Natural Fermentation Process Research Articles

Physicochemical, Nutritional, and Antioxidant Properties of Traditionally Fermented Thai Vegetables: A Promising Functional Plant-Based Food.

Fermented plant-based products were gathered from various regions in Thailand and categorized into 10 types of traditional commercial vegetables. Different vegetable materials and natural fermentation methods influence the diverse physical, chemical, nutritional, and functional attributes of the products. All the traditionally fermented Thai vegetable samples collected showed physicochemical properties associated with the fermentation process, contributing to the nutritional and functional quality of the final products. Achieving consistent research results is challenging due to the intricate nature of food matrices and biochemical processes during fermentation. The roles of microorganisms, especially probiotics, are crucial in delivering health benefits through fermented foods. Traditionally fermented Thai vegetable foods contain high levels of total soluble solids, titratable acidity, and salinity in pickled shallot and ginger as a result of the natural fermentation process and the ingredients used. The research findings were confirmed using a hierarchical cluster analysis (HCA)-derived dendrogram pattern. The nutritional compositions, total phenolic contents, and antioxidant activities varied among the different types of vegetables. The correlations among lipid, protein, fiber, total soluble solid (TSSs), total titratable acidity (TTA), and salinity as potential biomarkers in fermented vegetable products were examined. The results suggest that traditionally fermented Thai vegetable products significantly impacted food research by enhancing the quality and preserving the authenticity of traditionally fermented Thai vegetables.

Microbial succession and flavor impact during natural fermentation of Tartary buckwheat sourdough

In this study, the succession process and driving mechanisms of microbial communities during the fermentation of Tartary buckwheat sourdough were explored using high-throughput sequencing and microbiome co-occurrence network analysis. A gas chromatograph–mass spectrometer (GC–MS) was used to monitor the dynamic evolution of flavor compounds in Tartary buckwheat sourdough at different fermentation stages. Using GC–MS and principal component analysis, 47 volatile compounds were identified as the main differential volatile compounds during fermentation. The predominant bacterial genera observed in the natural fermentation of Tartary buckwheat sourdough included Enterococcus, Weissella, Cronobacter, Lactococcus, and Pediococcus. Among fungi, Alternaria, Botrytis, Trichothecium, and Vishniacozyma were the dominant genera. The correlation analysis results revealed that Weissella, Pediococcus, Lactobacillus, Acinetobacter, and Vishniacozyma were the core functional microbes involved in flavor formation. Organic acids were the primary driving force for microbial succession. This study provides a better understanding of the relationship between microbial communities and volatile components in the natural fermentation process of Tartary buckwheat sourdough as well as useful information for improving the flavor quality of Tartary buckwheat sourdough products, thereby helping to choose starter cultures with flavor modulation ability.

Effect of temperature regulation on microbial community, volatile flavours, amino acid profiles, and iridoid glycosides during noni (Morinda citrifolia L.) fruit fermentation

Noni fruit has an unpleasant flavour but is highly bioactive. Therefore, it is necessary to clarify the effect of temperature regulation on quality of fermented noni fruit. In the present study, the formation of flavours, amino acid profiles, and iridoid glycosides during noni fruit fermentation at different temperatures were investigated. We initially found that different temperatures affected core microbial communities. The general evolutionary trends of Acetobacter and Gluconobacter were influenced by different temperatures. Furthermore, high temperature helped maintain low octanoic and hexanoic acids. Subsequently, we found that high temperature improved total amino acids and iridoid glycosides. The correlation network analysis revealed that bacterial communities impacted the quality (volatile flavours, amino acid profiles, and iridoid glycosides) of fermented noni fruit. Overall, altering the temperature induced variations in microbial communities and quality during the noni fruit fermentation process. These results are instrumental in the pursuit of quality control in natural fermentation processes.

Exploring the Effects of Freeze-Dried Sourdoughs with Lactiplantibacillus pentosus 129 and Limosilactobacillus fermentum 139 on the Quality of Long-Fermentation Bread.

