Processing, Valorization and Application of Bio-Waste Derived Compounds from Potato, Tomato, Olive and Cereals: A Review

Yeast-driven whey biorefining to produce value-added aroma, flavor, and antioxidant compounds: technologies, challenges, and alternatives

Whey is a liquid residue generated during the production of cheese and yogurt. It has a pH between 3.9 and 5.6, and a high chemical oxygen demand (COD), from 60 to 80 g/L. Whey contains lactose, proteins, and minerals. Globally, approximately 50% of the whey generated is untreated and is released directly into the environment, which represents an environmental risk. To overcome whey management problems, conventional thermo-physical valorization treatments have been explored, which are complex, costly and energy-intensive. As an alternative, whey fermentation processes employing bacteria, fungi and yeast are economical and promising methods. Among them, yeast fermentation creates value-added products such as antimicrobials, biofuels, aromas, flavors, and antioxidants with no need for previous conditioning of the whey, such as hydrolysis of the lactose, prior to whey biorefining. The biorefining concept applied to whey is discussed using chemical and biological transformation pathways, showing their pluses and minuses, such as technical drawbacks. The main challenges and solutions for the production of fusel alcohols, specifically for 2-phenylethanol, are also discussed in this review.

Encapsulation of Bioactive Compounds from Aloe Vera Agrowastes in Electrospun Poly (Ethylene Oxide) Nanofibers

Aloe Vera is an ancient medicinal plant especially known for its beneficial properties for human health, due to its bioactive compounds. In this study, nanofibers with antioxidant activity were successfully obtained by electrospinning technique with the addition of a natural Aloe Vera skin extract (AVE) (at 0, 5, 10 and 20 wt% loadings) in poly(ethylene oxide) (PEO) solutions. The successful incorporation of AVE into PEO was evidenced by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA) and antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl radical scavenging (DPPH), 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging (ABTS) and ferric reducing power (FRAP) assays. The incorporation of AVE introduced some changes in the PEO/AVE nanofibers morphology showing bimodal diameter distributions for AVE contents in the range 10-20 wt%. Some decrease in thermal stability with AVE addition, in terms of decomposition onset temperature, was also observed and it was more evident at high loading AVE contents (10 and 20 wt%). High encapsulation efficiencies of 92%, 76% and 105% according to DPPH, FRAP and ABTS assays, respectively, were obtained at 5 wt% AVE content, retaining AVE its antioxidant capacity in the PEO/AVE electrospun nanofibers. The results suggested that the obtained nanofibers could be promising materials for their application in active food packaging to decrease oxidation of packaged food during storage.

Enhanced Lycopene Extraction from Tomato Peels by Optimized Mixed-Polarity Solvent Mixtures

Mounting evidence from clinical and epidemiological studies suggests that lycopene, the most abundant carotenoid in tomatoes, may be beneficial in the prevention or treatment of some important diseases. Ripe tomato peels are the richest source of lycopene, but the use of conventional solvent extraction methods without pretreatment of the plant material results in very poor recovery. The reason lies in the localization of lycopene in the plant tissue and the low permeability of the latter to solvent molecules. In this paper, a mixture design procedure was used to formulate solvent mixtures allowing the recovery of lycopene from non-pretreated tomato peels. Two ternary systems were investigated: (a) n-hexane-ethanol-acetone and (b) ethyl lactate-ethanol-acetone. Optimization of the ternary mixture composition led to a recovery of over 90% of the lycopene present in the peels. The high extraction efficiency was explained in terms of lycopene affinity combined with the ability to swell the plant material. A tomato oleoresin with high antioxidant activity and a lycopene content of about 13% (w/w) was also produced. Overall, the results indicate that highly effective solvents for direct recovery of lycopene from tomato peels can be easily prepared by a mixture design approach.

The Correlation between Soil Nutrient and Potato Quality in Loess Plateau of China Based on PLSR

Potato tuber quality is influenced by the interaction of soil nutrients. Hence, simple correlation analysis cannot accurately reflect the true relationship between soil nutrients and potato tuber quality. In this study, potato tuber quality and soil nutrient content were used as research materials in the Loess Plateau of China. The partial least square regression (PLSR) method was used to establish the regression equation between potato quality and soil nutrient. The major soil nutrient indexes influencing potato quality were screened out to provide theoretical basis for potato field management. The results showed that the major soil nutrient factors influencing the potato tuber quality in Loess Plateau were soil ammonium nitrogen, soil nitrate nitrogen, soil available phosphorus, pH, and soil available potassium. Soil pH value is the most important factor affecting potato starch, reducing sugar content, and soluble protein content. Soil nitrate nitrogen is one of the important factors affecting potato tuber soluble total sugar content, vitamin C, browning intensity, and polyphenol oxidase activity. Soil ammonium nitrogen was positively correlated with the total soluble sugar content of potato tubers, and negatively correlated with reducing sugar content, browning intensity, and polyphenol oxidase activity. However, soil available potassium has positive effects on potato starch and reducing sugar content, and negative effects on soluble protein and browning strength. Results of this study indicates that the major soil nutrient factors influencing potato tuber quality were soil nitrate nitrogen and soil pH value.

