Dear Marie Danica Cerna Geagonia , I guess you want to make emulsions with varying olive oil contents in water, correct?

For solutions, the fastest way to make a concentration series is to make a concentrated sample and dilute that to the desired concentrations. However, here you have olive oil in water which forms a very instable emulsion. In this instable emulsion the olive oil content is not uniformly distributed. So, if you take an aliquot from it, depending on where you take this, may have a range of concentrations. For emulsions you cannot use the common dilution approach but you need to make all samples by weighing in the appropriate weights of olive oil and water individually. You also need to weigh in these emulsions directly into the 'container' where you want to use them (point-of-use) because if you make them in a beaker and next transfer them into a bottle...... you risk losing part of the olive oil which may adhere to the beaker.

For systems like this I would also consider the following:

- instead of water, consider using a pH-buffer at a suitable pH and a concentration of, let's say 10 mM level

- if you want to keep these emulsions for longer times, remember, microbes may feast on your emulsions, check if you can use a very low level of an antimicrobial

Hope this helps, kind regards, Leo

You need to add an emulsifier like gum arabic, about 3 g in 100 mL water. Let the gum dissolve. Then add 2 g olive oil (for 2% solution) and shake vigorously. You will get a reasonably uniform emulsion. If you want to make dilutions from this emulsion (the oil does not dissolve to give a nice clear solution), you should use a solution of gum arabic again for dilution (e.g. 1 mL of 2% solution + 9 mL of gum arabic solution will give you 0.2% olive oil emulsion.

Your percent concentration of olive oil is not clear. Is it volume by volume (%v/v) or weight/weight - %w/w or weight by volume-%w/v or volume by weight %v/w? Please make us understand. Let us also know if your desire is to express concentration in molarity. It would be useful for definite answers.

Maurice Ekpenyong thank you for your reply, sir.

I forgot to mention it is by %v/v.

We're planning to put those 3 olive oil concentrations to tributyrin agar.

However, my mates are confused about how to make olive oil concentrations. Like if it will be from a powder or what?

Sorry for the delay in reply. I hope you can help, sir :)

Marie Danica Cerna Geagonia , olive oil is a liquid at room temperature. So, you can measure it in a measuring cylinder (if it doesn't need to be too accurate). The complexity you have is that you have solids (agar, other medium components), liquid (presumably water) and as second liquid your olive oil. Since dissolving the solids may lead to a volume change, first prepare the agar medium without olive oil. Now if you want to make a 3 v/v% olive oil, carefully measure e.g. 970 ml agar and add 30 ml of olive oil. Since you probably need to keep the agar at 40°C, to prevent gelling, also heat your olive oil and measuring cylinders in an oven. That reduces the measuring error and should avoid risk of gelling.

I need to point out that you still run a risk of having inhomogeneously distributed olive oil because when the agar starts gelling, it may push the olive oil to form droplets. Hence you will get droplets very rich in olive oil and parts where all the olive oil was displaced and very poor in olive oil. So, I would recommend to folow up on Nitin Fadnavis advice to add an emulsifier, make sure the oilive oil is well dispersed before allowing the agar to gel.

Kind regards, Leo