Impact of edible coating with or without anti-microbial agent on microbial growth during osmotic dehydration and refrigerated storage of a model plant material

The use of edible coating has proved a valuable tool in improving the efficiency of osmotic dehydration (OD) of plant material. In this study the impact of edible coating with or without an anti-microbial agent (A–M) on microbial growth was investigated. Potato cylinders (15 × 57 mm — D × L) were used as a model plant material. Calcium alginate (CA) coating was applied with or without incorporation of potassium sorbate (PS), at 0.3% of sample weight (before coating). OD took place for 3 h in stirred jars using sucrose solution at 50 °Brix and 40 °C. Microbial growth (Aerobic Plate Count — APC) was monitored both during OD (3 h) and during refrigerated storage at 5 °C (14 days). During OD, a significant reduction of the initial microbial load (ML) in the control (non-coated) treatment was observed, possibly due to a microbial “wash-out” effect. Both coating treatments resulted in a marginal decrease of initial ML in the OD product, suggesting some kind of protection against this effect. During refrigerated storage, the use of coating resulted in reaching the growth plateau several days earlier, which lead to significant reduction of maximum ML, compared to the control treatment. Besides this benefit, coating with A–M helped extend the lag phase and postpone time to reach maximum load by almost 4 days, compared to the simple coating treatment. These results can support further work on the use of more effective types and concentrations of preferably natural anti-microbials to achieve satisfactory stabilization of osmo-dehydrated/refrigerated products, without a negative impact on their minimal processing profile.Industrial relevanceOsmotic dehydration is a very potent processing tool that has been studied extensively in terms of mass transfer phenomena. Yet, microbial studies in this area are rather scarce; thus industrial applications are very difficult to proceed, due to lack of microbial stabilization data. This is especially crucial in the case of combined, minimal processing methods, such as osmotic dehydration and refrigeration. This work is using edible coating (which is known to promote dehydration efficiency) to incorporate a common anti-microbial agent, in an effort to establish an effective series of hurdles leading to microbial stabilization of osmo-dehydrated, refrigerated products.