1. Why does your tongue tingle when you eat fresh pineapple?
If you eat too much fresh pineapple, your tongue and lips might feel prickly or sore. Many sources explain that this happens because bromelain, an enzyme found in pineapple, breaks down proteins in your mouth, such as mucus [8]. Bromelain is officially registered as a protein-breaking enzyme found most abundantly in the stem of the pineapple [1]. While the fruit also contains bromelain, it is distinguished as a different enzyme from the one in the stem [1].
However, it is not clear exactly how much of the tingling sensation is caused by the enzyme alone. Some theories suggest that needle-like crystals in the fruit might work together with the enzyme to cause the irritation. To understand how well bromelain breaks down proteins, we can look at a simple experiment done by a student.
2. How did raw and canned fruit change gelatin jelly in one hour?
In a study presented at the Tokyo Children’s Science Exhibition, a 6th-grade student placed fruit on gelatin jelly and tilted the dish to record changes [2]. When raw pineapple and green kiwi were used, the fruit slid across the jelly after 5 minutes, developed dents after 30 minutes, and about half of it turned into liquid after 60 minutes [2]. In contrast, jelly topped with canned fruit, 100% juice, or grapes showed no changes in this experiment [2]. Golden kiwi also showed little change, except for slight melting after 30 minutes [2].
Since the main ingredient in gelatin is protein, the student concluded that protein-breaking enzymes in the raw fruit were at work [2]. The student thought that golden kiwi apparently contains fewer of these enzymes than green kiwi, resulting in different effects on the jelly [2]. It is important to note that this was a single experiment by one student, so it is not a general law. The "softness" was recorded by sight and touch. Whether heat is the key difference between raw and canned fruit cannot be determined from this experiment alone.
3. How does heat affect bromelain when fruit is used to tenderize meat?
The same student also tested how fruit purees affect pork. After leaving the meat at room temperature for 30 minutes, raw pineapple and green kiwi made the meat the most tender [2]. The study notes that enzymes are weak against high heat and work slowly at low temperatures, like in a refrigerator [2]. The student reasoned that if pineapple is added at the end of cooking, the heat does not destroy the enzyme, but it still takes about 30 minutes for the meat to become tender [2]. The link between heat and the lack of change in canned fruit cannot be fully determined from this experiment alone.
It is often said that bromelain is destroyed above 60°C (140°F). However, commercial bromelain from pineapple stems shows maximum activity at 60°C and a pH near 7 [3]. This means 60°C is the temperature where it works best, not where it breaks down. It is said to be weak against high heat, but the information here does not show the exact temperature at which it breaks down. So, what is the purpose of this enzyme for the pineapple itself?
4. Do enzymes and needle-shaped crystals help protect plants from insects and mold?
In 2014, a research team reported an experiment using kiwi. They combined raphides (needle-shaped calcium oxalate crystals) with cysteine proteases (protein-breaking enzymes) and gave them to silkworm larvae [4]. When both were present, the larvae’s growth was suppressed much more strongly, and the death rate increased compared to when they were used alone [4]. Calcium oxalate that was not needle-shaped did not have this effect [4].
The paper mentions that pineapple also contains raphides and the cysteine protease bromelain [4]. However, the experiment tested kiwi and silkworms, not human tongues. Another study reported that bromelain from pineapple stems can inhibit the growth of fungi that cause plant diseases [5]. This result was also from a test tube experiment. These findings suggest that bromelain may be part of the pineapple’s defense against insects and mold, but there is no proof that it evolved specifically for this purpose. How do people use this enzyme?
5. How is bromelain from the pineapple stem used in food and medicine?
Bromelain is found in both the stem and fruit of the pineapple. Because the stem is easy to extract after harvest, commercial bromelain is often made from the stem [6]. It is commonly used as a powder to tenderize meat [6].
In December 2012, the European Medicines Agency (EMA) approved a concentrated bromelain from pineapple stems, called NexoBrid, as a medicine to remove dead tissue (eschar) from burns [7]. This medicine is used by medical professionals and is left on the skin for 4 hours [7]. It is not a home remedy, and you should not apply raw pineapple to your skin for this purpose. In a main trial with 156 hospitalized patients, wounds that required surgical removal of dead tissue were about 15% (16 out of 106 sites) in the NexoBrid group, compared to about 63% (55 out of 88 sites) in the standard treatment group [7]. The enzyme in pineapple that can make your tongue tingle can also help reduce the need for surgery in hospitals.
6. How can you try the pineapple and jelly experiment yourself?
You can try an experiment with an adult. Make jelly using gelatin (since hot water is used, do this with a parent or guardian). Once it sets, place raw pineapple and canned pineapple on top. Gently tilt the dish every 30 minutes and record what happens. Do not eat the jelly you observed; throw it away. (Remove this repeated sentence.)
If you want to read more, the Tokyo Children’s Science Exhibition materials contain the original student experiment [2]. The EMA page for NexoBrid provides details on its approval as a burn medicine [7]. These are English-language resources.