High oil content inhibits humification in food waste composting by affecting microbial community succession and organic matter degradation

•Effect of oil as an additive on food waste composting was studied.•The maturity of composting was lower with high oil condition.•Humus formation during composting was reduced by 28.41% under high-oil content.•High oil content decreased the activity of key microbes involved in humification.•High oil altered organic degradation and microbial dynamics to inhibit humification.