Acid Pretreatment Research Articles

Effect of Surface Pretreatments on the Formation of Zr‐Based Conversion Layers on Zn–Al–Mg Alloy‐Coated Steel

ABSTRACTZr‐based conversion coatings represent an environmentally conscious alternative to traditional phosphating and chromating in the automotive industry. In this study, we employ XPS and LEIS to investigate the formation of Zr‐conversion layers on Zn–Mg–Al alloy after alkaline and acidic model pretreatments. On alkaline pretreated surfaces, a Zr‐oxide/oxyfluoride layer and an underlying Mg–Al–fluoride layer are formed, whereas acidic pretreatment results in only an oxidic layer. The thickness of the Zr‐layer depends on pretreatment pH and immersion time. Acidic treatment achieves an approximately 23 nm‐thick Zr‐oxide/oxyfluoride layer after 1 min, while prolonged treatment increases the thickness of the oxidic layer for strong alkaline and acidic conditions. Mild alkaline pretreatments, however, do not benefit from extended immersion. F‐induced corrosion pits are observed after mild alkaline treatment. The strong alkaline pretreatment proved to be the most efficient in creating a double‐layered Zr‐conversion coating with increased oxidic layer thickness over time.

Microwave-Assisted Acid and Alkali Pretreatment of Napier Grass for Enhanced Biohydrogen Production and Integrated Biorefinery Potential

Napier grass, a promising lignocellulosic energy crop, presents a complex composition that limits its bioconversion into fermentable products. To address this challenge, we applied microwave (MW) pretreatment assisted by acid and alkali, using varying chemical concentrations (0.5–1% w/v) and pretreatment times (3–10 min). Acid-catalyzed MW pretreatment achieved a maximal hemicellulose removal of 69.8%, while alkali-catalyzed MW pretreatment resulted in significant lignin removal of 65.5%. Without chemical catalysis, the pretreated hydrolysate significantly increased hydrogen yield to 38.0 ± 2.9 mL H2/g volatile solid (VS), five times greater than that obtained from untreated biomass. Hydrogen yield was further enhanced when the MW-pretreated solid underwent simultaneous saccharification and fermentation. The highest hydrogen yield of 89.2 ± 7.2 mL H2/g VS was achieved from alkali-catalyzed MW pretreated solid (0.5% w/v NaOH, 5 min), with a chemical oxygen demand (COD) solubilization of 62.6%. Increasing the NaOH concentration to 1% (w/v) slightly decreased hydrogen yield but significantly increased COD solubilization to 85.8%. The high carbohydrate content facilitated rapid cellulase hydrolysis, producing and accumulating a high concentration of fermentable sugars. However, this accumulation subsequently led to a shift towards lactic acid formation. The improved hydrogen yield and increased COD solubilization, along with the shift towards lactic acid production, suggest the possibility of optimizing this process for simultaneous production of multiple valuable products in an integrated biorefinery approach, potentially enhancing the economic viability of biomass conversion.

Optimization of Lipid Production from Paddy Straw Using Dilute Acid Pretreatment and Fermentation by Rhodosporidium Toruloides

<p style="margin-top:1px; text-align:justify; text-indent:14.2pt"><span lang="EN-GB" style="font-size:12.0pt"><span style="line-height:115%"><span style="font-family:"Times New Roman","serif"">Among the </span></span></span><span lang="EN-GB" style="font-size:12.0pt"><span style="line-height:115%"><span style="font-family:"Times New Roman","serif"">lignocellulose wastes Paddy Straw is the most abundant one which have the ability of being used as a feedstock for production of biofuel. In this work, paddy straw is subjected to dilute acid pretreatment, detoxification and fermentation processes for the production of lipids. Rhodosporidium Toruloides, an oleaginous yeast strain is used for fermentation and produce biomass and lipids. Straw of paddy is pre-processed with 2% (v/v) the sulfuric acid at 121<sup>o</sup> C for an hour that is 60 minutes and then detoxified. Fermentation process has to be optimized in order to achieve higher lipid yields and higher cellulose content. In this study, optimization is carried out by using response surface process and <a name="_Hlk175385141">Box Behnken Design (BBD) </a>for learning impact of concentration of inoculum, pH and temperature on fermentation. During hydrolysis and fermentation processes, sugar concentration is analysed using </span></span></span><span style="font-size:12.0pt"><span style="line-height:115%"><span style="font-family:"Times New Roman","serif"">dinitro salicylic </span></span></span><span lang="EN-GB" style="font-size:12.0pt"><span style="line-height:115%"><span style="font-family:"Times New Roman","serif"">acid reagent and standard curve of glucose. Observations show that highest yield of sugar from the dilute acid pre-treatment is 3.3 g/L. Optimum conditions for lipid yield from fermentation process is 10.88 g/L at a pH of 6, at a temperature of 25°C and at 10% inoculum loading.</span></span></span></p>

