Research into the production of white sesame oil by aqueous extraction has been promoted because of concerns about the environment, health, and cost. The advanced aqueous method using a 1.95:10 liquid-to-raw material ratio, which was finally developed in this study, recovered 96.06% white sesame oil and produced de-oiled meal with high quality (3.98% residual oil content). The acid value and peroxide value of the oil produced were quite low at 0.19 mg KOH/kg and < 3.25 mmol/kg, respectively, which were better than the values required by the Chinese national standard for first class edible sesame oils and oils produced by hexane extraction. No wastewater was discharged during the extraction of white sesame oils by an aqueous salt solution. The protein rich de-oiled meal may be a good material for making protein isolate with high purity (e.g. > 90%). It can also be a nutritious ingredient or raw material for producing many food products.
White sesame (
Recently, scientific evidence has indicated that white sesame seed oil (WSSO) has beneficial effects on health such as the improvement of blood lipid profile and the activities of anti-inflammation and antimutagenesis (Lee
The neuroprotective potential and antioxidant activity of de-oiled white sesame seed meal (DBSSM) has been reported in the literature (Ben
Therefore, a method able to obtain both oil and DBSSM with high quality is preferred for processing white sesame seeds. Hot pressing is not good for extracting oil from white sesame seeds because it produces dark DBSSM with denatured proteins. Although direct cold pressing can produce oil and DBSSM with high quality, its extraction efficiency is low. Although solvent (e.g. hexane) extraction is able to efficiently produce oil and DBSSM with high quality, it has many disadvantages, as reported in the literature (Tu
The objective of this study was to develop an advanced aqueous method of efficiently producing white sesame oil and de-oiled meal with high quality based on a new theory of separation of oil and relying on the aggregation of hydrophilic groups of compounds (with or without hydrophobic groups) through hydrogen bonds with the prevention of their solubilization or dispersion by adding a small quantity of water as a pre-treatment. The experiments involved the establishment of critical conditions affecting the recovery rate and quality of the oil and DBSSM produced and a comparison of the aqueous method based on the new theory to cold pressing, the traditional aqueous method assisted by enzymes and hexane extraction.
White sesame seeds were obtained from Yonghui Supermarket, Beibei District, Chongqing, China. All chemicals and reagents used were of analytical grade.
The flow chart for the general process to be studied is shown in
Flow chart for producing white sesame oil and de-oiled meal using an aqueous solution or water.
An investigation into the effect of several operating parameters on the final yield (FY) of WSSO was conducted by following the procedure mentioned in the above section. The operating parameters investigated are summarized in
Summary of single factor experiments on operating parameters
Baking time (min) |
Water added (ml/10 g) |
Baking temperature (°C) |
Agitation time (min) |
Particle size of seed slurry (μm) |
Aqueous salt solution added (ml/10 g) |
Concentration of aqueous salt solution (%; w/w) |
Agitation temperature (°C) |
---|---|---|---|---|---|---|---|
1.00 | 0.00 | 90 | 15 | 180 | 1.40 | 3.00 | 25 |
2.00 | 0.50 | 95 | 20 | 154 | 1.50 | 4.00 | 30 |
3.00 | 1.20 | 100 | 23 | 125 | 1.60 | 5.00 | 35 |
4.00 | 1.30 | 105 | 24 | 100 | 1.70 | 6.00 | 40 |
5.00 | 1.40 | 110 | 25 | 74 | 1.80 | 7.00 | 45 |
6.00 | 1.45 | 115 | 26 | 61 | 1.90 | 8.00 | 50 |
7.00 | 1.50 | 120 | 27 | 54 | 2.00 | 9.00 | 55 |
8.00 | 1.55 | - | 30 | 38 | 2.10 | 10.00 | 60 |
9.00 | 1.60 | - | 35 | - | 2.20 | - | 63 |
10.00 | 1.70 | - | - | - | - | - | 64 |
- | 1.80 | - | - | - | - | - | 65 |
- | - | - | - | - | - | - | 66 |
- | - | - | - | - | - | - | 67 |
- | - | - | - | - | - | - | 68 |
- | - | - | - | - | - | - | 69 |
- | - | - | - | - | - | - | 70 |
For all experiments except for investigation into effect of baking temperature, the seeds were baked at 110 °C.
