Aroma enhancement of instant green tea infusion using β-glucosidase and β-xylosidase

Nitrogen‑phosphorus responses and Vis/NIR prediction in fresh tea leaves

Nitrogen and phosphorus are essential nutrients for the growth and development of tea plants.However, the nitrogen content (NC) and phosphorus content (PC) in different parts of fresh tea has not been paid attention. In this study, the NC and PC responses different nitrogen stress were analyzed, and a quantitative regression model for predicting NC and PC was established by using Vis/NIR spectroscopy and a variety of intelligent algorithms. Among them, NC and PC of different parts had significant difference. The selection of preprocessing algorithms has a significant impact on the predictive performance of the model. The VMDSG-D1-VCPA-IRIV-SVR prediction model for NC and the VMDSG-CARS-Stacking prediction model for PC have better prediction effects, and the correlation coefficients of the test set are more than 0.85, and the RPD is greater than 1.8. In conclusion, this study is helpful to guide the precise fertilization and in-situ detection of fresh tea leaves.

Research progress of β-xylosidase in green synthesis

β-Xylosidase, an important hydrolase, catalyzes the degradation of xylan and xylosides, demonstrating significant potential for applications in biomass conversion and green synthesis. In recent years, with the rise of green chemistry, research on β-xylosidase in sustainable chemical synthesis has garnered increasing attention. Lignocellulosic biomass, a readily available and sustainable natural resource, requires the involvement of β-xylosidase for the production of biofuels. This enzyme not only efficiently degrades the xylan components of plant cell walls to produce biofuels but also synthesizes high-value glycosides through transglycosylation reactions, providing an eco-friendly catalytic tool for green chemical synthesis. This review summarizes the structural characteristics and catalytic mechanisms of β-xylosidase, along with related techniques to enhance its catalytic performance, such as enzyme immobilization, enzyme fusion technology, genetic engineering, and enzyme synergy. It focuses on recent advancements in its green applications, including the production of active compounds, waste degradation, bioenergy development, pulp bleaching, and deinking of waste paper (as shown in Fig. 1). Additionally, in light of current research trends, this review offers insights into the future prospects and challenges of β-xylosidase in green synthesis, aiming to provide valuable references for related fields.

Characterization of key aroma in Huangjincha black tea processed from four different cultivars

Huangjincha (HJC) is a cultivar rich in amino acids making it ideal for producing high-quality black tea. In this study, the aroma composition of HJC black tea from four different cultivars (HJC1, HJC2, HJC18, and HJC168) was analyzed by aroma sensory evaluation combined with volatile compound analysis. Among 271 identified volatiles, with 39 compounds as key odorants contributing to the diverse aromas of HJC black teas. The OAV and GC-O results indicated that geraniol and benzeneacetaldehyde (HJC1), 3-methylbutanal and 1-penten-3-ol (HJC2), (E, E)-2,4-hexadienal and damascenone (HJC18), as well as methyl salicylate and citral (HJC168) were the most significant aroma compounds. Furthermore, PLS analysis revealed four odorants contributed to floral characteristic, three were related to fruity attribute, four were associated with green attribute, three were connected to fresh attribute, three were linked to nutty profile, and three were tied to the sweet profile.

Advances in Spray-Drying and Freeze-Drying Technologies for the Microencapsulation of Instant Tea and Herbal Powders: The Role of Wall Materials

The microencapsulation of tea and herbal extracts is gaining considerable attention in the food industry, particularly in the production of instant powders. This review examines the application of spray-drying and freeze-drying technologies for the encapsulation of bioactive compounds, focusing on the role of wall materials. Over the past two decades, carbohydrate-based (e.g., maltodextrin), gum-based (e.g., gum Arabic), and protein-based (e.g., whey protein isolate) materials have been widely used due to their impact on sensory properties, stability, protection of bioactive compounds, and other critical attributes of encapsulated products. Despite their widespread use, these materials have distinct advantages and limitations, such as cost, availability, and compatibility with different extracts. This review provides a comprehensive analysis of their physical and chemical properties, examines alternative and emerging wall materials (e.g., beta-cyclodextrin, sodium alginate, and inulin), and highlights the potential of combining different materials to optimise encapsulation outcomes. It also identifies current research gaps and future directions to improve the efficacy and quality of encapsulated tea and herbal powders.