Electrochemical Oxidation of Glyphosate Using Graphite Rod Electrodes: Impact of Acetic Acid Pretreatment on Degradation Efficiency

The uncontrolled use of herbicides such as glyphosate (GLY) (N-phosphonomethylglycine) in agricultural production has resulted in its presence in water bodies and in negative impacts on the environment and public health. On the frame of understanding the interaction between GLY and graphite rod surfaces, this contribution relies on the study of electrochemical responses of different GLY concentrations by cyclic voltammetry under both open and closed-circuit conditions. Furthermore, the effect of the electrodes’ electrochemical pretreatment with acetic acid on the double-layer capacitance and the subsequent surface functionalization of the graphite rod materials were evaluated. The increment in GLY concentration showed a decrease in the electrochemical oxidation response associated with the adsorption of the contaminant on the surface of the graphite rod electrode and the concomitant blockage of the active sites. Electrochemical pretreatment of the electrodes with acetic acid and GLY concentration play crucial roles in electric double-layer formation due to their ability to interact with both positive and negative electrical charges. By means of optical microscope observations and Fourier Transform Infrared Spectroscopy analysis, it was possible to detect the formation of oxygenated functional groups on the electrode surfaces after the electrochemical pretreatment. Through a 23 factorial design analysis in repetition, the factors significant in the degradation of GLY were identified. The high degradation of GLY with the pretreated electrodes can be attributed to the preferential adsorption of the zwitterionic molecule at the interface, which allowed great direct oxidation of the contaminant on the anode’s surface.

Enhanced bioethanol production from Compositae plant stalks: Integrating dry acid pretreatment and fungal mediated biodetoxification

Compositae is an important economic plant with relatively high contents of water-soluble sugars in stalk section. The pretreatment of Compositae plant stalks quickly converts the water-soluble sugars into high titers of furan aldehydes, which inhibits the viability of consequent fermentation strains. This study used the typical Compositae plant stalks of sunflower, Jerusalem artichoke, and stevia as feedstocks for dry acid pretreatment under high solids loading, then a unique solid-state biodetoxification method was applied to degrade these high-titer inhibitors. The results showed that temperature and sulfuric acid concentration were two key parameters for enhancing pretreatment efficiency. Enzymatic hydrolysis yield of the above pretreated stalks reached up to 79.68%, 66.75% and 74.05%, respectively. For pretreated Jerusalem artichoke stalk, it contained 37.36% of cellulose, 2.72% of xylan, 3.04% of glucose, 11.64% of xylose, 20.54% of lignin, and some inhibitors (3.80% of acetate, 0.24% of HMF and 0.23% of furfural). After biodetoxification, 100% of furfural, 40% of HMF, and 36% of acetate were quickly removed by Amorphotheca resinae ZN1, which resulted in 55.57 g/L ethanol production (equivalent to 7.1% by volumetric percentage) with the yield of 55.54% from 73.59 g/L of glucose and 40.69 g/L of xylose by simultaneous saccharification and co-fermentation (SSCF). This study provides a combinational approach of dry acid pretreatment and biodetoxification for Compositae plant stalks biorefinery.

