How to preserve Vitamin C in potatoes

In the brief guide, we are going to answer the question “how to preserve Vitamin C in potatoes? ” and discuss the different techniques of preserving Vitamin C in potatoes during cooking and storage. 

How to preserve Vitamin C in potatoes

Cooking techniques such as steaming, microwaving, baking and boiling are known to preserve the content of Vitamin C in potatoes. Vitamin C in potatoes can be preserved during storage by using the optimum storage temperatures and conditions. A study showed that the vitamin C concentrations did not significantly decrease during cooking of potatoes, unless they were overcooked, that is, if potatoes were baked for an additional 15 minutes after being cooked. Cooking methods tested were microwaving, baking, boiling and stir-frying. One report suggested losses during boiling are due to leaching, not thermal degradation, or that the loss of potato vitamin C during several types of cooking was due to enzymatic degradation, not thermal (1).

Freshly harvested potatoes have a high content of Vitamin C. The content of Vitamin C reduces over time and the degree of reduction depends on the storage conditions and the cooking methods. Studies reveal that length of storage period is the single major factor in determining vitamin C concentration in fresh tubers (3).

Potatoes are currently grown on an estimated 19 million hectares of farmland globally, and the potato production worldwide stands at 378 million tons. China became the world’s largest potato producer in 1993 and currently accounts for almost one quarter of global potato production and about 28% of total cultivated areas (2).

How to preserve Vitamin C in potatoes during cooking

Vitamin C is water-soluble and heat sensitive. Vitamin C in potatoes can be preserved by reducing the amount of water and cooking time. Cooking techniques that use a minimal amount of water and low cooking times are best for preserving the Vitamin C content. Food preparation methods that maintain tuber skin intact, minimize shredding or cutting, utilize limited water, and/or involve reduced cooking times or temperatures appear to result in greater vitamin C retention (3).

Cooking techniques to preserve Vitamin C in potatoes

Steaming 

Steaming is generally one of the best cooking techniques to preserve the Vitamin C content of potatoes.

During steaming, food is kept separate from water so that Vitamin C remains in the potatoes without leaching into the water. Since potato is a hard vegetable, slicing before steaming will reduce the cooking time and retain more Vitamin C. Care must be taken not to slice into very small pieces as this exposes more surface area, causing more nutrients to be lost (3).

Microwaving 

Microwaving is also suitable for preserving the Vitamin C content of potatoes as it uses a minimal amount of water and has a short cooking time, so the Vitamin C content is preserved. However, studies showed that microwaving potatoes led to higher losses of vitamin C than steaming (4).

Baking

Baking involves the use of dry heat to cook. Since baking does not use water, the loss of Vitamin C into water is reduced. However, high temperatures and long cooking times may break down the Vitamin C content as well as other nutrients and minerals (2). Studies show that dry cooked potatoes retain higher levels of vitamin C than do wet cooked potatoes, probably because of vitamin C leaching during cooking in water (4). 

Boiling 

Boiling reduces the content of Vitamin C more than any other cooking technique. This is due to the leaching out of Vitamin C when potatoes are submerged in hot water (4).

Potatoes must be boiled using the minimum amount of water. The water remaining after boiling can be reused to produce a soup or stew. This will enable the use of the nutrients that were transferred to the water from the potatoes.

Boiling whole potatoes, leaving the skin-on will reduce the loss of Vitamin C due to leaching but it will also increase the cooking time (3).

Stir-frying and deep-frying

Stir-frying involves using a small amount of oil and a high temperature while deep-frying involves high temperatures as well as a large amount of oil. During both stir-frying and deep-frying, the absorption of oils and high temperature reduces the amount of Vitamin C. 

A study comparing different cooking methods for potatoes showed that there was a great loss of vitamin C after air-frying, frying in oil, and stir-frying: 90.42, 83.35, and 55.5%, respectively (4).

Overall, frying is not a good option for cooking if the Vitamin C content needs to be preserved.

How to preserve Vitamin C in cooked potatoes

Semi-processed and cooked potatoes can be frozen for later use. However, it is best to consume any potatoes within two days after cooking, as exposure to air may reduce the Vitamin C content.

