Dynamics of yeast immobilized-cell fluidized-bed bioreactors systems in ethanol fermentation from lactose-hydrolyzed whey and whey permeate

Cheese-whey permeate improves the fitness of Escherichia coli cells during recombinant protein production

BACKGROUND

Escherichia coli cells are the most frequently used hosts in recombinant protein production processes and mainly require molecules such as IPTG or pure lactose as inducers of heterologous expression. A possible way to reduce the production costs is to replace traditional inducers with waste materials such as cheese whey permeate (CWP). CWP is a secondary by-product generated from the production of the valuable whey proteins, which are obtained from ultrafiltration of cheese whey, a main by-product of the dairy industry, which is rich in lactose.

RESULTS

The effects of CWP collected from an Italian plant were compared with those of traditional inducers on the production of two model proteins (i.e., green fluorescent protein and the toxic Q55 variant of ataxin-3), in E. coli BL21 (DE3) cells. It was found that the high lactose content of CWP (165 g/L) and the antioxidant properties of its micronutrients (vitamins, cofactors and osmolytes) sustain production yields similar to those obtained with traditional inducers, accompanied by the improvement of cell fitness.

CONCLUSIONS

CWP has proven to be an effective and low-cost alternative inducer to produce recombinant proteins. Its use thus combines the advantage of exploiting a waste product with that of reducing the production costs of recombinant proteins.

Past, Present, and Future Perspectives on Whey as a Promising Feedstock for Bioethanol Production by Yeast

Concerns about fossil fuel depletion and the environmental effects of greenhouse gas emissions have led to widespread fermentation-based production of bioethanol from corn starch or sugarcane. However, competition for arable land with food production has led to the extensive investigation of lignocellulosic sources and waste products of the food industry as alternative sources of fermentable sugars. In particular, whey, a lactose-rich, inexpensive byproduct of dairy production, is available in stable, high quantities worldwide. This review summarizes strategies and specific factors essential for efficient lactose/whey fermentation to ethanol. In particular, we cover the most commonly used strains and approaches for developing high-performance strains that tolerate fermentation conditions. The relevant genes and regulatory systems controlling lactose utilization and sources of new genes are also discussed in detail. Moreover, this review covers the optimal conditions, various feedstocks that can be coupled with whey substrates, and enzyme supplements for increasing efficiency and yield. In addition to the historical advances in bioethanol production from whey, this review explores the future of yeast-based fermentation of lactose or whey products for beverage or fuel ethanol as a fertile research area for advanced, environmentally friendly uses of industrial waste products.

Characterization of Yeasts Isolated from Parmigiano Reggiano Cheese Natural Whey Starter: From Spoilage Agents to Potential Cell Factories for Whey Valorization

Whey is the main byproduct of the dairy industry and contains sugars (lactose) and proteins (especially serum proteins and, at lesser extent, residual caseins), which can be valorized by the fermentative action of yeasts. In the present study, we characterized the spoilage yeast population inhabiting natural whey starter (NWS), the undefined starter culture of thermophilic lactic acid bacteria used in Parmigiano Reggiano (PR) cheesemaking, and evaluated thermotolerance, mating type, and the aptitude to produce ethanol and bioactive peptides from whey lactose and proteins, respectively, in a selected pool of strains. PCR-RFLP assay of ribosomal ITS regions and phylogenetic analysis of 26S rDNA D1/D2 domains showed that PR NWS yeast population consists of the well-documented Kluyveromyces marxianus, as well as of other species (Saccharomyces cerevisiae, Wickerhamiella pararugosa, and Torulaspora delbrueckii), with multiple biotypes scored within each species as demonstrated by (GTG)₅-based MSP-PCR. Haploid and diploid K. marxianus strains were identified through MAT genotyping, while thermotolerance assay allowed the selection of strains suitable to grow up to 48 °C. In whey fermentation trials, one thermotolerant strain was suitable to release ethanol with a fermentation efficiency of 86.5%, while another candidate was able to produce the highest amounts of both ethanol and bioactive peptides with potentially anti-hypertensive function. The present work demonstrated that PR NWS is a reservoir of ethanol and bioactive peptides producer yeasts, which can be exploited to valorize whey, in agreement with the principles of circularity and sustainability.

