Can you eat old potatoes?

In this brief guide, we will answer the question, “Can you eat old potatoes?”. We will also elaborate on why it is not safe to eat old potatoes, the ways to prevent the sprouting of potatoes, and what are the food safety measures.

Can you eat old potatoes?

No, it is not allowed to eat old potatoes because of solanine production, a natural toxic material that gets accumulated on the skin of potatoes that is termed as the sprouting of potatoes. 

Solanine acts as the defensive system of potato, protecting it from various pests and diseases. Solanine exists in small quantities in and under potato peel. The allowable limit of solanine for safe consumption is 0.2 mg/g. However, when a potato is exposed to light, green granules appear on its skin called chlorophyll. If this greening coincides with sprouting, then increased levels of solanine (up to 1 mg/g) can be produced, causing poisoning (1).

This natural toxin behaves like a pesticide. So, the consumption of old potatoes can lead to the poisoning of solanine.

Sprouted potatoes

It looks so disgusting when we find potatoes sprouted in between the cooking of the meal. Potatoes are not always poisonous to health when they are sprouted. However, when sprouts are extended, it is a fair sign of high quantities of solanine (2). Along with sprouting, the texture also matters like if the potatoes still feel firm in texture on touching, then they are good to eat.

But if potatoes get wrinkled or their skin looks burnt and they shrink, then they are not good for eating. 

If the sprout occurred in a small area then you can separate that part of the potato but you must ensure that the rest of the potato has not gone too far, which means the best part is in good condition for consumption. Studies show that an increased concentration of solanine is present in metabolically active organs such as tuber sprouts (2).

Safety measures for potatoes

The nutrients of potatoes remain intact in a compact and small sprouted potato. The sprouting of potatoes follows a proper mechanism; it involves the transformation of the starch component into sugar that will nourish the new progeny of the potato which will grow from that sprouted part of the potato.

In the initial stage of sprouting, soft textured spots occur, around these soft spots eyes begin to form which then leads to sprouts. These sprouted parts or eyes should be removed easily from the potato with a paring knife and the best part could be used in any of the recipes.

Besides sprouting and increase in the solanine amount, many changes occur with long storage of potatoes, especially in higher temperatures. Tubers become softer and darker with the passage of storage time. Loss of some important chemical components such as ascorbic acid would constitute a loss in nutritional value (3).

What precautionary measures should be followed to avoid sprouting of potatoes?

To reduce the chances of sprouting, it is necessary to keep the potatoes in a dry, cool, and dark place. You should follow this step of storing if you want to keep your potatoes for a long time. It is also recommended to store potatoes far off from the onions that will delay the sprouting time. 

At the commercial level, they follow various precautionary measures to keep them safe from sprouting. A few simple suggestions could extend the shelf life of potatoes even from days to weeks or months.

Studies show that potatoes stored in the dark and at lower temperatures have increased dormancy period, that is, they begin to sprout later (4).

Some of the precautionary measures are described below:

• You should carefully choose the potato species if you want to harvest potatoes in a huge amount because some potatoes have a longer shelf life as compared to others.
• Heirloom is one of the best-considered varieties of potatoes that could stay longer as compared to other varieties of potato. 
• The potatoes are grown at the home level and then they are dried out which will also enhance the shelf life of potatoes. 
• Drying out the potatoes is the most important and simple step but if you skip this step then the potatoes will not stay as long as you want. 
• Natural compounds like mint essential oil or caraway and their volatiles have been described as environmentally friendly alternatives to inhibit sprouting (4)
• Avoid the use of transparent plastic bags for washed or brushed potatoes. Store tubers in the dark or pack them in black polythene (2).

How does sprouting affect the texture of potatoes? 

In the sprouted potatoes, the texture begins to get wrinkled along with the conversion of starch into sugar. The sprouted potatoes will have fewer nutrients as compared to fresh potatoes because many of their nutrients are busy nourishing the new progeny of potatoes. The protein profile also changes and shrinkage occurs due to loss of water (4).

So, it will be better to avoid eating the old potatoes because they will not be full of taste or appetizing.

Which type of toxins could be formed in old potatoes?

Solanine and chaconine are two types of toxins that are termed glycoalkaloids. These are also known as natural toxins which are found in plants of potatoes. These types of toxins are more concentrated in the eyes, skin, and sprouted parts of potatoes. They have antimicrobial, insecticidal and fungicidal properties which account for their activity against several insects, pests and herbivores (2).

This toxin can be dangerous to humans which can lead to headaches, many other digestive syndromes like vomiting. But if you remove these toxin-containing parts such as sprouts, eyes, and skin then it will eliminate all the effects of illness. 

Available information suggests that the susceptibility of humans to glycoalkaloid poisoning is both high and very variable: oral doses in the range 1–5mg kg−1 body weight are marginally to severely toxic, whereas 3–6mg kg−1 body weight can be lethal. Symptoms generally occur 8–12 h after ingestion, and include gastrointestinal disturbances and neurological disorders. Mild clinical symptoms of glycoalkaloid poisoning include headaches, dizziness, abdominal pain, nausea, vomiting, diarrhoea etc. Other neurological symptoms reported in patients are apathy, restlessness, drowsiness, mental confusion, rambling, incoherence, stupor, hallucinations, trembling and visual disturbances (2).

It is also recommended to peel out the green skin of potatoes before eating or using them for cooking a meal. Do take all these warnings regarding the green skin or sprouts of potatoes, as the green skin or sprouts can lead you towards sickness.

Processes such as boiling, freezing, frying and leaching potatoes can reduce the glycoalkaloid content, but they don’t eliminate it (2).

Other FAQs about Potatoes that you may be interested in.

Are raw potatoes bad for dogs?

Can potatoes cause constipation?

Can potatoes make electricity?

Can you live off of potatoes?

Conclusion 

In this brief guide, we have provided an answer to the question, “Can you eat old potatoes?”. We have also elaborated on why it is not safe to eat old potatoes, the ways to prevent the sprouting of potatoes, and what are the food safety measures.

References

1. Tavakoli, Maryam, and Mohsen Najafzadeh. Application of the image processing technique for separating sprouted potatoes in the sorting line. J App Environ Biol Sci, 2015, 4, 223-227. 
2. Nema, Prabhat K., et al. Potato glycoalkaloids: formation and strategies for mitigation. J Sci Food Agri, 2008, 88, 1869-1881.
3. 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.
4. Sonnewald, S., Sonnewald, U. Regulation of potato tuber sprouting. Planta , 2014, 239, 27–38.