Organic Acid Pretreatment Research Articles

The Effect of Organic Acid Pretreatment and Modified Atmosphere on Shelf Life of Dry Coleslaw Mix

The aim of the study was to determine the effect of soaking in ascorbic acid and citric acid solution and modified atmosphere packaging on the quality of a coleslaw mix stored for 12 days at 4C. Pretreatment caused a reduction by ∼2 logarithmic cycles for counts of psychrophilic bacteria from the genus Pseudomonas, and mesophilic yeasts, as well as a significant decrease in the counts of mesophilic bacteria and coliform bacteria. Packaging of tested samples in modified atmosphere with high contents of oxygen (70 or 50%) and carbon dioxide (30%) caused an inhibition of growth for mesophilic, psychrophilic, lactic acid and coliform bacteria during storage. Application of atmosphere with increased contents of CO2 (25 or 30%) resulted in the inhibition of growth of bacteria from the genus Pseudomonas, while in the case of elevated (70%) or reduced contents of oxygen (5%) a slower growth of yeasts was observed. Practical Application The using of the atmosphere with a high content of oxygen is the new trend in the minimal processing of fruits and vegetables. When applying atmosphere with a high oxygen content in packaging of fruit and vegetables it is recommended to use barrier films, which guarantees maintenance of high contents of this gas during product storage. In the case of coleslaw mix, sensory quality (particularly aroma) is not acceptable. Using pretreatment (soaking in ascorbic acid (5 g/L) and citric acid (5 g/L) solution) and atmosphere of 70% O2 and 30% CO2 with microperforated barrier film results in good sensory and microbiological quality (regarding to research parameters) of the coleslaw mix during 12 days of storage.

Effects of organic acid pretreatment on microstructure, functional and thermal properties of unripe banana flour

Starch availability has been implicated in unripe matured banana (Musa species), which when processed yields flour suitable for application in low gluten and composite wheat formulations. Unripe Musa species: Williams, Luvhele, Mabonde and Muomva-red obtained from fruit bunch were pretreated with ascorbic, citric and lactic acids, processed into 50 g of flour and characterised for their functional and thermal properties. Scanning electron microscope of unripe banana flour (UBF) showed varying micrographs of flour, with polygonal for Luvhele, oval for Mabonde, elongated for Muomva-red and between polygonal and spherical for Williams. The bulk density of UBF samples was within the range of 0.66–0.84 g/mL for all organic acid pretreatment while citric acid pretreated UBF had the least browning index. Significant difference (p < 0.05) was recorded in swelling power with no significant difference in water solubility index except for Mabonde UBF. Thermal properties showed single endothermic transition for all UBF samples at various pretreatment concentration. The onset temperature (To) of UBF ranges from 49.82 to 65.59 °C, peak temperature (Tp) from 60.11 to 76.71 °C, conclusion temperature (Tc) from 70.36 to 94.16 °C and enthalpy of gelatinization (ΔH) from 2.61 to 32.24 J/g. Short amylopectin chains present in starch of UBF was attributed to low To, Tp, Tc and ΔH values recorded for Mabonde cultivar, while the contribution of heat-moisture treatment rather than organic acid pretreatment of UBF samples was attributed to different gelatinization and transition temperatures recorded for all cultivars examined.

Enhancing enzymatic hydrolysis and biogas production from rice straw by pretreatment with organic acids

