Why are Fruits Shinier than Ever Now?



Food nutrients decay over time. That is the reason that food products have a certain “shelf life” or “best before/sell by” dates. We observe that some products have longer shelf lifes than others. So, food scientists classify food materials according to their perishability. There are perishable foods, semi-perishable foods, and stable foods.

Perishable foods are the foods with the lowest shelf life. They perish in hours to a few days since they naturally inhabit high numbers of microorganisms or sensitive compounds (lipids, proteins) that decompose fast. Perishable foods lack defensive properties against breaches. They are prone to invasions from bacteria, fungi, or animal because they contain valuable resources. Organisms are attracted to them visually and chemically. Examples of perishable foods are milk, meat, and poultry.  

Stable foods are foods that preserve their quality over long periods of time.  Some have low moisture content and quite dry. Low moisture content prevents microbial spoilage and enzyme activity. They have inert defenses including compounds with antibacterial and antiviral properties whereas others have physical defenses with hard and dry skins that prevent invasion. Examples of stable foods are sugar and rice.

Semi perishable foods have characteristics of both stable and perishable foods. Care must be taken to prevent spoilage since they seem healthy but may spoil unnoticeably.  They are stable for longer times than perishable foods and their handling and transportation are easier. The example of semi-perishable foods is potato and onions.

So, why do some foods degrade faster than others? The answer is in their chemistry and physical structure.

For example, milk contains proteins such as caseins and whey proteins. Also, fats and sugars (mainly lactose) which all are valuable for organisms to grow. To prevent spoilage, pasteurization is used to reduce microbial load (number of microbes in the milk). In addition, milk is cooled before and after processing to slow down microbial growth.

Meat and poultry are high in proteins, fats, and minerals. Leaving them in the open results in an invasion of animals and microbes. Flies find them easily and lay their eggs. Meat and poultry are rich environments for their larvae.

Aside from external stresses, many food components degrade naturally. Enzymes in the food itself introduce changes. They produce different colors, textures, and certain molecules. The processing of raw materials releases enzymes from cells. This is a problem for pasta and fruit juice production. Released enzymes may produce undesirable colors and coagulation, which are bad for product quality. Some enzymes require oxygen in the process, so vacuum processing would be a good choice for such foods. Heating (pasteurization) also solves the problem by destroying the enzymes.

Enzymes are released when the tissue is damaged. Bruising -and even touching- may disrupt tissue integrity, resulting in quality losses. This could be the reason why fruits in supermarkets are shinier than ever during the pandemic. Fewer people touching the fruits means more intact fruits with the higher appeal. Also, tissue damage allows microbes to enter the body of the fruits. As another aspect of transportation, bruising of the tissue should be minimized for a high-quality product.

Lipids are susceptible to oxidation. Oxidation results from enzyme activity or autocatalytic processes that do not require external agents. Light, oxygen, presence of metals affect its rate. So, both internal and external stresses develop the process. Oxidation produces off-flavors and tastes, reducing quality. Certain methods are introduced to slow down lipid oxidation. For example, use of antioxidants (vitamin C and EDTA, go and check your foods’ ingredients list) are common to prevent lipid oxidation. For oil products, the chemical composition is important and must be analyzed. Also, packaging must block light to prevent light-induced reactions.

Proteins denature upon various stresses such as light and pH.  Denatured proteins result in change in texture. Maillard reactions take place in cooked food proteins, extensive cooking results in loss of amino acid, texture changes, and excess color formations. The temperature of cooking, the chemical composition of the food must be known and analyze to minimize degradation. Yet, this is the industry’s concern, not the public.

To sum up, avoid “too”s. Too much heat, too much acid, too much damage, too much time food spends in open or even in the refrigerator. The list goes on. Time is the enemy of fresh products. Producers know this and try to act the “smartest” way to produce the best quality food they can. As the public, we also need to be smart to protect our food and avoid spoilage. Remember, spoilage leads to waste and consuming spoiled products have adverse effects on the human body. Understanding spoilage is a good step to prevent it.