Forastero and Criollo cocoa beans, differences on the profile of volatile and non-volatile compounds in the process from fermentation to liquor

Cocoa bean fermentation is an important process because during this process, aroma compounds are produced, the astringency decreases, and the embryo dies. The fermentation processes of the Criollo and Forastero types have been studied separately without comparing them at the same time and in the same place. The aim of this work was to determine differences in the profile of volatile and nonvolatile compounds of Criollo and Forastero cocoa from the fermentation process to the final stage of obtaining the liquor. The experiments were carried out at the same time in the Maya region. Volatile compounds were determined by HS-SPME GC-MS (headspace solid phase-microextraction with gas chromatography-mass spectrometry). Sugars, organic acids, and alkaloids were determined by ultrahigh-performance liquid chromatography (UHPLC-PDA/UV). Criollo cocoa liquor was defined by the volatile and nonvolatile compounds such as acetic acid, phenylethyl alcohol, benzaldehyde, 2-phenylethyl acetate, acetophenone and 3-methylbutanal., which are associated with sour, honey, almond, flowery and chocolate aroma. Forastero cocoa liquor was represented with a significant difference by acetic acid, isobutyl acetate, 2,3-diethyl-5-methylpyrazine and ethyl octanoate and these could provide aroma descriptors such as sour, fruity and nutty. This study characterized for the first time the dynamics of volatile compounds during the fermentation, drying, and roasting stages and in the final cocoa liquor of Criollo and Forastero from cocoa beans of the same origin.

Diploid genome assembly of Kluyveromyces marxianus NRRL Y-50883 (SLP1)

The yeast Kluyveromyces marxianus SLP1 has the potential for application in biotechnological processes because it can metabolize several sugars and produce high-value metabolites. K. marxianus SLP1 is a thermotolerant yeast isolated from the mezcal process, and it is tolerant to several cell growth inhibitors such as saponins, furan aldehydes, weak acids, and phenolics compounds. The genomic differences between dairy and nondairy strains related to K. marxianus variability are a focus of research attention, particularly the pathways leading this species toward polyploidy. We report the diploid genome assembly of K. marxianus SLP1 nonlactide strain into 32 contigs to reach a size of ∼12 Mb (N50 = 1.3 Mb) and a ∼39% GC content. Genome size is consistent with the k-mer frequency results. Genome annotation by Funannotate estimated 5000 genes in haplotype A and 4910 in haplotype B. The enriched annotated genes by ontology show differences between alleles in biological processes and cellular component. The analysis of variants related to DMKU3 and between haplotypes shows changes in LAC12 and INU1, which we hypothesize can impact carbon source performance. This report presents the first polyploid K. marxianus strain recovered from nonlactic fermenting medium.

Use of non-Saccharomyces yeasts in cider fermentation: Importance of the nutrients addition to obtain an efficient fermentation

The isolation of autochthonous yeast species presents a good strategy to select new microorganisms for developing an adequate inoculum to carry out fermentations and generate representative products of the cider production zone. However, non-Saccharomyces yeasts have been considered to have low capacity to carry out a complete fermentation as Saccharomyces cerevisiae. In this work, five autochthonous yeasts from a cider fermentation process were isolated and identified as Saccharomyces cerevisiae, Kluyveromyces marxianus, Pichia membranaefaciens, P. kluyveri and Zygosaccharomyces rouxii. A series of fermentations were developed at laboratory level, using each species individually and it was observed that only S. cerevisiae was able to finish the process. K. marxianus consumed less than 50% of the sugars; P. kluyveri and Z. rouxii consumed less than 70% and P. membranaefaciens consumed more than 90% but the yield (ethanol produced for sugar consumed (Y_P/S)) was 0.39. Nevertheless, the addition of magnesium, zinc and nitrogen increased the fermentative capacity of almost all species: K. marxianus, Z. rouxii and P. kluyveri, showed an increase in ethanol production when nutrients were added, obtaining more than 80 g/L of ethanol, and showing that those nutrients are necessary to complete the fermentation. This work describes the potential use of different non-Saccharomyces species to carry out fermentation of apple juice and highlights the importance of certain nutrients to enable an efficient alcoholic fermentation and the generation of desirable volatile compounds for cider production.

