ABSTRACT
RATIONALE: Fruit juices are naturally acidic, and the acidity is due to the formation of various organic acids formed in several metabolic processes. The content of acids varies due to various processing parameters during the preparation of fruit juices and their packaging for commercialization. Quantitative determination of organic acids provides the necessary information leading to changes occurred during processing. METHODS: The organic acids were extracted by ion-pair dispersive solid-phase extraction by multiwalled carbon nanotubes and analyzed using gas chromatography-mass spectrometry (GC-MS) and in situ butylation. RESULTS: The developed analytical method was validated, and the obtained results showed a linearity in the range of 0.5-5000 µg/L levels of the analytes with limit of detection and quantification values of 2-10 and 5-20 µg/L, respectively. The inter- and intra-day reproducibilities are less than 15% with 80%-98% recoveries and less than 20% matrix effect. The developed method was used for the quantitative determination of organic acids present in fresh and packaged apple, grape, orange, and pomegranate juice samples. The content of organic acids was observed in the range of 0.26-3793 µg/L. Pimelic acid was not detected in any of the analyzed fruit juices. Fumaric acid (FA) was observed to be a major organic diacid present in the natural fruit juices. The results indicated that the processing of fruit juices for packaging decreases the content of organic acids in fruits. CONCLUSIONS: The developed GC-MS-based analytical method for the analysis of organic acids has good sensitivity and reproducibility for the quantitative determination of various organic acids in fruit juices. FA was observed to be the major carboxylic acid present in fruits. The processed juice samples possess the lowest concentration of organic acids, suggesting that processing has a significant effect on the concentration of organic acids in fruits.
ABSTRACT
The effect of post-harvest ripening by ethylene and calcium carbide was studied by headspace solid-phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS) method. Sapota (sapodilla) fruits were ripened with ethylene gas, technical grade calcium carbide and pure calcium carbide ripeners and the samples were homogenised after complete ripening. The samples were subjected to HS-SPME-GC-MS and the obtained results showed the presence of various alcohols, aldehydes, acids, ketones and esters which were commonly present in the samples. The fruit samples ripened with technical grade calcium carbide showed the presence of 3,5-dimethyl-1,2,4-trithiolane isomers, which can be used as markers to identify sapota fruits ripened with technical grade calcium carbide. The technical grade calcium carbide contains divinyl sulphide which might have been transformed into the trithiolane isomers. These isomers were not observed in the fruits ripened with pure calcium carbide and also with ethylene gas. Hence the formation of trithiolane residues may be attributed to the presence of divinyl sulphide impurity present in calcium carbide and its conversion due to the action of ethylene releasing enzymes present in the fruits.
