Determining the Antimicrobial Properties of Spices

It has been known for centuries that some spices can have an antimicrobial effect, mainly in their use as preservatives of food.

You are going to test the effectiveness of different spices by observing the growth of microbial colonies on rice pudding.

The following ingredients will be required:

• A selection of household spices
• Packaged rice pudding

The following items will be required:

• Clingfilm or similar plastic wrap
• A kitchen weighing balance
• Small spoons to stir spices

Ensure that you read through all of the instructions before beginning the experiment to ensure that you understand exactly what will happen at each step.

Step 1: Measurement of Spice

First, select the spice that you wish to use. Add 1 g of your chosen spice to 190 g of rice pudding. This corresponds to the average size of a rice pudding microwave pot.

For each spice create a pudding where the spice is mixed into the rice pudding and also a pudding where the spice is simply sprinkled on the surface of the pudding.

In addition to the two rice pudding samples, for each spice, you will also need to create a control sample for the experiment. The control is treated the same way as all of the experimental samples, but, it does not have any spice added to it.

This allows us to see the effects of adding spices compared to adding no spices at all to our sample. Should we find that there is no significant difference between the microbial growth on an experimental spice sample compared to the control sample we can say that this spice has a comparatively weak or no antimicrobial activity.

Step 2: Heating

Follow the heating guidelines supplied with your rice pudding pots. Our samples were heated in the microwave for 50 seconds at a minimum of 800 Watts. Remember to heat your control sample too, it must experience exactly the same conditions that the experimental samples do – with the exception of the addition of spice.

After the rice pudding samples have been heated leave them to cool to room temperature. Once cooled take a cling film wrap and cover the top of the rice puddings (loosely, so that air can enter). Remember to label each rice pudding sample so that you know which is which.

Continue to observe your rice pudding samples for five days to seven days. Each day, take a picture of your rice pudding samples, and once the activity is finished post your collection so that we can pool data together and have a wide range of spices to analyse. Post on our open Padlet (we have included some examples from previous courses to help inspire you) and/or on Twitter or Instagram hashtag #FLchemistry.

Try experimenting with adding multiple spices to a single pot, is the effect of each spice augmented by the other? Does the same mass of rice pudding spread flat over a plate result in a faster growth rate of microbial colonies?

Safety

• Take care when warming the rice pudding: Rice pudding can get hot. Ensure that you handle any rice pudding pots with oven gloves or protective mitts.
• Dispose of rice pudding samples correctly: We strongly advise not to eat any of the rice pudding samples at any stage of the experiment. Ensure that all rice pudding samples are disposed of in a general waste bin.

Experiment adapted from: A.M. Sousa and W.R. Waldman, J. Chem. Educ., 2014, 91, 103.

You might also like to take a look at this article explaining how concentrated doses of common spices keep animals healthy and help them grow.

Watching Mould Grow

For some stunning images, showing the wide array of mould (mold) shapes, colours and sizes, you might like to see this clip.

In a Nutshell

Those of you who enjoy a pinch of nutmeg in their rice pudding might like to know that it contains small amounts of a psychoactive drug called myristicin (C₁₁H₁₂O₃). The psychoactive effects of nutmeg, at much higher concentrations than used in cooking, could be due to the breakdown of myristicin in the liver into the amphetamine MMDA (3-methoxy-4,5-methylenedioxyamphetamine, C₁₁H₁₅NO₃).