Techno-economic evaluation of strategies based on two steps organosolv pretreatment and enzymatic hydrolysis of sugarcane bagasse for ethanol production

Several strategies based on a two steps organosolv pretreatment followed by enzymatic hydrolysis of sugarcane bagasse (SCB) were evaluated with the objective of selecting operational conditions suitable to promote an efficient and low cost production of ethanol. Initially, the influence of six variables used for the organosolv pretreatment was studied. The variables included the time of the first organosolv pretreatment step, the use of 45% ethanol as pulping solution, solid-to-liquid ratio of the ethanol solution used during the first pretreatment step, time of second organosolv pretreatment, concentration of ethanol and concentration of NaOH solution used in the second pretreatment step. Further assays of enzymatic hydrolysis were carried out to promote additional reduction in the costs of the process and improve the results of cellulose conversion to glucose. Eliminating the milling step of the pretreated SCB, using a commercial tensoactive (composed of esters and several surfactants), and recycling 50% of the slurry obtained during the second step of organosolv pretreatment as reaction medium proved to be feasible for use during the enzymatic hydrolysis. Fermentation of the glucose medium produced under the selected pretreatment conditions to ethanol by Saccharomyces cerevisiae occurred with 81% efficiency and a cost of 102.88 $/hL of ethanol.     

Effects of high solid concentrations on the efficacy of enzymatic hydrolysis of yeast cells and the taste characteristics of the resulting hydrolysates

Effects of solid concentrations on enzymatic hydrolysis of yeast cells and the taste characteristics of the resulting hydrolysates were examined. Results showed that increased solid concentrations ranging from 10% to 30% resulted in a mild increase in degree of hydrolysis (DH) of hydrolysates during the whole hydrolysis process, whereas an obvious inhibition effect on DH was found at hydrolysates with 40% of solid concentration. The levels of amino nitrogen and total nitrogen of supernatant with 40% of solid concentration were six‐fold higher than those of hydrolysates with 10% of solid concentration at all hydrolysis time. After 21 h of hydrolysis, there was no significant difference in molecular weight distributions of hydrolysates with different solid concentrations, while a significant increase in amino acid contents of hydrolysates with high solid concentrations was found. Results from sensory evaluation showed that the intensities of umami, mouthfulness and continuity in umami solution could be significantly improved by supplementing with the resulting hydrolysates with high solid concentrations.     

Controlled feeding of lignocellulosic substrate enhances the performance of fed-batch enzymatic hydrolysis in a stirred tank reactor

High initial viscosity in the high-solids (>15% (w/v)) enzymatic hydrolysis of lignocellulose is problematic especially in stirred tank reactor concepts. One potential way to avoid the high viscosity is the fed-batch feeding of lignocellulosic material to the reactor. In the current study the hydrolysis of filter paper with final concentration of 19.1% (w/w) was evaluated with different fed-batch procedures. Feeding was based on visual observation, stepwise feeding and the power requirement of the stirrer motor. All the fed-batch procedures resulted in similar yields within 30 h (47–49%) which were higher than with the batch process in similar reactor (38%). However, the mixing behavior was superior in the power based feeding as the instantaneous power of the stirrer motor was kept lower (<10 W) than in other fed-batch procedures (>20 W). The power controlled procedure was further evaluated with different enzyme doses, tip speeds and the power levels of substrate feed. Further study showed that the power controlled feeding is applicable also to other hydrolysis and mixing conditions if power levels of substrate feed are set correctly. Higher (15 FPU/g) enzyme dose caused shorter feeding time (3.0 ± 0.5 h) and lower energy consumption during the feeding period (14 ± 3 Wh) compared with lower (5 FPU/g) enzyme dose (7.0 ± 1.3 h and 33 ± 5 Wh, respectively). The tip speed and the power level of substrate feed had fewer effect on these factors. The performance of the hydrolysis process can thus be enhanced by the substrate feed controlled by the power of the stirrer motor.     

