Fruit juice volatiles composition

As already mentioned, it is the volatile constituents that serve to identify fruit type and variety. Broadly speaking, qualitative analysis will identify the principal substances present in the volatiles fraction as representative of a particular fruit type, but it is the relative proportions of these substances that will reflect the variety. Alcohols, volatile acids, esters, carbonyl compounds, and low-boiling hydrocarbons are the principal groups represented. Analysis by GC-MS (gas chromatography coupled with mass spectroscopy) can be used to provide quantification and identification of the various constituents. 

Fruit juices, whether of natural strength or concentrated, are materials of commerce, to be sold direct or for use in a variety of food and drink applications. It is essential that they conform to legislative requirements for authenticity and purity, whether for labelling purposes (in avoidance of misleading statements), nutritional standards or in respect of food safety in the final product. 

On a global scale, there is good correlation between quality standards for fin it and fruit juice processed in different regions. In the European Union, legislative controls are set up, or modified, by the central European Council of Ministers, usually following discussion with and between trade organisations from the EU member countries. A new directive, once agreed and approved, is translated into the statutory laws of the member countries concerned. 

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Dienones 12A-12D were also detected as trace components in quince fruit volatiles after SDE sample preparation. However, as shown in Figure 3, except for the low amount of hydrocarbon 5, the distribution of thermal degradation products from 8 did not correspond to the composition of the major norisoprenoids 5-7 obtained after SDE of quince fruit juice. Consequently, diol 8 had to be excluded as their precursor. 

Some foods have special treatment in processing that may affect the composition of volatile components. As an example, in hybrid passion fruit, the presence of about 1-2% starch makes heat processing, i.e., pasteurization and concentration, impossible or impractical, unless the starch is removed before processing. However, the step of removing starch and concentration causes loss of volatile compounds of fruit juice (Kuo et al., 1985). 

Although the peaks in Figures 1 and 2 were not identified, it was apparent that the Ultrapress process caused insignificant changes in the volatile composition of the apple, indicating that fruit juices with aroma profiles nearly identical to that of the fresh fruit can be obtained. 

The aroma of intact black currant fruit is mostly produced by anabolic pathways of the plant, and production of fruit volatiles occurs mainly during a short ripening period [112]. The aroma profile of black currant shares similarities with that of other berry fruits, although terpenes are more abundantly present in black currant [107]. Black currant is mainly used for the production of juice. Over 150 volatile compounds have been reported from either black currant berries and/or juice, of which the major groups are monoterpenes, sesquiterpenes, esters and alcohols [107]. Processing of berries to juice has been shown to lead to major changes in the aroma composition [113-118]. 

Effect of wine ageing on monoterpene composition. Several studies have been made in which alterations in monoterpene distribution in wines over time or with increases in temperature were recorded (84-89). The effect on wine flavor of prolonged ageing or exposure to elevated temperatures is a loss of fruit bouquet. By contrast, brief heating of juices of aromatic grapes can enhance the fruit flavor by increasing the concentration of free volatile monoterpenes through hydrolysis of precursors. 

The composition of volatiles of juices and beverages prepared from the oils extracted from citrus fruit peels is slightly different. For example, juices contain ethyl vinyl ketone, ( )-pent-2-enal and ethyl butanoate as major aromatic substances. 

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