Lignocellulosic biomass is recalcitrant to enzymatic and microbial degradation due to its chemical compositions and physical structures that inhibit the hydrolysis reactions. To obtain a high sugar yield for biofuel production, pretreatment process is generally needed to improve efficiency of hydrolysis. Here, organic acids were used to pretreat rice straw. Using Response Surface Methodology (RSM), the effect of three pretreatment parameters, including acid concentration, treatment time, and reaction temperature, on pretreatment efficiency were evaluated and used to generate mathematic optimization model. The hydrolysis results indicated that oxalic acid pretreatment led to the highest enhancement of enzymatic saccharification up to 213.4mg (starting from 500mg of pretreated sample) when using 5.01% oxalic acid concentration at 135.91°C for 30.86min, which was 2.68 times higher than the untreated rice straw. The structural changes in the pretreated biomass were investigated using FT-IR analysis. The results suggested that lignin composition was significantly removed from the pretreated biomass, and the crystalline cellulose was also modified to amorphous form during pretreatment. Both untreated and pretreated rice straw were subjected to anaerobic digestion to evaluate the influence of organic acid pretreatment on biogas production. The highest biogas yield was 322.1ml/g-rice straw when using citric acid pretreatment which was 7.40 times higher than untreated biomass. These results demonstrated that organic acids can be used for pretreatment of lignocellulosic materials to enhance hydrolysis and biogas production.

Effect of organic acid pretreatment on some physical, functional and antioxidant properties of flour obtained from three unripe banana cultivars

Unripe banana flour (UBF) obtained from organic acid pretreatment of pulp from three non-commercial cultivars were profiled for physical, functional and antioxidant properties. UBF showed marked significant differences (p<0.05) in colour (CIEL∗a∗b∗ and CIELCH) and water holding capacity with no significant difference in oil holding capacity. The total polyphenol content (TPC) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) differed significantly with M-red UBF recording high TPC (1130.39±27.26mg GAE/100g d.w.) at 10g/L citric acid pretreatment. Correlation analysis between TPC and DPPH showed very strong positive correlation for Mabonde UBF in citric and lactic acid pretreatment (r=0.999, p<0.01; r=0.985, p<0.01), while inverse correlation was recorded in M-red UBF for ascorbic and lactic acid pretreatment (r=−0.031; r=−0.137). Organic acid pretreatment enhances the physical and antioxidant properties of UBF hitherto absent in composite food formulations.

Comparison of Dilute Organic and Sulfuric Acid Pretreatment for Enzymatic Hydrolysis of Bamboo

Pretreating bamboo is essential to overcome the recalcitrance of lignocellulose for bioethanol production. In this study, the effectiveness of formic, acetic, and sulfuric acids in pretreating bamboo were compared. To measure pretreatment efficiency, the enzymatic digestibility of the pretreated bamboo substrates was determined. Monomeric glucose conversion yield was measured after enzymatic hydrolysis. Additionally, the sugar degradation products fermentation inhibitors were measured after pretreatment. After conducting many tests, it was determined that pretreatment with dilute formic acid at 180 °C and 30 min can be an acceptable alternative to dilute sulfuric acid pretreatment.

Enzymatic and organic acid pretreatment of seaweed: effect on reducing sugars production and on biogas inhibition

Seaweeds are a valuable feedstock in the production of biofuels such as biogas. In order to achieve higher conversion rates, the biomass requires a pretreatment step. However, the use of harsh conditions is detrimental to the environment and negatively affects the biochemical composition of the seaweed, lowering the yields of the products. In this study, Laminaria digitata and Saccharina latissima were pretreated with organic acids and enzymes. The extent of hydrolysis was evaluated by the concentration of reducing sugars (RS) released from the seaweed. Thereafter, the effect of pretreatments on biogas production from L. digitata was investigated in 120 ml batch reactors incubated at 35°C. Oxalic acid and the enzymatic preparation Cellulase (Sigma C9748) improved the recovery of RS. Pretreatments inhibited the anaerobic digestion process and only a 6% increase in biogas production was obtained when the biomass was subjected to a combination of 2.5% citric acid and Cellulase.

Mass balance and transformation of corn stover by pretreatment with different dilute organic acids

Previous studies indicated high xylose yield could be achieved after pretreatment using organic acids, but it is necessary to systematically investigate the effects of different parameters during organic acid pretreatments. Corn stover was pretreated with sulfuric, oxalic, citric, tartaric and acetic acid at 50 and 90mM from 130 to 190°C. The xylan balance for each different acid was distinct, but all balances were very close to 100% by determining xylan recovery, xylooligomer yield, xylose yield and furfural yield. The effects of combined severity on the recovery or yields of these components were also studied. The acid pKa value affected the proportion of xylan degradation products. The maximum value of xylose and xylooligomer yield for specific acid pretreatment was also determined by pKa value. The maximum xylose yield was obtained after pretreatment with sulfuric and oxalic acid, but more xylooligomers were obtained after pretreatment with weaker acids.

