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Fermentation, Volume 3, Issue 1 (March 2017)

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Cover Story Potato is one of the most important food crops in the world. Potato protein liquor (PPL) is a waste [...] Read more.
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Editorial

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Open AccessEditorial Acknowledgement to Reviewers of Fermentation in 2016
Fermentation 2017, 3(1), 5; doi:10.3390/fermentation3010005 (registering DOI)
Received: 11 January 2017 / Revised: 11 January 2017 / Accepted: 11 January 2017 / Published: 11 January 2017
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Abstract
The editors of Fermentation would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...] Full article
Open AccessEditorial Yeast Biotechnology
Fermentation 2017, 3(1), 6; doi:10.3390/fermentation3010006
Received: 13 January 2017 / Revised: 24 January 2017 / Accepted: 24 January 2017 / Published: 26 January 2017
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Abstract
Yeasts are truly fascinating microorganisms. Due to their diverse and dynamic activities, they have been used for the production of many interesting products, such as beer, wine, bread, biofuels, and biopharmaceuticals. Saccharomyces cerevisiae (brewers’ or bakers’ yeast) is the yeast species that
[...] Read more.
Yeasts are truly fascinating microorganisms. Due to their diverse and dynamic activities, they have been used for the production of many interesting products, such as beer, wine, bread, biofuels, and biopharmaceuticals. Saccharomyces cerevisiae (brewers’ or bakers’ yeast) is the yeast species that is surely the most exploited by man.[...] Full article
(This article belongs to the Special Issue Yeast Biotechnology) Printed Edition available

Research

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Open AccessArticle Purification and Properties of Yeast Proteases Secreted by Wickerhamomyces anomalus 227 and Metschnikovia pulcherrima 446 during Growth in a White Grape Juice
Fermentation 2017, 3(1), 2; doi:10.3390/fermentation3010002
Received: 25 October 2016 / Revised: 19 December 2016 / Accepted: 19 December 2016 / Published: 26 December 2016
Cited by 1 | PDF Full-text (1785 KB) | HTML Full-text | XML Full-text
Abstract
Aspartic proteases are of significant importance for medicine and biotechnology. In spite of sufficient evidence that many non-Saccharomyces yeasts produce extracellular proteases, previous research has focused on the enzymes of Candida species because of their role as virulence factors. Nowadays, there
[...] Read more.
Aspartic proteases are of significant importance for medicine and biotechnology. In spite of sufficient evidence that many non-Saccharomyces yeasts produce extracellular proteases, previous research has focused on the enzymes of Candida species because of their role as virulence factors. Nowadays, there is also increasing interest for their applications in industrial processes, mainly because of their activities at low pH values. Here, we report the features of new acid proteases isolated from wine-relevant yeasts Metschnikovia pulcherrima and Wickerhamomyces anomalus. To our knowledge, this is the first detailed description of such an enzyme derived from strains of W. anomalus. Deviating to most former studies, we could demonstrate that the yeasts produce these enzymes in a natural substrate (grape juice) during the active growth phase. The enzymes were purified from concentrated grape juice by preparative isoelectric focusing. Biochemical data (maximum activity at ≈ pH 3.0, inhibition by pepstatin A) classify them as aspartic proteases. For W. anomalus 227, this assumption was confirmed by the protein sequence of WaAPR1 determined by LC-MS/MS. The sequence revealed a signal peptide for secretion, as well as a peptidase A1 domain with two aspartate residues in the active site. The enzyme has a calculated molecular mass of 47 kDa and an isolelectric point of 4.11. Full article
(This article belongs to the Special Issue Yeast Biotechnology) Printed Edition available
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Open AccessFeature PaperArticle Assessment of Acidified Fibrous Immobilization Materials for Improving Acetone-Butanol-Ethanol (ABE) Fermentation
Fermentation 2017, 3(1), 3; doi:10.3390/fermentation3010003
Received: 13 October 2016 / Revised: 15 December 2016 / Accepted: 23 December 2016 / Published: 30 December 2016
Cited by 2 | PDF Full-text (3612 KB) | HTML Full-text | XML Full-text
Abstract
Acetone-butanol-ethanol (ABE) fermentation using Clostridium acetobutylicum is a process that can be used to produce butanol, which can be utilized as an alternative to petroleum-based fuels. Immobilization of the bacteria using three different fibrous materials was studied in order to see how to
[...] Read more.
