Electronic sensor technologies in monitoring quality of tea: A review

Tea, after water, is the most frequently consumed beverage in the world. The fermentation of tea leaves has a pivotal role in its quality and is usually monitored using the laboratory analytical instruments and olfactory perception of tea tasters. Developing electronic sensing platforms (ESPs), in terms of an electronic nose (e-nose), electronic tongue (e-tongue), and electronic eye (e-eye) equipped with progressive data processing algorithms, not only can accurately accelerate the consumer-based sensory quality assessment of tea, but also can define new standards for this bioactive product, to meet worldwide market demand. Using the complex data sets from electronic signals integrated with multivariate statistics can, thus, contribute to quality prediction and discrimination. The latest achievements and available solutions, to solve future problems and for easy and accurate real-time analysis of the sensory-chemical properties of tea and its products, are reviewed using bio-mimicking ESPs. These advanced sensing technologies, which measure the aroma, taste, and color profiles and input the data into mathematical classification algorithms, can discriminate different teas based on their price, geographical origins, harvest, fermentation, storage times, quality grades, and adulteration ratio. Although voltammetric and fluorescent sensor arrays are emerging for designing e-tongue systems, potentiometric electrodes are more often employed to monitor the taste profiles of tea. The use of a feature-level fusion strategy can significantly improve the efficiency and accuracy of prediction models, accompanied by the pattern recognition associations between the sensory properties and biochemical profiles of tea

Machine Learning in Image Analysis and Pattern Recognition

This book is to chart the progress in applying machine learning, including deep learning, to a broad range of image analysis and pattern recognition problems and applications. In this book, we have assembled original research articles making unique contributions to the theory, methodology and applications of machine learning in image analysis and pattern recognition

Instrumental and chemometric methodologies to assess sensory quality of Mediterranean food

L'oli d'oliva, el vi o els fruits secs són productes típics de la regió Mediterrània que ofereixen un valor afegit gràcies als seus beneficis per a la salut i excel·lents característiques sensorials. Per aquest motiu és necessari un control de la qualitat i autenticitat d'aquests productes, que són altament susceptibles a fraus i adulteracions. Un aspecte important és l'avaluació de la qualitat sensorial, que descriu paràmetres percebuts pels sentits (gust, visió, olor i tacte) mitjançant panells validats i entrenats d'experts. Aquests panells tendeixen a ser subjectius i requereixen llargs temps d'anàlisi i alts costos. Com a conseqüència hi ha hagut un increment en el desenvolupament de tècniques d'anàlisi capaces de simular les respostes obtingudes amb el panell de tast humà. L'anomenat 'panell electrònic' ofereix respostes objectives mitjançant l'ús de tècniques multivariants que permeten establir correlacions entre els descriptors definits pels humans i els senyals obtingudes instrumentalment. Aquesta tesi pretén oferir tècniques instrumentals alternatives, ràpides i senzilles per determinar la qualitat sensorial d'aliments com l'oli d'oliva, el vi o les ametlles. Els estudis duts a terme inclouen el tractament de les respostes sensorials obtingudes mitjançant metodologies de referència (principalment panells de tast humans), l'optimització dels procediments analítics per treballar amb tècniques instrumentals i el desenvolupament d'eines quimiomètriques adequades per construir els models multivariants. També s'han desenvolupat estratègies de fusió de dades per combinar les diferents dades instrumentals que simulen els sentits humans (olor, gust i visió).El aceite de oliva, el vino o los frutos secos son productos típicos de la región Mediterránea que ofrecen un valor añadido gracias a sus beneficios para la salud y excelentes características sensoriales. Por este motivo es necesario un control de la calidad y autenticidad de estos productos, que son altamente susceptibles a fraudes y adulteraciones. Un aspecto importante es la evaluación de la calidad sensorial, que describe parámetros percibidos por los sentidos (gusto, visión, olor y tacto) mediante paneles validados y entrenados de expertos. Estos paneles tienden a ser subjetivos, requieren largos tiempos de análisis y altos costes. Como consecuencia ha habido un incremento en el desarrollo de técnicas de análisis capaces de simular las respuestas obtenidas con el panel de cata humano. El llamado 'panel electrónico' ofrece respuestas objetivas mediante el uso de técnicas multivariantes que permiten establecer correlaciones entre los descriptores definidos por los humanos y las señales obtenidas instrumentalmente. Esta tesis pretende ofrecer técnicas instrumentales alternativas, rápidas y sencillas para determinar la calidad sensorial de alimentos como el aceite de oliva, el vino o las almendras. Los estudios llevados a cabo incluyen el tratamiento de las respuestas sensoriales obtenidas mediante metodologías de referencia (principalmente paneles de cata humanos), la optimización de los procedimientos analíticos para trabajar con técnicas instrumentales y el desarrollo de herramientas quimiométricas adecuadas para construir los modelos multivariantes. También se han desarrollado estrategias de fusión de datos para combinar los diferentes datos instrumentales que simulan los sentidos humanos (olor, gusto y visión).Olive oil, wine or nuts are typical products of the Mediterranean region that offer added value thanks to its health benefits and excellent sensory characteristics. Therefore, the control the quality and authenticity of these products is necessary, mainly because they are highly susceptible to fraud and adulterations. An important aspect is the evaluation of sensory quality that describe parameters perceived by the senses (taste, sight, smell and touch) using validated and trained panels of experts. These panels tend to be subjective, requiring long-time analysis and high costs. As a result there has been an increase in the development of analytical techniques capable to simulate the responses obtained with the human taste panel. The so-called 'electronic panel' provides objective responses using multivariate techniques, which establish correlations between descriptors defined by humans and signals obtained instrumentally. This thesis aims to offer fast and simple alternative instrumental techniques to determine the sensory quality of foods such as olive oil, wine and almonds. Studies carried out include the treatment of sensory responses obtained by reference methodologies (mainly human taste panels), optimization of analytical procedures to work with instrumental techniques and the development of appropriate chemometric tools to build multivariate models. Data fusion strategies have also been studied by combining different instrumental data that simulate the human senses (smell, taste and sight)

