Fermentation Process Research Articles

Impact of climate and traditional practice on quality of homemade dahi.

This research communication aimed at assessing the microbial quality and preparation practices of dahi/thayir, a popular traditional fermented milk product, in households from two distinct agroecological zones in Kerala, India, namely the high-range and central midland, We highlighted the significant variations and potential food safety concerns associated with regional differences in production methods. The local climate significantly influenced the incubation temperature of dahi/thayir, thereby influencing the types of microflora involved in the fermentation process. Data on preparation practices and sensory preferences were collected from producers during the sampling process, covering 200 households. There were significant variations in preparation practices between the two regions, particularly concerning the type of container used, inoculation rate and incubation period. Samples from the high-range region exhibited significantly higher acidity and coliform count as well as yeast and mold count than the central midland region. The household fermentation of milk is often uncontrolled, causing increased acidity levels. This uncontrolled fermentation favored the growth of contaminants such as coliforms and yeast, posing a potential threat to food safety. This study underscores the importance of understanding microbial quality variations and preparation practices in dahi/thayir production, emphasizing the need for proper fermentation techniques and hygienic practices to ensure the safety and quality of this traditional fermented milk product.

Introducing CCD1 into isolated Rhodotorula strain enhances flavor production and improves cigar fermentation

IntroductionThe fermentation process plays an important role in enhancing the quality of cigar tobacco leaves. Through fermentation, microbial metabolism can degrade aromatic precursors and macromolecules, which increases the content of aroma compounds and reduces irritancy of tobacco leaves.MethodsTo further enhance the fermentation effect of cigar tobacco leaves, a Rhodotorula strain (Rh3), capable of producing carotenoids and improving fermentation quality, was isolated from cigar tobacco leaves. Subsequent genetic engineering techniques introduced the carotenoid cleavage dioxygenase 1 (CCD1) gene into the isolated Rh3.ResultsThe modified Rh3 exhibits a significant increase in carotenoid degradation products compared with the original Rh3 in culture medium (from 0.29 μg/mg to 15 μg/mg). Subsequent cigar tobacco leaf fermentation experiments revealed that the modified Rh3 produced 65.9% more carotenoid degradation products compared to the control group, outperforming the original strain, which achieved a 41.4% increase. Furthermore, the modified strain preserves its ability to improve the intrinsic chemical composition of cigar tobacco leaves.DiscussionWe show here that modified Rh3 can increase the content of carotenoid degradation products, thereby enhancing the fermentation effect of cigar tobacco leaves. This study presents a beneficial exploration to improve the quality of cigar tobacco leaves for future use and offers a promising strategy for producing flavor compounds from discarded tobacco leaves.

Effects of encapsulation and combining probiotics with different nitrate forms on methane emission and in vitro rumen fermentation characteristics

Abstract This study aimed to evaluate the effects of encapsulation and combining probiotics with different nitrate forms on methane emission and the in vitro fermentation process of ruminants. Sodium nitrate (NaNO3) and nitric acid (HNO3) were used as nitrate forms, while lactic acid bacteria Lactiplantibacillus plantarum TSD-10 was used as a probiotic source. Twelve different treatments with four replicates were allocated in the factorial block design (2 × 2 × 3). During each replicate, the test was conducted individually in a different week so that each block could be considered separately. Data analysis followed the analysis of variance (ANOVA) and then continued with the Duncan multiple range test. After encapsulation, significant increases (p < 0.05) in gas production, gas kinetics, total volatile fatty acids (TVFAs), and production of propionic acid were observed. In addition, encapsulation significantly decreased (p < 0.05) the pH, ammonia concentration (NH3), nutrient digestibility, and the ratio of acetic to propionic acid (p < 0.05). The addition of combined encapsulated probiotics and encapsulated nitrate significantly increased (p < 0.05) gas production, maximum gas production, TVFAs, and the molar portion of propionic acid, and significantly decreased (p < 0.05) enteric methane emission, acetic acid, ammonia concentration, pH, and nutrient digestibility. The addition of sodium nitrate significantly increased (p < 0.05) the concentration of TVFAs and acetic acid, while nitric acid significantly increased (p < 0.05) the gas production rate. However, there was no significant effect due to combining unencapsulated probiotics with unencapsulated nitrate forms on the rumen fermentation process. There was a significant interaction (p < 0.05) between encapsulation probiotics and nitrate on ammonia concentration. In conclusion, combining encapsulated probiotics with encapsulated nitrate is an alternative method for enhancing the fermentation process and mitigating enteric methane emission in ruminants.

