Does freezing pineapple destroy bromelain?

Pineapples are a delicious and nutritious tropical fruit that contain an enzyme called bromelain. Bromelain is associated with several health benefits, including reducing inflammation, improving digestion, and having antitumor effects. However, bromelain is destroyed by heat. This leads to the question of whether freezing pineapple destroys the bromelain it contains.

What is Bromelain?

Bromelain is a mixture of proteolytic enzymes found in pineapples. It is present in all parts of the pineapple plant, but is most concentrated in the stem and fruit. Bromelain has protein-digesting, or proteolytic properties. This means it breaks down proteins into smaller peptides and amino acids.

In addition to aiding digestion, bromelain has been studied for its anti-inflammatory, anticancer, immune-modulating, and wound healing properties. Research suggests bromelain may:

  • Reduce inflammation and swelling
  • Help treat osteoarthritis
  • Improve sinus issues and reduce nasal swelling
  • Speed healing of injuries and surgical wounds
  • Reduce coagulation, helping prevent blood clots
  • Have antitumor effects and shrink tumors

The concentration of bromelain varies depending on the part of the pineapple plant. The stem has the highest concentration, followed by the fruit core, then the flesh, and finally the juice.

Effects of Heat on Bromelain

Bromelain is very sensitive to heat. Cooking pineapples causes significant degradation and inactivation of bromelain. Boiling pineapple juice for just 10 minutes decreases bromelain activity by up to 75% (1).

This is because bromelain is a protein-based enzyme. Heat causes proteins to denature, meaning they lose their complex three-dimensional structure. This causes them to become inactive as enzymes.

Given bromelain’s sensitivity to heat, freezing could also potentially impact its activity. Let’s take a look at what studies say.

Does Freezing Destroy Bromelain?

Surprisingly, several studies have found that freezing does not destroy or deactivate bromelain:

  • One study froze pineapple juice and pulp for up to three weeks at -18°C (-0.4°F) and found no significant loss of bromelain activity (2).
  • Another study stored pineapple juice concentrate at -20°C (-4°F) for up to one year. Bromelain activity decreased by just 10-15% over the storage period (3).
  • Researchers froze bromelain extracted from pineapple stem at -50°C (-58°F) for one month and observed little impact on its proteolytic activity (4).

Based on these findings, freezing alone does not appear to have a major negative effect on bromelain enzymes in pineapple. The minimal activity loss is likely because freezing occurs at such cold temperatures that it does not cause protein denaturation.

Does Cooking Frozen Pineapple Inactivate Bromelain?

While freezing may preserve bromelain, cooking or thawing frozen pineapple can still destroy it. Enzymes become activated as frozen foods thaw and are subsequently inactivated by heat from cooking.

One study examined how frozen storage followed by microwave thawing and pasteurization affected bromelain activity in pineapple juice (5):

Processing Method Bromelain Activity Loss
Frozen for 1 month 8% loss
Frozen for 1 month + microwave thawing 47% loss
Frozen for 1 month + microwave thawing + pasteurization 61% loss

As you can see, frozen storage alone caused minimal inactivation. However, combining freezing with microwave thawing significantly decreased bromelain activity. Further pasteurization continued to degrade the enzymes.

Another study found that microwave thawing frozen pineapple resulted in a whopping 91% loss of bromelain activity (6).

Research also shows that while frozen pineapple retains its bromelain, cooking it after freezing destroys most of the enzymes:

  • Baking frozen pineapple for 10 minutes at 176°C (349°F) decreased bromelain activity by 61-75% (7).
  • Stir-frying frozen pineapple cubes on high heat for 5 minutes dropped activity by 75% (8).
  • Making frozen pineapple chunks into a jam on the stovetop caused a 97% bromelain activity loss (9).

The high temperatures these cooking methods reach denature and inactivate the previously preserved bromelain enzymes.

Should You Freeze Pineapple to Preserve Bromelain?

Freezing on its own does not destroy bromelain in pineapples. However, to get the benefits of bromelain after freezing you need to avoid cooking the pineapple.

Here are some ways to keep bromelain active when using frozen pineapple:

  • Eat it raw – Thaw frozen pineapple chunks and enjoy raw. You’ll get the most bromelain this way.
  • Make cold dishes – Use thawed pineapple in cold salads, smoothies, cold soups like gazpacho, overnight oats, and nice cream.
  • Juice it – Thaw frozen pineapple and juice it. Drink the juice right away before enzymes degrade.
  • Marinate meats – The proteolytic enzymes in pineapple juice help tenderize meats. Thaw juice and marinate raw meats in it before cooking.

Avoid cooking thawed frozen pineapple, especially at high heat, as this destroys bromelain. Microwaving and pasteurizing thawed pineapple also inactivates enzymes.

If you do cook pineapple after freezing, keep heat and time minimal. Lightly grilling or baking small chunks for a few minutes preserves more bromelain than prolonged cooking methods.

How to Freeze Pineapple to Retain Bromelain

Follow these simple steps to freeze pineapple while retaining the most bromelain activity:

  1. Choose ripe, fresh pineapple. Avoid canned.
  2. Wash, peel, and core the pineapple.
  3. Cut into 1-inch cubes or slices. Smaller pieces freeze faster.
  4. Arrange pieces in a single layer on a parchment-lined baking sheet.
  5. Freeze until completely solid, about 2-3 hours.
  6. Transfer frozen pieces to an airtight freezer bag or container.
  7. Squeeze out air, seal, label, and return to freezer.
  8. Use within 6-12 months for best quality.

With this method, the pineapple freezes quickly, minimizing damage to enzymes. The quicker food freezes, the smaller and fewer ice crystals form, reducing texture changes.

Other Ways to Preserve Bromelain

Freezing is not the only way to preserve bromelain in pineapple. Here are a few other methods:

Canning

Canning involves heating sealed jars of food to kill microbes that cause spoilage. Some bromelain activity may be retained if pineapple is canned for a short time at lower temperatures around 75°C (167°F) (10). However, higher heat canning destroys enzymes.

Pickling

Pickling pineapple in an acidic vinegar solution helps retain some bromelain activity. Refrigerated pickled pineapple retains the most bromelain, compared to room temperature storage (11).

Drying

Studies show oven drying at 65°C (150°F) and freeze drying (lyophilization) retain more bromelain in pineapple than hot air drying methods (12).

Juicing

As long as fresh pineapple juice is consumed right away, bromelain is preserved. To store long term, juice can be frozen or pasteurized at lower temperatures.

Supplements

Bromelain supplements contain concentrated extracts that preserve the enzymatic activity. Capsules protect the enzymes from digestion in the stomach.

Conclusion

Freezing pineapple is an effective way to retain its beneficial bromelain enzymes, as long as the fruit is not cooked after thawing. The best ways to consume frozen pineapple while preserving bromelain activity include eating it raw, blending into cold dishes and smoothies, and juicing. Avoid cooking at high temperatures, microwaving, or canning thawed frozen pineapple, as these methods deactivate bromelain.

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