Blackening of frozen potatoes

Dear All,

 

We are frozen food manufacturing unit in India. We have recently manufactured frozen diced potatoes. But after freezing we encountered an issue of potatoes getting blackened. The steps we followed in the process is as follows;

 

1. Mud Washing 

2. Skin Pealing ( Machine peeling)

3. Dicing ( 20mm cubes - Machine cutting )

4. Washing in RO Water - to remove starch

5. Hot water blanching & Cooling 

6. Packing ( as per customer spec.)

 

From internet I found out that if we add white vinegar / lemon juice ( something acidic) during the 3rd stage, we an avoid the blackening of the potatoes. 

Is it trues if so how much quantities can be added. 

 

 

Dear Sawad,

 

You have to avoid/ minimize your diced potato's exposure to oxygen/contact with air.

 

Just revisit your processing steps to apply this principle as suits to you. 

Thank you, As soon as peeling is finished it is transferred to water.

In the food science world, it is called enzymatic browning or greying effect.

Keep it in water to prevent it from oxidation. This is cheaper.

 

Adding any kind of preservatives (e.g., ascorbic acid, vinegar...) is an added cost and may not have ROI. 

I would recommend the following experiments, so you find the correct solution for your problem: 
Experiment 1: treat potato's before peeling (50-55 C) in hot water for 10-15 minutes. See the impact on the color of your peeled potato? 

Experiment 2: Peel it and submerge it in water until the next step in cold water. See how long it maintains its color. 

Experiment 3: Automate the next step just after peeling. Or simply speaking, CUT the wait time between peeling and the next step. 
Experiment 4: add a cover so it limits the outside air to the peeled potato's. See how it impacts the color and for how long it maintains the color? 

_______________________
Sayed M Naim Khalid
FSQA Professional

There are lots of reasons for blackening of potatoes. If they’ve been cooked, non enzymes browning is unlikely to be it. Two other options I’d look at are bruising and sudden temperature changes.

Bruising can happen in your process, I have no idea on the cost but you can get an “electronic potato” to measure impact on your lines but most potato processors have thick plastic curtains around their conveyors and / or convey using water. Be aware that bruising may not be visible fully before the potato is cooked.

Secondly, I forget the chemical which causes it but storage pre cooking is normally recommended to be about 10oC but considering ambient temperatures you may need to bring this down gradually as shocking on temperature is also a cause of blackening. Don’t be tempted to store them colder either. If you can temper slowly before cooking that will also help and don’t just go straight into blast freeze. Ideally cool gently after cooking if you can then freeze.

Yes potatoes that have been partially cooked and frozen can turn grey/black.  I to work for a potato company.  After the raw material has been blanched to remove starches and stop enzyme production the raw material goes through a flume where we add Sodium Acid Pyrophosphate which will eliminate the discoloring issue. any discoloration that you find there after is usually caused by bruising or defect of the raw material.