The study examined the influence of hybrid, long-term storage and inoculants addition on fermentation profile and grain total zein content in whole plant maize (Zea mays L.) ensiled in laboratory silos. Three yellow maize hybrids were grown under identical conditions in a split-plot field test in five replicates. Replicates were either untreated or mixed with the lactic acid bacterial additive (Sil-All 4x4, Danstar Ferment, Zug, Switzerland) at a concentration of 1 x 106 CFU · g⁻¹, then ensiled in 30-dm³ laboratory silos for one year. Silages were sampled after 3, 8 and 52 weeks, when whole plant crude protein, soluble crude protein, ammonium-N, lactic acid and grain total zein contents were assayed. Although crude protein level did not vary significantly during one-year storage, soluble crude protein and ammonium-N contents increased, while grain total zein content decreased. Addition of inoculant was associated with higher lactic acid concentration and lower grain total zein content at all time points. The greatest grain total zein degradation was found after week 52, and this growth was accompanied by a decline in lactic acid content. Trends were similar across the three tested hybrids, though the magnitude of changes differed significantly. The simultaneous decrease in grain total zein content and lactic acid content strongly suggests proteolytic zein degradation during prolonged storage.