Valorization of Greenhouse Horticulture Waste from a Biorefinery Perspective

Improving agricultural sustainability - A review of strategies to valorize tomato plant residues (TPR)

Considerations for the modification of agricultural practices and waste management to improve environmental sustainability remain a subject of great importance. Prioritization of intensive mass food production to meet the demand of an increasing human population has introduced a multitude of environmental issues due to, among other factors, the large volumes of waste output. Tomato production in greenhouses, for example, generates tonnes of bio-waste per hectare each harvest including green tomato plant residues (i.e., stems, leaves, branches). Giving value to these green tomato plant residues collected during the growing cycle and after harvest has not proven straightforward despite a massive yearly release of tonnes of carbon dioxide from stems and leaves disposed on landfills. This paper aims to summarize current research in tomato plant residue valorization and to identify considerations for future valorization strategies. Peer reviewed articles, scientific books and governmental, economic and statistical reports on the topic of tomato plant residues were collected and analyzed. Focuses included traditional valorization approaches, bio-refinement strategies and conversion of fiber-rich residues into high value packaging materials. Initiatives for sustainable agriculture, their market relevance, and the strengths and weaknesses of using tomato plant residues in these valorization approaches are discussed. Overall, it was concluded that valorization of tomato plant residues would be a highly integrative endeavor that would require coordination from multiple levels in the agricultural production chain.

Waste from the food industry: Innovations in biorefineries for sustainable use of resources and generation of value

Biorefineries have attracted significant attention from the scientific community and various industrial sectors due to their use of unconventional biomass sources to produce biofuels and other value-added compounds. Various agro-industrial residues can be applied in biorefinery systems, making them economically and environmentally attractive. However, the cost, efficiency, and profitability of the process are directly affected by the choice of biomass, pre-treatments, and desired products. In biorefineries, the simultaneous production of different products during processing is a valuable approach. Chemical, physical, biological, or combined treatments can generate numerous compounds of high commercial interest, such as phenolic compounds. These treatments, in addition to modifying the biomass structure, are essential for the process's viability. Over the years, complex treatments with high costs and environmental impacts have been simplified and improved, becoming more specific in generating high-value resources as secondary outputs to the main process (generally related to the release of sugars from lignocelluloses to produce second-generation ethanol). Innovative methods involving microorganisms and enzymes are the most promising in terms of efficiency and lower environmental impact. Biorefineries enable the use of varied raw materials, such as different agro-industrial residues, allowing for more efficient resource utilization and reducing dependence on non-renewable sources. In addition to producing low-carbon biofuels, biorefineries generate a variety of high-value by-products, such as packaging materials, pharmaceuticals, and nutritional ingredients. This not only increases the profitability of biorefineries but also contributes to a circular economy.

Pretreatment of Vine Shoot Biomass by Choline Chloride-Based Deep Eutectic Solvents to Promote Biomass Fractionation and Enhance Sugar Production

Vine shoots hold promise as a biomass source for fermentable sugars with efficient fractionation and conversion processes. The study explores vine shoots as a biomass source for fermentable sugars through pretreatment with two deep eutectic solvents mixtures: choline chloride:lactic acid 1:5 (ChCl:LA) and choline chloride:ethylene glycol 1:2 (ChCl:EG). Pretreatment conditions, such as temperature/time, solid/liquid ratio, and biomass particle size, were studied. Chemical composition, recovery yields, delignification extent, and carbohydrate conversion were evaluated, including the influence of washing solvents. Temperature and particle size notably affected hemicellulose and lignin dissolution, especially with ChCl:LA. Pretreatment yielded enriched cellulose substrates, with high carbohydrate conversion rates up to 75.2% for cellulose and 99.9% for xylan with ChCl:LA, and 54.6% for cellulose and 60.2% for xylan with ChCl:EG. A 50% acetone/water mixture increased the delignification ratios to 31.5%. The results underscore the potential of this pretreatment for vine shoot fractionation, particularly at 30% solid load, while acknowledging the need for further process enhancement.