Sourdough production is a complex fermentation process. Natural sourdough fermentation without standardization causes great variability in microbial communities and derived products. Starter cultures have emerged as alternatives to natural fermentation processes, which could improve bakery quality and produce bioactive compounds. This study aimed to evaluate the impacts of freeze-drying on the production and viability of sourdoughs with Lactiplantibacillus pentosus 129 (Lp) and Limosilactobacillus fermentum 139 (Lf), as well as their effects on the quality of long-fermentation bread. These strains were selected based on their better performance considering acidification and exopolysaccharide production capacity. Sourdough with Lp and Lf were propagated until the 10th day, when physicochemical and microbiological parameters were determined. The produced sourdoughs were freeze-dried, and bread samples were produced. The freeze-drying process resulted in high survival rates and few impacts on the metabolic activity of Lp and Lf until 60 days of storage. Incorporating Lp and Lf improved the microbiological and physicochemical properties of sourdough and long-fermentation breads. Tested freeze-dried sourdoughs led to reduced bread aging (higher specific volume and decreased starch retrogradation) and increased digestibility. The results show the potential of the freeze-dried sourdoughs produced with Lp and Lf as innovative strategies for standardizing production protocols for the bakery industry, especially for producing long-term fermentation bread.

Morphological variation and expressed sequence tags-simple sequence repeats-based genetic diversity of Aspergillus cristatus in Chinese dark tea.

Aspergillus cristatus is a homothallic fungus that is used in the natural fermentation process of Chinese Fuzhuan tea and has been linked to the production of bioactive components. However, not much is known about the variations present in the fungus. To understand the variation of the dominant microorganism, A. cristatus, within dark tea, the present study investigated the genetic and morphological diversity of 70 A. cristatus collected across six provinces of China. Expressed sequence tags-simple sequence repeats (EST-SSR) loci for A. cristatus were identified and corresponding primers were developed. Subsequently, 15 specimens were selected for PCR amplification. The phylogenetic tree obtained revealed four distinct clusters with a genetic similarity coefficient of 0.983, corresponding to previously identified morphological groups. Five strains (A1, A11, B1, D1, and JH1805) with considerable differences in EST-SSR results were selected for further physiological variation investigation. Microstructural examinations revealed no apparent differentiation among the representative strains. However, colony morphology under a range of culture media varied substantially between strains, as did the extracellular enzymatic activity (cellulase, pectinase, protease, and polyphenol oxidase); the data indicate that there are differences in physiological metabolic capacity among A. cristatus strains. Notably, JH1805, B1, and A11 exhibited higher enzymatic activity, indicating their potential application in the production of genetically improved strains. The findings provide valuable insights into species identification, genetic diversity determination, and marker-assisted breeding strategies for A. cristatus.

Determination of the region‐specific characteristics of traditional Korean doenjang produced in Chungcheongbuk‐do through physicochemical property, enzyme activity, and descriptive sensory analyses

AbstractThis study determined the region‐specific characteristics of traditional doenjang produced in Chungcheongbuk‐do by analyzing the physicochemical properties, enzyme activities, and aroma characteristics of the samples. Color, moisture, pH, soluble solid content, salinity, acid value, titratable acidity, amylase and protease activities, and NH2‐N, alcohol, and total/reducing sugar contents were analyzed. A descriptive sensory analysis involving trained sensory panelists was also conducted for aroma profile determination. Similarities were observed among the samples produced in the same city. The Yeongdong‐made samples had strong fermented and lipid/musty aromas. The Cheongju‐made doenjang had a high protease activity and a high NH2‐N content. The Goesan‐made samples had a high reducing sugar content due to amylase activities and a fishy aroma, and the Jincheon‐made doenjang had a high soluble solid content and an intense spice aroma. This study describes for the first time the region‐specific characteristics of traditional doenjang produced in Chungcheongbuk‐do.Practical applicationsTraditional food produced through a natural fermentation process may have differences in physicochemical properties and flavor due to the diversity of microbial communities depending on the region and environment. Previous studies have identified the characteristics of traditional Korean fermented foods such as doenjang and kimchi in each region, but this study is the first to analyze differences in the characteristics of traditional doenjang produced in a small city within a specific region (Chungcheongbuk‐do). The findings from this study can give baseline information on the doenjang produced by small‐ to mid‐sized doenjang manufacturers located in Chungcheongbuk‐do, and allow them to use it for strategic marketing to expand their market to the national market in Korea.

