Aeration, Agitation and Cell Immobilization on Corncobs and Oak Wood Chips Effects on Balsamic-Styled Vinegar Production

Enhancing small-scale acetification processes using adsorbed Acetobacter pasteurianus UMCC 2951 on κ-carrageenan-coated luffa sponge

Background

This study explored the utilization of luffa sponge (LS) in enhancing acetification processes. LS is known for having high porosity and specific surface area, and can provide a novel means of supporting the growth of acetic acid bacteria (AAB) to improve biomass yield and acetification rate, and thereby promote more efficient and sustainable vinegar production. Moreover, the promising potential of LS and luffa sponge coated with κ-carrageenan (LSK) means they may represent effective alternatives for the co-production of industrially valuable bioproducts, for example bacterial cellulose (BC) and acetic acid.

Methods

LS and LSK were employed as adsorbents for Acetobacter pasteurianus UMCC 2951 in a submerged semi-continuous acetification process. Experiments were conducted under reciprocal shaking at 1 Hz and a temperature of 32 °C. The performance of the two systems (LS-AAB and LSK-AAB respectively) was evaluated based on cell dry weight (CDW), acetification rate, and BC biofilm formation.

Results

The use of LS significantly increased the biomass yield during acetification, achieving a CDW of 3.34 mg/L versus the 0.91 mg/L obtained with planktonic cells. Coating LS with κ-carrageenan further enhanced yield, with a CDW of 4.45 mg/L. Acetification rates were also higher in the LSK-AAB system, reaching 3.33 ± 0.05 g/L d as opposed to 2.45 ± 0.05 g/L d for LS-AAB and 1.13 ± 0.05 g/L d for planktonic cells. Additionally, BC biofilm formation during the second operational cycle was more pronounced in the LSK-AAB system (37.0 ± 3.0 mg/L, as opposed to 25.0 ± 2.0 mg/L in LS-AAB).

Conclusions

This study demonstrates that LS significantly improves the efficiency of the acetification process, particularly when enhanced with κ-carrageenan. The increased biomass yield, accelerated acetification, and enhanced BC biofilm formation highlight the potential of the LS-AAB system, and especially the LSK-AAB variant, in sustainable and effective vinegar production. These systems offer a promising approach for small-scale, semi-continuous acetification processes that aligns with eco-friendly practices and caters to specialized market needs. Finally, this innovative method facilitates the dual production of acetic acid and bacterial cellulose, with potential applications in biotechnological fields.

Efficient conversion of cane molasses into Tremella fuciformis polysaccharides with enhanced bioactivity through repeated batch culture

Tremella fuciformis polysaccharide (TFPS) is a natural mushroom mucopolysaccharide widely used in health foods, medical care, cosmetic and surgical materials. In this study, we developed an efficient strategy for the repeated batch production of highly bioactive TFPS from the agro-industrial residue cane molasses. Cane molasses contained 39.92 % sucrose (w/w), 6.36 % fructose and 3.53 % glucose, all of which could be utilized by T. fuciformis spores, whereas, the TFPS production efficiency only reached 0.74 g/L/d. Corn cobs proved to be the best immobilized carrier that could tightly absorb spores and significantly shorten the fermentation lag period. The average yield of TFPS in eight repeated batch culture was 5.52 g/L with a production efficiency of 2.04 g/L/d. The average fermentation cycle after optimization was reduced by 61.61 % compared with the initial conditions. Compared to glucose as a carbon source, cane molasses significantly increased the proportion of low-molecular-weight TFPS (TFPS-2) in total polysaccharides from 3.54 % to 17.25 % (w/w). Moreover, TFPS-2 exhibited potent antioxidant capacity against four free radicals (O2-, ABTS+, OH, and DPPH). In conclusion, this study lays the foundation for the efficient conversion of cane molasses and production of TFPS with high bioactivity.

Evaluation of the biocontrol activity of Frateuria defendens-derived metabolites against mollicutes

Frateuria defendens is a candidate biocontrol agent that has been shown to reduce phytoplasma-related disease symptoms in grapevines and periwinkle plants. While a crude filtrate prepared from F. defendens can inhibit mollicute growth, the specific growth parameters for this bacterium, necessary to enhance this protective inhibitory response, remain unknown. Moreover, the separation of filtrate preparations from bacterial cells via centrifugation and filtration is laborious and time-consuming. As such, the present study was conducted to define the optimal growth conditions associated with maximal inhibitory activity of F. defendens and to establish a better approach to separating these bacterial cells from their secreted metabolites. To conduct these analyses, F. defendens was cultured in a range of media types, while associated inhibitory effects were tested in vitro using Spiroplasma melliferum as a model mollicute bacterium, and in planta using phytoplasma-infected periwinkle plantlets. These analyses revealed F. defendens growth patterns change based upon media composition, with filtrates prepared from a specific rich medium (S-medium) exhibiting beneficial activities, including the inhibition of S. melliferum and enhanced plant growth. When F. defendens cells were grown within semi-permeable, membrane-coated Small Bioreactor Platform (SBP) capsules, they could be more readily separated from the secreted metabolite fraction, obviating the need for filtration and/or centrifugation. This study is the first to have reported the use of SBP capsules to separate bacterial cells from their secreted metabolites under sterile conditions while retaining the ability of these metabolites to inhibit S. melliferum growth and to benefit the host plant. The results highlight promising new approaches to the effective biocontrol of phytoplasma-driven diseases in grapevines and other economically important plant species.

