Flavoring components of raw monsooned arabica coffee and their changes during radiation processing

Volatile aroma principles, nonvolatile taste constituents (caffeine and chlorogenic and caffeic acids), and glycosidically bound aroma compounds of monsooned and nonmonsooned raw arabica coffee were analyzed using gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC). Among the most potent odor active constituents known to contribute to the aroma of the green beans, 3-isopropyl-2-methoxypyrazine, 3-isobutyl-2-methoxypyrazine, 4-vinylguaiacol, beta-damascenone, (E)-2-nonenal, trans,trans-2,4-decadienal, phenylacetaldehyde, and 3-methylbutyric acid were detected by GC-MS in both samples. A decrease in content of methoxypyrazines and an increase in 4-vinylguaiacol and isoeugenol resulted in a dominant spicy note of monsooned coffee. These phenolic compounds exist partly as their glycosides, and their release from the bound precursors during monsooning accounted for their higher content in monsooned coffee. A considerable decrease in astringent chlorogenic acid as a consequence of hydrolysis to bitter caffeic acid was noted in monsooned coffee. Radiation processing of nonmonsooned beans at a dose of 5 kGy resulted in an increased rate of monsooning. At this dose a quantitative increase in most of the aroma active components could be observed in all samples studied. Hydrolysis of chlorogenic acid to caffeic acid was noted in radiation-processed monsooned coffee beans irrespective of whether the treatment was carried out before or after monsooning. These changes were, however, not observed in irradiated, nonmonsooned coffee beans, suggesting an enzymatic rather than a radiolytic cleavage of chlorogenic acid. A rationale behind the mechanism of monsooning and radiation-induced enhancement of the monsooning process is discussed.     

Characterization of free radicals in soluble coffee by electron paramagnetic resonance spectroscopy

EPR spectra of soluble coffee display single-line free radical signals in both the solid state and aqueous solution, along with signals from the paramagnetic ions Fe(III) and Mn(II). The intensity of the free radical signal in the pure solid was estimated to be ca. 7.5 x 10(16) unpaired electrons/g, and there was no significant change on dissolution in water. In aqueous solutions, however, the free radical signal declined rapidly over ca. 10-15 min in the temperature range 20-65 degrees C, after which only slow changes were observed. This decline, which was essentially independent of atmosphere, was greatest for the lowest temperatures used, and the intensity after 1 h fitted well to an exponential curve with respect to temperature. The free radicals responsible for the single-peak EPR signal did not react with any of the spin traps tested in the present experiments, but unstable free radicals with parameters consistent with adducts of C-centered radicals were detected in coffee solutions in the presence of PBN and 4-POBN spin traps. The presence of oxygen in the solutions increased the initial rate of formation of these free radical adducts. No adducts were detected when DEPMPO was used as spin trap. However, *OH adducts of DEPMPO were shown to be unstable in the presence of coffee, a fact which illustrates the strong free radical scavenging ability of coffee solutions.     

In vitro antioxidative effects and tyrosinase inhibitory activities of seven hydroxycinnamoyl derivatives in green coffee beans

