Yield Of Pyrazines Research Articles

Pyrazine yield and functional properties of rice bran protein hydrolysate formed by the Maillard reaction at varying pH.

Interest in plant-based protein sources has grown rapidly. Rice bran contains excellent quality protein, but it is still rare in the market, due to its poor functional properties and undesirable odors. Therefore, we studied the Maillard reaction at different pHs on the formation of pyrazines and improved functional properties of rice bran protein hydrolysate. Protein from rice bran was extracted and hydrolyzed, using alcalase, at 55°C for 4h. Fructose was added, and the pH of the hydrolysate was adjusted to pHs between 7.0 and 10.0, before spray drying. Five pyrazines were detected in the hydrolysate powder, with the highest yield at pH 9 ( p < 0.05). The highest odor active value came from 2-ethyl-3,5-dimethylpyrazine (26.26), which contributed coffee,nutty and caramel aromas, followed by 2,5-dimethylpyrazine (9.2) and 2-ethyl-5-methylpyrazine (5.0). Increased pH led to a darker color (L* = 58.5) and redder (a* = 11.7) and yellower (b* = 13.8) powder. Key functional properties-solubility, water and oil binding capacity and emulsion stability index and foaming capacity-were increased with pH ( p < 0.05). The optimum pH for pyrazine formation and improved properties of enzymatic rice bran protein hydrolysate was pH 9.0.

Optimization of α-Hydroxyketone and Pyrazine Syntheses Employing Preliminary Reactions of Glucose and Buffer Solutions

Summary Glucose and selected phosphate buffers have been reacted employing systematic variations in reaction temperature and time (150–160 °C for 60–90 min) to optimize the yield of acetol. This mixture was reacted further with NH4OH, systematically varying reaction conditions and reagent ratios to optimize pyrazine yield. The highest yield of pyrazine was obtained when 1 g of glucose was reacted with 25 mL of buffer at 150–160 °C for 60 min, which in turn was reacted with 1 mL of concentrated aqueous NH4OH at 120–130 °C for 17–18 h. Higher temperatures and higher concentrations of glucose caused a decrease in the yield of pyrazines. The addition of hydrolyzed tobacco-derived F1 protein as a secondary source of nitrogen increased the yield of pyrazines by 2–10% depending on F1 protein concentration. Furthermore, the addition of any α-hydroxyketone, similar in structure to acetol, as a pure reagent to the reaction mixture not only increased the yields of pyrazine by ranging from 25–100 % depending on the reagent concentration, but also significantly altered the qualitative and quantitative distribution of the pyrazines. With all of the reaction parameters examined (reaction time, temperature, reagent ratios, etc.) the most significant impacts on both pyrazine yield and distribution were noted when: 1) glucose was pre-reacted with buffer, 2) hydrolyzed F1 protein was added as a second nitrogen source, and 3) when pure α-hydroxyketones were employed as co-reagents. Use of these reaction parameters was found to dramatically shift the pyrazine distribution toward higher molecular weight resulting in a pyrazine array having more desirable physical and sensory attributes.

Optimal Synthesis of Substituted and Branched Pyrazines via Reaction of Alpha Hydroxy Ketones with Selected Nitrogen Sources

Summary Employment of 1-hydroxy-acetone as a carbon source and NH4OH as a source of base and nitrogen, has enabled arrays of pyrazines to be synthesized. Reaction conditions such as temperature, time, carbon/nitrogen mole ratios and pH were optimized to maximize the quantity of pyrazines, thereby providing the synthesis of at least 19–20 structurally different pyrazines. Addition of amino acids, selected aldehydes, and hydrolyzed tobacco-derived F1 protein has positively impacted the array of pyrazines from both qualitative and quantitative aspects. Results further showed that by changing the carbon source from 1-hydroxy-acetone to 1-hydroxy-2-butanone and/or 2-hydroxy-3-butanone, control of the type of pyrazines being synthesized could be realized in that the qualitative and quantitative distributions of the pyrazine array were shifted to higher molecular weight derivatives. A relatively large scale reaction (1.5 L) employing optimized parameters yielded &gt; 2 g of a diverse array of pyrazines dominated by multiple dimethylpyrazine derivatives. While systematically varying reaction conditions and reagent mole ratios can predictably alter the distribution and yield of pyrazines, the two most overwhelmingly significant factors governing these two pyrazine product characteristics included the structure of the carbon source and the presence or absence of aldehydes and free amino acids.

