Microbial and biochemical spoilage of foods: an overview.

During harvesting, processing and handling operations food may become contaminated with a wide range of microorganisms. Subsequently, during distribution and storage only a small fraction of these will develop and cause serious deteriorations. Which microorganisms will develop or what (bio)chemical reactions occur is dependent upon food derived or environmental factors. This paper will describe the main mechanisms involved in the loss of food quality for the most important food commodities. Food spoilage may be caused by a wide range of reactions including some that are mainly physical or chemical, others due to action of enzymes or microorganisms. The primary factors associated with food spoilage are associated with intrinsic food properties (e.g., endogenous enzymes, substrates, sensitivity for light, oxygen) and (cross)contamination during harvesting, slaughter and processing in combination with temperature abuse. For fresh foods the primary quality changes may be categorized as (i) bacterial growth and metabolism resulting in possible pH-changes and formation of toxic compounds, off-odours, gas and slime-formation, (ii) oxidation of lipids and pigments in fat-containing foods resulting in undesirable flavours, formation of compounds with adverse biological effects or discoloration. Although interrelated with the microbial spoilage, the last category is 'purely' chemical in nature and will, all other things being equal, increase in importance with decreasing temperature. Little is known about the relationship between microbial activity and (bio)chemical spoilage parameters under different packaging and storage conditions. Although there is much progress in the characterisation of the total microflora and metabolites developing during spoilage, not much is known about the identification of specific microorganisms in relation to food composition. Despite the fact that food spoilage is a huge economical problem world wide, it is obvious that the mechanisms and interaction leading to food spoilage are very poorly understood.