Hydrothermal (HT) reactions of agricultural and food-processing waste have been proposed as an alternative to conventional waste treatment technologies due to allowing several improvements in terms ...of process performance and energy and economical advantages, especially due to their great ability to process high moisture content biomass waste without prior dewatering. Complex structures of wastes and unique properties of water at higher temperatures and pressures enable a variety of physical–chemical reactions and a wide spectra of products. This paper’s aim is to give extensive information about the fundamentals and mechanisms of HT reactions and provide state of the research of agri-food waste HT conversion.
Being secondary plant metabolites, polyphenols represent a large and diverse group of substances abundantly present in a majority of fruits, herbs and vegetables. The current contribution is focused ...on their bioavailability, antioxidative and anticarcinogenic properties. An overview of extraction methods is also given, with supercritical fluid extraction highlighted as a promising eco-friendly alternative providing exceptional separation and protection from degradation of unstable polyphenols. The protective role of polyphenols against reactive oxygen and nitrogen species, UV light, plant pathogens, parasites and predators results in several beneficial biological activities giving rise to prophylaxis or possibly even to a cure for several prevailing human diseases, especially various cancer types. Omnipresence, specificity of the response and the absence of or low toxicity are crucial advantages of polyphenols as anticancer agents. The main problem represents their low bioavailability and rapid metabolism. One of the promising solutions lies in nanoformulation of polyphenols that prevents their degradation and thus enables significantly higher concentrations to reach the target cells. Another, more practiced, solution is the use of mixtures of various polyphenols that bring synergistic effects, resulting in lowering of the required therapeutic dose and in multitargeted action. The combination of polyphenols with existing drugs and therapies also shows promising results and significantly reduces their toxicity.
Optimal operating conditions for the extraction of phenolic compounds from grape marc and elder berry have been investigated. The aim was to obtain extracts with high anthocyanin content, which show ...stability during storage and would be potentially interesting for commercial applications as natural colorants. For this purpose three varieties of grape marc, native to Slovenia (Refošk, Merlot and Cabernet), were studied. The results were compared with the extraction of elder berry, which is known for its high anthocyanin content. Single-step batch extractions were performed with ethanol, ethyl-acetate and acetone in different ratios with water. Temperatures of 20 °C, 40 °C and 60 °C were applied. Influence of the change in pH values of the extraction media was investigated regarding the yield and degradation of anthocyanins. Two-step extractions, combining supercritical fluid extractions (SFE) and conventional batch extractions, were applied. The most efficient conventional solvents in single-step extractions were mixtures of organic solvent and water at 60 °C. Pre-treatment of the natural material with supercritical CO
2 (with or without ethanol as co-solvent) improved the extraction of polyphenols from the grape marc. This method provides an alternative to the pre-treatment of the plant materials, replacing toxic organic solvents (e.g. hexane). Acidified extraction media resulted in higher anthocyanin content in the extracts. However, the degradation of the anthocyanins during storage was higher, which led to the loss of the intensive colour. The addition of a commercially available rosemary extract to the extraction solvent improved the stability of the grape marc extract during storage.
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•PET waste was successfully decomposed to main product TPA in sub- and supercritical water.•Complete depolymerization of PET at short reaction times (1–30 min).•High yields (90%) and ...high purities (98%) of monomer TPA.•Benzoic acid, 1,4-dioxane, acetaldehyde, isophthalic acid and CO2 are also formed.•Before hydrothermal degradation, sorting of PET waste by color is not necessary.
As a consequence of the widespread use of polyethylene terephthalate (PET), huge amounts of PET waste are generated annually, and thus a critical point of waste management strategy is to reduce these amounts. This study presents the chemical recycling of PET waste using sub- and supercritical water (SubCW and SCW). Two types of PET waste were chosen to study hydrolytic depolymerization: colorless and colored bottles. The experiments were carried out in a batch reactor at temperatures from 250 to 400 °C, with reaction period of 1–30 min. During the hydrolysis of PET waste, primary and secondary products were formed. The highest yield of terephthalic acid (TPA) was identified at 300 °C and a reaction period of 30 min; 90.0 ± 0.4% yield was observed from colorless PET waste and 85.0 ± 0.2% from green PET waste. The purity of final TPA obtained from PET waste was near 100%. The formation of secondary products such as benzoic acid, 1,4-dioxane, acetaldehyde, isophthalic acid (IPA) and carbon dioxide (CO2) were detected.
•Subcritical water extraction of sunflower oil- and water-soluble phase is proposed.•We examined degree of hydrothermal degradation of both phases.•Hydrothermal degradation did not affect oil ...quality, only water soluble extract.•Antioxidant capacity of oil increases drastically at temperatures >100°C.•Hydrothermal degradation of proteins occurs to a lesser degree than carbohydrates.
In this study, the subcritical water extraction is proposed as an alternative and greener processing method for simultaneous removal of oil- and water-soluble phase from sunflower seeds. Extraction kinetics were studied at different temperatures and material/solvent ratios in a batch extractor. Degree of hydrothermal degradation of oils was observed by analysing amount of formed free fatty acids and their antioxidant capacities. Results were compared to oils obtained by conventional methods. Water soluble extracts were analysed for total proteins, carbohydrates and phenolics and some single products of hydrothermal degradation.