Antibacterial and Antitumoral Potentials of Phytosynthesized Silver/Silver Oxide Nanoparticles Using Tomato Flower Waste

This study presents the phytosynthesis of silver-based nanoparticles using tomato flower waste extracts for the first time in the literature. The determination of total polyphenolic and flavonoid contents in the extracts showed high gallic acid equivalents (6436-8802 mg GAE/kg dm) and high quercetin equivalents (378-633 mg QE/kg dm), respectively, dependent on the extraction method. By the Ultra Performance Liquid Chromatography technique, 14 polyphenolic compounds were identified and quantified in the tomato flower waste extracts. The abundant phenolic compounds were caffeic acid (36,902-32,217 mg/kg) and chlorogenic acid (1640-1728 mg/kg), and the abundant flavonoid compounds were catechin (292-251 mg/kg) and luteolin (246-108 mg/kg). Transmission electron microscopy of the nanoparticles revealed a particle size range of 14-40 nm. Fourier Transform infrared spectroscopy and X-ray diffraction studies confirmed the phytosynthesis of the silver/silver oxide nanoparticles. These findings hold significant results for the antibacterial and antitumoral potential applications of the obtained nanoparticles, opening new areas for research and development and inspiring further exploration. The impact of this research on the field of metallic nanoparticle phytosynthesis is substantial, as it introduces a novel approach and could lead to significant advancements in the field.

Challenges and prospects of yeast-based microbial oil production within a biorefinery concept

Biodiesel, unlike to its fossil-based homologue (diesel), is renewable. Its use contributes to greater sustainability in the energy sector, mainly by reducing greenhouse gas emissions. Current biodiesel production relies on plant- and animal-related feedstocks, resulting in high final costs to the prices of those raw materials. In addition, the production of those materials competes for arable land and has provoked a heated debate involving their use food vs. fuel. As an alternative, single-cell oils (SCOs) obtained from oleaginous microorganisms are attractive sources as a biofuel precursor due to their high lipid content, and composition similar to vegetable oils and animal fats. To make SCOs competitive from an economic point of view, the use of readily available low-cost substrates becomes essential. This work reviews the most recent advances in microbial oil production from non-synthetic sugar-rich media, particularly sugars from lignocellulosic wastes, highlighting the main challenges and prospects for deploying this technology fully in the framework of a Biorefinery concept.

Sustainable and circular agro-environmental practices: A review of the management of agricultural waste biomass in Spain and the Czech Republic

Sustainable and circular production models, such as the circular economy and circular bioeconomy, have become key mechanisms to leave behind the traditional linear model of food production. Under this approach and considering the waste biomass potential available in Spain and the Czech Republic, the main objective of this study is to analyse the most relevant aspects of the generation, use and regulation of agricultural waste biomass (AWB) in both countries. For this purpose, a scientometric analysis and systematic review of published research in the Scopus database were carried out. A complementary analysis of AWB management policies and regulations was also part of the methodology. The results show that Spain has published almost twice as much research as the Czech Republic. Furthermore, 91% of the retrieved research prioritizes the characterization and estimation of the potential of more than 15 AWB types. Among the main ones are olive residues, horticultural residues and wheat straw, which are used for producing organic amendments, bioenergy and biofuels. The results confirm that the reduction and valorization of AWB is an issue that has become more important in the last 13 years, mainly due to the policies and strategies for circular economy and circular bioeconomy. With this in mind, this study provides relevant information for governments on the aspects that need to be improved to advance in the valorization of AWB. This study also provides guidance to farmers on the reduction and/or recovery alternatives that they can implement to move towards sustainable and circular agriculture.

Efficient use of discarded vegetal residues as cost-effective feedstocks for microbial oil production

BACKGROUND

Horticultural intensive type systems dedicated in producing greenhouse vegetables are one of the primary industries generating organic waste. Towards the implementation of a zero-waste strategy, this work aims to use discarded vegetables (tomato, pepper and watermelon) as feedstock for producing microbial oil using the oleaginous yeast Cryptococcus curvatus.

RESULTS

The soluble fraction, resulting after crushing and centrifuging these residues, showed C/N ratios of about 15, with a total carbohydrate content (mainly glucose, fructose and sucrose) ranging from 30 g/L to 65 g/L. Using these liquid fractions as substrate under a pulse-feeding strategy with a concentrated glucose solution resulted in an intracellular total lipid accumulation of about 30% (w/w) of the total dry cell weight (DCW). To increase this intracellular lipid content, the initial C/N content was increased from 15 to 30 and 50. Under these conditions, the process performance of the pulse-feeding strategy increased by 20-36%, resulting in a total intracellular lipid concentration of 35-40% DCW (w/w).

CONCLUSION

These results demonstrate the potential of discarded vegetables as a substrate for producing bio-based products such as microbial oil when proper cultivation strategies are available.

