Comparing and Examining the Tannin Content of Potato Peel with Four Different Solvents

IntroductionTannins are a type of phenolic compound usually found in plants, with high molecular weights typically ranging from 500 to more than 3000 Da and even up to 20000 Da. The chemical structure of tannins is very diverse and varied. Tannin exists in plant cells in two forms: hydrolyzable and condensed. The tannin content in plants can vary from 0.2% to 25% of the dry weight of the plant. This can vary depending on the plant species, harvest time, plant habitat, and extraction method. Currently, tannin is used in various fields such as leather making, medicine, food, beverages, ink and glue making, paint and tanning industries, plastic resins, water treatment, and surface coatings. The application of tannins depends on the tannin concentration. Extraction of tannin from agricultural products is done by different methods. Maceration, decoction, pressurized water extraction, Soxhlet extraction, supercritical fluid extraction, ultrasound, and microwave are among these methods. Ultrasound extraction is an effective method for extracting chemical compounds, which is performed in a shorter period of time compared to other methods, and can be used for heat-sensitive compounds such as tannins.Materials and MethodsPotato peels were randomly selected, dried, and ground. Extraction was performed with an ultrasonic device, and after centrifugation, the total amount of phenolic compounds was measured using the Folin-Ciocalteu method. Afterward, utilizing the method used by Makkar et al. (2001), the amount of total tannins was calculated, and the condensed tannin content was calculated using the method introduced by Porter et al. (1986).Results and DiscussionThe average amount of total tannin extracted by using water as solvent was 142.8 ± 50.9 mg per 100 grams of dry powder in a period of 15 minutes, which was the highest amount of extraction. After water, methanol was the second solvent, yielding an extracted amount of 0.63 ± 55.9 mg per 100 grams of dry powder in 15 minutes. The lowest amount of extraction was related to the ethanol solvent in which was measured over a period of 10 minutes.Due to its higher polarity, water is the best-performing solvent for extraction. Comparing the results of this experiment with previous research, water is suitable for extracting tannins from potato peels. Additionally, water is a non-toxic and environmentally friendly solvent, and making it an ideal choice for extraction. Increasing the extraction time from 10 to 15 minutes, significantly affects the total amount of extracted tannin, more tannin being extracted during the longer the extraction period.The effect of extraction time on the amount of condensed tannin is not significant, and no variable in this study had a significant effect on the amount of extracted condensed tannin. It is expected that the increase in the total amount of tannin with the increase in extraction time is related to the increase in the amount of hydrolyzable tannin extracted from the sample.ConclusionIn this research, the amount of tannin extracted from potato peel was measured. The ultrasound method was used to prepare potato peel, which is a less expensive and faster alternative to other methods. The effect of different solvents were investigated over various extraction times. The results showed that the total amount of extracted tannin increases with the ultrasound extraction time, specifically from 10 to 15 minutes. However, with the increased extraction time, the amount of condensed tannin does not significantly increase. Among the studied solvents, water accounted for the highest amount of extracted tannin. After water, methanol was the second-best solvent, followed by acetone and ethanol. Water is an effective and environmentally friendly solvent for tannin extraction. Potato peels are rich in tannin and contain significantly less condensed tannin than hydrolyzable tannin.