Onion Waste Research Articles

Physicochemical and Thermal Characteristics of Onion Skin from Fifteen Indian Cultivars for Possible Food Applications

Every year tons of onion waste is produced worldwide. The dried outer onion skin contributed up to 70% of this waste. Outer-dried skins of fifteen prominent onion cultivars from India were selected for the study. A comparative study was done for proximate profiling, thermal characteristics, functional grouping, and mineral contents. Skin of cv. “NHRDF Red” contained the highest amount of crude protein (5.97 ± 0.15 g/100 g), ash (12.24 ± 0.59 g/100 g), and fiber (8.28 ± 0.20 g/100 g), whereas cv. “Pusa Red” possessed the highest amount of total fat (0.47 ± 0.02 g/100 g) and the maximum carbohydrates (76.66 ± 0.56 g/100 g) were found in “Pusa Riddhi.” Mineral analysis showed that cv. “NHRDF Red” had the maximum concentration of all 9 minerals along with sulphur content. Fourier transform infrared spectroscopy analysis explored the various metabolites present in each cultivar. The thermal analysis explored cv. “Agrifound Dark Red” as highly thermally stable having 70.98% residual mass. The lowest Tg temperature range was found between 64.4°C and 90.6°C for “Agrifound Dark Red.” Skin of cv. “NHRDF Red” was reported as the best source of protein, fiber, and minerals, which may be utilized for developing a food product.

Cyclodextrins as high-performance green co-solvents in the aqueous extraction of polyphenols and anthocyanin pigments from solid onion waste

Cyclodextrins as high-performance green co-solvents in the aqueous extraction of polyphenols and anthocyanin pigments from solid onion waste

Biological control of soil-borne phytopathogenic fungi through onion waste composting: implications for circular economy perspective

The production of onion waste derived mainly from bulbs affected by fungal diseases, during onion classification and storage presents an important agro-environmental issue in onion production regions. Composting is an environmentally friendly strategy to recycle agricultural waste and produce organic fertilizers. Modifications of the microbial community in soil can affect the ability of pathogen propagules to survive, germinate and infect plant roots. Hence, the main objective of this work was to exploring the mechanisms involved on the presence of three soil-borne phytopathogenic fungi during the composting process of onion waste under the hypothesis if that the resulting compost effectively prevents or minimizes the dispersion of phytopathogenic fungi. To this end, three composting piles of 60 tonnes each were built by layering onion waste affected by phytopathogenic fungi and cow dung at 1:1 ratio. Temperature, moisture, pH, electrical conductivity (EC) and Aspergillus niger, Penicillium sp. and Fusarium sp. growth were monitored for 100 days. During the first 28 days of composting, the presence of phytopathogenic fungi increased significantly showing thereafter a downward trend. Final estimations of fungal populations densities indicated a predominance of A. niger and an effective reduction in the abundance of Fusarium sp. This pilot-scale work demonstrates the feasibility of composting onion waste contaminated with phytopathogenic fungi and highlights the positive environmental impact associated with this practice. Therefore, the composting of onion waste and cow dung is a feasible and sustainable procedure to recycle onion waste and to promote circular economy in onion production regions.

MEWUJUDKAN DESA INOVASI TEKNOLOGI MELALUI PENGGUNAAN KOMPOSIT (RESIN DAN SERBUK LIMBAH BAWANG) DI DESA BANGSRI DAN DESA PESANTUNAN KABUPATEN BREBES

TThe area of harvested shallots in Brebes is 60.82% of the total harvested area in Central Java Province. Production of shallots in 2018 reached 10,519,484 quintals. Pesantunan Village, Wanasari District, has a high productivity of 121.544 quintals/Ha and Bangsri Village has a productivity of 98.28 quintals/Ha. The abundant potential of onions also has an impact on the abundant onion waste, so that the potential for this onion waste will be made a composite as the embodiment of the Innovation Village. The purpose of this community service activity is to create a Technology Innovation Village to community groups in Pesantunan and Bangsri Villages regarding the use of onion waste into a composite.The method offered is divided into two, namely Soft Program and Hard Program.The result of the composite technology innovation village program, number of participants in the Pesantunan Village was 25 from the "Santun Asri" community group and 15 people in the Bangsri Village from the "Bumdes" membership. Participants were provided with a soft program including waste management and technology innovation villages in the composite field. Participants were also provided with a Hard Program, is practicing making composites with waste onions

