Technological Strategies for the Sustainable Valorisation of Fruit and Vegetable Waste

Fruit and vegetable processing generates huge amounts of waste, which represents a wastage of valuable biomass and is characterised by high management cost and environmental impact. For these reasons, great attention has been dedicated in the last years to fruit and vegetable waste (FVW) valorisation, by its exploitation to produce value-added derivatives. Although it is generally assumed that FVW valorisation would deliver economic and environmental advantages, really few data on cost and energetic requirements of valorisation processes as well as on consumer response towards valorisation products are currently available. Based on these considerations, the aim of the Ph.D. research project \u201cTechnological Strategies for the Sustainable Valorisation of Fruit and Vegetable Waste\u201d was to develop a rational approach to FVW valorisation, useful to guarantee the production of value-added derivatives, but also to assess their technical feasibility, consumer acceptance, economic and environmental impact. The developed rational approach to FVW valorisation consists in four steps: waste characterisation, output definition, process design and feasibility study. This approach was validated on waste deriving from the production of fresh-cut lettuce (external leaves and cores), peach juice (pomace) and soy milk (okara). In particular, the characterisation step highlighted that waste generated during the processing of these vegetables ranges from 10 to 40%. Although the high water content (>76%), these wastes are particularly rich in fibre (>26% on dry weight basis) and polyphenolic compounds (>2.0 GAE/g of dry weight). Based on waste characteristics, different possible outputs were defined and specific processes exploiting the application of either traditional or novel sustainable technologies were designed: (i) convenient functional smoothies were produced from lettuce waste and okara using high pressure homogenization; (ii) antioxidant extracts were produced from lettuce waste and peach pomace using ultrasounds and microwaves; (iii) functional flour was obtained by air-drying and grinding of lettuce waste; (iv) supercritical-CO2-drying of lettuce waste allowed obtaining a porous material with high solvent loading capacity. The obtained valorisation outputs were then evaluated for their sensory acceptability and consumer response, in order to estimate their market potential. To this aim, the lettuce waste study-case, was analysed by the application of consumer-based methodologies. Obtained results highlighted the possibility to exploit nutritional and environmental claims to promote consumption of waste-derived food. Finally, a multi-objective method was applied to estimate the economic and environmental impact of the proposed valorisation strategies on an industrial scale. The developed approach could be considered a flexible decision support tool to guide stakeholders\u2019 aware choice and investment in the most sustainable valorisation strategies.Il processo produttivo di derivati di frutta e verdura genera enormi quantit\ue0 di scarto, che comporta la perdita di prodotti ad alto valore, elevati costi di gestione ed un notevole impatto ambientale. Per queste ragioni, negli ultimi anni, molta attenzione \ue8 stata dedicata alla valorizzazione degli scarti vegetali attraverso la loro trasformazione in derivati ad alto valore aggiunto. Sebbene la valorizzazione sia comunemente ritenuta vantaggiosa da un punto di vista economico ed ambientale, in realt\ue0 i dati disponibili su costi e richieste energetiche dei processi di valorizzazione, e sulla reazione dei consumatori nei confronti dei prodotti di valorizzazione sono molto limitati. Sulla base di queste considerazioni, lo scopo del progetto di Dottorato \u201cStrategie Tecnologiche per la Valorizzazione Sostenibile di Scarti Vegetali\u201d \ue8 stato quello di sviluppare un approccio razionale alla valorizzazione degli scarti vegetali, in grado di garantire l\u2019ottenimento di prodotti ad alto valore aggiunto, nonch\ue9 la loro fattibilit\ue0 tecnica, senza tralasciare la stima del livello di accettazione da parte dei consumatori e dell\u2019impatto economico ed ambientale. L\u2019approccio sviluppato nel corso del progetto consiste di 4 passaggi: caratterizzazione dello scarto, definizione dei prodotti di valorizzazione, design del processo produttivo e studio di fattibilit\ue0. Questo approccio \ue8 stato validato sugli scarti derivanti dalla produzione di insalata di IV gamma (foglie esterne e torsoli), succo di pesca (bucce e polpa residua) e latte di soia (okara). In particolare, la fase di caratterizzazione ha evidenziato che lo scarto generato durante la trasformazione di questi prodotti varia dal 10 al 40%. Nonostante l\u2019elevato contenuto di acqua (>76%), questi scarti presentano rilevanti quantit\ue0 di fibre (>26% su base secca) e composti fenolici (>2.0 GAE/g su base secca). Sulla base di queste caratteristiche sono stati identificati diversi possibili prodotti di valorizzazione e i corrispondenti processi produttivi, basati sull\u2019utilizzo di tecnologie sia tradizionali che innovative e sostenibili: (i) dagli scarti di insalata e dall\u2019okara, sfruttando l\u2019omogeneizzazione ad alta pressione, sono stati prodotti smoothies pronti all\u2019uso; (ii) dagli scarti di insalata e di pesca, utilizzando ultrasuoni e microonde, sono stati ottenuti estratti antiossidanti; (iii) dagli scarti di insalata, disidratati e macinati, \ue8 stata ricavata una farina funzionale; (iv) l\u2019applicazione dell\u2019essiccamento supercritico ha infine consentito di convertire gli scarti di insalata in un materiale poroso con elevata capacit\ue0 assorbente. I prodotti di valorizzazione cos\uec ottenuti sono stati analizzati in termini di accettabilit\ue0 sensoriale e attitudine dei consumatori, al fine di evidenziarne le potenzialit\ue0 di mercato. A questo scopo, \ue8 stato preso in considerazione il caso studio degli scarti di insalata, applicando metodi consumer-based. I risultati ottenuti hanno dimostrato la possibilit\ue0 di sfruttare claims nutrizionali e ambientali per promuovere il consumo di alimenti derivati da scarti vegetali. Infine, \ue8 stato applicato un metodo multi-objective per stimare l\u2019impatto economico ed ambientale delle strategie di valorizzazione proposte, se applicate su scala industriale. L\u2019approccio sviluppato in questo progetto pu\uf2 essere considerato un flessibile strumento di supporto alle decisioni, in grado di guidare gli stakeholders verso una scelta consapevole circa gli investimenti nelle strategie di valorizzazione pi\uf9 sostenibili

