Arabica complex

Figure 12.39 shows the almost hnear volt-ampere (I-V) characteristics of the illuminated solid Arabica complexes of the chromatophores specimens (a), (b), and (c) respectively, between applied p.d. 0-10 volt. Also shown is a comparison of the corresponding results obtained from measurement in near dark conditions. The nature of the graph shows that the current increases significantly in the presence of light, and calculated slopes of the respective curves show that in the presence of light the slope became almost half that of the dark measurement, i.e. electronic conductivities assumes about 100% enhancement due to photo induced charge separation in the specimens. In all cases the observed... 

Figure 12.39 DC V-I characteristics of Chromophores and Gum Arabica complexes, (i) specimen (a) - - with light and O- without light. (Sample thickness- 0.35 cm. Area- 2.25 sq cm), (ii) specimen (b) with light and A-.without light (Sample thickness- 0.25cm, Area- 2.25 sq cm) (iii) specimen (c) - with light o- without light (Sample dimension same as (ii)) All records are at RT [55].

In another study [55], solid specimens of the LHC based gum Arabica complex were prepared, and the optical, electrical, and photoelectrical characters were examined experimentally. The chromophore/LH molecules used were in the form of small chlorophyll clusters from Sigma Aldrich (USA) and those extracted from the deep green leaf of the neem plant. The former was purified and expensive, whereas the latter was crude and cost effective. The optical, molecular, and photo-electric aspects of both developed specimens were compared, and extracted crude LHC was employed to form specimen (e), a complex system with gum Arabica as a host EABP background. The experimental results of the above mentioned study are summarized below. 

Different Chromophore with Gum Arabica complex Total Conductivity (Ionic + Electronic) [S/cm] D.C Conductivity (Electronic) [S/cm]... 

The principal CGA isomers identified in green coffee include three caffeoylquinic acid isomers, 3-CQA [327-97-9], 4-CQA [905-99-7], and 5-CQA [906-33-2], three dicaffeoylquinic acid isomers, 3,4-diCQA [14534-61-3], 3,5-diCQA [2450-53-5], and 4,5-diCQA [57378-72-0], and three feruloylquinic acid isomers, 3-FQA [1899-29-2], 4-FQA, and 5-FQA [40242-06-6]. The total CGA level is somewhat higher in robustas compared to arabicas. The 5-CQA is the predominant isomer both in arabicas, ie, 4—5% dry basis (db), and in robustas, 5—6% db, and is known to form in vitro and possibly in vivo complexes with caffeine [58-08-2]. Greater compositional differences between robustas and arabicas are found in the minor CGA isomers, eg, 3,4-diCQA, 5-FQA,... 

One of the most significant differences between Arabica and Robusta coffees is in the caffeine content. Robusta coffees contain almost twice the caffeine found in Arabica coffees. There are some other differences recognized thus far Robustas contain almost no sucrose and only very small amounts of the kaurane and furokaurane-type diterpenes they contain higher proportions of phenols, complex carbohydrates (both soluble and hydrolyzable), volatile fatty acids on roasting, and sulfur compounds, all in comparison with Arabicas. References to these distinctions can be found in Chapter 6 of this book. 

More than 700 constituents have been identified in aroma extracts of roasted coffee. Heterocyclic aroma components represent the greatest amount of the steam volatile aroma complex (80 - 85 %) which amounts to 700 -900 ppm in medium roasted Arabica coffees. The concentration of individual components varies depending on coffee varieties and roasting conditions. Typical components are formed by thermal degradation of free and bound amino acid and chlorogenic acid precursors. Compared to other roasted foodstuffs, sulfur containing constituents and phenols are formed in high amounts and contribute to desirable coffee flavor or off-flavor. 

Caffeine and related purines are uncharged under physiological conditions and, due to their dual hydrophilic and lipophilic character, easily penetrate cell-, tissue- and organ-related barriers. In Coffea arabica, compartmentation of purine alkaloids, e.g. caffeine, depends exclusively on the physical chemistry of their vacuolar complexation with chlorogenic acid (Waldhauser and Baumann, 1996). 

Identified in an aroma complex of roasted coffee by Bondarovich et al. (1967) and a little later by Stoffelsma and Pypker (1968) and Stoffelsma et al. (1968), after steam distillation, fractionation and preparative GC for identification by IR spectroscopy, and comparison with authentic samples. Silwar et al. (1987) estimated its concentration at 2.0-3.0ppm (see F.19), and Ho et al. (1993) at 4.58ppm in a roasted Columbian coffee. The latter authors identified only two purely aliphatic esters in their analysis (see F.24). Ramos et al. (1998) identified it in a brewed arabica only after liquid-liquid extraction with methylene chloride (compare with F.8). 

