Introduction: The microbial food spoilage is one type of food spoilage that is caused by microorganisms. Food spoilage can define as the process in which the quality of the food deteriorates to some extent which is inconsumable for the person to eat. Food spoilage occurs as a result of the microbial attack, enzymatic digestion, chemical degradation, physical injury etc.
The microbial food spoilage can be determined physically by the following:
- Change in appearance: The appearance of the food changes by the microbial attack, which forms cloudiness and liquid formation in the food.
- Change in texture: Texture changes occur as a result of slime formation due to an accumulation of microbial cells and tissue degradation.
- Colour change: Colour changes due to the chlorophyll breakdown and by the growth of mycelia.
- Change in taste and odour: The taste and odour of the food changes due to the oxidation of nitrogenous compounds, sulphides, organic acids etc.
Content: Microbial Food Spoilage
- Definition of Microbial Food Spoilage
- Causes of Microbial Food Spoilage
- Classification of Food
- Microorganisms Involve in Food Spoilage
- The Process of Microbial Food Spoilage
Definition of Microbial Food Spoilage
Microbial food spoilage can define the biological process which involves microorganisms can degrade and decompose the food material, at optimal environmental conditions (temperature, ph, oxygen, moisture etc.) and brings some undesirable changes which make the food inedible to eat.
Causes of Microbial Food Spoilage
There are two common factors which favour the growth and multiplication of microorganisms, which includes:
Storage conditions of the food
The storage conditions basically involve two environmental factors like temperature, pH and oxygen that favours the microbial growth on food.
Temperature: The psychrophilic temperature i.e. -17 is considered to be safe and can prevent the growth of microorganisms. The temperature above this, refer as “Mesophilic temperature” which is the most favourable for the microbial growth. The mesophilic temperature is in between 20-40 degrees Celsius. Therefore, the warm temperature is optimal for microbial growth like mesophilic and thermophilic microorganisms.
Oxygen: There are aerobic and anaerobic microorganisms which attack the food in storage conditions either in presence or absence of oxygen. Aerobic storage conditions favour the aerobic bacteria and moulds. If there are anaerobic storage conditions then it will favour the growth of anaerobic bacteria like Clostridium sp.
Chemical properties of the food
Chemical properties is another major factor which causes spoilage due to the food’s own chemical properties. The chemical properties of the food that influence microbial growth includes:
The chemical composition of the food
In food, certain organic biomolecules like protein, carbohydrates and fats are present which are necessary for the microbial growth.
In protein-rich foods, the microorganisms which attack are “ Proteolytic microorganisms”. The proteolytic enzyme causes the degradation of protein into simpler forms like amino acids, amines etc.
The proteolytic microorganisms include gram-negative, spore-forming bacteria.
In carbohydrate-rich foods, the microorganisms which attack are “Carbohydrate fermenting microorganisms”. Carbohydrate fermenting microorganisms causes the degradation of carbohydrate into the fermentative products by producing acids, alcohols and gases.
The carbohydrate fermenting microorganisms include yeast, moulds and bacteria (Micrococcus sp., Streptococcus sp. Etc.).
Fat rich foods:
In fat-rich foods, the microorganisms which attack are “lipolytic microorganisms”. Lipolytic microorganisms cause the degradation of fat into simpler forms like fatty acids, glycerol etc.
The lipolytic microorganisms include moulds and some gram-negative bacteria.
The acidity of the food
The pH below 4.5 does not allow the subsequent bacterial growth and are affected mostly by yeasts and moulds like in citrus fruits and vegetables. The high pH allows bacterial growth occurs mainly in non-acid foods.
Moisture and osmotic concentration of food
In food, 13% of the free water favours microbial growth. High sugar and salt concentration prevent microbial growth. For the growth of moulds, the required sugar concentration is 65-70%. For the growth of yeasts and bacteria, the required sugar concentration is 50%.
Classification of Food
Based on the spoilage, the food can categorize into three types:
Non-perishable food has no water content and can be stored for a long time. These are having a long shelf life.
Semi-perishable food has less water content and can be stored for some time. These are having a medium shelf life.
Perishable food has high water content and cannot store for a longer period. These are having a short shelf life.
The high water or moisture content is a factor which will directly influence the microbial growth, as water promotes the growth of all living beings. Therefore, the food which is susceptible to the spoilage process refers to Perishable food.
Microorganisms Involve in Food Spoilage
There are commonly three kinds of microorganisms which causes food spoilage are as follows:
Yeasts: These are the type of fungi which are single-celled and cause “Fermentation of food”. Yeasts are of two types namely true yeasts and false yeasts. The favourable condition for the yeasts to cause food spoilage are low pH and low moisture. True yeasts convert sugar into alcohol and carbon dioxide. False yeasts grow on the food surface as a dry film.
Mould: These are also the type of fungi, which are multicellular and produce a tough visible mass on the food surface refers as “Mold growth”. These are aerobic organisms which require oxygen to grow, slightly acidic conditions, moisture, a temperature of 20-40 degrees Celsius. Mostly affects the bread, cheese, meat etc.
The Process of Microbial Food Spoilage
Microbial food spoilage involves the following steps:
Microbes first attack the food: As the food contain all the nutrients required by the microorganisms, at a favourable temperature, pH, moisture, oxygen etc.
Food degradation: Microorganisms not only degrades the food material by utilizing the nutrients available in the food but also decompose the food material.
Decomposition: The enzymatic reaction occurs between the food components like protein, lipid, fat, carbohydrates etc. and the microbial enzymes which carry out some chemical changes.
Changes as a result of food decomposition: The changes appear in the form of appearance, texture, colour, taste, odour etc. as a result of spoilage.