Valorization of Linen Processing By-Products for the Development of Injection-Molded Green Composite Pieces of Polylactide with Improved Performance

This work reports the development and characterization of green composites based on polylactide (PLA) containing fillers and additives obtained from by-products or waste-streams from the linen processing industry. Flaxseed flour (FSF) was first produced by the mechanical milling of golden flaxseeds. The resultant FSF particles were melt-compounded at 30 wt% with PLA in a twin-screw extruder. Two multi-functionalized oils derived from linseed, namely epoxidized linseed oil (ELO) and maleinized linseed oil (MLO), were also incorporated during melt mixing at 2.5 and 5 parts per hundred resin (phr) of composite. The melt-compounded pellets were thereafter shaped into pieces by injection molding and characterized. Results showed that the addition of both multi-functionalized linseed oils successfully increased ductility, toughness, and thermal stability of the green composite pieces whereas water diffusion was reduced. The improvement achieved was related to both a plasticizing effect and, more interestingly, an enhancement of the interfacial adhesion between the biopolymer and the lignocellulosic particles by the reactive vegetable oils. The most optimal performance was attained for the MLO-containing green composite pieces, even at the lowest content, which was ascribed to the higher solubility of MLO with the PLA matrix. Therefore, the present study demonstrates the potential use of by-products or waste from flax (Linum usitatissimum L.) to obtain renewable raw materials of suitable quality to develop green composites with high performance for market applications such as rigid food packaging and food-contact disposable articles in the frame of the Circular Economy and Bioeconomy.

Beyond Enzyme Production: Solid State Fermentation (SSF) as an Alternative Approach to Produce Antioxidant Polysaccharides

Solid state fermentation (SSF) is a sustainable process that uses low amounts of water and transforms plant-based agro-industrial residues into valuable products such as enzymes, biofuels, nanoparticles and other bioactive compounds. Many fungal species can be used in SSF because of their low requirements of water, O2 and light. During SSF, plant-based wastes rich in soluble and insoluble fiber are utilized by lignocellulolytic fungi that have enzymes such as lignases, celullases or hemicelullases that break fiber hard structure. During the hydrolysis of lignin, some phenolic compounds are released but fungi also synthetize bioactive compounds such as mycophenolic acid, dicerandrol C, phenylacetates, anthraquinones, benzofurans and alkenyl phenols that have health beneficial effects such as antitumoral, antimicrobial, antioxidant and antiviral activities. Another important group of compounds synthetized by fungi during SSF are polysaccharides that also have important health promoting properties. Polysaccharides have antioxidant, antiproliferative and immunomodulatory activities as well as prebiotic effects. Fungal SSF has also proved to be a process which can release high contents of phenolics and it also increases the bioactivity of these compounds.

Advances in combined enzymatic extraction of ferulic acid from wheat bran

Wheat bran could be utilised as feedstock for innovative and sustainable biorefinery processes. Here, an enzymatic hydrolysis process for ferulic acid (FA) extraction was optimised step by step for total wheat bran (Tritello) and then also applied to the outer bran layer (Bran 1). Proteins, reducing sugars, total phenols and FA were quantified. The highest FA yields (0.82-1.05 g/kg bran) were obtained either by rehydrating the bran by autoclaving (Tritello) or by steam explosion (Bran 1) using a bran/water ratio of 1:20, followed by enzymatic pre-treatment with Alcalase and Termamyl, to remove protein and sugars, and a final enzymatic hydrolysis with Pentopan and feruloyl esterase to solubilise phenol. FA was recovered from the final digestate via solid phase extraction. A 40-fold scale-up was also performed and the release of compounds along all the process steps and at increasing incubation times was monitored. Results showed that FA was initially present at a minimum level while it was specifically released during the enzymatic treatment. In the final optimized process, the FA extraction yield was higher than that obtained with NaOH control hydrolysis while, in comparison with other FA enzymatic extraction methods, fewer process steps were required and no buffers, strong acid/alkali nor toxic compounds were used. Furthermore, the proposed process may be easily scaled-up, confirming the feasibility of wheat bran valorisation by biorefinery processes to obtain valuable compounds having several areas of potential industrial exploitation.

