High Fermentation Temperature Research Articles

Innovative Analogs of Unpasteurized Kombucha Beverages: Comparative Analysis of Mint/Nettle Kombuchas, Considering Their Health-Promoting Effect, Polyphenolic Compounds and Chemical Composition.

Increasing demand for functional beverages is attracting consumers' attention and driving research to expand our knowledge of fermentation using symbiotic culture of bacteria and yeast (SCOBY) and demonstrate the health effects of consuming kombucha. The objective of this study was to develop innovative recipes for unpasteurized mint/nettle kombucha analogs, and to compare the products obtained under varying conditions in terms of chemical composition, bioactive polyphenols and health-promoting activity. Four variants of kombucha beverages (K1-K4), differing in the addition of sucrose and fermentation temperature, were formulated. The fermentation process provided data indicating the increase of antidiabetic, anti-inflammatory and anticholinergic properties, while a decrease in antioxidant capacity was observed. The content of polyphenolics was the highest on the seventh day of fermentation. A higher fermentation temperature and a larger amount of sucrose accelerated the fermentation process, which may be crucial for shortening the production time of kombucha drinks.

Intensification of high-gravity brewer’s wort fermentation process with the use of microelements

In high-gravity brewing, conditions arise that adversely affect the yeast. These are high osmotic pressure, high fermentation temperature, high ethanol content. As a result of these unfavorable factors, the intensity of yeast reproduction and the rate of fermentation decrease, the duration of the process increases, the degree of fermentation decreases, which leads to a change in the taste and aroma profile of the drink. Cofactors of important enzymes and stress modulators are microelement ions, the optimal content of which can be provided by adding appropriate salts to the wort. In this work, the influence of calcium and zinc on the fermentation of high-gravity beer wort with the participation of Saccharomyces cerevisiae yeast strain Saflager W-34/70 was investigated. The optimal dosage of CaCl2 and ZnSO4 salts was determined, which is 5.0 and 0.1 mg/dm3, respectively. It was established that adding CaCl2 to the wort leads to an increase in the rate of fermentation by 21.9 %, the apparent and actual degree of fermentation by 17.8 and 17.0 %, respectively. At the same time, the ethanol content in young beer increases by 19.1 %, the content of visible and actual extract decreases by 28.8 and 17.5 %, respectively, and the biomass of yeast accumulated during fermentation increases by 14.0 %. When using ZnSO4, the changes in the values of all these indicators are significantly smaller and lie in the range of 3.2‒5.8 %. Other physical-chemical parameters of the studied samples of young beer, namely acidity, pH value, content of vicinal diketones, do not undergo significant changes. To enhance the growth and metabolism of yeast under adverse conditions that occur during high-gravity brewing, it is recommended to add CaCl2 to beer wort in the amount of 5.0 mg/dm3. This will make it possible to reduce the duration of fermentation of wort with a dry matter content of 18 % at a temperature of 15 ℃ by 1.5 days (21 %)

Effect of addition of yeasts and enzymes during fermentation on physicochemical quality of fine aroma cocoa beans

Theobroma cacao is a recognized crop worldwide within the market for raw materials or processed products. Cocoa beans quality, industrial transformation and health benefits have been widely studied, but there are few studies on the fermentation process and even less on Ecuadorian cacao. In Latin America, this crop plays a very important role from an ecological and social viewpoint. Production is usually carried out by local farmers who also perform the natural fermentation of the beans, without specific management, which represents a challenge in terms of reliability and batch-to-batch homogeneity. This drawback can be effectively addressed by controlling the fermentation conditions. In addition, certain enzymes have the potential to improve the fermentation process. The aim of this work was to study the effect of using yeasts and/or enzymes during fermentation on the physicochemical quality characteristics of cocoa beans. Two trials were carried out, the first used yeasts (Saccharomyces cerevisiae), with and without molasses, and the second used enzymes (Polyphenoloxidase and Pectintranseliminase). During the fermentation process there was not external temperature control, although cocoa beans mass temperature was assessed. After the assay, the cutting test and physicochemical variables (percentage of testa, testa and cotyledon pH, moisture, ash, acidity, protein and fat contents) were evaluated. The yeasts trial stood out as the most favorable option, showing better fermentation in the cutting test, a slight increase in protein content and lower moisture. The inclusion of enzymes in the trials resulted in higher fermentation temperatures and fat content of the beans, but the samples showed lower fermentation percentage, higher moisture and mold presence, as enzymes make it difficult to completely dry the samples. It can be concluded that the addition of yeasts and/or enzymes influences fermentation and could improve the process in order to obtain high quality cocoa beans.

