Evaluation of Valorisation Strategies to Improve Spent Coffee Grounds’ Nutritional Value as an Ingredient for Ruminants’ Diets

{"Background": "Spent coffee grounds (SCG) represent a major food waste stream, with approximately 10.2 million tons of coffee consumed worldwide in 2020/2021, generating about 6.6 million tons of wet SCG (2 kg per kg of coffee). Current management in Europe relies heavily on landfilling, contributing a carbon footprint of about 1716 million kg CO2 eq/year. Although SCG have interesting nutritional value for ruminants\u2014with their high cellulose, hemicellulose, protein, fat, polyphenol, and mineral contents\u2014their acid detergent lignin (ADL) content around 27.83% limits digestibility and inclusion in animal diets. SCG have been successfully included at doses up to 10% of concentrate for dairy sheep and 5% for dairy cows without impairing performance, but higher inclusion is constrained by low fibre digestibility. This study aimed to identify valorisation strategies to break lignocellulosic bonds and improve SCG digestibility for ruminant feed applications.", "Methods": "SCG samples from the HORECA industry in northern Spain (Basque Country) were subjected to two factorial experiments. Experiment 1 used a 2\u00d75 design: thermal pre-treatment (autoclaving at 121 \u00b0C for 15 min, with/without) combined with enzymatic hydrolysis using four enzymes (Celuclast\u00ae, Ultimase\u00ae, Viscozyme\u00ae, Ultraflo\u00ae) or unprocessed control, with liquid fraction removed. Experiment 2 used a 2\u00d73 design: mechanical pre-treatment (unground, coarse grinding ~250 \u00b5m, fine grinding ~100 \u00b5m) combined with three hydrolysis conditions (unprocessed, hydrolysed with liquid removed, hydrolysed with liquid retained), using a combination of Viscozyme\u00ae and Ultimase\u00ae enzymes. Enzymatic hydrolysis was performed at pH 5, 55 \u00b0C, 20 h, 250 rpm with 1% (v/w) enzyme in a 1:1 SCG:water ratio. In vitro organic matter digestibility (IVOMD) was determined via 24-h batch fermentation using ruminal fluid from Latxa ewes fed fescue hay, following the Pell and Schofield method, with 500 mg substrate in 50 mL culture fluid (1:4 rumen fluid:phosphate-bicarbonate buffer). Chemical composition (DM, ash, CP, NDF, ADF, ADL, NDICP, ADICP) and bioactive compounds (TRS, TPC, TEAC, caffeine) were measured, with SCFA quantified by gas chromatography. Statistical analysis employed SAS GLM with Tukey adjustment at p<0.05.", "Key Results": "In Experiment 1, thermal pre-treatment showed no significant effect on SCG nutritional value, chemical composition, or IVOMD. Enzymatic hydrolysis reduced IVOMD between 21% and 32% compared with unprocessed SCG (p=0.001), although total SCFA production remained unaffected. All enzymes increased ADICP content (from 27 to 34%, p<0.001) and ADF concentration, while reducing ash content by 29\u201333% (p\u22640.003). All enzymes reduced propionic acid proportions by 7\u201310% (p<0.001) and increased the acetic:propionic ratio (p<0.001), with thermal pre-treatment increasing this ratio by 12% (p<0.001). In Experiment 2, fine grinding yielded the highest IVOMD (429 g/kg OM, p<0.001), followed by coarse grinding (297 g/kg OM, p=0.003), both significantly higher than unground samples (261 g/kg OM). Fine grinding increased SCFA production (4.52 vs. 3.85 mmol/100 mL for coarse, p<0.001). Hydrolysis with liquid fraction removed reduced IVOMD compared with unprocessed samples (272 vs. 350 g/kg OM, p<0.001), while hydrolysis without liquid removal showed IVOMD values similar to unprocessed SCG (p=0.403). Grinding increased crude protein (153 g/kg DM for fine, 152 for coarse vs. 150 for unground, p<0.001) and reduced ADF (fine: 409, coarse: 402 vs. 440 g/kg DM unground, p<0.001). The highest total reducing sugar content was found in hydrolysed samples without liquid removal with fine grinding (84 mg/g DM). Fine grinding reduced the acetic:propionic ratio (2.12 vs. 2.55 for unground, p<0.001), indicating more efficient fermentation. Caffeine content was reduced by grinding (0.41% fine, 0.42% coarse vs. 0.56% unground).", "Clinical Implications": "Grinding, particularly fine grinding to approximately 100 \u00b5m, is identified as the most effective valorisation strategy to enhance SCG nutritional value and in vitro rumen digestibility for ruminant diets. Enzymatic hydrolysis with cellulolytic enzymes (Celluclast\u00ae, Ultimase\u00ae, Viscozyme\u00ae, Ultraflo\u00ae) is counterproductive when the liquid fraction is removed, as valuable compounds including sugars and bioactive polyphenols are lost, resulting in a less digestible, more recalcitrant solid fraction with shifted fermentation profiles toward less efficient acetate production. However, when enzymatic hydrolysis is performed without removing the liquid fraction, the negative effects disappear, suggesting potential for monogastric animal applications where rumen microbial enzymatic activity is absent. Autoclaving at 121 \u00b0C for 15 min is insufficient to break lignocellulosic bonds in SCG. Implementing grinding pre-treatment could enable higher inclusion rates of SCG in ruminant rations, supporting circular economy objectives by diverting approximately 6.6 million tons of annual coffee waste from landfill, reducing the associated 1716 million kg CO2 eq/year carbon footprint, and providing a sustainable alternative feed ingredient amid rising feed costs in livestock production."}