The mining of thermostable β-glucosidase for tea aroma enhancement under brewing conditions

The β-glucosidases known to improve tea aroma are all mesothermal enzymes, limiting their use under brewing conditions. Based on the properties analysis and molecular docking, the thermostable β-glucosidase (TPG) from Thermotoga petrophlia showed potential to enhance tea aroma. Treatment by recombinant TPG at 90 °C, the floral, sweet and grassy notes of instant Oolong tea were increased, while the roasted, caramel and woody notes were decreased. The improved floral, sweet and grassy notes were related to increase releasing of benzyl alcohol (floral), geraniol (floral), (Z)-3-hexen-1-ol (grassy), benzaldehyde (sweet) and 1-hexanol (grassy) by TPG hydrolyzing of (Z)-3-hexenyl-β-D-glucopyranoside, hexanyl-β-D-glucopyranoside (HGP), benzyl-β-D-glucopyranoside, prunasin and geranyl-β-D-glucopyranoside (GGP), respectively. Although the catalytic efficiency of TGP to GGP was about twice that to HGP, HPG was more competitive than GGP when they mixed. Combined with microstructure analysis, the structure-function relationship of TPG-influencing tea aroma were understood. This study provided the method of how to mining new function of characterized β-glucosidases, as well as a theoretical basis for the development of new tea products.

Brewing method-dependent changes of volatile aroma constituents of green tea (Camellia sinensis L.)

The determination of optimal levels of green tea amount and brewing time would have a crucial role in the accumulation of desired aromatic volatile compounds to meet worldwide market demand. Aroma is the most important factor influencing tea consumers' choices along with taste, price, and brand. This study aims to determine how the brewing time and amount of green tea affect the aroma profile of green tea infusion. The effect of the amount of Turkish green tea (5-10 g) and brewing time (5-60 min) on aromatic volatile compounds was evaluated using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) technique. The SPME/GC-MS analysis identified 57 components in the aroma profile of green tea infusions including 13 esters, 12 alkanes, 7 unknowns, 6 ketones, 3 alcohols, 2 terpenes, 2 terpenoids, 1 alkaloid, 1 phenolic compound, 1 lactone, 1 pyrazine, and 1 norisoprenoid. The green tea amount and brewing time had significant effects on the number of chemical compounds. A total of 42, 47, and 36 aromatic volatile compounds were determined by brewing 5, 7.5, and 10 g of green tea. The most abundant constituents in green tea infusions were phytone, 2-decenal, lauric acid, unknown 1, methoxy-1-methylethyl pyrazine, α-ionone, β-ionone, and diethyl phthalate (DEP). With this study, the aroma structures of green tea infusion have been revealed for the first time depending on the brewing time and quantity.

Characterization of a novel multifunctional β-glucosidase/xylanase/feruloyl esterase and its effects on improving the quality of Longjing tea

Herein, a novel multifunctional enzyme β-glucosidase/xylanase/feruloyl esterase (GXF) was constructed by fusion of β-glucosidase and bifunctional xylanase/feruloyl esterase. The activities of β-glucosidase, xylanase, feruloyl esterase and acetyl xylan esterase displayed by GXF were 67.18 %, 49.54 %, 38.92 % and 23.54 %, respectively, higher than that of the corresponding single functional enzymes. Moreover, the GXF performed better in enhancing aroma and quality of Longjing tea than the single functional enzymes and their mixtures. After treatment with GXF, the grassy and floral odors of tea infusion were significantly improved. Moreover, GXF treatment could improve concentrations of flavonoid aglycones of myricetin, kaempferol and quercetin by 68.1-, 81.42- and 77.39-fold, respectively. In addition, GXF could accelerate the release of reducing sugars, ferulic acid and xylo-oligosaccharides by 9.48-, 8.25- and 4.11-fold, respectively. This multifunctional enzyme may have potential applications in other fields such as food production and biomass degradation.

Pruned tea biomass plays a significant role in functional food production: A review on characterization and comprehensive utilization of abandon-plucked fresh tea leaves

Tea is the second largest nonalcoholic beverage in the world due to its characteristic flavor and well-known functional properties in vitro and in vivo. Global tea production reaches 6.397 million tons in 2022 and continues to rise. Fresh tea leaves are mainly harvested in spring, whereas thousands of tons are discarded in summer and autumn. Herein, pruned tea biomass refers to abandon-plucked leaves being pruned in the non-plucking period, especially in summer and autumn. At present, no relevant concluding remarks have been made on this undervalued biomass. This review summarizes the seasonal differences of intrinsic metabolites and pays special attention to the most critical bioactive and flavor compounds, including polyphenols, theanine, and caffeine. Additionally, meaningful and profound methods to transform abandon-plucked fresh tea leaves into high-value products are reviewed. In summer and autumn, tea plants accumulate much more phenols than in spring, especially epigallocatechin gallate (galloyl catechin), anthocyanins (catechin derivatives), and proanthocyanidins (polymerized catechins). Vigorous carbon metabolism induced by high light intensity and temperature in summer and autumn also accumulates carbohydrates, such as soluble sugars and cellulose. The characteristics of abandon-plucked tea leaves make them not ideal raw materials for tea, but suitable for novel tea products like beverages and food ingredients using traditional or hybrid technologies such as enzymatic transformation, microbial fermentation, formula screening, and extraction, with the abundant polyphenols in summer and autumn tea serving as prominent flavor and bioactive contributors.