Recent advances on physical technologies for the pretreatment of food waste and lignocellulosic residues

The complete deployment of a bio-based economy is essential to meet the United Nations' Sustainable Development Goals from the 2030 Agenda. In this context, food waste and lignocellulosic residues are considered low-cost feedstocks for obtaining industrially attractive products through biological processes. The effective conversion of these raw materials is, however, still challenging, since they are recalcitrant to bioprocessing and must be first treated to alter their physicochemical properties and ease the accessibility to their structural components. Among the full pallet of pretreatments, physical methods are recognised to have a high potential to transform food waste and lignocellulosic residues. This review provides a critical discussion about the recent advances on milling, extrusion, ultrasound, and microwave pretreatments. Their mechanisms and modes of application are analysed and the main drawbacks and limitations for their use at an industrial scale are discussed.

Evaluation and Identification of Key Economic Bottlenecks for Cost-Effective Microbial Oil Production from Fruit and Vegetable Residues

Intensive horticultural systems for the production of vegetables in greenhouses represent one of the main industries generating organic waste, as those that do not meet the quality standards for the fresh market or the processing industry are discarded. This highlights the importance of using these residues as raw material for other applications, such as bioenergy and bioproducts production, within the framework of a bio-based economy that maximizes the utilization of biomass resources in a sustainable manner. In this work, the microbial oil production from discarded pepper using the oleaginous yeast Cryptococcus curvatus was evaluated. Overall, a total lipid accumulation of 16.8 g/L was achieved with a fatty acid profile suitable to produce biodiesel. The lipid yield obtained was 0.12 g/g sugars. In addition, experimental results were used to assess the techno-economic feasibility of a proposed microbial oil plant using the software Aspen Plus. This plant yields approximately 96 kg of microbial oils/ton dry discarded pepper, with an estimated Minimum Selling Price of 7 €·kg−1. These figures point out the necessity of increasing the yield of microbial oil production and considering the utilization of possible by-products, such as mannitol and cell debris, to improve the economic performance of the process.

Sustainable Drying and Green Deep Eutectic Extraction of Carotenoids from Tomato Pomace

The extraction of molecules with high added value plays an important role in the recovery of food waste. This work aimed to valorize tomato pomace, a by-product composed of skin and seeds, through extraction of carotenoids, especially lycopene and β-carotene. The tomato pomace was dried using three different methods (freeze-drying, heat drying, and non-thermal air-drying) to reduce its weight, volume, and water activity and to concentrate the carotenoid fraction. These drying approaches were compared considering the extractive potential. Three solvent mixtures were compared, a traditional one (n-hexane:acetone) and two green deep eutectic solvent mixtures (ethyl acetate:ethyl lactate and menthol:lactic acid) in combination with different drying procedures. The extract obtained using ethyl acetate:ethyl lactate with non-thermal air-drying showed the highest contents of lycopene and β-carotene (75.86 and 3950.08 µg/g of dried sample, respectively) compared with the other procedures.

Process efficiency in relation to enzyme pre-treatment duration in black soldier fly larvae composting

Black soldier fly larvae (BSFL) composting is a treatment in which biodegradable food waste is converted into animal-feed protein and organic fertiliser. BSFL composting has greatest potential for mixed food waste, but under European Union regulations only plant-based waste is permitted as feed for larvae. Biomass conversion efficiency (BCE) in BSFL composting is lower for plant-based waste than for mixed food waste. One way of improving BCE for plant-based waste is to add enzymes to make the waste more available to the larvae, but enzyme pre-treatment is not commonly applied prior to BSFL composting. Therefore this study examined the impact of enzyme pre-treatment duration on process efficiency in BSFL composting of lettuce-cabbage waste pre-treated with enzymes for 0-4 days. The results showed that total solids (TS) in larvae decreased with longer enzyme pre-treatment. Direct addition of enzymes at the start of BSFL treatment (0 day pre-treatment) resulted in 22% higher BCE on a volatile solids (VS) basis compared with the control, while longer pre-treatment did not improve BCE further. Much of the VS was respired in the 0-day pre-treatment, resulting in lower mass of residues at the end of treatment. Longer pre-treatment increased microbial respiration, suggesting that the microbial community consumed more easily available carbohydrates during the pre-treatment step, which counteracted the purpose of enzyme pre-treatment, i.e. increasing BCE during BSFL composting.