Tannins Concentrations in Three Citrus Fruits in Nigeria Using GC-MS

Tannins are polyphenolic compounds which are found in fruits and medicinal plants and are of importance. Although, tannins are nutritionally and medicinally important, little information is available on their presence in fruits commonly consumed in Rivers State, Nigeria. The current study was carried out to find the tannin content of Citrus sinensis (sweet orange), Vitis vinifera (grape) and Citrus limon (lemon) from the Choba market in Rivers State Nigeria. The fresh fruit samples were washed, blended and extracted by ethanol maceration method. The qualitative phytochemical screening was conducted using Ferric chloride and Lead acetate tests while quantitative determination was done using High-Performance Liquid Chromatography (HPLC). Gas Chromatography–Mass Spectrometry (GC–MS) was also used to identify the phytochemical content of Citrus sinensis and Citrus limon. The data collected were analyzed using Pearson correlation coefficient using Statistical Package for the Social Sciences (SPSS) software. All the three fruit samples gave positive result to qualitative phytochemical screening for the presence of tannins by observing the formation of cream or white precipitates in the lead acetate test and dark brown colour in the ferric chloride test. Citrus limon had the highest tannin content (13.59 ± 0.081 mg/L) followed by Citrus sinensis (12.28 ± 0.176 mg/L) and Vitis vinifera (4.20 ± 0.02 mg/L) respectively. Forty-five compounds were identified in Citrus limon and thirty-five compounds were identified in Citrus sinensis by using Gas Chromatography–Mass Spectrometry. In Citrus limon, 5-hydroxymethylfurfural (14.48%) was the predominant compound, while pentadecane, 2,6,10,14-tetramethyl (6.54%) was the main compound found in Citrus sinensis. Pearson's correlation analysis showed that there was a high negative but non-significant correlation between tannin content of Citrus sinensis and Vitis vinifera (–0.997, p = 0.052), a very low positive non-significant correlation between Citrus sinensis and Citrus limon (0.041, p = 0.974), and a low negative non-significant correlation between Vitis vinifera and Citrus limon (–0.123, p = 0.922). In conclusion, it is found that all these three fruits are source of natural tannins but the concentration of tannins is different in all the fruit. The study suggests the need for more extensive research on the distribution of tannins in various parts of the body, in different seasons, with larger sample sizes, and the use of more sophisticated chromatographic methods to gain further insight into tannin distribution and the implications for human nutrition and food functionalization.