Influence of Apple Juice Type on Fermentation Process and Volatile Compounds of Hard Apple Cider

Fermented apple cider is a refreshing alcoholic drink known since ancient times, and it is obtained by fermenting apple fruit juice. Using the standards of alcohol concentration (up to 8%) and carbonation, it belongs to drinks similar to beer. It can be produced using wild yeasts, but currently a fermentation starter can be purchased. This work aims to produce fermented cider using commercial pasteurized juices: clear apple juice and organic cloudy juice using commercial yeast for cider production. After fermentation, the physico-chemical characteristics of the drink were determined, alongside volatile compounds of the freshly produced ciders, as well after 1, 2, and 3 weeks of maturation. Acids, alcohols, carbonyl compounds, terpenes, esters, and volatile phenols were determined using headspace–solid phase microextraction–gas chromatography–mass spectrometry (HS-SPME-GC/MS). The results show that the fermentation was slower (14 days) in the cloudy juice in contrast to the sample produced from clear apple juice (10 days). Also, the volatile compounds related to aroma were abundantly found in the cider produced from cloudy apple juice compared to the cider produced from the clear apple juice. The conducted sensory analysis was in favor of cloudy juice.

Application of green synthetic iron oxide nanocatalyst in biohydrogen production from domestic wastewater.

Hydrogen (H2) is considered to be an energy carrier with high yields in future. Using green nanoparticles as the catalyst to produce H2 from organic wastes is an environmentally friendly and cost-effective approach. This study specifically addresses H2 production biologically from domestic wastewater using dark fermentation process with green nanoparticles in anaerobic condition. In this investigation, acid, alkaline, and heat pre-treated wastewater were utilized as the feedstock and identified that the alkaline pre-treated wastewater was an efficient feedstock for H2 production. The reaction conditions such as pH, time, and nanocatalyst dosage were optimized for the enhancement of H2 production. In addition, the green iron oxide nanoparticles (Fe3O4-NPs) were prepared by sustainable way using Murraya koenigii (curry leaves) with FeSO4 and characterized it using Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectrophotometer (UV-vis), power X-ray diffraction (pXRD), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), further tested for their 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging performance via in vitro antioxidant activities. This study demonstrates that a maximum production of bio-H2 was obtained (72.8mL/L) with 20mg of nanocatalyst load at alkaline condition (pH 9). The correlation coefficient value was highly significant for biohydrogen production with increasing pH (r = 0.9026) and catalyst dosage (r = 0.9962). The characterization studies confirmed the existence of iron oxide nanoparticles in the green synthesized nanoparticles. The in vitro antioxidant assay showed that Fe3O4-NPs effectively reduces the DPPH radical by significantly releasing H-atoms, thereby confirming that the plant extract functions as reducing/oxidizing agents. The high yield under the dark fermentation method has clearly been attributed to the enhancement in bio-H2 production by using the green Fe3O4-NPs based on M. koenigii.

An Effective Hybrid Metaheuristic Approach Based on the Genetic Algorithm

This paper presents an effective hybrid metaheuristic algorithm combining the genetic algorithm (GA) and a simple algorithm based on evolutionary computation. The evolutionary approach (EA) is applied to form the initial population of the GA, thus improving the algorithm’s performance, especially its convergence speed. To assess its effectiveness, the proposed hybrid algorithm, the EAGA, is evaluated on selected benchmark functions, as well as on a real optimisation process. The EAGA is used to identify parameters in a nonlinear system of differential equations modelling an E. coli fed-batch fermentation process. The obtained results are compared against published results from hybrid metaheuristic algorithms applied to the selected optimisation problems. The EAGA hybrid outperforms the competing algorithms due to its effective initial population generation strategy. The risk of premature convergence is reduced. Better numerical outcomes are achieved. The investigations validate the potential of the proposed hybrid metaheuristic EAGA for solving real complex nonlinear optimisation tasks.

