Fractionation by centrifugation of leaf proteins in press juices from Brassica and other species as a function of pH

Abstract

AbstractNon‐green leaf protein concentrates can be produced after separation of chlorophyll‐associated proteins from chlorophyll‐free proteins by sedimenting the chlorophyll‐containing membranes suspended in press juice. To make the use of low speed centrifugation possible, the influence of pH on protein sedimentation rate was investigated, especially for Brassica Oleracea (17 cultivars). Press juices produced on a laboratory scale from greenhouse grown plant material were adjusted to the desired pH and centrifuges briefly at 5000 g or 15,000 g. The chlorophyll‐associated protein from B. Oleraces sedimented rapidly at pH values both below and above 6.0(original pH of the press juice). When the pH of the press juice was adjusted to 7.5, all the chlorophyll‐associated protein sedimented at 15,000 g, whereas about 45%of the original protein remained in the supernatant. An increase in sedimented chlorophyll‐associated protein at higher pH was also observed for Brassica napus, Helianthus annuus and Vicia faba, but not for Beta vulgaris and Dactylis glomerata.Theoretically, the protein sedimentation pattern typical for B. oleracea might depend primarily on protein aggregation, but shrinking of thylakoids at pH values higher than 6 could contribute. The deviation from this pattern observed for B. vulgaris and D. glomerata might be caused by differences in composition of proteins or low molecular species. In practice, a pH above 7.0 seems to be useful for separation of chlorophyll‐associated proteins from chlorophyll‐free proteins by centrifugation of press juice from Brassica species without heat treatment.