Fractionation by centrifugation of leaf proteins from varieties and cultivars of Helianthus annuus and Helianthus debilis as a function of pH and temperature

Abstract

AbstractIn order to select plant material for obtaining a high proportion of chlorophyll‐free protein from Helianthus species by heat fractionation, leaf extracts from 11 field grown cultivars of H. annuus and H. debilis were investigated. In addition, press juices from H. annuus cv. Kinesisk were supplied with salts or urea before heat treatment in order to increase the proportion of chlorophyll‐free protein during heat fractionation.The extracts were adjusted to pH 5.0, 6.0 and 8.0; then left for 20 min at 20°C, 50°C or 60°C and centrifuged at 2,500 g. The highest percentage chlorophyll‐free protein of the total protein in the extract, more than 10%, was obtained for H. debilis cv. fl.pl. Sun Gold, H. annuus cv. Giganta, H. annuus cv. uniflorus and H. debilis cv. Stella, at pH 6.0 and 50°C.The low percentage chlorophyll‐free protein obtained could be explained by the fact that a considerable part of the chlorophyll‐free protein sedimented at original pH, low temperature and low centrifugation speed. This sedimentation at low temperature was probably due to interactions of phenolics. Besides, if the chlorophyll‐associated membranes were highly fragmented during the disintegration of the plant material, the high temperature required to precipitate them completely led to further aggregation and thus to loss of chlorophyll‐free proteins.Salts or urea present during heat treatment (pH 6.0/55°C for 20 min) did not considerably increase the proportion of chlorophyll‐free proteins obtained.