Other parameters: the seed slurry was passed through a sieve with a 154 μm pore size (100 meshes), the addition of 1.55 ml H2O and agitation at 65 °C for 25 min.
Other parameters: the seeds were baked for 1 min, the seed slurry was passed through a sieve with 154 μm pore size (100 meshes), agitation at 65 °C for 25 min.
Other parameters: the seeds were baked for 1 min, the seed slurry was passed through a sieve with154 μm pore size (100 meshes), the addition of 1.55 ml H2O and agitation at 65 °C for 25 min.
Other parameters: the seeds were baked for 1 min, the seed slurry was passed through a sieve having 154 μm pore size (100 meshes), the addition of 1.55 ml H2O and agitation at room temperature (25 °C) until the aggregation of all the hydrophilic compounds and liberation of free oil was observed.
Other parameters: the seeds were baked for 1 min, the addition of 1.55 ml H2O as well as agitation for 25 min.
Other parameters: the seed slurry was passed through a sieve with 154 μm pore size, the concentration of aqueous salt solution was 6.00% (w/w) as well as agitation at 65 °C for 25 min.
Other parameters: the seeds were baked for 1 min, the seed slurry was passed through a sieve with 154 μm pore size, the addition of 2.00 ml aqueous salt solution (6.00%, w/w) as well as agitation at 65 °C.
Other parameters: the seeds were baked for 1 min, the seed slurry was passed through a sieve with 154 μm pore size, the addition of 2.0 ml aqueous salt solution (6.00%, w/w) as well as agitation for 25 min.
The content of residual oil in the DBSSM was measured by the Soxhlet method. Three replicates were carried out. The FY of WSSO was calculated by using the following equation:
FY(%) = (X1-X2) ÷ X1 × 100%
In the equation, X1 (g) represents the amount of crude oil in the white sesame seed slurry (WSSS) [10 g × crude oil fraction in WSSS (water free)], while X2 (g) represents the amount of crude oil in DBSSM (amount of DBSSM (g, water free) × its residual oil fraction).
A response surface experiment was conducted to check whether the optimum aqueous extraction conditions established by single factor experimentation was the best and to study the cross-effect of these conditions on the FY of WSSO. By centering on the optimum extraction conditions established by single factor experimentation, Box-Benhnken’s central combined experimental design was implemented. Four extraction conditions including concentration of salt solution (A), amount of salt solution added (B), agitation temperature (C), and agitation time (D) were selected and assigned to three different levels for performing response surface experiments.
Sesame seeds were baked to constant weight and crushed to pass a sieve with 154 μm pore size. The oil in the crushed seed was extracted for 6 h by n-hexane using a Soxhlet extraction apparatus. After n-hexane was completely removed by rotary evaporation, and the oil was vacuum-dried to constant weight at 50 °C.
The extraction of WSSO by cold spiral pressing was also conducted for comparison. The residual oil content in DBSSM obtained by this method was determined.
Crude oil content, acid value, peroxide value, smell and taste, hexane content, and transparency were analyzed according to Chinese National Standards GB 5009.6-2016, GB 5009.229-2016, GB 5009.227-2016, GB/T 5525-2008, GB/T 5009.37, respectively. Color was analyzed using a colorimeter (HanterLab UltraScan Pro. USA) (Gerde
Experimental data were analyzed using one-way analysis of variance. Significant difference between pair data was estimated by the Student’s t-test. The P-value was calculated using Microsoft Office Excel. The response surface analysis was conducted by using Design Expert 8.0.6 software. A multi-factorial regression equation was established using SAS V8.0.
The crude fat content of the white sesame seeds studied was 51.25% (dry weight basis) while their protein content was 23.90%. All data in terms of FY of WSSO were calculated on the basis of these measurements. This sample was used for developing the advanced aqueous method of extracting WSSO and producing DBSSM with high quality.