Rapid Assessment of Anthocyanins Content of Onion Waste through Visible-Near-Short-Wave and Mid-Infrared Spectroscopy Combined with Machine Learning Techniques

A sustainable process for valorization of onion waste would need to entail preliminary sorting out of exhausted or suboptimal material as part of decision-making. In the present study, an approach for monitoring red onion skin (OS) phenolic composition was investigated through Visible Near-Short-Wave infrared (VNIR-SWIR) (350–2500 nm) and Fourier-Transform-Mid-Infrared (FT-MIR) (4000–600 cm−1) spectral analyses and Machine-Learning (ML) methods. Our stepwise approach consisted of: (i) chemical analyses to obtain reference values for Total Phenolic Content (TPC) and Total Monomeric Anthocyanin Content (TAC); (ii) spectroscopic analysis and creation of OS spectral libraries; (iii) generation of calibration and validation datasets; (iv) spectral exploratory analysis and regression modeling via several ML algorithms; and (v) model performance evaluation. Among all, the k-nearest neighbors model from 1st derivative VNIR-SWIR spectra at 350–2500 nm resulted promising for the prediction of TAC (R2 = 0.82, RMSE = 0.52 and RPIQ = 3.56). The 2nd derivative FT-MIR spectral fingerprint among 600–900 and 1500–1600 cm−1 proved more informative about the inherent phenolic composition of OS. Overall, the diagnostic value and predictive accuracy of our spectral data support the perspective of employing non-destructive spectroscopic tools in real-time quality control of onion waste.

Phytochemical Characterization and Screening of Antioxidant, Antimicrobial and Antiproliferative Properties of Allium × cornutum Clementi and Two Varieties of Allium cepa L. Peel Extracts.

Onions are one of the most widely grown vegetable crops. As production increases, so does the generation of waste from various parts of the onion, raising the need for efficient ecological disposal and use of such waste products. However, onion waste products are a rich source of antioxidants with a range of biological properties, therefore, they could potentially be used in food and pharmaceutical industries. In the present study, we identified the main flavonols and anthocyanins in peel extracts of Allium × cornutum Clement ex Visiani, 1842, and two varieties of Allium cepa L. and tested their antioxidant, antimicrobial and antiproliferative properties. Quercetin 3,4′-diglucolside, quercetin 4′-monoglucoside and quercetin are the most abundant flavonols in all onion extracts detected by high-performance liquid chromatography (HPLC) method. The composition of anthocyanins varied in all extracts. 2,2′-diphenyl-1-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) assays showed that the triploid onion A. × cornutum had the highest antioxidant power. Evaluation of antimicrobial activity by broth microdilution assay also showed that A. × cornutum had higher antimicrobial activity compared to the red and yellow onion varieties. Comparable antiproliferative activity was confirmed for all onion extracts tested on three cancer cell lines: Hela (cervical cancer cell line), HCT116 (human colon cancer cell line) and U2OS (human osteosarcoma cell line). The most abundant onion flavonols (quercetin 3,4′-diglucoside and quercetin 4′-monoglucoside) showed weaker antimicrobial as well as antiproliferative properties compared to the extracts, leading to the conclusion that other phytochemicals besides flavonols contribute to the biological activity of onion peel extracts. The results demonstrate the antioxidant and antimicrobial properties of onion peels, which have promising potential as cancer cell proliferation inhibitors.

