Why does pineapple spoil jello?

Pineapple is a fruit with which there is no middle ground: either you love it or you don’t like it; few are indifferent. Those people who like it use it in all kinds of culinary preparations, both sweet and salty. However, there is one dessert in which fresh pineapple cannot be used: gelatin.

In this article we will see why this happens. We will study what makes the gelatin set, and what it is about fresh pineapple that prevents this process from happening.

What is gelatin?

Gelatin is nothing more than a special type of animal protein called collagen. This protein is an important component in our skin, cartilage, tendons and other connective tissues that are part of our body. In the case of unflavored gelatin that is used both in confectionery and in many savory dishes, the gelatin powder or transparent sheet consists almost exclusively of collagen (more than 90%), plus some mineral salts that are in proportion very low. These presentations are used to prepare jellies and other foods with flavorings or natural ingredients.

On the other hand, flavored gelatin mixes that are sold ready-to-make contain mainly sugar, food coloring, flavoring, stabilizers and, of course, collagen.

Why does gelatin curdle?

Collagen is a fibrous protein that is made up of very long fibers that are soluble in hot water. However, upon cooling below 18°C, the collagen fibers or molecules begin to precipitate out of solution. However, instead of sticking together to form solid crystalline structures like many other solutes do, collagen fibers carry with them thousands of water molecules that stick to the surface of each fiber.

After a while, a network of hydrated fibers has been formed in which the water is trapped and cannot move freely. This is what causes the solution to lose its normal fluidity below a certain temperature. However, heating the curdled gelatin rapidly dissolves the collagen molecules again, and the original solution is recovered.

Why won’t fresh pineapple let the gelatin set?

Anyone who has ever made naturally flavored gelatin has likely experienced the disappointment of finding out the next day that their gelatin did not set. The reason why this happens is very simple.

Like many other fruits, pineapple juice contains a large amount of essential nutrients, as well as vitamins, sugars and more. However, apart from these substances, pineapple also contains an enzyme whose job is to catalyze the breakdown of other proteins. These types of enzymes are called proteases, and in the particular case of pineapple this protease is called bromelain.

Bromelain is capable of breaking down many other proteins, including the collagen from which gelatins are made. By destroying collagen, pineapple bromelain prevents the formation of the network of hydrated fibers that gives curd gelatin its structure.

Bromelain in pineapple can be deactivated

Despite what has been said so far, it is possible to prepare pineapple jelly. To achieve this, we must prevent bromelain from attacking collagen, and the easiest way to do this is to deactivate it. Deactivation can easily be accomplished by heating or cooking the pineapple for a set amount of time, as heat is capable of inactivating and denaturing most enzymes.

What this implies is that the pineapple can be used in the kitchen along with the gelatin, but only if it has been cooked first. In other words, you cannot make pineapple jelly using fresh pineapple.

Other fruits that present the same problem as pineapple

Pineapple is not the only fruit whose enzymes are capable of breaking down collagen, thus preventing gelatin from setting. This includes, but is not limited to:

• The papaya or lechoza, which contains papain.
• Kiwi, which contains actinidin.
• Figs, which contain ficin, also called ficain.

References

Belpois, J. (2013, March 6). Fruits that can ruin your jelly . cooking-easy.com. https://micocina-facil.com/frutas-que-puedan-arruinar-su-gelatina.php

Gelatin and a piece of pineapple serve to demonstrate enzyme catalysis . (2018, November 18). unusual chemistry. https://quimins.wordpress.com/2018/11/18/pina-qelatina-demostrar-catalisis-enzimtica/

Jacobsen, E. (1999, May 1). Soup or Salad? Investigating the Action of Enzymes in Fruit on Gelatin . J. Chem. Educ. 76 (5). https://pubs.acs.org/doi/10.1021/ed076p624A

Mollejo, V. (2021, October 15). The unique enzyme in pineapple that is able to prevent blood clots . feed.elconfidencial.com. https://www.alimente.elconfidencial.com/bienestar/2021-10-15/bromelina-enzima-pina-evita-coagulos_1824874/