Sorbitol production from mixtures of molasses and sugarcane bagasse hydrolysate using the thermally adapted Zymomonas mobilis ZM AD41

Byproducts from the sugarcane manufacturing process, specifically sugarcane molasses (SM) and sugarcane bagasse (SB), can be used as alternative raw materials for sorbitol production via the biological fermentation process. This study investigated the production of sorbitol from SM and sugarcane bagasse hydrolysate (SBH) using a thermally adapted Zymomonas mobilis ZM AD41. Various combinations of SM and SBH on sorbitol production using batch fermentation process were tested. The results revealed that SM alone (FM1) or a mixture of SM and SBH at a ratio of 3:1 (FM2) based on the sugar mass in the raw material proved to be the best condition for sorbitol production by ZM AD41 at 37 °C. Further optimization conditions for sorbitol production revealed that a sugar concentration of 200 g/L and a CaCl2 concentration of 5.0 g/L yielded the highest sorbitol content. The maximum sorbitol concentrations produced by ZM AD41 in the fermentation medium containing SM (FM1) or a mixture of SM and SBH (FM2) were 31.23 and 30.45 g/L, respectively, comparable to those reported in the literature using sucrose or a mixture of sucrose and maltose as feedstock. These results suggested that SBH could be used as an alternative feedstock to supplement or blend with SM for sustainable sorbitol production. In addition, the fermentation conditions established in this study could also be applied to large-scale sorbitol production. Moreover, the thermally adapted Z. mobilis ZM AD41 is also a promising sorbitol-producing bacterium for large-scale production at a relatively high fermentation temperature using agricultural byproducts, specifically SM and SB, as feedstock, which could reduce the operating cost due to minimizing the energy required for the cooling system.

Comparison of the Antioxidant and Sensorial Properties of Kvass Produced from Mountain Rye Bread with the Addition of Selected Plant Raw Materials

Consumers’ growing awareness of healthy nutrition results in an increase in demand for the production of beverages with health-promoting properties. An example of such a product is kvass produced in the fermentation process. This research aimed to determine the impact of plant additives on the antioxidant and sensorial properties of kvass made from bread based on mountain rye flour. The bread extract was fermented at different temperatures (28 and 34 °C). Additives of 3, 5, and 10% were used in the tests, which included black chokeberry juice and infusion, sea buckthorn fruit juice and infusion, and peppermint leaf infusion. A higher fermentation temperature in the production process resulted in an improvement in the organoleptic and antioxidant properties of the tested kvasses. The highest antioxidant activity was demonstrated by kvass with the addition of 10% black chokeberry juice (0.734 µmol Trolox g−1 (ABTS), 4.90 µmol of Trolox g−1 (DPPH)), and a peppermint leaf infusion (0.773 µmol Trolox g−1 (ABTS), 4.71 µmol Trolox g−1 (DPPH)). The conditions of kvass production and the type and amount of the additive influenced the selected physicochemical parameters of the obtained kvasses. The chromatographic analysis confirmed the content of 13 phenolic compounds in kvass with the addition of black chokeberry juice, which was 1.68–1.73 mg/100 mL of the finished product with a 10% share of the additive. The 11 phenolic compounds in kvass with the addition of peppermint infusion were confirmed for 7.65–6.86 mg/100 mL of the finished product with 10% of the additive. Kvass enriched with additives from black chokeberry fruit and peppermint leaves may be a promising new category of functional beverages with health-promoting properties resulting from the content of polyphenol compounds. It could be a better base for enrichment with raw materials that are richer in these compounds than pasteurized products.

