Use of glyoxyl-agarose immobilized ficin extract in milk coagulation: Unexpected importance of the ficin loading on the biocatalysts

Abstract

A protein extract obtained from fig tree (Ficus carica) latex containing ficin activity was immobilized on glyoxyl agarose. Different biocatalyst loadings were used (3, 10, 30 and 85 mg/g). When casein was used as substrate, the expressed activities were 60%, 58%, 41% and 14%, respectively, very likely due to casein diffusional limitations. As expected, an increase of the concentration of either free or immobilized ficin reduced the clotting time of casein solution and milk. However, maintaining the same amount of ficin, lowly loaded ficin biocatalysts were unable to produce the clotting neither of the casein solutions nor of the milk, while highly loaded catalysts produced a good aggregate. Performing the proteolytic milk treatment at 4 °C to prevent aggregation and them incubating the milk at 40 °C, the use of immobilized enzyme in milk clotting gave coagulum yields of 19%, 24% and 27% for the 10 mg/g, 30 mg/g and 85 mg/g immobilized ficin respectively, while free ficin gave a yield of around 20% under similar ficin concentrations.