2-Phenylethanol and 2-phenylethylacetate production by nonconventional yeasts using tequila vinasses as a substrate

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Yeast species influenced the de novo synthesis of 2-phenylethylacetate.

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Inhibitory compounds showed a strong influence on cell growth and 2-phenylethylacetate production for the evaluated yeasts.

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More than a 50 % reduction in the chemical and biochemical oxygen demand was achieved by yeast fermentation.

Vinasses from the tequila industry are wastewaters with highly elevated organic loads. Therefore, to obtain value-added products by yeast fermentations, such as 2-phenylethanol (2-PE) and 2-phenylethylacetate (2-PEA), could be interesting for industrial applications from tequila vinasses. In this study, four yeasts species (Wickerhamomyces anomalus, Candida glabrata, Candida utilis, and Candida parapsilosis) were evaluated with two different chemically defined media and tequila vinasses. Differences in the aroma compounds production were observed depending on the medium and yeast species used. In tequila vinasses, the highest concentration (65 mg/L) of 2-PEA was reached by C. glabrata, the inhibitory compounds decreased biomass production and synthesis of 2-PEA, and biochemical and chemical oxygen demands were reduced by more than 50 %. Tequila vinasses were suitable for the production of 2-phenylethylacetate by the shikimate pathway. A metabolic network was developed to obtain a guideline to improve 2-PE and 2-PEA production using flux balance analysis (FBA).

Analysis of volatile compounds of five varieties of Maya cocoa during fermentation and drying processes by Venn diagram and PCA

Fermented cocoa beans can be described as a complex matrix that integrates the chemical history of beans, their processing, and environmental factors. This study presents an analysis that aims to identify volatile compounds of five varieties of fine-aroma cocoa types. The cocoa types studied were Carmelo, Rojo Samuel, Lagarto, Arcoiris, Regalo de Dios, that grow in the Maya lands of Chiapas, Mexico. Profile of volatile compounds was obtained from each cacao type during fermentation and drying process. This profile of volatile compounds also was compared with beans unfermented, using a statistical analysis of Venn diagram and a multivariate Analysis of Principal Components (PCA). One hundred nine different compounds were identified by SPME-HS GC-MS, these compounds mainly related to desirable aromatic notes generated by esters, aldehydes, ketones, and alcohols. The differences in chemical composition of the volatile compounds were associated mainly with the process and not to cocoa varieties. Fermented dry cocoa beans showed a higher content of esters, aldehydes, pyrazines, alcohols, some acids, and furans where Lagarto (CL), Rojo Samuel (CR), and Regalo de Dios (TRD) cocoas type showed a more interesting aromatic profile. On the other hand, as expected dry unfermented cocoas presented a few numbers of aroma compounds, in the five cacao types, where alcohols, ketones and hydrocarbons predominated.

Fermentative capabilities of native yeast strains grown on juices from different Agave species used for tequila and mezcal production

The Asparagaceae family is endemic from America, being the Agave genus the most important. The Agave species possess economic relevance and are use as raw material to produce several distilled alcoholic beverages, as bacanora, tequila, and mezcal. The fermentation process has been carry out either spontaneously or by adding a selected yeast strain. The latter is generally responsible for the production of ethanol and volatile compounds. This study comprised five Agave species (A. angustifolia, A. cupreata, A. durangensis, A. salmiana, and A. tequilana) and eight endogenous yeast strains: five of them were non-Saccharomyces (Torulaspora delbrueckii, Zygosaccharomyces bisporus, Candida ethanolica, and two Kluyveromyces marxianus) and three Saccharomyces cerevisiae strains. The results showed that the S. cerevisiae strains were not able to grow on A. durangensis and A. salmiana juices. The Kluyveromyces marxianus strains grew and fermented all the agave juices and displayed high ethanol production (48-52 g L^-1) and volatile compounds. The ethanol production was higher on A. angustifolia juice (1.1-2.8-fold), whereas the volatile compound was dependent on both yeast strain and the Agave species. The use of endogenous non-Saccharomyces yeast strains is feasible, as they may outperform S. cerevisiae regarding the production of fermented beverages from agave plants with a high content of ethanol and aromatic compounds. Graphical abstract.