Metabolic engineering of Thermoanaerobacterium aotearoense strain SCUT27 for biofuels production from sucrose and molasses

BackgroundSucrose-rich sugarcane trash surpasses 28 million tons globally per year. Effective biorefinery systems could convert these biomasses to bioproducts, such as bioethanol from sugarcane sucrose in Brazil. Thermophilic microbes for biofuels have attracted great attention due to their higher fermentation temperature and wide substrate spectrum. However, few thermophiles using sucrose or molasses for biofuels production was reported. Thermoanaerobacterium aotearoense SCUT27 has been considered as an efficient ethanol producer, but it cannot directly utilize sucrose. In this study, various sucrose metabolic pathways were introduced and analyzed in Thermoanaerobaterium.ResultsThe sucrose-6-phosphate hydrolase (scrB), which was from a screened strain Thermoanaerobacterium thermosaccharolyticum G3-1 was overexpressed in T. aotearoense SCUT27 and endowed this strain with the ability to utilize sucrose. In addition, overexpression of the sucrose-specific PTS system (scrA) from Clostridium acetobutylicum accelerated the sucrose transport. To strengthen the alcohols production and substrates metabolism, the redox-sensing transcriptional repressor (rex) in T. aotearoense was further knocked out. Moreover, with the gene arginine repressor (argR) deleted, the ethanologenic mutant P8S10 showed great inhibitors-tolerance and finally accumulated ~ 34 g/L ethanol (a yield of 0.39 g/g sugars) from pretreated cane molasses in 5 L tank by fed-batch fermentation. When introducing butanol synthetic pathway, 3.22 g/L butanol was produced by P8SB4 with a yield of 0.44 g alcohols/g sugars at 50℃. This study demonstrated the potential application of T. aotearoense SCUT27 for ethanol and butanol production from low cost cane molasses.ConclusionsOur work provided strategies for sucrose utilization in thermophiles and improved biofuels production as well as stress tolerances of T. aotearoense SCUT27, demonstrating the potential application of the strain for cost-effective biofuels production from sucrose-based feedstocks.

Microbial Diversity of Anaerobic-Fermented Coffee and Potential for Inhibiting Ochratoxin-Produced Aspergillus niger.

Coffee flavor considerably depends on the fermentation process, with contributing factors including fermentation temperature, oxygen concentration, and microbial diversity. Efficient controlling of the fermentation can improve the quality of coffee beverages. Therefore, several studies on coffee fermentation processes have been conducted in various regions. The objective of this study was to assess the microbial diversity of coffee beans undergoing anaerobic fermentation at various temperatures (4 °C or 37 °C) and fermentation durations (12 h or 36 h) using full-length 16S rRNA sequencing. This analysis aimed to evaluate the inhibitory effects of the fermented metabolites against ochratoxin-producing Aspergillus niger. From our results, Acetobacter was identified as the dominant microbial community at higher fermentation temperatures, whereas Leuconostoc and Gluconobacter were the dominant genera at lower temperatures. However, at lower temperatures, changes in microbial communities were relatively slow. This study expands our knowledge of the microbial diversity involved in the anaerobic fermentation of coffee beans in Taiwan. The findings of this study can be used in future research to cultivate microorganisms linked to the quality and improve the quality of coffee beverages through fermentation.

Chemical Composition and Bioactivity of Laboratory-Fermented Bee Pollen in Comparison with Natural Bee Bread.

Bee bread is a valuable product obtained from the hive on a relatively small scale, while bee pollen is more easily available. Therefore, an effective laboratory method of converting pollen into a bee bread substitute is desired. The aim of the research was to verify the influence of selected factors (temperature, ultrasound) on the quality of obtained product using Lactobacillus rhamnosus inoculum. The composition of the fermented pollen was analyzed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Raman spectroscopy, and SDS-PAGE and compared to natural bee bread and the original pollen. In vitro biological activity was assessed as antioxidant activity using a yeast model (BY4741 and sod1∆ strains). Fermentation of pollen occurred spontaneously and after inoculation, as demonstrated by lower pH and higher lactic acid content. Raman spectroscopy and ICP-OES confirmed changes in composition compared to the initial pollen. Compared to bee bread, the fermented pollen showed a higher content of polyphenols and comparable antioxidant activity; moreover, it accelerated yeast growth rate. In addition, a protective effect was observed for Cu/Zn-superoxide dismutase 1 (sod1∆ yeast mutant exposed to hydrogen peroxide-induced oxidative stress). The higher fermentation temperature (25 °C) produces a more bee-bread-like product, while the use of ultrasound and starter culture seems to have no positive effect.