Comparative evaluation of the microbial diversity and metabolite profiles of Japanese-style and Cantonese-style soy sauce fermentation

Microorganisms play essential roles in flavor formation during soy sauce fermentation. Different soy sauce fermentation types significantly affect flavor formation. However, comparisons of microbial communities and metabolites between different fermentation types have been little studied. Here, we investigated variation in microbial communities, metabolite profiles, and metabolic pathways during Japanese-type (JP) and Cantonese-type (CP) fermentation. Free amino acids and volatile compound profiles varied significantly between fermentation types, with JP samples containing higher contents of esters (39.84%; p < 0.05), alcohols (44.70%; p < 0.05) in the 120 d fermentation samples. Volatile compound profiles varied significantly between fermentation types, with JP samples containing higher contents of esters, alcohols, and free amino acids (p < 0.05). Metagenomic analysis indicated that both JP and CP communities were dominated by Tetragenococcus, Staphylococcus, Weissella (bacteria), and Aspergillus (fungi), but the two communities varied differently over time. Tetragenococcus drastically increased in abundance throughout the fermentation (from 0.02 to 59.2%) in JP fermentation, whereas Tetragenococcus (36.7%) and Staphylococcus (29.7%) dominated at 120 d of fermentation in CP fermentation. Metagenomic functional profiles revealed that the abundances of most genes involved with carbohydrate, amino acid, and lipid metabolism exhibited significant differences between fermentation types (p < 0.05) during the middle to late fermentation stages. Furthermore, predicted metabolic pathways for volatile substance biosynthesis differed between JP and CP fermentation, likely explaining the differences in flavor metabolite profiles. In addition, most of the genes associated with flavor generation were affiliated with Tetragenococcus, Weissella, Staphylococcus, Bacillus, and Aspergillus, suggesting that these microbes play important roles in flavor production during soy sauce fermentation. This study significantly improves our understanding of microbial functions and their metabolic roles in flavor formation during different soy sauce fermentation processes.

Effect of alcoholic and acetous fermentations on the phenolic acids of Kei-apple (Dovyalis caffra L.) fruit

BACKGROUND

The Kei apple is a tree found on the African continent. Limited information exists on the effect of alcoholic and acetous fermentation on the phytochemicals of Kei apple. The fruit has increased concentrations of l-malic, ascorbic, and phenolic acids among other compounds. Juice was co-inoculated with Schizosaccharomyces pombe (Sp) and Saccharomyces cerevisiae (Sc) to induce alcoholic fermentation (AF). Acetous fermentation followed AF, using an acetic acid bacteria (AAB) consortium.

RESULTS

Saccharomyces cerevisiae + Sp wines and vinegars had the highest pH. Total acidity, soluble solids and l-malic acid decreased during AF and acetous fermentation, and was highest in Sc wines and vinegars. Volatile acidity (VA) concentration was highest in Sp vinegars but was not significantly different from Sc and Sc + Sp vinegars. Gallic acid was highest in Sp wines and vinegars, whereas syringic acid was highest in Sc wines and vinegars. The Sc + Sp wines were highest in caffeic, p-coumaric, and protocatechuic acids. Schizosaccharomyces pombe vinegars were highest in caffeic and p-coumaric acids. Highest concentrations of ferulic and sinapic acids were found in Sp and Sc wines, respectively. Chlorogenic acid was most abundant phenolic acid in both wines and vinegars.

CONCLUSION

Saccharomyces cerevisiae + Sp and Sc fermentation had a positive effect on most phenolic acids; Sc + AAB had an increased effect on syringic and chlorogenic acids, whereas Sp + AAB resulted in an increase in gallic, caffeic, and p-coumaric acids. The AAB selected had minimal performance with respect to VA production in comparison to commercial vinegars. Acetic acid bacteria selection for acetous fermentation should therefore be reconsidered and the decrease of certain phenolic acids during acetous fermentation needs to be investigated. © 2021 Society of Chemical Industry.

Reusability of Immobilized Cells for Subsequent Balsamic-Styled Vinegar Fermentations

Cell immobilization is a process augmentation technique aimed at improving microbial survival and activity under stressful conditions. It offers the opportunity to reuse the immobilized cells for several fermentation cycles. The present study investigated the use of recycled cells entrapped in calcium-alginate beads and cells adsorbed on corncobs (CC) and oakwood chips (OWC) in subsequent fermentation cycles for balsamic-styled vinegar (BSV) production. Sugars, pH, alcohol and total acidity were monitored during fermentation. Microbial activity and product formation declined when immobilized cells were reused for the second cycle for CC and OWC fermentations. Recycled cells entrapped in Ca-alginate beads completed the second cycle of fermentations, albeit at reduced acetification rates compared to the first cycle. Scanning electron microscope (SEM) imaging results further showed a substantial the structural integrity loss for Ca-alginate beads after the first cycle, and with minor changes in the structural integrity of CC. The OWC displayed a similar morphological structure before and after the first cycle. The sensory results showed that BSV produced using immobilized cells with Ca-alginate beads and CC was palatable, while those produced using OWC had negative attributes. Ca-alginate beads offered better protection for the fermentation consortium for culture reusability in BSV fermentations.