Growth Modeling of Aspergillus niger Strains Isolated from Citrus Fruit as a Function of Temperature on a Synthetic Medium from Lime (Citrus latifolia T.) Pericarp

Molds are responsible for postharvest spoilage of citrus fruits. The objective of this study was to evaluate the effect of temperature on growth rate and the time to visible growth of Aspergillus niger strains isolated from citrus fruits. The growth of these strains was studied on agar lime medium (AL) at different temperatures, and growth rate was estimated using the Baranyi and Roberts model (Int. J. Food Microbiol. 23:277-294, 1994). The Rosso et al. cardinal model with inflexion (L. Rosso, J. R. Lobry, S. Bajard, and J. P. Flandrois, J. Theor. Biol. 162:447-463, 1993) was used as a secondary model to describe the effect of temperature on growth rate and the lag phase. We hypothesized that the same model could be used to calculate the time for the mycelium to become visible (t_v) by substituting the lag phase (1/λ and 1/λ_opt) with the time to visible colony (1/t_v-opt and 1/t_v), respectively, in the Rosso et al.

MODEL

High variability was observed at suboptimal conditions. Extremes of temperature of growth for A. niger seem to have a normal variability. For the growth rate and time t_v, the model was satisfactorily compared with results of previous studies. An external validation was performed in lime fruits; the bias and accuracy factors were 1.3 and 1.5, respectively, for growth rate and 0.24 and 3.72, respectively, for the appearance time. The discrepancy may be due to the influence of external factors. A. niger grows significantly more slowly on lime fruit than in culture medium, probably because the nutrients are more easily available in medium than in fruits, where the peel consistency may be a physical barrier. These findings will help researchers understand the postharvest behavior of mold on lime fruits, host-pathogen interactions, and environmental conditions infecting fruit and also help them develop guidelines for future work in the field of predictive mycology to improve models for control of postharvest fungi.

Simultaneous saccharification and fermentation of Agave tequilana fructans by Kluyveromyces marxianus yeasts for bioethanol and tequila production

Agave tequilana fructans (ATF) constitute a substrate for bioethanol and tequila industries. As Kluyveromyces marxianus produces specific fructanases for ATF hydrolysis, as well as ethanol, it can perform simultaneous saccharification and fermentation. In this work, fifteen K. marxianus yeasts were evaluated to develop inoculums with fructanase activity on ATF. These inoculums were added to an ATF medium for simultaneous saccharification and fermentation. All the yeasts, showed exo-fructanhydrolase activity with different substrate specificities. The yeast with highest fructanase activity in the inoculums showed the lowest ethanol production level (20 g/l). Five K. marxianus strains were the most suitable for the simultaneous saccharification and fermentation of ATF. The volatile compounds composition was evaluated at the end of fermentation, and a high diversity was observed between yeasts, nevertheless all of them produced high levels of isobutyl alcohol. The simultaneous saccharification and fermentation of ATF with K. marxianus strains has potential for industrial application.

Fructanase and fructosyltransferase activity of non-Saccharomyces yeasts isolated from fermenting musts of Mezcal

Fructanase and fructosyltransferase are interesting for the tequila process and prebiotics production (functional food industry). In this study, one hundred thirty non-Saccharomyces yeasts isolated from "Mezcal de Oaxaca" were screened for fructanase and fructosyltransferase activity. On solid medium, fifty isolates grew on Agave tequilana fructans (ATF), inulin or levan. In liquid media, inulin and ATF induced fructanase activities of between 0.02 and 0.27U/ml depending of yeast isolate. High fructanase activity on sucrose was observed for Kluyveromyces marxianus and Torulaspora delbrueckii, while the highest fructanase activity on inulin and ATF was observed for Issatchenkia orientalis, Cryptococcus albidus, and Candida apicola. Zygosaccharomyces bisporus and Candida boidinii had a high hydrolytic activity on levan. Sixteen yeasts belonging to K. marxianus, T. delbrueckii and C. apicola species were positive for fructosyltransferase activity. Mezcal microbiota proved to showed to be a source for new fructanase and fructosyltransferases with potential application in the tequila and food industry.