Isolation, identification, and tolerance analysis of yeast during the natural fermentation process of Sidamo coffee beans.

Yeast, which plays a pivotal role in the brewing, food, and medical industries, exhibits a close relationship with human beings. In this study, we isolated and purified 60 yeast strains from the natural fermentation broth of Sidamo coffee beans to screen for indigenous beneficial yeasts. Among them, 25 strains were obtained through morphological characterization on nutritional agar medium from Wallerstein Laboratory (WL), with molecular biology identifying Saccharomyces cerevisiae strain YBB-47 and the remaining 24 yeast strains identified as Pichia kudriavzevii. We investigated the fermentation performance, alcohol tolerance, SO2 tolerance, pH tolerance, sugar tolerance, temperature tolerance, ester production capacity, ethanol production capacity, H2S production capacity, and other brewing characteristics of YBB-33 and YBB-47. The results demonstrated that both strains could tolerate up to 3% alcohol by volume at a high sucrose mass concentration (400g/L) under elevated temperature conditions (40 ℃), while also exhibiting a remarkable ability to withstand an SO2 mass concentration of 300g/L at pH 3.2. Moreover, S. cerevisiae YBB-47 displayed a rapid gas production rate and strong ethanol productivity. whereas P. kudriavzevii YBB-33 exhibited excellent alcohol tolerance. Furthermore, this systematic classification and characterization of coffee bean yeast strains from the Sidamo region can potentially uncover additional yeasts that offer high-quality resources for industrial-scale coffee bean production.

Investigation of the Physicochemical Properties and its Correlation during Koji-Moromi Fermentation Stage of Production Soy Sauce Naturally Brewed in Central Java, Indonesia

Soy sauce, a widely consumed condiment, undergoes intricate physicochemical transformations during its natural fermentation process. This research delved into the analysis of physical and chemical properties in naturally brewed soy sauce, aiming to elucidate the impact of fermentation stages (Koii, earlier moromi, final moromi, soy sauce product) and sample variations on these properties. Parameters such as pH, total acid, total soluble solids, and water activity (aw) were assessed. Additionally, chemical attributes were analyzed, including total nitrogen, crude protein, formol nitrogen, and sodium chloride (NaCl) content. The correlation between physical and chemical properties during the fermentation stages was determined using the principal component analysis (PCA) method. The fermentation process significantly affected soy sauce's physical and chemical properties. Key factors include total dissolved solids, water activity, total acids, salt, total nitrogen, crude protein, and formol nitrogen, which display distinct patterns. These fluctuations were primarily driven by microbial activity and enzymatic hydrolysis, and total nitrogen, crude protein, and formol nitrogen play pivotal roles in characterizing soy sauce quality. Remarkably, total acid content and pH values exhibited significant variations that deviate from expected correlations due to weak acids. Samples C and D were deemed the most suitable out of the five tested, aligning better with quality standards for soy sauce. This study sheds light on the complex physicochemical changes during soy sauce fermentation, emphasizing the impact of raw materials and microbial processes on its properties.

Determination of the physiochemical characteristics of traditional doenjang produced in Chungnam region in South Korea.

Traditional doenjang characteristically differs from commercial doenjang, as the former involves a long and natural fermentation process. This study determined the physiochemical characteristics of traditional doenjang produced in Chungnam region. Two commercial and thirteen traditional doenjang products were characterized in terms of color, moisture content, pH, °Brix, salinity, acid value, titratable acidity, NH2-N content, alcohol content, and total and reducing sugar contents. The traditional samples significantly differed from the commercial samples in terms of color, moisture, °Brix, acid value, and in alcohol, NH2-N content, and total sugar contents (p < 0.05), and the traditional samples were characteristically similar to those previously analyzed. Moreover, the samples produced in different cities could be clustered based on their physiochemical characteristics. The observed differences among the traditional samples were attributed to fermentation conditions, namely, duration and temperature, as these differences were not correlated with ingredient ratio.