From onion skin waste to multi-heteroatom self-doped highly wrinkled porous carbon nanosheets for high-performance supercapacitor device

Herein, we report the synthesis of N, S, P-self-doped porous and wrinkled graphene-like carbon nanosheets derived from the abundant waste onion skin via carbonization and activation strategy. The optimized onion skin derived carbon (OnC-900) exhibits highly wrinkled graphene-like morphology and multi-heteroatom doping without any external dopants is confirmed via field emission scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The OnC-900, acting as a supercapacitor electrode, exhibits excellent specific capacitance of 478 F g−1 at a current density of 1 A g−1 and maintains 241.7 F g−1 even at 6.7 A g−1 in the three-electrode cell indicating its excellent rate capability. The assembled symmetric supercapacitor device using aqueous neutral electrolyte (1 M Na2SO4) delivers outstanding specific energy of 17 Wh kg−1 with a wide potential window up to 1.4 V. The device also exhibits excellent cyclic stability by retaining 93% of initial capacitance over 10,000 cycles at a current density of 3 A g−1. This enhanced performance of the electrode is mainly due to the high specific surface area and the heteroatom co-doping that provides improved surface wettability by polarized surface, induced pseudocapacitance effect, and improved electronic conductivity. These results demonstrate that onion waste derived multi-heteroatom co-doped graphene-like carbon nanosheets have great potential for renewable and sustainable energy storage devices.

Antioxidant effect of ethanolic onion (Allium cepa) husk extract in ageing rats.

The role of natural antioxidants in preventing of age-relating diseases is evident. The vegetable industry generates a large amount of waste, which is a good source of antioxidants.The aim of the study was the investigation of the antioxidant effect of long-term consumption of ethanolic yellow onion husk extract in ageing laboratory rodents.Twenty male Wistar albino rats were divided randomly into two groups (n = 10): a control group and an experimental group that received ethanolic yellow onion husk extract (2 mL/rat diluted with distilled water; activity of 4.44 µmol-equiv. quercetin) for 188 days. Oxygen radical absorbance capacity and ferric reducing antioxidant power assays were used to determine the total antioxidant capacity of the extract, which amounted to 941.4 ± 32.7 µmol equiv. Trolox/g raw material and 167.4 ± 16.4 µmol-equiv. quercetin/g raw material, respectively. Oral intake of the onion husk extract affected the indicators of the antioxidant system of the liver and the brain but not of the blood and plasma, mainly due to elevations in the activity of catalase and superoxide dismutase in the liver by 44.4% and 79.1%, respectively, and in the brain by three-fold and 79.1%, respectively.The availability, cheapness and high antioxidant potential of onion waste qualifies it a good source of functional ingredients and bioactive substances applicable in the food and pharmaceutical industries.

Onion Peel: Turning a Food Waste into a Resource.

Food waste is a serious problem for food processing industries, especially when it represents a loss of a valuable source of nutrients and phytochemicals. Increasing consumer demand for processed food poses the problem of minimizing waste by conversion into useful products. In this regard, onion (Allium cepa) waste consisting mainly of onion skin is rich in bioactive phenolic compounds. Here, we characterized the flavonoid profiles and biological activities of onion skin wastes of two traditional varieties with protected geographical indication (PGI), the red “Rossa di Tropea” and the coppery “Ramata di Montoro”, typically cultivated in a niche area in southern Italy. The phytochemical profiles of exhaustive extracts, characterized by ultra-high-performance liquid chromatography coupled with ultraviolet (UV) detection and high-resolution mass spectrometry, revealed that flavonols and anthocyanins were the characteristic metabolite classes of onion skins. Quercetin, quercetin glucosides and their dimer and trimer derivatives, and, among anthocyanins, cyanidin 3-glucoside, were the most abundant bioactive compounds. The potential of onion skins was evaluated by testing several biological activities: ABTS/oxygen radical absorbance capacity (ORAC) and in vitro alpha-glucosidase assays were performed to evaluate the antioxidant and anti-diabetic properties of the extracts and of their main compounds, respectively, and proliferative activity was evaluated by MTT assay on human fibroblasts. In the present study, by observing various biological properties of “Rossa di Tropea” and “Ramata di Montoro” onion-dried skins, we clearly indicated that this agricultural waste can provide bioactive molecules for multiple applications, from industrial to nutraceutical and cosmetical sectors.

