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PRACTICAL ASPECT AND RECENT RESEARCH ON QUALITY ASPECTS OF COFFEES AND TEAS BASED ON EPR
Dr. Pradeep Gupta
Associate Professor- Physics, DSN Post Graduate College, Unnao, Uttar Pradesh
Abstract - Coffee and tea are both very rich in antioxidant molecules and both are beverages that are associated with health benefits. The quality attributes of these beverages are traditionally evaluated based on their sensory characteristics, but their antioxidant content is of additional value based on their contribution to a healthy diet. Represents a quality attribute.
Both beverages are produced by hot water extraction of pure plant-derived products, so their composition can change very rapidly as a result of oxidation on contact with air.
Oxidation processes often proceed via radical intermediates, sometimes leading to the formation of stable radical end products. Therefore, EPR spectroscopy is a good technique for studying some of the various free-radical reactions that occur in these beverages. This article reviews the progress of elucidating the free radical process in the preparation and storage of coffee and tea and discusses the results with respect to beverage quality standards.
Keywords: Coffee; tea; free radicals; antioxidants; EPR spectroscopy; quality.
1. INTRODUCTION
Coffee and tea are two of the most consumed drinks in the world. Neither is considered a traditional medicine, but both have a history of association with medicinal properties. Traditionally, the quality of tea and coffee is associated with the consumer's primary direct experience and is therefore evaluated by a panel of tasters' experts based on sensory attributes. However, in recent years we have learned that both beverages contain molecules that are believed to be beneficial for long-term health and well- being. This is a characteristic that consumers are increasingly aware of and value. As a result, our definition and understanding of coffee and tea quality is slowly but steadily expanding, including long-term health benefits in addition to immediate sensory effects.
The most important and beneficial molecule belongs to a class of compounds known as antioxidants, and its main function in biology is to protect cells from oxidative damage. This is done in one of three ways. By 1) inhibiting the formation of oxidants, 2) by selectively removing the oxidants, or 3) by removing the reaction products of the oxidants, it can itself cause cell damage. I have. Mechanisms 1) generally include antioxidant enzymes, but 2) and 3) can be performed by either small or large molecules. However, a common property of biological antioxidants is the ability to perform a
redox cycle between reduced and oxidized forms, both of which are generally stable.
Stable form of molecular oxygen,
3O2 is a free radical having two non- unforgiving electrons, and the various products derived there from tend to be more reactive than O2 itself, so they tend to be more reactive than itself. It is known as reactive oxygen species (ROS). Some of them are one electron reduction, 2 and its protonated form. OH and hydroxyl radical. It is also a free radical containing the product of OH, and its unstable form,
1O2 and hydrogen peroxide, H2O2 There.
However, both 1O2 and H2O2 are readily participate in the reaction, which is free radical development and free radicals, which are the general characteristics of the biological oxidation process. Thus, antioxidants are often assumed to be free radical scavengers, which are aggression of their chemical behavior, but controlling free radical reactions in antioxidants and biological and composite food systems.
There is a narrow connection between them. Coffee and tea are the main cause of antioxidants in many dietas and can be stored on a long air panel, and the oxidation process affects their antioxidant content, at least in their chemical composition it can affect changes in their morphology that may affect. The leg wall produced by water removal. However, such reactions are so complex that we are just beginning to understand the various chemical processes involved. Current
2 publications address various aspects of beverage production containing free radicals derived from O2 and are based on the measurement of chemical species by unpaired electrons such as free radicals and paramagnetic metal ions, electron paramagnetic resonance (EPR).
The results obtained using spectroscopy show them and the complex.
2. ANTIOXIDANTS AND FREE RADICAL SPECIES IN COFFEE PRODUCTION Coffee is most commonly associated with alkaloid caffeine, but is said to have some antioxidant properties because it is converted to oxocaffeine (1-methyluric acid) during coffee oxidation. , Beverages contain other bioactive compounds. Also, caffeine is not a true antioxidant, as the formation of oxocaffeine in drinks is likely to be the result of a reaction with hydroxyl radicals that react virtually indiscriminately with organic molecules.