Effect of single factors on the final yield of white sesame oil.
However, a further increase in the amount of water to higher than 1.55 ml gradually reduced the FY of WSSO. The reason for this may be that some hydrophilic compounds such as free fatty acids, phospholipids and phenolic compounds can dissolve in water so that the emulsification is enhanced and FY is reduced. Of all the added amounts of water, 1.55 ml gave the maximum FY of WSSO. This study demonstrates that adding the right amount of water is necessary for the effective extraction of WSSO.
The design and results from the response surface experiment and the analysis of variance are shown in
Design and results of surface response experimentation
Run | Factor 1 A: Concentration oncentration of aqueous salt solution (%) | Factor 2 B: Amount of aqueous salt solution added (ml) | Factor 3 C: Agitation temperature (°C) | Factor 4 D: Agitation time (min) | Response Final oil yield (%) |
---|---|---|---|---|---|
1 | 6.00 | 1.95 | 66.00 | 25.00 | 96.04 |
2 | 6.00 | 2.05 | 66.00 | 25.00 | 94.17 |
3 | 6.50 | 2.00 | 65.00 | 26.00 | 91.58 |
4 | 6.00 | 2.05 | 65.00 | 26.00 | 94.51 |
5 | 6.00 | 2.00 | 64.00 | 24.00 | 95.59 |
6 | 6.00 | 2.00 | 65.00 | 25.00 | 95.71 |
7 | 6.00 | 2.00 | 64.00 | 26.00 | 95.68 |
8 | 6.00 | 2.00 | 65.00 | 25.00 | 95.89 |
9 | 6.00 | 2.00 | 66.00 | 24.00 | 95.69 |
10 | 5.50 | 1.95 | 65.00 | 25.00 | 94.63 |
11 | 6.00 | 2.00 | 65.00 | 25.00 | 95.98 |
12 | 6.00 | 1.95 | 64.00 | 25.00 | 96.06 |
13 | 5.50 | 2.00 | 65.00 | 24.00 | 94.14 |
14 | 6.00 | 2.00 | 65.00 | 25.00 | 95.98 |
15 | 6.00 | 2.05 | 65.00 | 24.00 | 94.81 |
16 | 6.00 | 1.95 | 65.00 | 26.00 | 96.03 |
17 | 6.00 | 2.00 | 66.00 | 26.00 | 95.68 |
18 | 6.00 | 2.05 | 64.00 | 25.00 | 94.72 |
19 | 6.50 | 2.00 | 66.00 | 25.00 | 91.49 |
20 | 5.50 | 2.00 | 65.00 | 26.00 | 94.32 |
21 | 5.50 | 2.00 | 64.00 | 25.00 | 93.98 |
22 | 6.00 | 1.95 | 65.00 | 24.00 | 96.06 |
23 | 6.50 | 2.00 | 65.00 | 24.00 | 91.16 |
24 | 6.50 | 2.00 | 64.00 | 25.00 | 91.71 |
25 | 5.50 | 2.05 | 65.00 | 25.00 | 93.04 |
26 | 6.50 | 1.95 | 65.00 | 25.00 | 92.36 |
27 | 5.50 | 2.00 | 66.00 | 25.00 | 93.55 |
28 | 6.50 | 2.05 | 65.00 | 25.00 | 90.01 |
29 | 6.00 | 2.00 | 65.00 | 25.00 | 95.76 |
ANOVA for Response Surface Quadratic Model Analysis of variance table [Partial sum of squares - Type III]
Source | Sum of Squares | df | Mean Square | F Value | P-Value Prob > F | |
---|---|---|---|---|---|---|
Model | 88.03 | 14 | 6.29 | 124.59 | < 0.0001 | significant |
A-Concentration of aqueous salt solution | 19.64 | 1 | 19.64 | 389.07 | < 0.0001 | - |
B-Amount of aqueous salt solution added | 8.20 | 1 | 8.20 | 162.49 | < 0.0001 | - |
C-Agitation temperature | 0.10 | 1 | 0.10 | 2.07 | 0.1721 | - |
D-Agitation time | 0.010 | 1 | 0.010 | 0.20 | 0.6598 | - |
AB | 0.14 | 1 | 0.14 | 2.86 | 0.1129 | - |
AC | 0.011 | 1 | 0.011 | 0.22 | 0.6474 | - |