Structural characteristics and paste properties of wheat starch in natural fermentation during traditional Chinese Mianpi processing

Fermentation plays a crucial role in traditional Chinese mianpi processing, where short-term natural fermentation (within 24 h) is considered advantageous for mianpi production. However, the influence of short-term natural fermentation on the properties of wheat starch is not explored yet. Hence, structural characteristics and paste properties of wheat starch during natural fermentation were investigated in this study. The findings revealed that fermenting for 24 h had a slight effect on the morphology of wheat starch but significantly decreased the particle size of starch. Compared to native wheat starch, the enzyme activity produced during fermentation may destroy the integrity of starch granules, resulting in a lower molecular weight but higher relative crystallinity and orderliness of starch. After 24 h of natural fermentation, higher solubility and swelling power were obtained compared to non-fermentation. Regarding paste properties, fermented starches exhibited higher peak viscosity and breakdown, along with lower final viscosity, tough viscosity, and setback. Furthermore, the hardness, gel strength, G', and G" decreased after fermentation. Clarifying changes in starch during the short-term natural fermentation process could provide theoretical guidance for improving the quality and production of short-term naturally fermented foods such as mianpi, as discussed in this study.

Statins-From Fungi to Pharmacy.

Statins have been used in the treatment of hyperlipidemia, both as monotherapy and in combination therapy. Natural fermentation processes of fungi such as Monascus spp., Penicillium spp., Aspergillus terreus, and Pleurotus ostreatus have given rise to natural statins. Compactin (mevastatin), the original naturally occurring statin, is the primary biotransformation substrate in the manufacturing process of marketed drugs. Statins are classified into natural, semi-synthetic derivatives of natural statins, and synthetic ones. Synthetic statins differ from natural statins in their structural composition, with the only common feature being the HMG-CoA-like moiety responsible for suppressing HMG-CoA reductase. Statins do not differ significantly regarding their pleiotropic and adverse effects, but their characteristics depend on their pharmacokinetic parameters and chemical properties. This paper focuses on describing the processes of obtaining natural statins, detailing the pharmacokinetics of available statins, divided into natural and synthetic, and indicating their pleiotropic effects.

Enhanced antioxidant, tyrosinase inhibition, and anti-inflammatory activities of Praeparatum mungo and three of its derivatives

The main objective of this study is to explore the functions of Praeparatum mungo (PM) and three of its derivatives, Praeparatum mungo/turmeric (PM/T), Praeparatum mungo/bromelain (PM/B), and Praeparatum mungo/inorganic elements (PM/IE). The results indicated that additives included in the fermentation process of PM enhanced PM’s antioxidant properties. PM/B exhibited the highest total phenolic content (19.18 ± 0.46 mg gallic acid equivalent/g), DPPH free radical scavenging activity, and ferric reducing power. PM/IE exhibited the highest ABTS free radical scavenging activity and chelating ferrous ion activity. PM/T exhibited the best inhibitory tyrosinase activity. The 625 μg/mL PM extract can extensively reduce nitric oxide production of RAW264.7 macrophages stimulated by 1 μg/mL LPS and exhibited no cytotoxicity for anti-inflammatory applications. Additives in PM natural fermentation process can enhance antioxidant, tyrosinase inhibition, and anti-inflammatory properties of PM for future applications.

