Development of an aqueous ultrasound‐assisted extraction process of bioactive compounds from beet leaves: a proposal for reducing losses and increasing biomass utilization

Abstract

BACKGROUND Red beet plants are cultivated worldwide for the consumption of their roots, generating large amounts of unexploited by‐products. In particular, beet leaves (BLs) represent about 50% of the whole plant and are usually discarded as waste. This constitutes not only an economic issue, since multiple resources invested in the production will be wasted, but also an environmental problem because of the pollution associated with their disposal. However, BLs comprise an important source of functional compounds (polyphenols and betalains) that could be recovered from the raw material, representing a sustainable solution for the underutilization of this by‐product. This study proposes the recovery of polyphenols and betalains using an aqueous ultrasound‐assisted extraction (UAE) process at different powers (35, 50, and 100 W) that was characterized and optimized. RESULTS UAE significantly enhanced the recovery of bioactive compounds and shortened the time required for extraction in comparison with traditional macerations (35 < 50 < 100 W). During UAE, the temperature of the systems increased as a function of the power applied, favouring the recovery of these phytochemicals. Additionally, a Box–Behnken design and response surface methodology were employed to optimize UAE conditions (90 W ultrasound power, 1:20 solid:liquid ratio, 16 min extraction time), under which the yields were 14.9 mg g−1 (polyphenols), 949.1 μg g−1 (betaxanthins), and 562.2 μg g−1 (betacyanins), consistent with the values predicted by the models. CONCLUSION This study enabled the development of a green‐solvent UAE process that constitutes an effective post‐harvest by‐products strategy to minimize losses and increase biomass utilization through the recovery of bioactive compounds from BLs, promoting sustainability in the agri‐food chain. © 2020 Society of Chemical Industry

The use of ultrasound in the South Cone region. Advances in organic and inorganic synthesis and in analytical methods

“… [158] Total phenolics Passion fruit rinds UAPLE ES: ethanol–water 70% v/v 3.0 g of fresh passion fruit 30 min 60 ◦C, 10 MPa and 360 W/cm2) with solvent flow rate of 10 g/min Penetration of the solvent into the pores of the plant improves mass transfer due to the disruption of cellular structures caused by cavitation [159] Phenolic and flavonoids compounds Quinoa (Chenopodium quinoa) seeds UAE ES: 80% ethanol 20 g samples, 400 mL of solvent, Solid-solvent ratio (1:20), sonicated (USB) 30.8 kHz, 250 W/L (maximal power input density), 60 °C, 60 min Ultrasound is not always adequate to enhance the extraction yields due to the nature of the vegetal matrix. [160] Polyphenols and betalains Beet leaves UAE ES: water 20 g of sample and 200 mL of water sonicated (UP) for 30 min at 100 W 20 kHz [161] Poliphenols (Theobromine, chlorogenic acid, Caffeic acid, caffeine, and kaempferol) Yerba mate leaves UAE ES: ethanol 20 g of yerba mate leaves suspended in 200 mL of ethanol and twice-sonicated (UP) (750 W, 20 kHz, 95.2 μm, 25 °C, 10 min) Improved the mass transfer of analytes from the sample solution due to the formation of the high-frequency ultrasonic waves [162] Total phenolic and total flavonoid compounds Strawberry by-products UAE ES: methanol/water/ethanol-formic acid A mixture of ground sample plus the solvent (1:5 w/v) sonicated (40 kHz, 160 W) for 15 min (twice) Improved the mass transfer of analytes from the sample solution [163] Phenolic compounds Argentinean yerba mate (Ilex paraguariensis) UAE ES: ultra-pure water 5 g of sample with 50 mL of water (USB) sonicated for 30 min ------ [164] Organic acids and polyphenols Polish wine samples UASE-PMLS ES: EtAc/dichloromethane (1:1) 25 μL of wine sample, 1 mL of ES, sonicated (USB) 25 min ------ [165] Antioxidant compounds and pigments Blackcurrant, raspberry and elderberry UAE <...>…”

“…Undoubtedly, the most explored topic throughout the South Cone region is the extraction of polyphenols assisted by ultrasound. Table 1 shows 29 works from Chile [140] , [141] , [142] , [143] , [144] , [145] , [146] , Uruguay [147] , [148] , Southern Brazil [149] , [150] , [151] , [152] , [153] , [154] , [155] , [156] , [157] , [158] , [159] and Argentina [160] , [161] , [162] , [163] , [164] , [165] , [166] , [167] , [168] , [169] reported during the last 10 years The most important aspects highlighted were that ultrasound helped and improved extraction procedures, reduced operational time, enhanced extraction yields and made it greener in comparison to traditional extraction methods, according to others publication [170] . Nevertheless, the use of ultrasound did not always improve the performance of an analytical procedure or showed an important benefit in an extraction process [140] , [160] , [171] , [172] , [173] .…”

Environmentally Friendly Techniques for the Recovery of Polyphenols from Food By-Products and Their Impact on Polyphenol Oxidase: A Critical Review

“…In other words, the increase in the power in the UAE method could increase the extraction yield of polyphenols and shorten the time required for the extraction. In addition, the reduction of UAE time can lessen energy consumption significantly [62]. Increasing the extraction time higher than a threshold has no meaningful change in the phenolic content.…”

“…Since UAE is a nonthermal method, some works in the literature have proposed using thermal profiling to control the temperature of the extraction process [62,67]. However, when ultrasound is used as an extraction method, the heat generated in the medium solvent may be advantageous for enhancing extraction yield because it alters the membrane structure of herbal cells and simplifies the distribution of the extracted molecules into the solvent [62,68]. Nevertheless, due to the sensitivity of polyphenols to heat, their antioxidant activity may be lost when the temperature is greater than 55 °C [61].…”

Development of an Ultrasonic-Assisted Extraction Technique for the Extraction of Natural Coloring Substance Chlorophyll from Leaves of <i>Carica papaya</i>

“…It i.e, 35 , 40 45 and 50 while keeping the other parameters constant. During the extraction process, solutions were prepared by adding different amounts of papaya leaf powder such as 0.4 grams, 0.6 grams, 0.8 grams, and 1 gram, respectively 18,19 .…”