Arunangshu Ghosh

Monitoring the Fermentation Process and Detection of Optimum Fermentation Time of Black Tea Using an Electronic Tongue

This paper presents a new methodology to monitor the fermentation process and detect the optimum fermentation time of crush tear curl black tea with a voltammetric electronic tongue. An electronic tongue with an array of five noble metal working electrodes has been developed for this purpose. A suitable large amplitude pulse voltammetric waveform has been employed for probing the chemical changes in tea samples under fermentation. Good correlation between the electronic tongue responses and the biochemical changes has been obtained by principal component analysis (PCA) during various stages of fermentation. The electronic tongue fermentation profile has been derived from PCA analysis and it is observed that such a profile enables detection of optimum fermentation times. Finally, a model based on partial least squares regression technique has been developed for real-time indication of fermentation level. The optimum fermentation times observed from the electronic tongue fermentation profiles derived from PCA and partial least squares regression correlate by a factor of 0.97 and 0.96, respectively, with the reference values obtained from an ultraviolet-visible spectrophotometer-based instrumental analysis.

A Quartz Crystal Microbalance Sensor for Detection of Geraniol in Black Tea

Geraniol is one of the important qualities determining volatile components of black tea. This paper presents a quartz crystal microbalance sensor to detect geraniol from black tea aroma. The sensor is developed using β-cyclodextrin (β-CD). β-CD is a flavor encapsulating material with toroidal bucket-like structure, whose inside-cavity is hydrophobic and the outside is hydrophilic and it is found to be a suitable coating material for detecting geraniol. Extensive experiments have been carried out with the β-CD sensor and it is observed that the sensor offers better sensitivity for geraniol in comparison with other important constituents of black tea such as linalool, linalool oxide, methyl salicylate, and trans-2-hexenal. Experiments with ten Darjeeling orthodox black tea samples have been carried out with the developed sensor and a correlation factor of 0.9925 has been obtained with the corresponding gas chromatography mass spectrometry analysis.

Detection of Optimum Fermentation Time of Black CTC Tea Using a Voltammetric Electronic Tongue

A voltammetric electronic tongue (E-tongue) has been used to detect the optimum fermentation time (OFT) of crush tear curl black tea. An E-tongue with an array of five noble metal working electrodes has been developed for this purpose. A suitable large amplitude pulse voltammetric waveform is used and a simple feature extraction technique based on the charge activity of working electrodes is proposed. The principal component analysis reveals a significant correlation between the E-tongue responses and the biochemical changes during various stages of fermentation. Principal component regression models are developed to assess the effectiveness of the features derived from E-tongue response to model the temporal variations of theaflavins, a key quality compound of tea, produced during the fermentation process. The OFTs detected by the E-tongue correlate by a factor of 0.97 with the estimates obtained from an ultraviolet-visible spectrophotometer-based reference method.

Fragrance Profiling of Jasminum Sambac Ait. Flowers Using Electronic Nose

The extract of Jasmine called concrete is an important floricultural export commodity of India. The major quality attribute of both jasmine and concrete is fragrance. The fragrance profile of jasmine flower has been studied using a custom built handheld e-Nose (HEN). Three species of jasmine, J. Sambac, J. Grandiflorum, and J. Auriculatum were applied to e-Nose one by one. The principal component analysis of the responses showed that distinct clusters were formed for different species. Another study was made on the mostly cultivated J. Sambac species to find out a relationship between concrete quality with various flowering stages as well as with seasonal variation. Experiments were carried out over 200 samples collected from various gardens of South India. Multivariate sensor data were computed in a single dimensional intensity value termed as fragrance index (FI). Flowering stages were classified by Industry experts in terms of bud opening indicator (BOI). HEN was trained to formulate a scale of BOI in the range of 0-2 based on the FI. Best quality of concrete is found to be obtained from jasmine flower with BOI level of 1.5. Jasmine concrete, produced at laboratory from flowers harvested at different time-of-the-day, i.e., with different BOI levels were analysed using GC-MS to check the volatile emission patterns. Results showed that concrete produced with BOI level 1.5 emitted maximum aroma generating volatiles. These observations showed that e-Nose can be a potential gadget for fragrance profiling as well as selection of best quality flowers for concrete extraction.

