Fractionation by centrifugation of leaf proteins from Brassica napus, Brassica oleracea, Helianthus annuus and Atriplex hortensis as a function of pH and temperature

Chlorophyll-free leaf protein concentrates for human consumption can be produced after separation of the chlorophyll-associated protein from the rest of the leaf protein. This protein separation was studied in four plant species using heat fractiona-tion. Press juice was prepared on a laboratory scale from field grown Atriplex hortensis, Brassica napus. Brassica oleracea and Helianthus annuus. Some further experiments were made with greenhouse grown plant material. After adjustment of pH to values between 4.0 and 8.0 the press juice was heated in water baths at 20, 35, 40, 45, 50, 55 and 60°C with or without 20 min holding time at appropriate temperature. Thereafter the juices were briefly centrifuged at 2500g. The protein content of the sediment was determined and the colour of the supernatant was observed. The species showed different protein sedimentation patterns, especially at neutral and weakly alkaline pH. Brassica napus had rapidly sedimenting proteins, low temperature was sufficient for complete sedimentation of chlorophyll-associated proteins and gave a high percentage of the total press juice protein as chlorophyll-free protein. Atriplex hortensis had slowly sedimenting proteins irrespective of temperature, required high temperature for complete sedimentation of chlorophyll-associated proteins and gave a low percentage chlorophyll-free proteins. Brassica oleracea and Helianthus annuus showed intermediated properties. Reasons for these differences among the species are discussed.