The heating performance of enzyme-assisted aqueous processing-extracted blended oil (EAEPO), hexane-extracted blended oil (HEBO), and three kinds of blended oils was investigated by varying the heating times. Oil degradation was monitored by analysis of the acid value (AV), peroxide value (PV),
In recent times, the use of oils with a balanced fatty acid ratio has emerged as one of the most important concerns for maintaining a healthy diet. The blending of several oils with different characteristics is one of the simplest procedures for controlling the characteristics of edible oil [
The quality characteristics of many oils, including Deglet Nour, Allig, olive, sunflower, and hydrogenated soybean oil, have been investigated [
In this paper, the oxidative stability of oils extracted using various techniques, including solvent and aqueous enzymatic methods, is determined. The major reaction conditions and corresponding physical and chemical alterations during heating are also studied by comparative analysis of three blended oils with fatty acid compositions similar to that of EAEPO and HEBO.
Dehulled and full-fat soybean flakes were obtained from a company in Shijiazhuang, and rape seed, purple perilla, fructus cannabis, and scabish were obtained from Anhui, Jiangsu, Guangxi, and Muyang, respectively. Three different types of oils, namely, Golden Arowana blend oil (GABO), Fook Lam Moon Grain blend oil (FGBO), and Fook Lam Moon balanced blend oil (FBBO), were obtained from a local market (RT-Mart, Harbin). Alcalase 2.4 L was sourced from Novo-Nordisk A/S (Bagsvaerd, Denmark). The fatty acid methyl ester (FAME) standards were obtained from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA).
Water was sprayed onto the cracked soybean flakes to achieve the desired moisture content of 14.5% while tumbling the seeds in a mixer (TMV-100, China). The moisture content of 14.5% was chosen on the basis of previous work on oil extraction using EAEP [
Prior to the extraction procedure, the dehulled forms of rape seed (31.5%), purple perilla (11.8%), fructus cannabis (33.3%), and scabish (21.2%) were individually cracked and then mixed together with the extruded soybean (2.3%). The beaker filled with the seed mixtures and additional water (1 : 6 w/w) was subjected to ultrasonic treatment for 50 min at 55°C at a power of 500 W and then incubated at 55°C in a water bath; the pH of the slurry was adjusted to 9 by the addition of 2 N NaOH [
The blending flakes (100 g) (extruded soybean 2.3%, dehulled rape seed 31.5%, dehulled purple perilla 11.8%, dehulled fructus cannabis 33.3%, and dehulled scabish 21.2%) were placed in a Soxhlet extractor equipped with a 0.5 L round-bottom flask and a water condenser. The extraction was carried out on a water bath for 6 h using 3 L of
To simulate conventional times used in cooking, the heating period was varied as 1, 2, 4, 6, and 8 h. For each oil type and time, three subsamples of 80 mL were, respectively, placed in a domestic electronic heater plate with an intelligent magnetic stirrer (ZNCL, China) and the samples were heated at 200°C. Unheated samples of each oil type were used as controls (corresponding to 0 h). After heating, samples were stored in a brown bottle in a refrigerator (4°C) prior to analysis.
The trans-fatty acid composition of the oil types was analyzed using a gas chromatograph connected to a mass spectrometer (GC-MS). The fatty acid methyl esters were prepared in two steps: the oils were first saponified with 0.5 M KOH and subsequently methylated with 40% BF3 in methanol. The separation was performed using an HP-88 capillary column (100 mm × 0.25 mm i.d., 0.2
The acid value was determined according to a literature method (AOAC, Cd-63), where 125 mL of the neutralized solvent mixture and 2 mL phenolphthalein indicator solution were placed into an Erlenmeyer flask and neutralized with alkali to a faint but permanent pink color. The oil sample was then weighed (
The
An accurately measured amount of oil (100 mg) was dissolved in 25 mL, and the absorbance was measured at 350 nm using a UV-vis spectrophotometer (1600PC, China). This solution (2.5 mL) was combined with 0.5 mL of 0.5% (w/v)
The color was determined using a Lovibond Tintometer (WSL-2, China) in the transmittance mode and expressed as red (R) and yellow (Y) values.