Green coffee beans are a rich source of chlorogenic acid, a family of polyphenol antioxidants found in many traditional Asian medicines, and are believed to have beneficial health benefits from coffee consumption. I am.
Chlorogenic acid (Fig. 1) is an ester of quinic acid and various polyphenols, mainly caffeic acid, pucmaric acid and ferulic acid. There are a variety of mono,
di and triesters, and 70 chlorogenic acids have been identified in green coffee bean extracts.
The most important change in coffee beans that occurs during roasting is the formation of melanoidin, an undefined colorant, by the Maillard and caramelization reactions. The Maillard reaction involves a condensation reaction between the free amino group of an amino acid, peptide, or protein and the carbonyl group of a reducing sugar, whereas the caramelization reaction depends on reactions involving only sugars or carbohydrates. However, both reactions are very complex and lead to the formation of a wide range of products, including melanoidins. Melanoidin has been described as having a mutagenic effect, but it is also associated with health-promoting properties. In addition, the Maillard reaction produces compounds with strong antioxidant properties, and coffee is described as an overall anticarcinogen. Understanding the chemistry of the coffee roasting process is a major challenge, but it is a necessary challenge to improve existing processes to produce higher quality products. During roasting, the chlorogenic acid content is reduced, but some are incorporated into the melanoidin component and can be released later during digestion. But
Figure 1 Chemical structures of chlorogenic acids; these are esters of quinic acid and 1 or more phenolic acids, such as p-coumaric, caffeic or ferulic acid/
because of the antioxidant properties of melanoidins, the roasting process results in an overall increase in the an- tioxidant content of the beverage, with maximum activity being reported for medium roasted beans. The roasting of coffee also results in the formation of sub- stantial
quantities of free radicals the contents of which are influenced by a number of factors including the water content of the green beans prior to roasting.
It is in addressing issues involving free radicals and other paramagnetic chemical species that EPR spectroscopy
3 can make important contributions to the science of coffee. Changes in free radical concentrations can be monitored in essentially real time in an EPR spectrometer (Figure 2) and thus this technique allows the possibility of investigating how variables such as the temperature profile and gas flow rate influence free radical concentrations during the roasting process for differ- ent bean types.
3. OXIDATIVE PROCESSES DURING THE STORAGE OF ROASTED COFFEE PRODUCTS
The oxidation process affects the composition of roasted coffee during subsequent storage, as evidenced by the
increased lipid peroxidation. In addition, storage in air leads to a gradual increase in the EPR signal of free radicals, but in the absence of air a gradual decrease is observed. Therefore, these results indicate that roasted coffee is not an inert material, but that changes in free radical components are the result of a process that involves both formation and disintegration. In addition, a recent study by Yeretzian et al. The increase in free radical signals when roasted and ground coffee (R & G) is stored in the air is primarily the result of the reaction of coffee components with O2 and is a direct result of the physical damage caused by the grinding process. It shows that it is not the result.
Figure 2 Profiles for EPR free radical signal intensities during the roasting in N2 of (a) Robusta and (b) Arabica coffee beans (adapted from reference). Note the much higher
free radical concentration in Arabica beans.
4. FREE RADICAL REACTIONS IN COFFEE BEVERAGES
After preparation, the sensory characteristics of coffee beverages change rapidly. EPR measurements show that changes in free radical contents also occur, and although “cause and effect”
relationships have not been established it seems likely that hydroxyl radicals are involved, because of the presence in coffee of the chemical components appropriate for Fenton reaction chemistry. With solutions of “instant” coffee, Pascual et al.
described a temperature independent decay of the initial free radical signal on a timescale similar to that observed by Hofmann et al. for the radicals formed on disso lution in water of dialkylpyrazinium diquaternary salts (diquat), which are early products of the Maillard reaction.
However, Pascual et al. also observed a temperature dependent production of a free radical signal with similar spectral characteristics to that of the original radical, a result which indicates that free radical reactions occur continuously in the coffee beverage. Furthermore, these authors also demonstrated that O2 was involved in the production of this new signal, possibly as a source of hydroxyl radicals by enzymatic conversion to H2O2
followed by Fenton reaction chemistry.
