Ever wondered why the walnuts taste bitter only a few days after buying them? Do you ever wonder why the bag of potato chips has more air than the amount of chips in it? The bitter taste in the walnuts is due to a bio chemical process ‘ called rancidity and potato chips are packed with nitrogen air to prevent ‘rancidity’. Read this article to know more about rancidity and products prone to rancidity. It also gives tips how end users or consumers can avoid rancidity by handling food products properly.
What is Rancidity?
Rancidity could be defined as the development of undesirable odour and flavour in the food items due to the deterioration (breakdown) of fat or oil present in the food item.
Types of Rancidity
Rancidity can occur due to three reasons- Contact of fat in the food with air, moisture or microbes. Based on this, the spoilage/breakdown is of three types-
- When the fat compounds in the food particles react with the oxygen in the air, it leads to oxidization of the fat molecules present in the food item. This is known as oxidative It is usually seen in the meat products, walnuts and flaxseeds. The rate of this process increases in the presence of heat and light.
- When the fat molecules come in contact with the moisture, it leads to the breakdown of fatty compounds due to addition of water. This is known as hydrolytic rancidity. The off flavour in the butter is due to the hydrolytic rancidity.
- When the fat particle come in contact with bacteria and moulds with the fat molecules leading rancidity o the breakdown of fat molecules. This is known as microbial/ketonic. It is often observed in butter, coconut, kernel oil etc.
What are the effects on our health of consuming rancid food products?
Rancid products have an altered taste and odour. This makes them less palatable and unacceptable. Consuming them wouldn’t cause a disease in the short run. Although, eating rancid products has been associated with accelerated aging, tissue damage and development of cancer diabetes and Alzheimer’s disease in the long run. This is because of the free radicals present in the rancid oils. Rancidity also reduces the nutritional value of the food product. It can reduce the availability of the Vitamin A and E present in the food product.
Which food items prone to rancidity?
Almost all the food products containing fat or oil are prone to rancidity. So, all cooking oils such as- olive oil, mustard oil, sunflower oil etc, meat product, nuts, snacks containing fat are prone to get rancid. But, it is very important to note that Poly unsaturated fats (PUFA) are more susceptible to rancidity than other type of fats. This is why nuts such as walnuts and seeds such as flaxseed and chia seeds and their oils are more susceptible to rancidity as they have high amount of PUFA fats.
Heat pressed oils and seed powders are more prone to rancidity than the cold pressed ones. The reason for this is explained in the next section.
How to handle food products prone to rancidity
To prevent rancidity in the food products, the food busines operators add antioxidants in them. This extends the shelf life of the food item as antioxidants slowdown the process of rancidity. Vitamin C & Vitamin E are naturally occurring antioxidants. Some of the synthetic antioxidants commonly used in the food industry are - Butylated Hydroxyanisole (BHA), Butylated Hydroxytoluene (BHT), Tertiary Butylhydroquinone (TBHQ). The naturally occurring antioxidants are sensitive to heat or light and which is why they have a short-life. The synthetic antioxidants are used commonly for a long-term stability. Although, they are often criticized for causing adverse health effects in human beings, if taken in high amount.
There is another common practice in the industry to prevent rancidity i.e. packing a food item in the nitrogen gas. Products like walnut kernels and potato chips are packed in nitrogen gas. This is done to prevent any contact between food and oxygen.
Cold Press Technique and Rancidity
It’s a technique in which the seeds are pressed in a manner that requires minimal heat application. The oils and seeds produced via this technique are less prone to rancidity.This is because of the reduced heat application. In the presence of heat, the natural antioxidants present in the seeds are destroyed. As heat is controlled, in this technique, the antioxidants remain intact thus making cold pressed oils less prone to rancidity. So, when you pick a cold press oil from the super market’s shelf. It is less rancid than the hot pressed oils.
Handling tips for end users to avoid rancidity
- It is very important to store the food items containing fats in a cool and dark place. Also, keep these items in an airtight container which in not transparent in nature.
- Buy small quantities of oil, butter, nuts and other food items containing fats, based on one’s requirement.
- Reheating oil and fats again and again could lead to composition changes of oil and fats. It can also cause rancidity. Thus, the cooking oil and other fats must not be heated again and again and should not be added to the fresh oil.
- Nuts like walnuts and seeds like flax seeds could be kept in the refrigerator till they are consumed. This could delay the rancidity process for a few days.
- To prevent hydrolytic rancidity in butter, it must be stored in an air tight container in the refrigerator.
- Cold pressed oils could be purchased whenever it is possible.