Purification and substrate specificities of a fructanase from Kluyveromyces marxianus isolated from the fermentation process of Mezcal

A fructanase, produced by a Kluyveromyces marxianus strain isolated during the fermentation step of the elaboration process of "Mezcal de Guerrero" was purified and biochemically characterized. The active protein was a glycosylated dimer with a molecular weight of approximately 250 kDa. The specific enzymatic activity of the protein was determined for different substrates: sucrose, inulin, Agave tequilana fructan, levan and Actilight® and compared with the activity of Fructozyme®. The hydrolysis profile of the different substrates analyzed by HPAEC-PAD showed that the enzyme has different affinities over the substrates tested with a sucrose/inulin enzymatic activity ratio (S/I) of 125. For the hydrolysis of Agave tequilana fructans, the enzyme also showed a higher enzymatic activity and specificity than Fructozyme®, which is important for its potential application in the tequila industry.

Effects of the addition of different nitrogen sources in the tequila fermentation process at high sugar concentration

AIMS

To study the effect of the addition of different nitrogen sources at high sugar concentration in the tequila fermentation process.

METHODS AND RESULTS

Fermentations were performed at high sugar concentration (170 g l(-1)) using Agave tequilana Weber blue variety with and without added nitrogen from different sources (ammonium sulfate; glutamic acid; a mixture of ammonium sulfate and amino acids) during the exponential phase of growth. All the additions increased the fermentation rate and alcohol efficiency. The level of synthesis of volatile compounds depended on the source added. The concentration of amyl alcohols and isobutanol were decreased while propanol and acetaldehyde concentration increased.

CONCLUSIONS

The most efficient nitrogen sources for fermentation rate were ammonium sulfate and the mixture of ammonium sulfate and amino acids. The level of volatile compounds produced depended upon types of nitrogen. The synthesis of some volatile compounds increased while others decreased with nitrogen addition.

SIGNIFICANCE AND IMPACT OF THE STUDY

The addition of nitrogen could be a strategy for improving the fermentation rate and efficiency in the tequila fermentation process at high sugar Agave tequilana concentration. Furthermore, the sensory quality of the final product may change because the synthesis of the volatile compounds is modified.

Fermentation behaviour and volatile compound production by agave and grape must yeasts in high sugar Agave tequilana and grape must fermentations

Few studies have been performed on the characterization of yeasts involved in the production of agave distilled beverages and their individual fermentation properties. In this study, a comparison and evaluation of yeasts of different origins in the tequila and wine industries were carried out for technological traits. Fermentations were carried out in high (300 g l(-1)) and low (30 g l(-1)) sugar concentrations of Agave tequilana juice, in musts obtained from Fiano (white) and Aglianico (red) grapes and in YPD medium (with 270 g l(-1) of glucose added) as a control. Grape yeasts exhibited a reduced performance in high-sugar agave fermentation, while both agave and grape yeasts showed similar fermentation behaviour in grape musts. Production levels of volatile compounds by grape and agave yeasts differed in both fermentations.

Increasing fermentation efficiency at high sugar concentrations by supplementing an additional source of nitrogen during the exponential phase of the tequila fermentation process

In the tequila industry, fermentation is traditionally achieved at sugar concentrations ranging from 50 to 100 g x L(-1). In this work, the behaviour of the Saccharomyces cerevisiae yeast (isolated from the juices of the Agave tequilana Weber blue variety) during the agave juice fermentation is compared at different sugar concentrations to determine if it is feasible for the industry to run fermentation at higher sugar concentrations. Fermentation efficiency is shown to be higher (above 90%) at a high concentration of initial sugar (170 g x L(-1)) when an additional source of nitrogen (a mixture of amino acids and ammonium sulphate, different than a grape must nitrogen composition) is added during the exponential growth phase.