Seven kinds of hydroxycinnamic acid derivatives identified as 3-caffeoylquinic acid (3-CQA), 4-caffeolyquinic acid (4-CQA), 5-caffeoylquinic acid (5-CQA), 5-feruloylquinic acid (5-FQA), 3,4-dicaffeoylquinic acid (3,4-diCQA), 3,5-dicaffeoylquinic acid (3,5-diCQA), and 4,5-dicaffoylquinic acid (4,5-diCQA) by MS, 1H NMR, and HPLC analyses were isolated from low-quality (immature) and commercial quality green coffee beans. The quantity of chlorogenic acid isomers (10.4 g/100 g), especially 5-CQA, in commercial green coffee beans [West Indische Bereiding (West India processing beans from Sumatra Island, Indonesia, WIB)] was higher than that in low-quality beans [9.1 g/100 g, Eerste Kwaliteit (Export low-quality beans from Java Island, Indonesia, EK-1, grade 4)], whereas little difference in diCQAs was detected between the two kinds of beans. The free radical scavenging activity of these isolates was evaluated in assay systems using DPPH free radicals and superoxide anion radicals generated by xanthine-XOD. The diCQAs showed strong (1.0-1.8-fold) free radical scavenging activity compared to commonly used antioxidants such as alpha-tocopherol and ascorbic acid. The potency order of superoxide anion radical scavenging activity was diCQAs > caffeic acid, CQAs > 5-FQA. The activities of the diCQAs were twice as effective as those of CQAs and 4 times as effective as that of 5-FQA. The diCQAs also exhibited more potent (2.0-2.2-fold) tyrosinase inhibitory activities compared to CQAs, arbutin, and ascorbic acid. The isolates exhibited antiproliferation activities in four cancer cell lines, U937, KB, MCF7, and WI38-VA. Among these, KB cells were most sensitive (IC50 = 0.10-0.56 mM).     

Reduction of nitrous Acid to nitric oxide by coffee melanoidins and enhancement of the reduction by thiocyanate: possibility of its occurrence in the stomach

Reactions of nitrous acid with freeze-dried instant coffee and its methanol-insoluble melanoidin fractions were studied at pH 2 in the presence and absence of thiocyanate (SCN (-)), simulating the mixture of coffee, saliva, and gastric juice. Coffee contained stable radicals, and the radical concentration increased by ferricyanide and decreased by ascorbic acid. This result indicates that the radical concentration was affected by the redox state of coffee and that the nature of the radical was due to quinhydrone structure that might be included in coffee melanoidins. Nitrite also increased the electron spin resonance (ESR) signal intensity at pH 2, suggesting that nitrite oxidized melanoidins producing nitric oxide (NO). The formation of NO could be detected by oxygen uptake due to the autoxidation of NO and using an NO-trapping agent. SCN (-) largely enhanced NO formation in coffee and methanol-insoluble melanoidin fractions but only slightly in a methanol-soluble fraction, and the enhancement accompanied the consumption of SCN (-) but did not accompany the formation of a stable ESR signal. The enhancement was explained by the reduction of NOSCN by melanoidins in methanol-insoluble fractions and that the consumption was due to binding of SCN (-) to melanoidins during their oxidation by nitrous acid. The result obtained in this study suggests that when coffee is ingested, in addition to chlorogenic acid and its isomers, melanoidins can also react with salivary nitrite and SCN (-) in the gastric lumen, producing NO.     

Evolution of green coffee protein profiles with maturation and relationship to coffee cup quality

Coffee flavor is the product of a complex chain of chemical transformations. The green bean has only a faint odor that is not at all reminiscent of coffee aroma. It contains, however, all of the necessary precursors to generate the unmistakable coffee flavor during roasting. The levels and biochemical status of these precursors may vary in relation to genetic traits, environmental factors, maturation level, postharvest treatment, and storage. To improve our understanding of coffee flavor generation, the sensory and biochemical impact of maturation was assessed. Maturation clearly favored the development of high-quality flavor in the coffee brew. A specific subclass of green coffee beans, however, generated high-quality coffee flavor irrespective of maturation. Biochemical aspects were examined using a dynamic system: immature and mature green coffee suspensions were incubated under air or argon. On the analytical side, a specific pool of flavor precursors was monitored: chlorogenic acids, green coffee proteins, and free amino acids. A link between maturation, the redox behavior of green coffee suspensions, and their sensory scores was identified. Compared to ripe beans, unripe beans were found to be more sensitive to oxidation of chlorogenic acids. Aerobic incubation also triggered the fragmentation or digestion of the 11S seed storage protein and the release of free amino acids.     

Free radical scavenging activity of grape seed extract and antioxidants by electron spin resonance spectrometry in an H(2)O(2)/NaOH/DMSO system.

