UMTaste: Understanding the mechanisms by which umami taste influences salty and bitter taste to enable umami to drive salt reduction and improvement i

The UK has been prioritising salt reduction since 2004 in response to the Scientific Advisory Committee on Nutrition (SACN) 2003 report on salt and health. In addition, the National Food Strategy has recommended eating less meat to reduce methane emission. Salt (NaCl) is used in foods for taste, preservation (reducing water activity), and for its impact on structure.

Salty taste remains the predominant driver for salt in many foods. Research has focused on finding sodium replacers (e.g. KCl), or extending salty taste (e.g. controlling salt distribution within a food matrix).

Such strategies are limited. Another approach is to use umami taste (UT), the savoury taste associated with compounds such as monosodium glutamate (MSG). Umami and salty are perceived through the activation of different receptors.

NaCl activates ion channels (eg epithelial sodium channel, ENaC), umami tastants activate type 1 G-protein coupled receptors (eg T1R1-T1R3 heterodimer). Compounds such as 5'-nucleotides act synergistically on glutamate, enhancing T1R1-T1R3 response. UT has been shown to enable salt reduction in numerous foods; although in most studies the outcome measure was palatability rather than matched salty taste(1).

Beyond salt, understanding and controlling the contribution of UT to overall taste may lead to improvements in plant-based protein foods through savoury taste and reduction in characteristic bitter taste. Umami fractions (from soy sauce) rich in amino acids and glutamyl peptides were demonstrated to reduce bitter perception and suppress activity of specific bitter taste receptors (T2R-GPCRs)(2).

However, the mechanism by which UT enables salt reduction and bitter suppression remains inconclusive. Our group has investigated the interaction of UT from glutamate with four other basic tastes in equi-intense solutions(3). We concluded that UT did not enhance or suppress the trained panelists' perception of other tastes.

This demonstrates how umami is perceptually different from all other tastes which suppress each other; here both umami and salty taste were maintained. The panel were trained to isolate different taste sensations, which might explain why they did not conclude salty taste enhancement; yet consumer perception is holistic and aggregated. In addition, MSG has been shown to increase duration of salty taste(4) (temporal dominance), which may partly account for its success in salt reduction.

Umami compounds (aminoacids, 5'-nucleotides and glutamyl-peptides) work synergistically and not additively in generating UT. Their individual and combined effects on salt and bitter perception (immediate and temporal), total taste intensity, and preference for salt-reduced and meat-alternative protein foods needs to be established, particularly determining whether interactions occur at a receptor or cognitive level.

H1: Umami tastants enable salt reduction through both receptor and cognitive mechanisms. H2: The ability of umami tastants to suppress bitter taste is compound specific. Objectives:

O1: Develop appropriate aqueous and semi-solid food models and sensory methods. Design and run first experimental designs to test the individual and combined effects of aminoacids, 5'-nucleotides and available glutamyl-peptide standards on salt and bitter perception in the developed models.

O2: Prepare and characterise taste fractions that include a wider range of glutamyl-peptides from sources such as miso or seaweed. Scale this up using pilot filtration, evaporation, reverse-osmosis and spray-drying at Aberystwyth. O3: Evaluate the taste fractions collected in O2 on salt and bitter perception in the developed models.

O4: Set up in-vitro receptor cell assays O5 Test the individual and combined effects of aminoacids, 5'-nucleotides and glutamyl-peptides on cell signalling.

O6 : In addition to writing papers (O1-O5) write a briefing document on how best to utilise UT for salt reduction and plant-protein food development