Chapter 52

Squeeze the Day! The Detectives Help a Client Analyze Essential Oils in Citrus Fruits

📂 A client seeking to bring a selection of citrus fruit juices to market needs the assistance of the food detectives to ensure their products meet regulations. The client doesn’t have any lab equipment and lacks knowledge of the analysis process. Do the detectives have what it takes to put their knowledge to the test and perform the analysis themselves? Can the client succeed in getting their product to market? And will Cornlumbo ever stop with the dreadful puns and save Miss Mapple from losing her cool? Read on to find out!

Having helped a client perform a return-on-investment (ROI) analysis before installing NIR equipment in their dairy processing facility, the detectives are taking a well-deserved break and waiting for another case. Cornlumbo, enjoying his breakfast, holds up his toast and declares, “A toast to a beautiful day!” He then raises his cup of tea and shouts, “Life is brew-tiful!” Miss Mapple rolls her eyes and calls him a fool. “Omelet that slide,” says Cornlumbo, not being deterred. There is a knock on the door, and Shallot Holmes goes to investigate. On returning, he is carrying a crate containing a selection of citrus fruits and juices with a note attached:


Dear Detectives,

I have been producing organic fruit juice from my family’s estate and would like to bring the product to market. I have heard several declarations need to be made before I can sell my citrus juices wholesale, but I do not know what needs to be done. Can you please perform the relevant analysis on this trial batch so that I may try to sell it to some wholesalers – I do not want to fall at the first hurdle. If I can impress the buyers, I will need your assistance in setting up a large processing facility and getting all the equipment required to ensure the quality and consistency of my products.

I hear you’re the best in the business, and I trust you with the fruits of my labor.

Yours faithfully,

Marie-Clément Rodier


“Perform the analysis ourselves,” says Eggcule questioningly. Holmes agrees that it’s not how they usually work, but it could be rewarding if they are successful. “Well, it sounds very a-peel-ing to me,” says Cornlumbo as he reaches into the box to inspect its contents. Holmes asks the group if anyone knows what regulatory compliance issues they must address. Nancy Beef says the letter mentions the produce is organic, and they must comply with EU regulations regarding organic production and labeling; she then sets about researching the applicable laws. Miss Mapple says other labeling requirements, such as fat, carbohydrate, and protein content declaration, are necessary. Eggcule says that pesticide residues in food are also strictly regulated, which being organic, shouldn’t be a problem; however, they better analyze the juice to be sure. Having finished her research, Nancy tells the group that the concentration of essential oils is a quality measure with maximum limits set by authorities such as the European Fruit Juice Association and the United States Department of Agriculture. “Good work Nancy,” says Holmes, who reminds the detectives of previous fat determination and protein analysis cases they have worked on.

the concentration of essential oils is a quality measure with maximum limits set by authorities such as the EFJA and the USDA

From the corner of her eye, Miss Mapple can see Cornlumbo, who appears to be talking to one of the oranges in the container. “What on earth are you doing now, Cornlumbo?” she inquires. “I’m trying to learn Mandarin,” says Cornlumbo thinking he’s hilarious. To refocus the group’s attention, Holmes asks the detectives what factors influence the concentration of essential oils. Recalling Cornlumbos dreadful ‘a-peel-ing’ pun, Miss Mapple remembers that most essential oils are contained in the peels of the fruits; when they are squeezed for extraction, the oil from the peels enters the juice. If levels are too high in the juice, it may be because of the methods used to extract it. Eggcule points out that seasonal and geographic changes also affect the composition of essential oils, and Nancy mentions that a high concentration can have an irritant effect on the throat of the consumer; therefore, it is important to determine the amount for quality control and safety. “Excellent work detectives,” says Holmes who sets about devising the best means of performing the analysis. Cornlumbo, who is still staring at the orange juice, says, “I once thought I was turning orange; thankfully, it was just a pigment of my imagination”. Miss Mapple imagines squeezing lemon juice into Cornlumbos eyes before getting on with the task at hand. She joins Holmes, and together they devise a method for performing the analysis:

The Quantification of D-Limonene from Citrus Fruits by Distillation and Colorimetric Titration.


1. A solution of methyl orange in hydrochloric acid (HCl) is prepared and added to a receiving vessel.
2. A stock solution of potassium bromide (KBr) and potassium bromate (KBrO3) is prepared. This is further diluted to create the titrant solution.
3. A priming and preheating step is performed.
4. Blanks of distilled water and isopropyl alcohol are measured to set a reference for the titration.
5. Samples are prepared by distilling the juice sample along with isopropyl alcohol.

Colorimetric Titration

1. The distillate is collected in the receiving vessel and left to sit for a short while after distillation.
2. The distillate is then titrated with the KBr / KBrO3 solution.

The bromine reacts with the limonene molecules’ C-C double bonds during titration. When all the limonene molecules are saturated with bromine, the remaining bromine reacts with the methyl orange, causing a loss of red color that can be detected with a colorimetric sensor at a wavelength of 520 nm.

In addition to the d-limonene, which is detected by this method, other volatile compounds are also detected since they also have C-C double bonds that react in this method.


The amount of essential oil in the sample is calculated using the volumes of the titrant used for the sample and the blank and the sample volume.

Having completed the methodology, the detectives performed the distillation and titration and analyzed the results, which they compared to spiked reference samples. The detectives were happy with the results as they complied with the IFU 45 and AOAC 968.20 norms with low relative standard deviations (RSD) of < 2 %. All the citrus fruits had compliant levels of essential oils apart from the orange juice. The detectives couldn’t figure out what could have caused the high levels detected. Miss Mapple then noticed that Cornlumbo was still staring intently at the orange juice as if in a trance. “Are you still staring at that carton of orange juice?” asked Miss Mapple. “Yes,” replied Cornlumbo. “Why?” Miss Mapple inquired. “It says concentrate,” says Cornlumbo bursting into a fit of laughter. “Oh, you really are a complete twit,” says Miss Mapple before Shallot Holmes interjected, he looked at Cornlumbo and said, “It may be that you are not yourself luminous, but that you are a conductor of light. Some people without possessing genius have the remarkable power of stimulating it – the orange juice had been concentrated – and concentrated orange juice may contain elevated levels of essential oils if they were captured during the evaporation process and reintroduced to maintain the flavor profile.”

The results complied with the IFU 45 and AOAC 968.20 norms with low relative standard deviations (RSD) of < 2 %

The detectives proceeded to perform all the other analyses required for regulatory compliance. They passed on the results to the client so the necessary adjustments could be made to their juice-making process. The client was very happy with the analysis performed by the detectives and made the necessary changes to ensure his product was fully compliant and ready to be bought to market. A few days passed, and the detectives received some fantastic news – the client had secured a wholesaler for his citrus juices that would now be available nationwide. They also received a month’s supply of fruit juice and secured a job helping the client set up a huge processing facility so they could meet their quota. In celebration, Cornlumbo ran up to the box of fruit juices and was just about to speak when Miss Mapple said, “Don’t even think about saying something daft, or I’ll give you more than a fruit punch!” and with that, the detectives all fell about laughing and celebrating a job well done.