Investigating the Variation of Volatile Compound Composition in Maotai-Flavoured Liquor During Its Multiple Fermentation Steps Using Statistical Methods.

The use of multiple fermentations is one of the most specific characteristics of Maotai--flavoured liquor production. In this research, the variation of volatile composition of Maotai-flavoured liquor during its multiple fermentations is investigated using statistical approaches. Cluster analysis shows that the obtained samples are grouped mainly according to the fermentation steps rather than the distillery they originate from, and the samples from the first two fermentation steps show the greatest difference, suggesting that multiple fermentation and distillation steps result in the end in similar volatile composition of the liquor. Back-propagation neural network (BNN) models were developed that satisfactorily predict the number of fermentation steps and the organoleptic evaluation scores of liquor samples from their volatile compositions. Mean impact value (MIV) analysis shows that ethyl lactate, furfural and some high-boiling-point acids play important roles, while pyrazine contributes much less to the improvement of the flavour and taste of Maotai-flavoured liquor during its production. This study contributes to further understanding of the mechanisms of Maotai-flavoured liquor production.

Step enzymatic hydrolysis of sodium hydroxide-pretreated Chinese liquor distillers' grains for ethanol production.

Distillers' grains are a co-product of ethanol production. In China, only a small portion of distillers' grains have been used to feed the livestock because the amount was so huge. Nowadays, it has been reported that the distillers' grains have the potential for fuel ethanol production because they are composed of lignocelluloses and residual starch. In order to effectively convert distillers' grains to fuel ethanol and other valuable production, sodium hydroxide pretreatment, step-by-step enzymatic hydrolysis, and simultaneous saccharification and fermentation (SSF) were investigated. The residual starch was first recycled from wet distillers' grains (WDG) with glucoamylase to obtain glucose-rich liquid. The total sugar concentration was 21.3 g/L, and 111.9% theoretical starch was hydrolyzed. Then the removed-starch dry distillers' grains (RDDG) were pretreated with NaOH under optimal conditions and the pretreated dry distillers' grains (PDDG) were used for xylanase hydrolysis. The xylose concentration was 19.4 g/L and 68.6% theoretical xylose was hydrolyzed. The cellulose-enriched dry distillers' grains (CDDG) obtained from xylanase hydrolysis were used in SSF for ethanol production. The ethanol concentration was 42.1 g/L and the ethanol productivity was 28.7 g/100 g CDDG. After the experiment, approximately 80.6% of the fermentable sugars in WDG was converted to ethanol.

A comparison of different dilute solution explosions pretreatment for conversion of distillers' grains into ethanol.

In order to improve the efficiency of distillers' grains converting to ethanol, 13 dilute solution explosions were evaluated based on the optimization of pure water explosion. To decrease residual inhibitor content, the exploded slurry was dried at 105°C. Using a 1.1 mol/L butanone solution explosion, with the explosion temperature set at 160°C (pressure at 1.9 MPa), the residence time at 10 min, and the dried distillers' grains-to-water ratio at 1:2 (w/w), the yields of total sugar, glucose, and xylose were 86%, 89%, and 84% (w/w), respectively, and the ethanol yield was 25.3 g/100 g distillers' grains dry matter. Moreover, the eight other reagent solution explosions improved the efficiency of enzymatic hydrolysis, and of simultaneous saccharification and co-fermentation, and the residual contents of furfural, 5-hydroxymethylfurfural, and acetic acid decreased to an acceptable concentration range after detoxification by drying. The results suggested that compared with pure water explosions, the use of volatile solutions lowered the explosive temperature and improved the sugar yield. This study offers a reference for the further study of lignocellulosic materials with higher starch and hemicelluloses contents as raw materials for converting biomass to bioethanol.

Bioinformatics analysis of amino acid decarboxylases related to four major biogenic amines in pickles.

