Effects of Temperature and Time on Polyphenolic Content and Antioxidant Activity in the Pressurized Hot Water Extraction of Deodorized Thyme (Thymus vulgaris)

Abstract

The effects of temperature (50-200 °C) and contact time (5-30 min) on the pressurized hot water extraction of deodorized thyme were explored for antioxidant activity, polyphenol profiles, and total antioxidants. Six not previously reported polyphenolic compounds were identified in thyme. An inverse correlation was found between the antioxidant activity and total antioxidants with the amount and diversity of polyphenols. The highest total extract yield and antioxidant activity were obtained at 200 °C, although maximum polyphenol extraction yields of hydroxycinnamic acids, flavones, flavonols/flavanones, and total polyphenols were detected at 100 °C and 5 min. Higher temperatures and longer exposure times reduced extract polyphenol diversity. Dihydroxyphenyllactic acid was the only phenolic compound for which extraction yield increased with temperature, probably as a product of the thermal degradation of rosmarinic acid. Consequently, for extracting phenolics from thyme, 100 °C and 5 min would be appropriate operating conditions, whereas antioxidant-active nonphenolic compounds were favored at higher temperatures and exposure times.

Polyphenols extraction from plant sources

“…According to Fecka and Turek (2008), in hot water and methanol extracts of T. serpyllum and T. vulgaris, the extraction time did not significantly affect polyphenols content. Additionally, the exposure time had no statistically significant influence on polyphenols extraction from wild sage and thyme (Vergara-Salinas et al, 2012;Dent et al, 2013). Moreover, both high temperature and long exposure time can reduce the extraction yield, because of temperature sensitivity and enzymatic degradation and oxidation of polyphenols, as well as polymerization among insoluble constituents (Vergara-Salinas et al, 2012).…”

“…Additionally, the exposure time had no statistically significant influence on polyphenols extraction from wild sage and thyme (Vergara-Salinas et al, 2012;Dent et al, 2013). Moreover, both high temperature and long exposure time can reduce the extraction yield, because of temperature sensitivity and enzymatic degradation and oxidation of polyphenols, as well as polymerization among insoluble constituents (Vergara-Salinas et al, 2012). The main advantages of heat-assisted extraction include (1) the enhancement of polyphenols solubility and mass transfer caused by high temperature, (2) faster kinetics, (3) the efficient extraction and higher polyphenols yield, and (4) simple apparatus and method.…”

“…High temperature decreases viscosity of the extraction medium, which helps the solvent to penetrate the plant matrix, and results in faster kinetics (Miron et al, 2011). According to Vergara-Salinas et al (2012), the increment of solvent temperature decreases surface tension and, consequently, enhances wetting of the plant particles, leading to higher extraction yield. In the extraction at high temperature, the decrease in particle size of Vitis vinifera seeds, skins and stems causes the increase of polyphenols yield (Bucić-Kojić et al, 2007;Pinelo et al, 2005).…”

Combined effects of gamma-irradiation and preparation method on antioxidant activity and phenolic composition of Tuberaria lignosa

“…Porcine (Sus scrofa) brains were obtained from official slaughtered animals, dissected, and homogenised with a Polytron in ice-cold Tris-HCl buffer (20 mM, pH 7.4), to produce a 1 : 2 (w/v) brain tissue homogenate which was centrifuged at 3000g for 10 min. An aliquot (0.1 mL) of the supernatant was incubated with the different solution concentrations (0.2 mL) in the presence of FeSO 4 (10 mM; 0.1 mL) and ascorbic acid (0.1 mM; 0.1 mL) at 37 C for 1 h. The reaction was stopped by the addition of trichloroacetic acid (28% w/v, 0.5 mL), followed by thiobarbituric acid (TBA, 2%, w/v, 0.38 mL), and the mixture was then heated at 80 C for 20 min. Aer centrifugation at 3000g for 10 min to remove the precipitated protein, the colour intensity of the malondialdehyde (MDA)-TBA complex in the supernatant was measured by its absorbance at 532 nm.…”

“…Vergara-Salinas et al 37 reported that for extracting phenolics from thyme with water, 100 C and 5 min are appropriate operating conditions, whereas antioxidantactive non-phenolic compounds were favored at higher temperatures and exposure times. Another recent study, conducted by Martínez-Las Heras et al, 38 concluded that the drying method (including shade-and freeze-drying) and preparation procedures have a great inuence on the stability and extractability of bioactive compounds from persimmon leaves.…”