Production of Sugars and Ethanol from Acid–Alkaline-Pretreated Agave sisalana Residue

Drylands in Brazil have been exploring sisal (Agave sisalana) as an essential source of income. However, the solid residues generated because of this activity still need suitable destinations; therefore, research has been carried out to transform them into added-value products. Therefore, the present study evaluated the potential of sisal or agave solid residue as a precursor feedstock for second-generation ethanol production. Acid and acid–alkaline pretreatments were carried out on sisal residues to enrich the biomass with cellulose and maximize enzymatic digestibility. Second-generation ethanol production was carried out using Semi-simultaneous saccharification and fermentation (SSSF). Regardless of catalyst dosage and incubation time, oxalic acid pretreatments generated samples with a similar chemical composition to those pretreated with sulfuric acid. However, samples pretreated with oxalic acid showed lower enzymatic digestibility. Samples pretreated with oxalic acid and sodium hydroxide obtained 14.28 g/L of glucose and cellulose conversion of 79.1% (at 5% solids), while 21.49 g/L glucose and 91.2% of cellulose conversion were obtained in the hydrolysis of pretreated samples with sulfuric acid and sodium hydroxide combined pretreatments. The pretreatment sequence efficiently reduced cellulase dosage from 20 to 10 FPU/g without compromising sugar release. SSSF achieved maximum production of 40 g/L ethanol and 43% ethanol conversion using 30% solids and gradually adding biomass and cellulases.

An integrated approach for plastic polymer degradation by the gut bacterial resident of superworm, Zophobas morio (Coleoptera:Tenebrionidae).

The potential of superworm to remove certain plastic polymers has recently been noted. In this study, aerobic bacterial strains were isolated from the gut of Zophobas morio larvae which were fed with polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS) polymers. Strains P2 (Leminorella), P6 (Bacillus), P9 (Bacillus), and P5 (Citrobacter) were associated with the highest PS (2.7%), PP (1.3%), PET (1.1%), and PE (0.42%) weight loss after 28days, respectively. Pretreatments including thermal treatment (80°C for 10days), weathering (4months in the free environment), and nitric and sulfuric acids (1 N, 10days) improved the degradation of PE (1.3%), PET (1.9%), PP (5.2%), and PS (8.3%) by the same strains, respectively. Further analyses on the PS degradation by Leminorella sp. P2 revealed acid pretreatment promoted the formation of the C = C, C = O, and O-H functional groups. Surface irregularities, as well as a 3.6-fold increase in surface roughness, were observed in the PS film subjected to biodegradation. The contact angle dropped from 98.4° to 42.2° following the biodegradation. Bacterial depolymerization was confirmed by the 8.7% and 3.4% reduction of Mn and Mw and the change in polydispersity from 1.65 to 1.75. The results suggest that Zophobas morio microbiota in combination with abiotic pretreatment can be considered for plastic waste management.

Peracetic acid enhanced anaerobic co-digestion of excess sludge and food waste: performance and mechanism

ABSTRACT Anaerobic co-digestion of excess sludge (ES) and food waste (FW) has been proven to be a clean and efficient strategy for the resource recovery of organic waste. However, the methane production from the anaerobic co-digestion of ES and FW is not optimal. This study reports a new strategy of using peracetic acid (PAA) pretreatment to enhance the anaerobic co-digestion of ES and FW and reveals the underlying mechanisms. The results confirm that PAA can effectively promote the production of methane from the anaerobic co-digestion of ES and FW, with the maximum methane yield reaching 416 mL/g volatile suspended solids at a PAA content of 9% (w/w). Mechanistic analysis indicates that PAA efficiently facilitates the solubilization of organic matter, promoting the release of soluble proteins and polysaccharides, and accelerating the metabolic conversion of volatile fatty acids (VFAs) to prevent excessive acidification. The maximum output of VFA in the PAA group was 1,511–1,974 mg/L, which was lower than that in the control group. Batch experimental analysis revealed that PAA promoted the hydrolysis and acidification processes, but inhibited the methanogenic process. The PAA pretreatment technique provides a theoretical basis for the efficient treatment of organic matter in urban areas.