Bioconversion of Onion Waste to Valuable Biosugar as an Alternative Feed Source for Honey Bee

White sugar is the main commodity used to feed honey bees during the off-season as a nectar substitute. However, the price of sugar is increasing every year, thereby making bee keeping an expensive enterprise. Hence, it is necessary to find an alternative bee feed that is cheaper than sugar. The study aims to determine the potential of an alternative bee feed from renewable resources using onion waste (OW), which has a similar sugar composition to that of honey. The OW produces biosugar from in-house produced enzymes at a 90% conversion rate. The efficiency of enzymatic hydrolysis increases by more than 2 times after popping pretreatment. Furthermore, a removal rate of 98.5% for sulfur compounds, which caused the distinctive smell of onion, is obtained using a continuous column process with an activated carbon-containing alginate bead (AC-AB) adsorbent. In addition, after popping pretreatment and continuous AC-AB adsorbent column treatment, the feed intake is increased and the mortality is decreased by 3.2 times compared to that of none-popping and desulfurization treatment. Moreover, the combination of alternative feed with pollen decreases the mortality rate to almost 5.4 times. The results clearly demonstrates that OW can be a possible alternative feed source for honey bees.

Bioanodes containing catalysts from onion waste and Bacillus subtilis for energy generation from pharmaceutical wastewater in a microbial fuel cell

Performance of the FAOW8 + B. subtilis bioanode in an MFC (a 14-day test) using pharmaceutical wastewater (pH = 9.2) as a substrate.

Studies on assessment of safety and nutritional quality of shallot waste fractions

The production and processing of shallot expels different waste that has never been emphasized for composition and potential applications. These waste streams were initially analyzed for safety. Further, they were analyzed for sugar profile, fatty acid profile, mineral profile, and phytochemicals. The waste streams were found safe for application in food systems. All the streams were found rich in fiber and shallot peel contains 54.76%, highest among all. The fatty acid profile of fat extracted from shallot waste showed the abundance of saturated fatty acids in peel, stalk, and petiole. Unlike other, shallot flower fat contains 55.44% and 31.69% of linoleic (omega-6 fatty acid) and oleic acid (omega-9 fatty acids), respectively. Moreover, waste streams were good source of minerals and most significantly petiole contains 2,355.730 mg/kg iron. The waste streams were also found to contain a spectrum of phytochemicals and most significant compound is β-sitosterol found in all waste streams. Practical applications Shallot (Allium cepa var. aggregatum) is widely consumed throughout the world. Distinct production practices and processing of shallot expel various waste viz. peel, stalk, flower, and petiole. Most of these waste end up in landfill causing environmental pollution. Moreover, disposal as mere waste causes losses of various high value active compounds. Peel from Allium cepa L. has been studied widely for its composition and application and found to be rich in the active compounds such as quercetin, fructo-oligosacharides, etc. However, such compositional data are not available for shallot wastes affecting its utilization. The compositional study of shallot waste may pave the way for its effective utilization directly as food ingredient or source of active compounds. In a nutshell, shallot waste are cheap source of various active compounds, soluble and insoluble dietary fibers, flavoring oil, and their effective utilization may give mutual economic and environmental benefits to producers and processors. This study emphasized the onion waste as a potential source for various food application.

Correlation between empirical formulae based stoichiometric and experimental methane potential and calorific energy values for vegetable solid wastes