Although chemical spin trapping combined with EPR spectroscopy is a recognized method for the identification of unstable free radical intermediates the results of such measurements indicated the trapping of centred radicals. However, unlike the superoxide radical anion, the hydroxyl radical reacts virtually
4 indiscriminately with organic molecules.
Thus in complex systems such as coffee solutions, most of these radicals will react via hydrogen atom extraction with organic components in the beverage and it is the resulting Ccentred radicals that are observed after reaction with the spin trap.
5. PROBLEMS ASSOCIATED WITH THE STORAGE OF LIQUID COFFEE PRODUCTS
As referred to with inside the preceding paragraph, the sensory residences extrade swiftly after education of espresso beverages. In addition to losing mild on the fast time period radical methods that arise with inside the beverage, EPR spectroscopy has additionally been proven to be doubtlessly beneficial in knowledge methods that arise all through long run garage of liquid espresso merchandise below managed conditions. Recently, Pascual et al. have used EPR spectroscopy to research the outcomes of different factors that have an effect on the steadiness of liquid espresso organized from aqueous extracts of complete roasted espresso beans. They determined that the unfastened radical EPR sign depth is touchy to the O2 content material of the water used for extraction and the garage temperature, however now no longer the garage atmosphere (headspace). In comparable measurements on focused espresso solutions, Yeretzian et al. (2013) additionally observed that the O2 content material of the water used for extraction become the biggest thing which affected the adjustments with inside the unfastened radical EPR sign all through garage. However, while the intensities of the sign from complete bean extracts multiplied all through garage, the ones from espresso concentrates decreased, therefore indicating the problems in generating easy interpretations of the effects from such measurements.
6. DEGRADATION OF COFFEE AROMA The aroma of coffee generated during roasting is considered one of the most attractive features of drinks and is generally considered an important quality standard. However, its chemical composition is very complex, each representing a combination of hundreds (thousands?) of molecules present at low concentrations. In addition, some
important aroma molecules, especially those with thiol groups, have limited oxidative stability, resulting in diminished sensory properties during storage. One such molecule is flufuryl mercaptan, whose degradation under Fenton reaction conditions has been reported by Blank et al. It was examined in detail. This reaction was found to be very complex and generate both C and perfume radicals early in the decomposition process.
An ab initio computational technique to discover the stableness of extensive variety of espresso aroma compounds has been said via way of means of Munro et al. These research targeted at the numerous loose radical procedures that would result in aroma degradation all through garage of liquid espresso, and worried research of >one hundred radicals that is probably fashioned all through the reactions of key aroma compounds. These radical merchandise had been categorised in step with their thermodynamic stabilities relative to not unusualplace radical reassets that would exist in liquid espresso extracts. The re- sults anticipated that maximum aroma molecules have to be re- sistant to each peroxidation and assault from phenolic antioxidants, however are risky with recognize to response with OH.
7. ANTIOXIDANTS IN TEA LEAVES AND
THEIR CHANGES DURING
PROCESSING
The tea beverage is ready via way of means of warm water extraction of dried leaves of the plant Camellia sinensis.
Different kinds of tea are categorised in keeping with the diploma of processing to which the leaves are subjected previous to packaging, with the quantity of oxidation growing with inside the order white inexperienced < pink < black (Note the Chinese pink tea is more or less equal to the Indian black tea while the Chinese Pu`er tea is a black tea this is al- lowed to go through a few fermentation earlier than being proc- essed). The stability (shelf life) of the goods follows a comparable fashion and Pu`er tea is strong over many decades.