Study on the effect of phenoxyethanol-citric acid pretreatment for the enzymatic hydrolysis of bamboo residues.

This study investigated the biphasic phenoxyethanol-citric acid (PECA) pretreatment for bamboo residues (BRs) and its corresponding effects on the enzymatic hydrolysis performance. It is found that increasing the concentration of citric acid in the pretreatment system from 2.5% to 15% greatly enhanced the delignification and xylan removal for BRs. Consequently, the enzymatic hydrolysis yield of pretreated BRs significantly enhanced, increasing from 12.4% to 58.2% and 28.0%72.4% when the concentration of citric acid was increased from 2.5% to 15.0% at 160°C and 170°C, respectively. The characterization results from cellulose crystallinity, accessibility, and hydrophobicity of pretreated bamboo residues indicated that their changes possessed a beneficial performance on the enzymatic hydrolysis yield, which could result from the synergistic removal of lignin and xylan. The Chrastil model analysis showed that pretreatment at higher conditions resulted in the pretreated BRs possessing weaker diffusion resistance for cellulase, which is attributed to its higher enzymatic hydrolysis yield.

Persistence of post-stress blood pressure elevation requires activation of astrocytes

The reflexive excitation of the sympathetic nervous system in response to psychological stress leads to elevated blood pressure, a condition that persists even after the stress has been alleviated. This sustained increase in blood pressure, which may contribute to the pathophysiology of hypertension, could be linked to neural plasticity in sympathetic nervous activity. Given the critical role of astrocytes in various forms of neural plasticity, we investigated their involvement in maintaining elevated blood pressure during the post-stress phase. Specifically, we examined the effects of arundic acid, an astrocytic inhibitor, on blood pressure and heart rate responses to air-jet stress. First, we confirmed that the inhibitory effect of arundic acid is specific to astrocytes. Using c-Fos immunohistology, we then observed that psychological stress activates neurons in cardiovascular brain regions, and that this stress-induced neuronal activation was suppressed by arundic acid pre-treatment in rats. By evaluating astrocytic process thickness, we also confirmed that astrocytes in the cardiovascular brain regions were activated by stress, and this activation was blocked by arundic acid pre-treatment. Next, we conducted blood pressure measurements on unanesthetized, unrestrained rats. Air-jet stress elevated blood pressure, which remained high for a significant period during the post-stress phase. However, pre-treatment with arundic acid, which inhibited astrocytic activation, suppressed stress-induced blood pressure elevation both during and after stress. In contrast, arundic acid had no significant impact on heart rate. These findings suggest that both neurons and astrocytes play integral roles in stress-induced blood pressure elevation and its persistence after stress, offering new insights into the pathophysiological mechanisms underlying hypertension.

PH-controlled acetic acid pretreatment for coproduction of low degree of polymerization xylo-oligosaccharides and glucose from corncobs

Acetic acid (HAc) pretreatment has been widely used for the production of xylo-oligosaccharides (XOS), requiring harsh reaction conditions because XOS are intermediates during the xylan degradation process. This complexity makes the pretreatment process difficult to regulate. In this study, a pH-controlled HAc pretreatment using sodium hydroxide (NaOH) was proposed to enhance the yield of XOS and to reduce its degree of polymerization (DP) from corncobs (CC). By employing this method (0.3 M-2.7), 49.7 % of XOS with DP 2–6 was obtained, alongside a notable increase in the fraction of XOS with DP 2–4 (10.1 g/L). This performance significantly surpassed that of the HAc alone (0.3 M). Moreover, the glucose yield from CC via pH-controlled HAc pretreatment was as high as 93.1 % after 72-h enzymatic hydrolysis. These results suggested that the pH-controlled HAc pretreatment could be a promising strategy for the coproduction of low-DP XOS and fermentable sugars.