The scavenging effects of grape seed extract (GSE) on free radicals formed in an H(2)O(2)/NaOH/DMSO system were examined using a spin-trapping electron spin resonance (ESR) method and compared with other natural antioxidants, ascorbic acid, dl-alpha-tocopherol, and beta-carotene. GSE reduced greatly the ESR signal intensity of superoxide radical-5,5-dimethyl-1-pyrroline-N-oxide (DMPO) adducts. GSE also exhibited weak scavenging activity on hydroxyl radical and a little scavenging activity on methyl radical. Ascorbic acid exhibited strong superoxide and hydroxyl radical scavenging activities, but it increased the amount of methyl radical at high concentration. dl-alpha-Tocopherol reduced the amount of superoxide anion, especially the amount of methyl radical. However, it slightly reduced the amount of hydroxyl radical. beta-Carotene reduced the amount of hydroxyl radical and methyl radical, but it also slightly reduced superoxide anion. In the case of combination use of beta-carotene and dl-alpha-tocopherol, all radical species were suppressed. Combination of GSE and dl-alpha-tocopherol also could reduce all radical species. beta-Carotene and dl-alpha-tocopherol could reduce the methyl radical formation induced by ascorbic acid.     

Free radical scavenging properties of conjugated linoleic acids.

Conjugated linoleic acids (CLA) were investigated for free radical scavenging properties against the stable 2,2-diphenyl-1-picryhydrazyl radical (DPPH.) by electron spin resonance (ESR) spectrometry and spectrophotometric methods. ESR results demonstrated that CLA directly reacted and quenched free DPPH radicals in benzene, while spectrophotometric analysis showed the radical scavenging capacity of CLA in ethanol. Dose and time effects of CLA-DPPH. reactions were observed in both tests. The ED(50) of CLA was 18 mg/mL under experimental conditions. CLA are much weaker radical scavengers as compared to vitamin E, vitamin C, and BHT. Kinetics of CLA-DPPH. reactions was different to that of linoleic acid (LA)-DPPH. reactions. CLA reacted and quenched DPPH radicals at all tested levels without a lag phase, while LA had a lag phase and showed no radical quenching activity at levels of 5-80 mg/mL in 30 min. These data indicated that CLA can provide immediate protection against free radicals, but LA cannot.     

Electron paramagnetic resonance in humic substances

Electron spin resonance (ESR) measurements of soil and its fractions (humic acids, fulvic acids, post-extraction residues and bitumens) were performed and particular attention given to free radicals of organic origin. For such radicals in soil, two lines with g factors 2.004 and 2.002 were observed. For all four fractions one line was observed. To obtain more information on the radical structure, the samples were carbonized. This allowed the different chemical structures of each of the two organic radicals to be differentiated. However, it was not possible to ascribe any definite structure to these radicals. Heat-treatment measurements indicated that the humification process shows some similarity to the process of carbonization at low temperature.     

Electron spin resonance studies of free radicals in gamma-irradiated soybean paste.

Free radicals in gamma-irradiated soybean paste were investigated by electron spin resonance (ESR) spectroscopy to determine the effect of temperature (77-296 K) and moisture content (1-54%) of samples irradiated at high dose (1-40 kGy). The samples were kept in liquid nitrogen (77 K) during irradiation and subsequent ESR measurements. The spectra shown at 77 K consisted of the hydrogen atom lines at low and high field and complicated symmetric spectrum. By increasing the microwave power, the line shape of ESR spectra altered, which indicated the detection of different paramagnetic centers at different microwave powers. In saturation curves, it was possible to select four types of spectra components which were different in their relaxation times. By the different irradiation doses, the change in free radical concentration showed a curvilinearly increasing relationship with irradiation dose in wet samples, whereas a proportional relationship was observed with dried samples. This might indicate that the indirect process of free radical formation was involved with the existence of free water radicals in the wet samples.     