The correlation between stoichiometric (sMP, sCEV) and experimental biochemical methane potential (eBMP) and calorific energy values (eCEV) of vegetable wastes were evaluated. The elemental composition based empirical formulae were simulated for vegetable wastes and calculated stoichiometric chemical oxygen demand (sCOD), sMP, sCEV and compared with experimental results. Among twelve vegetable wastes chosen, minimum total solids, volatile solids, eCEV, and eBMP were observed in bottle guard (4.2%), beetroot (79.37%), okra(12.9MJ kg−1), onion (0.15 Nm LCH4 g−1VSr), whereas the maximum was recorded in beetroot (16%), radish (95%), tomato (19 MJ kg−1), tomato (0.42 Nm L CH4 g−1VSr), respectively. Similarly, the minima sCOD, sMP and sCEV was recorded as 1.10gCOD g−1VS (okra), 0.40 Nm L CH4 g−1VSr (onion), 15.89MJ kg−1 (Radish), whereas maxima was observed as 1.82 g COD. g−1VS (tomato), 0.62 Nm L CH4 g−1VSr (tomato), 22.29 MJ kg−1 (tomato). The observed lower and higher biogas yield in onion and tomato waste was coincided with the recorded lower carbon to nitrogen (C/N) ratio (16.31), higher amino sulfoxides (sulfonic acid) content and higher C/N ratio, moisture, glucose and fructose content in the former and later respectively. However, the lowest biogas yield in banana plantain waste in spite of highest C/N ratio was attributed to the presence of high cellulose content. Interestingly, the ascending trend in carbon, hydrogen and nitrogen content per gram of dry vegetable waste was correlated well with increased eCEV, sMP, on contrast reverse trend was depicted for oxygen. Among five different reported sCEV model results correlated with present study, the ultimate analysis based Scheurer-Kestner’s model depicted high R2 (0.89) compared to physical and proximate analysis based sCEV models for vegetable waste. Thus, the observed high correlation between sMP and eBMP (0.80), sCEV and eCEV (0.89), sCOD and eCEV (0.87) confirmed as an alternative short-term method that can replace tedious eBMP and eCEV for the design of biogas plants using vegetable organic solid wastes.

Development of ultrasonic extracts with strong antioxidant properties from red onion wastes

Development of ultrasonic extracts with strong antioxidant properties from red onion wastes

Enhanced Yield of Bioactivities from Onion (Allium cepa L.) Skin and Their Antioxidant and Anti-α-Amylase Activities.

There is increasing concern for reduction of the ecological impacts of industrial waste caused by fruits and vegetables. To reduce costs of onion waste disposal while obtaining value-added products, onion skin can be used to extract quercetin, a natural flavonoid with antioxidant, anti-inflammatory and anti-cancer effects. The aim was to optimize quercetin extraction from brown onion (Allium cepa L.) skin through investigation of the effects of different parameters on quercetin yield. Operational parameters for conventional maceration extraction and for ultrasound-assisted extraction were compared: solvent type, mass-to-liquid ratio, extraction time and temperature. Antioxidant capacity was determined using DPPH· radical scavenging assays and quercetin yield using HPLC/DAD. Anti-α-amylase activity of onion skin extracts was investigated using α-amylase inhibition assays. Optimal extraction conditions of quercetin from onion skin were obtained with maceration extraction, 50% ethanol, 1:100 mass-to-liquid ratio, 25 °C, for 15 min. Under these conditions, the antioxidant capacity (expressed as quercetin equivalents) was 18.7 mg/g and the mass fraction of quercetin was 7.96 mg/g. The onion skin extracts showed a dose-dependent relationship between dry extract concentration and α-amylase inhibition, which confirms that this onion skin extract can be considered as an anti-diabetes agent.

Life under Extreme Conditions: Aeropyrum pernix and Pernisine

Life under Extreme Conditions: Aeropyrum pernix and Pernisine

Spraying Agro-Industrial Compost Tea on Baby Spinach Crops: Evaluation of Yield, Plant Quality and Soil Health in Field Experiments

Compost tea is a liquid fraction extracted from composts, and it is of great interest in sustainable agriculture because it reduces the unsustainable use of chemical-based pesticides and fertilizers. In this study, during two spinach field cycles, we evaluated the potential beneficial effect of the foliar application of a compost tea made from onion and vineyard composts either by itself (CT) or implemented with the beneficial microorganism Trichoderma harzianum T78 (CT + Th) on the “healthy quality” and yield of baby spinach. Results showed that both the CT and CT + Th treatments produced a higher spinach yield than the control, but these treatments did not result in an increase in soil dehydrogenase activity (DHA) or soil nutrient content. Furthermore, CT + Th treatment showed the highest yield, phenolic content, antioxidant capacity and flavonoid levels. Nitrate levels were below legal amounts, and they were significantly (p ≤ 0.05) lower in the CT and CT + Th treatments than in the control. Data suggest that compost tea extracts from onion waste and vineyard compost and/or enriched with T. harzianum can be used in a sustainable agriculture to increase yield and quality of baby spinach.

