Optimization of technological parameters for osmotic dehydration of black chokeberry

Many plant extracts selected for their high in vitro antibacterial activity in microbiological media have a far lower in situ antibacterial activity in foods. This is likely due to interactions of plant antimicrobial molecules with food components such as proteins or dispersed fat at the expense of their interaction with target unwanted bacteria. Gaillac red wine powder and Cinnamon cassia essential oil were selected for their in vitro antibacterial activity against Staphylococcus aureus CNRZ3 and Listeria innocua LRGIA 01, respectively. In order to assess their potential application to the preservation of raw meat or dairy products, respectively, their antibacterial activity was tested in Mueller Hinton broth (MHB) supplemented with up to 20% beef meat proteins to mimick raw beef meat protein content and in TSB, skimmed, semi-skimmed and whole milk, respectively. Supplementation of MHB with beef extract proteins annihilated the antibacterial activity of Gaillac red wine powder as well as of resveratrol, a stilbene polyphenol present in red wine. The comparison of the  anti-Listeria innocua activity of C. cassia essential oil in TSB 1% (w/w), skimmed, semi-skimmed and whole milk led to the conclusion that its antibacterial activity was significantly reduced in the presence of milk fat globules but not significantly by milk proteins. Complexified microbiological media or liquid foods such as sterilized milk with various milk fat contents might thus be valuable tools for the rapid screening of antibacterial plant extracts of interest for perishable foods preservation.