The effect of instant tea on the aroma of duck meat

Tea products, such as instant tea, have been shown to improve the aroma of meat products. However, the mechanisms by which tea products enhance meat aroma have not been adequately explained. In this study, we analyzed the impact of instant tea on the aroma of duck meat. Our results showed that treatment with instant tea led to increases in floral, baked, and grassy notes while reducing fishy and fatty notes. Several alcohols, aldehydes, ketones, indole and dihydroactinidiolide exhibited significantly increased OAVs. Conversely, certain saturated aldehydes, unsaturated aldehydes and alcohols displayed significantly decreased OAVs. The enhanced floral, baked and grassy notes were attributed to volatile compounds present in instant tea. The reduction in fishy and fatty notes was linked to polyphenols in instant tea interacting with nonanal, undecanal, (E)-2-octenal, (E)-2-nonenal, (E)-2-decenal, and 2,4-decadienal through hydrophobic interactions and electronic effects. This study enhances our understanding of how tea products improve meat aromas.

The enhancement of flowery-like aroma in green tea under optimized processing conditions by sensory-directed flavor analysis

Flowery-like aroma are positive contributors to green tea. Here, the optimal processing conditions for green tea with flowery-like aroma were designed using spreading time, fixation time and drying temperature as three factors designed by response surface methodology (RSM), and the response value of aroma sensory evaluation score. The volatiles in batches of tea samples were analyzed by GC-MS. The optimal quality was obtained with a flowery-like aroma by RSM under a spreading time of 8.97 h, fixation time of 162.3 s, and drying temperature of 103.32 °C. GC-O and odor activity values further revealed floral-like volatiles, including decanal, linalool oxide, β-lonone, geraniol, (Z)-jasmone, linalool, nonanal, and benzeneacetaldehyde. The recombination of these floral volatiles confirmed the consistency with the floral green tea. Furthermore, the extending spreading duration (8-10 h), reducing fixation duration (160-190 s), and increasing drying temperature (100-115 °C) promote their accumulation in green tea. This study provides new perspectives for the precise enhancement of floral odorants for green tea.

A Thermotolerant Yeast Cyberlindnera rhodanensis DK Isolated from Laphet-so Capable of Extracellular Thermostable β-Glucosidase Production

This study aims to utilize the microbial resources found within Laphet-so, a traditional fermented tea in Myanmar. A total of 18 isolates of thermotolerant yeasts were obtained from eight samples of Laphet-so collected from southern Shan state, Myanmar. All isolates demonstrated the tannin tolerance, and six isolates were resistant to 5% (w/v) tannin concentration. All 18 isolates were capable of carboxy-methyl cellulose (CMC) degrading, but only the isolate DK showed ethanol production at 45 °C noticed by gas formation. This ethanol producing yeast was identified to be Cyberlindnera rhodanensis based on the sequence analysis of the D1/D2 domain on rRNA gene. C. rhodanensis DK produced 1.70 ± 0.01 U of thermostable extracellular β-glucosidase when cultured at 37 °C for 24 h using 0.5% (w/v) CMC as a carbon source. The best two carbon sources for extracellular β-glucosidase production were found to be either xylose or xylan, with β-glucosidase activity of 3.07-3.08 U/mL when the yeast was cultivated in the yeast malt extract (YM) broth containing either 1% (w/v) xylose or xylan as a sole carbon source at 37 °C for 48 h. The optimal medium compositions for enzyme production predicted by Plackett-Burman design and central composite design (CCD) was composed of yeast extract 5.83 g/L, peptone 10.81 g/L and xylose 20.20 g/L, resulting in a production of 7.96 U/mL, while the medium composed (g/L) of yeast extract 5.79, peptone 13.68 and xylan 20.16 gave 9.45 ± 0.03 U/mL for 48 h cultivation at 37 °C. Crude β-glucosidase exhibited a remarkable stability of 100%, 88% and 75% stable for 3 h at 35, 45 and 55 °C, respectively.

Microbial production and applications of β-glucosidase-A review

β-Glucosidase exists in all areas of living organisms, and microbial β-glucosidase has become the main source of its production because of its unique physicochemical properties and the advantages of high-yield production by fermentation. With the rise of the green circular economy, the production of enzymes through the fermentation of waste as the substrate has become a popular trend. Lignocellulosic biomass is an easily accessible and sustainable feedstock that exists in nature, and the production of biofuels from lignocellulosic biomass requires the involvement of β-glucosidase. This review proposes ways to improve β-glucosidase yield and catalytic efficiency. Optimization of growth conditions and purification strategies of enzymes can increase enzyme yield, and enzyme immobilization, genetic engineering, protein engineering, and whole-cell catalysis provide solutions to enhance the catalytic efficiency and activity of β-glucosidase. Besides, the diversified industrial applications, challenges and prospects of β-glucosidase are also described.

