Unlocking the potential of spent coffee grounds via a comprehensive biorefinery approach: production of microbial oil and carotenoids under fed-batch fermentation.

The valorization of renewable feedstock to produce a plethora of value-added products could promote the transition towards a circular bioeconomy. This study presents the development of cascade processes to bioconvert spent coffee grounds (SCGs) into microbial oil and carotenoids employing sustainable practices. The stepwise recovery of crude phenolic extract and coffee oil was carried out using green or recyclable solvents, i.e., aqueous ethanol and hexane. Palmitic acid (43.3%) and linoleic acid (38.9%) were the major fatty acids in the oil fraction of SCGs. The LC-MS analysis of crude phenolic extracts revealed that chlorogenic acid dominated (45.7%), while neochlorogenic acid was also detected in substantial amounts (24.0%). SCGs free of coffee oil and phenolic compounds were subjected to microwave-assisted pretreatment under different irradiations and solvents to enhance subsequent enzymatic saccharification. Microwave/water pretreatment at 400 W, followed by enzymatic hydrolysis with proteases, hemicellulases, and cellulases, at 50 g/L initial SCGs, led to satisfying overall yields of cellulose (75.4%), hemicellulose (50.3%), and holocellulose (55.3%). Mannan was the most extractable polysaccharide followed by galactan and arabinan. SCGs hydrolysate was used in fed-batch bioreactor fermentations with Rhodosporidium toruloides to produce 24.0 g/L microbial oil and carotenoids of 432.9 µg/g biomass.

Commercialization potential of agro-based polyhydroxyalkanoates biorefinery: A technical perspective on advances and critical barriers.

The exponential increase in the use and careless discard of synthetic plastics has created an alarming concern over the environmental health due to the detrimental effects of petroleum based synthetic polymeric compounds. Piling up of these plastic commodities on various ecological niches and entry of their fragmented parts into soil and water has clearly affected the quality of these ecosystems in the past few decades. Among the many constructive strategies developed to tackle this global issue, use of biopolymers like polyhydroxyalkanoates as sustainable alternatives for synthetic plastics has gained momentum. Despite their excellent material properties and significant biodegradability, polyhydroxyalkanoates still fails to compete with their synthetic counterparts majorly due to the high cost associated with their production and purification thereby limiting their commercialization. Usage of renewable feedstocks as substrates for polyhydroxyalkanoates production has been the thrust area of research to attain the sustainability tag. This review work attempts to provide insights about the recent developments in the production of polyhydroxyalkanoates using renewable feedstock along with various pretreatment methods used for substrate preparation for polyhydroxyalkanoates production. Further, the application of blends based on polyhydroxyalkanoates, and the challenges associated with the waste valorization based polyhydroxyalkanoates production strategy is elaborated in this review work.

Prospects on bio-based 2,3-butanediol and acetoin production: Recent progress and advances.

The bio-based platform chemicals 2,3-butanediol (BDO) and acetoin have various applications in chemical, cosmetics, food, agriculture, and pharmaceutical industries, whereas the derivatives of BDO could be used as fuel additives, polymer and synthetic rubber production. This review summarizes the novel technological developments in adapting genetic and metabolic engineering strategies for selection and construction of chassis strains for BDO and acetoin production. The valorization of renewable feedstocks and bioprocess development for the upstream and downstream stages of bio-based BDO and acetoin production are discussed. The techno-economic aspects evaluating the viability and industrial potential of bio-based BDO production are presented. The commercialization of bio-based BDO and acetoin production requires the utilization of crude renewable resources, the chassis strains with high fermentation production efficiencies and development of sustainable purification or conversion technologies.

Geographical origin discrimination of "Ntopia" olive oil cultivar from Ionian islands using volatile compounds analysis and computational statistics.

The aim of the present study was to characterize the aroma profile of olive oil of the "Ntopia" (local) cultivar from the Ionian islands (Zakynthos, Kefalonia, Leukada, and Kerkyra) (Greece), and investigate whether specific volatile compounds could be considered as indicators of olive oil geographical origin, using computational statistics. In this context, 137 olive oil samples were subjected to headspace solid phase microextraction coupled to gas chromatography/mass spectrometry using the internal standard method. Computational statistics on the semi-quantitative data of olive oil samples, as rapid machine learning algorithms, showed that specific volatile compounds could be used as indicators of geographical origin of olive oil of the "Ntopia" cultivar, among the four main Ionian islands. Volatile compounds such as ethanol, pentanal, 2,4-dimethylheptane, 3,7-dimethyl-1,3,6-octatriene (E), 2,5-dimethylnonane, 1-hexanol, 6-methyl-5-hepten-2-one, octanal, dl-Limonene, acetic acid hexyl ester and dodecane could aid to the geographical origin discrimination of "Ntopia" olive oil cultivar when two (Zakynthos and Kefalonia) or four (Zakynthos, Kefalonia, Leukada and Kerkyra) Ionian islands are subjected to statistical analysis. The discrimination rate using the cross-validation method was 100% and 85.7%, respectively. These results were further evaluated using training and holdout partitions, during which a comparable classification rate was obtained. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00217-021-03863-2.

