor perceptual routes, and odor/taste congruency. Then, the current review discusses the neurocognitive mechanisms of OITE by synthesizing human neuroimaging studies related to brain processing of odor, taste, or their integrations. In addition, the review discusses the potential nutritional and clinical implications or application of OITE. Finally, the article presents some current issues regarding OITE and future research directions. By identifying gaps in the neurocognitive mechanisms of OITE, this review could hopefully inspire future multidisciplinary research on identifying more odors with potent taste-enhancing effects and clarifying the conditions under which taste perception can be enhanced by these odors.

Section snippets

Method

To identify relevant studies, we conducted our search in three databases: PubMed, Web of Science, and PsycInfo. Our search criteria included the following terms: (odor OR odour OR odorant OR olfactory OR smell OR aroma OR olfaction) AND (taste OR sweet OR sour OR salty OR umami OR bitter OR gustation OR gustatory) AND (enhancement OR enhancing OR enhance OR reduction OR modulation OR interaction). Within the databases, no data filter was applied but the search was limited to human species and

Summary of research on odor-induced taste enhancement

A summary of research on OITE grouped by taste modalities is provided in Table 1. Most studies have focused on the odor-induced enhancement of sweet or salty taste perception, which is possibly due to the predominant roles these two taste qualities play in food flavor formation (Lease et al., 2016). The experiments were mainly conducted with aqueous taste solutions, although some studies used real or model foods with multiple food-related attributes (e.g., texture or composition)

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