Block freeze-concentration of coffee extract: Effect of freezing and thawing stages on solute recovery and bioactive compounds

• Coffee extract was freeze-concentrated by the block technique.
• The initial coffee mass fraction influenced the solute recovery.
• The control of freezing direction improved the concentration.
• The bioactive compounds were distributed in proportion to the total solid content.
• The technique preserved the functional properties of the coffee extract.

Coffee extract was freeze-concentrated using the total block technique. The effects of four parameters were evaluated: the initial coffee mass fraction (5 and 15% w/w), the cooling temperature (−10 and −20 °C), the heating temperature (20 and 40 °C) and the freezing direction (parallel and counter-flow to the thawing direction). The solid concentration was measured during the thawing stage to quantify the solute recovery and the concentration index for one stage of freeze concentration. The coffee mass fraction, the freezing direction and the cooling temperature significantly influenced the solute recovery. A concentration index between 1 and 2.3 was obtained in one cycle. The effect of block freeze concentration on the bioactive compound concentration and the antioxidant activity was measured. The coffee bioactive compounds were distributed in proportion to the total solid content in the ice and liquid. Therefore, block freeze concentration is an effective technique to preserve functional properties of coffee extracts.