An accurately measured amount of oil (300 mg) was dissolved in 9.9 mL of chloroform/methanol (7 : 3, v/v) after which 50.0
Data from replicate analyses of all samples were subjected to a variance analysis (ANOVA) test using SPSS 18.0 for Windows. The significant difference between the means was determined by Duncan’s New Multiple Range Test (
The acid value is considered in the food industry as an indicator of the quality of the oil and the degree of its degradation during heating. An increase in the acid value leads to the development of unpleasant tastes and odors in oils. Although the initial acid values of the oils varied from 0.08 (EAEPO) to 0.16 (HEBO) as shown in Figure
Changes in acid value.
The results also indicated a significant increase in the acid value of the various oil types as heating progressed, which may be attributed to the hydrolysis of TAG and/or cleavage and oxidation of fatty acid double bonds [
Figure
Changes in peroxide value.
The peroxide levels of all of the oil types remained similar to the original values during heating with slight variations from the initial amounts (2–4 mEq O2/kg) due to the volatile nature of peroxides [
The PV of the EAEPO and HEBO samples increased during the first 1 h, followed by a decline to the initial levels (3.63 mEq O2/kg and 2.76 mEq O2/kg, resp.). In the case of FGBO and FBBO, the PV continued to increase up to 6 h with an eventual return to the initial levels of ca. 4.02 mEq O2/kg and 3.96 mEq O2/kg, respectively. The peroxide value of GABO increased to 3.81 mEq O2/kg after 2 h. The rapid increase in the PV of the EAEPO and HEBO samples indicates that these oils were unstable to oxidative degradation. The EAEPO and HEBO samples had the highest percentage of polyunsaturated fatty acids and demonstrated less stability to oxidation, which is in agreement with the data previously reported for olive oil [
The
Figure
Changes in
It was also noted that the trend in the variation of the
Color is an important food evaluation indicator for rapid monitoring of the quality of heated oil. For the unheated oils, HEBO had the highest R parameter of 34.97 compared to the other blended oils due to the extraction of pigments by the organic solvent. The yellow color of EAEPO was more prominent than that of the other blended oils (55.01), indicative of the presence of more yellow pigments, such as carotenoids, in the EAEPO sample (Tables
Variation of yellow color of blended oils.
Y | ||||||
---|---|---|---|---|---|---|
0 h | 1 h | 2 h | 4 h | 6 h | 8 h | |
FGBO | 15.08 ± 0.14aB | 15.53 ± 0.09bB | 15.94 ± 0.05cB | 16.09 ± 0.04cB | 16.37 ± 0.03215dB | 16.65 ± 0.08eB |
FBBO | 19.70 ± 0.02aC | 20.17 ± 0.03bC | 20.25 ± 0.03bC | 20.39 ± 0.08cC | 20.60 ± 0.02082dC | 20.87 ± 0.04eC |
GABO | 29.29 ± 0.05aD | 29.49 ± 0.06bD | 29.87 ± 0.08cD | 30.09 ± 0.01dD | 30.26 ± 0.06110dD | 30.57 ± 0.09eD |
EAEPO | 55.01 ± 0.09aE | 55.32 ± 0.03bE | 55.37 ± 0.07bE | 55.80 ± 0.09cE | 55.85 ± 0.07000cdE | 56.05 ± 0.07eE |
HEBO | 2.13 ± 0.09aA | 2.74 ± 0.03bA | 3.07 ± 0.03cA | 3.07 ± 0.06dA | 3.52 ± 0.02517dA | 3.78 ± 0.02eA |
Mean values within each row followed by different letters (a, b, c, etc.) are significantly (
Variation of red color of blended oils.
