Diversity at Genotypic Level Determines Whether LAB Strains Are Food Spoilers

17 Mar 2014 --- Diversity at genotypic level, rather than the species type, determines whether a lactic acid bacterial strain is a food spoiler. That is the outcome of recent research carried out by NIZO food research in which 121 lactobacillus strains of 6 different species were tested for their phenotypes relating to growth on carbon source and preservation conditions.

Microbial food spoilage occurs through random contamination with microbes from the environment. The nature and character of a contaminant are not known before the food-microbe contact occurs. Consequently, in food preservation, one has to account for ‘all’ possible contaminants, but in practice this is not feasible. Improved characterisation of potential contaminants helps us to define the boundaries for preservation of particular food categories. This is relevant in today’s markets where consumers demand foods that are high quality, stable and contain the minimum of preservatives.

Lactobacilli are common spoilage bacteria in sauces, soups, condiments, and spreads, where contamination during repetitive use is likely to occur.  Risks can be assessed properly by knowing the conditions under which the species and their strains grow. Based on this information, product specifications can be determined to minimise the growth of most common spoilage bacteria to which foods during use are exposed.

Until now, the risk of spoilage has been assessed based on specific (mostly lactobacillus) species. By linking the genome of lactobacilli species and strains with phenotypic parameters, NIZO scientists were able to determine the genes that are responsible for growth in specific carbon sources (food medium) and under specific treatments.  Michiel Wels, Group Leader of the Safe & Certain Research Team at NIZO, found that the classic methodology is too limited. “We found that differences between strains within one species are often larger than between species. Diversity at the genetic level determines whether a microbe will spoil a food under specific conditions”.

The growth of  121 strains of  the 6 most common lactobacillus species was measured on  21 carbon sources and under 27 preservation-related phenotypic parameters. The match between the genotype  and the phenotype was established using the fully automated bioinformatics tools developed at NIZO. Wels says: ”Every scientist will recognise that the genotypic information of  the spoilage bacteria that are encountered can be applied to determine preservation boundaries. Further development to reduce the time from cell extraction to genotypic characterisation will enable routine analysis to be carried out in production plants in future. With the current bioinformatics tools and databases available at NIZO, we are well prepared to fill this market need.”

The work was carried out at NIZO food research, commissioned by and in collaboration with Unilever R&D.