(71f) Mango (Mangifera indica L.) By-Products for Food, Cosmetics and Water Treatment Applications: A Zero-Waste and Biorefinery Approach with Classic and New Generation Solvents

This work applies green engineering, zero-waste, bioeconomy, biorefining and circular economy concepts around mango fruit waste. Fruit and vegetable industrialization by-products contain valuable chemical compounds called secondary metabolites and structural biopolymers, considered renewable raw materials with significant properties and characteristics that can be recovered and converted in high value-added compounds. These can be incorporated in new applications in pharmaceutical, food, nutraceuticals, cosmetics, textiles, pulp and paper, among other industries. Mango residual biomass was submitted to pigments and oil extraction. Besides using classic solvents for the extraction of bioactive chemicals, the novel aspect of this project is to use deep eutectic solvents (DES) for oil/butter extraction from the mango kernel. Moreover, mango peel flour and mango-derived biofilters (endocarp) have been used for the removal of carbamazepine, ibuprofen and acesulfame from artificial water.

The Haden mango is a species produced mainly on the Ecuadorian coast, of which 25-40% of their by-products are discarded [1]. Mango has beneficial properties, since it is rich in fatty acids, antioxidants, polyphenols, tannins and vitamins [2]. The kernel has important nutrients [3], [4] such as sugars; natural pigments such as β-carotenes and polyphenols such as tannins; as well as structural biopolymers such as pectin, cellulose, hemicellulose and lignin [5]. In fact, the kernel is rich in mangiferin, noratiol, and resveratrol [6], powerful polyphenols with antioxidant properties that can be used to protect humans against diseases such as cancer and diabetes [1]. The kernel is composed of an outer woody layer called endocarp, which is thick and hard and encapsulates the seed (cotyledon) in an appropriate manner. Within the endocarp, there is a thin paper type wrap that protects the seed, and serves as a coating [7]. Natural colorants can be obtained from the different by-products: seed, peels, pulp, for instance, and these could be used as potential substitutes of artificial food colorants and nutraceutical applications [8]. Mango oil/butter can be extracted using organic solvents, such as hexane, which has been demonstrated to be the one of the best solvents for this purpose. However, greener technologies are being explored in order to substitute these toxic solvents and carry out the extraction procedure at room temperature. Deep eutectic (new generation) solvents [9] have been used for oil extraction from microalgae [10] obtaining comparable yields under specific conditions, and have also being used for polyphenolic antioxidants recovery [11]. Regarding biofilters, the extractive-free fibrous skin (endocarp) can be used as a substitute of different material widely used in industry such as activated carbon or zeolite.

Sample preparation steps were followed by drying and grinding procedure, then two oil extraction methods were used: through Soxhlet/hexane technique [12] and a DES mixture application. The DES consisted of a choline chloride:urea (1:2) mixture for the fractionation of mango seed to aid the seed-oil recovery avoiding the use of hexane. A modified method of Tommasi et al. (2017) [10] was used where dried and crushed mango seed was placed together with the DES mixture and kept under stirring for 24 hours at room temperature. The mixture was centrifuged and the supernatant was removed. A rigorous washing procedure with distilled water was performed and the final mixture, lyophilized.

Determination of parameters such as pH, melting point, specific gravity, saponification index [13], free fatty acids and acidity value [14] were performed. Proximal analysis of by-products (mango peel (exocarp) flour, seed, endocarp) [15] were conducted as well. Colorant extraction was performed by maceration with 37% ethanol [16]. Mango seed oil was characterized through GC-MS prior oil derivatization. Finally, cosmetic and food prototypes were prepared.

Ground endocarp was dried for 24 h at 50^oC and submitted to Soxhlet extractions with water for 4 h and then with ethanol 90% [17]. The extractive-free endocarp was dried at room temperature. Biofilters were packed in borosilicate columns (1.1 cm in diameter) until filled up to 30 cm and 45 cm heights. Artificial contaminated water was fed from the top of the columns at a 13.8 mL/min flowrate and each test lasted 1 hour [18]. Acesulfame (ACS), ibuprofen (IBP) and carbamazepine (CBZ) at an initial concentration of 10 ppm [mg/L] each, were quantified using a UV-VIS Spectrophotometer.

