Recently, I am focusing the pretreatment of crude glycerol from the biodiesel industry. After acidification, light white yellow floating layer could be observed. Subsequent hexane wash seem not to be able to remove the color because light yellow bottom layer is founded. Compared to that of filtration via 0.45 um Nylon membrane after acidification, the hexane wash shows very limiting ability of color removal. So I really want to know the chemical composition resulting in the yellow color in the cooking oil. Can anybody help to resolve this question? Thank you very much!
Brief description of the attach figure. The smaller bottle is the filtrated sample after acidification while the large bottle is the sample after 12 hours` hexane wash following acidification. In the large bottle, the upper layer is the hexane while the bottom one is the aquatic layer. It seems very interesting that the hexane could be extract the color. Therefore, I am very curious about the chemical composition of the color prior to further microbial consumption test. There might be light issue when I took the picture but there are significant color difference between the hexane washed sample and filtrated sample.
Color of the cooking oil is due to carotenoids and some other pigments. Usually 3.5 to 5 mg of beta-carotene colors 500 g of product. In nature beta carotene is a precursor to vitamin A. Beta-carotene is a safe source of Vitamin A, as the body converts the Beta-carotene into Vitamin A when Vitamin A levels are low. As a physiological antioxidant Beta-carotene can also prevent damage caused by free radicals.
Hello Chaozhi! I would suppose, it should be derivative from sulphur, which can be a constituent of biodiesel. There are, probably, specific odour?
Mustaq Ahmad, thank you for your reply and comments. Even if I got similar answer from the literature as you mentioned, i think the color component was not the beta-carotene. Because when i used the hexane to extract some organic, the hexane phase was transparent without anything color. I may suspect it other compound.
Hello, Svetlana Victorovna Obydenkova. Thank you for your comments, indeed there is a light odour but different from that of hydrogen sulfide.
The mixture still looks turbid to me. It might be partially burnt glycerol. Try adding activated char coal and stir and centrifuge it. Hopefully you may end up with a clear layer. Just a thought!!!
Narashimharao Kondamudi, thank you for your recommendation. I will consider the activated carbon to adsorb the color-resulting substance.
Hai Chaozhi Pan,
I think you may take yellow layer and try to test run by using GC to identify either it is glycerol or oil or FFA. Hope this easier technique will help you to solve your current problem.
Thank you.
Hi, Rozaini Abdullah. Thank you for your comments, according to my previous results, the bottom layer in the hexane washing is the aquatic phase, which is not compatible with GC operation condition. I sure there major component in the aquatic phase is glycerol but what i want to know the chemical composition of the color. Because, after the pre-treatment i will use the solution to feed bacteria.
Usually, any color of any organic compound arises by oxy-species groups consisted of the so-called chromophores. Particulrly, yellow-reddish colouring is created by molecular block containing of a continuous conjugated chain of single/double bonds O=C=…-(R)-…=C=O (R is any hydrocarbon radical). Chromoforic group O=C=… results in the appearance of the spatial ionic charge {…±Ӫ…} - i.e., the structure of the para-benzoquinone molecule is of the form ...
As to the yellow colour of cooking oils, it may be conditioned by quinone O=C╡˂C4H4˃╞C=O, non-specifyed kinetic route of its generation being of the form
˂oil˃+{O2, H2O}→…oxidation→…CH3CHO+CH3OH→ akrolein CH2=CH-CHO→ quinone O=C╡˂C4H4 ˃╞C=O
The quinone has high color index and coloring power. It absorbs the blue region of the visible spectrum Δλ=4350-4800 Å[angstrom] and emits efficiently in the yellow region Δλ=5500-5850 Å [Chichibabin, A.E., 1983. Fundamental in organic chemistry. Gosizdat, Moscow (Rus)].
I am currently studying the problem with the quality of distilled glycerin. When stored, it acquires a pink tint (see photo). We analyzed glycerol on a gas chromatography mass spectrometer. In the sample 1099/2, the following impurities were found:
1,2,3-Propanetriol, 1-acetate CAS No. 106-61-6;
3-Methoxy-1,2-propanediol CAS No. 623-39-2;
1,3-Dimethoxypropan-2-ol CAS No. 623-69-8;
2-tert-butylhydroquinone CAS No. 1948-33-0.
Which of these substances can give a pink color and why?
Joachim Müller Sebastian Romuli
What is your idea regarding this interesting question? My dear colleages.
Our sesame oil is absorbing light at about 490nm in the hyperspectral image.
The information I searched showed that 1,4 quinone is actually poisonous
A quite old paper showed it shoud because carotenoids and some other pigments. doi: Article Characteristics of Colors in Vegetable Oils and Methods of Removal
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