STUDIES ON UMAMI TASTE.PREPARATION OF HYDROLYZED VEGETABLE PROTEINS(HVPS) AND GLUTAMATE-RIBONUCLEOTIDE HYBRIDS

Studies on Umami Taste. Preparation of Hydrolyzed Vegetable Proteins (HVPs) and Glutamate-Ribonucleotide Hybrids - ABSTRACT. Until the 1980’s, it was assumed that there were only four basic tastes: salty, sweat, sour, and bitter. It is now well recognized that a taste quality exists which is distinct from any combination of the four basic ones. This palatable fifth taste was first discovered in 1908 by K. Ikeda. He identified it as “umami”, a Japanese word that means delicious. Related terms can be savory, meaty, broth-like, mouthfilling, etc. Umami is an essential element in our appreciation of food and is imparted by monosodium L-glutamate (MSG) and 5’-ribonucleotides such as disodium inosine 5’-monophosphate (IMP) and disodium guanosine 5’-monophosphate (GMP). These compounds are now used extensively as seasonings or condiments to supplement, enhance or round-off the flavor of many savory-based processed foods. They are the best flavor enhancers that are in commercial use worldwide. The term flavor enhancer (or potentiator) is reserved for substances which have very little taste of their own but have the ability to significantly influence the taste perception of others, e.g. the components of certain types of food so that these foods become organoleptically attractive to the human palate. What is perhaps the most interesting property about MSG and 5’-ribonucleotides is their capacity to interact synergistically, i.e. the detection threshold of MSG was markedly lowered in the presence of IMP (or GMP) and vice versa. It is noteworthy that the synergistic interactions of MSG with IMP and/or GMP also occur in certain savory foods bringing about a flavor effect which is greater than the sum of the individual flavor-enhancing effects. This phenomenon of synergism is of the utmost importance, because it provides an opportunity for the food processor to use less MSG in the formulation without affecting flavor quality. For instance, it has been found that food processors who use 100 g of MSG can reduce usage levels to 17 g in the presence of 0.9 g of 50:50 blends of IMP and GMP with a substantial (25-30%) cost reduction and without an adverse effect on the organoleptic properties of the processed food. Furthermore, considering that excessive sodium intake (resulting from the traditional usage of table salt as a seasoning and a preservative agent) is believed to contribute to hypertension and the development of cardiovascular disease, it has been suggested that the low pleasantness of reduced-salt foods could be increased by addition of appropriate blends of umami flavor enhancers. Recently, the negative aura around MSG, which is accused of causing the so called Chinese restaurant syndrome, has strongly stimulated research for new umami compounds. Among them some peptides isolated from Hydrolyzed Vegetable Proteins (HVPs) have a preeminent role. HVPs are produced by chemical and/or enzymatic hydrolysis of vegetable materials rich in proteins. During this thesis we found that the mixture of peptides obtained from rice middlings and hemp seeds through enzymatic hydrolysis elicit intense glutamate-like umami taste. Such hydrolyzed vegetable proteins could then potentially be used as ingredients in culinary products. In addition, despite extensive investigations on taste receptors, the mechanisms of perception, flavor enhancement, and synergism connected with umami substances are still unclear at molecular level. To get further insight into the phenomenon of synergism, we synthesized hybrid compounds in which the umami moieties (glutamate and purine 5’-ribonucleotide) are covalently connected through flexible linkers of variable length with the aim to reach both umami receptor sites through a single molecule.