Effect of ultrasounds and high pressure homogenization on the extraction of antioxidant polyphenols from lettuce waste

The possibility to exploit ultrasound (US) and high pressure homogenization (HPH) to obtain ethanolic antioxidant extracts from lettuce waste was studied. The application of US (400\u202fW, 24\u202fkHz) for 120\u202fs led to polyphenol extraction yield (81\u202f\u3bcg/mL) and antioxidant activity (101\u202f\u3bcg\u202fTE/mL) significantly higher than those obtained by traditional solid-liquid extraction at 50\u202f\ub0C for 15\u202fmin. Despite the intense cell rupture effect, the application of HPH pre-treatments resulted in 25% lower phenolic yields as compared to US solely, possibly due to the 40% activation of polyphenoloxidase (PPO) upon HPH treatment. Industrial relevance The waste generated by fresh-cut processing of lettuce poses environmental and economic issues to companies, leading to the need for alternative strategies for its management. US can be successfully exploited as time-saving extraction procedure for obtaining antioxidant extracts from lettuce waste

Innovative bioaerogel-like materials from fresh-cut salad waste via supercritical-CO2-drying

Fresh-cut salad waste was dried by means of supercritical carbon dioxide technology using ethanol as co-solvent. The obtained material was characterized by a white color and a brittle texture. Microscopic images revealed an aerated structure, with well-evident intra and inter-cellular spaces. Based on the high internal surface (> 100m2/g), the extremely low density ( 80%), supercritical-dried salad waste can be regarded as a bioaerogel-like material. One gram of this material absorbed 33 and 19 g of water and oil respectively. Industrial application: Fresh-cut processing of salad generates large amounts of solid waste which is not suitable for conversion into biogas or fertilizers. This waste poses management issues for producers and represents an environmental burden. Fresh-cut salad waste could be valorized to produce bioaerogel-like materials with enhanced solvent uptake ability, to be exploited as food ingredients, packaging, absorbents or innovative carriers for both lipophilic and hydrophilic compounds

