Clarification of red raspberry juice using microfiltration with gas backwashing: A viable strategy to maximize permeate flux and minimize a loss of anthocyanins

• Juice clarified by UF had a superior clarity but the recovery of anthocyanins was low.
• A maximum recovery of pigments in a fresh and reconstituted juice was achieved by MF.
• Treatment with gelatin and bentonite resulted in more turbid juice than UF and MF.
• The permeate flux in MF was maintained at high levels by periodic gas backwashing.
• Cake compaction at high pressures was prevented by short filtration cycles.

Red raspberry (Rubus idaeus) juice was produced by maceration of raspberry pulp at 50 °C for 2 h using 400 mg kg−1 Klerzyme®150 enzymatic pectolitic preparation followed by raw juice clarification with gelatin and bentonite or cross-flow membrane filtration. A minimal loss of anthocyanins from 630 to 540 mg l−1 was obtained when the juice was clarified using a ceramic multichannel microfilter (MF) with a pore size of 0.2 μm. A light transmission at 625 nm in MF permeate was above 85% and the residual pectin (900 mg l−1) was completely removed. During ultrafiltration through ceramic or polysulfone membranes with a molecular weight cut-off of 30–300 kDa, the content of anthocyanins was reduced to 220–370 mg l−1, but a light transmission at 625 nm was as high as 96%. The permeate flux in MF was maintained at high values above 170 l m−2 h−1 at 3 bar for more than 2 h by backwashing the membrane with a compressed air every 6 min for 1 min. The cake compression at high pressures was avoided by short filtration times between backwashing.

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