Acetone-butanol-ethanol (ABE) fermentation using Clostridium acetobutylicum is a process that can be used to produce butanol, which can be utilized as an alternative to petroleum-based fuels. Immobilization of the bacteria using three different fibrous materials was studied in order to see how to improve the ABE fermentation process. The results were compared to those of non-immobilized bacteria. Modal and charcoal fibers had OD levels below one at 72 h with the butanol concentration reaching 11.0 ± 0.5 and 10.7 ± 0.6 g/L, respectively, each of which were close to the free cell concentration at 11.1 ± 0.4 g/L. This suggests that bacteria can be efficiently immobilized in these fibrous materials. Although an extended lag phase was found in the fermentation time course, this can be easily solved by pre-treating fibrous materials with 3.5% HCl for 12 h. From comparisons with previous studies, data in this study suggests that a hydrophilic surface facilitates the adsorption of C. acetobutylicum. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production) Printed Edition available
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Open AccessFeature PaperArticle Gravity-Driven Adaptive Evolution of an Industrial Brewer’s Yeast Strain towards a Snowflake Phenotype in a 3D-Printed Mini Tower Fermentor
Fermentation 2017, 3(1), 4; doi:10.3390/fermentation3010004
Received: 29 August 2016 / Revised: 14 December 2016 / Accepted: 3 January 2017 / Published: 5 January 2017
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Abstract
We designed a mini tower fermentor that is suitable to perform adaptive laboratory evolution (ALE) with gravity imposed as selective pressure, and suitable to evolve a weak flocculating industrial brewers’ strain towards a strain with a more extended aggregation phenotype. This phenotype is
[...] Read more.
We designed a mini tower fermentor that is suitable to perform adaptive laboratory evolution (ALE) with gravity imposed as selective pressure, and suitable to evolve a weak flocculating industrial brewers’ strain towards a strain with a more extended aggregation phenotype. This phenotype is of particular interest in the brewing industry, since it simplifies yeast removal at the end of the fermentation, and many industrial strains are still not sufficiently flocculent. The flow of particles (yeast cells and flocs) was simulated, and the theoretical retainment advantage of aggregating cells over single cells in the tower fermentor was demonstrated. A desktop stereolithography (SLA) printer was used to construct the mini reactor from transparent methacrylic acid esters resin. The printed structures were biocompatible for yeast growth, and could be sterilised by autoclaving. The flexibility of 3D printing allowed the design to be optimized quickly. During the ALE experiment, yeast flocs were observed within two weeks after the start of the continuous cultivation. The flocs showed a “snowflake” morphology, and were not the result of flocculin interactions, but probably the result of (a) mutation(s) in gene(s) that are involved in the mother/daughter separation process. Full article
(This article belongs to the Special Issue Yeast Biotechnology) Printed Edition available
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Open AccessArticle Optimization of Thermo-Alkali Stable Amylase Production and Biomass Yield from Bacillus sp. Under Submerged Cultivation
Fermentation 2017, 3(1), 7; doi:10.3390/fermentation3010007
Received: 28 October 2016 / Revised: 13 January 2017 / Accepted: 20 January 2017 / Published: 4 February 2017
Cited by 2 | PDF Full-text (2332 KB) | HTML Full-text | XML Full-text
Abstract
The present context was investigated to optimize amylase production and cell biomass of poultry-associated Bacillus sp. using a conventional as well as statistical approach. Box-Behnken design (BBD) matrix at N = 29 was employed to optimize four independent variables, selected from one factor
[...] Read more.