R | ||||||
---|---|---|---|---|---|---|
0 h | 1 h | 2 h | 4 h | 6 h | 8 h | |
FGBO | 1.21 ± 0.02aA | 1.57 ± 0.11bA | 2.00 ± 0.06cA | 2.56 ± 0.06dB | 2.79 ± 0.04eC | 3.50 ± 0.09fB |
FBBO | 1.49 ± 0.02aC | 1.87 ± 0.04bC | 2.00 ± 0.05bcA | 2.07 ± 0.11cA | 2.63 ± 0.07cB | 2.76 ± 0.04dA |
GABO | 1.37 ± 0.04aB | 1.77 ± 0.04bB | 1.97 ± 0.04cA | 2.04 ± 0.04cdA | 2.15 ± 0.04dA | 4.11 ± 0.109eC |
EAEPO | 2.57 ± 0.05aD | 3.60 ± 0.03bD | 3.64 ± 0.02bB | 4.55 ± 0.05cC | 4.67 ± 0.02cD | 5.86 ± 0.04dD |
HEBO | 34.97 ± 0.03aE | 38.03 ± 0.09bE | 38.27 ± 0.07bC | 38.90 ± 0.11cD | 39.37 ± 0.05dE | 39.72 ± 0.10eE |
Mean values within each row followed by different letters (a, b, c, etc.) are significantly (
Heat treatment induced a considerable increase in the R and Y parameters. In general, the reddish and yellowish coloration intensifies when the pigments developed during oxidation and thermal decomposition of fatty acids diffuse into the oil during heating. In addition, these changes may also be due to traces of carotenoids [
The fatty acid composition is the most important oil constituent parameter, and the nature of these fatty acids, particularly the degree of unsaturation, determines the oxidative stability of the oils. The unheated oils comprised four major fatty acids: palmitic, stearic, oleic, and linoleic acids (Table
Main fatty acids (%) profile.
FAs | |||||||
---|---|---|---|---|---|---|---|
0 h | 1 h | 2 h | 4 h | 6 h | 8 h | ||
|
FGBO | 9.87 ± 0.03aD | 17.25 ± 0.03bB | 17.70 ± 0.01bcB | 17.48 ± 0.01cB | 17.48 ± 0.35cB | 18.05 ± 0.02dB |
FBBO | 9.15 ± 0.02aC | 12.41 ± 0.03bC | 13.07 ± 0.02cE | 13.14 ± 0.03dD | 13.71 ± 0.03eD | 16.42 ± 0.04fD | |
GABO | 12.12 ± 0.02aE | 13.12 ± 0.02bD | 17.11 ± 0.04cD | 17.76 ± 0.04dE | 17.76 ± 0.01dE | 17.74 ± 0.02dC | |
EAEPO | 7.60 ± 0.02aB | 15.50 ± 0.04bE | 16.32 ± 0.01cC | 16.71 ± 0.02dA | 16.78 ± 0.02eA | 16.89 ± 0.02fA | |
HEBO | 6.61 ± 0.04aA | 15.92 ± 0.01bA | 16.03 ± 0.02cA | 17.22 ± 0.02dC | 17.31 ± 0.02eC | 18.15 ± 0.01fE | |
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|
FGBO | 4.10 ± 0.010aC | 6.37 ± 0.02bD | 7.14 ± 0.03cD | 7.60 ± 0.02dD | 7.53 ± 0.13dC | 9.07 ± 0.02eC |
FBBO | 9.15 ± 0.011aE | 12.41 ± 0.03bE | 13.05 ± 0.02cE | 13.13 ± 0.03dE | 13.75 ± 0.01eD | 16.44 ± 0.00fD | |
