T. A. Wheaton

Continuous flow separation of carotenoids by liquid chromatography.

Abstract A liquid chromatographic system has been developed that gives good separation of complex mixtures of carotenoids. Carotenes are separated on magnesium oxide and xanthophylls on zinc carbonate. The columns are regenerated after each sample which virtually eliminates repacking. Submicrogram quantities of carotenoids are readily detected and many cis-trans isomers are separated. An antioxidant is included to reduce on-column losses and isomerization of carotenoids. The method is quantitative, reproducible, sensitive, moderately rapid, and suitable for routine analysis. Use of the system for the study of isomer formation of carotenoids and for the identification of citrus peel pigments is included.

Quantitative analysis of phenolic amines using ion-exchange chromatography

Abstract A method has been developed for the quantitative analysis of mixtures of phenolie amines by separation on a column of a strong-acid ion-exchange resin and measurement of UV absorbance of the column effluent. Satisfactory results were obtained with samples containing 0.01 to 0.2 μmole of octopamine, synephrine, hordenine, tyramine, and N-methyltyramine. Little sample preparation is required for the citrus juices studied and a chromatogram may be completed in 2 hr.

Conversion of β-citraurin to reticulataxanthin and β-apo-8′-carotenal to citranaxanthin during the isolation of carotenoids from Citrus

Abstract Reticulataxanthin and citranaxanthin were found to be artifacts formed from β-citraurin and β-apo-8′-carotenal during the saponification of citrus carotenoids in the presence of small amounts of acetone. The reaction takes place at room temperature under normal conditions of extraction. Based on these studies it was concluded that β-citraurin rather than reticulataxanthin is the main pigment contributing to the external reddish color of a number of citrus cultivars.

Biosynthesis of synephrine in citrus

Abstract Synephrine is formed in citrus by a pathway involving tyramine and N-methyltyramine. Octopamine is probably not an important intermediate. 14 C-labeled tyramine was converted to N-methyltyramine, hordenine, octopamine, and synephrine in one of the citrus cultivars studied. Tyrosine was a less efficient precursor and phenylalanine, serine, ethanolamine, and epinephrine were ineffective.

l-Octopamine in Citrus: Isolation and Identification

l-Octopamine, [l-p-hydroxy-α-(aminomethyl)benzyl alcohol], has been isolated and identified from extracts of juice and leaves of the Meyer lemon. Identification was by chromatography, optical rotation, ultraviolet absorption curves, fluorescence spectra, and infrared spectroscopy. l-Octopamine has not previously been isolated and identified from plants.

Formation of diacetonamine and triacetonamine in plant extracts

Abstract Diacetonamine and triacetonamine were isolated from extracts of tangerine leaves and shown to be artifacts formed during the isolation procedure.

Isolation of citrosamine from citrus leaves

Abstract A nitrogen containing trisaccharide was found in citrus leaves, identified as glucosamido-glucuronido-inositol and given the trivial name citrosamine.

SEASONAL NITROGEN BUDGETS OF MATURE CITRUS TREES ON A SANDY ENTISOL

Approximately 30% of Florida citrus is grown on well-drained Entisols with low nutrient-holding capacity, which are prone to high nitrogen (N) leaching losses. However, increasing application frequency of N-fertilizer via multiple fertigations does not increase crop yield, whereas in agronomic crops, such an approach typically enhances N uptake efficiency. We assessed seasonal tree N tissue concentration dynamics as affected by N rate for mature fourteen-year-old ‘Hamlin’ orange (Citrus sinensis L. Osbeck) trees on either Carrizo citrange (C. sinsensis L. Osbeck X Poncirus trifoliata L. Raf.) or Swingle citrumelo (C. paradisi Macf. X P. trifoliata L. Raf.) rootstocks. Nitrogen was applied as ammonium nitrate in six split fertigation applications with N target values of 179 and 269 kg ha−1yr−1. Leaf, twig, and branch bark tissue N concentrations decreased through the spring to minima in May and June. This time period corresponds to a period of high N demand associated with both vegetative and reproductive growth. Tissue N concentrations increased from late spring minimums to fall and winter maximum concentrations. Reduction in branch bark and wood tissue N concentrations may have been due to a redistribution of N to leaf, twig, and fruit tissues in response to low N supply. The majority of the spring N should be supplied prior to May.