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.

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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.

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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.