Acid Hydrolysis of Proteins for Chromatographic Analysis of Amino Acids

Zumwalt, Robert W.; Absheer, Joseph S; Kaiser, Floyd E; Gehrke, Charles W.

doi:10.1093/jaoac/70.1.147

Cited by 13 publications

(10 citation statements)

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“…Protein content was determined according to the Dumas method (PRIMACS, Carbon-Nitrogen/Protein analyzer, Skalar, The Netherlands), by multiplying the nitrogen content by 6.25. Amino acid analysis was performed by gas chromatography of the heptafluorobutyl isobutyl derivatives after acid hydrolysis . The condensed phenolic content of the HMWM and ethanol-precipitated fractions were determined after alkaline fusion and analysis by GC-MS as described previously .…”

Section: Methodsmentioning

confidence: 99%

Insight into the Mechanism of Coffee Melanoidin Formation Using Modified “in Bean” Models

Nunes

Cruz

Coimbra

2012

J. Agric. Food Chem.

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To study the mechanism of coffee melanoidin formation, green coffee beans were prepared by (1) removal of the hot water extractable components (WECoffee); (2) direct incorporation of sucrose (SucCoffee); and (3) direct incorporation of type II arabinogalactan-proteins (AGPCoffee). As a control of sucrose and AGP incorporation, lyophilized green coffee beans were also immersed in water (control). The original coffee and the four modified "in bean" coffee models were roasted and their chemical characteristics compared. The formation of material not identified as carbohydrates or protein, usually referred to as "unknown material" and related to melanoidins, and the development of the brown color during coffee roasting have distinct origins. Therefore, a new parameter for coffee melanoidin evaluation, named the "melanoidin browning index" (MBI), was introduced to handle simultaneously the two concepts. Sucrose is important for the formation of colored structures but not to the formation of "unknown material". Type II AGPs also increase the brown color of the melanoidins, but did not increase the amount of "unknown material". The green coffee hot water extractable components are essential for coffee melanoidin formation during roasting. The cell wall material was able to generate a large amount of "unknown material". The galactomannans modified by the roasting and the melanoidin populations enriched in galactomannans accounted for 47% of the high molecular weight brown color material, showing that these polysaccharides are very relevant for coffee melanoidin formation.

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Section: Methodsmentioning

confidence: 99%

Insight into the Mechanism of Coffee Melanoidin Formation Using Modified “in Bean” Models

Nunes

Cruz

Coimbra

2012

J. Agric. Food Chem.

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“…Aliquots (100 µL) of the reaction mixtures were hydrolyzed overnight at 105 °C in 6 m HCl [46]. After hydrolysis the samples were neutralized with 6 m NaOH and 20 µL of the hydrolyzed sample was injected into an HPLC column (Microsorb 100‐5 C‐18, 250 × 4.6, Varian, Walnut Creek, CA, USA), which was equilibrated with 4% (v/v) acetonitrile in aqueous 0.10 m citric acid, pH 2.6, with a flow rate of 1 mL·min −1 .…”

Section: Methodsmentioning

confidence: 99%

Laccase‐catalyzed polymerization of tyrosine‐containing peptides

Mattinen¹,

Kruus²,

Büchert³

et al. 2005

The FEBS Journal

119

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Laccase (EC 1.10.3.2) is a multicopper enzyme belonging to the blue multicopper oxidase family. The most studied laccases are of fungal and plant origin [1][2][3][4][5], however, some bacterial laccases [6,7] have also been isolated. In addition, these enzymes have been found in some insects [8][9][10]. Laccases catalyze the oxidation of a wide range of organic and inorganic substances [11]. Typical organic substrates are aromatic compounds, such as different phenols, anilines and benzenethiols [11][12][13][14][15][16][17]. Laccases catalyze single-electron oxidation of the substrate, with concomitant reduction of molecular oxygen to water as shown in Scheme 1 [18]:Attempts to utilize the reactivity of laccase on phenolic substrates have been made, e.g., in pulp and paper, textile and food applications. Denim bleaching with a laccase-mediator system has been launched in the textile industry. The other applications, i.e., kraft pulp bleaching and detoxification have been only tested in laboratory or pilot scale [19]. Interest in the use of laccases in food processing is also increasing [20][21][22][23]. Laccases have been tested in bread making, where they can improve bread volume [24]. They can cross-link pentosans and arabinoxylans via ferulic acid (FA) side-chains [25,26]. It has been suggested that this kind of cross-linking of feroylated carbohydrates by laccase is similar to the peroxidase-catalyzed reaction, the aromatic ring of FA being the initiating site for enzymatic oxidation [25]. It has also been shown that laccase can cross-link whey proteins in the presence of phenolic acid [27]. However, in order to be able to develop new applications for laccases in foods, it is crucial also to understand enzymatic reactions on proteins at the molecular level. At present, laccase-catalyzed reactions resulting in oxidation of proteins are poorly understood. Very Laccase-catalyzed polymerization of tyrosine and tyrosine-containing peptides was studied in the presence and absence of ferulic acid (FA). Advanced spectroscopic methods such as MALDI-TOF MS, EPR, FTIR microscopy and HPLC-fluorescence, as well as more conventional analytical tools: oxygen consumption measurements and SDS ⁄ PAGE were used in the reaction mechanism studies. Laccase was found to oxidize tyrosine and tyrosine-containing peptides, with consequent polymerization of the compounds. The covalent linkage connecting the compounds was found to be an ether bond. Only small amounts of dityrosine bonds were detected in the polymers. When FA was added to the reaction mixtures, it was found to be incorporated into the polymer structure. Thus, in addition to homopolymers, different heteropolymers containing two or four FA residues were formed in the reactions.

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“…Each subsample was hydrolyzed by adding 0.3 mL of 6 M HCl to the vial and was tightly capped. To heat the samples, an aluminum block with holes to accommodate the glass vials was mounted on a hot-plate for 24 h at 110 C. [29][30][31]40 Aer cooling the solution to room temperature for 5 min, the solutions were ltered and dried under a constant 4 L min À1 nitrogen stream because the existence of excess moisture can result in poor reaction yield and instability of the derivatized products. The three subsamples of hair from the same individual were digested across spans of 3 days.…”

Section: Hair Analysismentioning

confidence: 99%

“…28 For this reason, this study focuses on the 14 most abundant amino acids in the protein of human hair, as obtained by acid hydrolysis using 6 M of hydrochloric acid (HCl). [28][29][30][31] The amino acids were quantied via their trimethylsilyl (TMS) derivatives [32][33][34][35] using gas chromatography/mass spectrometry (GC/MS). 29,36,37 The main objective of this study is to provide a discriminating technique for distinguishing between hair samples from different human subjects based on factors related to sex, age, dietary habits, and region of origin that have been assumed to contribute to variations in the amino acid contents of human scalp hair.…”

Section: Introductionmentioning

confidence: 99%