Highest amount of oil was obtained at 130°C at a material/solvent ratio of 1/20g/mL after 30min of extraction. For all obtained oils minimal degree of hydrothermal degradation could be identified. High antioxidant capacities of oil samples could be observed. Water soluble extracts were degraded at temperatures ⩾100°C, producing various products of hydrothermal degradation.
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•On overview on the research on the biomass conversion for production of chemicals.•Experimental results on isolation of substances from biomass using sub- and SCW.•Extraction of ...value added compounds from natural sources.•Assessment of biomass potential and benefits of diverse bioenergy options.
Review summarizes the research on the biomass conversion for production of chemicals and an overview on recent activities of our research group on isolation of substances from biomass using sub- and supercritical water. Herein, hydrothermal processing of biomass waste represents an alternative approach to upswing the productivity chemicals, basic chemicals for synthesis and plant-based pharmaceutical compounds. The processing concepts to obtain products and product classes based on biological raw materials in gaseous, liquid, or solid state are presented. Subcritical water is discussed as a highly reactive media to enhance extraction affinity of value added compounds, such as proteins and amino acids, essential oils, oils and fatty acids, carbohydrates and phenolic compounds from natural sources.
A new rapid method has been developed for the determination of low levels of rosmarinic acid extracted from rosemary (Rosmarinus officinalis L.) and has been used as an antioxidant in meat and meat ...products after cold storage at 4°C. The method is a high performance liquid chromatography using a coulometric electrochemical detector. It provides a significant improvement on the limit of detection, which was 0.33 ppb, while the limit of quantification was 1 ppb of rosmarinic acid. The advantage of the method also lies in the simpler and faster sample preparation, which can quantify a very low concentration of rosmarinic acid (60 ppb), and is more than 40 ppb below the limits of previously existing methods. A coulometric method is well suited for determining low analyte concentrations and is one of the most sensitive analytical approaches available today, in addition to being time efficient and cost effective.
Practical Application
A new method for determining low concentrations (60 ppb) of rosmarinic acid in meat and meat products is presented. The method is user‐friendly, as it does not require complex sample preparation. It is a selective, precise, and accurate method that makes it useful for routine applications in the meat and other food industries.
•Chemical recycling of PE (virgin LDPE, colored PE waste) in SCW at 425 °C and 450 °C.•High yields of wax/oil phase (up to 98%) were obtained.•Wax/oil phases were rich with aliphatic, alicyclic and ...aromatic hydrocarbons.•Main light hydrocarbons in gas phases were C2–C4.•Potential mechanism of hydrothermal degradation of PE has been proposed.
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In the present study the supercritical water (SCW) degradation of polyethylene (PE) plastics (virgin LDPE, PE waste) has been investigated in a batch reactor at 380–450 °C and reaction time of 15–240 min. The experiments (virgin LDPE) were also performed with the addition of acetic acid. During the SCW decomposition of PE plastics oil or wax, aqueous, gas and solid (only in PE waste) phases were formed. The obtained oil phase was composed of alkanes, alkenes, cycloalkanes, aromatics, and alcohols, while the gas phase manly contained light hydrocarbons (C1–C6). By performing reaction at high temperatures (425–450 °C) and reaction times from 30 to 240 min the concentrations of long-chain hydrocarbons (>C20) and C9–C20 (diesel) fraction in oil phase decreased, while concentration of C6–C8 hydrocarbons (gasoline fraction) increased. Finally, the influence of acetic acid on the PE degradation has been discussed and the potential degradation mechanism of PE waste in SCW is proposed.
The removal efficiency of lead, iron, and copper ions from aqueous solutions with the use of zeolite, bentonite, and steel slag as adsorbents was investigated. Adsorption experiments were conducted ...at room temperature with aqueous solutions of individual metal ions of lead, copper, and iron, and an equimolar aqueous mixture of all three metal ions. The influence of pH value and initial concentration of the solutions and interaction of the selected ions and their impact on the adsorption have been studied. Experimental adsorption data were analyzed with the Langmuir and Freundlich isotherm model. The experiments showed promising results. In solutions with single metal ion removal percent obtained by bentonite were 98.1% for lead, 99.81% for copper, and 98.16% for iron. By using zeolite removal percent was 99.53% for lead, 98.47% for copper, and 96.11% for iron, while by using steel slag it was 99.98% for iron, 99.96% for copper, and 85.92% for lead. By examining the trinary solution, it could be seen that higher initial concentrations promote adsorption of lead and iron on zeolite and bentonite in the presence of other ions. When using steel slag removal percent of lead was noticeably higher in the trinary solution.
The aim of the work was the optimization of the subcritical water extraction process of chestnut bark using Box-Behnken response surface methodology. The influence of process parameters, such as ...temperature, extraction time and solvent-solid ratio, on extraction yield, yield of the main compounds, total phenol content, total tannin content and antioxidant activity has been investigated. The identified compounds were ellagic and gallic acids, ellagitannins (vescalagin, castalagin, 1-
-galloyl castalagin, vescalin and castalin), sugars (maltose, glucose, fructose and arabinose) and sugar derivatives (5-HMF, furfural and levulinic acid). Finally, the optimal process conditions for obtaining the bark extract highly rich in ellagic acid and with satisfactory levels of total phenols and total tannins have been determined.
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