Radical scavenging activity of black cumin (Nigella sativa L.), coriander (Coriandrum sativum L.), and niger (Guizotia abyssinica Cass.) crude seed oils and oil fractions

Crude vegetable oils are usually oxidatively more stable than the corresponding refined oils. Tocopherols, phospholipids (PL), phytosterols, and phenols are the most important natural antioxidants in crude oils. Processing of vegetable oils, moreover, could induce the formation of antioxidants. Black cumin (Nigella sativa L.), coriander (Coriandrum sativum L.), and niger (Guizotia abyssinica Cass.) crude seed oils were extracted with n-hexane and the oils were further fractionated into neutral lipids (NL), glycolipids (GL), and PL. Crude oils and their fractions were investigated for their radical scavenging activity (RSA) toward the stable galvinoxyl radical by electron spin resonance (ESR) spectrometry and toward 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical by spectrophotometric method. Coriander seed oil and its fractions exhibited the strongest RSA compared to black cumin and niger seed oils. The data correlated well with the total content of polyunsaturated fatty acids, unsaponifiables, and PL, as well as the initial peroxide values of crude oils. In overall ranking, RSA of oil fractions showed similar patterns wherein the PL exhibited greater activity to scavenge both free radicals followed by GL and NL, respectively. The positive relationship observed between the RSA of crude oils and their color intensity suggests the Maillard reaction products may have contributed to the RSA of seed oils and their polar fractions. The results demonstrate the importance of minor components in crude seed oils on their oxidative stability, which will reflect on their food value and shelf life. As part of the effort to assess the potential of these seed oils, the information is also of importance in processing and utilizing the crude oils and their byproducts.     

Free radical scavenging properties of wheat extracts

Three hard winter wheat varieties (Akron, Trego, and Platte) were examined and compared for their free radical scavenging properties and total phenolic contents (TPC). Free radical scavenging properties of wheat grain extracts were evaluated by spectrophotometric and electron spin resonance (ESR) spectrometry methods against stable 2,2-diphenyl-1-picryhydrazyl radical (DPPH*) and radical cation ABTS*+ (2,2'-azino-di[3-ethylbenzthiazoline sulfonate]). The results showed that the three wheat extracts differed in their capacities to quench or inhibit DPPH* and ABTS*+. Akron showed the greatest activity to quench DPPH radicals, while Platte had the highest capacity against ABTS*+. The ED50 values of wheat extracts against DPPH radicals were 0.60 mg/mL for Akron, 7.1 mg/mL for Trego, and 0.95 mg/mL for Platte under the experimental conditions. The trolox equivalents against ABTS*+ were 1.31 +/- 0.44, 1.08 +/- 0.05, and 1.91 +/- 0.06 micromol/g of grain for Akron, Trego, and Platte wheat, respectively. ESR results confirmed that wheat extracts directly reacted with and quenched free radicals. The TPC were 487.9 +/- 927.8 microg gallic acid equivalents/g of grain. No correlation was observed between TPC and radical scavenging capacities for DPPH* and ABTS*+ (p = 0.15 and p > 0.5, respectively).     

Aging, free radicals, and antioxidants in wheat seeds

Free radical oxidative attack is considered a major cause of disruption and deteriorative changes observed in aged seeds. Antioxidant defense mechanisms may remove potentially damaging molecular species, and carotenoids may act as radical scavengers. The content of lutein, the major carotenoid in wheat seeds, was determined in the flours. It showed a rapid decrease during seed aging. In addition, the content of free radicals in glutens made from flours of wheat seeds after long-term storage was studied. The concentration of radicals appeared to be age dependent, because the highest content of radicals was detected between 13 and 15 years of aging over 36 years of storage. Specific spin labeling of the sulfhydryl groups of gluten proteins enabled comparative EPR studies of the rigidity of the protein chains. A progressive stiffening of polymeric gluten with seed storage was found.     

EPR studies on gamma-irradiated barley seeds: identification of trapped electrons.