GABO | 4.54 ± 0.047cD | 4.15 ± 0.04bC | 4.21 ± 0.00bC | 4.05 ± 0.01aC | 4.07 ± 0.02aB | 4.56 ± 0.04cB | |
EAEPO | 3.60 ± 0.030cB | 3.46 ± 0.03aB | 3.12 ± 0.00dB | 3.48 ± 0.01aB | 3.54 ± 0.01bA | 3.59 ± 0.00cA | |
HEBO | 3.14 ± 0.036aA | 3.23 ± 0.020bA | 3.12 ± 0.01aA | 3.36 ± 0.01cA | 3.44 ± 0.02dA | 3.61 ± 0.02eA | |
|
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|
FGBO | 46.74 ± 0.036fD | 40.90 ± 0.02dD | 40.54 ± 0.04cD | 40.09 ± 0.02bC | 41.21 ± 0.03eD | 40.02 ± 0.02aC |
FBBO | 47.35 ± 0.025fE | 46.53 ± 0.04eE | 45.75 ± 0.01cE | 46.13 ± 0.03dE | 44.87 ± 0.02bE | 42.62 ± 0.04aE | |
GABO | 45.81 ± 0.032eC | 39.79 ± 0.02aC | 39.99 ± 0.12bC | 40.21 ± 0.03cD | 40.55 ± 0.04dC | 40.30 ± 0.03cD | |
EAEPO | 44.49 ± 0.036fB | 37.91 ± 0.03eB | 35.12 ± 0.02dA | 34.67 ± 0.06cA | 34.37 ± 0.04bA | 34.28 ± 0.02aA | |
HEBO | 40.49 ± 0.025fA | 35.79 ± 0.03eA | 35.45 ± 0.01dB | 35.23 ± 0.02cB | 34.94 ± 0.02bB | 34.84 ± 0.03aB | |
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|
FGBO | 36.34 ± 0.025fB | 30.79 ± 0.03eA | 30.51 ± 0.04dA | 30.18 ± 0.03cA | 29.97 ± 0.03bA | 27.79 ± 0.03aA |
FBBO | 35.17 ± 0.015dA | 33.58 ± 0.03cB | 32.40 ± 0.02aB | 32.37 ± 0.08aB | 33.24 ± 0.03bC | 32.35 ± 0.02aA | |
GABO | 35.57 ± 0.05cA | 36.30 ± 0.53dC | 32.22 ± 0.037abB | 32.60 ± 0.07bC | 32.40 ± 0.02abB | 32.05 ± 0.03aA | |
EAEPO | 40.46 ± 0.55bC | 39.51 ± 0.03aD | 39.63 ± 0.03aC | 39.72 ± 0.06aE | 39.74 ± 0.02aE | 39.82 ± 0.04aB | |
HEBO | 44.63 ± 0.01eD | 39.96 ± 0.01cE | 40.20 ± 0.01dD | 38.97 ± 0.02bD | 38.94 ± 0.02bD | 38.68 ± 0.04aB |
Mean values within each row followed by different letters (a, b, c, etc.) are significantly (
Typical chromatogram of fatty acid methyl ester prepared from EAEPO before heating. Peaks: 1: hexadecanoic acid; 2: octadecanoic acid; 3: 9-octadecenoic acid; 4: 9-octadecenoic acid; 5: 9,12-octadecadienoic acid; 6: 12,15-octadecadienoic acid.
Typical chromatogram of fatty acid methyl ester prepared from EAEPO after heating. Peaks: 1: hexadecanoic acid; 2: octadecanoic acid; 3: 9-octadecenoic acid; 4: 9-octadecenoic acid; 5: 9,12-octadecadienoic acid; 6: 12,15-octadecadienoic acid.
Table
Changes in saturated, monounsaturated, and polyunsaturated fatty acids.