Structure of oleogels from \u3ba-carrageenan templates as affected by supercritical-CO2-drying, freeze-drying and lettuce-filler addition

Templates intended for food-grade oleogel production were produced by supercritical-CO2-drying and freezedrying of \u3ba-carrageenan hydrogels (0.4 g/100 g). Supercritical-CO2-drying produced hard (61 N firmness) and shrunk oleogels, which presented 80% oil content and no oil release. Freeze-drying allowed obtaining soft (2 N) oleogels, with 97% oil content but presenting a high oil release (49%). Lettuce homogenate, used as water phase of the hydrogel, acted as inactive filler agent of template network. It allowed reducing shrinkage and firmness (10 N) of supercritical-CO2-dried oleogels, which presented 94% oil content and 5% oil release. In the case of freeze-dried templates, lettuce-filler increased firmness (4 N) but reduced oil release (34%). SEM image analysis highlighted that the physical properties of \u3ba-carrageenan oleogels can be explained based on the effect of drying technique and lettuce-filler addition on the porous microstructure of the dried templates

Controlling aerogel surface porosity to enhance functionality in foods

Aerogels based on biopolymers, such as proteins, are food-grade materials characterized by distinctive physical properties, which make them intriguing candidates for the development of new ingredients with unique functionalities. The aerogel typical aerated structure can be exploited to deliver health-protecting bioactives or reduce food calories by increasing air content. However, aerogel porosity is easily lost upon contact with liquid food ingredients (water and oil). This issue might be overcome by closing the pores at the aerogel surface. In this work, processing and formulation strategies were applied to increase the structural stability of whey protein aerogels obtained by traditional ethanol exchange and supercritical-CO2-drying. Aerogels characterized by different levels of surface collapse were obtained by subjecting alcolgels to a controlled ethanol evaporation procedure prior to supercritical-CO2-drying. Alternatively, aerogels were coated with hydrophilic (alginate, agar) or hydrophobic (ethylcellulose) polymers. Aerogel microstructure was studied by SEM. Water and oil absorption kinetics were then measured. Ethanol evaporation time, polymer concentration and gelation rate were identified as key parameters affecting aerogel surface structure, allowing to significantly decrease water and oil absorption kinetics in the aerogels. This study suggests that aerogel structure-driven functionalities could be maintained in complex food formulations by controlling aerogel surface porosity

Combined high-power ultrasound and high-pressure homogenization nanoemulsification: The effect of energy density, oil content and emulsifier type and content

Combinations of ultrasound (US) and high-pressure homogenization (HPH) at low-medium energy densities were studied as alternative processes to individual US and HPH to produce Tween 80 and whey protein stabilized nanoemulsions, while reducing the energy input. To this aim, preliminary trials were performed to compare emulsification efficacy of single and combined HPH and US treatments delivering low-medium energy densities. Results highlighted the efficacy of US-HPH combined process in reducing the energy required to produce nanoemulsions stabilized with both Tween 80 and whey protein isolate. Subsequently, the effect of emulsifier content (1-3% w/w), oil amount (10-20% w/w) and energy density (47-175 MJ/m(3)) on emulsion mean particle diameter was evaluated by means of a central composite design. Particles of 140-190 nm were obtained by delivering 175 MJ/m(3) energy density at emulsions containing 3% (w/w) Tween 80 and 10% (w/w) oil. In the case of whey protein isolate stabilized emulsions, a reduced emulsifier amount (1% w/w) and intermediate energy density (120 MJ/m(3)) allowed a minimum droplet size around 220-250 nm to be achieved. Results showed that, in both cases, at least 50% of the energy density should be delivered by HPH to obtain the minimum particle diameter.Peer reviewe