Construction of a dynamic model to predict the growth of Staphylococcus aureus and the formation of enterotoxins during Kazak cheese maturation.

Staphylococcus aureus is a common pathogen found in cheese whose Staphylococcal enterotoxins (SE) are the main pathogenic factors that cause food poisoning. The objective of this study was to construct two models to evaluate the safety of Kazak cheese products in terms of composition, changes in S. aureus inoculation amount, Aw, fermentation temperature during processing, and growth of S. aureus in the fermentation stage. A total of 66 experiments comprised of five levels of inoculation amount (2.7-4 log CFU/g), five levels of Aw (0.878-0.961), and six levels of fermentation temperature (32-44°C) were performed to confirm the growth of S. aureus and the presence of SE limit conditions. Two artificial neural networks (ANN) successfully described the relationship between the assayed conditions and the growth kinetic parameters (maximum growth rates and lag times) of the strain. The good fitting accuracy (R2 values were 0.918 and 0.976, respectively) showed that the ANN was appropriate. Experimental results showed fermentation temperature had the greatest influence on the maximum growth rate and lag time, followed by the Aw and inoculation amount. Furthermore, a probability model was built to predict the production of SE by logistic regression and neural network under the assayed conditions, which proved to be concordant in 80.8-83.8% of the cases with the observed probabilities. The maximum total number of colonies predicted by the growth model in all combinations detected with SE exceeded 5 log CFU/g. Within the range of variables, the minimum Aw for predicting SE production was 0.938, and the minimum inoculation amount for predicting SE production was 3.22 log CFU/g. Additionally, as competition between S. aureus and lactic acid bacteria (LAB) occurs in the fermentation stage, higher fermentation temperatures are conducive to the growth of LAB, which can reduce the risk of S. aureus producing SE. This study can help manufacturers to make decisions on the most appropriate production parameters for Kazak cheese products and to prevent S. aureus growth and SE production.

Changes in the physicochemical properties and metabolites of Myeolchi-jeot (salted-fermented anchovy) based on fermentation time

Food fermentation enables long-term food storage; however, the safety and quality of fermented food varies according to the applied fermentation parameters. Despite advances in fishery product fermentation, few studies have addressed possible temperature-dependent changes in the quality and stability of Myeolchi-jeot(MJ), following long-term fermentation. Herein, physicochemical and microbiological changes in MJ were investigated following long-term fermentation at low(10 °C; LT-MJ) and high(30 °C; HT-MJ) temperatures and performed metabolic profiling to evaluate these alterations at the molecular level. Both fermentation temperatures showed continuous increases in amino nitrogen(AN) and total nitrogen(TN) from 15 to 480 days. The AN and TN levels were higher in HT-MJ than in LT-MJ, as fermentation time increased, suggesting higher activities of proteases or halophilic bacteria at higher fermentation temperatures. The amino acids detected in MJ were tryptophan, tyrosine, histidine, arginine, lysine, and ornithine, and their contents increased with fermentation time. Changes in volatile basic nitrogen and histamine contents were higher in HT-MJ relative to LT-MJ, and metabolomics analysis revealed a continuous increase in histamine during fermentation. The quality of HT-MJ was decreased compared to that of LT-MJ, suggesting that the quality and safety of fermented seafood products from anchovy might be ensured by low-temperature fermentation for ≤1 year.