Identified by Stoffelsma et at. (1968) in roasted coffee flavor. In fact, the authors did not specify the furanic structure but, as they referred to Stoll et al. (1967) for the m-isomer, there is little doubt about the identification. Friedel et al. (1971) confirmed the identification for the /ram-isomer in an aroma complex of coffee (method in Gianturco et al., 1963). Cantergiani et al. (2001) found it in a green Mexican arabica (1.56% of the volatiles by GC on a polar column). 

Biomaterials and the various aspects of their study is an extremely wide field. However, their complex molecular structures have made them unpopular over the last century as a potential field of study. The work presented here is a study on biomaterials from a material science point of view, and its aim is to investigate the electrical, thermodynamic, structural, and electrochemical character of gum Arabica along with its possible real-life apphcation. 

Biomaterials such as natural gums are extracted from living matter. The molecules forming these biomaterials are known to be very complex in nature. Water content in biomaterials is an essential characteristic of them. The water content plays a crucial role in its physical properties like electrical conduction through it. Since these materials are either a covalent or a hydrogen bonded system they cannot be used and tested at temperatures above 120°C. It is apparent, therefore, that not all conventional methods of material characterization can be applied. Thus, as a method of material characterization, some of the conventional methods are used in a restricted way so as to retain the biomaterial characteristics. The characterization method used in the study of natural gum Arabica is summarized in the following sections. 

Gum Arabica and its complexes used in the present study contain fine structures which affect their properties. The microscopy may be informative in investigating the molecular domain and block structure in it. The different types of microscopy used in the characterization of gum specimen are (i) Optical microscopy, where only structures separated about Ipm across can be investigated. (ii) Electron microscopy in the form of transmission electron microscopy (TEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The mentioned techniques and tools are able to provide a magnification up to 10 and at very high resolution. 

Bulk electrical conduction The gross feature of the electroactivity of a material is best understood from the a.c. experiment. The variation of complex impedance and loss angle with frequency of the applied voltage was studied for better information about the a.c. conductance of the biopolymer gum Arabica. This measurement was carried out on a gum Arabica sample caste on a plane copper surface between frequency ranges 0.5 Hz - 100 KHz and between... 

The physical appearance of pure gum and its complexes were often found to exhibit colour therefore their optical absorption characteristics in the UV-VIS region were studied in order to investigate their optical absorption, absorbance region, and the photo-charge separation therein. The optical absorption in the UV-VIS region was measured for coloured complex of gum Arabica, and when and where it was important. 

The gum Arabica powder specimen (SI) was collected from Merk (India) and was subjected to a sol-gel process along with pure water so that the polysaccharide host chain could form more complex higher polymers over those in normal powder form. Next, the sol specimens are extracted at initial state 30, 60, and 120 minutes. The experimental specimens (S2, S3, S4, and S5 respectively) were developed by adequate drying of the sols at environmental condition. The developed gum Arabica specimens (S2-S5) are supposed to exhibit a change in molecular structure over that in SI due to prolongation of the sol gel process. FTIR analysis on pure gum Arabica was carried out to examine its molecular structure and dynamical information. The analysis was carried out at high resolution FTIR setup in a KBr window (shown in Figure 12.14). 

Figure 12.18 V-I characteristics of Citric acid complex of Arabica (specimen size A=1 cm d = 0.3 mm) [34],...

Figure 12.22 shows the variation of a.c. conductivity with an increasing concentration of HjPO complex of gum Arabica at 25°C. The observed variation may be described by Jonscher s power law. Increase in phosphate ions and mobile counterions enhance the bulk conductivity of the specimens, which is summarized in Table 12.2. 

The present discussion [47] deals with the formation of natural self-assembly of CuS nanoclusters in dielectric substrates of gum Arabica biopolymer. Low concentration of ammonium complex of copper oxide solution was dissolved in gum Acacia Arabica solution at 60°C and stirred. H2S gas was passed in the same environment for 1 minute. Heating the resulting solution to about 100°C evaporates any possible trace of ammonia. The resulting nanocomplex was caste in the form of very thin film by spin coating technique. The developed specimen was used for experimental investigations, namely TEM, XRD, and electrical experiments such as impedance spectroscopy, and the Arrhenius plot and I-V characteristics were measured in the applied field direction perpendicular to the 2-D plane. 

Figure 12.30 Comparison of o-V variation for the developed nano-complex specimens in Gum Arabica matrix measured at RT and at 45°C with voltage step 10 mV. Sample thickness 0.096 cm, CSA = 1.62 sq. cm for RT and 0.112 cm, CSA =1.2 cm for 45°C [63a].

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