Microwave-assisted organic acid pretreatment for enzymatic hydrolysis of rice straw

Pretreatment of lignocellulosic materials is considered a critical step in the production of cellulosic ethanol because it can significantly break the structure and remove the unwanted components of lignocellulose to improve the hydrolysis efficiency of cellulose. In this study, the microwave-assisted pretreatment method was adopted to treat rice straw as an alternative to conventional pretreatment methods. After pretreatment, the product was further hydrolyzed by cellulase. The influences of acid concentration, solid–liquid ratio, microwave intensity, irradiating time, and catalyst concentration on the removal ratio of lignin were investigated. The optimal conditions of pretreatment were obtained using an orthogonal test. After pretreatment, the infrared spectrum of the solution was tested, and micro-morphology was observed by scanning electron microscopy (SEM). The removal ratio of lignin and the yield of reducing sugar were determined by spectrophotometry. The results indicate that the sequence of influential factors is microwave intensity > solid–liquid ratio > acetic acid concentration > microwave irradiating time. Under optimal conditions (25% acid concentration, 1:15 solid–liquid ratio, 230 W microwave intensity, and 5 min irradiating time), the removal ratios of lignin are 46.1 and 51.54%, and the sugar yields are 71.41 and 80.08% when acetic acid and propionic acid are used as solvents, respectively. The sugar yield was only 35.28% in the blank sample. SEM images reveal that the surface of rice straw changed noticably when microwave-assisted pretreatment is used. This suggests that microwave-assisted organic acid pretreatment is effective in improving the enzymatic hydrolysis sugar yield of rice straw.

Methane production from rice straw pretreated by a mixture of acetic–propionic acid

Rice straw was treated with a mixed solution of acetic acid and propionic acid to enhance its biodegradability. The effect of acid concentration, pretreatment time, and the ratio of solid to liquid on the delignification performance of rice straw were investigated. It was found that the optimal conditions for hydrolysis were 0.75 mol/L acid concentration, 2 h pretreatment time and 1:20 solid to liquid ratio. Batch methane fermentation of untreated rice straw, pretreated rice straw, and the hydrolysates (the liquid fraction) of pretreatment were conducted at 35 °C for 30 days, and the results indicated that methane production of rice straw can be enhanced by dilute organic acid pretreatment. Moreover, most of the acid in hydrolysates can also be converted into methane gas.

Comparison of dilute mineral and organic acid pretreatment for enzymatic hydrolysis of wheat straw

The efficiencies of fumaric, maleic, and sulfuric acid in wheat straw pretreatment were compared. As a measure for pretreatment efficiency, enzymatic digestibility of the lignocellulose was determined. Monomeric glucose and xylose concentrations were measured after subsequent enzymatic hydrolysis, as were levels of sugar degradation products furfural and hydroxymethylfurfural after pretreatment. The influence of pretreatment temperature and of wheat straw loading was studied. It is shown that, at 150 °C and 20–30% (w/w) dry wheat straw, the pretreatment with dilute fumaric or maleic acid can be a serious alternative to dilute sulfuric acid pretreatment.

Organosolv pretreatment of lignocellulosic biomass for enzymatic hydrolysis

Production of ethanol by bioconversion of lignocellulosic biomass has attracted much interest in recent years. However, the pretreatment process for increasing the enzymatic digestibility of cellulose has become a key step in commercialized production of cellulosic ethanol. During the last decades, many pretreatment processes have been developed for decreasing the biomass recalcitrance, but only a few of them seem to be promising. From the point of view for integrated utilization of lignocellulosic biomass, organosolv pretreatment provides a pathway for biorefining of biomass. This review presents the progress of organosolv pretreatment of lignocellulosic biomass in recent decades, especially on alcohol, organic acid, organic peracid and acetone pretreatments, and corresponding action mechanisms. Evaluation and prospect of organosolv pretreatment were performed. Finally, some recommendations for future investigation of this pretreatment method were given.

