Phenolics, Tocopherols, and Volatiles Changes During Virgin Pistachio Oil Processing Under Different Technological Conditions

Abstract

The present work aims to study the influence of different processing conditions, including temperature, roasting, the use of whole nuts, pressure (nozzle size) and speed of the screw‐press extraction process, on the minor components, mainly tocopherols, phenolics, and volatile components, contained in virgin pistachio oils (VPO) and their corresponding partially defatted residual cakes. An important increase in total polar phenolic (TPP) is observed in VPO processed at a temperature above 60 °C (e.g., 16.7–65.3 and 76.4 mg kg−1 at 130 °C and roasting conditions). TPP and the corresponding antioxidant activity also increase when a smaller nozzle diameter (3 mm) is used (16.7–35.4 mg kg−1; DPPH increases 36%), but no differences are observed when changing the screw speed. It is remarkable that the use of the whole pistachio (with its shell) helps to greatly enrich the oil in aromatic volatile compounds by up to 135%, with terpenes being the main family (e.g., 38.6–90.9 mg kg−1). Phenolic compounds and their antioxidant activity are higher in the residual cake when a higher processing temperature is used, for example, from 7260 to 12 250 mg kg−1 (at 40 and 130 °C, respectively). This result indicates their potential use as functional ingredients in food formulations. Practical Applications: The edible oil market is expanding and creating new products, where nut oils are gaining space in the preferences of consumers. In this sense, the study of the effect of different oil extraction conditions on the minor composition may help to produce VPOs with a higher bioactive compound content and/or with desired organoleptic characteristics. Virgin nut oils are minimally processed foods characterized by their typical aroma, taste, and minor bioactive compounds depending on the extraction and processing methods employed. Different technological conditions are studied using a screw‐press expeller to produce added value pistachio virgin oils and their residual cakes.

Chemical Characterization of Virgin Almond and Hazelnut Oils and Their By‐Products

“…An important increase in acids and alcohols is observed at higher extraction temperature (>100 °C) or employing roasted nuts (e.g., ref. []), as indeed observed in the commercial oils studied (Table ,b), as mentioned above.…”

“…Table ,b highlights the broad concentration ranges of the volatiles from the different families present in the commercial almond and hazelnut oils, as exemplified by the acids (1.47–21.81 mg kg –1 almonds and 1.44–18.14 mg kg –1 hazelnuts), aldehydes (3.06–7.11 mg kg –1 almonds and 1.86–14.47 mg kg –1 hazelnuts), and alcohols (0.17–4.16 mg kg –1 almonds and 0.00–2.43 mg kg –1 hazelnuts). The high concentration of acids (18.14 mg kg –1 ), as well as the presence of filbertone (5‐methyl‐( E )‐2‐hepten‐4‐one), pyrazines, and furans (data not shown), is probably related to the extraction conditions employed in the commercial oils (mainly high temperatures) and the use of roasted nuts, which contributes to the typical nutty–roasty aroma …”

Effect of screw-press extraction process parameters on the recovery and quality of pistachio oil

“…In the present work the obtained oil had a total tocopherol content of 1000 mg/kg oil (Table 4), similar to the value obtained by Ojeda-Amador et al, (2018b) from roasted Larnaka pistachio oil (830 mg/Kg), but much higher than Ling et al, (2016) who reported a maximum of 367 mg/Kg oil. In acconcordance with these works g -tocopherol was the most abundant isomer found and in agreement with Ojeda-Amador et al, (2018b), the increase in temperature during the extraction process did not significantly favor tocopherol solubility in oil. With respect to the total phenol contents (TPC) ( Table 4), both extracted oils presented a lower TPC (10.3-11.28 mg GA/Kg oil) than those reported by Rabadán et al, (2017) (24.31 mg GA/kg oil), Ling et al, (2016) (38.7-49.5 mg GA/kg oil) and by Ojeda-Amador et al, (2018b) (approximately 16-76 mg GA/kg).These differences among studies can be attributed to the fact that the TPC of nuts are affected not only by the genotype, but also the orchard location, harvest year, maturity index, processing, and storage conditions (Bolling et al, 2011).…”

“…In this context, the screw-press extraction technique is as an alternative process to solvent removal, especially for specialty oils because it provides an easy and reliable method of processing seeds and nuts with high oil contents (Wiesenborn et al, 2001;Singh et al, 2002;Zengh et al, 2003;Martínez et al, 2008;2017a;2107b). There are previous studies in which pistachio oil extraction by pressing was analyzed (Alvarez-Ortí et al, 2012;Sena Moreno et al, 2015;Ling et al, 2016;Rabadán et al, 2017;Ojeda-Amador et al, 2018b). Particularly, Rabadán et al, (2017) and Alvarez-Ortí et al, (2012) compared hydraulic and screw-press, and concluded that a higher oil recovery (70 and 40%, respectively) was obtained by screw pressing regardless of the processing conditions.…”

“…The oils did not present differences in chemical quality parameters in wither of the evaluated methods. Ojeda-Amador et al, (2018b) mainly studied the influence of several processing conditions, including roasting, temperature, restriction die and screw-press speed, on the minor components contained in virgin pistachio oils. Sena-Moreno et al, (2015) evaluated the effect of the drying temperature of pistachio nuts on the sensory and physicochemical characteristics of the oils, as well as the chemical composition.…”