Precooked products can be stored under a variety of conditions, unlike storing fresh potatoes where options are limited. Research studies show that storing potatoes as processed products may not provide a significant advantage in vitamin C preservation over storing fresh tubers. Frozen baked potatoes, stored for only 1 week at −20°C, declined from 5.8 to 4.8 mg/100 g (3).

Using the optimum storage temperature 

According to a research, 90 % of the Vitamin C content can be preserved for four months if the potatoes are stored in cool temperatures. Potatoes stored in warm temperatures lose around 20 % of their Vitamin C content within a month.

The decrease was more rapid at higher temperatures. For instance, it decreased from 3800 to 3100 mg/100 g in potatoes stored a t 20°C after 35 d, whereas storage at 4°C reduced the vitamin C to only 3400 mg/100 g even after 133 d (5).

It is best to store raw potatoes slightly above refrigeration temperature. Raw potatoes must never be stored in the freezer or fridge as low temperatures may cause the formation reducing sugars. Lower temperatures of storage favores conversion of starch to reducing sugars, which has been linked to induce undesirable color changes in fried potatoes (5).

Proper ventilation and lightning

Potatoes must be stored in an area with good ventilation and must not be kept in sealed bags or boxes. Potatoes must be stored away from direct sunlight and fluorescent light to prevent the production of the toxic chemical named solanine (2).

How to preserve Vitamin C in potatoes during cleaning

Potatoes must not be soaked in water. Loss of nutrients such as Vitamin C can be minimized by scrubbing off the loose soil and dirt under cool, running water and using a paper towel to pat dry the washed potatoes. Food preparation methods that maintain tuber skin intact, minimize shredding or cutting, utilize limited water, and/ or involve reduced cooking times or temperatures appear to result in greater vitamin C retention (3).

Potato skins and Vitamin C

Most of the nutrients of potatoes, including Vitamin C, are found on the potato skin. Including potato skin on the diet will greatly increase the Vitamin C intake. 

Care must be taken to ensure that the potatoes are pesticide-free before consuming the potato skin. Rinsing with a salt and vinegar solution at 10 % concentration is effective in removing pesticide residue. In a study, potatoes were washed for 10 min in tap water, an acid solution (5 or 10% solutions of an aqueous extract of radish leaves, acetic acid, citric acid, ascorbic acid or H2O2), a neutral solution (5 or 10% NaCl) or an alkaline solution (5 or 10% NaHCO3). Acidic solutions were found to be more effective for extraction of organochlorine pesticides from potatoes than the other washing solutions used (7).

Another option is to purchase pesticide-free, organic potatoes.

Skin-on potatoes can be prepared by any cooking technique including baking, microwaving, boiling and frying.

Other FAQs about Potatoes that you may be interested in.

Can you eat moldy potatoes?

Is sweet potato bad for you?

How to store potatoes in the fridge?

What can I substitute for potato starch?

Conclusion

In this brief guide, we answered the question “How to preserve Vitamin C in potatoes?” and discussed the different methods of preserving Vitamin C in potatoes during cooking and storage. We also discussed the best methods for cleaning potatoes and consuming potato skin.

References 

1. Campos, Hugo, and Oscar Ortiz. The potato crop: its agricultural, nutritional and social contribution to humankind. Springer Nature, 2020. 
2. Navarre, Duroy A., et al. The effect of different cooking methods on phenolics and vitamin C in developmentally young potato tubers. Am J Potato Res, 2010, 87, 350-359.  
3. Love, S. L., and J. J. Pavek. Positioning the potato as a primary food source of vitamin C. Am J Potato Res, 2008, 85, 277-285. 
4. Jayanty, S.S., Diganta, K. & Raven, B. Effects of Cooking Methods on Nutritional Content in Potato Tubers. Am. J. Potato Res. 2019, 96, 183–194.  
5. Nourian, F., H. S. Ramaswamy, and A. C. Kushalappa. Kinetics of quality change associated with potatoes stored at different temperatures. LWT-Food Sci Technol, 2003, 36, 49-65.
6. Pinhero, Reena Grittle, Robert Coffin, and Rickey Y. Yada. Post-harvest storage of potatoes. Advances in potato chemistry and technology. Academic press, 2009. 339-370.  
7. Bajwa U, Sandhu KS. Effect of handling and processing on pesticide residues in food- a review. J Food Sci Technol. 2014, 51, 201-220.