Potato Peels as a Source of Novel Green Extracts Suitable as Antioxidant Additives for Fresh-Cut Fruits

Potato is a source of different bioactive compounds, and the potato transformation industry produces conspicuous quantities of potato peels as waste. In this context, the objective of this research was twofold: (i) the evaluation of the recovery of bioactive compounds from organic potato byproducts through an innovative multistep green extraction process; (ii) to evaluate the preservation during storage of the main quality-physicochemical parameters of minimally processed apples treated with two different natural extracts obtained. The potato extracts were obtained by solid CO2 cryomaceration followed by solid/liquid extraction based on water or 10% ethanol/water solutions. The efficacy of potato extracts, with or without 1% of citric acid, was tested in comparison with traditional preserving compounds in minimally processed apple preparation. All the extracts were characterized by a high antioxidant power and were rich in phenol compounds, showing a good activity in keeping the qualitative parameters of fresh-cut apple. A significant anti-browning effect as well as a slowing down of the softening of fruits during storage were observed. The obtained results suggest the suitability of the potato extracts as antioxidant additives for fresh-cut fruits, thus avoiding the use of unsafe chemicals.

Olive Mill Wastewater Valorization in Multifunctional Biopolymer Composites for Antibacterial Packaging Application

Olive mill wastewater (OMW) is the aqueous waste derived from the production of virgin olive oil. OMW typically contains a wide range of phenol-type molecules, which are natural antioxidants and/or antibacterials. In order to exploit the bioactive molecules and simultaneously decrease the environmental impact of such a food waste stream, OMW has been intercalated into the host structure of ZnAl layered double hydroxide (LDH) and employed as an integrative filler for the preparation of poly(butylene succinate) (PBS) composites by in situ polymerization. From the view point of the polymer continuous phase as well as from the side of the hybrid filler, an investigation was performed in terms of molecular and morphological characteristics by gel permeation chromatography (GPC) and X-ray diffraction (XRD); also, the thermal and mechanical properties were evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic thermomechanical analysis (DMTA). Antibacterial properties have been assessed against a Gram-positive and a Gram-negative bacterium, Staphylococcus aureus and Escherichia coli, respectively, as representatives of potential agents of foodborne illnesses.

Epoxidation of Karanja (Millettia pinnata) Oil Methyl Esters in the Presence of Hydrogen Peroxide over a Simple Niobium-Containing Catalyst

The synthesis, characterization and catalytic performance of a conceptually simple, novel NbOx-SiO2 catalyst are here described. The niobium(V)-silica catalyst was prepared starting from cheap and viable reactants, by alkaline deposition of NH4Nb(C2O4)2·H2O in the presence of fructose as a stabilizer and subsequent calcination. The NbOx-SiO2 solid (0.95 Nb wt.%) was tested in the liquid-phase epoxidation with aqueous hydrogen peroxide of methyl oleate, as a model substrate. It was then tested in the epoxidation of a mixture of methyl esters (FAMEs) obtained by transesterification with methanol and purification of karanja oil, extracted from the autochthonous Indian variety of Millettia pinnata tree. The catalyst showed a promising performance in terms of methyl oleate conversion (up to 75%) and selectivity to epoxide (up to 82%). It was then tested on the FAME mixture from karanja oil, where interesting conversion values were attained (up to 70%), although with lower selectivities and yields to the mixture of desired epoxidized FAMEs. The solid withstood four catalytic cycles overall, during which a non-negligible surface reorganization of the Nb(V) sites was observed. However, this restructuring did not negatively affect the performance of the catalysts in terms of conversion or selectivity.

Thermal, Mechanical, Viscoelastic and Morphological Properties of Poly(lactic acid) based Biocomposites with Potato Pulp Powder Treated with Waxes

The thermal, mechanical and viscoelastic properties of biocomposites of poly(lactic acid) (PLA) with 20 wt.% of potato pulp powder were investigated. The potato pulp powder utilized is a byproduct from the production and extraction of starch. The results showed that the potato pulp powder does not act as reinforcement, but as filler for PLA, due to an unfavorable aspect ratio and the irregular shape of the particles. In order to improve the mechanical response of the PLA/potato pulp powder biocomposites, surface treatment of the potato pulp particles with bio-based and petroleum-based waxes was investigated. This treatment was found to improve the properties of the biocomposites, enhancing the adhesion between the PLA based polymeric matrix and the potato pulp fibers. The best result is obtained with a petroleum-based wax, but also the bio-based waxes lead to good mechanical properties of the biocomposite. Thus, the addition to PLA of potato pulp powder, treated with waxes, appears a method able to (i) utilize and valorize an abundant agro-food biomass such as potato pulp, according to the principles of circular economy, (ii) favor the production of articles with properties valuable for practical applications, and (iii) reduce the cost of the final products, considering the relatively high cost of PLA.

