Biochemical and microbiological characterization of Coffea arabica sidestreams for food ingredient applications

Coffee processing generates substantial waste, with about 94% of the cherry discarded as by-products (skin and pulp ≈ 43%, mucilage ≈ 12%, parchment ≈ 6%, silverskin ≈2%, and spent coffee grounds ≈ 31%). This study presents the first comprehensive biochemical and microbiological analysis of Arabica coffee side-streams to evaluate their potential as sustainable food ingredients. Nutritional composition of the side-streams showed high crude fiber (44–62 g/100 g), crude protein (5 –16 g/100 g), and carbohydrates (17–39 g/100 g), supporting their use in fortified and nutritionally enhanced plant-based foods and ingredients. Using microwave-assisted extraction, the following bioactive compounds were quantified: total phenolics (5–20 mg GAE/g), total flavonoids (2–17 mg QE/g), tannins (6–72 mg TAE/g), and caffeine (6–15 mg/g). The DPPH assay showed antioxidant capacity with an IC₅₀ range of 1–5 mg/mL, where lower values denote stronger activity. Heavy metals were measured within safety limits, especially for cadmium and lead. Microbial analyses revealed total plate counts (2 × 10⁴–3 × 10⁵ cfu/g) and yeasts/moulds (2 × 10⁴–2 × 10⁵ cfu/g), with relatively low Gram-negative bacteria (2 × 10¹–3 × 10³ cfu/g). These loads are substantially lower than those in the pulping water (TPA: 2 × 10⁶ cfu/mL; Gram-negative: 5 × 10⁴ cfu/mL; yeasts/moulds: 2 × 10⁵ cfu/mL), underscoring the need for strict water quality control during wet processing and supporting high-temperature treatment (160–230 °C) to mitigate potential endotoxins. Overall, coffee side-streams are voluminous and should be valorized in a future circular bioeconomy.