Comparative analyses of aromas of fresh, naringinase-treated and resin-absorbed juices of pummelo by GC-MS and sensory evaluation

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.

Unraveling the relationship between aroma characteristics and lipid profile of abalone (Haliotis discus hannai) during seasonal fluctuation and thermal processing

Abalone, a highly sought-after aquatic product, possesses significant nutritional value. In this study, the relationship between aroma characteristics and lipid profile of abalone (Haliotis discus hannai) during seasonal fluctuation and thermal processing were profiled via volatolomics and lipidomics. 46 aroma compounds and 371 lipids were identified by HS-SPME-GC-MS and UPLC-Q-Extractive Orbitrap-MS, respectively. Multivariate statistical analysis indicated that carbonyls (aldehydes and ketones) and alcohols were the characteristic aroma compounds of abalone. The fluctuations in the aroma compound and lipid composition of abalone were consistent with the seasonal variation, especially seawater temperature. In addition, based on the correlation analysis, it was found that carbonyls (aldehydes and ketones) and alcohols had a positive correlation with phospholipids (lysophosphatidylethanolamines and lysophosphatidylcholines), while a negative correlation was observed with fatty acyls. These findings suggested that the effect of seasonal variations on the aroma changes of abalone might achieved by modulating the lipids composition of abalone.

The characteristic terpenes in sea cucumber soaked in star anise solution were characterized by HS-SPME-GC-MS and PCA analysis

The quality of sea cucumber is closely associated with its processing technology. In this study, the response surface methodology (RSM) was employed to optimize the thermal process conditions for seasoned sea cucumber, while gas chromatography-mass spectrometry (GC-MS) technique identified 25 characteristic compounds. Terpenes and their oxygen derivatives constituted approximately 70% of all compounds detected. Among these, trans-anethole emerged as the predominant volatile aroma compound in seasoned sea cucumber at a concentration of 39.99 ± 4.52 mg/g, followed by p-anisaldehyde, cis-anethole, linalool, estragole, and d-limonene. Principal component analysis (PCA) revealed that trans-anethole, cis-anethole, estragole, and d-limonene collectively contributed over 45.0% to the flavor profile of sea cucumber. This investigation provides an initial exploration into the alterations in volatile compounds within star anise-seasoned seasoned sea cucumber, thereby establishing a foundation for instant sea cucumbers' flavor processing.

Nutritional and volatile profiles of pulp and flavedo from four local pummelo cultivars grown in Fujian province of China

The nutritional and volatile profiles of pulp and flavedo samples from four distinct local pummelo landraces ("Siji," "Pingshan," "Wendan," and "Guanxi") cultivated in Fujian province of China were investigated. "Guanxi" pummelo exhibited relatively high contents of vitamin C (42.01 mg/100 mL) and phenols (360.61 mg/L) and displayed a robust antioxidant capacity (41.15 mg/100 mL). Conversely, the red pulp from "Pingshan" demonstrated relatively high values of carotenoids (55.96 µg/g) and flavonoids (79.79 mg/L). Considerable differences were observed in volatile compositions between the two fruit tissues and among the four genotypes. A total of 166 and 255 volatile compounds were detected in the pulp and flavedo samples, respectively. Notably, limonene and β-myrcene were identified as the principal volatile compounds in flavedo, whereas hexanal was highly abundant in the pulp of "Siji," "Pingshan," and "Guanxi." "Wendan" displayed distinct separation from the other three pummelo cultivars in principal component analysis based on the pulp volatile compositions. This distinction was attributed to the higher number and content of volatile compounds in "Wendan" pulp, particularly the remarkable enrichment of β-myrcene. The newly characterized pummelo landraces and genotype/tissue-dependent variations in volatiles provide essential information for the genetic improvement of pummelo aroma, as well as for fruit processing and utilization.