Differences in the quality of black tea (Camellia sinensis var. Yinghong No. 9) in different seasons and the underlying factors

Spring green tea is usually considered to be better than summer green tea. Whether this phenomenon applies to black tea is unknown. Black tea produced using Camellia sinensis var. Yinghong No. 9 leaves is popular in South China and analyzed in the study. The taste and color quality of the infusion was higher for spring tea than for summer tea. Compared with summer tea, the main catechin contents were lower in spring tea, whereas caffeine and total amino acid contents were higher, especially glutamic acid, which may be responsible for the differences between teas. Moreover, spring tea had a higher theabrownin content and a lower L* value. The compounds contributing to the infusion taste and color were correlated with the chromaticity value (i.e., useful indicator of black tea quality). This study revealed the seasonal differences in Yinghong No. 9 black tea quality and the key underlying factors.

Rutinosidase and other diglycosidases: Rising stars in biotechnology

Diglycosidases are a special class of glycosidases (EC 3.2.1) that catalyze the separation of intact disaccharide moieties from the aglycone part. The main diglycosidase representatives comprise rutinosidases that cleave rutinose (α-l-Rha-(1-6)-β-d-Glc) from rutin or other rutinosides, and (iso)primeverosidases processing (iso)primeverosides (d-Xyl-(1-6)-β-d-Glc), but other activities are known. Notably, some diglycosidases may be ranked as monoglucosidases with enlarged substrate specificity. Diglycosidases are found in various microorganisms and plants. Diglycosidases are used in the food industry for aroma enhancement and flavor modification. Besides their hydrolytic activity, they also possess pronounced synthetic (transglycosylating) capabilities. Recently, they have been demonstrated to glycosylate various substrates in a high yield, including peculiar species like inorganic azide or carboxylic acids, which is a unique feature in biocatalysis. Rhamnose-containing compounds such as rutinose are currently receiving increased attention due to their proven activity in anti-cancer and dermatological experimental studies. This review demonstrates the vast and yet underrated biotechnological potential of diglycosidases from various sources (plant, microbial), and reveals perspectives on the use of these catalysts as well as of their products in biotechnology.

Decoding the Chemical Signatures and Sensory Profiles of Enshi Yulu: Insights from Diverse Tea Cultivars

Enshi Yulu, a renowned Chinese steamed green tea, is highly valued for its unique sensory attributes. To enhance our comprehensive understanding of the metabolic variation induced by steaming fixation, we investigated the overall chemical profiles and organoleptic quality of Enshi Yulu from different tea cultivars (Longjing 43, Xiapu Chunbolv, and Zhongcha 108). The relationships between sensory traits and non-volatiles/volatiles were evaluated. A total of 58 volatiles and 18 non-volatiles were identified as characteristic compounds for discriminating among the three tea cultivars, and the majority were correlated with sensory attributes. The "mellow" taste was associated with L-aspartic acid, L-asparagine, L-tyrosine, L-valine, EGC, EC, and ECG, while gallic acid and theobromine contributed to the "astringent" taste. "Kokumi" contributors were identified as L-methionine, L-lysine, and GCG. Enshi Yulu displayed a "pure" and "clean and refreshing" aroma associated with similar volatiles like benzyl alcohol, δ-cadinene, and muurolol. The composition of volatile compounds related to the "chestnut" flavor was complex, including aromatic heterocycles, acids, ketones, terpenes, and terpene derivatives. The key contributors to the "fresh" flavor were identified as linalool oxides. This study provides valuable insights into the sensory-related chemical profiles of Enshi Yulu, offering essential information for flavor and quality identification of Enshi Yulu.

Isolation and Identification of β-Glucosidases-Producing Non-Saccharomyces Yeast Strains and Its Influence on the Aroma of Fermented Mango Juice

The cultivation and enrichment of different soils in a vineyard yielded 95 yeast species. Among them, seven strains capable of producing β-glucosidases were identified using the aescin colorimetric method. One non-Saccharomyces yeast strain was isolated from a plate containing lysine and identified using internal transcription (ITS) as Candida cf. sorbosivorans (C. cf. sorbosivorans), which was named Candida cf. sorbosivorans X1. Additionally, the enzymatic characteristics of the β-glucosidases produced by this strain were investigated. The β-glucosidases generated by C. cf. sorbosivorans X1 displayed high enzymatic activity and enzyme-activity retention in a pH range of 3.0 to 5.4 and at temperatures of 30 °C to 35 °C. Using non-targeted metabolomics methods, we investigated the alterations in metabolites during the fermentation of mango juice. The strain C. cf. sorbosivorans X1 demonstrated activity against phenols and terpenes. In the fermented mango juice (X1FMJ), we identified 41 differential metabolites. These included 14 esters, 4 hydrocarbons, 3 aldehydes, 5 ketones, 4 terpenoids, 4 alcohols, 1 aromatic hydrocarbon, 2 amines, 1 acid, and 3 heterocyclic compounds. The metabolic pathways of these differential metabolites were analyzed, revealing four key pathways: tyrosine metabolism, phenylpropanoid biosynthesis, monoterpene biosynthesis, and α-linolenic acid metabolism, which promoted the formation of aroma compounds in the fermented mango juice.