Electron paramagnetic resonance (EPR) studies were conducted on barley seeds exposed to normal (H(2)O) and deuterated (D(2)O) moisture, irradiated with 750 Gy at 77 K. Reported here, for the first time, are the trapped electrons formed on gamma-irradiation of seeds at 77 K. Electrons are stabilized/solvated with an increase in the moisture content (H(2)O/D(2)O) of seeds. The recombination of the trapped electron with radical cation gave intense thermoluminescence emission at 110 K. With the increase in temperature and the destruction of singlet, unmasking of an underlying heterogeneous population of free radicals was observed. These free radicals emanate mainly from the endosperm (approximately 95% by wt of the seed), whereas irradiated embryos show a broad multiplet of comparatively low amplitude. Radiolysis of carbohydrate, proteins (approximately 95% of endosperm), and lipids could possibly be responsible for the heterogeneous population of free radicals. Peroxyl radicals were also observed on annealing.     

Detection of free radical transfer in lipoxygenase I-B-catalyzed linoleic acid-soybean protein interaction by electron spin resonance spectroscopy (ESR)

Effects of lipoxygenase I-B (LOX)-catalyzed oxidation of linoleic acid on soybean proteins was evaluated by electron spin resonance (ESR) and fluorescence spectroscopy in different model systems in the presence or absence of antioxidants. A strong central singlet signal was detected by ESR spectroscopy and identified as the carbon radical (g value range 2.0041-2.0054). A downfield shoulder attributed to the sulfur radical (g value 2.019-2.028) was also observed. The changes in soybean proteins were accompanied by an increase in fluorescence, indicating the formation of cross-links. Natural antioxidants such as ascorbic acid and alpha-tocopherol as well as synthetic antioxidants butyl hydroxytoluene (BHT) inhibited the development of both the free radical signal and the fluorescence when added to soybean proteins prior to incubation with linoleic acid and lipoxygenase I-B; the central singlet signal attributed to the carbon radical was reduced by 35-65%. This paper clearly indicates direct free radical transfer from oxidizing linoleic acid catalyzed by LOX to soybean proteins.     

Evolution of the Levels of Free Radicals Generated on Wheat Flour and Wheat Bran by Electron Beam

This paper presents the experimental data regarding the levels of free radicals investigated by electron spin resonance (ESR) on wheat flour and wheat bran exposed to an electron beam. Samples were irradiated with an electron linear accelerator of 6 MeV and then stored at room temperature in air. ESR spectra of the samples indicated presence of free radicals induced by electron beam. Three types of free radicals have been detected in wheat flour, and signals typical for cellulose‐like radicals have been noticed for wheat bran, their concentration increasing with the irradiation dose. The postirradiation storage of both sample types caused radical decay with a two‐step pattern associated with fast decay of short‐life radicals followed by slow reduction of long‐life radicals. However, in the first step, the irradiated wheat bran exhibited more rapid decay of radicals than irradiated flour owing to their different complex matrixes, which led to paramagnetic structures of different origin after exposure to an electron beam. The ESR technique allows the detection of free radicals induced in wheat flour and bran by electron beam for a limited period after irradiation that could be shorter than the shelf life of the products.     

Studies of selenium-containing volatiles in roasted coffee

Coffee has been an important and heavily used beverage in many cultures over a long period of time. Although sulfur species have been found to be abundant constituents, no work to date has explored the presence of selenium analogues. Investigation of volatile selenium species from green coffee beans, roasted beans, and brewed coffee drink was performed using solid phase microextraction (SPME) sample preconcentration in conjunction with GC/ICP-MS. Several volatile selenium species at trace levels were detected from roasted coffee beans as well as in the steam from brewed coffee drinks. No detectable selenium (and sulfur) species, however, were found in the headspace of green beans, indicating that selenium-containing volatiles are formed during roasting, as is the case for the sulfur volatiles. Matching standards were prepared and used to identify the compounds found in coffee. Artificial supplementation of the green coffee beans with selenium before roasting was performed to further characterize the selenium-containing volatiles formed during the coffee-roasting process.     