Protein aerogels as functional ingredients able to replace fat and modulate lipid digestion

Introduction The direct relation between saturated fat consumption and chronic diseases such as cardiovascular diseases, diabetes type II and obesity is nowadays well-established. However, fat substitution in foods is not simple, due to the important structural and sensorial properties of solid fat, which are hardly replicated by liquid oil. Nevertheless, oil can be structured into semi-solid materials (oleogels) by different “oleogelation” strategies. Oleogels not only mimic the structural properties of fats, but have been also shown to be useful in the modulation of lipid digestion. The aerogel-template approach, is a recent oleogelation strategy, based on the ability of aerogels to absorb oil in their porous network. In particular, food-grade protein aerogel particles have shown the peculiar ability to structure huge oil amounts into plastic systems presenting the mechanical properties of traditional fats. The aim of the present study was to assess the effect of aerogel-template oleogelation on lipid digestibility and to investigate the possibility to use aerogel-templated oleogels in the preparation of low-saturated fat cocoa creams. Experimental Methods Whey protein (WP) aerogel particles were prepared by grinding a heat-set WP hydrogel (20% w/w, pH=5.7), which was then subjected to ethanol exchange and supercritical-CO2 drying (SCD). Oleogels were than obtained by absorption of sunflower oil (SO) into aerogel particles. Lipid digestibility of the oleogel containing 80% (w/w) SO and 20% WP aerogel (w/w) was assessed by in vitro digestion, according to the INFOGEST protocol. Lipid digestibility was expressed as free fatty acids (FFA %), assessed by pH-stat method, i.e., by measuring the volume of NaOH (0.25 M) required to maintain the pH at 8.00 during digestion occurring in the small intestine. The choice of using pH 8.00 instead of 7.00 was based on the technical specifications of the used lipase. The digestate samples were analyzed by using dynamic light scattering (DLS) and confocal microscopy. The WP aerogel particles were then used to prepare cocoa creams containing sunflower oil (SO), icing sugar and cocoa powder. Different oil amounts were tested (40-65% w/w), while maintaining constant the ratio among the dried ingredients (WP aerogel:sugar:cocoa =1.5:5:1). Additional control samples were prepared by using native WP. The obtained creams were analyzed for oil release and rheological properties and compared to cocoa spreads available on the market. Results and discussion WP aerogel particles were used to structure SO into an oleogel, whose digestibility was then assessed. The lipid digestibility of SO and of the oleogel resulted respectively of 70% and 80%. These results can be attributed to the ability of aerogel protein particles to improve the emulsification of oil in the intestinal digestive mixture, leading to an enhanced activity of lipolytic enzymes. DLS, in fact, evidenced that the lipidic micelles formed during intestinal digestion of the oleogel resulted significantly smaller than those formed during SO digestion. This is probably attributable to the surface activity of WP aerogels, which are able to cover and stabilize the oil droplets in the digestive mixture. The applicability of WP aerogel particles as key ingredients for the preparation of low-saturated fat cocoa creams was then demonstrated, combining WP aerogel particles with SO in presence of sugar and cocoa powder. Native WP did not show oil structuring ability, leading to liquid-like cocoa creams, showing an apparent viscosity lower than 2 Pa∙s (50 1/s) and evident oil release upon resting at room temperature. By contrast, aerogel particles produced thicker creams, showing no flow under gravity, a significantly higher viscosity (50 Pa∙s), and no oil release under standard storage conditions. This was attributed to the modifications undergone by WP during conversion into porous aerogel particles. The range of rheological properties covered by the WP aerogel cocoa creams resulted comparable with a wide variety of commercial products (e.g. sauces and batters). Conclusions This work demonstrates the potentialities of WP aerogel particles as oil structuring agents, exploitable in the formulation of healthier food products with a reduced amount of saturated fatty acids. Such formulation strategy would not compromise the lipolytic action during digestion, making aerogels suitable carriers of bioactive molecules in the gastrointestinal tract