Enhancing aerobic composting of food waste by adding hydrolytically active microorganisms

The biomass of native microorganisms in food waste (FW) suitable for accelerated composting is initially low and requires time for adaptation. Adding of efficient hydrolytic microorganisms should be able to enhance compost-specific microbial activity, adjust microbial community structure, and potentially hasten FW biodegradation. This study aimed to identify bacterial and fungal strains with growth characteristics suitable for accelerating FW composting. Over 7 weeks, FW was composted in a pilot-scale test, either inoculated at the start or on day 28 with three different mixtures of 10 autochthonous Bacillus and Penicillium spp. strains known for their high hydrolytic activity. The effects of inoculation were assessed by measuring the rate of carbon dioxide (CO2) and ammonia (NH3) production and also the increase in temperature due to spontaneous exothermic activity of the enhanced microbial population degrading FW. Inoculation with Bacillus spp., particularly B. amyloliquefaciens and B. subtilis, at the beginning of composting increased CO2 production nearly 3-fold while maintaining stable ammonia production and temperature. The high concentration of Bacillus relative to native FW microorganisms led to dominant fermentation processes even in the presence of oxygen, resulting in moderate heat release and elevated production of volatile organic compounds. Introducing Penicillium spp. at a later stage (day 28) increased CO2 production nearly 2-fold, along with higher NH3 levels and temperature. These findings highlight the significance of inoculation timing and microbial composition in regulating metabolic pathways during FW composting degradation, offering insights for designing effective microbial formulations for composting.

Study on volatile metabolites and microbial community in the fermentation process of black tea (Jiuqu hongmei tea)

Jiuqu hongmei tea (JQHM tea), unique to Zhejiang Province, China, is celebrated for its vibrant, delightful taste and distinctive flavor profile. This research explored the relationship between the tea's characteristic flavor during fermentation and the dynamics of microbial communities. Volatile organic compounds (VOCs) were analyzed using Headspace Solid-Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS) at three key stages: machine kneading (MK, 0.5 hours), primary fermentation (F1, 1.5 hours), and secondary fermentation (F2, 3 hours). Concurrently, microbial communities were characterized through high-throughput sequencing. The study identified 12 significant VOCs and pinpointed 10 core bacterial and 9 core fungal genera. These findings revealed the intricate changes in aroma compounds and microbial populations throughout JQHM tea's fermentation process, highlighting the interplay between key aroma compounds and principal microbial genera. This knowledge provided a crucial theoretical foundation for refining the tea's processing stages and enhancing its flavor quality.

Antioxidant content following fermentation of lemongrass for herbal beverage development.

Consumers have increasingly favoured fermented drinks due to their high content of probiotic secondary metabolites. These beverages are believed to possess the capacity to safeguard against non-communicable ailments such as coronary heart disease, cancer, diabetes, antimicrobial infections, and other dietary-related disorders. Lemongrass (Cymbopogon citratus) is a commonly used botanical ingredient in therapeutic tea production. It is renowned for its highly valuable essential oil, which has significant commercial demand. This study examines the functional content and antioxidant effects of fermented beverages derived from lemongrass. We employed the yeast Saccharomyces cerevisiae to carry out the fermentation process on the lemongrass compositions, extending the duration from t = 24 to t = 96h. We used non-fermented samples as control. This investigation identified numerous active biomolecules and polyphenols in the fermented samples, including flavonoids, tannins, cardiac glycosides, coumarins, terpenoids, steroids, saponins, and reducing sugars. After t = 24h fermentation, the radical-scavenging activity reached its maximum level of 89.1%, and the antioxidant content reached 13.06µg/ml, which is equivalent to the amount of ascorbic acid. After t = 36h fermentation, the total phenolic content reached a concentration of 237.19µg/ml, while the flavonoid content reached its peak at 55.21µg/ml after t = 72h fermentation. Lemongrass fermentation exhibits a wide range of phytochemicals and bioactive components that effectively eliminate free radicals, despite the antioxidant content fluctuation throughout the fermentation period of t = 24 to t = 96h.