SFA, MUFA, and PUFA | |||||||
---|---|---|---|---|---|---|---|
0 h | 1 h | 2 h | 4 h | 6 h | 8 h | ||
SFA | FGBO | 15.28 ± 0.04 aC | 26.83 ± 0.04bE | 27.75 ± 0.01cE | 28.94 ± 0.03dD | 27.87 ± 0.04eE | 31.45 ± 0.01fE |
FBBO | 15.51 ± 0.04aD | 18.34 ± 0.02bA | 19.92 ± 0.02cA | 19.85 ± 0.04dA | 20.22 ± 0.02eA | 25.32 ± 0.01fC | |
GABO | 17.93 ± 0.06aE | 19.78 ± 0.03bB | 24.23 ± 0.01cD | 24.74 ± 0.02dC | 24.69 ± 0.07dD | 25.35 ± 0.01eD | |
EAEPO | 11.93 ± 0.03aB | 20.13 ± 0.02bD | 21.11 ± 0.02cC | 21.30 ± 0.02dB | 21.44 ± 0.00eB | 21.65 ± 0.01fA | |
HEBO | 10.57 ± 0.02aA | 20.01 ± 0.02bC | 20.03 ± 0.02bB | 21.36 ± 0.02cB | 21.57 ± 0.02dC | 22.54 ± 0.01eB | |
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MUFA | FGBO | 47.12 ± 0.02fCD | 41.64 ± 0.02dC | 41.11 ± 0.01cC | 40.70 ± 0.02cB | 41.78 ± 0.04eB | 40.54 ± 0.02aC |
FBBO | 48.15 ± 0.04eD | 47.43 ± 0.02dE | 46.93 ± 0.05cE | 47.65 ± 0.49cD | 45.85 ± 0.02bC | 41.65 ± 0.03aD | |
GABO | 45.97 ± 0.01eBC | 45.13 ± 0.03dD | 41.53 ± 0.01aD | 41.55 ± 0.04cC | 41.86 ± 0.08cB | 41.77 ± 0.01bE | |
EAEPO | 44.48 ± 0.04cB | 40.12 ± 0.02bB | 39.28 ± 0.04abA | 38.87 ± 0.03abA | 38.53 ± 0.02abA | 38.46 ± 0.02aA | |
HEBO | 42.22 ± 0.02dA | 39.98 ± 0.02cA | 40.18 ± 0.04bB | 39.30 ± 0.58cA | 38.53 ± 0.65aA | 38.74 ± 0.02abB | |
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PUFA | FGBO | 37.11 ± 0.01fC | 31.46 ± 0.02eA | 31.16 ± 0.02cA | 30.63 ± 0.02cA | 30.31 ± 0.01bA | 27.96 ± 0.02aA |
FBBO | 36.29 ± 0.03eA | 34.24 ± 0.02dB | 33.12 ± 0.02bB | 33.14 ± 0.03bB | 33.91 ± 0.03cC | 32.95 ± 0.04aB | |
GABO | 36.44 ± 0.02fB | 35.65 ± 0.01eC | 34.23 ± 0.03cC | 33.73 ± 0.03cC | 33.41 ± 0.02bB | 32.95 ± 0.01aB | |
EAEPO | 42.13 ± 0.03dD | 39.54 ± 0.02aD | 39.58 ± 0.03aD | 39.73 ± 0.05bE | 39.74 ± 0.03bE | 39.84 ± 0.03cD | |
HEBO | 45.64 ± 0.02fE | 39.97 ± 0.01dE | 40.18 ± 0.04dE | 38.96 ± 0.02cD | 38.89 ± 0.02bD | 38.74 ± 0.02aC |
Mean values within each row followed by different letters (a, b, c, etc.) are significantly (
The fatty acid ratio of EAEPO and HEBO (0.27 : 1.03 : 0.96 and 0.27 : 1.08 : 1.16) approached the ideal fatty acid ratio of 0.27 : 1 : 1 (SFA : MUFA : PUFA), as shown in Table
Variation of SFA : MUFA : PUFA ratio of blended oils.