Structures, Biochemical Characteristics, and Functions of β-Xylosidases

The complete degradation of abundant xylan derived from plants requires the participation of β-xylosidases to produce the xylose which can be converted to xylitol, ethanol, and other valuable chemicals. Some phytochemicals can also be hydrolyzed by β-xylosidases into bioactive substances, such as ginsenosides, 10-deacetyltaxol, cycloastragenol, and anthocyanidins. On the contrary, some hydroxyl-containing substances such as alcohols, sugars, and phenols can be xylosylated by β-xylosidases into new chemicals such as alkyl xylosides, oligosaccharides, and xylosylated phenols. Thus, β-xylosidases shows great application prospects in food, brewing, and pharmaceutical industries. This review focuses on the molecular structures, biochemical properties, and bioactive substance transformation function of β-xylosidases derived from bacteria, fungi, actinomycetes, and metagenomes. The molecular mechanisms of β-xylosidases related to the properties and functions are also discussed. This review will serve as a reference for the engineering and application of β-xylosidases in food, brewing, and pharmaceutical industries.

Chemical Composition and In Vitro Antioxidant Activity and Anti-Acetylcholinesterase Activity of Essential Oils from Tadehagi triquetrum (L.) Ohashi

The present study aimed to determine the chemical compositions of essential oils (EOs) from Tadehagi triquetrum (L.) Ohashi and evaluate their antioxidant and anti-cholinesterase activity under the comprehensive influence of chemical components. The essential oils were extracted from T. triquetrum (L.) Ohashi by hydrodistillation. A total of 58 organic compounds were identified by GC-FID and GC-MS analysis. The major components of T. triquetrum (L.) Ohashi EOs were identified as palmitic acid (22.46%), 1-Octen-3-ol (14.07%), Caryophyllene (7.20%), (Z)-18-Octadec-9-enolide (6.04%), and 3-Hexen-1-ol (4.55%). The antioxidant activity of the essential oils was determined by using ABTS assay, DPPH assay, and FRAP assay, with IC₅₀ values of 2.12 ± 0.05 mg/mL, 4.73 ± 0.91 mg/mL against the ABTS, DPPH, and FRAP value 117.42 ± 8.10 mM/g. The result showed that it had moderate antioxidant activities in the experiment, which why it is likely that it will be used as an antioxidant. At the same time, the EOs also showed moderate anti-acetylcholinesterase activity. This study expands the chemical and biological knowledge of the EOs of T. triquetrum.

Characterization of the off-flavor from Pichia pastoris GS115 during the overexpression of an α-l-rhamnosidase

The off-flavor of Pichia pastoris strains is a negative characteristic of proteins overexpressed with this yeast. In the present study, P. pastoris GS115 overexpressing an α-l-rhamnosidase was taken as the example to characterize the off-flavor via sensory evaluation, gas chromatography-mass spectrometer, gas chromatography-olfaction, and omission test. The result showed that the off-flavor was due to the strong sweaty note, and moderate metallic and plastic notes. Four volatile compounds, that is, tetramethylpyrazine, 2,4-di-tert-butylphenol, isovaleric acid, and 2-methylbutyric acid, were identified to be major contributors to the sweaty note. Dodecanol and 2-acetylbutyrolactone were identified to be contributors to the metallic and plastic notes, respectively. It is the first study on the off-flavor of P. pastoris strains, helping understand metabolites with off-flavor of this yeast. Interestingly, it is the first study illustrating 2-acetylbutyrolactone and dodecanol with plastic and metallic notes, providing new information about the aromatic contributors of biological products.

IMPORTANCE

The methylotrophic yeast Pichia pastoris is an important host for the industrial expression of functional proteins. In our previous studies, P. pastoris strains have been sniffed with a strong off-flavor during the overexpression of various functional proteins, limiting the application of these proteins. Although many yeast strains have been reported with off-flavor, no attention has been paid to characterize the off-flavor in P. pastoris so far. Considering that P. pastoris has advantages over other established expression systems of functional proteins, it is of interest to identify the compounds with off-flavor synthesized in the overexpression of functional proteins with P. pastoris strains. In this study, the off-flavor synthesized from P. pastoris GS115 was characterized during the overexpression of an α-l-rhamnosidase, which helps understand the aromatic metabolites with off-flavor of P. pastoris strains. In addition, 2-acetylbutyrolactone and dodecanol were newly revealed with plastic and metallic notes, enriching the aromatic contributors of biological products. Thus, this study is important for understanding the metabolites with off-flavor of P. pastoris strains and other organisms, providing important knowledge to improve the flavor of products yielding with P. pastoris strains and other organisms.

