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Pecan nut oil is conventionally obtained by mechanical extraction characterized by a low oil extraction yield (OEY) compared to solvent extraction. Pulsed electric fields (PEF) have been employed as a pretreatment to enhance OEY from several oilseeds, but no studies have been found regarding tree nut oil. Hence, PEF was applied at different specific energy inputs (0.5–17.6 kJ kg−1) to evaluate its impact on OEY, oil acidity, and antioxidant capacity (AC), along with total phenolics (TP), condensed tannins (CT), and AC of the by-product generated from oil extraction. Kernels treated by PEF were compared against untreated and soaked kernels due to sample water immersion during PEF processing. The water immersion reduced the initial oil content of soaked and PEF-treated kernels (7.3–11.7%), transferring between 3.8 ± 0.0 and 6.2 ± 0.1 g of oil into the soaking water ( $${o}_{SW}$$ ). OEYTOTAL of soaked and PEF-treated samples was calculated considering $${o}_{SW}$$ . The application of 0.5 kJ kg−1 increased OEYTOTAL by 21.4 and 17.6% compared to untreated and soaked kernels, respectively, while oil acidity and AC of PEF-treated kernels were within values reported for pecan nut oil. The highest concentration of TP and CT in the by-product was achieved at 0.8 kJ kg−1, increasing 9.5 and 30.1%, respectively, compared to untreated kernels. Results evidenced that PEF processing might be a suitable technology to increase OEY from pecan nuts, but the oil extracted during kernels water immersion must be recovered. Furthermore, the by-product of PEF-treated kernels displayed an enhanced content of phenolic compounds increasing its potential as food ingredient.

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).

0000-0002-0427-7547 Pecan nut kernels have been identified as an important source of mono- and polyunsaturated fatty acids, phytosterols, tocopherols, and phenolic compounds. Likewise, the oil commonly extracted by mechanical pressing of pecan nut kernels, is considered a specialty product due to its phytochemical profile. However, the effect of processing and storage on these bioactive compounds and how to improve the mechanical extraction of pecan nut oil have been scarcely investigated. Pulsed electric fields (PEF) are being applied as a pretreatment to improve oil extraction from different seeds increasing the oil extraction yield (OEY) and enhancing the oil phytochemical profile. Therefore, this dissertation aimed to evaluate i) the effect of drying and storage conditions on phytochemical content and antioxidant capacity (AC) of pecan nuts, and ii) the application of PEF as a pecan nuts pretreatment to improve OEY along with its effect on oil stability and bioactive compounds concentration of the oil and by-product generated usually named cake. Fatty acids, tocopherols, phenolic compounds (PC), and AC of fresh and dry kernels were determined to assess the effect of drying on pecan nuts. PC and AC of kernels and in-shells nuts stored during 240 days at 4 and 25°C were analyzed to study the effect of storage conditions. PEF was evaluated on fresh and dry pecan nuts by comparison of PEF-treated kernels against untreated and soaked kernels. Fresh kernels were pretreated at different levels of specific energy inputs (0.5–17.6 kJ·kg-1) to evaluate OEYTOTAL, oil acidity and AC along with cake PC and AC. Dry kernels were pretreated at 0.8, 7.8, and 15.0 kJ·kg-1 to assess OEYTOTAL and kernels microstructure. Oil stability was investigated by determination of acidity, AC, oil stability index (OSI), phytosterols, tocopherols, and lipoxygenase (LOX) activity. Cake PC and AC were also analyzed. The results showed that the drying process reduced the initial concentration of PC and AC (33.2 and 22.3%, respectively), but it helped to preserve pecan nut kernels for 240 days without microbial deterioration. During storage, a decrement of condensed tannins (CT) concentration (31.5–41.8%) and an increment of AC (188.4–216.4%) on both kernels and in-shell nuts were observed. Regarding the evaluation of PEF, water immersion of fresh kernels to PEF pretreatment decreased the initial oil content (7.3–11.7%). Despite that, the highest OEYTOTAL was achieved in kernels pretreated at 0.5 kJ·kg-1, being 21.4 and 17.6% higher than values of untreated and soaked kernels, respectively. A rise of PC content was observed in cakes generated from kernels pretreated at 0.8 kJ·kg-1 in comparison with cakes from untreated and soaked kernels (9.5–17.8 and 30.1–39.3% for PC and CT, respectively). Despite PC improvement, the PEF pretreatment did not increase the AC of cakes. Dry kernels water immersion also caused a reduction of the initial oil content (9.7%). OEY of untreated kernels was 88.7%, being higher than OEYTOTAL of soaked (76.5–83.0) and PEF-treated kernels (79.8–85.0%). The microstructural analysis of kernels pretreated at 0.8 kJ·kg-1 showed that PEF processing induced oleosomes fusion within the intracellular space of kernels cotyledon tissue. Neither soaking nor PEF processing significantly modified oil acidity, AC, OSI, and LOX activity. In contrast, the application of 0.8 kJ·kg-1 to dry kernels increased cake CT and AC by 43.5 and 21.8%, respectively, compared to untreated kernels while in comparison with control kernels was 27.0 and 24.3% higher, respectively. This dissertation proved that PC and AC 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. The microstructural analysis showed that the application of PEF modifies kernels oleosomes. Oil extracted from PEF-treated kernels displayed comparable characteristics to pecan nut oil extracted by mechanical and solvent processes. The by-product generated from PEF-treated kernels exhibited an improved CT concentration, making it an attractive ingredient to consider in food formulations. Doctor en Biotecnología

The selection of species that accumulate oil with potential for biofuel production has favored advancements in the scientific and technological domains within the Brazilian biofuel program. The equipments and methods used for such selection have always prosecuted the objective of increasing oil extraction. The aim of this paper was to evaluate the yield of oil extracted from five vegetable species – castor oil plant (Ricinus communis), physic nut (Jatropha curcas), soybean (Glycine max), groundnut (Arachis hypogaea L.), and crambe (Crambe abyssinica) with two different moisture contents and using two different solvents, hexane and ethanol. The experimental design was factorial (5 × 2 × 2), in which grains of each of the five vegetable species in two different moisture contents were used for oil extraction. It can be concluded from this study that grain moisture content and solvent type had great influence in determining oil yield; and that hexane extraction was most efficient. J. curcas had the greatest increase of oil yield with 30.70% when performing extraction with grain moisture. The smallest differences between the solvents were found in the species R. communis with 12% of higher efficiency with hexane extraction. Key words: Biodiesel, ethanol, hexane, oil extraction yield.