In the beginning, food can be very delicious, good to look at, smell nice, and look like it is never going to change its look but remember, Good food doesn't last forever. When foods start to spoil, depending on the type of food, the first sign you would see is mold. Let's have a post of "Nothing Good Last Forever".
It is a moldy day
Mold is usually common but not singular to bread. Mold can be found in a lot of food but there is a difference as some can be eaten, like Blue cheese, while molds from bread should not be eaten. The question that comes to mind next is why?
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Molds are microscopic fungi that grow from tiny spores of 3 to 4 microns long, found everywhere in the air, and start growing when the condition is right for them such as warmth, moisture, and nutrient. They love our temperature, but then even if you place them in refrigerators, they would still form. Spores of molds release root threads known as mycelia into whatever food they are about to form or grow on, which could be fruit or food. Mycelia are difficult to see with the naked eyes but when the fungi spore rises above the food item, we tend to see them, and the stalks give them the color you see.
Molds digest their foods first before eating them, and the mycelium breaks down the organic matters. I would not advise that you cut and throw away paths where you think the mold mycelia hasn't reached especially with soft food, because of Mycotoxins which are produced around the mycelium. Molds that produces mycotoxins are found in grains and nuts. A type of dangerous mycotoxin is Aflatoxin produced by Aspergillus flavus,and Aspergillus parasiticus. Molds in blue cheeses and shilton do not produce aflatoxin. They are introduced into the cheeses to breakdown complex moleculeds in the cheese, and they give it the unique taste and smell.
Fruits Going Brown
The enzyme Polyphenol Oxidase (PPO) is one enzyme that is found in fruits and they oxidise phenols in the presence of oxygen and this gives of melanin which is the same pigment found in humans. When plant cells are damaged, melanin are produced to slow down and prevent infection into the cells. That is why when you cut an Apple or a Banana and leave them for a while, they become brown. So many fruits such as Cocoa, coffee, and tea also go through that oxidation reaction.
My Meat is Rotten
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Meat is another food item that gets spoilt. Although its best buy date is around a week after purchase, but it can spoil within hours or days because it is a breeding ground for bacteria because of its wet, nutrient-densed property, causing bacteria to multiply over a few days. These bacteria such as Pseudomonas, or Lactobacilli feed on meats and cause nasty byproducts known as Volatile Organic Compounds which includes hydrogen sulfide which converts natural muscle pigment into greenish color.
I don't Want My Food To Go Bad
You must have heard of Probiotic food which breaks down sugar to give lactic acid known as Lacto-fermentation. The bacteria in your gut or intestines is Lactobacillus Acidophilus. These bacteria are salt tolerant, so this process of lacto-fermentation has to do with partially digesting food with bacteria thereby keeping them more safe and not spoil easily, with lactic acid acting as a natural preservative.
Reference
https://agricultureandfoodsecurity.biomedcentral.com
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7150063/
https://pubmed.ncbi.nlm.nih.gov/8913811/
https://www.frontiersin.org/articles/10.3389/fmicb.2021.819684/full
https://www.usaemergencysupply.com
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9752900/