Implementation of Digital Technologies on Beverage Fermentation

In the food and beverage industries, implementing novel methods using digital technologies such as artificial intelligence (AI), sensors, robotics, computer vision, machine learning (ML), and sensory analysis using augmented reality (AR) has become critical to maintaining and increasing the products’ quality traits and international competitiveness, especially within the past five years. Fermented beverages have been one of the most researched industries to implement these technologies to assess product composition and improve production processes and product quality. This Special Issue (SI) is focused on the latest research on the application of digital technologies on beverage fermentation monitoring and the improvement of processing performance, product quality and sensory acceptability

UNTARGETED AND TARGETED AROMA PROFILE ANALYSIS OF RAW AND BAKED JUJUBE

Winter jujube is described as having fresh and green aroma characteristics. However, there was no systematic research to clarify the geographical distribution effect on the aroma of winter jujube. The quality of red jujube from Xinjiang Province, China, is superior to other regions, but no studies have been carried out to reveal its regional aroma characteristics. Besides, the aroma of baked red jujube has not been revealed yet. Firstly, gas chromatography-ion mobility spectrometry (GC-IMS), GC-mass spectrometry (MS), and E-nose were applied for the aroma analysis of winter jujube from different regions. The results showed benzyl alcohol, octanoic acid, 2-hexenal, linalool, 2-nonenal, and ethyl decanoate were the most common compounds presented in all winter jujubes. 1-Penten-3-ol, ethyl hexanoate, methyl laurate, and 2-methylbenzaldehyde were induced as the potential markers of XJAKS with a green and fruity aroma. SXYC could be labeled by acetone and 2-methoxyphenol with woody and pungent aroma. Secondly, six cultivars of red jujubes (cv. JC, JZ, HZ, QYX, HTDZ, and YZ) grown in Xinjiang Province, China were collected. GC-IMS and E-Nose were used to study the volatile profile. JC, JZ, HZ, and YZ were different from the others, while QYX and HTDZ were similar to each other. Acetoin, E-2-hexanol, hexanal, acetic acid, and ethyl acetate were crucial for the classification. Correlation analysis showed jujube ID might be related to phenylacetaldehyde and isobutanoic acid that formed by the transamination or dehydrogenation of amino acids.Meanwhile, the sweet attribute was correlated with amino acids including threonine, glutamic acid, etc. Thirdly, the particular aroma of baked red jujube has not been evaluated until now. Molecular sensory sciences were applied for the identification of key odors. 5-Methyl-2-furancarboxaldehyde, β-damascenone, benzaldehyde, limonene, hexanoic acid, 5-butyltetrahydro-2-furanone, and DDMP were the key odorants for baked red jujube. The baking process stimulated the formation of aromatic hydrocarbon compounds like 1H-pyrrole-2-carboxaldehyde and DDMP. Finally, HS-SPME-GC-MS/MS was applied to quantitatively analyze targeted compounds. DDMP (2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one), formed during the baking of red jujube, is characterized by bitter odor and potential toxicity. Alkyl-substituted pyrazines perceived as nutty, roasted, or sweet odors contribute a lot to red jujube aroma. The standard curve of DDMP was linear between the ranges of 0.01 and 100 μg/mL, with a limit of detection at 0.1 ng/g below the sensory threshold of DDMP (2.06 μg/g). Good linear correlation coefficients (0.9947–0.9988) were obtained over the ranges of 1–10000 ng/mL for the alkyl pyrazines. The limits of detection (LODs) and limits of quantitation (LOQs) for the pyrazines were in the range of 0.5–10 pg/g and 1.5–30 pg/g, respectively. Trimethylpyrazine, which accounted for 38.71%–59.50% of the total pyrazine, was the main alkyl pyrazine in raw red jujube. Methylpyrazine accounted for 35.52%–49.76%, the highest portion of alkyl pyrazine in baked red jujube. The baking process might stimulate the dealkylation of alkyl pyrazines