All teas comprise significant portions of polyphenolic antioxidants, however their molecular compositions and sizes boom in keeping with the diploma of
5 oxidation they ex- perience throughout processing. Thus the polyphenols with inside the gently processed white and inexperienced teas are ruled via way of means of surprisingly easy catechins, called inexperienced tea poly- phenols (GTP); the fundamental GTP are (−)- epigallocatechin gallate (EGCG), (−)- epigallocatechin (EGC), (−)-epicatechin gallate (ECG), (−)-epicatechin (EC), and (+)-catechin (CT) (Figure 3). In addition, gallic acid (GA) can also be observed. In contrast, the dominant polyphenols in black teas the greater complicated theaflavins, thearubigins and greater distinctly polymerized substances. The GTP have obtained huge interest for the affiliation of inexperienced tea intake with useful fitness proper- ties however there's proof that the diverse kinds of tea have comparable useful fitness effects.
8. AUTOXIDATION REACTIONS IN TEAS
As referred to with inside the preceding section, teas comprise ap- preciable portions of polyphenols, which can be usually assumed to be liable for the useful fitness outcomes of the beverage.
During their conduct as antioxidants, polyphenols are oxidized to phenoxy or greater generally semiquinone radicals, and this response pro- ceeds greater hastily at excessive pH values.
Consequently, alkaline autoxidation is regularly used as an experimental manner for expanded oxidation so one can beneathneath- stand the chemistry of the tea polyphenols. Under such conditions, EPR spectra may be with ease discovere, and effects display that indicators are discovered from every of the principle
inexperienced tea polyphenols in alkaline answers of inexperienced tea extracts while the spectra from equal black tea samples are ruled with the aid of using the unconventional similar to oxidized gallic acid. Thus there can be vast variations with inside the anti- oxidant chemistry reactions of various varieties of tea, and EPR will be a beneficial approach for evaluating reactions in teas which have been subjected to exclusive varieties of processing. However, warning wishes to be exercised in extrapolating effects from alkaline autoxidation to reactions beneathneath physiological conditions, on account that oxidation of EGCG with the aid of using superoxide at close to impartial pH values proceeds through a exclusive mechanism to that discovered on alkaline autoxidation.
An critical belongings of plant- derived polyphenols is their cappotential to feature as antimicrobial molecules.
However, the microbial degradation of white/inexperienced tea leaves has a prime impact now no longer simply at the without difficulty oxidizable GTP, however additionally different compounds including caffeine, which usually aren't prone to alteration for the duration of storage (Klaus Stolze, unpublished effects). This then represents every other instance of complicated chemical conduct in a beverage that wishes to be investigated further.
9. OTHER MOLECULES IN TEA EXTRACTS THAT COULD CONTRIBUTE TO THEIR BIOACTIVITY
The potentially beneficial molecules in teas are not limited to their polyphenolic components, and other bio-
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Figure 3 Chemical structures of the green tea polyphenols (−)-epicatechin (EC), (+)- catechin (CT), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG), and (−)-
epigallocatechin gallate (EGCG).
Figure 4 EPR spectra of autoxidized (a) green tea and (b) black (Pu’er) tea. Details of the interpretation of the green tea spectrum are given in reference.
10. GENERAL DISCUSSION, CONCLUSIONS AND FORWARD LOOK Although we are just beginning to understand the role of antioxidants and free-radical reactions in coffee and tea chemistry, little is known about their relationship to traditional quality assessments based on sensory properties.
However, it is now recognized that antioxidant-rich foods are associated with health-promoting properties, and as a result, both coffee and tea can make a valuable contribution to a healthy diet.
In coffee, the most important antioxidants are chlorogenic acid and melanoidin and the relative importance of these two groups of molecules depends on both the genetics of the plant and the depth of roasting. The medicinal properties of chlorogenic acid are well known and these molecules are found in
many traditional Asian medicines, but the biological effects of melanoidin are still controversial. Therefore, these molecules need further research and characterization, but this is a very difficult field of study due to the undefined nature of this molecular family and the large molecular size.
For tea, it is generally accepted that the beneficial properties are derived from the polyphenolic component.
However, their chemistry depends on the post-harvest treatment that tea leaves receive, and only GTP has been studied in detail. Nevertheless, green tea and black tea have similar antioxidant properties, and epidemiological studies suggest that their health-promoting effects are also similar. In addition, tea contains other bioactive molecules such as the anine and unidentified molecules that have the
7 ability to chelate metal ions such as Cu (II) at very low pH levels.
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