Green and facile synthesis of cellulose nanofibres from Peltophorum pterocarpum pods cellulose using a eutectic solvent

ABSTRACT This study focuses on isolating, optimising and characterising cellulose from Peltophorum pterocarpum pods and synthesising cellulose nanofibres (CNF) using a eutectic solvent (ES). Three methods were evaluated: Soxhlet extraction, formic acid, and autoclave-assisted pre-treatment. The autoclave-assisted method yielded the highest cellulose content, approximately 43.6% w/w, at 121°C for 40 min. CP-MAS13C NMR and FTIR spectroscopy confirmed the cellulose’s carbon atoms and functional groups, and XRD analysis indicated a high crystallinity index (82.92%) and the transformation from cellulose I to cellulose II. SEM and TGA analyses assessed the morphological and thermal properties. CNFs were synthesised using a green solvent (ChCl/Lactic acid, 1:2) at 80°C, with TEM confirming their nanofibrous structure. The CNF zeta particle size was 262.1 nm, with a potential of −19.0 mV. The use of ES in the CNF synthesis is a novel and eco-friendly process that aligns with 5 of the 12 principles of green chemistry.

Optimizing the energy values of solid biofuel through acidic pre-treatment: An evolutionary-based neuro-fuzzy modelling and feature importance analysis

The increasing focus on sustainable energy solutions and eco-friendly fuel alternatives has sparked interest in exploring methods to enhance the energy content of solid biofuels through pre-treatment processes. This study investigates the impact of acidic (H2SO4) pretreatment on the energy content of solid biofuel derived from watermelon peel waste using machine learning methods. The biofuel properties, and calorific value (CV) were determined experimentally for both H2SO4-treated and untreated biofuel samples. Subsequently, an Adaptive neuro-fuzzy inference system (ANFIS) model with Genetic Algorithm (GA) and Grid Partitioning (GP) clustering techniques was developed to predict heating value of the biofuel, with performance evaluation based on root mean square error (RMSE), mean absolute percentage error (MAPE), mean absolute deviation (MAD), Mean Absolute Error (MAE) and R2-values. The decision tree regressor was employed to evaluate the feature importance, predictive power and impact of each input variable on CV prediction based on Gini importance metrics. To establish its superior performance, the hybrid ANFIS-GA-GP model was compared with ordinary-ANFIS and ANN model using same metrics. Results show that acid-pretreatment increased the CV of the solid biofuel by 3.53 MJ/kg (31.83 % improvement) and reduced ash content by 1.77 %. FTIR analysis revealed surface modifications, and a shift in the C-O vibrational stretch, while SEM micrographs displayed denser surfaces and reduced porosity as indicated by a lesser fiber diameter in treated samples. The GP-clustered ANFIS-GA model with a triangular membership function (tri-MF) exhibited superior performance and higher accuracy (RMSE of 0.1309, MAPE of 9.343, MAD of 0.1036, MAE of 0.1110, and R2-value of 0.9773 at model training). Furthermore, a tree decision regressor identified Fixed carbon as the most significant predictor for CV with a Gini importance of 0.988375. This study demonstrates the substantial enhancement in the energy content of biofuel using acidic pre-treatment and insights into a cutting-edge approach of improving the combustion properties of solid biofuel with machine learning models. This significantly contributes to the field of sustainable bioenergy research.

Enhancement of xylooligosaccharides production as a novel antioxidant source through autoclave-assisted oxalic acid pretreatment of sugarcane trash

Enhancement of xylooligosaccharides production as a novel antioxidant source through autoclave-assisted oxalic acid pretreatment of sugarcane trash

A novel microwave-assisted γ-valerolactone and glycolic acid pretreatment for green and sustainable production of hemp fibres

