Vegetable free amino acid

Pyrazol-1 -ylalanine, an isomer of histidine, was isolated from Citrullus vulgaris (watermelon) seed and its structure was confirmed by comparison with synthetic material 107). It was the major free amino acid in the dormant dry seed but was present in only trace amounts in vegetative tissue. While present in seed extracts of other members of the Cucurbitaceae, it has not been identified as occurring in members of other plant families. 

The use of nitrogen fertilization results in higher content of N-containing compounds, including free amino acids, and also increases in terpene content in wood plants, whilst starch, total carbohydrates, phenylpropanoids and total carbon-based phytochemicals decreased (Koricheva et al., 1998). Higher levels of nitrogen favoured its uptake and increased the nitrate content of the crop, which is critical for salad vegetables and baby foods. 

Anon (1999c) Fruit and vegetable juices. Determination of free amino acids content liquid chromatographic method. BS EN 12742 1999. Available from the British Standards Institute (BSI) or one of the other EU standards bodies. 

In this paper, we discuss 1)some tastes of free amino acids and some peptides, 2)the role of free amino acids in the characteristic tastes of vegetables and marine foods, 3)the role of the bitter peptides in cheese and the traditional Japanese foods "miso" and "natto", and 4.)the contribution of free amino acids and peptides to the improvement of the meat taste during storage of meats (beef, pork and chicken). 

ROLE OF FREE AMINO ACIDS AND PEPTIDES IN FOOD TASTES Vegetable Foods... 

Free amino acids play an Important role in the taste of vegetables. There are large amounts of Glu, Asp, Ser, Val, Ala, Pro and Gin in vegetables as shown in Table 7 ( ). The detailed research on the taste of green tea, onion and potato reveals the presence of umami substances. The most important umami substances of green tea are Glu and L-theanine, which is an ethylamide derivative of Glu (39-41). It has been shown that the most Important umami substance of onion ( ) is Glu. Buri al. ( ) examined the role of free amino acids in the flavor of boiled potatoes. Analytical data has shown that the taste of boiled potato soup stock was similar to that of synthetic potato soup composed of free amino acids and nucleotides. This indicated that free amino acids are very important in potato taste. Although they contain large amounts of Glu and Asp, there are... 

Table 7. Contents of Free Amino Acids in Vegetables...

Some microorganisms associated with fruit and vegetable fermentations may cause the enzymatic formation of BA from free amino acids by the activity of substrate-specific amino acid decarboxylases. BA are small biologically active organic bases and are both physiologically/chemically and pharmacologically of great interest. They interfere in... 

Free amino acids are only found in small amounts in most foods. Therefore, they only influence the flavour of foods when production is based on proteolysis (some cheeses, but also meat and fish). Enzymatic hydrolysates of proteins (such as soy sauces) or hydrolysed vegetable proteins (add hydrolysates), which contain only amino acids, are used extensively as seasonings. 

Flavor enhancers are substances that carry the property of umami (see Chapter 7) and comprise glutamates and nucleotides. Glutamic acid is a component amino acid of proteins but also occurs in many protein-containing foods as free glutamic acid. In spite of their low protein content, many vegetables... 

Thiamine is another key sulphur precursor used for meat-like process flavours. Bid-mead and co-workers [95] used thiamine as precursor in combination with an aliphatic carboxylic acid to obtain roasted meat flavours. The reaction can be carried out in presence or absence of a carbohydrate. For example, refluxing thiamine, cysteine hydrochloride and a carbohydrate-free HVP (hydrolysed vegetable protein) for 4 hours results in a product with beef flavour. Giacino [69] proposes the reaction of thiamine with a cysteine-containing peptide, e.g. glutathione or an amino acid mixture containing cysteine, and adding aldehydes and ketones after the reaction. The reaction is preferably carried out in fat. 

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