Revealing the co-fermentation of Saccharomyces cerevisiae and Schizosaccharomyces pombe on the quality of cider based on the metabolomic and transcriptomic analysis

This study aimed to explore the interaction between S. cerevisiae and S. pombe on the quality of cider fermentation based on metabolic characteristics and transcriptional changes in pure and mixed cultures. The relatively high fermentation temperature (28 °C) was beneficial to the growth of yeasts and the acceleration of fermentation progress, while ensuring safety and quality of the cider. Additionally, the co-fermentation degraded malic acid to reduce the acidity, adjusted the content of polyphenols to decrease the bitterness, and improved the diversity and richness of volatile compounds. The transcriptomic analysis revealed that most of differentially expressed genes in co-fermentation process were mainly enriched in the carbohydrate and amino acids metabolism, including TCA cycle, pyruvate metabolism, glycine, serine and threonine metabolism when compared to the other two single fermentation groups. The results provided the useful knowledge for the manipulation of fermentation process with S. pombe and S. cerevisiae in cider.

Influence of different fermentation conditions on the analytical and sensory properties of craft beers: Hopping, fermentation temperature and yeast strain

The influence of the hopping method (boiling stage hopping or dry hopping), the fermentation temperature (12 and 18 °C), and the yeast strain (five different yeasts) on the physical-chemical characteristics (bitterness, color, alcohol content), the phenolic content, the volatile compounds, as well as the sensory profile of beers, has been studied. The hopping method was much more influential than temperature and yeast strain, however, its influence on volatile content clearly depended on the fermentation temperature, with a higher content of volatile compounds, when a higher fermentation temperature was employed. For phenolic compounds, dry hopping produced less polyphenol-rich beers, regardless of the fermentation temperature. Sensorily, it resulted in more floral and fruity beers than those produced by boiling stage hopping, which exhibited a more intense toasted aroma. Concerning yeast strain, no relationship could be established between the type of commercial yeast (bottom or top-fermenting) and the resulting volatile content.

Reduction of biogenic amines accumulation with improved flavor of low-salt fermented bream (Parabramis pekinensis) by two-stage fermentation with different temperature

How to ensure low-salt fermented food safety with good flavor under non-acidic conditions is a challenge. Temperature is one of the key environmental parameters that affect the growth of microorganism and enzyme activity. The effects of fermentation for 4 days at 4 °C, 10 °C, 20 °C and 20-10 °C (20 °C for 2 days followed by 10 °C for 2 days) on the flavor, microbial and physicochemical properties of low-salt fermented bream were investigated. Results showed that compared with 4 °C-fermentation, higher fermentation temperature (10 °C, 20 °C, 20-10 °C) could accelerate protein degradation and facilitate the formation of flavor substances during fermentation of bream. The volatile flavor compounds of 20 °C and 20-10 °C two-stage fermentation groups were similar. After 4 days of fermentation, highest content of alcohols, ketones and esters were observed in two-stage fermentation group (20-10 °C). For comparison with 20 °C-fermentation, two-stage fermentation (20-10 °C) reduced the contents of total volatile basic nitrogen, cadaverine, putrescine and total biogenic amines significantly (p < 0.05), and inhibited the growth of harmful microorganisms (Pseudomonas and Coliforms). Results suggested that two-stage fermentation with different temperature provided a potential method that facilitated improving the flavor and safety of low-salt fermented bream.

Impact of fermentation temperature and grape solids content on the chemical composition and sensory profiles of Cabernet Sauvignon wines made from flash détente treated must fermented off-skins

This study investigated the color, phenolic, polysaccharide, volatile and sensory profiles of Cabernet Sauvignon wines made from flash détente (FD) treated musts fermented at different temperatures (16, 24 or 32 °C), with and without suspended grape solids. Low fermentation temperature and low solids content increased the concentration of esters, whereas the opposite conditions increased the concentration of fusel alcohols, polysaccharides and glycerol. Higher fermentation temperatures also increased linalool concentration independent of solids content. Traditional maceration fermentation conditions gave the highest concentration of fusel alcohols and 1-hexanol relative to FD treatments. Pre-fermentation removal of grape solids from FD juice created wines with increased red fruit and confectionery attributes, whereas inclusion of 3.5% grape solids increased dark fruit notes. In comparison, control wines had significantly higher green and savory attributes compared to wines from FD treatments. Research findings demonstrated the potential for FD to be used to create differentiated red wine styles.

