Brown juice is a byproduct of fractionated green biomass during leaf protein isolation. It represents approximately 45%–50% of the total pressed fresh biomass. Disposal of brown juice is a serious issue in leaf protein production due to its high biological oxygen demand and carbohydrates content. The current study aimed to find a possible potential use of brown juice. Therefore, chemical and biochemical properties of brown juice—derived from alfalfa green biomass—were determined before and after fermentation by lactic acid bacteria. Additionally, the growth stimulation potential of fermented brown juice on plumed cockscomb (Celosia argantea var. plumose ‘Arrabona’) plants were tested. Celosia seedlings were sprayed at different rates of fermented brown juice (i.e., 0.5%, 1%, 2.5%, 5%, and 10%) and tap water was applied as control. The results revealed that lactic acid bacteria successfully enhanced the stabilization of brown juice via reducing sugars content and increasing organic acids content. After fermentation, contents of glucose monomers were 15 times lower; while concentrations of lactic and acetic acids increased by 7- and 10-fold, respectively. This caused a reduction in the pH of fermented brown juice by 13.9%. Treating Celosia plants at lower rates of fermented brown juice (up to 1.0%) significantly induced their growth dynamics and antioxidant capacity. Higher values of vegetative parameters were measured in treated plants compared to control. The brown juice treatments caused significant changes in histological parameters as well. The activity of catalase and peroxidase increased in plants that received fermented brown juice especially at low rates. Moreover, an increase in water-soluble protein and phenol was measured in different tissues of plants sprayed with fermented brown juice. Malondialdehyde content was lowered in treated plants compared to control. Fermented brown juice at high rates slightly reduced the amount of photosynthetic pigments; however, this reduction was not reported for low rates of fermented brown juice. These results surely illustrate the potential use of fermented alfalfa brown juice as a growth stimulator for crops particularly at rates below 2.5%.

Corn stover is a lignocellulosic biomass, an agricultural by-product, a possible raw material for xylose production. In this study corn stover was hydrolyzed with sulfuric and hydrochloric acid. In the presented work, hydrochloric acid resulted in the highest, 88.8 % xylose yield of theoretical under the conditions of 2 % (w/w) hydrochloric acid concentration, 40-minute reaction time, 10 % (w/w) dry matter, at 120 °C. Sulfuric acid experiments resulted in 81.9 % xylose yield of theoretical by using 1.5 % (w/w) sulfuric acid, 60-minute reaction time, at 140 °C, 7 % (w/w) dry matter. Acid hydrolysis at low dry matter content resulted in relatively low sugar concentrations. Hydrolyzate recycling concentrated xylose to three-times, while the recycling does not decrease the xylose yields. It is also shown that the pseudo first-order and biphasic kinetic models can be based on total sugar concentrations.

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Xylitol is produced by the heterogeneous catalytic hydrogenation of xylose over Raney nickel. The hydrogenation must typically be followed by several purification steps, which makes the chemical production relatively complex and expensive. In this study, activated carbon and bio-purification treatments of corn stover hydrolysates and subsequent nickel-catalyzed hydrogenation of xylose to xylitol were investigated. The activated carbon treatment was used to eliminate inhibitory compounds and increase the efficiency of the bio-purification step. It was found that the glucose could be completely eliminated from the hydrolysate. The hydrogenation reactions of corn stover hydrolysate demonstrated that a high reaction temperature resulted in high sugar alcohol yields and selectivity. At a given temperature, the flow rate had no significant effect on xylitol yield. Figure 1. Hydrogenation of xylose to xylitol over Raney nickel.

Brewer’s spent grain (BSG) is the main by-product of the beer brewing process. It has a huge potential as a feedstock for bio-based manufacturing processes to produce high-value bio-products, biofuels, and platform chemicals. For the valorisation of BSG in a biorefinery process, efficient fractionation and bio-conversion processes are required. The aim of our study was to develop a novel fractionation of BSG for the production of arabinose, arabino-xylooligomers, xylose, and bioethanol. A fractionation process including two-step acidic and enzymatic hydrolysis steps was investigated and optimised by a response surface methodology and a desirability function approach to fractionate the carbohydrate content of BSG. In the first acidic hydrolysis, high arabinose yield (76%) was achieved under the optimised conditions (90 °C, 1.85 w/w% sulphuric acid, 19.5 min) and an arabinose- and arabino-xylooligomer-rich supernatant was obtained. In the second acidic hydrolysis, the remaining xylan was solubilised (90% xylose yield) resulting in a xylose-rich hydrolysate. The last, enzymatic hydrolysis step resulted in a glucose-rich supernatant (46 g/L) under optimised conditions (15 w/w% solids loading, 0.04 g/g enzyme dosage). The glucose-rich fraction was successfully used for bioethanol production (72% ethanol yield by commercial baker’s yeast). The developed and optimised process offers an efficient way for the value-added utilisation of BSG. Based on the validated models, the amounts of the produced sugars, the composition of the sugar streams and solubilised oligo-saccharides are predictable and variable by changing the reaction conditions of the process.