Conjugated linoleic acid isomers differ in their free radical scavenging properties

Conjugated linoleic acid (CLA) isomers were investigated for free radical scavenging properties against the stable 2,2-diphenyl-1-picryhydrazyl radical (DPPH(*)) by electron spin resonance (ESR) spectrometry and spectrophotometric methods. ESR measurements confirmed that both c9,t11-CLA and t10,c12-CLA directly reacted with and quenched DPPH radicals, whereas spectrophotometric analysis demonstrated that c9,t11-CLA and t10,c12-CLA differed in their kinetic and thermodynamic properties in reacting with DPPH radicals. t10,c12-CLA was shown to exhibit a greater initial velocity in CLA-DPPH radical reactions at levels of 2.5-80 mg/mL, and c9,t11-CLA scavenged more DPPH radicals at steady state. Similar dose and time relationships were observed for both isomers. In addition, a mixture of c9,t11- and t10,c12-CLA isomers demonstrated a greater initial velocity in quenching DPPH radicals than either isomer alone on the same concentration basis, suggesting that a synergistic effect between CLA isomers existed in their reactions with DPPH radicals. These results support the conclusion that individual CLA isomers differ in their biological actions and indicate that interaction(s) between isomers may contribute to their beneficial effects.     

Free radical scavenging activity of chitooligosaccharides by electron spin resonance spectrometry

The radical scavenging effects of chitooligosaccharides (COSs) on hydroxyl radical, superoxide radical, alkyl radical, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical were investigated using a spin-trapping electron spin resonance (ESR) method and compared with the ESR signal intensity. COSs exhibited strong scavenging activity on hydroxyl radical and superoxide radical and weak scavenging activity on alkyl radical and DPPH radical. The radical scavenging activity of COSs increased with increment of concentration, and it was also dependent on molecular weight. These results suggest that the scavenging activity of COSs is dependent on their molecular weights and tested radicals.     

Reactive oxygen scavenging effect of enzymatic extracts from Sargassum thunbergii

The free radical scavenging activity of water soluble natural antioxidants from Sargassum thunbergii, which is a brown marine alga, was evaluated by examining the radical scavenging activities of the extracts of hydrolyzates from S. thunbergii on hydroxyl, 1,1-diphenyl-2-picrylhydrazyl (DPPH), and alkyl radicals. A spin-trapping electron spin resonance (ESR) spectrometer was employed, and the results were compared for their ESR signal intensity. S. thunbergii was enzymatically hydrolyzed to prepare water soluble extracts by five carbohydrases (AMG, Celluclast, Termamyl, Ultraflo, and Viscozyme) and proteases (Alcalase, Flavorzyme, Kojizyme, Neutrase, and Protamex). The scavenging activity of the radicals increased with increased concentrations of the extracts. The scavenging results were higher for hydroxyl and alkyl radicals and lower for DPPH radical as compared with vitamin C as a reference. The hydrogen peroxide scavenging activity of the extracts was also investigated; the Alcalase extract showed the highest scavenging activity among the extracts prepared with the five proteases and five carbohydrates. In addition, the DNA damage was determined by using the comet assay with alkaline electrophoresis and was quantified by measuring the tail length. The preventive effect of Alcalase extract from S. thunbergii against DNA damage increased with increments of concentration of the enzymatic extracts.     

同步辐射(软X射线)对冬小麦的诱变效应及机理研究Ⅲ.辐照种子产生的自由基和辐照引起种胚DNA非按期合成的研究

应用电子自旋 (ESR)波谱术研究了同步辐射辐照种子产生的自由基及其与辐射损伤之间的关系。结果表明 ,同步辐射辐照的种子产生了大量的自由基 ,其种类、性质不同于γ射线 ,短寿命自由基 (小于 48h)产额高于γ射线 ,长寿命自由基 (大于48h)的稳定性大于γ射线。同步辐射自由基产额与辐照剂量呈线性关系。用3H TdR掺入法研究了受辐照种胚萌发早期DNA的合成动态 ,结果表明 ,同步辐射能够引起种胚DNA的损伤修复合成 ,其特点不同于γ射线。原冬 6号和北京41 1品种的DNA修复合成出现在种胚吸水后第一个正常的DNA合成峰之前 ,京冬8号品种出现在第一个小峰之后和 2个高峰之前