Valorization of Desugarized Sugar Beet Molasses to Develop a Culture Medium for the Enumeration of Yeasts and Moulds

Desugarized sugar beet molasses (DSBM), a nutrient-rich by-product of sugar production, is a promising and largely unexplored substrate for the production of microbiological media. This study aimed to develop and validate a ready-to-use (RTU) medium based on DSBM for the enumeration of yeasts and moulds in foods and feeds with water activity (aw) less than or equal to 0.95. DSBM from three production seasons was characterized physicochemically and microbiologically and used to prepare three medium variants, evaluated for productivity and specificity, and evaluated in a single-laboratory method comparison study conducted in accordance with the method comparison protocol described in ISO 16140-2:2016. The three DSBM batches obtained from different production seasons covered dry matter contents of 49.33-52.00%, total sugar contents of 9.46-11.88%, and nitrogen contents of 1.68-1.95%. Potassium and sodium predominated among the minerals. Microbial counts were below the limit of quantification, with no detectable Salmonella spp. or Listeria monocytogenes. All medium variants met the productivity criterion specified in ISO 21527-2:2008 and completely inhibited the growth of 21 tested bacteria. They showed close agreement with the reference DG18 agar across six food and one feed category (0.60 < aw ≤ 0.95), with mean biases within ±0.025 log10 CFU/g and all results within the predefined acceptance limit of ±0.5 log10 CFU/g. All 80% β-expectation tolerance intervals in the AP were within the ±0.5 log10 CFU/g acceptance limit, and proficiency testing schemes confirmed acceptable performance. Therefore, the novel medium provides a new value-added application for DSBM, supporting the valorization of this underutilized resource from sugar beet processing.