Optimal Control Applied to Oenological Management of Red Wine Fermentative Macerations

The management of wineries for industrial red winemaking is limited by the capacity and availability of fermentation tanks over the harvest season. The winemakers aim to optimize the wine quality, the fermentative maceration length, and the fermentation tank’s productive cycle simultaneously. Maceration in varietal wine production is carried out until a specific sugar content (digging-out point) is attained, finishing before alcoholic fermentation. Winemakers have found that by trial and error handling of the digging-out point, they can improve the winery capacity and production cost. In this work, we develop an optimal control problem for managing the digging-out point considering two objectives associated with process efficiency and costs. A good compromise between these objectives was found by applying multi-criteria decision-making (MCDM) techniques and the knee point. Two control strategies were compared: free nutrition and traditional nutrition. TOPSIS and LINMAP algorithms were used to choose the most suitable strategy that coincided with the knee point. The preferred option was nitrogen addition only at the beginning of fermentation (6.6–10.6 g/hL of DAP) and a high fermentation temperature (30 °C), yielding the desired digging-out point with a small error (6–9 g/L).

Effects of initial temperature on microbial community succession rate and volatile flavors during Baijiu fermentation process

The importance of fermentation temperature has been highlighted as it correlates with biodiversity and microbial metabolism for a microbial community. In this study, microbial community succession and volatile flavors during sauce-flavor Baijiu fermentation at different initial temperatures (LT group: 28 ± 2 °C and HT group: 37 ± 2 °C) were investigated using Illumina Miseq sequencing and gas chromatography-mass spectrometry (GC-MS). First, we found that different initial temperatures had a significant effect on fermentation parameters (P < 0.001); specifically, a higher initial temperature increased the accumulation of acetic acid and decreased the production of ethanol. Second, the microbial communities were characterized by decreased α-diversity and increased β-diversity (P < 0.05) during heap fermentation. A higher initial temperature accelerated the increase in Lactobacillus and led to a faster microbial succession rate. Lactobacillus could be used as microbial markers of microbial succession rate in sauce-flavor Baijiu fermentation. Next, we found that acetic acid drove microbial succession under a higher fermentation temperature. Molecular ecological network analysis showed that different fermentation temperatures affected microbial interactions. The higher temperature enhanced microbial interactions of Lactobacillus. In addition, 50 volatile flavors were identified in the fermented grains. High temperature increased the content of total acid and reduced total esters, and Lactobacillus and Saccharomyces were the important microbiota related to different flavor compounds between the two groups. Collectively, altering the initial temperature led to differences in microbial succession rates and volatile flavors in the sauce-flavor Baijiu fermentation process. Therefore, these results are valuable for exploring quality control and management strategies in the spontaneous fermentation process.

Lachancea fermentati Strains Isolated From Kombucha: Fundamental Insights, and Practical Application in Low Alcohol Beer Brewing.

With a growing interest in non-alcoholic and low alcohol beer (NABLAB), researchers are looking into non-conventional yeasts to harness their special metabolic traits for their production. One of the investigated species is Lachancea fermentati, which possesses the uncommon ability to produce significant amounts of lactic acid during alcoholic fermentation, resulting in the accumulation of lactic acid while exhibiting reduced ethanol production. In this study, four Lachancea fermentati strains isolated from individual kombucha cultures were investigated. Whole genome sequencing was performed, and the strains were characterized for important brewing characteristics (e.g., sugar utilization) and sensitivities toward stress factors. A screening in wort extract was performed to elucidate strain-dependent differences, followed by fermentation optimization to enhance lactic acid production. Finally, a low alcohol beer was produced at 60 L pilot-scale. The genomes of the kombucha isolates were diverse and could be separated into two phylogenetic groups, which were related to their geographical origin. Compared to a Saccharomyces cerevisiae brewers’ yeast, the strains’ sensitivities to alcohol and acidic conditions were low, while their sensitivities toward osmotic stress were higher. In the screening, lactic acid production showed significant, strain-dependent differences. Fermentation optimization by means of response surface methodology (RSM) revealed an increased lactic acid production at a low pitching rate, high fermentation temperature, and high extract content. It was shown that a high initial glucose concentration led to the highest lactic acid production (max. 18.0 mM). The data indicated that simultaneous lactic acid production and ethanol production occurred as long as glucose was present. When glucose was depleted and/or lactic acid concentrations were high, the production shifted toward the ethanol pathway as the sole pathway. A low alcohol beer (<1.3% ABV) was produced at 60 L pilot-scale by means of stopped fermentation. The beer exhibited a balanced ratio of sweetness from residual sugars and acidity from the lactic acid produced (13.6 mM). However, due to the stopped fermentation, high levels of diacetyl were present, which could necessitate further process intervention to reduce concentrations to acceptable levels.