Citrus juice off-flavor during different processing and storage: Review of odorants, formation pathways, and analytical techniques

As the most widespread juice produced and consumed globally, citrus juice (mandarin juice, orange juice, and grapefruit juice) is appreciated for its attractive and distinct aroma. While the decrease of characteristic aroma-active compounds and the formation of off-flavor compounds are easy to occur in processing and storage conditions. This review provides a comprehensive literature of recent research and discovery on citrus juice off-flavor, primarily focusing on off-flavor compounds induced during processing and storage (i.e., thermal, storage, light, oxygen, package, fruit maturity, diseases, centrifugal pretreatment, and debittering process), formation pathways (i.e., terpene acid-catalyzed hydration, caramelization reaction, Maillard reaction, Strecker degradation, and other oxidative degradation) of the off-flavor compounds, effective inhibitor pathway to off-flavor (i.e., electrical treatments, high pressure processing, microwave processing, ultrasound processing, and chemical treatment), as well as odor assessment techniques based on molecular sensory science. The possible precursors (terpenes, sulfur-containing amino acids, carbohydrates, carotenoids, vitamins, and phenolic acids) of citrus juice off-flavor are listed and are also proposed. This review intends to unravel the regularities of aroma variations and even off-flavor formation of citrus juice during processing and storage. Future aroma analysis techniques will evolve toward a colorimetric sensor array for odor visualization to obtain a "marker" of off-flavor in citrus juice.

Enzymatic treatment, unfermented and fermented fruit-based products: current state of knowledge

In recent years, food manufacturers are increasingly utilizing enzymes in the production of fruit-based (unfermented and fermented) products to increase yield and maximize product quality in a cost-effective manner. Depending on the fruits and desired product characteristics, different enzymes (e.g. pectinase, cellulase, hemicellulase, amylase, and protease) are used alone or in combinations to achieve optimized processing conditions and improve nutritional and sensorial quality. In this review, the mechanisms of action and sources of different enzymes, as well as their effects on the physicochemical, nutritional, and organoleptic properties of unfermented and fermented fruit-based products are summarized and discussed, respectively. In general, the application of enzymatic hydrolysis treatment (EHT) in unfermented fruit-based product helps to achieve four main purposes: (i) viscosity reduction (easy to filter), (ii) clarification (improved appearance/clarity), (iii) better nutritional quality (increase in polyphenolics) and (iv) enhanced organoleptic characteristic (brighter color and complex aroma profile). In addition, EHT provides numerous other advantages to fermented fruit-based products such as better fermentation efficiency and enrichment in aroma. To meet the demand for new market trends, researchers and manufacturers are increasingly employing non-Saccharomyces yeast (with enzymatic activities) alone or in tandem with Saccharomyces cerevisiae to produce complex flavor profile in fermented fruit-based products. Therefore, this review also evaluates the potential of some non-Saccharomyces yeasts with enzymatic activities and how their utilization helps to tailor wines with unique aroma profile. Lastly, in view of an increase in lactose-intolerant individuals, the potential of fermented probiotic fruit juice as an alternative to dairy-based probiotic products is discussed.

Identification and iterative combinatorial mutagenesis of a new naringinase-producing strain, Aspergillus tubingensis MN589840

Naringinase was mainly obtained by microbial fermentation, and mutagenesis was a major way for obtaining excellent mutants. The aim of this study was to screen out a high naringinase yielding mutant to enhance the potential application value of its industrialization and compare the effects of different mutagenic methods on the enzyme activity of the strain. A novel producing naringinase strain, Aspergillus tubingensis MN589840, was isolated from mildewed pomelo peel, later subjected to mutagenesis including UV, ARTP and UV-ARTP. After five rounds iterative mutagenesis, the mutants U1, A6 and UA13 were screened out with 1448·49, 1848·71, 2475·16 U mg^-1 enzyme activity, the naringinase productivity raised by 79·08, 123·56 and 206%, respectively. In addition, the naringinase activity of three mutants rose after each round of iterative mutagenesis. These results indicated that the mutagenesis efficiency of UV-ARTP was higher than that of single ARTP, and both are better than UV. In summary, the iterative UV-ARTP mutagenesis is an effective strategy for screening high naringinase-producing strains.