The DES treatment resulted in a 6.57% yield which is lower than the average yield through a Soxhlet extraction (9.65%). Nonetheless, the obtained yield for DES gives insight that this procedure can partially substitute Soxhlet-hexane processes. The ideal DES mixture for oil recovery is currently under investigation. The goal, is to eventually substitute the organic solvents and keep the process with the least amount of energy input. Colorant recovery from the peels and fibrous skin will also be tested using DES technology to aid the extraction processes.

Seed oil/butter (Figure 1a) contains 40.91% oleic acid, 35.20% stearic acid, 10.65% palmitic acid, 9.33% linoleic acid (omega 6), 2.49% arachidic acid, 0.98% α-linoleic acid (omega 3), and 0.44% capric acid, which compare to results from other authors [19]–[22]. The differences in fatty acids in cocoa butter in the study conducted by López Hernández (2013) [23], showed a higher content of palmitic acid and slightly less than that of oleic acid; mango butter had a greater amount of linoleic acid (omega 6) than cocoa butter, and for the other fatty acids the results are quite similar [19]. On the other hand, palm oil has a much higher amount of palmitic acid and a smaller amount of stearic acid [24] and because mango oil is rich in stearic and oleic acid, it can be said that this is more stable than many other rich vegetable oils is unsaturated fatty acids.

The percentage of proteins found in the mango seed was 6.16 ± 0.52%, which is similar to the result of ref. [25]; the shell presented 4.19 ± 0.02%, which is very similar to that obtained by ref. [26]; and the seed, 1.27 ± 0.51%. The percentage of fats obtained for the seed was 9.31 ± 0.12%, a result close to that of [20]; for the shell, this was 2.19 ± 0.23%, within range to that obtained by ref. [27]; and for the seed, this was 0.29 ± 0.09%. Regarding the percentage of ash, the mango seed had 2.32 ± 0.05%, also similar to ref. [28]; the shell, 3.00 ± 0.31%; and the seed, 0.66 ± 0.03%. In terms of percentage of humidity, the seed resulted in 9.21 ± 0.16%, supported by ref. [29]; the shell, 5.94 ± 0.36%; and the seed, 9.11 ± 1.36%. In addition, it must be considered that the results depend on the variety of mango.

Mango butter had a melting point of 33.42 ± 0.64 °C, which is in the range of results mentioned by ref. [30]; a pH of 6.42 ± 0.04, similar to the results obtained by ref. [31]; it had a specific gravity of 0.88 ± 0.04 g / mL, close to that obtained by [30] the saponification index was 136.83 ± 1.50 mg KOH/g oil, similar close to the results of ref. [14]; its free fatty acids and acidity value were 3.48 ± 0.42% and 6.92 ± 0.83 mg NaOH/g oil respectively, similar to the results obtained by [14] and [20].

Natural colorant extraction by maceration (Figure 1b) and DES is currently under further investigation. The flour obtained by crushing the seed and dried mango peel (Figure 1c,d), can be applied in the food industry, for the preparation of bakery products in different concentrations and formulations [32]. As for the cosmetic prototypes (Figure 1e,f) a lip balm and moisturizer were developed. Due to the properties of the ingredients used, the skin was shiny, moisturized and without adverse effects at the time of its application.

Results for the three contaminants are shown in Figure 1g,f. The concentration of ACS, IBP and CBZ in a 30 cm column height were 8.68, 8.55, and 7.21 ppm, respectively; while removals reached were: 10.29, 15.47 and 28.35%, respectively. The concentration of ACS, IBP and CBZ in a 45 cm column height were 9.21, 8.71, and 4.26 ppm, respectively; while removals reached were: 9.99, 12.39 and 58.20%, respectively. The most persistent contaminants through the filter arrangement are IBP and ACS, while CBZ achieves almost six-fold the IBP removal percentage after 1-hour treatment. Also, it can be observed, that ACS behavior is independent of the two column heights.

There are very few studies related to the reuse of mango by-products and the extraction of oil from mango seed in Ecuador. The goal of this project is to use mango by-products to recover their valuable components which have applications in the development of products with industrial potential (food, nutraceutics, cosmetics, water treatment/environment), applying the concept of zero waste technology and circular bioeconomy.