Food colorants processed via agro-industrial wastes are in demand as food waste management becomes vital not only for its health benefits but also for cost reduction through waste valorization. Huge efforts have been made to recover valuable components from food wastes and applied in various fields to prove their versatility rather than for feed ruminant usage only. Betalains and phenolics, antioxidant-rich compounds responsible for host color and so commonly used as natural colorants in food and cosmetic industries, are copiously present in several kinds of fruits and vegetables as well as their wastes. Technological innovation has brought extensive convenient ways of bioactive compounds extraction with many advantages like less use of solvents and energy in a short period of processing time in comparison with the classical solid–liquid extraction methods. Emerging technologies, particularly microwave irradiation, have been amenable to electromagnetic technology for decades. Practically, they have been deployed for functional and supplement food production. In this review, the feasibility of dielectric heating (microwave irradiation) in the extraction of betalain and phenolic compounds mostly from fruit and vegetable wastes was discussed.

Consumer concern over artificial food additives has stimulated production of pigments from natural sources. The aim of this study was to examine the effects of process variables on the content of colour compounds (betaxanthin and betacyanin) in beetroot peel juice extracted by conventional method. In this research, the extraction processes were carried out according to the central composite design with different process variables. Quantitative measurements of the basic colour compounds in beetroot extract were performed using spectrophotometer. From our experiment, it was found that the most adequate extraction conditions, which gave the highest yield of colour compounds (952.5 mg l^–1 of betaxanthin and 1361 mg l^–1 of betacyanin), were extraction time 1 h, operating temperature 20 ºC, and solvent ratio 0.8 w/v. Being a conventional heating method, it is a simple and cost efficient process with relatively high yield.

Betalains are natural color compounds with high water affinity, unstable, and fragile; hence, understanding their thermal tolerance is always beneficial either in manufacturing them or in their application in betalain-rich functional foods for better handling. In our study, the extractability of betalains via microwave-assisted extraction (MAE) from the peel of beetroot was implemented at 100–800 W for 30–150 s with four different solvents. Among the maximum amounts of total betalains (202.08 ± 2.23 mg/100 g FW), betacyanin (115.89 ± 1.08 mg/100 g FW) and betaxanthin (86.21 ± 1.16 mg/100 g FW) were generated by pure water solvent after 150 s of MAE at 800 W. Alternatively, the susceptibility of beetroot peel extracts to processing conditions was investigated by heating them at 30–70 °C, and the thermal instability of betalains was evaluated by half-life (t_1/2), temperature quotient (Q₁₀), and activation energy (E_a), using the Arrhenius equation. The resulted retention percentage (R%) proved that ascorbic acid improved the R% of total betalains from 22 to 51% and betacyanin from 3 to 29% and in contrast reduced R% of betaxanthin from 56 to 40% after the heat treatment at 70 °C for 5 h.

Recovery of valuable products from organic wastes with conventional extraction method plus modern separation technology is becoming popular in solid waste management. The major attention of this project was to test the efficiencies of two different types of reverse osmosis membranes (RO99 and X20) on juice concentration extracted from peel of beetroot which is "waste". The extractions of beetroot peel were completed using water and ethanol-water (15 v/v%) solvents at 22 °C for 60 minutes. The applied transmembrane pressure, temperature, and recirculation flow rate of membrane separation process were 40 bars, 30 °C, and 400 L/h, respectively. Quantifications of valuable compounds were detected using spectrophotometer. The permeate flux profiles were investigated and lower permeate flux was experienced with RO99 compared to X20 in both methods. Additionally, from the aspect of efficiency, RO99 outstripped X20 membrane on concentration of some compounds such as betalains, and phenolic components. Betaxanthin, betacyanin, antioxidant and TPC contents in final retentates of RO99 membrane concentration were as follow: 292.47±1.93 mg/L, 499.03±1.3 mg/L, 1133.15±25.74 mg/L,1243.96±106.56 mg/L (water solvent) and 337.26±4.31 mg/L, 585.2±5.83 mg/L, 698.55±22.53 mg/L, 1268.87±48.69 mg/L (ethanol-water solvent), respectively. From this experiment, expectation can be made that membrane technology can widen its applications in food and pharmaceutical industries.

Since significant percentage of fruits and vegetables go to waste during processing, investigation of how to improve the valuable products of extraction from the wastes is an undeniably effective way to save the planet. Beetroot (root, peel, and stalk) is a chief source of natural betalain color compounds and phenolic compounds with copious radical scavenging activity. The major emphasis of this work is to optimize process variables which are extraction time (10–60 min), operating temperature (20–50 °C), and aqueous ethanol solvent with the concentration of (25–75%) for effective extraction of valuable compounds such as betalains, total polyphenols, and antioxidant activity from beetroot peel. Spectrophotometric analysis was applied for quantification of those compounds. Amongst which, lowest solvent concentration (25% v/v) together with the highest temperature (50 °C) and extraction time (50 min) brought yielded higher results. The process optimization was carried out using Design Expert (11.0.3) statistical software. Overall, it can be noted that extraction process can be improved by controlling operating time and temperature, avoiding unnecessary overuse of costly solvent.

In the context of “waste valorization,” recovery of biomolecules from agri‐food wastes by the innovative extraction technique has come to the forefront. In this investigation, the effect of microwave pretreatment on aqueous extraction of betacyanin (BC), phenolic, flavonoid, and antioxidant from the crown part of Cylindra‐type beetroot (Beta vulgaris L.) has been studied. Two major operating parameters of leaching, such as temperature and extraction time have been varied, ranging from 30°C to 60°C and 20–60 min, respectively to optimize the extraction of mentioned biomolecules through the response surface methodology technique. Moreover, the extraction of mentioned biomolecules by leaching was increased by microwave pretreatment (at 800 W for 3 min). As an example: the microwave‐assisted aqueous leaching process provided BC color compound 17.12 ± 0.37 mg/g dry matter (DM), total phenolic compounds (TPC) 57.89 ± 1.14 mg gallic acid equivalent (GAE)/g DM, total flavonoids content (TFC) 10.37 ± 0.00 mg quercetin equivalent (QUE)/g DM and total antioxidant activity (AA) 56.13 ± 0.92 mg ascorbic acid equivalent (ASE)/g DM. Whereas, BC, TPC, TFC, and AA were 3.04 ± 0.07 mg/g DM, 2.81 ± 0.11 mg GAE/g DM, 2.43 ± 0.41 mg QUE/g DM, and 4.38 ± 0.18 mg ASE/g DM by aqueous leaching process without microwave pretreatment. Subsequently, the existence of two major different BC, such as betanin and iso‐betanin have been examined by high‐performance liquid chromatography‐diode array detector‐electrospray ionization‐quadrupole‐time‐of‐flight. In addition, changes in the morphology of the plant matrix were pointed out by field emission scanning electron microscope. Our investigation has proven the positive impacts of microwave pretreatment on the extraction of mentioned bioactive compounds by infusion and maceration processes as well.Practical Applications: The application of innovative emerging technologies for the effective scavenging of bioactive compounds from agro‐industrial discharges has been focused on. Under the study range, microwave‐assisted leaching extraction was found to be the most efficient method as it exhibited the utmost amounts of betacyanin, phenolic, flavonoid, and antioxidants in microwave‐assisted maceration and infusion processes. This investigation encourages the short‐time microwave pretreatment before the performance of traditional solid–liquid extractions in order to improve the extraction efficacy of plant compounds.