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.

Characterization of the Aroma of an Instant White Tea Dried by Freeze Drying

The aroma of an instant white tea (IWT) was extracted through simultaneous distillation–extraction (SDE) and analyzed by sensory evaluation, gas chromatography-mass spectrometry-olfactometry (GC-MS-O), aroma reconstruction, omission test and synergistic interaction analysis. Sensory evaluation showed the IWT was dominated with floral and sweet notes. The SDE extract had the aroma similar to the IWT. The main volatile components in the SDE extract were benzyl alcohol, linalool, hotrienol, geraniol, α-terpineol, coumarin, camphene, benzeneacetaldehyde, 2-hexanone, cis-jasmin lactone and phenylethyl alcohol. GC-MS-O and aroma reconstruction experiments showed 16 aroma-active compounds. Linalool, trans-β-damascenone and camphene were the major contributors to floral, sweet and green notes based on flavor dilution analysis and omission test. Linalool and trans-β-damascenone had synergistic effect to promote floral and sweet notes. Camphene and trans-β-damascenone had synergistic effect to reduce green and sweet notes. The study helps to understand the aroma of IWT and antagonism interactions among aroma-active volatiles.

Suppressive Interaction Approach for Masking Stale Note of Instant Ripened Pu-Erh Tea Products

The unpleasant stale note is a negative factor hindering the consumption of instant ripened Pu-erh tea products. This study focused on investigating volatile chemicals in instant ripened Pu-erh tea that could mask the stale note via sensory evaluation, gas chromatography-mass spectrometry (GC-MS), and gas chromatography-olfactometry (GC-O) analyses. GC-MS and GC-O analyses showed that linalool, linalool oxides, trans-β-ionone, benzeneacetaldehyde, and methoxybenzenes were the major aroma contributors to the simultaneous distillation and extraction (SDE) extract of instant ripened Pu-erh tea. Sensory evaluation showed that the SDE extract had a strong stale note, which was due to methoxybenzenes. By investigating suppressive interaction among flavour components, the stale note from methoxybenzenes was shown to have reciprocal masking interactions with sweet, floral, and green notes. Moreover, the validation experiment showed that the addition of 40 μg/mL of trans-β-ionone in the instant ripened Pu-erh tea completely masked the stale note and improved the overall aromatic acceptance. These results elucidate the volatile chemicals that could mask the stale note of instant ripened Pu-erh tea products, which might help to develop high quality products made from instant ripened Pu-erh tea.

Heterologous Expression and Characterization of a New Clade of Aspergillus α-L-Rhamnosidase Suitable for Citrus Juice Processing

α-L-Rhamnosidase is a glycoside hydrolase capable of removing naringin from citrus juice. However, α-L-rhamnosidases always have broad substrate spectra, causing negative effects on citrus juice. In this study, a α-L-rhamnosidase-expressing fungal strain, JMU-TS529, was identified, and its α-L-rhamnosidase was characterized. As a result, JMU-TS529 was identified as Aspergillus tubingensis via morphological and molecular characteristics. The predicted protein sequence shared an amino acid identity of less than 30% with previously characterized α-L-rhamnosidases. The optimal pH and temperature were 4.0 and 50-60 °C, respectively. Most importantly, the α-L-rhamnosidase showed a strong ability to hydrolyze naringin but scarcely acted on other substrates. Furthermore, the enzyme could efficiently remove naringin from pomelo juice without changing its attractive aroma. These results indicate that the present enzyme represents a new clade of Aspergillus α-L-rhamnosidase that is desirable for debittering citrus juice, providing a better alternative for improving the quality of citrus juice.