AD | 0.014 | 1 | 0.014 | 0.29 | 0.6016 | - |
BC | 0.070 | 1 | 0.070 | 1.39 | 0.2578 | - |
BD | 0.018 | 1 | 0.018 | 0.36 | 0.5575 | - |
CD | 2.500E-003 | 1 | 2.500E-003 | 0.050 | 0.8271 | - |
A2 | 57.52 | 1 | 57.52 | 1139.72 | < 0.0001 | - |
B2 | 1.14 | 1 | 1.14 | 22.57 | 0.0003 | - |
C2 | 0.21 | 1 | 0.21 | 4.12 | 0.0618 | - |
D2 | 0.030 | 1 | 0.030 | 0.59 | 0.4547 | - |
Residual | 0.71 | 14 | 0.050 | - | ||
Lack of Fit | 0.64 | 10 | 0.064 | 4.15 | 0.0913 | not significant |
Pure Error | 0.062 | 4 | 0.016 | - | - | - |
Cor Total | 88.74 | 28 | - | - | - |
Note: “*” indicates significant, p < 0.05; “**” indicates extremely significant, p < 0.01; “-” indicates not significant, p > 0.05; R2=0.9920, R2Adj=0.9841.
The Model F-value of 124.59 implies the model is significant. There is only a 0.01% chance that a “Model F-Value” this large could occur due to noise.
Values of “Prob > F” less than 0.0500 indicate model terms are significant.
In this case A, B, A++2+-, B++2+- are significant model terms.
Values greater than 0.1000 indicate the model terms are not significant.
If there are many insignificant model terms (not counting those required to support hierarchy), model reduction may improve the model.
The “Lack of Fit F-value” of 4.15 implies there is a 9.13% chance that a “Lack of Fit F-value” this large could occur due to noise. Lack of fit is bad -- we want the model to fit. This relatively low probability (<10%) is troubling.
Production efficiency of white sesame oil by the advanced aqueous method and other methods as well as the characteristics of the oil produced as compared with Chinese National Standard (CNS; GB1536-2004) for 1st class refined oil (Only bold items are mandatory while others are not.)
Items | CNS | Aqueous | Enzyme-assisted aqueous | Hexane | Cold pressing |
---|---|---|---|---|---|
Extraction yield of oils (%) | — | 96.02 | 69.33 |
99.03 | 74.43 |
Smell, taste |
b | b | — | b | b |
Transparency | C, T |
C, T |
— | C, T |
C, T |
0.19 | — | 1.93 | 1.60 | ||
3.25 | — | 5.74 | 5.13 | ||
ND |
ND |
50 | ND |
||
Residual oil content in de-oiled meal (%) | — | 3.98 | — | 1.01 | 21.37 |
Final yield of oils (%) | — | 96.02 | 65.71e | 95.18 | 72.26 |
The highest extraction yield of white sesame oil by enzyme-assisted aqueous method reported in the literature (Wang
Having the inherent smell and taste of sesame oil, no adverse smell
C,T-Clarify, transparent
ND- not detectable.
Response surface interactions of AB and AC. A-Concentration of aqueous salt solution, B-Amount of aqueous salt solution added and C-Agitation temperature.
Response surface interactions of AD or BC. A-Concentration of aqueous salt solution, B-Amount of aqueous salt solution added, C-Agitation temperature and D-Agitation time.
Response surface interactions of BD and CD. B-Amount of aqueous salt solution added, C-Agitation temperature and D-Agitation time.
