Abstract
Cold-pressed pumpkin seed oil is a valuable source of bioactive molecules, including phenolic compounds. Oleogels are designed for trans and saturated fats substitution in foods, but also demonstrate protection and delivery of bioactive compounds. Consequently, the present work aimed to assess individual phenolic compounds dynamics and infrared fingerprints during the ambient storage of pumpkin seed oil and thereof oleogel. For oleogels production, a 5% ternary mixture of waxes, composed by 3% beewax, 1% sunflower wax and 1% rice bran wax, was used. Phenolic compounds were extracted by traditional liquid–liquid extraction, followed by HPLC-MS quantification. FTIR (400–4000 cm−1) was used for characterizing and monitoring the oxidative stability of all samples and for the evaluation of intermolecular forces between oleogelator mixtures and oil. Specific wavenumbers indicated oxidative processes in stored sample sets; storage time and sample clustering patterns were revealed by chemometrics. Isolariciresinol, vanillin, caffeic and syringic acids were quantified. The main changes were determined for isolariciresinol, which decreased in liquid pumpkin seed oil samples from 0.77 (T1) to 0.13 mg/100 g (T4), while for oleogel samples it decreased from 0.64 (T1) to 0.12 mg/100 g (T4). However, during the storage at room temperature, it was concluded that oleogelation technique might show potential protection of specific phenolic compounds such as syringic acid and vanillin after 8 months of storage. For isolariciresinol, higher amounts are registered in the oleogel (0.411 mg/100 g oil) than in the oil (0.37 mg/100 g oil) after 5 months of ambient temperature storage (T3). Oxidation processes occurred after 5 months storage for both oil and oleogel samples.
Highlights
Cold-pressed pumpkin seed oil is a dichromatic, viscous oil, abundant in valuable compounds such as unsaturated fatty acids, tocopherols, sterols, β-carotene, and lutein, the content of the bioactive compounds differing among the species and varieties, or due to climate and cultivation conditions [1,2]
The High-performance liquid chromatography (HPLC)-MS analysis allowed the identification and quantification of individual polyphenolic components and revealed the presence of isolariciresinol, vanillin, caffeic and syringic acids, based on the parameters described in Table 1, both in the oil and oleogel samples
The extraction method proved efficiency, since in another study, where the phenolic compounds extracted with the solid phase method (SPE) from a sample consisting of cold-pressed pumpkin seed oil produced for commercial purpose could not be individually identified [5]
Summary
Cold-pressed pumpkin seed oil is a dichromatic, viscous oil, abundant in valuable compounds such as unsaturated fatty acids (mostly linoleic and oleic), tocopherols, sterols, β-carotene, and lutein, the content of the bioactive compounds differing among the species and varieties, or due to climate and cultivation conditions [1,2]. The versatility of oleogel process design permits the inclusion of certain fatty acids in foods, and different liposoluble molecules and bioactive compounds, originating from the oil, from the structuring agents or added purposefully, to increase the nutritional value of the products [17,18,19]. Polyphenols are able to form stable crystals which stabilize emulsion template oleogels and transform the oleogel into a functional matrix due to their biological activity [8,31] Polyunsaturated vegetable oils, such as pumpkin seed oil, which are already abundant in polyphenols or other biologically active compounds, are more desirable for oleogel formulation and inclusion in food products such as meats, diary, pastry, and confectionary, to improve their nutritional profile. The present work aimed to assess individual phenolic compounds dynamics in fresh state (T1) and during the ambient storage of pumpkin seed oil and thereof oleogel, after one month (T2), five months (T3) and eight months (T4), and the infrared fingerprints and chemometrics, in order to study oxidation and the implication of the oloegel in retarding the phenomenon or the polyphenols’ antioxidant effect
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