Effect of Pulsed Electric Fields (PEF) on Extraction Yield and Stability of Oil Obtained from Dry Pecan Nuts (Carya illinoinensis (Wangenh. K. Koch))

Pulsed electric fields (PEF) have been reported to increase the total oil extraction yield (OEYTOTAL) of fresh pecan nuts maintaining oil characteristics and increasing phenolic compounds in the remaining by-product. However, there is no information regarding the PEF effect on dry pecan nuts. Dry kernels were pretreated at three specific energy inputs (0.8, 7.8 and 15.0 kJ/kg) and compared against untreated kernels and kernels soaked at 3, 20 and 35 min. OEYTOTAL, kernels microstructure, oil stability (acidity, antioxidant capacity (AC), oil stability index, phytosterols and lipoxygenase activity), along with by-products phenolic compounds (total phenolics (TP), condensed tannins (CT)) and AC were evaluated. Untreated kernels yielded 88.7 ± 3.0%, whereas OEYTOTAL of soaked and PEF-treated kernels were 76.5–83.0 and 79.8–85.0%, respectively. Kernels microstructural analysis evidenced that the 0.8 kJ/kg pretreatment induced oleosomes fusion, while no differences were observed in the stability of extracted oils. PEF applied at 0.8 kJ/kg also increased by-products CT by 27.0–43.5% and AC by 21.8–24.3% compared to soaked and untreated kernels. These results showed that PEF does not improve OEYTOTAL when it is applied to dry pecan nuts, demonstrating that kernelsʹ moisture, oil content and microstructure play an important role in the effectiveness of PEF.This research was funded by Tecnológico de Monterrey and Consejo Nacional de Ciencia y Tecnología (CONACyT) scholarship programs (CVU 418204)

Evaluation of compositional changes in pecan nuts during storage and the use of pulsed electric fields as an aid to enhance oil extraction yield

Les nous pacanes són una font important d’àcids grassos mono- i poliinsaturats, fitosterols, tocoferols i compostos fenòlics. La tecnologia de polsos elèctrics (PE) s’està aplicant com a pretractament per millorar l’extracció d’oli de diferents llavors augmentant el rendiment d’extracció d’oli (REO). Aquesta tesi va demostrar que compostos fenòlics i capacitat antioxidant de les nous pacanes tenen molta relació amb l'assecat i temps d'emmagatzematge, evidenciant el seu impacte en les seves propietats funcionals. Pel que fa al tractament amb PE, la immersió de les nous en aigua per a l'aplicació de PE va disminuir el contingut inicial d'oli tant en les nous fresques com seques, demostrant que cal tenir en compte l'oli extret en l'aigua de remull. A més, l'efectivitat de la tecnologia de PE va ser depenent de la nou pacana utilitzada incrementant el REATOTAL a nou fresca però no en nou seca.La almendra de nuez pecanera es una fuente importante de ácidos grasos mono- y poliinsaturados, fitoesteroles, tocoferoles y compuestos fenólicos. Una alternativa para mejorar el rendimiento de extracción de aceite total (REATOTAL) del aceite de nuez es la tecnología de campos eléctricos pulsados (CEP). En esta tesis doctoral se evidenció que tanto el contenido de compuestos fenólicos como la capacidad antioxidante de la nuez pecanera son alterados por el proceso de secado y el tiempo de almacenamiento lo que podría repercutir en las propiedades funcionales de este alimento. Respecto a la aplicación de CEP, es necesario considerar la recuperación del aceite extraído en el agua de remojo. Además, la efectividad de la tecnología de CEP fue dependiente de la nuez pecanera utilizada incrementando el REATOTAL en nuez fresca pero no en nuez seca.Pecan nut kernels have been identified as an important source of mono- and polyunsaturated fatty acids, phytosterols, tocopherols, and phenolic compounds. Pulsed electric fields (PEF) are being applied as a pretreatment to improve oil extraction from different seeds increasing the oil extraction yield (OEY). This dissertation proved that phenolic compounds and antioxidant capacity of kernels are highly susceptible to drying and storage time, evidencing their impact on the functional properties of pecan nuts. Concerning pretreatment with PEF, it was demonstrated that it is necessary to take into consideration the recovery of the oil retained into the soaking water. Furthermore, the effectiveness of PEF to improve OEYTOTAL depended on whether the pretreatment was applied to fresh or dry pecan nuts, improving OEYTOTAL of fresh kernels but with no effect on OEYTOTAL of dry kernels