Synthesis of Pyrazines Using Sugar Derived from Tobacco Cellulose and Hydrolyzed Tobacco F1 Protein as an Amino Acid Source

Summary An array of pyrazines have been synthesized using sugars derived from tobacco cellulose (CDS), ammonium hydroxide, and hydrolyzed tobacco F1 protein as a source of free amino acids (isolated amino acids from F1 hydrolysate, from filtered F1 hydrolysate and from non-filtered F1 hydrolysate). All reactions were performed at 120 °C for 60 min using a 40-mL Parr reaction vessel. Results showed that the addition of hydrolyzed F1 protein as free amino acid source increased the number of pyrazines with branched alkyl chains (for example, 2-butyl-3-methyl pyrazine) compared to when no amino acids were added. However, using isolated amino acids from hydrolyzed F1 protein versus just hydrolyzed F1 protein (filtered or not filtered) did not make a difference in yield or type of branched pyrazines. When non-filtered hydrolyzed F1 protein was used, the solution was much more viscous and contained suspended solid material when compared to the use of filtered hydrolyzed F1 protein. Addition of threonine (THR) to the reaction mixture did not increase the yield of pyrazines but did slightly shift the distribution of pyrazines toward those with three and four carbons attached. Similar but not identical arrays of pyrazines were obtained when somewhat resembling reaction conditions were applied on a larger reaction scale (~1.5 L). A significant 50%-decrease in pyrazine yield was observed when the reaction temperature was reduced from 120 to 100 °C. No noticeable difference in the array of pyrazines from these two reactions was observed. In the majority of cases, the presence of free amino acids resulted in an increase in pyrazine yield coupled with a change in the qualitative array of pyrazines. These results clearly illustrate that sugar prepared from tobacco cellulose (glucose) can be used just like high fructose corn syrup to prepare flavor compounds via Amadori and Maillard reactions. The evidence highlights that hydrolyzed amino acids from F1 tobacco protein can be used via Maillard reactions to produce complementary arrays of pyrazine flavor compounds.

Conversion of Tobacco Biomass to Flavor Components by Means of Microwave and Parr Reactors

Summary In the present work, microwave and Parr reactors were utilized for synthesis of pyrazines from plant-based biomass in the presence of ammonia and different amino acids. Using these techniques led to synthesis of a relatively wide range of pyrazines with sweet odor and chocolate-like smell. The optimum synthetic conditions to have maximum pyrazine yield for both the microwave and Parr reactions were 41 g of fructose/glucose syrup derived from cellulosic biomass, 28 mL NH4OH (30%), and 0.96 g L-threonine, 0.56 g L-valine, 0.5 g L-leucine, and 0.5 g L-isoleucine at 120 °C for 30 min. Quantitative results obtained via gas chromatography-mass spectrometry (GC-MS) using the traditional open-heated oil bath method have been compared with data obtained via microwave and Parr reactors. In these two latter methods, sealed vessels under high pressure and higher temperature were used. The yield of synthesized pyrazines increased dramatically with both microwave and Parr reactors. Surprisingly, the yield of synthesized pyrazines was both reproducible and nearly two times higher via the Parr reactor than that observed with the microwave reactor under comparable conditions.

Sugar and selected amino acid influences on the structure of pyrazines in microwave heat‐treated formulations

AbstractThe amount and type of selected sugars and selected amino acids have been shown to significantly impact the structure of headspace‐volatile pyrazines produced in aqueous microwave heat‐treated formulations. Selection of sugar and amino acid can dictate the structure, yield and distribution of headspace‐volatile pyrazines. Under the same reaction conditions and sugar to ammonium hydroxide ratios, rhamnose was found to produce more pyrazines than did high‐fructose corn syrup (HFCS). With rhamnose, the yield of pyrazines approached 4500 µg mL−1. Formulations selectively enriched in ethyldimethylpyrazines can be prepared by stepwise substitution of HFCS with rhamnose. Formulations preferably enriched in methyl‐ and dimethyl‐(3‐methylbutyl)‐ as well as methyl‐ and dimethyl‐(2‐methylpropyl)pyrazines were prepared through selective combinations of rhamnose/HFCS and amino acids. Stepwise substitution of HFCS with rhamnose coupled with the use of selected amino acids allowed for the control of the yield, structure and distribution of volatile pyrazines in microwave heat‐treated aqueous formulations. Reaction temperature was also found to significantly influence pyrazine yield and distribution. Statistical modeling of the reaction yields as functions of reaction variables produced surfaces with acceptable modeling coefficients. Mechanisms were postulated to account for the increased yields and selected distributions pyrazines when rhamnose was employed. Copyright © 2005 Society of Chemical Industry

Formation of Strecker aldehydes and pyrazines in a fried potato model system.

Sugars and amino acids were removed from potato slices by soaking in water and ethanol. They were then infused with various combinations of sugars (glucose and/or fructose) and amino acids (asparagine, glutamine, leucine, isoleucine, phenylalanine, and/or methionine) and fried. Volatile compounds were trapped onto Tenax prior to gas chromatography-mass spectrometry. Relative amounts of compounds (relative to the internal standard) and relative yields (per mole of amino acid infused into the slices) were determined. Amounts of 10 pyrazines, 4 Strecker aldehydes, and 4 other compounds were monitored. Relative amounts and relative yields of compounds varied according to the composition of the system. For the single amino acid-glucose systems, leucine gave the highest relative amount and relative yield of its Strecker aldehyde. Asparagine and phenylalanine gave the highest total relative amount and total relative yield, respectively, of pyrazines. In the system containing all of the amino acids and glucose, the relative amount of 3-methylbutanal was higher, whereas the amounts of the other monitored Strecker aldehydes were lower. Most of the relative amounts of individual pyrazines were lower compared to the glucose-asparagine system, whereas the total relative yield of pyrazines was lower, compared to all of the single amino acid-glucose mixtures. Addition of fructose to the mixed amino acid-glucose model system generated Strecker aldehydes and pyrazines in ratios that were more similar to those of untreated potato chips than to those from the same system but without fructose. Both the sugars and the amino acids present in potato are crucial to the development of flavor compounds in fried potato slices.