The present context was investigated to optimize amylase production and cell biomass of poultry-associated Bacillus sp. using a conventional as well as statistical approach. Box-Behnken design (BBD) matrix at N = 29 was employed to optimize four independent variables, selected from one factor at a time (OFAT) technique, for maximum amylase production and biomass yield. The relative activity of crude amylase obtained from the isolate showed stability at high temperature (60 °C) and alkaline condition (pH 9) up to 4 h of incubation, thereby indicating its alkali-tolerant and thermo-stable property. The BBD resulted in enhanced amylase activity of 145.32 U/mL when the basal medium was slightly acidic (pH 6) and kept at a temperature of 35 °C with the shaking speed of 130 rpm, in addition to being incubated for 24 h. The selected factors, when employed with this statistical optimization approach, showed 1.5-fold and 2-fold enhancements in the amylase production and biomass yield respectively compared to the OFAT method. Analysis of variance (ANOVA) revealed high coefficient of determination (R2) of 0.96 to 0.99 for both the responses at significant level (p < 0.05). Three-dimensional response and 2D contour plot of the quadratic model showed interdependent interaction between the effective variables. Long-term thermo-alkali stability of amylase obtained from Bacillus sp. suggested not only its wide applications in pharmaceutical, food and biotechnological industries, but also suggested a potent replacement of existing amylases on the market. Full article
(This article belongs to the Special Issue Industrial Biotechnology: An Emerging Area)
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Open AccessArticle Anhydrous Ammonia Pretreatment of Corn Stover and Enzymatic Hydrolysis of Glucan from Pretreated Corn Stover
Fermentation 2017, 3(1), 9; doi:10.3390/fermentation3010009
Received: 27 October 2016 / Revised: 15 February 2017 / Accepted: 15 February 2017 / Published: 17 February 2017
Cited by 1 | PDF Full-text (788 KB) | HTML Full-text | XML Full-text
Abstract
As a promising alternative of fossil fuel, ethanol has been widely used. In recent years, much attention has been devoted to bioethanol production from lignocellulosic biomass. In previous research, it is found that the pretreatment method named low-moisture anhydrous ammonia (LMAA) has the
[...] Read more.
As a promising alternative of fossil fuel, ethanol has been widely used. In recent years, much attention has been devoted to bioethanol production from lignocellulosic biomass. In previous research, it is found that the pretreatment method named low-moisture anhydrous ammonia (LMAA) has the advantage of high conversion efficiency and less washing requirements. The purpose of this study was to explore the optimal conditions by employing the LMAA pretreatment method. Corn stover was treated under three levels of moisture content: 20, 50, 80 w.b.% (wet basis), and three levels of particle size: <0.09, 0.09–2, >2 mm; it was also ammoniated with a loading rate of 0.1g NH3/g biomass (dry matter). Ammoniated corn stover was then subjected to different pretreatment times (24, 96, 168 h) and temperatures (20, 75, 130 °C). After pretreatment, compositional analysis and enzymatic digestibility were conducted to determine the highest glucose yield. As a result, the highest glucose yield was obtained under the condition of 96 h and 75 °C with 50 w.b.% and 0.09–2 mm of corn stover. The main findings of this study could improve the efficiency of bioethanol production processing in the near future. Full article
(This article belongs to the Special Issue Biofuels and Biochemicals Production) Printed Edition available
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Open AccessArticle Mixed Carboxylic Acid Production by Megasphaera elsdenii from Glucose and Lignocellulosic Hydrolysate
Fermentation 2017, 3(1), 10; doi:10.3390/fermentation3010010
Received: 7 December 2016 / Revised: 22 February 2017 / Accepted: 23 February 2017 / Published: 1 March 2017
Cited by 3 | PDF Full-text (1043 KB) | HTML Full-text | XML Full-text
Abstract
Volatile fatty acids (VFAs) can be readily produced from many anaerobic microbes and subsequently utilized as precursors to renewable biofuels and biochemicals. Megasphaera elsdenii represents a promising host for production of VFAs, butyric acid (BA) and hexanoic acid (HA). However, due to the
[...] Read more.