Detection of black tea fermentation quality based on optimized deep neural network and hyperspectral imaging

The quality of black tea significantly relies on its fermentation process. Nevertheless, achieving precise and objective evaluations remains challenging due to the subjective nature of manual judgment involved in quality monitoring. To address this problem, hyperspectral imaging combined with the deep learning algorithms are proposed to identify the fermentation quality of black tea. Firstly, the hyperspectral data of Yinghong No. 9 black tea during five fermentation time intervals within 0–5 h are collected. Then, the Support Vector Machine (SVM), Artificial Neural Network (ANN), Partial Least Squares Discriminant Analysis (PLS-DA), and Naive Bayesian (NB) are used to construct black tea fermentation quality detection models based on full spectrum and selected spectrum data. Furthermore, deep learning algorithms including the Convolutional Neural Network (CNN), Long Short-Term Memory (LSTM), CNN-LSTM, and Swarm Optimization (PSO) optimized CNN-LSTM (PSO-CNN-LSTM) are also used to build the detection model using the spectral images. The experimental results indicate that deep learning algorithms have obvious advantages over traditional machine learning algorithms in tea fermentation quality detection. Besides, the PSO-CNN-LSTM model shows the best classification performance compared to other algorithms and achieves an accuracy of 96.78% on the test set. This study demonstrates the significant potential of combining deep learning with hyperspectral imaging for predicting black tea fermentation quality. This provides a new approach for effective monitoring of the black tea fermentation process and a useful reference for other applications in similar fields.

Study on the relationship between microbial community succession and physicochemical factors in the fermentation of rice-flavor Baijiu based on high-throughput and redundancy analysis techniques

Fermented grains are the main carrier of microbial fermentation and the direct source of Baijiu flavor substances, but so far, there are few studies on the changes in the fermented grains of rice-flavor Baijiu. This experiment systematically analyzed the correlation between microbial community succession and physicochemical factors in the fermentation process of two different types of rice (japonica: M and indica: H) fermented grains. The results showed that during the fermentation process, the changes in total acid, pH, starch, and total phenols of H and M were consistent. However, M and H showed different trends in terms of reducing sugar content and alcohol content. At the phylum level, both types of fermented grains had Firmicutes and Proteobacteria as the absolute dominant phyla. At the genus level, there was a slight difference in the dominant genera of M and H in the early stages, but the main genera in the later stages of fermentation were different. RDA analyses showed different correlations between dominant genera and physicochemical factors with some interesting results. The results of this study will provide a theoretical basis for the regulation of rice-flavor Baijiu fermentation.

Portable paper-based sheet for visual detection of ethyl carbamate in Chinese Baijiu based on aptamer recognition and laccase-like activity of cubic Ag2O nanoparticles

Ethyl carbamate (EC) is a small compound produced and stored during fermentation processes from ethanol, urea, citrulline, and carbamoyl phosphate. EC is commonly found in fermented foods and alcoholic beverages. Prolonged exposure to EC can cause nervous system diseases and liver damage in human beings. EC lacks stable physicochemical properties, and the presence of numerous interfering substances in alcoholic beverages poses challenges for its detection. Herein, it is found that EC1-34 aptamer bound to EC can enhance the laccase-like activity of cubic Ag2O nanoparticles (NPs). Subsequently, Ag2O NPs are wrapped with EC1-34 aptamer to prepare recognition probes, which are immobilized on a carrier membrane. Thus, a portable paper-based sheet for EC detection in Chinese Baijiu is designed. The visual detection limit of the developed paper-based sheet for EC is 10 μg⋅L-1, and shows an outstanding linear relationship within the range of 10-200 μg⋅L-1. Moreover, this colorimetric paper-based sheet has a good practicality in various Chinese Baijiu samples. It is believed that such paper-based sheet can facilitate portable inspection for EC in Baijiu, and may also become a beneficial tool for monitoring EC molecules in other fermented foods.

