Enhancing of pretreatment on high solids enzymatic hydrolysis of food waste: Sugar yield, trimming of substrate structure

Enhancing the decomposition and composting of food waste by in situ directional enzymatic hydrolysis: performance, ARGs removal and engineering application

This research utilized food waste (FW) as substrate, innovatively developed a directional multienzyme applied for accelerating FW hydrolysis and composting, and an in situ enzymatic hydrolysis combining in composting has been developed to manage FW. Results showed that the composting was achieved at 4 days and the humification index was increased by 2.60 compared with that of without enzymatic hydrolysis. FTIR analysis revealed that following multienzyme pretreatment, the primary constituents of FW, including protein, starch and lipid, underwent structural breakdown, among which protein exhibited the higher susceptibility to multienzyme action and was the first to disintegrated, and the structure also became looser. Moreover, the total antibiotic resistance gene (ARGs) was reduced more than 90 % in the proposed composting process. Analysis of microbial communities and metagenomes showed that multienzyme pretreatment reshaped microbial communities towards favoring FW hydrolysis and humification. The engineering application analysis further implied that the proposed composting approach is scale flexible, engineering applicable, economic viability and environmentally sustainability. It was anticipated that this study has the potential to trigger a paradigm shift in future in-situ treatment of FW to achieve full resource recovery towards zero solid discharge.

Insight into the mechanism of alkali-thermal pretreatment of food-waste solid residue through fluorescence spectroscopy coupled with parallel factor analysis

Food-waste solid residue is the remaining solid after food waste treatment, with high yield, high solid content, high protein and fiber content. Effective pretreatment is necessary to improve the efficiency of hydrolysis and acidification for anaerobic digestion of food-waste solid residue. In this study, fluorescence spectroscopy coupled with parallel factor analysis were used to insight into the mechanism of food-waste solid residue during three pretreatments (alkali, thermal and alkali-thermal). Pretreatments increased the solubility of lignocellulosic substrate and destroyed structure of starch, while lignocellulosic analogs were effectively cracked, changing the composition and improving the degradability. Soluble chemical oxygen demand, soluble protein and soluble polysaccharide concentrations were increased by 144.60%, 350.57% and 138.72% after pretreatment under the condition of 120 °C + 2% CaO, respectively. Three-dimensional fluorescence spectra showed the region of maximum fluorescence intensity under alkali-thermal pretreatments, indicating chemical bonds (such as OC-C) were easier broken and the solubility of organic substances were increased. Three main fluorescence components were obtained by parallel factor analysis, which were humic acid-like, lignocellulose-like and protein-like, respectively, while the lignocellulose-like had the maximum Fmax value. The fluorescence intensity of samples under alkali-thermal pretreatment varied in the range from 59.48 × 105 to 13.18 × 106, which was an increase of 174.27%-507.74% over the control (21.68 × 105), indicating that alkali-thermal pretreatment observably accelerated the breaking of chemical bonds, and thus promoted the dissolution of organic matter. This study deeply revealed the mechanism of alkali-thermal pretreatment of food-waste solid residue, which is of great significance for efficient resource utilization of food waste and food-waste solid residue.

Changes in physicochemical properties and formation process of colloidal nanoparticles (CNPs) during the lamb soup stewing

Colloidal nanoparticles (CNPs), as carriers of nutrients, naturally exist in food or form during cooking. In this study, the colloidal properties, structures, rheological properties, and chemical composition location of CNPs were analyzed during 15 min to 5 h lamb soup stewing. With the increasing stewing time, the particle size and absolute value of the zeta potential of CNPs increased, indicating that CNPs became more stable. As the stewing time increased, the blue-shifted Fourier transform infrared spectroscopy absorption peaks and the red-shifted fluorescence spectroscopy absorption peaks certificated the structural changes in CNPs. And α-helix and β-turn content decreased, while β-sheet and random coil content increased in processing, potentially resulting in the opening CNPs structures. In addition, our findings revealed that proteins were encapsulated within the lipids in the inner part, while carbohydrates were dispersed in the outermost layers of the CNPs with a phospholipid bilayer.

Quantitative correlation analysis between particle liquefaction and saccharification through dynamic changes of slurry rheological behavior and particle characteristics during high-solid enzymatic hydrolysis of sugarcane bagasse

This study identified the intrinsic relationships among slurry rheology, particle characteristics, and lignocellulosic liquefaction/saccharification based on correlation analysis and principal component analysis during the hydrolysis of sugarcane bagasse pretreated by deep eutectic solvents (DES) and mechanical milling (MM). The DES-MM pretreated lignocellulosic slurry (20% solids) exhibited high apparent viscosity of 1.4 × 104 Pa·s and shear stress of 929.0 Pa under steady state. Glucose production had a negative linear correlation with slurry viscosity (R2, 0.69-0.97), whereas its correlation with yield stress (R2, 0.85-0.98) depended on the particle liquefaction rate. The availability of free water provided a major contribution to improving slurry rheology. However, the size reduction of submillimeter particles and the changes in particle hydrophilicity during liquefaction were not significantly correlated with rheological changes. Various interrelated particle characteristics and rheological changes were integrated into two simple principal variables to predict glucose production with a high R2 of 0.96.

Effects of sucrase enzymatic hydrolysis combined with Maillard reaction on soy protein hydrolysates: Bitterness and functional properties

In this study, sucrase was added to convert non-reducing sugars into reducing sugars in skim obtained by enzyme-assisted aqueous extraction processing (EAEP), then the variation of soy protein hydrolysates (SPH) from the skim under different Maillard reaction times were studied. We conducted one-factor experiment and selected 2 mg/mL sucrase for enzymatic hydrolysis for 2 h. The structure of SPH was investigated by Fourier transform infrared spectroscopy, intrinsic fluorescence spectroscopy, and amino acid composition. Results showed that the Maillard reaction loosened the SPH structure and produced new functional groups. Sensory evaluation, electronic tongue, electronic nose and GC-MS were used to study the sensory characteristics of SPH, we found that the bitterness value was significantly reduced to 1.71 from 4.63 after 2 h of the Maillard reaction. The change of bitterness was related to amino acid composition and the production of pyrazine. Additionally, the iron reduction ability, DPPH free radical scavenging ability, and emulsifying activity reached the highest at 2 h of reaction with 0.80, 73.94 %, and 56.09 %. The solubility, emulsifying stability, and foaming capacity increased and gradually stabilized with the increasing reaction time. Therefore, this paper presents an effective method for generating SPH with low bitterness and high functional properties.

Performance of high solids enzymatic hydrolysis and bioethanol fermentation of food waste under the regulation of saponin

Bioethanol recovery from food waste through high solids enzymatic hydrolysis (HSEH) and high solids bioethanol fermentation (HSBF) alleviate the energy crisis. However, this cause decreased glucose and bioethanol yields due to the high solids content. In this study, saponin was introduced into food waste HSEH and HSBF systems to enhance the product yields. Under the regulation of saponin, the substrate released >90% of the theoretical reducing sugar. The glucose concentration increased by 137.41 g/L after 24 h of HSEH with 2.0% saponin. The bioethanol titer reached 73.2 g/L (1.0%-saponin). Untargeted metabolomics illustrating that saponin had higher antifungal properties at lower concentrations (0.5%-saponin) that caused a decrease in bioethanol yield. The addition of saponin concentrations of 1.0%∼3.0% promoted HSEH, HSBF, and the metabolism of Saccharomyces cerevisiae; thus, 1.0% was suggested for practical use. This study deepened the understanding of saponin in enhancing HSBF and provides theoretical support for further application.