title: Ultrasound-based protein determination in maize seeds.
abstract: The need for a simple and accurate method for protein estimation in alcoholic extracts led to the reexamination of the optimum conditions of a colorimetric assay based on the biuret reaction. Sonication time and the other experimental parameters were optimized after kinetics study on the extraction of either zein or total proteins. Zein extraction and purity were investigated by (1)H and (13)C NMR spectroscopy, SDS-PAGE electrophoresis, and UV-visible spectrophotometry (UV-vis). A zein assay was proposed, which involves the reaction of copper ions in copper phosphate powder with zein extracted in ethanolic solutions under strong alkaline environment. Furthermore, we extended this procedure to determine total proteins in maize samples simultaneously with their ultrasonic-assisted (US) extraction with an alkaline-alcoholic solution. Proteins in both types of extracts were well characterized by UV-vis spectroscopy. However, the 545 nm absorbance of the violet-colored supernatants which is proportional to the protein content was found to be the key parameter of the improved biuret-based protein assay. Comparison of values obtained by this procedure and by Micro-Kjeldahl method was in excellent agreement. A scaled-down procedure agreed well with the standard procedure. Enhanced accuracy and repeatability was found in protein determination in maize using the modified biuret method. The optimization of reagent concentrations and incubation times were studied as well.
authors.affiliation: "Petru Poni" Institute of Macromolecular Chemistry, 41A Grigore Ghica Voda Alee, Iasi 700487, Romania; Faculty of Chemistry, "Al. I. Cuza" University of Iasi, 11 Carol I, Iasi 700506, Romania. Electronic address: gabidr@uaic.ro.
authors.forename: Gabi
authors.initials: G
authors.lastname: Drochioiu
authors.affiliation: "Petru Poni" Institute of Macromolecular Chemistry, 41A Grigore Ghica Voda Alee, Iasi 700487, Romania; Faculty of Chemistry, "Al. I. Cuza" University of Iasi, 11 Carol I, Iasi 700506, Romania.
authors.forename: Catalina Ionica
authors.initials: CI
authors.lastname: Ciobanu
authors.affiliation: Faculty of Chemistry, "Al. I. Cuza" University of Iasi, 11 Carol I, Iasi 700506, Romania.
authors.forename: Sabina
authors.initials: S
authors.lastname: Bancila
authors.affiliation: Faculty of Chemistry, "Al. I. Cuza" University of Iasi, 11 Carol I, Iasi 700506, Romania.
authors.forename: Laura
authors.initials: L
authors.lastname: Ion
authors.affiliation: "Petru Poni" Institute of Macromolecular Chemistry, 41A Grigore Ghica Voda Alee, Iasi 700487, Romania; Faculty of Chemistry, "Al. I. Cuza" University of Iasi, 11 Carol I, Iasi 700506, Romania.
authors.forename: Brindusa Alina
authors.initials: BA
authors.lastname: Petre
authors.affiliation: Faculty of Chemistry, "Al. I. Cuza" University of Iasi, 11 Carol I, Iasi 700506, Romania.
authors.forename: Claudia
authors.initials: C
authors.lastname: Andries
authors.affiliation: Faculty of Chemistry, "Al. I. Cuza" University of Iasi, 11 Carol I, Iasi 700506, Romania.
authors.forename: Robert Vasile
authors.initials: RV
authors.lastname: Gradinaru
authors.affiliation: "Petru Poni" Institute of Macromolecular Chemistry, 41A Grigore Ghica Voda Alee, Iasi 700487, Romania.
authors.forename: Manuela
authors.initials: M
authors.lastname: Murariu
mesh_terms: D002498:Centrifugation; D003300:Copper / Q000737:chemistry; D012015:Reference Standards; D012639:Seeds / Q000737:chemistry*; D000069453:Ultrasonic Waves; D003313:Zea mays / Q000737:chemistry*; D015028:Zein / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification*
chemical_list: D003300:Copper; D015028:Zein
keywords: NMR; Protein determination; SDS–PAGE; UV–vis spectroscopy; Ultrasound-assisted extraction; Zein