Optimization of astaxanthin production by Phaffia rhodozyma through factorial design and response surface methodology

Sequential methodology based on the application of three types of experimental designs was used to optimize the astaxanthin production of the mutant strain 25-2 of Phaffia rhodozyma in shake flask cultures. The first design employed was a factorial design 2(5), where the factors studied were: pH, temperature, percent of inoculum, carbon and nitrogen concentrations, each one at two levels. This design was performed in two medium types: rich YM medium and minimal medium, based on date juice (Yucca medium). With this first design the most important factors were determined (carbon concentration and temperature) that were used in the second experimental strategy: the method of steepest ascent was applied in order to rapidly approach the optimum. Finally, a second-order response surface design was applied using temperature and carbon concentration as factors. The optimal conditions stimulating the highest astaxanthin production were: 19.7 degrees C temperature; 11.25 g l(-1) carbon concentration; 6.0 pH; 5% inoculum and 0.5 g l(-1) nitrogen concentration. Under these conditions the astaxanthin production was 8100 microg l(-1), 92% higher than the production under the initial conditions.

Effects of pulse addition of carbon sources on continuous cultivation of Escherichia coli containing a recombinant E. coli gapA gene

At high glucose concentrations, Escherichia coli produces acetate (Crabtree effect). To look for the influence of glucose and/or acetate in the medium on the expression of a recombinant gene in E. coli, the effect of a pulse addition of glucose, on transcription of a cloned E. coli gapA gene and the resulting glyceraldehyde-3P-dehydrogenase activity (GAPDH), was tested during continuous cultivation of E. coli HB101 transformed with the plasmid pBR::EcogapA. Stable continuous cultures were established in a semi-synthetic medium supplemented with 5 g/L of glucose. After the addition of 7 g of glucose within a few seconds, gapA gene expression was strongly and very rapidly induced. As shown by primer-extension analysis, promoter P1, one of the four transcriptional promoters of the gapA gene, was strongly activated, and GAPDH activity increased. However, after rapid glucose consumption, acetate was produced and acetate concentrations above 2 g/L induced stress conditions. This is shown by a strong activation of promoter P2, that is recognized by the stress specific Esigma32 RNA polymerase. During this period, the total cellular RNA content was strongly diminished. Later, when acetate was partially consumed a high level of total RNA was restored, translation was efficient and a regular increase of the GAPDH-specific activity was observed. The transitions between glucose metabolism, acetate production and the end of acetate consumption, were marked by large increases in RNase and protease activities. For comparison, pulse-addition experiments were also performed with serine and alanine. A transient increase of GAPDH production associated with an increase in biomass was also found for serine that can be utilized as an energy source, whereas the addition of alanine, which is only incorporated into newly synthesized proteins, did not increase GAPDH production. The implication of these data for overproduction of recombinant proteins in E. coli is discussed.

Glucose and acetate influences on the behavior of the recombinant strain Escherichia coli HB 101 (GAPDH)

This study highlights data about the production of a recombinant protein (glyceraldehyde-3-phosphate dehydrogenase) by E. coli HB 101 (GAPDH) during batch and fed-batch fermentations in a complex medium. From a small number of experiments, this strain has been characterized in terms of protein production performance and glucose and acetate influences on growth and recombinant protein production. The present results show that this strain is suitable for recombinant protein production, in fed-batch culture 55 g L-1 of biomass and 6 g L-1 of GAPDH are obtained. However this strain, and especially GAPDH overproduction is sensitive to glucose availability. During fermentations, maximum yields of GAPDH production have been obtained in batch experiments for glucose concentration of 10 g L-1, and in fed-batch experiments for glucose availability of 10 g h-1 (initial volume 1.5 L). The growth of the strain and GAPDH overproduction are also inhibited by acetate. Moreover acetate has been noted as an activator of its own formation.