Effect of Solid-State Fermentation on Nutritional Value of Pineapple Leaves

Pineapple leaves, a by-product of cultivation, are generally discarded and burned at the farm sites before replanting. As the demand for pineapple products increases yearly, the number of discarded leaves also increases. Valorisation of the leaves through solid-state fermentation (SSF) is a sustainable waste management approach that converts the low-nutrient substrate into valuable resources for animal feed. This study investigated the enrichment of pineapple leaf nutritional values using SSF. The process parameters such as fermentation time, inoculum type and size, additional carbon source and particle size were optimised using the one-factor-at-a-time (OFAT) method. The nutrient compositions were analysed for their total protein, total phenolic, antioxidant activity, reducing sugar and crude fibre using Bradford, Folin–Ciocalteu, DPPH (2,2-diphenyl-1-picrylhydrazyl), DNS (3,5-dinitrosalicylic acid) and AOAC978.10 methods, respectively. The optimal conditions were determined to be a 2 mm leaf particle size, 2% (w/w) Rhizopus sp. inoculum, and a fermentation duration of 2 days without the addition of a carbon source. Under these conditions, the nutrient enrichment resulted in a total protein content of 24.14 ± 0.31 mg/g, total phenolics of 11.81 ± 0.50 mg/g, antioxidant activity of 3.17 ± 0.04 mg/g, and a reducing sugar content of 12.03 ± 0.97 mg/g. Crude fibre content decreased from 20.37 ± 1.10% in unfermented leaves to 6.77 ± 0.44% after fermentation, potentially improving nutrient digestibility due to the reduction of indigestible fibre. These results demonstrate that SSF is a promising method to enhance the nutrient content of pineapple leaves, offering an alternative nutrient source for animal feed.