Valorization of onion extracts as anti-browning agents

The enzymatic browning, whose main responsible is polyphenol oxidase (PPO, EC 1.14.18.1), is involved in the phenolic oxidation and colour alteration of minimally-processed fruits and vegetables. Currently, the research of new strategies to inactivate PPO is moving towards replacing synthetic additives such as organic acids and sulphites with natural inhibitors. The present study is focused on investigating the anti-browning performance of juices and distillates obtained from three onion varieties (white, yellow, and red) and Borettana onion wastes (inner layers). Their inhibitory activity on a commercial mushroom tyrosinase and some plant PPOs has been evaluated by spectrophotometric and electrophoretic analysis. The in vivo trials has been also carried out by monitoring over time at room temperature the colour change on potato slices under accelerated browning conditions. The effectiveness of onion samples in limiting enzymatic browning was affected by not only the enzyme source but also inhibitor type. Although distillates had higher anti-PPO capacity as confirmed by in vitro assays, juices showed better in vivo effectiveness. Hence, onions and their wastes can be valorised as a natural source of anti-browning agents to control PPO activity thus preserving sensory, antioxidant and nutritional properties of agro-food products.

Hyperthermophilic hydrogen production in a simplified reaction medium containing onion wastes as a source of carbon and sulfur

In this study, the hyperthermophilic dark fermentation of onion wastes (OW) for hydrogen production was investigated. OW were used at different proportions in mixed fruit and vegetable wastes (FVW) to evaluate their effect on hydrogen production by Thermotoga maritima. Fermentations were performed in a pH-controlled batch stirred tank reactor (BSTR) using seawater as a simplified reaction medium. Results showed that increasing OW proportions in total fruit and vegetable wastes (tFVW) improved H2 production. Therefore, increasing the OW to tFVW ratio from 0 to 0.8 increased the cumulative H2 production from 109 to 223.6mmol/L. The H2 productivity was also improved from 7.3 to 28.82mmol/h.L. In fact, OW contain carbohydrates, sulfur compounds, and other nutrients, which were used as a carbon source and energetic substrate for H2 production by the halophilic bacterium T. maritima in seawater without additional chemical compounds. Then, a H2 yield of 3.36mol H2/mol hexose was achieved using 200mL of OW, containing 55mmol/L of carbohydrates. A concept of H2 production from FVW at high proportions of OW in a simplified reaction medium was proposed. It allowed a H2 yield of 209LH2/kg volatile solids which could be an interesting future alternative to the current fossil fuel.

Thermal stability and bioavailability of bioactive compounds after baking of bread enriched with different onion by-products

This study investigated the effects of the addition of onion waste fractions into gluten-free (GF) bread to promote its health benefits. 5% of the control (C) GF flour blend was replaced with three waste fractions in the form of: fried onion (FO), dried onion (DO) and onion peel (OP). Antioxidant activity, content of flavonols and total polyphenols of breads increased in the following order: C < FO < DO < OP. No differences were observed in sensory analysis. We found that quercetin glycosides, dimers and trimer in OP-bread, determined according to their mass spectra, decomposed during baking and released free quercetin, which points to their thermal instability. Cross-over study revealed that consumption of OP-bread significantly increased (p < 0.05) antioxidant activity of consumers’ blood compared to control bread consumption, indicating good bioavailability of flavonols. Results suggest incorporation of OP into GF bread can increase its biological value with satisfactory sensory acceptance.