Hemp, a sustainable crop, offers superior material properties suitable for diverse applications. This study aims to produce hemp fibre using a green and sustainable pretreatment method, thus exploring a novel microwave-assisted pretreatment method using a γ-valerolactone (GVL) and glycolic acid (GA) solution system, referred to as the GVL/GA pretreatment method. By optimising solid loading and reaction time, we significantly reduced water usage (50 %) and energy consumption (61.5 %) while maintaining fibre quality. The pretreatment method effectively removed lignin (88.7 %) and hemicellulose (39.3 %) without damaging the cellulose structure. The pretreated samples demonstrated a 45.7 % increase in glucose yield. Additionally, the characterisation of pretreated fibres revealed impressive fineness (4.4 dtex) and tenacity (4.0 cN/dtex), and the crystal structure remained intact with increased crystallinity (86 %). The HSQC NMR analysis unveiled that lignin undergoes structural modifications, enabling efficient lignin removal. GVL/GA pretreatment promotes green chemistry by minimising environmental impact and waste, using renewable resources. It provides a sustainable alternative to traditional methods, contributing to a greener industry.

Y and ZSM-5 Hierarchical Zeolites Prepared Using a Surfactant-Mediated Strategy: Effect of the Treatment Conditions.

Diffusional limitations associated with zeolite microporous systems can be overcome by developing hierarchical zeolites, i.e., materials with a micro- and mesoporous framework. In this work, Y and ZSM-5 zeolites were modified using a surfactant-mediated hydrothermal alkaline method, with NaOH and cetyltrimethylammonium bromide (CTAB). For Y zeolite, after a mild acidic pretreatment, the effect of the NaOH+CTAB treatment time was investigated. For ZSM-5 zeolite, different concentrations of the base and acid solutions were tested in the two-step pretreatment preceding the hydrothermal treatment. The properties of the materials were studied with different physical-chemical techniques. Hierarchical Y zeolites were characterized by 3.3-5 nm pores formed during the alkaline treatment through the structure reconstruction around the surfactant aggregates. The effectiveness of the NaOH+CTAB treatment was highly dependent on the duration. For intermediate treatment times (6-12 h), both smaller and larger mesopores were also obtained. Hierarchical ZSM-5 zeolites showed a disordered mesoporosity, mainly resulting from the pretreatment rather than from the subsequent hydrothermal treatment. High mesoporosity was obtained when the concentration of the pretreating base solution was sufficiently high and that of the acid one was not excessive. Hierarchical materials can be obtained for both zeolite structures, but the pretreatment and treatment conditions must be tailored to the starting zeolite and the desired type of mesoporosity.

Two-Step Macromolecule Separation Process with Acid Pretreatment and High-Shear-Assisted Extraction for Microalgae-Based Biorefinery

A simple two-stage extraction and recovery method for macromolecules from microalgae biomass, termed CASS (concentrating the microalgae solution, acid pretreatment, high-shear-assisted lipid extraction, and separation), was developed. This method effectively processed the wet biomass of Chlorella sp. ABC-001 at a moderately low biomass concentration (50 g/L). The optimal conditions were acid pretreatment with 5 wt.% H2SO4 at 100 °C for 1 h, followed by high-shear extraction using hexane at 3000 rpm for 30 min. The acid pretreatment hydrolyzed carbohydrates and phospholipids, disrupting the cell wall and membrane, while high-shear mixing enhanced mass transfer rates between solvents and lipids, overcoming the hydraulic barrier at the cell surface. Within 10 min after completing the process, the extraction mixture achieved natural phase separation into water, solvent, and biomass residue layers, each enriched with carbohydrates, lipids, and proteins, respectively. The CASS process demonstrated high esterifiable lipid yields (91%), along with substantial recovery of glucose (90%) and proteins (100%). The stable phase separation prevented emulsion formation, simplifying downstream processing. This study presents the results on cell disruption, optimal acid treatment concentration, and high-shear mixing to achieve macromolecule separation, expanding the lipid-centric microalgal process to a comprehensive biorefinery concept.

