Antioxidant activity and phytochemical analysis of garlic extracts after cooking with different salts at different conditions

Abstract

The use of natural food additives such as garlic is increasing over synthetic food additives due to fewer side effects if any and is also eco-friendly. Food is usually cooked in the presence of other additives such as salt. Cooking and additive-additive interactions may cause decrease in phytochemicals and antioxidant activity. This may result in consumption of decreased or lack of available antioxidants leading to health complications as a result of deviance in food preparation. The effect of cooking temperature and time on garlic in the presence of salt as a food additive is not documented. The study aimed at investigating the effect of cooking conditions (temperature and time) on phytochemicals and antioxidant activity (AOA) of garlic in the presence of refined salt (Kensalt) and unrefined salt (indigenous reed salt). The specific objectives were to; determine the total phenolic content (TPC) and total flavonoid content (TFC) of garlic, characterize phytochemical constituents of garlic, evaluate the effect of cooking temperature and time on phytochemicals and the AOA of garlic and to establish the effect of concentration of Kensalt and indigenous reed salt on phytochemicals and AOA of garlic. The phytochemicals of raw and cooked garlic were extracted using maceration with ethanol and distilled water. The water used for cooking at different conditions was analyzed separately. The TPC and TFC were determined using Folin-Ciocalteu’s and Aluminium Chloride colorimetric methods respectively. Characterization was done using Fourier Transform Infrared (FTIR) spectroscopy and Liquid Chromatography tandem Mass spectroscopy (LC-MS/MS). The data was analyzed using SPSS software with ANOVA used to test the effect of cooking conditions. The TPC of fresh garlic was 637.91 ± 15.30 mg gallic acid equivalent (GAE)/100 g and 301.29 ± 6.58 mg GAE/100 g for the ethanolic extract and aqueous extract respectively. TFC was 258.21 ± 12.37 mg quercetin equivalent (QE)/100 g and 109.68 ± 6.78 QE/100 g for ethanolic and aqueous extracts respectively. FTIR spectral data showed absorptions in the range 3400-2400 cm-1 for carboxylic acids, 3650-3600 cm-1 for free O-H, bonded O-H at 3400-3200 cm-1, C-O around 1300-1000 cm-1 for esters, carboxylic acids and alcohols. LC-MS/MS analysis revealed the presence of flavonoids; Quercetin, Hesperidin, Rutin and Catechin and Phenolic compounds; Ferulic acid, Gentisic acid, Caffeic acid, Gallic and Chlorogenic acid. Cooking temperature under the tested conditions had a significant effect (p-value ˂ 0.01, alpha = 5%) on TPC and TFC while cooking time did not have a significant effect on phytochemicals and AOA (p-value = 0.511, alpha =5%). Salt had a significant effect on phytochemicals (p-value = 0.03, alpha = 5%) and AOA, however, the effect was higher on indigenous reed salt than iodized Kensalt. In conclusion, cooking at higher temperature in the presence of salt enhances extraction of phytochemicals and increases the AOA of garlic. It is recommended that garlic should be cooked at temperatures above 100⁰C in the presence of indigenous reed salt for optimum phytochemicals and AOA for more health benefits.