Internal factors of shelf life
Internal factors of shelf life, the most common factors explained.
Water is often the major constituent in foods. Even relatively ‘dry’ foods like bread usually contain more than 35% water. The state of water in a food can be most usefully described in terms of water activity. Next to temperature (an external factor), aw is considered as one of the important parameters in food preservation and processing.
There are many humectants that can decrease the water activity drastically and extend the shelf life of bakery products. Overall, the most popular are sugars or derived products of sugar such as glycerol, dextrose and glucose syrups. Probably the most important/common ingredient to decrease the water activity is salt. (sodium chloride)
Preservation, pH value and type of acid
Increasing the acidity of bakery products has been used as a preservation method since ancient times. It is a well established fact that microorganisms can only multiply within certain pH ranges. The pH of a system is related to the concentration of hydrogen ions. In case of food, come from ‘acid’ ingredients that dissociate in water, releasing them in the process.
This can be achieved by adding acidulates like sorbic- and propionic acids. Sorbates are more effective in inhibiting mould growth in bakery products, but have the disadvantage of a poor water solubility and that they are affecting yeasts as well. This last disadvantage can result in a reduction of loaf volume and making dough sticky, which makes it difficult to handle. To avoid this problem, sorbate could be sprayed onto the product’s surface after baking or mixing an hydrates of sorbic acid with fatty acids.
Product composition and formulation
The composition and formulation of bakery products is another important shelf life determining factor. In contrast to the use of eggs in E-number free products. Many other ingredients have a positive effect on shelf life extension. Margarine for example, contains at least 80% fat that limits the growth of most microorganisms. The size of the aqueous phase droplets and the inability of microorganisms to move been droplet reduce the growth of microorganisms.
Product- make-up and structure
Product make-up and structure are often underestimated intrinsic parameters that can influence shelf life. Bakery products, which are mainly solid or semi-solid, do not have a truly homogenous and uniform structure. Therefore chemical and physical conditions relevant to microbial growth, or chemical- or biochemical reactions can strongly depend on the position in the food. The smaller mobility of micro-organisms in solid foods allows spatial segregation which causes pattern formation. Evidence is given for the fact that taking space into account has an influence on the behaviour of micro-organisms. Significant differences in lipid oxidation between bulk fat and emulsified fat, which can be presented in cakes and crèmes . This is an example of a biochemical reaction that depends on product structure, in particular the micro structure.
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