Thermal and Mechanical Properties of Biocomposites Made of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Potato Pulp Powder

The thermal and mechanical properties of biocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 5 wt % of valerate units, with 20 wt % of potato pulp powder were investigated in order (i) to obtain information on possible miscibility/compatibility between the biopolymers and the potato pulp, and (ii) to quantify how the addition of this filler modifies the properties of the polymeric material. The potato pulp powder utilized is a residue of processing for the production and extraction of starch. The final aim of this study is the preparation of PHBV based materials with reduced cost, thanks to biomass valorization, in agreement with the circular economy policy, as result of the incorporation of agricultural organic waste. The results showed that the potato pulp powder does not act as reinforcement, but rather as filler for the PHBV polymeric matrix. A moderate loss in mechanical properties is detected (decrease in elastic modulus, tensile strength and elongation at break), which regardless still meets the technical requirements indicated for rigid packaging production. In order to improve the mechanical response of the PHBV/potato pulp powder biocomposites, surface treatment of the potato pulp powder with bio-based and petroleum-based waxes was investigated. Good enhancement of the mechanical properties was achieved with the natural carnauba and bee waxes.

Thermal, Mechanical, and Rheological Properties of Biocomposites Made of Poly(lactic acid) and Potato Pulp Powder

The thermal, mechanical, and rheological properties of biocomposites of poly(lactic acid) (PLA) with potato pulp powder were investigated in order to (1) quantify how the addition of this filler modifies the structure of the polymeric material and (2) to obtain information on the possible miscibility and compatibility between PLA and the potato pulp. The potato pulp powder utilized is a residue of the processing for the production and extraction of starch. The study was conducted by analyzing the effect of the potato pulp concentration on the thermal, mechanical, and rheological properties of the biocomposites. The results showed that the potato pulp powder does not act as reinforcement but as filler for the PLA polymeric matrix. A progressive decrease in elastic modulus, tensile strength, and elongation at break was observed with increasing the potato pulp percentage. This moderate loss of mechanical properties, however, still meets the technical requirements indicated for the production of rigid packaging items. The incorporation of potato pulp powder to PLA offers the possibility to reduce the cost of the final products and promotes a circular economy approach for the valorization of agro-food waste biomass.

Deoxydehydration of glycerol in presence of rhenium compounds: reactivity and mechanistic aspects

Re compounds in different oxidation states are activated during a delay time into an active Re alkoxide precipitate catalysing the DODH of glycerol.

Lignin and holocellulose from pecan nutshell as reinforcing fillers in poly (lactic acid) biocomposites

Lignocellulose from agro-food biowaste represents a valuable source of cost-effective structural fillers for wholly renewable polymer composites. In this work, pecan (Carya illinoinensis) nutshell (NS) fiber and its structural components, holocellulose (HC) and acid insoluble lignin (AIL), were isolated, characterized and used as reinforcing fillers to manufacture poly(lactic acid) (PLA) based biocomposites. Thermal, morphological and mechanical properties of the prepared materials were analyzed. NS and HC acted as heterogeneous nucleating agents, potentially able to control PLA physical aging. Moreover, they significantly enhanced the viscoelastic response of PLA, mainly restricting the melt molecular mobility due to hydrodynamic effects and the formation of a three-dimensional particulate network. Flexural tests demonstrated that HC induced a 25% increase in modulus compared to the plain polymer. AIL, conversely, conferred higher ductility to the PLA matrix producing an increase in stress and strain at break of 55% and 65%, respectively. Finally, all the biocomposites showed lower resilience with respect to plain PLA due to the lack of chemical adhesion between filler and matrix. These results emphasize the potential of NS as a source of reinforcing filler in polymer-based biocomposites.

Developing Biostimulants From Agro-Food and Industrial By-Products

In modern agriculture, seeking eco-friendly ways to promote plant growth and enhance crop productivity is of priority. Biostimulants are a group of substances from natural origin that contribute to boosting plant yield and nutrient uptake, while reducing the dependency on chemical fertilizers. Developing biostimulants from by-products paves the path to waste recycling and reduction, generating benefits for growers, food industry, registration and distribution companies, as well as consumers. The criteria to select designated by-products for valorizing as biostimulant are: absence of pesticide residue, low cost of collection and storage, sufficient supply and synergy with other valorization paths. Over the years, projects on national and international levels such as NOSHAN, SUNNIVA, and Bio2Bio have been initiated (i) to explore valorization of by-products for food and agriculture industries; (ii) to investigate mode of action of biostimulants from organic waste streams. Several classes of waste-derived biostimulants or raw organic material with biostimulant components were shown to be effective in agriculture and horticulture, including vermicompost, composted urban waste, sewage sludge, protein hydrolysate, and chitin/chitosan derivatives. As the global market for biostimulants continues to rise, it is expected that more research and development will expand the list of biostimulants from by-products. Global nutrient imbalance also requires biostimulant to be developed for targeted market. Here, we review examples of biostimulants derived from agricultural by-products and discuss why agricultural biomass is a particularly valuable source for the development of new agrochemical products.