Chemometrics for estimating the fermentation and quality properties of kimchi based on hyperspectral image analysis

Kimchi is a traditional Korean dish made from fermenting vegetables. The fermentation process is crucial for enhancing its quality and flavor during storage. Approaches such as hyperspectral imaging (HSI) and chemometrics (PLS, partial least square; SVR, support vector regression) including principal component analysis (PCA), and 2-dimensional correlation spectroscopy (2D-COS) can detect key physical and chemical components and changes in total soluble solids (TSS), pH, titratable acidity (TA), salinity, and lactic acid bacteria (LAB). Multivariate analytical models were developed to predict the quality properties using full and characteristic wavelengths and preprocessed data. The results showed that the ratio of prediction to deviation (RPD) values of the PLS prediction model constructed using the full wavelengths of TSS, salinity, pH, TA, and LAB were 1.57, 2.33, 2.79, 2.91, and 2.73, respectively. The Savitzky Golay 1st derivative preprocessed SVR model established based on characteristic wavelengths (951, 1020, 1139, 1174, 1216, 1321, and 1384 nm) extracted by PCA and a 2D-COS matrix showed the best results and increased efficiency in predicting pH (Rp2 = 0.9166, RPD = 3.281) and the number of LAB (Rp2 = 0.8488, RPD = 2.466). Additionally, the visualization process accurately illustrated the distribution of various quality indicators of kimchi across different periods. These results demonstrate that our proposed HSI strategy successfully assessed the degree of kimchi fermentation.

Effects of exogenous selenium application on quality characteristics, selenium speciation, and in vitro bioaccessibility of rice pancakes

Selenium is an essential trace element for human health. To date, a hotspot of functional foods is strengthening the content of organic Se in food using biological Se enrichment. Herein, Se-enriched rice pancakes were produced by directly adding different sodium selenite concentrations into the fermentation process. The effects of sodium selenite addition on the texture properties, structure, and Se species of rice pancakes were investigated. Meanwhile, the bioaccessibility of Se and the changes of Se species in Se-enriched rice pancakes were determined by digestion experiments in vitro. The results showed significant differences in hardness, adhesiveness, chewiness, porosity, and flavor substances of Se-enriched rice pancakes after adding sodium selenite (p < 0.05). In Se-enriched rice pancakes, selenocystine (SeCys2) and methylselenocysteine (MeSeCys) are the main Se species. When sodium selenite was added at 3.3 μg/ml, the maximum values of SeCys2 and MeSeCys were 328.35 ± 33.43 and 311.11 ± 49.48 μg/kg, respectively. Se bioaccessibility was negatively correlated with sodium selenite content. The electronic nose results of Se-enriched rice pancakes showed that the sulfur compounds, nitrogen substances, alcohol substances, alkane substances, alcohols, aldehydes, and ketones in rice pancakes significantly increased following sodium selenite addition. The results can provide a significant basis for developing high efficiency Se-enriched fermented food and the processing of Se-enriched rice pancakes.

