The main goal was to evaluate if dried cyanobacterium () biomass added to unpasteurised apple juice could inhibit growth of fungi dominant in apples and which fraction of cyanobacterium biomass contributed to this phenomenon. biomass, its protein and/or polysaccharide fraction were added to the sterilised apple juice inoculated with LW14 and stored at 4 °C for 96 h. Samples were tested against number of fungi and selected physical-chemical parameters. In the last research stage, protein fraction was added to the unpasteurised apple juice inoculated with LW14 to test its potency against fungi, lactic acid bacteria and acetic acid bacteria. When biomass was added to the sterilised apple juice (1.15% w/v), it effectively inhibited growth of LW14 and the metabolism of all analysed sugars (glucose, sucrose and fructose). Protein fraction added to the sterilised apple juice contributed significantly to mycostatic properties of . When protein fraction was added to unpasteurised apple juice, the same conclusions were obtained, however, except for inhibiting growth of LW14, it inhibited growth of some bacteria.