Potentialities of plant protein aerogels as innovative food ingredients

Protein aerogels are attracting large attention in the food sector, since presenting appealing characteristics as innovative food ingredients. Being made by proteins, commonly used food ingredients, they are largely accepted by consumers. Moreover, the structure of protein aerogels can be fine-tuned by acting on multiple processing (e.g., drying technique) and formulation (e.g., protein type, pH) factors, thus allowing the engineering of systems with a wide range of tailor-made functionalities. As a result, protein aerogels have been proposed as advanced food ingredients to develop bioactive delivery systems in the gastrointestinal tract, and structure liquid oil into plastic materials able to replace saturated fats in foods. Surprisingly, to date, the potentialities of protein aerogels as innovative food ingredients have been only demonstrated for animal protein-based systems, mainly egg and milk proteins, and studies regarding the development of aerogels from plant proteins are very limited. Nevertheless, the current concern about the poor environmental sustainability of animal proteins and their production is boosting the so-defined “plant-protein transition”, which has been identified as a key strategy to increase of food sustainability. In this context, plant-protein-based aerogels could represent an influential opportunity to favor the inlet of aerogels in the food sector. Based on these considerations, the aim of the present work was to study the possibility of producing food-grade aerogels based on plant proteins (pea and soy) and to collect preliminary data on their compatibility with food systems. To this aim, soy and pea protein isolate (SPI, PPI) hydrogels (10-20% w/w, pH 4.5 or 7.0) were converted into aerogel particles by grinding followed by ethanol solvent exchange and supercritical-CO2-drying. The obtained aerogel particles were analyzed for physical properties (BET surface area, porosity, density), and ability to interact with water and oil, commonly used food solvents. To this aim, aerogel water solubility and water and oil holding capacity (WHC, OHC) were assessed and compared to those of SPI and PPI. Aerogelation of SPI and PPI allowed obtaining porous particles, with BET internal surface and porosity in the range 50-150 m2/g and 60-80% respectively. The lowest values were found, as expected, at pH 4.5, corresponding to the isoelectric point. As compared to SPI and PPI, which presented a water solubility higher than 80%, the corresponding aerogels showed a water solubility around 25%. Aerogelation also significantly increased the WHC and OHC as compared to the protein isolates. The results obtained in this study demonstrate the possibility to produce plant-protein-based aerogels in the form of porous powders. The high ability to absorb water and oil, which can be exploited in the formulation of complex foods requiring rheological modulation (e.g., creams, spreads, dressings), associated with the vegetable origin of the used proteins, can be regarded as key characteristics able to stimulate the interest of the food sector in innovative aerogel ingredients

Optimizing the antioxidant biocompound recovery from peach waste extractionassisted by ultrasounds or microwaves

The possibility to valorize peach juice waste, either frozen or air-dried, through microwave (MAE) and ultrasound assisted extraction (UAE) was evaluated. MAE power, UAE amplitude and time were optimized using a 22-factorial design. For frozen waste, optimal MAE (540 W, 50 s) and UAE (23%, 120 s) processes gave extracts presenting analogous content (on 100 g dry matter) of polyphenols (309-317 mg GAE), flavonoids (94-120 mg QE), anthocyanins (8-9 mg CGE), and similar antioxidant activity (2.1-2.2 mg TE). Extracts from dried waste resulted higher in polyphenols (630-670 mg GAE) but lower in flavonoids (75-90 mg QE), anthocyanins and vitamin C (not detectable). Although developing an energy density 2-fold higher than that of UAE, MAE more efficaciously extracted vitamin C (108 mg/100 g dm) and required half extraction time (50 s). MAE would also be less impactful than UAE in terms of greenhouse gas emission and energy requirements on industrial scale. The industrial valorization of peach waste through the application of microwave and ultrasound assisted extraction requires quantitative data, able to encourage company interest and investment. This study not only identifies optimal MAE and UAE parameters to assist the extraction of peach waste bioactive compounds but also provides a preliminary estimation of the potential economic and environmental impact on an industrial scale of these technologies