Tobacco Leaf Protein: II. Genetic and Fractionation Approaches to Improving Tobacco Leaf Protein Production

Abstract

SUMMARYTobacco variety T. I. 401 was evaluated for seasonal leaf protein yields and crossbred with other genotypes to determine whether leaf protein yield was a genetically transmissible trait. Relatively high leaf protein yields associated with later maturity were observed in preliminary trials but additional crossbreeding and selection is deemed necessary to achieve stable integration of improved leaf protein yields and desirable agronomic performance. Chromatographic and electrophoretic analyses demonstrated that high leaf protein yield of T. I. 401 was not associated with a particular protein fraction but rather was a general phenomenon affecting all major protein classes. Besides examining genetic factors for improving leaf protein yields, two mechanical improvements in leaf protein fractionation technology were introduced into the process. A mild acidification step (to pH 5.5) with a subsequent moderate heat treatment (50 °C) resulted in a green coagulum which was readily removed by brief low speed centrifugation without substantial loss of the fraction containing soluble protein which precipitates as a white pellet when heated to 80 oc_ Hollowfiber membrane technology was also investigated as a means of producing a purified concentrate with high levels of undegraded protein. The membrane system tested was relatively efficient and greatly improved the quality of the protein product. RESUMEOn a analyse les vanatwns saisonmeres des teneurs en proteines foliaires clans la variete de tabac T.I. 401 et Cl·oise cette variete avec d'autres genotypes pour determiner si la teneur en proteines foliaires etait une caracteristique genetique. Des essais preliminaires ont rendu comte des teneurs elevees en proteines foliaires associees a une maturite retardee, mais l'hybridation et la selection etaient jugees necessaire pour arriver a une integration stable de la teneur augmentee en proteines foliaires et pour assurer des performances agronomiques desirables. Des analyses chromatographiques et electrophoretiques ont revele que la teneur elevee en proteines foliaire clans T.I. 401 n'etait pas associee a une fraction proteique particuliere mais qu'il s'agissait plutot d'un phenomene general qui se rapportait a toutes les classes proteiques importantes.Outre 1' examen des effets de facteurs genetiques sur la teneur en proteines foliaires, deux techniques ameliorees ont ete introduites clans le processus de fractionnement du contenu proteique des feuilles. L'acidification legere (jusqu'a pH 5.5) et le rechauffement modere a 50 ac ont fourni un coagulum vert qui etait facilement elimine par une courte centrifugation a vitesse moderee, ceci sans entrainer la perte des proteines solubles. Celles-ci precipitent sous forme de culot apres rechauffement a 80 oc. La filtration sur membrane en fibre creuses a ete utilisee pour obtenir un concentre proteique purifie contenant un taux eleve en proteines denatures. Le systeme de filtre moleculaire teste etait relativement efficace et apportait une amelioration de la qualite proteique.