ONE-SENTENCE SUMMARY

Characterize the sensory and chemical profile of the off-flavor produced by one strain of P. pastoris in vitro.

Profiling Real-Time Aroma from Green Tea Infusion during Brewing

Aroma substances are the most crucial criteria for the sensory evaluation of tea quality, and also key attractors influencing consumers to make the decision for purchasing tea. Understanding the aromatic properties of tea infusion during different brewing time is crucial to control the tea aromatic quality. Here, headspace and direct immersion solid-phase microextraction (HS-SPME and DI-SPME), coupled with GC-MS, were employed to investigate the impact of brewing time on the changes of the volatile features of green tea infusion. Esters, aldehydes, alcohols, fatty acids, and alkaloids were the predominant volatile groups from tea infusions. Two to three minutes was identified as the best duration for the tea brewing that can maximize the abundance of aromatic chemicals in the headspace emitted from the tea infusions. The variation of the key aromatic contributors between the tea infusion and the headspace over the infusion tended to equilibrate during the tea brewing process. This study provides a theory-based reference method by analyzing the real-time aromatic characteristics in green tea. The optimal time was determined for aromatic quality control, and the complementary relationship between the volatiles in the headspace and its counterpart, tea infusion, was primarily elucidated.

Optimized Clarification Technology of Bayberry Juice by Chitosan/Sodium Alginate and Changes in Quality Characteristics during Clarification

In this study, a novel method to clarify bayberry juice with composite clarifiers, chitosan and sodium alginate, has been designed. The optimal conditions were as follows: using chitosan 0.05 g/L first and then sodium alginate 0.05 g/L as composite clarifiers, standing for 2 h at 25 °C. The transmittance increased from 0.08 to 91.2% after treating by composite clarifiers, which was significantly higher than using chitosan (44.29%) and sodium alginate (38.46%) alone. It was also found that sedimentation time of juice treated by composite clarifiers was about 60% shorter than using single clarifiers. Meanwhile, the reduction of anthocyanin in juice was 9.16% for composite clarifiers treatment, being less than that for the single sodium alginate and previous related researches. In addition, the color and aroma of bayberry juice treated by composite clarifiers were improved. Juice treated by composite clarifiers had the highest L* value with 52.48 and looked more attractive. The present research revealed that content of beta-damascenone and dihydro-5-pentyl-2(3H)-furanone increased after treatment with composite clarifiers which contributed more to the pleasant aroma. Overall, the developed method improved the clarification effect and sensory quality, and reduced the sedimentation time, which may be promising in the production of clear bayberry juice.

An effective immobilization of β-glucosidases by partly cross-linking enzyme aggregates

Enzyme immobilization provides ideal operating conditions for enzymes stabilization and sustainable recycling. In this work, as a kind of clay material, montmorillonite (MTL) was chosen for immobilizing the β-glucosidase extracted from Agrocybe aegirit. The immobilized β-glucosidase via partly cross-linking enzyme aggregates (pCLEAs) formed by self-catalysis provided biocatalysts with satisfactory thermal and pH stability. Compared to the glutaraldehyde cross-linked, the immobilized β-glucosidase (β-G-pCLEAs@MTL) exhibited significantly higher immobilization efficiency (IE) and immobilization yield (IY), which were 80.6% and 76.9%, respectively. The β-G-pCLEAs@MTL also showed better stability and preferable reusability. And the activity of the β-G-pCLEAs@MTL remained 85.0% after 5 cycles and 74.7% after 10 cycles. Therefore, the method based on the pre- crosslinking to form pCLEAs and after-immobilization can effectively improve IY and IE. In addition, MTL seems to be a good alternative carrier to immobilize other enzymes for industrial application.