Volumetric oxygen transfer coefficient as fermentation control parameter to manipulate the production of either acetoin or D-2,3-butanediol using bakery waste.

The formation of either acetoin or D-2,3-butanediol (D-BDO) by Bacillus amyloliquefaciens cultivated on bakery waste hydrolysates has been evaluated in bioreactor cultures by varying the volumetric oxygen transfer coefficient (kLa). The highest D-BDO production (55.2 g L-1) was attained in batch fermentations with kLa value of 64 h-1. Batch fermentations performed at 203 h-1 led to the highest productivity (2.16 g L-1h-1) and acetoin production (47.4 g L-1). The utilization of bakery waste hydrolysate in fed-batch cultures conducted at kLa of 110 h-1 led to combined production of acetoin, meso-BDO and D-BDO (103.9 g L-1). Higher kLa value (200 h-1) resulted to 65.9 g L-1 acetoin with 1.57 g L-1h-1 productivity. It has been demonstrated that the kLa value may divert the bacterial metabolism towards high acetoin or D-BDO production during fermentation carried out in crude bakery waste hydrolysates.

Evaluation of 1,3-propanediol production by twoCitrobacter freundiistrains using crude glycerol and soybean cake hydrolysate.

Biodiesel production processes using soybean as feedstock generates soybean cake and crude glycerol as by-products. These by-product streams were used as sole feedstocks for the production of 1,3-propanediol (PDO) using two bacterial strains of Citrobacter freundii. Soybean cake has been converted into a nutrient-rich hydrolysate by crude enzymes produced via solid state fermentation. The effect of initial glycerol and free amino nitrogen concentration on bacterial growth and PDO production has been evaluated in batch bioreactor cultures showing that C. freundii VK-19 is a more efficient PDO producer than C. freundii FMCC-8. The cultivation of C. freundii VK-19 in fed-batch bioreactor cultures using crude glycerol and soybean cake hydrolysates led to PDO concentration of 47.4 g/L with yield and productivity of 0.49 g/g and 1.01 g/L/h, respectively. The effect of PDO, metabolic by-products, and sodium and potassium salts on bacterial growth was evaluated showing that potassium salts initially enhance bacterial growth, whereas sodium salts cause significant inhibition to bacterial growth. Soybean cake hydrolysate and crude glycerol could be utilized for PDO production, but the fermentation efficiency is influenced by the catalyst used during biodiesel production.

Improvement on bioprocess economics for 2,3-butanediol production from very high polarity cane sugar via optimisation of bioreactor operation.

This study focuses on the optimisation of 2,3-butanediol (BDO) production in fed-batch cultures carried out with the bacterial strain Enterobacter ludwigii using very high polarity (VHP) sugar from sugarcane mills. Various kLa values were evaluated using either complex or synthetic fermentation media demonstrating that the latter enhance BDO production efficiency with low by-product formation. The pH (6.3) and temperature (33.9 °C) employed in fed-batch bioreactor cultures has been optimised via experimental design. Fed-batch cultures carried out at the optimum temperature and pH and varying kLa values resulted in BDO concentration, yield and productivity of 86.8 g/L, 0.37 g/g and 3.95 g L-1 h-1. Using this fermentation efficiency, the minimum selling price of BDO for annual production capacities of 10,000 t and 50,000 t was estimated at $3.12/kg and $2.67/kg, respectively, for a VHP cane sugar market price of $0.4/kg.

Microbial oil production from various carbon sources by newly isolated oleaginous yeasts.

Microbial oil production has received significant attention as a potential precursor for the production of biofuels, oleochemicals and food products. In this study, six oleaginous yeasts, isolated from fruits, were selected based on their ability to accumulate high intracellular content of microbial oil (20-48% w/w of total dry weight). The highest content of saturated fatty acids was 68.7% (w/w), whereas the highest content of oleic acid was 62.7% (w/w). Furthermore, nutrient-rich hydrolysates produced via enzymatic hydrolysis of flour-rich waste streams generated by a confectionery industry were evaluated as fermentation media for microbial oil production via fed-batch bioreactor cultures using one of the most promising isolates, namely VV_D4. A total dry weight of 40 g/L with a microbial oil content of 39% (w/w) was produced by isolate VV_D4. Critical biodiesel properties were estimated based on the fatty acid composition and correlated with the international standards. The microbial oil produced by the new isolates could be potentially used for biodiesel production.