Inactivation of polyphenol oxidase in Camellia sinensis for the production of high quality instant green tea

A concerning situation has developed over the past few years where several tea estates had to close down due to high labour costs and low profitability. Solutions are desperately required to save these estates from further regression and to prevent others from joining their ranks. One solution is to redirect the tea factories from the current production of black tea to producing a value added commodity such as a high quality green tea extract with an increased market value. The aim of this study was to find an economically viable PPO inactivation method that can be implemented in existing tea factories for the production of high quality instant green tea. Further enhancement of quality may then be achieved by high throughput cultivar screening where those with a higher natural catechin to caffeine content will be favourable. Six different PPO inactivation methods (steaming, blanching, fluid bed drying, panfrying, grilling over direct heat and grilling over indirect heat) were explored. Four independent experiments were performed in duplicate with these six methods using fresh tea leaves donated by a tea estate in Tzaneen, South Africa. All samples were dried in a fluid bed drier and milled after PPO inactivation. Biochemical analysis of specific quality parameters followed where extractions from these green tea leaf samples were tested for theaflavin content, caffeine content, flavan-3-ol content, total free amino acid content, colour and taste. The six PPO inactivation methods were compared by data evaluation of the individual quality parameters where certain quality parameters carried a higher weight than others. For the purpose of this project, the catechin to caffeine ratio was the most important quality determinant to yield a high value IGT. Also, to prove effectiveness of the PPO inactivation method, low TF content was compulsory. All PPO inactivation methods explored proved successful in rapidly inactivating PPO enzyme. As hypothesised, a significant difference in biochemical composition is brought about between green teas produced by employing different PPO inactivation methods. Blanching was found to be the most efficient PPO inactivation method as well as the method resulting in the highest catechin to caffeine ratio (16.67:1 for 4 min blanch vs. 5.72:1 for 17 min FBD as determined by HPLC analysis). A freeze dried extract from a 1.5 minute blanched sample (IGT) was compared with foreign IGTs originating from Sri-Lanka, Kenya, China and India by HPLC analysis. A more than two fold greater catechin to caffeine ratio was obtained for the sample originating from the blanching method (9.08:1 vs. 2.81-5.02:1). A high quality, naturally low caffeine, instant green tea can therefore be produced by utilizing the blanching method of PPO inactivation. To allow for inter and intra cultivar screening, tentative identification of novel catechins (digallated catechins) and their HPLC retention times was done using HPLC-ESI-MS/MS. Potential HPLC retention times for EC-digallate were detected at tR 62.0 ± 0.2, 70.7 ± 0.1 and 76.7 ± 0.2 minutes while tR 64.6 ± 0.1 and 65.8 ± 0.1 minutes were detected for EGC-digallate. With this information at hand, cultivars of a higher quality, hence increased economical potential, can be identified upon confirmation by NMR. HPLC-ESI-MS/MS screening coupled with NMR confirmation is to be continued to detect several other novel flavan-3-ols that could not be detected in the 4 IGTs of different origin used in this study. This study gives an overview of the biochemical differences between green tea leaves prepared using six different PPO inactivation methods. The aim of this study was met by identification of the significant increase in quality brought about by PPO inactivation using the blanching method, which is also economical for use in Africa. Blanching of tea leaves caused a significant decrease in caffeine. Therefore, the 1st hypothesis, stating that the six polyphenol oxidase inactivation methods investigated will produce instant green teas with different catechin to caffeine ratios, is accepted. Also, a means to perform large scale screening of individual tea trees in Africa for their novel flavan-3-ol content was provided by tentative identification of these novel catechins by LC-MS. Thus, the 2nd hypothesis, stating that application of LC-MS will aid in the identification of HPLC retention times of compounds (novel catechins) from a crude extract, is also accepted.Dissertation (MSc)--University of Pretoria, 2009.Biochemistryunrestricte

Education for the children of wandering labours, in the context of salt workers (Agariyas), in little Rann of Kutch

Not availabl