Oxidative Stability Of Cold-pressed Oil Research Articles

Seed-Roasting Process Affects Oxidative Stability of Cold-Pressed Oils.

The oxidative stability of vegetable oils mainly depends on their fatty acid composition, their degree of unsaturation, and the presence of compounds with antioxidant activity. This paper reports on the effects of the process of roasting oil seeds, prior to pressing them, on the basic characteristics of the oils produced and their oxidative stability. The differential scanning calorimetry (DSC) technique was used to study the process of oxidation of the oil samples in an oxygen-flow cell. Chromatographic analysis revealed that roasting the seeds increased the levels of chlorophyll and β-carotene in all the cold-pressed oils. Similar results were observed for the oil’s antioxidant activity, measured by the scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical method. Our results also indicated that roasting seeds prior to pressing them for oil had a positive effect on the oil’s stability, as determined by the DSC method. This manifested in both the extension of oxidation induction time and the final oxidation time.

Changes in chemical composition and oxidative stability of cold-pressed oils obtained from by-product roasted berry seeds

This study aimed to determine the effect of seed roasting on compositional parameters and oxidative stability of cold-pressed blackcurrant, raspberry, chokeberry, and strawberry seed oils, with rapeseed oil as a control sample. Roasting seeds decreased the peroxide concentration by about 50%, while secondary oxidation products increased by 9%–91%. There were no significant differences in the fatty acid composition of the berry seed oils following roasting. 7%–27% and 2%–26% of tocochromanols and phytosterols respectively were lost after roasting. Roasting increased the thermo-oxidative stability of the berry seed oils by almost 40% (except chokeberry seed oil). No significant decrease in the compositional parameters or oxidative stability of roasted rapeseed oil was found, probably due to presence of canolol (327.60 μg/g). Raspberry seed oil has similar oxidative stability to rapeseed oil, probably due to the high concentration of γ-T, δ-T, and ellagic acid possessing high antioxidant activity.

Dielectric Pretreatment of Rapeseed 1: Influence on the Drying Characteristics of the Seeds and Physico-chemical Properties of Cold-Pressed Oil

The aim of this study was to explore the effect of dielectric pretreatments on the drying characteristics of rapeseeds and physico-chemical attributes of cold-pressed rapeseed oil. Rapeseeds were adjusted to moisture contents of 15% and underwent dielectric pretreatments prior to oil extraction by cold pressing at frequencies of 27, 915, and 2450 MHz for 45, 30, and 22 min, respectively. Results showed that 2450 MHz dielectric heating had the highest temperature rising rate but the most nonuniform temperature distribution. Compared to the control samples, oil extraction yields were increased by 12.28, 17.25, and 22.08% for 27, 915, and 2450 MHz dielectric pretreatments, respectively. The SEM analysis indicated that the cell structures of pretreated rapeseed samples were severely damaged, thereby improving the extraction efficiency. Additionally, dielectric pretreatments significantly increased the total tocopherol content and improved the oxidative stability of cold-pressed oil (p 0.05). These results suggested that dielectric pretreatment, a promising and environment-friendly technique, could be useful in the food industry for oil extraction.

Roasting pumpkin seeds and changes in the composition and oxidative stability of cold-pressed oils.

Pumpkin seed oil is valuable oil for its distinctive taste and aroma, as well as supposed health- promoting properties. The aim of this study was to investigate how roasting pumpkin seeds influences the physicochemical properties of cold-pressed oils. The fatty acid composition, content of phytosterols, carotenoids and tocopherols, oxidative stability and colour were determined in oils after cold pressing and storage for 3 months using GC-FID, GCxGC-ToFMS, HPLC, Rancimat and spectrophotometric methods. The results of this study indicate that the seed-roasting and storage process have no effect on the fatty acid composition of pumpkin seed oils, but does affect phytosterols and tocopherols. The carotenoid content decreased after storage. The colour of the roasted oil was darker and changed significantly during storage. Pumpkin oil obtained from roasted seeds shows better physicochemical properties and oxidative stability than oil from unroasted seeds.

Roasting pumpkin seeds and changes in the composition and oxidative stability of cold-pressed oils [pdf

Roasting pumpkin seeds and changes in the composition and oxidative stability of cold-pressed oils [pdf

The Antioxidant Activity and Oxidative Stability of Cold-Pressed Oils.