Environmental footprint performance improvement of black tea using the life cycle assessment approach

The cultivation and production of black tea are associated with significant energy consumption and adverse environmental concerns, largely stemming from inefficient practices, equipment incompatibility, and suboptimal cultivation methods. In response, this study employs a comprehensive life cycle assessment (LCA) to address these issues and identify potential environmental improvements across the entire black tea system, encompassing both the cultivation and production phases. The primary focus of this analysis is the evaluation of key environmental metrics, including global warming potential (GWP), primary energy demand (PED), and water usage (WU). The study's findings highlight that a reduction in the use of chemical fertilizers during the black tea cultivation stage can effectively mitigate GWP, PED, and WU. A sustainable approach involves shifting towards a fertilization scenario that incorporates 70% organic fertilizers and 30% chemical fertilizers. This adjustment makes the cultivation stage more environmentally friendly, resulting in reduced resource depletion and water consumption. Furthermore, the analysis reveals that the application of artificial grass covering, as opposed to herbicides, has a significantly more negative impact on GWP, PED, and WU. Similarly, the use of insecticides during black tea cultivation leads to higher values for GWP, PED, and WU in comparison to employing solar pest control lamps. Additionally, the LCA analysis underscores the effectiveness of integrating solar pest control lamps and herbicide treatments during the black tea cultivation stage to achieve lower GWP and reduced resource consumption. On the other hand, the black tea production stage makes a substantial contribution to the system's GWP, PED, and WU, primarily due to the heated withering and natural fermentation processes. However, transitioning to frozen withering and aerobic fermentation processes presents a more environmentally friendly approach, resulting in a black tea production method that is lower in carbon emissions and energy-efficient, with minimal adverse environmental impact.

Natural fermentation with delayed inoculation of the yeast Torulaspora delbrueckii: Impact on the chemical composition and sensory profile of natural coffee

All coffee production stages occur in a microbiome, which is generally composed of bacteria, yeasts, and filamentous fungi. The use of starter cultures in post-harvest processing stages is an interesting alternative, since they promote faster removal of mucilage and incorporation of compounds that improve sensory quality, which can result in diverse sensory attributes for the beverage. This study was therefore developed with the objective of evaluating the effect of the following processing procedures on the chemical and sensory characteristics of the coffee beverage: first, fermentation of coffee fruit of the yellow Catucaí variety of Coffea arabica with indigenous microorganisms, followed by inoculation of the starter culture Torulaspora delbrueckii CCMA 0684 during the drying stage. The fruit was divided into two lots, which were differentiated by a natural fermentation process before drying began. The starter culture was inoculated on the coffee at different times during the drying process: at 0 h, 24 h, 48 h, or 72 h after drying began. The sensory attributes, the volatile compound composition of the roasted beans, the organic acid profile, the bioactive compounds, and the fatty acid profile of the green coffee beans were analyzed. The fatty acid and bioactive compound content showed little variation among treatments. Analysis of volatile compounds and organic acids and evaluation of sensory attributes made it possible to distinguish the two treatments. We conclude that natural fermentation of coffee fruit improve the chemical and sensory quality of the coffee beverage. The effect of natural fermentation may be before inoculation of the starter cultures or even during drying.

Mycotoxin reduction and metabolite profiles of ogi produced using traditional fermentation methods

Mycotoxins are widely present in maize, a favourite staple food in sub-Saharan Africa. Food processing methods, like fermentation, have been suggested as potential ways to reduce mycotoxin contamination levels in the grain and, as a result, limit the exposure of crop consumers to the harmful effects of the toxins. The influence of four traditional fermentation processes [cold (with changed steeping liquor (CSL) and unchanged steeping liquor (USL), Fon and Goun procedures] on the mycotoxin reduction and metabolites profile of ogi, a fermented maize product, was studied. Ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) and gas chromatography linked to high resolution time-of-flight mass spectrometry (GC-HR-TOF-MS) were respectively employed for the mycotoxin and metabolite profiles analyses of the samples. Among the nine mycotoxins detected in the raw maize samples, aflatoxin B1 (AFB1) and fumonisin B1 (FB1) + fumonisin B2 (FB2) concentrations were found to exceed the European Union (EU) maximum limit. Both cold (containing USL and CSL) and Goun fermentation techniques were able to lower the AFB1 concentration below this threshold. The metabolomics result revealed that ogi produced using the cold (USL) and Fon fermentation processes had the highest number of most of the detected important compounds, whereas the Goun fermentation process produced the fewest compounds in total. There was no statistically significant difference in the ability of the specified natural fermentation processes to lower FB1, FB2, FB3, deoxynivalenol (DON), sterigmatocystin (STERIG), and zearalenone concentrations in maize (ZEN). In addition, the results demonstrated that the four natural fermentation processes evaluated had varying effects.

