The nutritional composition of the food also determines the kind of microbes that can grow. Each microbe differs in its ability to digest a particular nutrient. Nutrients that are easy to access, assimilate and digest will invite a larger number of microbes. For instance, foods that are rich in sugars have a greater chance of getting affected by microbes than ones that have a high proportion of polysaccharides. Sugar levels also determine the nature and spread of microbial growth. Other ingredients like lysozyme, which are found in eggs, prevent food spoilage. Thus, the nutrients and their proportions are an intrinsic factor that affect food freshness.
The purpose of packaging food is to reduce the incidence of microbial infestation. This is achieved in two ways. First, the packaging prevents airborne and water borne microbes from entering the food. Secondly, by blocking out air and water, the essential conditions for microbial growth are eliminated. Having said this, each food item, whether naturally obtained or processed in factories, will have their own ideal packaging material. Choosing the right packaging material involves consideration of temperature, penetrable light, foil thickness, humidity, etc. So this is an extrinsic factor responsible for spoilage of food.
Many commonly used food items are susceptible to spoilage due to fungus. For example, Botrytis cinerea makes grapes and strawberry to rot quickly and blue mould rotting in tomatoes is a result of Penicilliumi infestation. Another fungus called Guignardia bidwellii also acts on grapes. The primary cause of spoilage in apples is Sclerotinia sclerotiorum and spoilage in oranges is induced by Penicillium digitatum. So, all varieties of foods can be spoilt and poisoned by micro-organisms.
In this context, a discussion of the “hurdle concept” is relevant. Hurdle concept is essentially placing hurdles before the factors discussed above, so that their detrimental impact on the food will be negated or reduced. In other words, creating conditions or adding ingredients in the processing and packaging of food so as to minimize food spoilage is called the “hurdle concept”. The application of the “hurdle concept” has advanced very much over the last few decades. Traditionally hurdles were determined based on common observations and knowledge of basic bio-chemistry. But with the advance in technology, hurdles are developed that act at a molecular level. Some hurdles even change the DNA of an organism so as to make it resistant to microbial intoxication.
Hurdles are applied to almost all food that we consume. Hurdles are used in the preservation of milk. There are lots of factors responsible for reducing the shelf life of milk. Bacteria can be a threat and so can high temperature. An internal factor that influences milk spoilage is the vulnerability of fat content in the milk. By applying one or more of the following techniques the shelf-life of milk can be prolonged. They include High-Temperature/Short-Time Pasteurization, Ultra-pasteurization, Enhanced Thermal Processing, Higher-Heat/Shorter-Time, etc.
The degree of success of any food preservation strategy can have profound implications. Diseases such as Salmonellosis, Enterohaemorrhagic E. coli and listeriosis, Cholera, Campylobacteriosis, etc., are all food borne diseases. Salmonellosis is caused by bacteria that are found in Salmonella. Such staple food items like meat, milk and eggs can carry these micro toxins. Campylobacteriosis is another common ailment. Some of the symptoms of this disease include severe stomach cramps, diarrhoea, vomiting and fever. These diseases consume numerous human lives each year. So the importance of food safety and the application of hurdles in preserving food items cannot be overemphasized.