Characterisation of the volatile compounds profile of Chinese pan-fried green tea in comparison with baked green tea, steamed green tea, and sun-dried green tea using approaches of molecular sensory science

Pan-fried green tea (PGT) is an easily acceptable tea drink for general consumers. In this study, volatile profiles and characteristic aroma of 22 representative Chinese PGT samples were extracted using stir bar sorptive extraction (SBSE) and analysed by gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O) analysis, and odour activity value (OAV) calculations. In total, 88 volatile compounds were identified. Alcohols (45%), esters (19%), and ketones (16%) were the dominant volatiles, and geraniol (484.8 μg/kg) was the most abundant volatile component in PGT, followed by trans-β-ionone and linalool. In addition, the differences of aroma characteristics among PGT and other three types of green tea, namely baked green tea, steamed green tea, and sun-dried green tea, were also observed using partial least squares discriminant analysis (PLS-DA) and heatmap analysis, and it was found that β-myrcene, methyl salicylate, (E)-nerolidol, geraniol, methyl jasmonate were generally present at higher content in PGT. This is the first comprehensive report describing the volatile profiles of Chinese PGT, and the findings from this study can advance our understanding of PGT aroma quality, and provide important theoretical basis for processing and quality control of green tea products.

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Volatiles of pan-fried green teas were extracted using stir bar sorptive extraction.

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Pan-fried green tea was rich in alcohols, esters, and ketones.

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Trans-β-ionone has both the highest odour activity value and aroma intensity.

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Sixteen key aroma compounds were identified by means of molecular sensory science.

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The differences of volatiles among four types of green teas were revealed.

Enhancement of Black Tea Aroma by Adding the β-Glucosidase Enzyme during Fermentation on Black Tea Processing

Black tea aroma is one of the essential attributes in determining the quality of black tea. β-Glucosidases were investigated for their ability to enhance the aroma of black tea by hydrolyzing the glycoside compound. The addition of β-glucosidase was done by dissolving the enzyme on a sodium citrate buffer (pH 5.0), which was then sprayed on tea leaves during black tea processing. The β-glucosidase treatment significantly increases the volatile compound from glycoside precursors such as linalool, geraniol, and methyl salicylate. Moreover, the volatile compound from carotenoid and lipid precursors (nerolidol and β-cyclocitral) was also increased with β-glucosidase treatment.

Ability of Yeast Metabolic Activity to Reduce Sugars and Stabilize Betalains in Red Beet Juice

To lower the risk of obesity, diabetes, and other related diseases, the WHO recommends that consumers reduce their consumption of sugars. Here, we propose a microbiological method to reduce the sugar content in red beet juice, while incurring only slight losses in the betalain content and maintaining the correct proportion of the other beet juice components. Several yeast strains with different metabolic activities were investigated for their ability to reduce the sugar content in red beet juice, which resulted in a decrease in the extract level corresponding to sugar content from 49.7% to 58.2%. This strategy was found to have the additional advantage of increasing the chemical and microbial stability of the red beet juice. Only slight losses of betalain pigments were noted, to final concentrations of 5.11% w/v and 2.56% w/v for the red and yellow fractions, respectively.

Rapid characterization of the volatile profiles in Pu-erh tea by gas phase electronic nose and microchamber/thermal extractor combined with TD-GC-MS

Aroma plays an important role in the quality of Pu-erh tea. However, the quality evaluation of Pu-erh tea aroma is heavily relied on the experience of sensory evaluation, and the theoretical research is relatively scarce. In the present work, the volatile compounds in Pu-erh tea were characterized by using gas phase electronic nose (e-nose) and microchamber/thermal extractor (µ-CTE) combined with thermal desorption coupled to gas chromatography-mass spectrometry (TD-GC-MS). A satisfactory discrimination model (R² Y = 0.95, Q²  = 0.807) was obtained by using orthogonal partial least squares discriminant analysis (OPLS-DA) based on the odor fingerprint of different brands of Pu-erh tea. In addition, based on the double criterion of multivariate analysis with VIP >1.0 and univariate analysis with p ≤ 0.001, 39 volatile components were identified to contribute greatly to the discrimination of five brands of Pu-erh tea. The results suggested that gas phase e-nose and µ-CTE combined with TD-GC/MS were simple, rapid techniques to characterize the volatile compounds in Pu-erh tea and were allowed to effectively distinguish different brands of Pu-erh tea, which would provide an important reference on the quality assessment of Pu-erh tea. PRACTICAL APPLICATION: This work demonstrates that the volatile compounds in Pu-erh tea are simply and rapidly characterized by using µ-CTE/TD-GC/MS and gas phase e-nose, allowing to effectively distinguish different brands of Pu-erh tea, which can provide an important reference for the quality assessment and authentication of Pu-erh tea.

Influence of Eurotium cristatum and Aspergillus niger individual and collaborative inoculation on volatile profile in liquid-state fermentation of instant dark teas

The three instant dark teas were produced from instant green tea (IGT) by liquid-state fermentations using the microorganisms Eurotium cristatum (EFT), Aspergillus niger (AFT), and sequential inoculation of E. cristatum/A. niger (EAFT), respectively. The volatile compounds of four tea samples were extracted by headspace-solid phase microextraction (HS-SPME) and analyzed using gas chromatography-mass spectrometry (GC-MS) coupled with chemometrics. A total of 97 volatile compounds were tentatively identified to distinguish three fermented instant dark from IGT. Alcohols, acids, esters, ketones, aldehydes, and heterocyclics could be clearly distinguished by principal component analysis (PCA), venn diagram, heatmap analysis and hierarchical cluster analysis (HCA). Descriptive sensory analysis revealed that AFT had a moldy, woody and herbal aroma; EFT showed woody and herbal aroma; and EAFT smelled an herbal, sweet, minty and floral aroma. This study indicates that fermentation using different microorganisms is critical in forming unique aroma characteristics of instant dark teas.

