by Disha Shantaram Shenai

Pineapples eating you!

This is based on a really old meme that has popped up quite a few times in my feed now.

The classic tongue itch that accompanies eating sweet pineapples is because of the enzyme Bromelain. I found this interesting and thought the edginess of pineapples, and bromelain needs more elaboration.

So, what is Bromelain and what are its sources?

How does it work and why do our tongues feel weird?

What are its current applications?

Let me try and break it down for you to my undergraduate level of understanding.

What is Bromelain?

Bromelain is in fact a group of digesting enzymes.

The name comes from the monocot plants of the family Bromeliaceae i.e., the Bromeliads which include the Pineapple (Ananas comosus). A crude extract from any part of the pineapple will contain bromelain, but the stem is the most preferred source followed by the fruit. Both these parts of the plant will produce slight variations of the enzyme combinations.

It contains a complex mixture of two major proteases along with small amounts of phosphatases, glucosidases, peroxidases, cellulases, escharases, glycoproteins, and carbohydrates along with several protease inhibitors.

How does it work?

Bromelain is a glycoprotein complex. The two proteases of bromelain are thiol-endopeptidases (hydrolases containing sulfhydryl group) – a type of plant cysteine proteases. They have cysteine residues in their active site in the form of a catalytic dyad or triad. These act like a nucleophile and attack the electrophilic groups on the substrate. The deprotonated thiol group then catalyzes the hydrolysis of the peptide bonds. The enzyme is acidic and functions optimally at neutral pH 7.

Current applications?

Here are some of the applications of bromelain:

Industrial:

  1. Meat tenderization: SDS-PAGE studies have shown that bromelain hydrolyses myosin and myofibrillar proteins in chicken, meat, fish etc.
  2. Baking industry: Bromelain allows dough relaxation by breaking down gluten which forms lattices in the bread which leads to shrinking of the dough. It also has been used in the production of hypoallergenic flour for people with gluten allergies.
  3. Protein hydrolysates: These substances have various uses as nitrogen sources in media for cell cultures, nutritional supplements, pharmaceutical agents, flavor enhancers, cosmetics, and beverages. They can be produced chemically with the help of acids and alkalis or enzymatically with the help of proteases like bromelain which add to their flavor as well as functional properties.  
  4. Anti-browning agent for fruits: Phenols and quinones in fruits get oxidized easily on exposure to air and interact with other substances leading to brown coloration. This worsens the quality and flavor of the fruits. Bromelain functions similarly to sulphites acting as reducing agents to prevent browning.
  5.  Animal feed additive: Proteases added to animal feed improve the protein availability thereby providing ample nitrogen sources in food.
  6. In textiles: It has been employed in softening of silkworm cocoons and in pre-treatment of silks and wools to increase dye uptake and maintain the tensile strength of the threads.
  7. For teeth: It can help with tooth whitening by preventing discoloration and can work as a dentifrice.
  8. Cosmetics: Bromelain as an active ingredient can help alleviate wrinkles, acne, and dryness of skin. It digests dead skin cells and brings out a new skin layer.

Clinical:

Bromelain gets easily absorbed by the gastrointestinal tract and functions optimally in the pH range 5.0-7.0. This also provides this enzyme complex with several clinical uses.

  1. As an anticoagulant: Bromelain shows fibrinolytic activity. It prevents clotting by breaking down active fibrin as it is instrumental in conversion of plasminogen to plasmin that degrades fibrin. This prevents cardiovascular complications like angina and ischemia by ensuring proper blood supply to the heart.
  2. Against arthritic pain: Bromelain can act as an analgesic (like several other non-steroidal anti-inflammatory drugs or NSAIDs) in adjunction to osteoarthritic therapeutics. Its anti-inflammatory properties help to alleviate oedema and pain by regulating the expression of transforming growth factor TGF-beta which plays a role in inflammation during arthritis.
  3. Immunomodulation: It can regulate lymphocyte migration to the site of infection. It also activates natural killer cells, enhances the production of IL-2 and IL-6, and decreases T-cell activation.
  4. Prevents diarrhea: Bromelain shows an antimicrobial property as an anti-adhesion agent. It modifies the receptors for various bacterial enterotoxins from microbes like Escherichia coli and Vibrio cholerae. Some in vitro studies also suggest anthelminthic properties.
  5. Antitumor properties: It selectively brings about apoptosis of tumor cells by upregulating expression of p53 and the mitochondrial apoptotic pathway. It also is known to prevent metastasis and angiogenesis.
  6. Helps during labor: Studies have shown that pineapples during labor may aid uterine contractions by a mechanism similar to acetylcholine.   
  7. COVID-19: The SARS-CoV-2 uses ACE2 (Angiotensin Converting Enzyme 2) receptors in the cell membrane for entry into the cell. The viral entry also requires the priming of spike protein (cleavage of S1 and S2 subunits of the viral S protein) in the receptor binding domain of the virus with TMPRSS2 (Transmembrane protease serine 2) receptors on the host cell surface. This ensures better binding of the receptor. Bromelain treatment was found to be capable of decreasing the expression of ACE2 and TMPRSS2 receptors on the host cell surface. This prevents viral entry and chances of infection.  

References:

15th July 2021