Influence of ultrasound‐assisted extraction techniques on the valorization of agro‐based industrial organic waste – A review

Recent advances in the implementation of ultrasound technology for the extraction of essential oils from terrestrial plant materials: A comprehensive review

Ultrasound-assisted extraction (UAE) is an innovative process for recovering valuable substances and compounds from plants and various biomaterials. This technology holds promise for resource recovery while maintaining the quality of the extracted products. The review comprehensively discusses UAE's mechanism, applications, advantages, and limitations, focusing on extracting essential oils (EOs) from diverse terrestrial plant materials. These oils exhibit preservation, flavor enhancement, antimicrobial action, antioxidant effects, and anti-inflammatory benefits due to the diverse range of specific compounds in their composition. Conventional extraction techniques have been traditionally employed, and their limitations have prompted the introduction of novel extraction methods. Therefore, the review emphasizes that the use of UAE, alone or in combination with other cutting-edge technologies, can enhance the extraction of EOs. By promoting resource recovery, reduced energy consumption, and minimal solvent use, UAE paves the way for a more sustainable approach to harnessing the valuable properties of EOs. With its diverse applications in food, pharmaceuticals, and other industries, further research into UAE and its synergies with other cutting-edge technologies is required to unlock its full potential in sustainable resource recovery and product quality preservation.

Towards green extraction of bioactive natural compounds

The increasing interest in natural bioactive compounds is pushing the development of new extraction processes that may allow their recovery from a variety of different natural matrices and biomasses. These processes are clearly sought to be more environmentally friendly than the conventional alternatives that have traditionally been used and are closely related to the 6 principles of green extraction of natural products. In this trend article, the most critical aspects regarding the current state of this topic are described, showing the different lines followed to make extraction processes greener, illustrated by relevant examples. These include the implementation of new extraction technologies, the research on new bio-based solvents, and the development of new sequential process and biorefinery approaches to produce a full valorization of the natural sources. Moreover, the future outlook in the field is presented, in which the main areas of evolution are identified and discussed.

Optimization of Bioactive Compound Extraction from Saffron Petals Using Ultrasound-Assisted Acidified Ethanol Solvent: Adding Value to Food Waste

The saffron industry produces large by-products, including petals with potential bioactive compounds, which are cheap and abundant, making them an attractive alternative to expensive stigmas for extracting bioactive components. This study aimed to optimize the extraction conditions of bioactive compounds from vacuum-dried saffron petals using an ultrasound-assisted acidified ethanol solvent. Three factors were considered: ethanol concentration (0-96%), citric acid concentration in the final solvent (0-1%), and ultrasound power (0-400 watt). This study examined the effects of these factors on parameters like maximum antioxidant activity, total anthocyanin content, total phenolic content, and the total flavonoid content of the extraction. This study found that saffron petal extract's antioxidant activity increases with higher ethanol concentration, citric acid dose, and ultrasound power, but that an increased water content leads to non-antioxidant compounds. Increasing the dosage of citric acid improved the extraction of cyanidin-3-glucoside at different ultrasound power levels. The highest extraction was achieved with 400 watts of ultrasound power and 1% citric acid. Ethanol concentration did not affect anthocyanin extraction. Higher ethanol concentration and greater citric acid concentration doses resulted in the maximum extraction of total phenolic content, with a noticeable drop in extraction at higher purity levels. This study found that increasing the proportion of citric acid in the final solvent did not affect flavonoid extraction at high ethanol concentration levels, and the highest efficiency was observed at 200 watts of ultrasound power. The optimum values of the independent parameters for extracting bioactive compounds from saffron petals included 96% ethanol concentration, 0.67% citric acid concentration, and 216 watts of ultrasound power, resulting in a desirability value of 0.82. This ultrasound-assisted acidified ethanolic extract can be used in the food industry as a natural antioxidant and pigment source.

