Valorization of spent black tea by recovery of antioxidant polyphenolic compounds: Subcritical solvent extraction and microencapsulation

Extraction and Separation of Natural Products from Microalgae and Other Natural Sources Using Liquefied Dimethyl Ether, a Green Solvent: A Review

Microalgae are a sustainable source for the production of biofuels and bioactive compounds. This review discusses significant research on innovative extraction techniques using dimethyl ether (DME) as a green subcritical fluid. DME, which is characterized by its low boiling point and safety as an organic solvent, exhibits remarkable properties that enable high extraction rates of various active compounds, including lipids and bioactive compounds, from high-water-content microalgae without the need for drying. In this review, the superiority of liquefied DME extraction technology for microalgae over conventional methods is discussed in detail. In addition, we elucidate the extraction mechanism of this technology and address its safety for human health and the environment. This review also covers aspects related to extraction equipment, various applications of different extraction processes, and the estimation and trend analysis of the Hansen solubility parameters. In addition, we anticipate a promising trajectory for the expansion of this technology for the extraction of various resources.

Recent advances incombined Avant-garde technologies (thermal-thermal, non-thermal-non-thermal, and thermal-non-thermal matrix) to extract polyphenols from agro byproducts

Because food byproducts (waste) are rich in phytoconstituents, valorizing them is crucial for global food security. However, conventional extraction (CE), including decoction, maceration, Soxhlet, etc., for agro byproducts' polyphenol extraction are time-consuming and rely significantly on vast volumes of potentially aggressive solvents. Hence, Avantgarde extraction technologies, including non-thermal (high hydrostatic pressure (HHPE), pulsed-electric field (PEF), high voltage electrical discharges (HVED), etc.) and thermal extraction (supercritical fluid (SCF), subcritical water extraction (SWE), microwave-assisted extraction (MAE), etc.), as well as their thermal combinations (SCF-PLE, SCCO2-SWE, SCCO2-MAE, etc.), non-thermal combinations (HHPE + UAE, PEF + UAE, HVED + UAE, etc.) and combined thermalnon-thermal (MAE-UAE, etc.) are increasingly replacing CE. However, a review of combined Avant-garde extraction escalation technologies (non-thermal/thermal extraction matrix) for extracting polyphenols from agro-byproducts is limited. Hence, this manuscript reviewed Avant-garde extraction technologies (non-thermal/thermal extraction matrix) for extracting phenolics from agro-byproducts in the last 5 years. The key factors affecting polyphenols' extraction from the byproduct, the recent applications of Avant-garde technologies, and their principle were reviewed using databases from Web of Science and Lens.org. The results demonstrated that combined Avant-garde extraction escalation technologies increase extractability, resulting in polyphenols with higher extraction rates, fewer contaminants, and preservation of thermosensitive components. Therefore, combined Avant-garde extraction technologies should be explored over the next five years. Implementing an integrated process and the strategic sequencing of diverse Avant-garde extraction technologies are important. Thus, further investigation is required to explore the sequencing process and its potential impact on the extraction of phenolics from agro-byproducts.

Sustainable environmental practices of tea waste-a comprehensive review

Tea, the major beverage worldwide, is one of the oldest commercial commodities traded from ancient times. Apart from many of its advantages, including health, socio-economic, climatic, and agro-ecological values, FAO has recognized that the tea value chain covering its growth in the field, processing and marketing, and finally, the hot cup at the user's hand needs to be made sustainable during all these stages. Tea generates a lot of waste in different forms in different stages of its growth and processing, and these wastes, if not managed properly, may cause environmental pollution. A planned utilization of these wastes as feedstocks for various processes can generate more income, create rural livelihood opportunities, help grow tea environmentally sustainable, avoid GHG emissions, and make a real contribution to SDGs. Thermochemical and biological conversion of tea wastes generates value-added products. This review provides an overview on the impacts of the tea wastes on the environment, tea waste valorization processes, and applications of value-added products. The application of value-added products for energy generation, wastewater treatment, soil conditioners, adsorbents, biofertilizers, food additives, dietary supplements, animal feed bioactive chemicals, dye, colourant, and phytochemicals has been reviewed. Further, the challenges in sustainable utilization of tea wastes and opportunities for commercial exploitation of value-added products from tea wastes have been reviewed.

Pilot-scale extraction of polyphenols from spent black tea by semi-continuous subcritical solvent extraction

•

Subcritical solvent extraction is a novel method to recover polyphenols from spent black tea at pilot-scale.

•

After hot water extraction, non-extractable polyphenols were found in spent black tea.

•

Subcritical solvent extraction recovered the non-extractable polyphenols from spent black tea.