Real-time monitoring of multiparameter in 1,3-propanediol production process with near-infrared spectroscopy

1,3-propanediol (1,3-PDO) is a significant product of fermentation, with glycerol serving as the primary substrate in most cases. Bioprocess control based on real-time information of feedstock and main products is crucial for reducing the cost of production. However, rapid quantification of 1,3-PDO and glycerol remains challenging due to their highly similar molecular structures. In this study, the feasibility of near-infrared (NIR) spectroscopy to monitor 1,3-PDO, glycerol, acetate, and butyrate concentrations in the fermentation process using strain Clostridium pasteurianum was evaluated. NIR spectra were acquired through at-line measurement involving sampling and ex-situ analysis or on-line measurement with a fiber optic probe immersed in fermentation broth, integrated with Partial Least Squares (PLS) regression to establish calibration models on a laboratory-scale and pilot-scale. The best PLS regressions of 1,3-PDO, glycerol, acetate, and butyrate with two measurement approaches provided excellent performance, with the root-mean-squared errors of prediction (RMSEP) of 1.656g/L, 1.502g/L, 0.746g/L, and 0.557g/L in at-line measurement and 1.113g/L, 1.581g/L, 0.415g/L, and 0.526g/L in on-line measurement. The cross-scale application performance of at-line measurement was evaluated by an external fermentation trial and an acceptable result was achieved. At-line measurement technique represents a superior choice for the optimization of fermentation process since the robustness across varying fermentation scales and its applicability in multiple bioreactors. Thus, a calibration model developed for one bioreactor is likely to be used in other bioreactors, which enables the reduction of modeling costs. On-line measurement technique, owing to its automated operation and frequent data acquisition, enables real-time monitoring and precise control of the fermentation process, thereby reducing cost and improving production efficiency.

A combination of acetic acid and deep eutectic solvent pretreatment on poplar for coproduction of bioethanol, bio-oil and energy recovery

This work proposed an acetic acid (AC) pre-hydrolysis and a deep eutectic solvent (DES) post-delignification strategy for efficient fractionation of hemicellulose and lignin from lignocellulosic biomass, providing an easily hydrolyzed cellulose, which could be effectively converted to ethanol through semi-simultaneous saccharification and fermentation (SSSF) process. Results showed that, 11.20 kg xylo-oligosaccharides (XOSs), 19.91 kg ethanol and 25.89 kg lignin could be produced from lignocellulosic biorefinery based on the AC-DES pretreatment of 100 kg poplar. In addition, the lignin recovered from DES showed the potential as feedstock for production of hydrocarbon enriched bio-oil by pyrolysis. Higher heating values (HHV) of 27.19 MJ/kg and 31.56 MJ/kg for oil were measured, after pyrolysis of DES lignin and DES lignin/low-density polyethylene (LDPE) with ratio of 7:3, respectively. Finally, mass balance and energy analysis revealed that, lignocellulosic biorefinery based on AC-DES combined pretreatment to co-produce XOSs, bioerthanol and DES lignin could achieve an energy recovery of 78 %.

Improved textural properties of transglutaminase treated milk acid gel: Influence of citric acid

Keeping the stability of yogurt during the fermentation, storage and transportation process is necessary to reduce the syneresis. To achieve this goal, the combination of the acid treatment and transglutaminase (TG) was proposed to improve the textural properties of milk acid gels. We investigated the synergistic effect of acid treatment and TG on the water holding capacity (WHC) and physical stability of milk acid gels. As the pH of the skimmed milk decreased from 6.7 to 5.2, the casein micelles dissociated into smaller particles, exposing more site for the crosslinking of TG. The WHC and stability of the TG-treated acid gels were significantly enhanced as the particle size of casein micelles decreased. Our results suggested that the combination of the treatment of acid and TG could significantly improve the textural properties of milk acid gels by the dissociation of casein micelles induced and increase in the covalent-crosslinking. This study provided a simple and novel method to improve the stability of the milk gels, which showed enormous potential for dairy processing.

Effect of rhamnolipid on the performance of compound thermophilic bacteria agent pretreatment system for waste sludge hydrolysis.