A regression equation was obtained by using the SAS RSREG program to perform regression fitting on response values and various factors. The final equation established in terms of coded factors was as follows:
FY of WSSO = + 95.86 - 1.28*A - 0.83*B - 0.093*C + 0.029*D - 0.19*A*B + 0.053*A*C + 0.060*A*D - 0.13*B*C - 0.067*B*D - 0.025*C*D - 2.98*A2 - 0.42*B2 - 0.18*C2 - 0.068*D2
In the equation, A represents the concentration of the aqueous salt solution; B represents the amount of aqueous salt solution added; C represents agitation temperature; D represents agitation time. The optimum combination of operating parameters for obtaining the highest FY of WSSO was as follows: A = 6.00% (w/w), B = 1.95 ml, C = 64 °C, and D = 25 min. The highest FY of WSSO obtained by using these optimum operating parameters was 96.02%, which was not significantly different from that (95.76%) obtained from using those established by the single factor experiment.
Therefore, the advanced aqueous method for extracting WSSO followed the same procedure as the one described in “
The WSSO produced by the advanced aqueous method finally established in this study was clear and transparent.
The color indices for the oil produced by the advanced aqueous method were as the follows: L* = 57.76, a* = -5.68, and b* = 86.01; while those produced by hexane extraction were L* = 40.63, a* = -12.16, and b* = 51.79; and those obtained from direct cold pressing were L* =60.67, a* =15.97, and b* =97.44. The oil obtained by the advanced aqueous method had a lighter color than the oil produced by hexane extraction.
The DBSSM obtained from the advanced aqueous method showed 45.52% protein content and 3.98% residual oil content. Although the color of DBSSM from the advanced aqueous method was slightly deeper than that obtained by hexane extraction, it may be directly applied to the food industry or food recipes since whole sesame seeds with their peel are edible.
The traditional aqueous method using large quantities of water (usually liquid:raw material ratio > 2) relies on the solubilization of hydrophilic compounds such as proteins, free fatty acids, or free amino acids and the formation of emulsion for the efficient extraction of oil. By this method, it is difficult to obtain clear free oil because of serious emulsion though a high extraction rate can be achieved. Therefore, the recovery rate of oil from sesame seeds is quite low, i.e. less than 90%. Another disadvantage of this method is that it produces a large quantity of waste water, causes a loss in water soluble compounds and difficulty in drying the de-oiled residue.
The aqueous method established in this study uses a small amount of water (liquid:raw material ratio being only1.95:10). Our method is based on a new theory of separating oil. Its mechanism is associated with the work of cohesion of oil or hydrophilic compounds as well as the work of adhesion of oil to solid particles containing proteins, saccharides, free amino acids and free fatty acids via a hydrophobic interaction. The aggregation of hydrophilic groups of compounds such as proteins, saccharides, free amino acids, free fatty acids and phospholipids (with or without hydrophobic groups) through hydrogen bonds is promoted by adding the proper amount of water which can avoid their solubilization or dispersion as a prerequisite. This process results in the work of cohesion becoming larger than the work of adhesion so that release of free oil is carried out. Therefore, the mechanism of this new aqueous method is completely different from that of traditional aqueous method using large amounts of water and relying on the solubilization or dispersion of hydrophilic compounds such as proteins, saccharides, free amino acids, free fatty acids and phospholipids.
The recovery rate of oil from white sesame seeds is as high as 96.06%. No waste water is produced during the extraction of the oil. The water content of the de-oiled meal is quite low so that it can be easily dried. Full utilization of white sesame seeds is achieved.
It was concluded that the advanced aqueous method eventually developed in this study recovered 96.02% of WSSO. The acid value at 0.19 mg KOH/kg and peroxide value at 3.25 mmol/kg were quite low, and better than that required by the Chinese national standard for first-class edible sesame oil and that of oil produced by hexane extraction. The oil obtained from the advanced aqueous method had a lighter color than the oil produced by hexane extraction. The residual oil content in the DBSSM was 3.98%, while its protein content was 45.52%. No wastewater was discharged during the aqueous extraction of oil. The results of this study should provide valuable scientific guidance for the future development of production technology of high-quality WSSO and DBSSM with high-quality and low cost on an industrial scale.