•

Water–ethanol mixture at hot-pressurised conditions promoted the recovery of non-extractable polyphenols.

Spent black tea (SBT) is a residue from tea beverage production and considered as a potential source of active polyphenols. This study aimed to develop a pilot-scale process on semi-continuous subcritical solvent extraction (SSE) of polyphenols from SBT by exploiting the lab-scale knowledge. Treatment of SBT with ethanol–water (50% w/w) as solvent at 125 °C and 0.3 MPa achieved a significantly higher yield of polyphenols (80.82 g gallic acid equivalents/kg black tea) with antioxidant activity (64.20 g gallic acid equivalents/kg black tea), compared to hot water extraction (HWE). SSE increased the soluble matter content in extracts than HWE. Based on the results of LC-MS, theaflavin-3,3′-digallate was the most abundant polyphenol from a total of 12 compounds to be extracted by SBT with 50% ethanol. The results suggested that SSE can be used as a scale-up extraction method to recover polyphenols from SBT.

Advances in bioconversion of spent tea leaves to value-added products

Spent tea leaves (STL) are generated after the extraction of liquor from processed tea leaves and are regarded as an underutilized waste. STL are rich in essential amino acids, ω-6 and ω-3 fatty acids, alkaloids (theobromine and caffeine), polyphenols (catechin, theaflavins and rutin) and minerals (Ca, P, K, Mg, Mn) that could be utilized for the production of industrially important products. Vermicomposting, anaerobic digestion, silage preparation and fermentation are currently used as low cost methods for the bioconversion of STL to a usable form. Structural, morphological and chemical modification of STL after suitable bioconversion enables its application in the development of biopolymers, biofuels, catechin derivatives, biochar, absorbents for dye, and for removal of Cd, Hg, Cr(IV), As(V) and aspirin. This review discusses the composition, characterization, bioconversion and value added product generation from STL while highlighting prospective applications of STL in developing battery electrodes, nanocatalysts, insulation materials and edible bioactive peptides.

Effects of Lipase Addition, Hydrothermal Processing, Their Combination, and Co-Digestion with Crude Glycerol on Food Waste Anaerobic Digestion

To enhance anaerobic fermentation during food waste (FW) digestion, pretreatments can be applied or the FW can be co-digested with other waste. In this study, lipase addition (LA), hydrothermal pretreatment (HTP), and a combination of both methods (HL) were applied to hydrolyze organic matter in FW. Furthermore, the effects of crude glycerol (CG), which provided 5%, 10%, and 15% of the volatile solids (VS) as co-substrate (denoted as CG5, CG10, and CG15, respectively), on the anaerobic digestion of FW were assessed. With an increasing proportion of CG in the co-digestion experiment, CG10 showed higher methane production, while CG15 negatively affected the anaerobic digestion (AD) performance owing to propionic acid accumulation acidifying the reactors and inhibiting methanogen growth. As the pretreatments partially decomposed hard-to-degrade substances in advance, pretreated FW showed a stronger methane production ability compared with raw FW, especially using the HL method, which was significantly better than co-digestion. HL pretreatment was shown to be a promising option for enhancing the methane potential value (1.773 NL CH4/g VS) according to the modified Gompertz model.

Development and Characterization of Functional Starch-Based Films Incorporating Free or Microencapsulated Spent Black Tea Extract

Antioxidant polyphenols in black tea residue are an underused source of bioactive compounds. Microencapsulation can turn them into a valuable functional ingredient for different food applications. This study investigated the potential of using spent black tea extract (SBT) as an active ingredient in food packaging. Free or microencapsulated forms of SBT, using a pectin-sodium caseinate mixture as a wall material, were incorporated in a cassava starch matrix and films developed by casting. The effect of incorporating SBT at different polyphenol contents (0.17% and 0.34%) on the structural, physical, and antioxidant properties of the films, the migration of active compounds into different food simulants and their performance at preventing lipid oxidation were evaluated. The results showed that adding free SBT modified the film structure by forming hydrogen bonds with starch, creating a less elastic film with antioxidant activity (173 and 587 µg(GAE)/g film). Incorporating microencapsulated SBT improved the mechanical properties of active films and preserved their antioxidant activity (276 and 627 µg(GAE)/g film). Encapsulates significantly enhanced the release of antioxidant polyphenols into both aqueous and fatty food simulants. Both types of active film exhibited better barrier properties against UV light and water vapour than the control starch film and delayed lipid oxidation up to 35 d. This study revealed that starch film incorporating microencapsulated SBT can be used as a functional food packaging to protect fatty foods from oxidation.