Comparative Evaluation of Key Aroma-Active Compounds in Sweet Osmanthus (Osmanthus fragrans Lour.) with Different Enzymatic Treatments

Sweet osmanthus (Osmanthus fragrans Lour.) (OF) is one of the ten most famous flowers in China for its unique and delicate fragrance. A combined solid-phase microextraction and solvent-assisted flavor evaporation method was used to accurately capture the overall aromatic profile and characterize the predominant odorants of fresh osmanthus with the help of gas chromatography (GC)-olfactometry and comprehensive two-dimensional GC-quadrupole time-of-flight mass spectrometry (GC × GC-QTOF-MS). Twenty-six volatiles were identified for the first time in OF. A total of 23 potent odorants, dominated by monoterpene oxides and C₆ aliphatic aldehydes, were identified. The efficacy of pectinase, β-glucosidase, and their combination on the aroma enhancement of OF was evaluated by quantitation of the target aroma components using GC-triple quadrupole-MS. The total concentration of key aroma components increased in all three enzyme treatment groups, and the increase was more significant in two β-glucosidase-treated groups. Changes in odor activity values and odor spectrum values of key odorants indicated that the pectinase-treated sample had more prominent floral, green, and potato-like scents. In contrast, the β-glucosidase-treated sample had more dominant floral, woody, almond-like, and fruity notes but less green odor, which was confirmed by sensory evaluation. β-Glucosidase and pectinase complement one another very well, and together, promote a remarkable aroma enhancement in OF.

Enzymatic hydrolysis and auto-isomerization during β-glucosidase treatment improve the aroma of instant white tea infusion

The aroma changes in instant white tea resulting from β-glucosidase treatment was investigated by quantitative descriptive analysis (QDA), gas chromatography-mass spectrometry (GC-MS), odour activity value analysis (OAV), aroma reconstruction and omission tests. The grassy, floral and sweet notes increased significantly (P < 0.05), and the roasted note decreased significantly (P < 0.05) upon β-glucosidase treatment. Quantitative analysis showed that the concentrations of benzaldehyde, benzeneacetaldehyde, (Z)-3-hexen-1-ol, linalool, phenylethyl alcohol, cis-linalool oxide, trans-linalool oxide, hexanol, hotrienol and (E)-2-hexen-1-ol increased significantly (P < 0.05) after treatment; however, (Z)-3-hexen-1-ol isomerized to (E)-2-hexen-1-ol. OAV analysis, aroma reconstruction and the omission test showed that the grassy, floral and sweet notes increased as the (Z)-3-hexen-1-ol, cis/trans-linalool oxide and benzeneacetaldehyde increased, whereas the roasted note declined under the same conditions. The enzymatic hydrolysis of glycosidic precursors and the auto-isomerization of volatile compounds provide new information for understanding how β-glucosidase treatment improves the aroma of tea products.

Quality assessment of instant green tea using portable NIR spectrometer

Caffeine and catechin are two main components of instant green tea, and are essential components of tea quality. This paper mainly focuses on the feasibility of rapidly determining instant green tea components by using a portable near infrared (NIR) spectrometer. The two main components (caffeine and catechin) were studied. In addition, the instrument performance levels of portable and benchtop NIR spectrometers were studied and compared. Quantitative models developed using portable and benchtop spectrometers for measuring caffeine, total catechins, and four individual catechins were established and compared. After preprocessing using standard normal variate (SNV), the Rp values of the caffeine, total catechins, (-)-epigallocatechin, (-)-epigallocatechin 3-gallate, (-)-epicatechin, and (-)-epicatechin gallate in the partial least squares models for a portable NIR spectrometer were 0.974, 0.962, 0.669, 0.945, 0.942 and 0.905, respectively. For a benchtop NIR spectrometer, Rp values were 0.993, 0.958, 0.883, 0.955, 0.966 and 0.936, respectively. Passing-Bablok regression method results indicated no significant differences between the two instruments. A genetic algorithm (GA) and the successive projections algorithm (SPA) were used to screen the wavelength of the NIR spectrum and establish the model. The GA obtained more robust modeling results. This study concludes that the developed portable spectroscopy system combined with appropriate variable selection methods can be effectively used for rapid determination of caffeine, total catechins, and four individual catechins in instant green tea.