The taste-imparting property of glutamate has long been used around the world to enhance the palatability of foods.

The glutamate that naturally occurs in many foods and the glutamate added as monosodium glutamate (MSG) are exactly the same. The body metabolizes all glutamate in the same way, whatever its source. Glutamate is glutamate whether it comes from seasoning (in the form of MSG, ‘salt from seaweed’, mushroom extract, or hydrolysates) or foods such as cheese, tomatoes or mushrooms. Glutamate is important for healthy metabolism, however most of the dietary glutamate we consume is used as fuel by the cells of the digestive system.

In a study designed to determine the levels of free glutamate and 5′-ribonucleotides in belecan (shrimp paste) and in a range of Malaysian dishes, the researchers found that dishes to which the condiment was added were rated more highly in a sensory evaluation. Belecan is one of the most popular traditional condiments used in Malaysian cuisine. It has a salty taste and strong shrimp odour and is likely to influence palatability through aroma and flavour as well as through its free glutamate content. Belecan is known as kapi in Thailand, ngapi in Burma, trasi in Indonesia and andaramang in the Philippines.

Sensory attributes of dishes containing shrimp paste with different concentrations of glutamate and 5′-nucleotides

Jinap.S et al
Appetite (2010), doi:10.1016/j.appet.2010.06.007

The shrimp paste called belacan is a traditional umami taste condiment extensively used in Malaysia that is rich in glutamate and 5′-nucleotides. The aim of this study was to determine the concentration of glutamate and 5′-nucleotides of various types of foods prepared with belacan and to measure their sensory attributes. The concentration of free glutamic acid found in different brands of belacan was 180・30 mg/100 g and in local dishes 601・207 mg/100 g. The total amount of 5′-nucleotides in belacan samples ranged from 0.85 to 42.25 オg/g. A Quantitative Descriptive Analysis (QDA) using a list of 17 sensory attributes showed a good correlation between belacan concentration in the final food and a range of positive sensory attributes, except for bitter, sweet, sour taste and astringency. Belacan also contains bitter, sweet and sour compounds that change the positive attributes of belacan at higher concentrations. The highest aroma attributes were linked to nasi goreng belacan (belacan fried rice) while the highest flavour attributes were found in sambal belacan. There was a 32 folds significant increase of umami attributes with the addition of belacan to final foods. The optimum amount of belacan was 0.45% for asam pedas (tamarind flavoured dish with belacan), 18% for sambal belacan (chilli belacan), 1.5・.5% for kangkong goreng belacan (stir fried water convolous with belacan), and 2% for nasi goreng belacan.

Scientists at the University of Reading have found that the pulp of tomatoes, which contains the seeds, has more umami taste than the flesh.

Differences in glutamic acid and 5′-ribonucleotide contents between flesh and pulp of tomatoes and the relationship with umami taste.

Oruna-Concha MJ, Methven L, Blumenthal H, Young C, Mottram DS.
J Agric Food Chem. 2007 Jul 11;55(14):5776-80. Epub 2007 Jun 14.

A difference in taste characteristics between the outer flesh and the inner pulp of tomatoes has been observed; in particular the pulp, which contains the seeds, had more umami taste. Analysis of the free amino acids and 5′-ribonucleotides in the different parts of 13 varieties of tomatoes showed that in all cases the pulp contained higher levels of glutamic acid, 5′-adenosine monophosphate (AMP), 5′-guanosine monophosphate, 5′-uridine monophosphate, and 5′-cytidine monophosphate. The mean concentration of glutamic acid in the flesh was 1.26 g/kg and that in the pulp 4.56 g/kg but in some varieties the difference between pulp and flesh was more than 6-fold. For AMP, the mean concentration in the flesh was 80 mg/kg and that in the pulp was 295 mg/kg with one variety showing an 11-fold difference between pulp and flesh. These differences in concentration of these compounds, which are known to possess umami characteristics, provide an explanation for the perceived difference in umami taste between the flesh and pulp of tomatoes.

Umami compounds are a determinant of the flavor of potato (Solanum tuberosum L.)

Wayne L. Morris, Heather A. Ross, Laurence J. M. Ducreux, John E. Bradshaw, Glenn J. Bryan and Mark A. Taylor

A team of researchers at the Scottish Crop Research Institute has discovered umami compounds in potatoes, according to research published in the Journal of Agricultural and Food Chemistry. In the research, a taste evaluation panel was set up to carry out flavour assessments and the potato varieties with the most umami compounds (particularly glutamate and 5′-nucleotides) were preferred by the panel. Dr Mark Taylor, who led the research, believes that this discovery will enable the creation of more delicious potato varieties and will help the researchers to monitor whether taste is affected during storage.

Umami compounds are a determinant of the flavor of potato (Solanum tuberosum L.)

Wayne L. Morris, Heather A. Ross, Laurence J. M. Ducreux, John E. Bradshaw, Glenn J. Bryan and Mark A. Taylor
Journal of Agricultural and Food Chemistry 55 (23), 9627・633

Vegetable flavor is an important factor in consumer choice but a trait that is difficult to assess quantitatively. The purpose of this study was to assess the levels of the major umami compounds in boiled potato tubers, in cultivars previously assessed for sensory quality. The free levels of the major umami amino acids, glutamate and aspartate, and the 5′-nucleotides, GMP and AMP, were measured in potato samples during the cooking process. Tubers were sampled at several time points during the growing season. The levels of both glutamate and 5′-nucleotides were significantly higher in mature tubers of two Solanum phureja cultivars compared with two Solanum tuberosum cultivars. The equivalent umami concentration was calculated for five cultivars, and there were strong positive correlations with flavor attributes and acceptability scores from a trained evaluation panel, suggesting that umami is an important component of potato flavor.