Chemical Changes Caused by Microorganisms in Food

Chemical Changes Caused by Microorganisms in Food

Chemical Changes Caused by Microorganisms in Food

These following changes are occurred in food by microorganisms:

1. Changes in nitrogenous organic compounds

Most of the nitrogen in foods is in the form of proteins. Proteins are hydrolyzed to polypeptides, simpler peptides or amino acids by microbial enzymes before they can serve as nitrogenous food for most organisms. Proteinases catalyze the hydrolysis of proteins to peptides gives bitter taste to foods. Peptidases catalyze the hydrolysis of polypeptides to simpler peptides and finally to amino acids.

Peptides give desirable or undesirable flavors to foods, for example, amino acids cause the flavor of ripened cheese.

Anaerobic decomposition of proteins, peptides or amino acids result in the production of undesirable odors called putrefaction.  Putrefaction results in foul smelling, sulphur containing products such as hydrogen, methyl and ethyl sulfide and mercaptans, amines, indole, skatole.

When microorganisms act on amino acids, they may delaminate them, decarboxylate them.

For example,  Escherichia coli produce glyoxylic acid, acetic acid and ammonia from glycine.

Pseudomonas produces methylamine and carbon dioxide, Clostridia gives acetic acid, ammonia, methane.

From alanine these three organisms produces -

a)  alpha- keto amino acid, ammonia and carbon dioxide

b) acetic acid, ammonia and carbon dioxide

c) propionate,  acetic acid,  ammonia and carbon dioxide.

Other nitrogenous compounds are -

Amides, imides, urea – final product ia ammonia.

Guanidine, creatine – final products are urea and ammonia.

Amines, purines, pyrimidines – ammonia, carbon dioxide, organic acids.

2. Changes in non-nitrogenous organic compounds

Main non-nitrogenous foods for microorganisms, mostly used to obtain energy but possibly serving as source of carbon, include carbohydrates, organic acids, aldehydes and ketones, alcohols, glycosides, cyclic compounds and lipids.

A ) Carbohydrates:

Carbohydrates act as energy source by microorganisms. Complex, di, tri, or polysaccharides usually are hydrolyzed to sugars before utilization.

A monosaccharide aerobically would be oxidized to carbon- dioxide and water. Glucose is anaerobically decomposed to -

1. An alcoholic fermentation by yeasts with ethanol and carbon dioxide as the principal products.

2. A simple lactic acid fermentation by homo fermentative lactic acid bacteria.

3. A mixed lactic acid fermentation by hetero fermentative lactic acid bacteria with lactic acids and acetic acids, ethanol, glycerol and carbon dioxide.

4. The coli type fermentation by coliform

bacteria with the production of lactic acids, acetic acids, formic acids, ethanol, carbon dioxide, hydrogen.

5. The propionic acid fermentation by propionic bacteria.

6. Butyric butyl isopropyl fermentation results in butyric and acetic acids, carbon dioxide, hydrogen.

b) Organic acids

Organic acids usually occurring in foods as salts are oxidized by organisms to carbonates causing the medium to become alkaline. Aerobically the organic acids may be oxidized to carbon dioxide and water. Saturated fatty acids or ketonic derivatives are degraded to acetic acids.

c) Lipids

Fats are hydrolyzed to glycerol and fatty acids by lipase. Phospholipids may be degraded to their constituent phosphate,  glycerol, fatty acids and nitrogenous base such as choline.

d) Pectins

Pectins are water soluble polymer of galactouronic acid substances. Protopectin is water insoluble found in plants and can be converted into pectin.

Pectin esterases causes hydrolysis of the methyl ester linkage of pectin to yield pectic acid and methanol.

Polygalactouronase destroy the linkage between galactouronic acid units of pectin to form smaller chains and ultimately free D-galactouronic acids, which may be degraded to simple sugars.

The Daily Youth- tdy24.com Present

"Chemical Changes Caused by Microorganisms in Food"

Written By

Sadia Akhtar

Student of Department of Microbiology

Jagannath University.

Email- sadiabd810@yahoo.com