SFA, MUFA, and PUFA | ||||||
---|---|---|---|---|---|---|
0 h | 1 h | 2 h | 4 h | 6 h | 8 h | |
FGBO | 0.27 : 0.65 : 0.8 | 0.27 : 0.42 : 0.32 | 0.27 : 0.40 : 0.30 | 0.27 : 0.38 : 0.29 | 0.27 : 0.41 : 0.29 | 0.27 : 0.35 : 0.24 |
FBBO | 0.27 : 0.6 : 0.84 | 0.27 : 0.70 : 0.50 | 0.27 : 0.64 : 0.45 | 0.27 : 0.64 : 0.45 | 0.27 : 0.61 : 0.45 | 0.27 : 0.44 : 0.35 |
GABO | 0.27 : 0.61 : 0.79 | 0.27 : 0.62 : 0.49 | 0.27 : 0.46 : 0.38 | 0.27 : 0.45 : 0.37 | 0.27 : 0.45 : 0.35 | 0.27 : 0.45 : 0.35 |
EAEPO | 0.27 : 1.03 : 0.96 | 0.27 : 0.54 : 0.53 | 0.27 : 0.49 : 0.50 | 0.27 : 0.48 : 0.50 | 0.27 : 0.48 : 0.50 | 0.27 : 0.48 : 0.49 |
HEBO | 0.27 : 1.08 : 1.16 | 0.27 : 0.51 : 0.54 | 0.27 : 0.50 : 0.54 | 0.27 : 0.47 : 0.49 | 0.27 : 0.46 : 0.49 | 0.27 : 0.43 : 0.46 |
Epidemiological evidence has suggested that the level of trans-fatty acid (TFA) intake is connected to the risk of cardiovascular disease [
Changes in trans-fatty acid profile (mg/mL).
TFAs | ||||||
---|---|---|---|---|---|---|
0 h | 1 h | 2 h | 4 h | 6 h | 8 h | |
FGBO | 0.01 ± 0.01aA | 4.94 ± 0.01bA | 17.18 ± 0.02cA | 59.68 ± 0.03dA | 157.83 ± 0.08eA | 280.16 ± 0.18fA |
FBBO | 0.01 ± 0.04aC | 5.78 ± 0.03bC | 21.32 ± 0.01cC | 68.79 ± 0.04dC | 188.48 ± 0.03eC | 257.14 ± 0.08fC |
GABO | 0.01 ± 0.01aB | 5.07 ± 0.06bB | 18.54 ± 0.05cB | 64.61 ± 0.08dB | 162.39 ± 0.03eB | 333.44 ± 0.09fB |
EAEPO | 0.02 ± 0.01aD | 9.55 ± 0.03bD | 29.88 ± 0.05cD | 88.64 ± 0.02dD | 232.52 ± 0.07eD | 542.39 ± 0.08fD |
HEBO | 0.02 ± 0.01aC | 12.43 ± 0.02bE | 30.51 ± 0.03cE | 93.09 ± 0.037dE | 256.70 ± 0.06eE | 558.60 ± 0.14fE |
Mean values within each row followed by different letters (a, b, c, etc.) are significantly (
The results of this study demonstrate that the quality of enzyme-assisted aqueous processing extracted blended oil (EAEPO) is superior to that of hexane-extracted blended oil (HEBO) from the initial to the final heating time, which is possibly due to the extraction method of the former that utilizes water as an extraction and separation medium thereby maintaining a higher antioxidant content. However, compared to the other three refined oil samples, the EAEPO and HEBO samples were less stable towards oxidative degradation. Nevertheless, EAEPO was found to have the lowest acid value and offers the additional advantage of containing an ideal fatty acid ratio after heat treatment of the oils (0.27 : 0.48 : 0.49), which has been linked to reduced risk of high cholesterol and heart disease. The advantageous characteristics may be attributed to the superior initial fatty acid composition of EAEPO.
The authors declare that there is no conflict of interests regarding the publication of this paper.
Lianzhou Jiang and Yang Li contributed equally to this paper.
The authors are grateful to the National High-Tech R&D Program of China (863 Program) (no. 2013AA102104), the Key Laboratory of Soybean Biology of the Chinese Education Ministry, Northeast Agricultural University (no. SB12C01), the Establishment of Modern Agricultural R&D Systems (no. Nycytx-004), and the National Research Center of Soybean Engineering and Technology for support of this project. The authors are also grateful to the anonymous referees for helpful comments on an earlier draft.