Protein enrichment of jackfruit peel waste through solid-state fermentation

The physical and chemical characteristics of jackfruit (Artocarpus heterophyllus Lam.) indicate the possibility of utilizing its wastes in the development of a new product, a nutritional supplement. Therefore, we aimed to study the protein enrichment of the waste from jackfruit peel by solid-state fermentation by using Saccharomyces cerevisiae and the experimental design associated to the response surface methodology in order to verify the effects of input variables (yeast concentration and fermentation temperature) on the protein increase. The yeast concentrations added to the substrate were of 1, 3 and 5% and the used temperatures were 30, 35 and 40 °C. The highest protein increase value found in the studied substrates was of 164%, which corresponded to 17.1% of crude protein, dry basis, achieved after 72 h of processing by using a higher concentration of yeast and higher fermentation temperature. Using yeast in the semi-solid medium of the waste from jackfruit peel enables obtaining a protein supplement, which can later be used as an alternative source for animal feed.

Effects of temperature on microbial succession and quality of sour meat during fermentation

Little is known about the relationship between physicochemical characteristics and bacterial community of sour meat, a traditional fermented meat product in China. In this study, temperature effects on bacterial community and quality of sour meats during fermentation were investigated. The results showed the reduction of pH, TBARS, and water content was closely related to the increase in temperature. Microbial succession, in which the dominant microorganism species found in the microbial community changes, was observed during the fermentation process of sour meat. The dominant species found in the early stages of fermentation was Lactobacillus sakei whereas the dominant species was Lactobacillus curvatus during the middle stage and Lactobacillus plantarum during the later stage. Higher temperatures were found to be related to the shift of water populations T2 (including T2b1, T2b2, T21, and T22) toward faster relaxation times. Rapid fermentation and better quality were obtained at higher fermentation temperatures (particularly at 25 °C), which might be due to increased inhibition of Enterobacteriaceae and Pseudomonas growth as well as tougher texture. Redundancy analysis (RDA) showed a close relationship between L. plantarum and desired product characteristics, which indicated that L. plantarum could be regarded as an indicator of fermentation maturation and product quality.

Selection of a new Saccharomyces yeast to enhance relevant sorghum beer aroma components, higher alcohols and esters

The selection of Saccharomyces yeast which is able to produce high amounts of relevant aroma components from sorghum wort has been scarcely explored. Furthermore, generating sorghum beer with low levels of vicinal diketones (VDKs) is a permanent concern of brewers because of the wort's low amino acid content. To address these challenges, a performant Saccharomyces cerevisiae yeast was selected based on the higher alcohols and esters it synthesizes, and conditions influencing the young beer's VDK content were studied. Our results confirm that the low amino acid content limits aromagenesis by industrial ale yeast. By contrast, the selected yeast is able to efficiently produce higher alcohols and esters and is well adapted to tropical temperatures (27 °C). The young beer obtained from 13 °P sorghum wort using the isolated strain is characterized by a higher amount of aroma-active components such as isoamyl alcohol (116.25 ± 0.38 mg/L), isoamyl acetate (1.81 ± 0.02 mg/L) and ethyl acetate (22.07 ± 0.74 mg/L). The VDK content, however, is not only yeast strain dependent; it is strongly reduced by high fermentation temperature (27 °C) and increased wort gravity.