This study innovatively introduced rhamnolipid (RL) to compound thermophilic bacteria (TB) agent pretreatment system for further accelerating the waste sludge hydrolysis and substrates transformation. The results showed that combined pretreatment was beneficial for the sludge extracellular polymers (EPS) rupture and dissolved organic matters (DOM) release. In the optimal dosage of 40mg/g SS RL, the activities of protease and α-glucosidase increased by 20.7% and 33.3% than that without RL addition, respectively. The addition of RL enhanced efficient contacts between hydrolases and organic substrates, and excitation emission matrix (EEM) spectrum revealed that combined pretreatment with 40mg/g SS RL could achieve higher soluble microbial by-products occupancy (54%) and lower fulvic acid-like substances (6%) occupancy in DOM, promoting the waste sludge biodegradability. High organics availability conducted to more shifts in microbial community structure, compared with TB agent pretreatment, the relative abundance of genus Geobacillus and norank_f__Synergistaceae were enhanced by 29.08 and 0.33 times in combined pretreatment system, respectively, which was conducive to sludge hydrolysis and subsequent anaerobic fermentation process.

Effects of aging of polyethylene microplastics and polystyrene nanoplastics on antibiotic resistance gene transfer during primary sludge fermentation

The increasing presence of nano and microplastics (NPs/MPs) in wastewater treatment plants and their inevitable accumulation in the sludge has raised serious concerns in recent years. This study investigated the effects of pristine and aged polyethylene microplastics (PEMPs), polystyrene nanoplastics (PsNPs), and their mixtures on the primary sludge fermentation process. Pristine MPs/NPs (150 μg/L and 2 g/L for PsNPs and PEMPs, respectively) underwent two weeks of weathering in the presence of humic and alginic acids. The results from a batch fermentation experiment (15 days, pH 10) revealed that the exposure to aged PEMPs/PsNPs experienced greater VFA production than pristine samples. Notably, the aged PEMPs/PsNPs mixture showed a 23.12% increase in VFA production over the pristine mixture. The relative abundance and total concentration of antibiotic resistance genes (ARGs) increased in all PEMPs/PsNPs batches compared to the control, with the most significant rise in total ARGs observed in the aged PEMPs sample. Aged PEMPs exhibited a 26.22-fold increase in tetA genes, while aged mix samples showed a 19.68-fold increase in tetM genes compared to their pristine counterparts. Both pristine and aged PEMPs/PsNPs, particularly the aged PEMPs adversely affected the microbial communities at the genus level and altered the microbial structure. Microbial richness and diversity were enhanced in samples exposed to pristine PEMPs/PsNPs and aged PsNPs but decreased in aged PEMPs and in the aged mixture group, suggesting a negative impact of aged polyethylene microplastics on microbial communities. Correlation analysis suggested that phyla Planctomycetes, Proteobacteria, and TM7 are potential hosts of ARGs. These findings manifest the substantial effects of aged nano/microplastics compared to their pristine forms, emphasizing the complex interplay between various forms of PEMPs/PsNPs and microbial dynamics in sludge fermentation processes.

Optimizing Huangjiu Fermentation for Enhanced Aroma: Insights into Saccharomyces cerevisiae jiangnan1# Strain

Higher alcohols (HAs) and acetate esters (AEs) are crucial volatile flavor compounds in Chinese huangjiu. The imbalance between HAs and AEs leads to poor flavor quality, lack of drinking comfort and headaches after drinking. By comparing the metabolic profiles and gene expression of Saccharomyces cerevisiae jiangnan1# with control strain (85#), 12.38% reduction in HA levels during unilateral fermentation was identified, especially a significant 47.32% drop in 2-phenethyl alcohol, without affecting AEs levels (P > 0.05). Bilateral fermentation strategies further optimized HA reduction by 8.33% and increased AEs significantly. Transcriptome data highlighted the down-regulation of key enzymes ARO9 and ARO10 in the Ehrlich pathway, linked to reduced HA synthesis, and the up-regulation of ALDH and acetyl-CoA synthase, promoting AE accumulation. The results showed that jiangnan1# strain-specific fermentation characteristics, particularly the regulation of key metabolic pathways, are the primary drivers of differences in HAs and AEs in huangjiu fermentation. These findings are instrumental in developing targeted metabolic strategies for enhancing the aroma profile of huangjiu, emphasizing the role of microbial modulation in food fermentation processes.