Volatile fatty acids (VFAs) can be readily produced from many anaerobic microbes and subsequently utilized as precursors to renewable biofuels and biochemicals. Megasphaera elsdenii represents a promising host for production of VFAs, butyric acid (BA) and hexanoic acid (HA). However, due to the toxicity of these acids, product removal via an extractive fermentation system is required to achieve high titers and productivities. Here, we examine multiple aspects of extractive separations to produce BA and HA from glucose and lignocellulosic hydrolysate with M. elsdenii. A mixture of oleyl alcohol and 10% (v/v) trioctylamine was selected as an extraction solvent due to its insignificant inhibitory effect on the bacteria. Batch extractive fermentations were conducted in the pH range of 5.0 to 6.5 to select the best cell growth rate and extraction efficiency combination. Subsequently, fed-batch pertractive fermentations were run over 230 h, demonstrating high BA and HA concentrations in the extracted fraction (57.2 g/L from ~190 g/L glucose) and productivity (0.26 g/L/h). To our knowledge, these are the highest combined acid titers and productivity values reported for M. elsdenii and bacterial mono-cultures from sugars. Lastly, the production of BA and HA (up to 17 g/L) from lignocellulosic sugars was demonstrated. Full article
(This article belongs to the Special Issue Carboxylic Acid Production) Printed Edition available
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Open AccessArticle Yeast Diversity and Physicochemical Characteristics Associated with Coffee Bean Fermentation from the Brazilian Cerrado Mineiro Region
Fermentation 2017, 3(1), 11; doi:10.3390/fermentation3010011
Received: 20 January 2017 / Revised: 3 March 2017 / Accepted: 12 March 2017 / Published: 16 March 2017
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Abstract
The aim of this study was to evaluate the yeast diversity and physicochemical characteristics of spontaneous coffee bean fermentation conducted in the coffee-producing region in Cerrado Mineiro, Brazil. During 48 h of fermentation, yeast population increased from 6.60 to 7.89 log CFU·g−1
[...] Read more.
The aim of this study was to evaluate the yeast diversity and physicochemical characteristics of spontaneous coffee bean fermentation conducted in the coffee-producing region in Cerrado Mineiro, Brazil. During 48 h of fermentation, yeast population increased from 6.60 to 7.89 log CFU·g−1, with concomitant pulp sugar consumption and organic acids production (mainly lactic (3.35 g·L−1) and acetic (1.27 g·L−1) acids). According to ITS-rRNA gene sequencing, yeast population was mainly represented by Saccharomyces sp., followed by Torulaspora delbrueckii, Pichia kluyveri, Hanseniaspora uvarum, H. vineae and Meyerozyma caribbica. SPME-GC-MS analysis revealed a total of 25 volatile organic compounds with predominance of hydrocarbons (9 compounds) and higher alcohols (6 compounds). The resulting fermented, roasted coffee beans were analyzed by diverse chemical analysis methods, including Fourier Transform Infrared (FTIR) spectroscopy and mineral and thermogravimetric analysis. The thermal decomposition of the coffee beans occurred in four stages between 90 and 390 °C, with significant mass loss (68%) after the second stage at 190 °C. FTIR spectroscopy confirmed the presence of the main organic functions associated with coffee aroma, such as aromatic acids, ketones, aldehydes and aliphatic esters. The results presented in this study enrich our knowledge concerning yeast diversity and physicochemical characteristics associated with coffee bean fermentation, and can be used to promote a controlled on-farm processing. Full article
(This article belongs to the Special Issue Microbiology and Food Hygiene)
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Open AccessFeature PaperArticle Production of Edible Fungi from Potato Protein Liquor (PPL) in Airlift Bioreactor
Fermentation 2017, 3(1), 12; doi:10.3390/fermentation3010012
Received: 13 February 2017 / Revised: 10 March 2017 / Accepted: 16 March 2017 / Published: 21 March 2017
Cited by 1 | PDF Full-text (1560 KB) | HTML Full-text | XML Full-text
Abstract
Potato protein liquor (PPL), a side stream from the potato starch industry, is normally used as fertilizer. However, with more than 100 g/L of sugars, 20 g/L of Kjeldahl nitrogen and Chemical Oxigen Demand (COD) of 300 g/L, it represents serious environmental challenges.