Microbial amino acid decarboxylases (AADs) produce biogenic amines (BAs) in fermented food. However, a systematic comparison of the AADs' properties from different microorganisms in pickle fermentation remains unexplored. Here, we bioinformatically analyzed the amino acid sequences of AADs corresponding to four major BAs for common microorganisms in pickle fermentation. We showed that their sequences, besides tyrosine decarboxylase, differed among microorganisms. Overall, the AAD sequences varied lesser among bacterial species than between bacteria and fungi, with those in Lactobacillus sharing occasionally high similarity with other bacteria. Most AADs were predicted as stable cytosolic endoenzymes. Molecular docking showed that most commonly used spice components in pickle production, especially pepper, chili, and ginger, strongly bind to the AAD active sites, thus may inhibit the enzymes and reduce the BA accumulation. This study provides insights for deeply understanding the different microbial AAD properties in pickle fermentation and reducing BAs by appropriately using spices.

Analysis of fermentation control factors on volatile compounds of primary microorganisms in Jiang-flavor Daqu.

Chinese Jiang-flavor Baijiu is the most widely consumed liquor. Jiang-flavor Daqu, a fermentation starter, is important sources of key flavors of Jiang-flavor Baijiu. Some microbes play significant roles in flavor formation of Daqu. In order to clarify the microbial population that promotes the formation of Daqu flavor, we use high throughput sequencing technology combined with headspace solid-phase microextraction gas chromatography-mass spectrometry to investigate microbial population and volatile compounds in Jiang-flavor Daqu. In addition, the dynamic changes of physicochemical factors and enzyme activities in Jiang-flavor Daqu were investigated. Correlations between microbial population, volatile compounds, physicochemical factors, and enzyme activities of Jiang-flavor Daqu were disclosed by redundancy analysis and Spearman correlation analysis. A total of 66 volatile compounds were identified and 14 primary microorganisms were selected. Results showed that high temperature environment could promote the formation of acids, aldehydes and ketones, phenols, furans by affecting the growth of Monascus, Trichomonascus, Cutaneotrichosporon, Wallemia, Millerozyma, Nigrospora, Cladosporium, Bacillus, and Pediococcus in the early fermentation stage. While high nitrogen environment was more suitable for the growth of Virgibacillus and Kroppenstedtia, who could promote the formation of pyrazines in the late fermentation stage. PRACTICAL APPLICATIONS: This study has provided a scientific basis for the directed regulation of Daqu fermentation through physicochemical factors, developed scientific basis for artificially constructing Daqu microbial population and obtaining an easy-to-operate, reproducible fermentation system for Daqu production.

Pretreatment of rice straw using a butanone or an acetaldehyde dilute solution explosion for producing ethanol.

Ethanol conversion from rice straw using butanone and acetaldehyde dilute solution explosions was evaluated based on the optimization of pure water explosion. To decrease residual inhibitor content, the exploded slurry was dried and investigated at different temperature. Using a 0.9-mol/L butanone solution explosion, with the explosion pressure set at 3.1 MPa, the residence time at 7 min, the dried rice straw-to-water ratio at 1:3 (w/w), and the exploded slurry drying temperuture at 90 °C for 8 h, the yields of total sugar, glucose, and xylose were 85%, 88%, 82% (w/w), respectively, and the ethanol productivity was 26.0 g/100 g rice straw dry matter. Moreover, 0.5-mol/L acetaldehyde dilute solution explosion improved the efficiency of enzymatic hydrolysis (EH) and simultaneous saccharification and co-fermentation (SSCF), and the residual inhibitors had negligible effects on EH and SSCF after detoxification by drying. The results suggested that compared with pure water explosions, the use of butanone and of acetaldehyde dilute solution explosions lowered the explosive temperature and improved the sugar yield, although relative crystallinity of the rice straw dry matter was increased after the explosion.

Phosphate assimilation by Chlorella and adjustment of phosphate concentration in basal medium for its cultivation.

Assimilation of phosphate by Chlorella pyrenoidosa was 0.81-8.1 mg PO(4)-P/g dry weight for heterotrophic cultures and 0.81-16.1 mg/g for mixotrophic cultures. Optimal carbon:phosphorous (C/P) ratios were 206:1-2060:1 and 103:1-2060:1 for heterotrophic and mixotrophic cultivations, respectively. These requirements for phosphate for growth of C. pyrenoidosa under either heterotrophic or mixotrophic conditions are much less (6.25-62.5 or 3.12-62.5-fold at 10 g glucose/l) than its concentration in basal medium.