In a standard Lebanese garlic paste recipe prepared with the same proportions of ingredients and the same process (garlic cloves, lemon juice, olive/sunflower oil and salt), it has been noticed that the final product is yellowish with olive oil while completely white with sunflower oil. What could be the reason behind this? I know the citric acid could have an effect on the color of the emulsion rather than the type of oil, and evidently olive oil is darker in color than sunflower oil. I will be looking at both results under the microscope and measuring the color by colorimetry. Thoughts?
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In South Africa lemon juice is preserved with SO2, this can either bleach or maintain the colour of the garlic, the oil will behave in colour as intended. The citric acid is giving a desired or typical Ph to prevent colour discolouration as well in combination with sorbic acid if added. Some Lemon juice might also have Ascorbic acid Added. Check which Additives especially preservatives and antioxidants your country allows in oil and lemon juice
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Thanks so much for your reply. I was thinking of freshly squeezed lemon juice though. I’m trying to look it up in the literature with little success. Do you think there would be any color pigments in the garlic or oil that are responsible for this? and the acid maybe increasing the rate of pigment production maybe? or chemical and enzymatic reactions…This is a picture of the garlic pastes I obtained using the same ingredient quantities and process.
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Practically olive oil is darker than sunflower oil due to presence of chlorophyll specially in the virgin grade, so it should influence the color of the finished condiments.
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so maybe a bigger quantity of lemon juice (citric acid) could render it white eventually? but the emulsion may be affected…
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IF this is a traditional recipe from Your ancestors originally made with olive oil, then why change it.?
Besides the olive oil savory taste can impart its own flavor to the prepared condiments that compliments the overall taste
If you want a brighter color but slightly bland in flavor then stick with sunflower oil or if you can find some grades of olive oil that is lighter in color.
As the saying goes… “, If ain’t broken why fix it?”
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@paulakhaty
Garlic contain sulphur containing compounds, also when garlic is crushed the enzymes act with release of such compounds. Is there a possibility of reactions of these compounds with fatty acids present in the 2 types of oils, obviously the major FA in these two oils ( differences).
The other thought could be to conduct a control trial with avocado oil or grape seed oil (green tinge), or try using another oil of the yellow coloured variety and counter check the effect.
Finally the smell, or aroma that comes for each of these products might give you more clue as well.
May be to check on some organosulfur compound and aroma profiles.
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They are clearly 2 different products, different taste and Colour and two different costing pastes. Olive oil is the traditional and the sunflower is maybe a modern made in kitchen product. The products will have different shelf life too.
Olive oil will not be white, but can become lighter with different colour oils like Roy articulated or with Combining with sunflower, rapeseed (canola) etc. Traditionalists may give the second one a skip thinking the second is an inferior product.They will behave differently when stored in refrigerator, but I believe will not last the evening on a good flat bread.
@nanoscientist thank you! so it is more the initial color of the oil than the effect of citric acid on the garlic you would say? I basically have one day of experiments to conduct in the laboratory, so would you suggest that I first make the two different pastes (one with virgin olive oil and one with sunflower oil) without lemon juice (maybe replace with water so the emulsion works) then measure the color of the two pastes via a colorimeter? and then I add lemon juice to the recipe and check its whitening effect? Thanks, I;m just trying to brainstorm so that I make sense of it… 
should I maybe also check the pH of the pastes?
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You should start with the two oils and get a reading as a standard, add the water and oil ratio, take reading as a ratio, then replace with oil, lemon juice as ratio. Look up the fatty acids profile of the two oils and record. The neutral colour of sunflower oil is allowing non colouring of end paste, the lemon juice is preventing the garlic from discolouring. When garlic is dried into small garlic pieces, browning of garlic occurs, when reconstituted to give garlic pieces in solution, often the oil, vinegar solution has a brownish colour to it. Manufacturers have been known to try to bleach this, to give whiter garlic as trying to show of fresh garlic but can’t.
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I think checking Ph would be a confirmation that Ph is not so a great differentiator. Citric acid is used in oil production as a polisher for clarity of oil too. It is a colour protector in food stuffs too, if the colours are stable in that Ph range. Good luck with your experiment.
Thanks @waynevannieuwenh! but I’m not sure what you mean by “add the water and oil ratio, take reading etc.” First I will measure the color of the oils separately and then mix with the garlic and measure again and then with the garlic and lemon juice and measure. Is that what you mean?
@paulakhaty I love artisana/l traditional food products ; even if I know the means to change its appearance by using alternative materials and additives I will not tamper my ancestors recipes as its a form of disrespect to tradition.
I don’t understand the reason of modifying it just to fit ones narrow personal needs.
I am not changing it “just to fit my narrow personal needs” . I’m conducting an experiment to find out why my ancestors passed this information down through generations.
Well your answer belies your intent, as is obvious, the traditional recipe is so simple, the taste is great then Why complicate matters unnecessarily… 
If you want to make that traditional condiments as white as mayonnaise to fit your personal needs then you should think how this creamy sauce is made? 
I have done some work with toum.
If you want a white color, even with olive oil, add some egg white to the formulation.
That’s correct
Many outlets add corn starch to the recipe to give it a whiter color and more volume. Some also add potato starch.
@paulakhaty: Blanching :Try putting them in hot water for a short period of time, which might slow down or inactivate the enzymes.
as might be colour change due to sulfer containing garlic and enzyme reactions at that PH of citric acid try to blanch as its wet process may work
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Correct, to show no colour change happens to oil.