Natural fermentation as an inoculation strategy for dark fermentation of Ulva spp. hydrolysate

Dark fermentation from Ulva spp. hydrolysate, a third-generation feedstock, can be exploited as sustainable alternative for biofuel production as it possesses a high carbohydrate content, contributes to decarbonisation and allows the simultaneous production of bioH2 and chemicals. However, it requires microorganisms with enzymatic capability to metabolise the sugars released by the macroalgae. In the present study, the natural fermentation process exploring the microbial community growing attached onto the Ulva spp. was for the first time assessed as an alternative inoculation method for bioH2 production from Ulva spp. hydrolysate. Inoculum enrichment from Ulva spp was tested at 4, 30 and 55 °C in a batch experiment. Then, the liquid phase was assessed as inoculum of a continuous up-flow anaerobic structured bed reactor (AnSTBR) fed with diluted acid-thermal Ulva spp. hydrolysate at 30 and 55 °C. At initial pH 6.5 the sulfidogenic pathway was predominant, however decreasing the pH to 5.5 stimulated the bioH2 production, with higher production at 55 °C, resulting in a median volumetric hydrogen production rate (VHPR) of 297.5 NmL L−1 d−1. The main soluble metabolites (SM) at 55 °C were butyric acid (HBu) and acetic acid (HAc), reaching medians of 912.9 and 483.4 mg L−1. At 30 °C, the primary pathway was solventogenic, resulting in ethanol (EtOH) and HAc production at a ratio 2.5:1. Therefore, the natural fermentation strategy was found to be a suitable strategy to inoculate the dark fermentation reactor.

Spatial and temporal distribution of environmental microbiota in Chinese rice wine (Huangjiu) natural fermentation wineries

Huangjiu brewing workshop is a small ecosystem with complex microbial community growth. This micro ecosystem is the main provider of microorganisms in the process of Huangjiu fermentation. Its existence may greatly affect the quality and flavor of Huangjiu. Environmental microbial communities of the same brewing workshop in different historical periods were collected. Full-length High-throughput sequencing and Source Tracker were used to study the correlation between brewing raw materials, fermented mash and brewing environment, and to explore the involvement of environmental microorganisms in the fermentation process. The resident functional fungi in fermented Huangjiu mash were the main components of the fungal community detected in the environment. The wheat koji, tool and interior environment contributed greatly to the source of fermented fungi in Huangjiu. Compared with the bacterial community, the environmental origin of the fungal community in fermented mash was clearer. For bacteria, the increased contribution of community aggregation was attributed to the role of deterministic processes, and community structure became more stable, showing its unique role in fermentation. This study could be implemented in a more abundant natural fermentation environment, which was of great significance to control the natural fermentation process of Huangjiu.

Comparative Analysis of Microbial and Mycotoxin Contamination in Korean Traditional Soybean Paste and Soy Sauce Production with and without Starter