Performance of xylose-fermenting yeasts in oat and soybean hulls hydrolysate and improvement of ethanol production using immobilized cell systems

We investigated the fermentation of a mixture of oat and soybean hulls (1:1) subjected to acid (AH) or enzymatic (EH) hydrolyses, with both showing high osmotic pressures (> 1200 Osm kg-1) for the production of ethanol. Yeasts of genera Spathaspora, Scheffersomyces, Sugiymaella, and Candida, most of them biodiverse Brazilian isolates and previously untested in bioprocesses, were cultivated in these hydrolysates. Spathaspora passalidarum UFMG-CM-469 showed the best ethanol production kinetics in suspended cells cultures in acid hydrolysate, under microaerobic and anaerobic conditions. This strain was immobilized in LentiKats® (polyvinyl alcohol) and cultured in AH and EH. Supplementation of hydrolysates with crude yeast extract and peptone was also performed. The highest ethanol production was obtained using hydrolysates supplemented with crude yeast extract (AH-CYE and EH-CYE) showing yields of 0.40 and 0.44 g g-1, and productivities of 0.39 and 0.29 g (L h)-1, respectively. The reuse of the immobilized cells was tested in sequential fermentations of AH-CYE, EH-CYE, and a mixture of acid and enzymatic hydrolysates (AEH-CYE) operated under batch fluidized bed, with ethanol yields ranging from 0.31 to 0.40 g g-1 and productivities from 0.14 to 0.23 g (L h)-1. These results warrant further research using Spathaspora yeasts for second-generation ethanol production.

Porungo cheese whey: β-galactosidase production, characterization and lactose hydrolysis

Abstract This study evaluated the lactose hydrolysis by immobilized β-galactosidase, which was produced by Kluyveromyces marxianus using porungo cheese whey as substrate. Initially, the yeast was cultivated in porungo cheese medium at 30 °C and 200 rpm, showing a maximal β-galactosidase production of 14.19 U mL-1. The crude extract obtained was used to evaluate the enzymatic hydrolysis in lactose solution. The optimal pH and temperature of the free and immobilized enzyme was investigated, whereas the lactose hydrolysis was carried out using two enzyme solutions (total activities of 2 U and 6 U) for both forms of the biocatalyst. Ca-alginate immobilization of β-galactosidase increased optimal temperature range to 40 °C, compared to the value for the free enzyme, which was 37 °C. The optimal pH was also increased by immobilization to 7.0, from pH 6.5 observed for the free enzyme. The highest lactose hydrolysis conversion was 15.82% using 6 U of free enzyme and 13.77% for 2 U of immobilized enzyme. Although, free enzyme showed higher conversion rates in the initial reaction time, the immobilized enzyme kept operational stability throughout reaction time, suggesting the advantage of using this technology. The use of porungo cheese whey allowed to aggregate value to this agro-industrial by-product, with the concomitant production of β-galactosidase to be used in the food industry chain itself.

Batch and Fed-Batch Ethanol Fermentation of Cheese-Whey Powder with Mixed Cultures of Different Yeasts

Eight yeast strains of Lachancea thermotolerans, Kluyveromyces marxianus, and Kluyveromyces waltii have been tested for their ability to ferment lactose into ethanol in mashes containing 10% (w/v) cheese whey powder (CWP). The K. marxianus NCAIM Y00963 achieved 3.5% (v/v) ethanol concentration at 96–120 h of fermentation. The ethanol production by the selected lactose-positive strains and the well-known ethanologenic Saccharomyces cerevisiae (Levuline Fb) in mixed culture was also investigated at different CWP concentrations and inoculation techniques in batch mode. The mixed culture in an equal ratio (1:1) of cell counts of K. marxianus and S. serevisiae showed an increase in lactose conversion rate. The two yeast strains in a ratio of 3:1 (three-quarters of K. marxianus and a quarter of S. cerevisiae in a total of 4.5 × 1010 cells) resulted in 72.33% efficiency of lactose bioconversion and 7.6% (v/v) ethanol production at 17.5% (w/v) of CWP concentration. In the repeated inoculation process, with the addition of three-quarter part of 3:1 ratio of mixed culture (3.3 × 1010 cells of K. marxianus) into 150 mL CWP mash at initiation and the rest quarter part (1.2 × 1010 cells of S. cerevisiae) at 24 h, 8.86% (v/v) ethanol content with 87.5% efficiency of lactose conversion was reached. Both the ethanol concentration and efficiency of bioconversion were increased to 10.34% (v/v) and 92%, respectively, by combination with fed-batch fermentation technology. Our results can serve a very good basis for the development of industrial technology for the utilization of cheese whey.