[...] Read more.
Potato protein liquor (PPL), a side stream from the potato starch industry, is normally used as fertilizer. However, with more than 100 g/L of sugars, 20 g/L of Kjeldahl nitrogen and Chemical Oxigen Demand (COD) of 300 g/L, it represents serious environmental challenges. The use of PPL for fungal cultivation is a promising solution to convert this waste into valuable products. In this study, PPL was characterized and used to cultivate edible zygomycete Rhizopus oryzae, which is widely used in Southeast Asian cuisine to prepare e.g., tempeh. Moreover, it can be potentially used as a protein source in animal feed worldwide. Under the best conditions, 65.47 ± 2.91 g of fungal biomass per litre of PPL was obtained in airlift bioreactors. The total Kjeldahl nitrogen content of the biomass was above 70 g/kg dry biomass. The best results showed 51% reduction of COD and 98.7% reduction in the total sugar content of PPL. Full article
(This article belongs to the Special Issue Membrane Bioreactors)
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Review

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Open AccessReview Microbiological Exploration of Different Types of Kefir Grains
Fermentation 2017, 3(1), 1; doi:10.3390/fermentation3010001
Received: 4 November 2016 / Revised: 15 December 2016 / Accepted: 20 December 2016 / Published: 23 December 2016
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Abstract
Many studies have been published lately verifying the probiotic character of kefir grains. Most of them focused on the benefits to human health through the consumption of fermented food with kefir grains. However, the challenge is to characterize and isolate specific probiotic microorganisms
[...] Read more.
Many studies have been published lately verifying the probiotic character of kefir grains. Most of them focused on the benefits to human health through the consumption of fermented food with kefir grains. However, the challenge is to characterize and isolate specific probiotic microorganisms involved in the kefir microbiota. The main reason for this is that the food industry prefers to apply isolated probiotic microorganisms from kefir grains rather than kefir grains in order to produce respective fermented products with added value. Thus, modern molecular techniques such as polymerase chain reaction (PCR)-based amplification, new generation sequencing (NGS) or denaturing gradient gel electrophoresis (DGGE) analyses have been applied. Furthermore, this review emphasizes the latest outcomes regarding the health benefits of the consumption of foods fermented with kefir grains and particularly the isolation of microorganisms from kefir grains worldwide, some of them exhibiting probiotic properties. Full article
(This article belongs to the Special Issue Microbiology and Food Hygiene)
Open AccessFeature PaperReview Recent Progress in the Microbial Production of Pyruvic Acid
Fermentation 2017, 3(1), 8; doi:10.3390/fermentation3010008
Received: 10 January 2017 / Revised: 5 February 2017 / Accepted: 6 February 2017 / Published: 13 February 2017
Cited by 2 | PDF Full-text (475 KB) | HTML Full-text | XML Full-text
Abstract
Pyruvic acid (pyruvate) is a cellular metabolite found at the biochemical junction of glycolysis and the tricarboxylic acid cycle. Pyruvate is used in food, cosmetics, pharmaceutical and agricultural applications. Microbial production of pyruvate from either yeast or bacteria relies on restricting the natural
[...] Read more.
Pyruvic acid (pyruvate) is a cellular metabolite found at the biochemical junction of glycolysis and the tricarboxylic acid cycle. Pyruvate is used in food, cosmetics, pharmaceutical and agricultural applications. Microbial production of pyruvate from either yeast or bacteria relies on restricting the natural catabolism of pyruvate, while also limiting the accumulation of the numerous potential by-products. In this review we describe research to improve pyruvate formation which has targeted both strain development and process development. Strain development requires an understanding of carbohydrate metabolism and the many competing enzymes which use pyruvate as a substrate, and it often combines classical mutation/isolation approaches with modern metabolic engineering strategies. Process development requires an understanding of operational modes and their differing effects on microbial growth and product formation. Full article
(This article belongs to the Special Issue Carboxylic Acid Production) Printed Edition available
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