What was it all about?

This project, which ran from 2016 to 2019, had a focus on keeping vegetables healthy and safe by delivering and verifying new biocontrol agents (new strains of beneficial bacteria termed ‘ProbiSafe’) to inhibit the growth of harmful bacteria. The project also explored commercial probiotic delivery using vegetables as an alternative to dairy or capsule/tablet-based probiotic products. The project achieved promising results, however further research will need to be done to determine its commercial viability.

ProbiSafe bacteria inhibiting salmonella growth

ProbiSafe bacteria were tested for inhibiting Salmonella growth on fresh-cut iceberg lettuce at different conditions. Initial ProbiSafe levels of 100 million bacteria per gram lettuce did not compromise the quality of lettuce when stored under normal refrigerated conditions. However, upon storage at slightly higher temperatures, the increased initial concentrations of ProbiSafe strains led to adverse effects on the lettuce appearance and firmness, but also significantly inhibited Salmonella growth. Using new DNA sequencing technology all the genes in the ProbiSafe bacteria were analysed and found to be safe, with no genes for antibiotic resistance or which allow infection found. Therefore, ProbiSafe bacteria can be useful in ensuring safe leafy green products during potential storage temperature abuse.

Commercial probiotic delivery using vegetables

Sixteen commercial probiotic bacteria were evaluated for their survival in baby spinach leaves. Most of these probiotic strains showed excellent survival in spinach leaves, suggesting that probiotic delivery using commercial bagged salads is feasible. Levels of more than 1 billion live probiotic cells in a 100g serve of spinach appear possible. The addition of various salad dressings to probiotic-supplemented spinach did not significantly reduce the number of probiotics. Probiotic bacteria tested also survived well during laboratory simulated digestion (stomach and intestine) trials. Taste testing trials performed by 40 human volunteers demonstrated that the quality of spinach leaves was not adversely affected by the addition of commercial probiotics. A new category of probiotic containing salad products has the potential to provide additional health-promoting properties to consumers.

Recommendations

While the initial findings have demonstrated that there is potential in using ProbiSafe bacteria to inhibit the growth of harmful bacteria and deliver probiotics via vegetables, the project team recommends the following next steps for industry to explore this further:

• Large scale industry trials of probiotic application
• Further research on the application methods (i.e. soaking, spraying) of adding ProbiSafe or probiotic strains into salad products at a commercial scale should be done
• Effects of ProbiSafe on the sensory properties and nutritional quality of salad products during shelf-life should be examined
• Consumer research into salad consumer’s interest in the addition of probiotics should be carried out.
• Testing ProbiSafe strains for antibiotic resistance profiles
• Communication of results to industry