Enzyme Activity in Vegetables
Enzymes are large protein molecules in fruits and vegetables that promote chemical reactions, such as ripening, and can affect the quality of your product. Enzyme activity speeds up the breakdown of foods, which leads to the deterioration of food quality. The activity of enzymes is specific for the actual type of enzyme and is dependent on both pH and temperature. Enzyme activity affects the quality of your product and leads to a loss of nutrients and changes in color, texture, and flavor.
Freezing does not stop enzyme activity; only blanching inactivates enzymes in vegetables.
Blanching Vegetables
Blanching is the process of quickly exposing vegetables to either boiling water or steam for a specified amount of time, and then rapidly cooling. It is not required from a food safety standpoint; however, it will affect the quality of frozen vegetables.
- Destroys microorganisms on the surface of vegetables.
- Softens the vegetable, brightens color, and slows the loss of vitamins.
- Inactivates enzymes which can lead to loss of flavor, color, and texture in frozen produce.
Steps for Blanching Vegetables
- Use 1 gallon of boiling water per 1 pound of prepared vegetables.
- Place vegetable in a blanching basket and lower into vigorously boiling water. Place a lid on the kettle.
- The water should return to boiling within 1 minute. If water does not return to a boil within 1 minute, too many vegetables are being used for the amount of boiling water.
- Begin counting blanching time as soon as water returns to a boil.
- Keep heat on high during the indicated blanching time.
Vegetable Blanching Times
| Vegetable | Time in Minutes |
|---|---|
| Artichoke – Globe (Hearts) | 7 minutes |
| Artichoke – Jerusalem 3 | 3 to 5 minutes |
| Asparagus: Small Stalk | 2 minutes |
| Asparagus: Medium Stalk | 3 minutes |
| Asparagus: Large Stalk | 4 minutes |
| Beans (Snap, Green or Waxed) | 3 minutes |
| Beans (Lima, Butter or Pinto): Small | 2 minutes |
| Beans (Lima, Butter or Pinto): Medium | 3 minutes |
| Beans (Lima, Butter or Pinto): Large | 4 minutes |
| Broccoli Flowerets (1-½ inches across) | 3 minutes |
| Broccoli: Steamed | 5 minutes |
| Cauliflower Flowerets (1 inch across) | 3 minutes |
| Cauliflower: Steamed | 5 minutes |
| Carrots: Small | 5 minutes |
| Carrots: Diced, Sliced, or Lengthwise | 5 minutes |
| Celery | 3 minutes |
| Collard Greens | 3 minutes |
| Greens, All Other | 2 minutes |
| Corn on Cob: Small Ears | 7 minutes |
| Corn on Cob: Medium Ears | 9 minutes |
| Corn on Cob: Large Ears | 11 minutes |
| Corn, Whole Kernel or Cream Style (Ears blanched before cutting corn from cob) | 4 minutes |
| Peas, Edible Pod | 2 to 3 minutes |
| Peas, Field (Black-eyed) | 2 minutes |
| Peas, Green | 1.5 to 2.5 minutes |