by Amanda Linke
The first time I saw a picture of a pineapple plant growing a fruit I thought the picture was fake. It looked like someone put a pineapple on a stick and stuck it in the ground next to another plant. Remarkably, this is how pineapple fruit grows. Pineapple fruit starts as a flower cluster which can take 6 months to mature, and a pineapple plant can fruit up to three times before the plant dies.
That’s not the only strangely interesting thing about pineapple. You can grow a new plant from just the pineapple fruit top (as you can see from the pictures of my own pineapple plant!
Pineapple is part of the Bromeliaceae family, along with air plants and bromelia, which are popular houseplants. Pineapples are grown in tropical climates like India, Thailand, the Philippines, and Costa Rica. From the 1950s to 1980s Hawaii was a key area of pineapple growing and canning, so much so that working in a canning factory became part of Hawaiian culture. Many Hawaiians share stories of working summers in the factory as teens, making enough money for the whole year over the summer, and coming home smelling of pineapple. However, many also have stories of developing rashes, painful itching, and strategies of wearing multiple layers of Vaseline, baby powder, and socks under their thick rubber gloves to protect their skin from pineapple juice (below). They had to do this because, most strangely of all, when you eat a pineapple, the pineapple is also eating you.
Pineapple is a unique fruit because it has bromelain. Bromelain is a protease, which is a protein that digests other proteins. Proteins are made up of a combination of 20 amino acids, and a protein’s unique combination of amino acids gives them different properties. Bromelain can digest proteins into smaller pieces in specific places by using a cysteine molecule (one of the 20 amino acids). This makes bromelain a cysteine protease. There are other proteases which cut proteins using different amino acids: for example, serine proteases cut with a serine residue, while threonine proteases cut with a threonine residue. This property makes bromelain great as a meat tenderizer and is thought to help digestion, as the bromelain breaks up the proteins in the meat to make it softer. However, bromelain does not work forever – it can be denatured (lose activity) by heat. Cooking pineapple causes the intricate protein structure of bromelain to break down. In biology, structure equals function, so if a protein loses its structure, it also loses its function. This is why canned pineapple doesn’t sting your mouth: the pineapple is cooked as part of the canning process which denatures the bromelain. This is also why canned pineapple must be used for jello and jam. Bromelain would break down the gelatin, the protein which causes jello to set, leaving it runny or even liquifying set jello.
Proteases are not just used in nature; they are also important tools used almost every day in biology laboratories. Many researchers perform experiments on human or animal cells grown in plastic dishes. These cells grab onto the plastic with proteins to prevent themselves from floating away in the liquid growth medium. However, researchers need to unstick the cells before they can be used for experiments. How do you do this without killing the cells? Proteases! Researchers will use trypsin, a serine protease that is also found in your gut, to cut the proteins anchoring the cells to the plastic plate without killing the cells. This technique is an important step that is used every day in biology labs and allows researchers to study cells outside of a living model organism.
Proteases are used widely in nature and in labs. Proteases are in all the cells in your body, helping break down cellular waste and being excreted in your digestive system, where they help you break down your food. Proteases are found in fruits like pineapple, figs, kiwi, and papaya. And proteases are even used in labs to support experiments and new discoveries.