Water dynamics of Ser-His-Glu-Cys-Asn powder and effects of moisture absorption on its chemical properties

BACKGROUND

This study has elucidated moisture dynamics in the soybean peptide, Ser-His-Glu-Cys-Asn (SHECN) powder by using dynamic vapor sorption (DVS) and nuclear magnetic resonance (NMR). We also tried to investigate the effects of moisture absorption on the biological activity and chemical properties of SHECN with some effective methods such as mid-infrared (MIR) spectroscopy and gas chromatography-mass spectrometry (GC-MS).

RESULTS

DVS results showed that the moisture absorption of SHECN could reach a maximum of 33%, and the SHECN powder after synthesis actually existed in a trihydrate state of SHECN.3H2 O. Low-field NMR revealed that three water proportions including strong combined water, binding water and bulk water were involved in SHECN moisture absorption and absored water dominantly existed in the form of combined water. Magnetic resonance imaging (MRI) and MIR spectroscopy results indicated that moisture absorption could change the morphology and structure of SHECN. After moisture absorption at 50% and 75% relative humidity, 19 volatiles were identified by GC-MS analysis. Additionally, this study showed that a part of reductive groups in SHECN was oxidized and its antioxidant ability declined significantly (P < 0.05) after moisture absorption.

CONCLUSION

Water absorbed into SHECN powder can significantly change its microstructure and cause its activity to decrease. We must prevent SHECN from absorbing moisture during storage because the water can accelerate the oxidation of samples and promote microbial reactions. © 2016 Society of Chemical Industry.

Effects of two enzyme extracts of Aspergillus niger on green tea aromas

Green tea was investigated in terms of its aroma changes induced by two enzyme extracts of Aspergillus niger, i.e., crude enzyme extracted from fermentation using tea stalk medium (CETSM) and crude enzyme yielded in potato dextrose medium. The result showed that the former had significant effects on sensory indexes and volatile constituents, with significant increases in toasty and mushroom notes, while the latter had little influence on the aforementioned indexes. In addition, the volatile constituents were significantly affected; in particular, the contents of cis-3-hexenol, 1-octen-3-ol, eucalyptol, hexanol, and benzaldehyde increased. Furthermore, gas chromatography-olfactometry (GC-O) analysis showed that an increase in 1-octen-3-ol strengthened the mushroom note. These results indicate that CETSM contains some novel enzymes that can modify the aroma profile of green tea. This study also provides valuable information and suggestions to use fermented enzymes to modify food aromas.

Volatile Composition in Two Pummelo Cultivars (Citrus grandis L. Osbeck) from Different Cultivation Regions in China

This study investigated the composition of volatile compounds in two pummelo cultivars, including ‘Shatian’ and ‘Guanxi’, cultivated in different regions of China with the aim of studying the effect of cultivar and cultivation condition on biosynthesis of volatile compounds in pummelo. Volatile compounds were extracted from pummelo juice using head-space microextraction and then analyzed using gas chromatography coupled with mass spectrometry. Results showed that a total of 49 volatile compounds was detected in the study, including 11 aldehydes, 7 alcohols, 3 ketones, 7 esters, 19 terpenes and 2 other volatiles. The ‘Guanxi’ pummelo cultivar possessed a more complex composition of volatile compounds compared with the ‘Shatian’ cultivar. Meanwhile, the volatile compounds appeared to exhibit a higher concentration in the ‘Guanxi’ cultivar samples than the ‘Shatian’ cultivar. Cluster analysis revealed that the ‘Guanxi’ cultivar samples from the different regions were grouped together, whereas the ‘Shatian’ cultivar samples were assembled. Principal component analysis showed that an obvious separation was observed between the ‘Guanxi’ and ‘Shatian’ cultivar. However, the ‘Shatian-SC15’ was significantly separated from the other ‘Shatian’ cultivar samples. These indicated that cultivar genotype was the primary factor that determined the volatile profile of the pummelo cultivar. Cultivation region might affect the biosynthesis of volatile compounds, resulting in the differentiation of the volatile composition in each pummelo cultivar.