Effects of organic acid pretreatment on the structure and pyrolysis reactivity of coals

Following the 2004 ‘Boxing day’ tsunami, a determination has been made of the activity concentrations of 226Ra, 232Th and 40K in beach sand samples which have been collected from various locations along the Andaman coast of the Thai peninsula. Use has been made of a HPGe detector-based, low-background gamma-ray counting system. The natural radioactivity levels of 226Ra, 232Th and 40K measured from these samples was found to lie in the range 1.6–52.5, 0.3–73.9and 2.8–1111.9 Bq/kg respectively for the west coast and 3.5–83.1, 4.5–42.0, and 9.6–1376 Bq/kg respectively for the east coast. The radioactivity concentrations of 226Ra, 232Th and 40K along the Andaman coast are comparable to that of the east coast, which was not exposed to the tsunami. The corresponding annual effective dose varies from 1.6–105.9 μSv/y with a mean value of 59.1±0.3 μSv/y, significantly lower than the worldwide average as reported by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (2000).

Effects of organic acid pretreatment on the structure and pyrolysis reactivity of coals

Mild acid pretreatment was performed using aqueous acetic acid or methoxyethoxy acetic acid to remove bridging cations through oxygen functional groups and to improve the pyrolytic reactivity of three coals (Beulah-Zap, BZ; Wyodak, WY; Illinois #6, IL). The acid pretreatment removed ion-exchangeable cations such as Ca and Mg from lower ranking coals, and enhanced their swelling by pyridine, and increased their volatile yield in the flash pyrolysis. The CO/CO 2 ratio produced in the flash pyrolysis from lower rank coals increased by the acid treatment. The pretreatment liberates the cation-bridging network through the oxygen functional groups of coal. The acid treatment converts the carboxylates into their free carboxylic acids, enhancing the thermal decomposition into smaller hydrocarbons and their devolatilization through the pores. Acid treatment appears to loosen the π–π stacking and intensify the alkyl entanglement. The slow step scan XRD confirms the more influences of such treatments on the lower rank coals.

Effect of organic acid pretreatment on the regeneration and development (conversion) of whole plants from callus cultures of alfalfa, Medicago sativa L.

Cultures of uninduced alfalfa callus have been pretreated with various organic acids for one subculture cycle prior to embryo induction with 2,4-dichlorophenoxyacetic acid (2,4-D) and regeneration on hormone-free medium. This culture pretreatment regime results in decreased callus growth, changes the morphology of the callus and causes an increase in embryo yield after induction and regeneration of the callus. The effective organic acids and their optimum concentrations are K +-citrate (20 mM), K +-malate (60 mM), K +-succinate (≤50 mM), K +-tartrate (70 mM) and K +-oxadate (10 mM). The effect of K +-citrate can be enhanced by the addition of amino acids such as proline or glutamine to the pretreatment medium. The embrys which form from pretreated callus have more normal morphology than embryos coming from untreated callus cells. A further effect of organic acid pretreatment is to increase the percentage of whole plants which develop (conversion) compared to control treatments. The efficiency of regeneration of callus to whole plants was determined for control and organic acid pretreated cultures. The results indicate that while callus growth rate is 44–64% less during organic acid pretreatment compared to the control, the overall efficiency of regeneration is increased by 88–320%. The effects on culture buffering and chelation apparently do not account for the organic acid pretreatment effect. Organic acid pretreatment alone does not satisfy the requirement for induction of callus with a strong auxin such as 2,4-D. The results are discussed with reference to physiological selection of callus which is competent to undergo embryogenesis.