Utilization of cotton stalk waste for sustainable isopropanol production via hydrolysis and coculture fermentation

The present investigation focused on isopropanol production from lignocellulosic cotton stalk biomass (CSB) using conventional pretreatment, enzymatic hydrolysis and fermentation methods. In comparison to alkaline (NaOH) pretreatment, dilute sulphuric acid (H2SO4) pretreatment showed higher cellulose exposure (448.5 mg/g). Further, ultrasono assisted acid and alkali pretreatment was performed for maximum exposure of cellulose and it was found 616.9 and 586.15 mg/g respectively. Chemical pretreated CSB was additionally exposed to independent enzymatic hydrolysis using commercial enzymes (Celluclast and Viscozymes) following Response Surface Methodology (RSM), which revealed a maximal production of glucose and xylose yield (544.6 mg/g and 41.8 mg/g). Pretreated and enzymatic hydrolyzed cotton stalk biomass at various conditions were analysed using SEM, FTIR, and XRD to determine the structural and functional changes. Further, a co-culture strategy was employed on pretreated and hydrolyzed CSB using two fermented yeast strains (Saccharomyces cerevisiae and Pichia pastoris) for isopropanol production. HR-MS analysis revealed that the maximum concentration of isopropanol (126.228 mM) was produced in 2:1 proportionate ratio of two fermented yeasts with 20 g/L of substrate loadings at 72 h of incubation time. These results indicate that the production of isopropanol (7.46 g/L) from CSB with different parametric conditions is an encouraging step and can be exploited further for various industrial applications.

Impact of Pretreatment With Acid and Ultrasound on the Production and Characteristics of Goat Skin Gelatin

Goat skin is a potential raw material source for gelatin production using acid-ultrasound pretreatment. The objective of this study was to investigate the use of ultrasound in combination with acid pretreatment for the preparation of goat skin gelatin. Gelatin was extracted from goat skin using different pretreatments: acetic acid (T1), acetic acid followed by ultrasound (20 kHz and 750 W) (T2), and without pretreatment (T0). The results showed that the combination of acetic acid and ultrasound pretreatment significantly impacted the quality of the resulting gelatin. The study results showed an increase in yield (9.24 to 25.48%), hydroxyproline content (102.07 to 231.31 mg/g), gel strength (4.76 to 197.62 g), viscosity (6.80 to 48.00 cP), melting point (32.47 to 35.85 oC), EAI (18.24 to 23.58 m2/g), and ESI (24.90 to 62.63 min). However, there was a decrease in pH, the value of color L*, and turbidity. The SDS-PAGE patterns showed differences in molecular weight distribution due to variations in pretreatment. All gelatin samples exhibited α1 and α2 chains as the predominant components. Interestingly, the ultrasound effect highlighted the β-chain more boldly compared to other pretreatments. FTIR spectroscopy analysis shows changes in molecular interactions due to acetic acid pretreatment followed by ultrasound, which results in shifts in the Amide A, Amide B, Amide I, Amide II, and Amide III groups. Ultrasonic treatment caused more dense and disturbed structures in the sample. Therefore, the combination of acetic acid and ultrasound pretreatment yielded the superior properties of goat skin gelatin.

Epinecidin-1 and lactic acid synergistically inhibit Aeromonas hydrophila through membrane disruption

Epinecidin-1 (Epi-1) is an antimicrobial peptide originated from fish with various pharmacological activities but carries the risk of acquiring resistance with long-term use. In the present study, we use L-lactic acid to enhance the antibacterial activity of synthesized Epi-1 against the aquaculture and food pathogen Aeromonas hydrophila. The results showed that 5.5 mmol/L lactic acid increased the inhibitory and bactericidal activity of 25 μmol/L Epi-1 against two strains of A. hydrophila. The laser confocal images proved that lactic acid pre-treatment improved the attachment efficiency of Epi-1 in A.hydrophila cells. In addition, lactic acid enhanced the damaging effect of Epi-1 on the cell membrane of A. hydrophila, evidenced by releasing more nucleic acids, proteins, and transmembrane pH ingredients decrease and electromotive force dissipation. SEM images showed that compared with the single Epi-1 treatment, the co-treatment of Epi-1 and lactic acid caused more outer membrane vesicles (OMVs) and more severe cell deformation. These findings proved that lactic acid could enhance the efficiency of Epi-1 against A. hydrophila and shed light on new aspects to avoid resistance of pathogens against Epi-1.