Isolation,purification, and characterization of the globulin from wheat germ

This research optimized the extraction and purification of globulin from wheat germ and assessed the molecular weight distribution and structure properties of the globulin obtained. The results showed that the relative extraction efficiency and purity of wheat germ globulin (WGG) reached 18.0% and 89.1% under the enzymolysis conditions of 0.32‰ α-amylase, pH 6.5, and 55 °C. The maximal precipitation rate of WGG (91.3%) was obtained with pH 4.3 (acid precipitation). Additionally, the molecular weight of WGG was mainly distributed below 70 kDa. FT-IR confirmed that random coils (30.95%), β-sheet (27.02%), α-helix (26.55%), and β-turn (15.48%) were the secondary structures of WGG. Furthermore, LTQ mass spectrometry showed that WGG was rich in variety and high in complexity, which retrieved 1274 proteins belonging to 392 proteomes by inverse peptide analysis. The findings endow a great potential of preparing WGG with superior functionality for food applications.     

Effect of rice bran protein extract on enzymatic browning inhibition in potato puree

Effect of rice bran protein extract (RBPE) on enzymatic browning inhibition in potato puree was studied by colour measurement and polyphenol oxidase (PPO) inhibition. RBPE inhibited browning in potato puree and showed a higher per cent potato PPO inhibition at pH 4.0 and 5.0 than those at pH 3.0, 6.0 and 7.0 (P ≤ 0.05). RBPE heated to 40 and 60 °C had browning inhibition in potato puree and per cent potato PPO inhibition at a similar extent to unheated RBPE (P > 0.05). Browning inhibition and per cent potato PPO inhibition of RBPE were decreased when it was heated to 80 °C (P ≤ 0.05). RBPE inhibited browning in potato puree higher than 5, 10 and 20 mm ascorbic acid and 5 and 10 mm citric acid (P ≤ 0.05). Regarding the kinetics study, RBPE exhibited a mixed‐type inhibition for potato PPO. Therefore, RBPE has a potential to be used as a natural antibrowning agent in the potato industry.     

Se in Se‐enriched peanut,and losses during peanut protein preparation

This study determined the Se species in Se‐enriched peanut, and Se losses during peanut protein processing by enzymatic extraction, high‐performance liquid chromatography (HPLC) separation and inductively coupled plasma‐mass spectrometry determination. The study revealed that mixed enzymes (protease and lipase, 2:1 w/w) in Na₂S₂O₃, assisted by 1 h ultrasonic processing, could effectively extract Se speciation from defatted peanut powder. Separation of organic Se by HPLC was optimised using pentafluoropropionic anhydride at a concentration of 0.1% in 2% methanol as mobile phase. Selenomethionine is the dominant Se species in peanut, accounting for 65% of the total Se. During the peanut protein preparation, nearly 37% of Se losses were due to the complexity of the multistage process. The loss can be ascribed to volatilisation, dissolution, degradation or other physical modes of transfer or loss.     

Pretreatment of cassava stems and peelings by thermohydrolysis to enhance hydrolysis yield of cellulose in bioethanol production process

The potential of wastes obtained from the cultivation of Manihot esculenta Crantz as raw material for bioethanol production was studied. The objective was to determine the optimal conditions of hemicellulose thermohydrolysis of cassava stems and peelings and evaluate their impact on the enzymatic hydrolysis yield of cellulose. An experimental design was conducted to model the influence of factors on the pentose, reducing sugar and phenolic compound contents. Residues obtained from the optimal pretreatment conditions were hydrolysed with cellulase (filter paper activity 40 FPU/g). The hydrolysates from pretreatment and enzymatic hydrolysis were fermented respectively using Rhyzopus spp. and Sacharomyces cerevisiae. The yield of enzymatic hydrolysis obtained under the optimal conditions were respectively 73.1% and 86.6% for stems and peelings resulting in an increase of 39.84% and 55.40% respectively as compared to the non-treated substrates. The ethanol concentrations obtained after fermentation of enzymatic hydrolysates were 1.3 and 1.2 g/L respectively for the stem and peeling hydrolysates. The pentose and phenolic compound concentrations obtained from the multi-response optimization were 10.2 g/L; 0.8 g/L and 10.1 g/L; 1.3 g/L respectively for stems and peelings. The hydrolysates of stems and peelings under these optimal conditions respectively gave ethanol concentrations of 5.27 g/100 g for cassava stems and 2.6 g/100 g for cassava peelings.