Subcritical extraction of phenolic compounds: an alternative to add value to pecan nutshells

RODRÍGUEZ-RUIZ, A.C.; CARDONA JIMENEZ, M. E.; VELEZ, A.R.; AGUDELO-LAVERDE, L. M.; SANTAGAPITA, P. R.; BODOIRA, R.

Los Cocos, Córdoba

Conferencia; VI Iberoamerican Conference on Supercritical Fluids (PROSCIBA 2023); 2023

IPQA/PLAPIQUI

Changes in food trends such as the enhancement of consumer’s awareness regarding the nutritional properties of food products, have caused an increase in the consumption of nuts, particularly pecan nuts. According to data from the Pecan Cluster in Argentina, pecan nut production [Carya illinoinensis (Wangenh) K.Koch], is estimated to be over 2000 tons per year. The shell, which is produced during walnuts shelling, is equivalent to 40-50% of the waste generated by this productive system, and it is only used for energy generation.Many authors have reported the presence of bioactive components in pecan nutshells, including phenolic compounds with antioxidant, antiradical, or chelating capacity. This has generated a growing interest in studying this by-product and determining the best extraction method for recovering these compounds. Among the so-called green techniques, subcritical extraction stands out utilizing water or ethanol + water mixtures at temperatures between 100 and 374 °C, and pressures above atmospheric to maintain the solvent in a liquid state. It is a safe and fast technique that achieves high extraction yields of medium and high polarity compounds from asolid matrix.Considering these aspects, the use of water + ethanol mixtures at subcritical conditions for the extraction of phenolic compounds from pecan nutshells was evaluated in the present work. The pecan nutshell obtained as result of the peeling process was donated by Producor S.A (San Jerónimo, Santa Fe, Argentina). They were washed, disinfected, dried, milled and sifted before extraction. The pecan nutshell powder (PNSP) was subjected to different extraction conditions.The studied variables were temperature (T: 100, 140, 180, and 220°C), ethanol composition in the solvent mixture (S: 0, 25, 50, 75, and 100 %w/w), and solvent mass flow rate (F: 2.5, 5.0, and 7.5 g/min). The total phenolic content (TPC) expressed as mg gallic acid equivalents (GAE)/ g dry PNSP, and antioxidant activity by FRAP and ABTS methods expressed as mmol Trolox equivalents (Tx eq)/ g dry PNSP of each extract were measured.The TPC of the extracts varied between 165.93 and 454.61 mg GAE/g dry PNSP, and the antioxidant activity with a range between 2.41 to 7.63 mmol Tx eq/g dry PNSP, and 1.92 to 5.50 mmol Tx eq/g dry PNSP for FRAP an ABTS, respectively. It was observed that increasing the extraction temperature enhances the recovery of phenolic compounds, while the opposite effect is observed with an increase in the ethanol content in the solvent mixture, which leads to a reduction in TPC values and antioxidant activities. Thus, regarding the bioactive content, the best extraction conditions were T 200°C, F 2.5 g/min, and S 50% w/w of ethanol.The results showed that the selected variables were influential in the extraction of bioactive compounds. The ethanol + water subcritical extraction is an alternative for recovering phenolic compounds and adding value to pecan nutshells.