Amino free, fruit

Kugler, F. et ah. Determination of free amino compounds in betalainic fruits and vegetables by gas chromatography with flame ionization and mass spectrometric detection, J. Agric. Food Chem., 54, 4311, 2006. 

The alkali-soluble protein of the peel of lemons treated with hydrogen sulfide, sulfur dioxide, and sulfuric acid contained radioactive sulfur, but the fruit treated with hydrogen sulfide had a significantly lower per cent specific activity in the alkali-soluble protein fraction than did the sulfur dioxide or sulfuric acid treated fruits (Table VII). These results suggest that sulfur dioxide and sulfuric acid react with protein more directly, while hydrogen sulfide perhaps must be oxidized first, as indicated in Table III. It also appears (from Table VII) that the alkali-soluble protein may have been dismuted as the amounts isolated were less in both the hydrogen sulfide and sulfur dioxide treated fruit than in the incubated or nonincubated controls. Other evidence of dismutation has been obtained in experiments where incubation at 60° C. was accompanied by the production of free ammonia (18), and the recovery of free ammonia and six amino acids in the exudates of incubated and sulfur-dusted fruits (18). 

Several inferences can be drawn from these data that may suggest the impacts to be expected at the consumer and decomposer levels. Accelerated leaf drop may influence the development of pests—namely, aphids, scale insects, and red citrus mites. Pest populations might be increased if injured leaves had higher concentrations of amino acids or free sugars before abscission (see Chapter 11) or diminished if leaves fell too rapidly. Leaf and fruit drop would provide a larger substrate for populations of decomposer organisms at the soil surface. 

Amine and Aminophenol Derivatives. Amines and aminophenols (Table VIII) react with the F-C reagent about as predicted considering the aromatic amino groups equivalent to phenolic hydroxyls. This would be an important interference with total phenol assay in samples with appreciable aromatic amine content. Fortunately, for this and other reasons as well, the major wine grapes and most other fruit and vegetable products are free of significant concentrations of aromatic amines which would interfere. Correction might be made for methyl anthranilate... 

The overwhelming majority of foods contain amino acids, either in the free form (e.g., fruit juice) or in the form of protein (partially hydrolyzed or intact). Proteins are polymers, and their monomeric units are amino acids. Predominantly, proteins are comprised of 20 amino acids (see Fig. 1). In addition, some structural proteins contain large amounts of hydroxyproline (e.g., collagen). Far less abundant is the amino acid hydroxy lysine. The principal sources of dietary amino acids for humans are proteins, which are enzymatically digested to liberate their constituent amino acids. 

It has long been commonplace to determine the concentration of free amino acids in the beverage industries (e.g., wine, beer, fruit juice). In recent years, it has become more common to analyze for free amino acid content in other food and nutritional products. This is due, in part, to the growing practice of supplementing nutritional products with added free amino acids. Since these free amino acids are often being added in response to specific/special nutritional requirements of a target population, it is very important to ensure the fortification levels in these products. 

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. 

The amount of protein in citrus fruit is relatively low (Table II), and the juice and peel have about the same amount (29). Much of the value that is considered as protein is either free amino acids or non-protein constituents which contain nitrogen. 

The protein in citrus is generally associated with the solid portions of the fruit, i.e., the seeds, flavedo, albedo, chroma-tophores, and pulp. Some of these components find their way into the juice along with the available free amino acids during extraction and processing and storage. Studies conducted in our laboratories (42,43,44) and by others (45) have shown that reductions in the pulp content of juice slow the rate of browning. 

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