An equivalent electrical network of an electronic tongue: A case study with tea samples

Electrical equivalent of a physical process helps uncover important information about the characteristics of the process. In this paper, an equivalent electrical circuit of electronic tongue has been presented following system identification techniques with tea infusion as an analyte. The electronic tongue is often used for the detection of important bio-chemical quality markers of various food items. The steady and transient responses obtained from the electronic tongue during experiments contain valuable information regarding the characteristics of tea sample. In order to overcome the problems associated with the existing model, the process model has been modified for the given system. Unlike the existing equivalent circuit of the three electrode electrochemical system, the proposed circuit is able to produce similar output response as that of the actual electronic tongue system. A new equivalent circuit has been presented and the circuit parameters have been calculated.

Age Analysis of Jasmine Concrete Using Electronic Nose

The effect of aging on quality of jasmine (Jasminum Sambac) concrete in terms of aroma was studied with the intention of estimating the shelf life of this highly priced export oriented commodity. A handheld electronic nose was developed and customized to find out aroma intensity of fresh and aged commercial concrete samples. The same fresh and aged samples were also analyzed with the help of a gas chromatography–mass spectrometry (GC–MS). Between first and final experiment, the samples were kept in air-tight containers. The electronic nose showed very high sensitivity toward the concrete’s aroma molecules and could detect aroma volatiles from concrete samples at a minimum sample weight of 0.05 g. The e-nose also showed the decrease in aroma intensity in the samples with aging. The GC-MS results established a strong correlation with the e-nose observations. The aroma intensity of concrete was observed to be decreased almost linearly over a period of one year. Electronic nose has been found to be a potent tool for rapid prediction of concrete age.

Chapter 24 – Electronic Tongue for the Estimation of Important Quality Compounds in Finished Tea

In this chapter, a voltammetric electronic tongue (e-tongue) based on an array of noble metal electrodes has been described for the detection of quality affecting biochemicals in black tea. Two groups of compounds—the theaflavins and thearubigins—contribute significantly to the taste and appearance of tea liquor. The e-tongue was found to detect the amount of these compounds as well as their fractions using suitable data processing steps. The prediction models were developed from the e-tongue response with neural networks and partial least squares. The predictions agree with the spectrophotometric estimations at accuracy of over 95%. Interestingly, best accuracy has been obtained for theaflavin digallate and theaflavin monogallate, indicating the dominant effect of these astringent compounds on modeling performance. The results positively imply the feasibility of e-tongue based on an array of noble metal electrodes toward the detection of important quality compounds in finished tea.

Selection of Optimum Level of Data Compression for Voltam metric Electronic Tongue Signal Using DWT

A voltammetric electronic tongue has been developed for black tea assessment. While attempting to standardize the voltammetric electronic tongue a basic taste recognition test has been conducted. This electronic tongue works on cyclic voltammetric principle and has a three electrode configuration (working, reference, and counter electrode). The voltage is applied across the working and reference electrode and the response current is obtained from the counter and reference electrode. Now the huge amount of data, obtained from these response current pulses, was compressed by discrete wavelet transform (DWT). In this paper, in order to determine the optimum level of compression mean square error, separation index and principal component analysis have been employed.

Quartz crystal microbalance sensors for discrimination of black tea

The quality evaluation of black tea is based on organoleptic methods of “Tea- tasters”. However the present quality estimation involving Tea-tasters is not a very reliable method as professional acumen, mood and other personal factors affect the judgment of tea quality. Electronic nose consists of an array of gas sensors with overlapping selectivity patterns, signal handling and classifier modules. An array of quartz crystal microbalance (QCM) sensors has been developed to differentiate among different tea samples. The important volatile components responsible for aroma of tea have been considered and the corresponding sensing materials have been identified. Five AT-cut 10 MHz Quartz crystal blanks coated with different sensing materials have been used to differentiate the aroma of orthodox and cut-tear-curl (CTC) tea samples. The developed sensors can distinguish not only between the orthodox and CTC tea but distinct clusters are also obtained for the four different tea-samples, as visualized through principal component analysis (PCA).

Improvement of quality perception for black CTC tea by means of an electronic tongue

Electronic tongue has already been used to estimate the quality of tea in terms of tea-tasters scores that are subjective and limited by human sensory organs. It is known that, chemical constituents play significant role to determine the quality of tea. Thus the perception of quality as understood from an electronic tongue can be improved if it can be trained to estimate the amount of major chemicals responsible for quality of tea. An alternate method of rapid quality evaluation of tea is proposed using a voltammetric electronic tongue to determine two major taste descriptors in black tea. The correlation model is developed between the electronic tongue signatures and theaflavins/thearubigins contents of tea using multi-layer perceptrons. The perception of taste is further improved using scaled conjugate gradient as a weight optimization algorithm.