Fermentation and Refrigerated Storage of Millet-Based Beverages with Yoghurt and Propionic Acid Bacteria

Abstract

Millet beverages require fermentation processes that provide acidification, culturable starter populations and resistance to serum separation. Beverages containing 0 to 3% (w/v) millet flour were fermented with a yoghurt starter, Propionibacterium freudenreichii subsp. shermanii, or both cultures. Fermentation was conducted at 37 °C for 6 h with yoghurt or mixed cultures and 18 h with the propionic starter, followed by storage at 6 °C for 28 days. Two independent production experiments were performed, each with duplicate samples. Acidification, bacterial counts, pH, penetration forces, centrifugal syneresis and selected carbohydrates were assessed. Mixed cultures yielded higher presumptive propionibacteria counts after fermentation and storage, reaching 6.7 log CFU/mL on day 28 with 2% flour. Their pH remained approximately 4.1–4.2. Flour increased hardness and reduced centrifugal serum release. With 3% flour, syneresis on day 28 was 48.3% for yoghurt and 57.8% for mixed cultures. Carbohydrate concentrations below 0.50 mg/g were treated as semiquantitative estimates. The results describe formulation-dependent technological responses without establishing metabolic synergy. Limited independent replication, substantial centrifugal serum release and the absence of rheological and sensory measurements restrict statistical inference and conclusions about commercial suitability.