Ultrasound-Assisted Extraction of Antioxidant Compounds from "Cẩm" Purple Rice Bran for Modulation of Starch Digestion

Purple rice, locally known as "Cẩm" rice, is cultivated in the southern region of Vietnam. The bran of "Cẩm" rice is often disregarded and underutilized; nevertheless, it harbours substantial nutritive value, particularly in terms of antioxidant compounds. Additionally, sonication, an emerging and "green" technological approach, has been employed to augment the extraction efficiency of these antioxidants. This research is aimed at optimizing and maximizing the antioxidant recovery capacity including phenolic and total flavonoid compounds, along with their antioxidant activities, through the assistance of ultrasound waves. The effect of the extract on the starch digestion process was also investigated. The study employed the Box-Behnken experimental design, encompassing three variables: extraction time (20-40 minutes), temperature (60-80°C), and solvent-to-material ratio (8 : 1 to 12 : 1). Analysis was conducted on total phenolic compounds, total flavonoid content, and antioxidant activities. Results demonstrated that the peak yield of antioxidant compounds and their corresponding activities were attained at an extraction duration of 29.38 minutes, a temperature of 69°C, and a solvent-to-material ratio of 9.92. Under these optimal conditions, the yields were as follows: total phenolic compounds at 60.821 mg GAE/g, total flavonoid compounds at 3.2696 mg QE/g, percentage inhibition of DPPH at 74.778%, and FRAP value at 54.112 μmol Fe (II)/g. The established models were validated and exhibited a strong alignment between predicted and actual values, with disparities of less than 3% under optimal conditions. Furthermore, the extract was codigested with cooked corn starch, revealing a dose-dependent effect on starch digestibility. The sluggishness of digestion rate was observed when 20 mg of the extract was supplemented to 200 mg of cooked corn starch. This suggests that rice bran extract holds promise as an effective ingredient for mitigating starch digestion, particularly beneficial for individuals dealing with diabetes.

Alteration of volatile compounds profile of brewers' spent grain by bath-ultrasonication and its combination with conventional water-bath and autoclave treatment

The study aimed to investigate the capability of bath-ultrasonication and its combination with conventional water-bath and autoclave treatment in modifying the volatile composition of brewers' spent grain (BSG). It was hypothesized that the treatments modified the volatile composition of BSG due to the sonochemical modification. The results demonstrated that the treatments intensified the desirable odor and removed the undesirable one which might allow the possibility of masking and renewing the odor perception of BSG. Besides the influence on odor perception related compounds, it is worth to highlight that the treatments eliminated herbicidal compounds such as (E,E)-2,4-heptadienal and (E)-2-hexenal which might be present from herbicidal treatment. Combination of bath-ultrasonication with autoclave treatment modified the volatile aldehydes while its combination with conventional water-bath generated the same profile as it was in untreated BSG. Time elevation on bath-ultrasonication had no significant impact on the amount of ketones and alkanes, while the fluctuation occurred as an impact of thermal exposures. Moreover, the treatment reduced the amount of alcohol and increased the fatty acids. In conclusion, bath-ultrasonication and its combination with thermal exposure modified the volatile compositions of BSG.

Valorization of Agro-Industrial Wastes by Ultrasound-Assisted Extraction as a Source of Proteins, Antioxidants and Cutin: A Cascade Approach

The use of agro-industrial wastes to obtain compounds with a high added-value is increasing in the last few years in accordance with the circular economy concept. In this work, a cascade extraction approach was developed based on ultrasound-assisted extraction (UAE) for tomato, watermelon, and apple peel wastes. The protein and antioxidant compounds were obtained during the first extraction step (NaOH 3 wt.%, 98.6 W, 100% amplitude, 6.48 W/cm², 6 min). The watermelon peels (WP) showed higher proteins and total phenolic contents (857 ± 1 mg BSA/g extract and 107.2 ± 0.2 mg GAE/100 g dm, respectively), whereas the highest antioxidant activity was obtained for apple peels (1559 ± 20 µmol TE/100 g dm, 1767 ± 5 µmol TE/100 g dm, and 902 ± 16 µmol TE/100 g dm for ABTS, FRAP and DPPH assays, respectively). The remaining residue obtained from the first extraction was subsequently extracted to obtain cutin (ethanol 40 wt.%, 58 W, 100% amplitude, 2 W/cm², 17 min, 1/80 g/mL, pH 2.5). The morphological studies confirmed the great efficiency of UAE in damaging the vegetal cell walls. WP showed a higher non-hydrolysable cutin content (55 wt.% of the initial cutin). A different monomers’ profile was obtained for the cutin composition by GC-MS, with the cutin from tomato and apple peels being rich in polyhydroxy fatty acids whereas the cutin extracted from WP was mainly based on unsaturated fatty acids. All of the cutin samples showed an initial degradation temperature higher than 200 °C, presenting an excellent thermal stability. The strategy followed in this work has proved to be an effective valorization methodology with a high scaling-up potential for applications in the food, pharmaceutical, nutraceutical, cosmetics and biopolymer sectors.