Evaluation of chemical parameters for authenticity of commercial lime juice

Citrus fruits are rich sources of dietary fibre and bioactive compounds, including vitamin C, phenolics and flavonoids, with potential health-promoting properties. Nowadays citrus production is the main activity of the producers of fruit trees in the world (104 million tons, 7.1 _ 106 ha) and the countries with higher production are Brazil, China, India, USA, Mexico and Spain, as well as many other tropical and subtropical regions in the world. The authenticity and safety of food is of great importance to both producers and consumers. Foods must be produced in accordance with legal requirements. Adulterated foods affect the consumer negatively in terms of nutrition, health and economics; they cause an imbalance in the domestic market and furthermore, they cause harm to regional economics. The expensive production and consumption of adulterated foods is widespread. Profit is gained with the adulterate, the consumer is deceived as well. The adulteration of citrus juice is a significant worldwide problem. Fruit juices may have undergone dilution with water (Boland, 1988), addition of sugar (Brause et al., 1987), acidification and aroma intensification (Benk, 1976; Richard, 1978). Addition of foreign substances to the juices or addition of juices from other fruits are the other fraudulent practices (Iranzo, 1977). The AIJN, Association of the Industry of Juices and Nectars of the European Union (EU), has established reference guidelines for several fruit juices, including lime. The referred values in these guidelines are based on pure, authentic fruit juices obtained from the edible part of mature and sound fruits of different varieties and geographical origins obtained by mechanical processes.  The characterisation of Iranian lime juices by measuring their physicochemical quality parameters is of special interest to contrast them with the actual international standards: Codex Alimentarius and AIJN Code of practices. It is also very useful to detect adulteration or dilution of juices and to distinguish these high-quality juices. The aim of this study was to contribute to the knowledge of commercial lime juice and pure lime juice characteristics, the obtained parameters will be compared with the international standards.

Ten samples of lime juice were obtained from different fruit juice factories in 2016. Three samples were prepared in laboratory by pressing fresh fruits. All samples were analyzed in duplicate .A panel of different analytical techniques established by IFU (International Federation of Fruit Juice Producers, Paris, France), codex and ISIRI were used for determination of physicochemical parameters, organic and mineral contents in lime juices.

Parameters that characterize the absolute quality requirements:According to these results, relative density of the all lime juice samples varied between 1.030 and 1.040.in all lime juice samples tested, relative density was higher  than 1.0298, the maximum prescribed value by AIJN (2016). Titratable acidity of juices typically varied between 50 and 90 g/L calculated as anhydrous citric acid. In all lime juice samples tested, titratable acidity was found to be acceptable. Ethanol and volatile acids are not present in sound fruits; they are indicators of spoilage by epiphytic microorganisms such as yeasts, acetic acid bacteria (AAB) and lactic acid bacteria (LAB). The small amounts detected can be taken as an indication of the processing of good quality and absence of fermentation processes in juice. The amounts detected in juices from all samples was lower than the maximum (universal) limit of 0.4 g/L. Heavy metal elements contained in fertilizer and contaminated soils are transmitted into fruits and other farm produces. Heavy metal contents detected in all samples by atomic absorption spectrometry (AAS) were acceptable. 5-Hydroxymetylfurfural (5-HMF) is practically not present in fresh fruit juice, but it is naturally generated during heating or storage processes in the Maillard reaction as well as sugar caramelization and degradation. Therefore, 5-HMF can be used as an indicator for excess heat treatment and deterioration. In all lime juice samples tested, concentration of 5-HMF was much lower than 20 mg/L, the maximum prescribed value by AIJN. Synthetic color and preservative material such as sorbic and benzoic acids were also carry out. Values were not obtained for these parameters. Criteria relevant to the evaluation of identity and authenticity: Analysis of  proteins, formol index, calcium, magnesium, sodium, potassium, phosphorus and sucrose have indicated ash, mineral elements and protein and formol index to be useful parameters for detection of adulteration. Ash and phosphorus content are fairly independent of regional variation and soil and are a fair criterion of added water in berry and fruit juices. The ash that represents the total mineral content of lime juice was between 2.84 and 3.85 g/L. The concentration of various elements in the tested samples were, in decreasing order, potassium (10-1350 mg/L) > sodium (63-907mg/L) > calcium (34–172 mg/L) >phosphorous (0-123 mg/L)>magnesium (10-75 mg/L).Potassium typically is the main mineral in lime. The finding of 1350 mg/L is consistent with this knowledge. Also 9 commercial samples did not reach the limits proposed by AIJN for more than one of these elements. The formol number, or formol titration, is merely an index which reflects the amount of free amino acid. It varied between 18 and 30 mL NaOH 0.1 N/100 mL. A chemical matrix method which allows identification of several compounds such as L-malic acid, chlorogenic acid and the fructose/glucose ratio, sucrose, fructose ,glucose can detect adulteration in apple and orange juices such as dilution with water, and addition of sugar, high fructose corn syrup, beet sugar and spent process water. Glucose, fructose and sucrose were detected and quantified in all juices tested. The presence of sucrose, glucose and fructose in lime juices varied between 0.0 - 4.6 g/L,1.48-12.7 and 0-9.8 respectively. 4 commercial samples did not reach the limits proposed by AIJN for these sugars.