Synthesis of materials rich in pyrazines employing no sugar

The characteristics of the headspace volatiles above materials rich in pyrazines prepared with no added sugars have been determined. Formulations void of sugar and rich in branched alkyl side chain pyrazines can be prepared in a microwave oven from formulations containing hydroxyketones, selected low-molecular-weight aldehydes, selected amino acids and an additional nitrogen compound such as ammonium hydroxide. A relatively low temperature of 105 °C coupled with short reaction times, 60 min, affords formulations with rich aromas and relatively high concentrations of alkyl pyrazines with straight and branched alkyl side chains. The amount and type of branched chain-containing pyrazines are a function of the amount and type of hydroxyketone, aldehyde and amino acid employed. Stepwise substitution of the hydroxyketones for high-fructose corn syrup (HFCS) produces stepwise increases in total pyrazines. Stepwise increase in the amount of added aldehyde produces stepwise increases in the amount of pyrazines containing branched alkyl side chains. Use of 3-hydroxy-2-propanone produces materials containing a set of pyrazines characterised by the presence of cis- and/or trans-propenyl side chains. The semi-quantitative yield of pyrazines, ∼3500 µg mL−1, and per cent branched alkyl side chain pyrazines, ∼35%, from these formulations were determined through the use of an internal standard in the headspace measurements. Previously postulated reaction mechanisms for the formation of pyrazines are confirmed through the use of selected reagents. © 2000 Society of Chemical Industry

The effect of pH on the volatiles formed in an extruded starch-glucose-lysine model system

Starch-glucose-lysine extrudates were produced using a twin-screw co-rotating machine. The final barrel zone and die temperatures were 150 ± 3 °C and 150 ± 7 °C, respectively. The residence time was 32 s, the moisture content of the feed was 18% (m m −1) and the feed pH was 4.0, 5.0 or 7.7. Isolates of the volatile components were prepared using continuous steam distillation-solvent extraction with pentane:ether (9:1, v/v) as the solvent. Analysis by gas chromatography-mass spectrometry resulted in the identification of 32, 20 and 16 compounds, respectively, from each isolate. At pH 7.7, nitrogen compounds dominated the isolate and pyrazines accounted for over 80% (m m −1) of the volatiles. At pH values of 5.0 and 4.0, the yield of pyrazines was less than 10% of that at pH 7.7 and furans comprised more than 80% (m m −1) of these aroma isolates. The yield of total volatiles was more than 60% greater at pH 7.7 than at the other pH values.

Band assignments in the i.r. spectra of pyridine and pyrazine adducts of nickel(II) glycinate by multiple isotopic labelling

The i.r. spectra of [Ni(gly) 2(py) 2] (gly = glycinate ion, py = pyridine) and [Ni(gly 2(pz)] · 1 1 2 H 2O (pz=pyrazine) and their isotopically labelled analogues have been determined over the range 3300-150 cm −1. 18O-, 1- 13C-, 2- 13C-, 15N- and 2.2-d 2-Labelling of the coordinated glycinate yields assignments for the glycinate and metal-oxygen vibrations while d 5-labelled pyridine and d 4-labelled pyrazine yield assignments for the internal vibrations of the heterocyclic rings and metal—nitrogen vibrations. The results indicate that there is considerable vibrational coupling in these complexes.

Catalytic synthesis of pyrazine, piperazine, and 1,4-diaza[2,2,2]-bicyclooctane

A study is made of the deamination of diethylenetriamine over acidalkali catalysts, i. e., kaolin and alumina with promoters. Promoters which raise the acidity of the catalyst, affect the formation of triethylene diamine favorably. Increasing the amount of additive increases the amount of triethylenediamine, and cuts the optimum temperature at which it is formed. On kaolin or Al2O3+15% B2O3, the yield of triethylenediamine amounts to 30% theory. Addition of MoO3 facilitates dehydrodeamination and hydrogenolysis of the diethylenetriamine. The optimum promoter for preparing pyrazine is MoO3 along with a small amount of acid oxides. On the Al2O3+5% MoO3+1% P2O5, the pyrazine yield is 27.5% theory. Triethylenediamine can be separated from mixtures of it with piperazine by azeotropic distillation with mxylene or a mixture of mesitylene and α-memylnaphthalene.