Taste

Animals learn the value of foods on the basis of their postingestive effects and thereby develop aversions to foods that are toxic1-10 and preferences to those that are nutritious11-13. However, it remains unclear how the brain is able to assign credit to flavours experienced during a meal with postingestive feedback signals that can arise after a substantial delay. Here we reveal an unexpected role for the postingestive reactivation of neural flavour representations in this temporal credit-assignment process. To begin, we leverage the fact that mice learn to associate novel14,15, but not familiar, flavours with delayed gastrointestinal malaise signals to investigate how the brain represents flavours that support aversive postingestive learning. Analyses of brain-wide activation patterns reveal that a network of amygdala regions is unique in being preferentially activated by novel flavours across every stage of learning (consumption, delayed malaise and memory retrieval). By combining high-density recordings in the amygdala with optogenetic stimulation of malaise-coding hindbrain neurons, we show that delayed malaise signals selectively reactivate flavour representations in the amygdala from a recent meal. The degree of malaise-driven reactivation of individual neurons predicts the strengthening of flavour responses upon memory retrieval, which in turn leads to stabilization of the population-level representation of the recently consumed flavour. By contrast, flavour representations in the amygdala degrade in the absence of unexpected postingestive consequences. Thus, we demonstrate that postingestive reactivation and plasticity of neural flavour representations may support learning from delayed feedback.

Bitter taste receptors (TAS2R) are expressed in the oral cavity, intestine, airways, and vascular smooth muscle, where they regulate physiological processes, including immune responses. However, the activation of TAS2R triggers signaling pathways that influence inflammation, metabolism, and cell proliferation, suggesting their potential as therapeutic targets for diseases such as Alzheimer's disease, Parkinson's disease, asthma, and cancer. Bitter compounds capable of activating TAS2R have shown potential in modulating these pathways, presenting novel opportunities for drug development. This review examines the expression of TAS2R across diverse tissues, their complex physiological roles, and potential therapeutic applications, including disease management and targeted drug delivery.

Mouthfeel is a complex and multidimensional sensory experience that plays an important role in how people perceive flavor and accept food and beverages. Although it is a key part of the eating and drinking experience, mouthfeel is still not clearly defined and is difficult to measure. This review explores mouthfeel from a flavor perspective by examining the physiological processes, chemical interactions, and main sensory qualities involved, such as viscosity, crunchiness, astringency, and thermal sensations like cooling and warming. During consumption, food and beverages release a variety of chemical components in the mouth. These are broadly classified as volatile and non-volatile compounds. Volatile compounds, which act as odorants and some irritants, stimulate the olfactory system and contribute to aroma perception. In contrast, non-volatile compounds include tastants, irritants, and texture-related molecules that activate the gustatory and trigeminal systems. The integration of these chemical and physical signals from multiple sensory pathways is essential to flavor perception and underpins the experience of mouthfeel. The roles of oral processing, saliva, and the sensory systems, particularly the trigeminal system, are discussed to better understand how mouthfeel is created and perceived. The review also looks at current sensory and instrumental methods used to evaluate mouthfeel, outlining their uses and limitations. Beer, especially non- and low-alcoholic beers, is used as a case study to show how mouthfeel affects product development and consumer acceptance. By combining insights from sensory science, food chemistry, and neuroscience, this review highlights the need for better tools and clearer frameworks to study and improve mouthfeel in modern food and beverage products.

Human bitter taste plays an important role in the quality assessment of food. The presence of the corresponding receptors, the taste receptor 2 family (TAS2Rs), in nongustatory tissues without direct contact to the environment suggested that, apart from food compounds, putative endogenous agonists may also exist. Recent studies on bitter taste receptors of vertebrates, including humans, identified occasional steroid hormones as agonists for these receptors; therefore, steroid hormones represent relevant, potentially endogenous agonists for TAS2Rs. In this study, a comprehensive analysis of 19 steroid hormones, cholesterol, and two plant-derived hormones was performed using functional assays to assess the activation of TAS2Rs. Two TAS2Rs, TAS2R14 and TAS2R46, were found to be differentially activated by the test compounds, with TAS2R46 being in almost all cases the more sensitive receptor. Some steroid hormones activated TAS2R46 with extraordinarily high potencies. Comparison with a human metabolite database revealed that several steroid hormone levels reach activating concentrations for TAS2Rs, suggesting that TAS2Rs indeed could act as sensors for circulating steroid hormones.