In our study, we characterized the antioxidant activity and oxidative stability of cold-pressed macadamia, avocado, sesame, safflower, pumpkin, rose hip, Linola, flaxseed, walnut, hempseed, poppy, and milk thistle oils. The radical scavenging activity of the non-fractionated fresh oil, as well as the lipophilic and hydrophilic fractions of the oil was determined using a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The fatty acid composition of the fresh and stored oils was analyzed by gas chromatography. The acid value, peroxide value, p-anisidine value and conjugated diene and triene contents in the fresh oils, as well as in those stored throughout the whole period of their shelf life, were measured by CEN ISO methods. The antioxidant activity of the oils expressed as Trolox equivalent antioxidant capacity (TEAC), ranged from 0.17 to 2.32 mM. The lipophilic fractions of the oils were characterized by much higher antioxidant activity than the hydrophilic ones. There were no significant changes in fatty acid composition and only slight changes in the oxidative stability parameters of the oils during their shelf life. Through the assessment of the relationship between antiradical activity and the oxidative stability of oils, it is proposed that a DPPH assay predicts the formation of oxidation products in cold-pressed oils—however, the correlations differ in fractionated and nonfractionated oils.

Physicochemical Properties of Plukenetia volubilis L. Seeds and Oxidative Stability of Cold-pressed Oil (Green Nut Oil)

Cold-pressed oil from the seeds of Plukenetia volubilis L. (green nut oil, GNO) has been shown to be rich in n-3 fatty acid content, similar to flaxseed and perilla oils. These fatty acids are readily oxidized at high temperatures and under UV irradiation, limiting their potential applications. We therefore set out to clarify the physicochemical properties of green nuts. In addition, to explore means of the degradation process, we investigated the oxidation characteristics of GNO and the effects of oxidation on fatty acids. Results showed that GNO was stable up to 140 degrees C and exhibited greater UV resistance than the other oils. This may be related to the 10% lower alpha-linolenic acid content of GNO, compared to the other oils, as well as the presence of gamma- and delta-tocopherols. GNO was capable of tolerating a certain degree of heat processing.

Minor components and oxidative stability of cold-pressed oil from rapeseed cultivars in China

The contents of the minor components and induction period (IP) of cold-pressed oils from 203 rapeseed varieties from the Yangtze River Valley in China were determined. The average contents of total phenolics, phytosterols, tocopherols, β-carotene, lutein and chlorophyll of the samples were 36mg/100g, 826mg/100g, 378mg/kg, 2.4mg/kg, 104mg/kg and 8.2mg/kg, respectively. There were significant differences (p<0.0001) among the varieties in the content of these minor components. Correlation analysis revealed there was a positive correlation between the IP and content of total polyphenols (r=0.303, p<0.0001), lutein (r=0.250, p<0.0001) and total tocopherols (r=0.225, p=0.001). Additionally, the IP negatively correlated with total phytosterols and chlorophyll content. Principal component analysis differentiated the rapeseed oils based on their IP and total phenolic, tocopherol, β-carotene, lutein and chlorophyll content.

Oxidative stability and minor constituents of virgin olive oil and cold-pressed rapeseed oil

The oxidative stability and minor constituents of three cold-pressed low erucic acid rapeseed oils and three virgin olive oils were compared. The rapeseed oils were more easily oxidized, in part due to their higher contents of polyunsaturated fatty acids. The rapeseed oils were rich in γ-tocopherol and had low initial peroxide values (PVs), but their hydrophilic phenol content was low, only 3–4 ppm. Olive oils contained α-tocopherol and 40–100 times more hydrophilic phenols compared to the rapeseed oils. The initial PVs of fresh olive oils were much higher than those of rapeseed oils. Lutein and β-carotene were present in all oils but chlorophylls (pheophytin a) only in the olive oils. The phenolic extract from the olive oils protected both bulk and emulsified methyl linoleate (MeLo) from oxidation at the 100 ppm level. The extracts obtained from the rapeseed oils had either moderate or no antioxidative effect in MeLo. Testing of the extracts for their 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity yielded similar results. We conclude that phenolic compounds contribute significantly to the oxidative stability of cold-pressed oils.