Protein Putrification

It is the microbial or enzymatic deterioration / degradation process of proteins on the amino acid level. It occurs as a result of microbial spoilage (eg. tuna), or fermentations (eg. camembert cheese), or in fruits and vegetables (enzymatic, pinaple)

Decarboxylation (remove co2 group) and Deamination (produce ammonia and Co2) are happening. For this we need to have a free amino acid. When we have a free amino acid we can obtain a decarboxylation or a deamination.

Deamination: is not so important because produce carboxylic acid, which are intermediate products of the amino acid metabolism, so they will be converted into energy in the body, burned in creb cycle. Not toxic, not produce taste.  

Decarboxylation: Production of CO2 and Biogenic amines (amines produced a biological way, being the enzymatic decarboxylation of a free amino acid). This process is typically linked to microbial spoilage. Biogenic amines are considered to be the most relevant in this reaction, because some of them might be toxic (histamine), while others have an impact on the sensorial properties of the food (typical ammonia like odor). Biogenic amines originate from an amino acid so they can produce ethyl amine (from ethyl amine) and short chain amines. So it can produce volatile amines which have ammonia like odors (eg. typical aroma of fermented or ripe cheese such as camembert. During the fermentation the proteins are hydrolyzed and free amino acids are produced, giving rise to the typical aroma).
So there will be sensorial effects (degradation of taste and smell) which can be desirable or undesirable, eg. Rotten fish smell, camembert cheese.  (sensorial effect, with regards to a particular smell and taste due to action of the biogenic amines).
Another important effect is the Safety; a particular amino acid (histidine) which gives rise to  a biogenic amine known as histidine, which is toxic. It is a small hormone in our body and regulates muscles responsible for respiration can be controlled by histamine. When take histamine (exogenouse histamine) from the food, due to the increase presence of this molecule in the body you will develop an intoxication (allergy like effect) by exogenously taking it. Gives asthma, skin rush, irritation vomiting, etc. typical foods are fish products, like fermented fish, fish sauce.

Other important biogenic amines that can be produced are putricine (derived from ornithine) and cadaverine (derived from lysine) which give a very unpleasant odor, like dead bodies, so they can also give very strong taste deterioration.

 Some biogenic amines are naturally occurring (eg. in grape fruit, pinaple), they are adrenaline analogs like serotonin, so they have a similar effect in our body. Antidepressants inhibit the degradation of biogenic amino acids, so people who are under medication of antidepressants are more vulnerable. Biogenic amines are also responsible for bad smell of some cheese (putrecine and cadaverine)