Sustainable valorization of artisanal sour buttermilk using nanofiltration and spray drying

Sour buttermilk is formed when milk fat is conserved as clarified fat using a traditional household method. It has low total solids (TS) and high acidity. Often, people discard sour buttermilk due to a lack of an effective preservation method. This investigation aimed to concentrate sour buttermilk using nanofiltration (NF) equipped with a 200 Da molecular weight cut-off polyamide membrane (AFC 40), tubular B1 parallel flow module, operated at 20 ± 1 bar pressure and 35 ± 1 °C temperature. The process yielded an NF retentate with 19.61% total solids. The retentate was then spray dried at 185/75 ± 5 °C to produce sour buttermilk powder. This powder showed excellent wettability (3 s, instant) and flowability. The NF permeate contained 0.42 ± 0.05% TS, 0.12 ± 0.03% ash, 0.37 ± 0.02% lactic acidity, and 1.79 ± 0.21 mPa.s apparent viscosity at 20 °C. It was used as a natural coagulant to prepare heat and acid-coagulated milk gel (chhana) from buffalo milk. Usually, buffalo milk chhana has a hard texture and grainy body. When prepared with NF permeate, buffalo milk chhana had significantly (p < 0.05) lower hardness and higher yield compared to cow milk chhana made with citric acid. Overall, this investigation showed that NF and spray drying can sustainably valorize sour buttermilk with zero waste generation.