Oat pulp, a by-product of oat milk production, is highly nutritious but prone to spoilage due to its high moisture content (over 60%), suggesting effective drying for preservation and further utilisation. This study investigated the thin-layer drying kinetics of oat pulp using hot air drying (HAD) and vacuum drying (VD) at different temperatures (70 °C, 90 °C, 110 °C) and thicknesses (0.5 cm, 0.75 cm, 1 cm). Drying performance was evaluated based on drying rate, water activity, phenolic retention, antioxidant activity and energy consumption. Results indicated that higher temperatures and thinner layers increased drying rates and reduced drying times. Effective moisture diffusivity ranged from 5.49 × 10^–10 ± 2.64 × 10^–11 to 8.93 × 10^–9 ± 1.06 × 10^–10 m²/s, with HAD exhibiting higher values than VD. Activation energy varied between 10.25 ± 1.67 and 23.76 ± 3.39 kJ/mol. The Henderson and Pabis model best describes oat pulp drying behaviours across tested conditions. Both HAD and VD at 90 °C and 110 °C reduced energy consumption, lowered water activity, and preserved more bioactive compounds compared to 70 °C. HAD was more energy efficient than VD while maintaining higher phenolic content and antioxidant properties. HAD at 110 °C for 2.5 h with a 1 cm thickness provided a balance of energy consumption, batch capacity, and bioactive retention. The dried oat pulp had 60% less weight and water activity of 0.33, ensuring microbiological stability and facilitating easier transport and storage. These findings provide valuable insights for optimizing oat pulp drying for further applications. Graphical Abstract

Brewer’s spent grain (BSG) and spent coffee ground (SCG) are solid sidestreams from beverage production increasingly being upcycled into food, feed and other value-added products. These solid sidestreams are prone to microbial spoilage, negatively impacting their upcycling potential. Three samples each of BSG and SCG were obtained from generators and recycling facilities in Singapore, and their chemical, elemental, and microbial composition was characterized. The spoilage mechanisms were investigated during storage under anaerobic and aerobic conditions. Bacterial loads of sidestreams were low from craft brewery and café sources (6 log₁₀ CFU/g). The microbiome of BSG from recycling facilities was dominated by Bacilli, and B. coagulans was identified as the most prevalent species. SCG from recycling facilities was dominated by lactic acid bacteria, with L. panis being the most prevalent species. Storage up to 14 days under anaerobic conditions led to further bacterial proliferation mainly by Bacilli, lactic acid bacteria, and acetic acid bacteria, while aerobic storage led to extensive fungal contamination, including potential aflatoxin-producing Aspergillus flavus. The results shed light on the spoilage mechanisms, while highlighting the short shelf-life and food safety risks of BSG and SCG to inform valorization strategies.