Doenjang and ganjang are traditional, Korean fermented foods. They are manufactured by fermenting jangs, either through the traditional natural fermentation, using straw, or the commercial inoculating starter cultures. However, both Bacillus cereus and aflatoxins have been detected in jangs, compromising their safety. Aflatoxins have been detected on numerous occasions. However, studies are yet to be conducted on whether these safety issues differ depending on the manufacturing method. In this study, we evaluated whether the manufacturing methods of doenjang and ganjang alter their safety. Samples of traditional and commercial doenjang and ganjang were analyzed for aflatoxin and B. cereus contamination. Microbiome taxonomic profiling was performed to assess microbial composition. The experimental methodology involved sample collection from various stages of production, including the use of starter cultures and natural fermentation processes. Aflatoxin levels were determined using regulatory limits, and B. cereus content was evaluated against specific thresholds. Aflatoxins were detected in both traditional and commercial doenjang and ganjang, with either the total aflatoxin (15 μg/kg) or aflatoxin B1 (10 μg/kg) exceeding the regulatory limits. However, ochratoxin A was not detected in any of the samples. B. cereus was detected in some samples, within the regulatory limit (4 log CFU/g), and was not influenced by the manufacturing method. Analysis at the production stage showed that aflatoxin increased alongside the fermentation time in traditional doenjang. However, in ganjang, no significant differences were associated with the fermentation period. When using starter cultures, the fermentation period did not affect the toxin level in both foods. Both methods showed lower aflatoxin content in the initial doenjang and ganjang samples than in meju. B. cereus was not detected in either method, as its content decreased over the fermentation period. Microbiome taxonomic profiling confirmed that even when using starter cultures, B. cereus was not a dominant species and was considerably affected by the environment. Staphylococcus aureus and Pseudomonas, pathogenic in nature, were detected in products manufactured using the traditional method; hence, the potential risk of this method was higher than that of the commercial method. The experimental methodology employed in this study contributes to understanding the microbial composition and toxin contamination levels in doenjang and ganjang, contributing to the overall knowledge of their safety and quality control.

Revealing the influence of microbiota on the flavor of kombucha during natural fermentation process by metagenomic and GC-MS analysis

In this work, raw Pu-erh tea (RAPT) was employed for kombucha preparation, and the microbial composition and volatile flavor compounds of the fermented tea had been investigated during natural fermentation process. The head space-solid phase microextraction-gas chromatograph mass spectrometry (HS-SPME-GC-MS) was performed for volatiles analysis of unfermented tea and kombucha fermented for 3 days (KF-3) and 6 days (KF-6). Meanwhile, the microbial community of KF-3 and KF-6 were evaluated by metagenomic analysis. A total of 72 volatile compounds were identified and obvious changes in volatiles were observed during the fermentation process based on the results of GC-MS and principal component analysis (PCA). Metagenomic sequencing analysis demonstrated that bacterium Komagataeibacter saccharivorans and unclassified-g-komagataeibacter and yeast Saccharomyces cerevisiae and Brettanomyces bruxellensis were the most common microbes contained in the sampled kombucha communities. Furthermore, the relevance among microbial community and volatile compounds was evaluated through correlation heatmap analysis. The results suggested that the main flavor volatiles of kombucha (i.e., acids, esters and terpenes) were closely related to species of genus Komagataeibacter, Gluconacetobacter, Saccharomyces, Brettanomyces, Acetobacter, Novacetimonas and Pichia microorganisms. The obtained results would help to better understand microbial communities and volatile compounds of kombucha, which could provide useful information for enhancing the flavor quality of kombucha products.

Recovery and valorization of food industry by-products through the application of Olea europaea L. leaves in kombucha tea manufacturing

The present study investigated the application of a sustainable production model to the manufacturing technology of kombucha. In order to comply with the principles of circular economy, a newly-formulated beverage, obtained through the use of olive mill by-products as a fermentation substrate, was examined. The total polyphenol content, antioxidant activity and sensory profile of the final product was analyzed with the intention of evaluating the bioactive and sensory contribution made by olive leaves, when used in substitution of tea for kombucha fermentation. The initial level of oleuropein (394.7 mg/L) obtained in the olive leaves extract did not inhibit the natural fermentation process of Symbiotic Culture of Bacteria and Yeast (SCOBY). The addition of increasing percentages of the by-product during the fermentation produced several kombucha samples rich in secoiridoid bioactive compounds with a concentration of oleuropein and hydroxytyrosol ranged from 306.4 mg/L to 91.2 mg/L and from 29.0 mg/L to 9.3 mg/L, respectively. Since tea stands out as one of the main cost items in kombucha tea manufacturing, this study demonstrated that the use of olive leaves, as a polyphenol-rich substrate, may represent a viable strategy to valorize the agro-industrial waste, reduce production costs, preserve the antioxidant properties of kombucha and enrich its sensory profile.