Valorization of Wasted Plant Parts: Mineral Bioavailability, Antioxidant, and Antimicrobial Properties of Wasted Aerial Parts of Selected Root Vegetables

Abstract

This study aims to investigate the valorization of the wasted aerial parts of root vegetables (onion, white radish, red radish, carrot, and beetroot) as a source of minerals and antioxidant compounds. The findings revealed that the aerial parts of the plants contained valuable amounts of the total phenolic and total flavonoid content with high antioxidant activity, particularly those of carrots. Additionally, the contents of vitamin C, gamma-aminobutyric acid (GABA), and anthocyanin were found in appreciable amounts in most of the samples, except those parts of onion in which the lowest quantity of vitamin C and GABA were detected. Among the phenolic and flavonoid compounds, quercetin was recorded as the major phenolic compound, followed by kaempferol in beetroot, carrot, white radish, and red radish aerial parts. Interestingly, the extraction from the wasted parts of the studied plant exhibited high antimicrobial activity against several species of pathogenic bacteria. Moreover, these aerial wasted parts of the root vegetables had considerable Ca, Mg, Na, K, P, Zn, and Fe content with moderately high bioavailability. Overall, the aerial wasted parts of root vegetables are rich in bioactive compounds and minerals, paving the way for potential utilization in food and feed applications.

1. Introduction

Root vegetables such as potatoes, radish, beetroot, and carrots are precious for human consumption. They are most abundant in the food supply chain, with an annual production of 906.8 million tons in 2022 [1]. Aerial parts of root vegetables, which account for up to 50% of the total yield, are considered valuable by-products of root vegetable production processes used for animal nutrition or discarded into the environment as hazardous wastes [2]. These wastes contain high moisture content, are easily contaminated by microorganisms, and have high biodegradability; therefore, they can cause high environmental contamination [3]. Root vegetables’ aerial parts are very rich in nutrients with high potential utilization in food applications for developing functional foods and supplements [2,4]. They also contain valuable antioxidant compounds with high activity [5]. Beet root and carrot leaves are reported to contain 18–25% protein, 7–35% dietary fiber, 2–5% lipids, and 46–71% carbohydrates on a dry weight base and considerable amounts of betalains, carotenoid, chlorophyll, flavonoids, phenolic acids, vitamins, and essential minerals [6,7,8]. The phenolic compounds in carrot leaves were reported to be higher than fresh carrots by more than 10-fold [9]. The aerial parts of radish are rich in phenolic compounds with total phenolic contents of 86.16 and 78.77 mg/g dry extract in radish leaves and stems, respectively, in addition to various phytochemicals such as catechin, coumaric acid, ferulic acid, myricetin, protocatechuic acid, quercetin, sinapic acid, syringic acid, and vanillic acid [10]. Leaves of several onion species were reported as being rich sources of numerous phytochemicals, including flavonoids, phenolics, and tannins, and exhibited antibacterial, antifungal, antioxidant, anti-inflammatory, and antiplatelet properties [11]. Previous reports examined the effect of different extraction solvents on the bioactive properties of aerial parts of carrot, onion, beetroot, and white and red radish. It revealed that the highest total phenolic contents and flavonoids were obtained in absolute methanol and ethanol extracts, respectively.

In contrast, the highest antioxidant activity was achieved with 70% ethanolic and methanolic extracts [5]. It is well known that aerial parts of root vegetables are of high nutritional and health value; however, they are usually discarded into the environmental systems, posing more ecological impacts [10]. Aerial parts of root vegetables are considered as potential sources of minerals such as calcium, magnesium, phosphorus, potassium, ferric, and zinc. However, the nutritional advantages mostly depend on their bioavailability, which is greatly affected by some antinutritional factors such as tannin, phytate, and oxalates [12]. To utilize the efficacy of aerial parts, analyses of nutritional bioactivity, mineral content, and bioavailability are still needed. Evaluating such parameters will help explore their suitability for valorization in the food and feed industries and support their application as sustainable and cost-effective ingredients in animal feed formulations and functional food products. Additionally, sustainable utilization of these wasted parts could help to reduce agricultural waste, increase nutritional security, and encourage eco-friendly resource utilization. Therefore, this study investigated the bioactive properties, antimicrobial activity mineral content, and bioavailability of wasted aerial parts of selected root vegetables.

2. Materials and Methods

2.1. Materials

Wasted aerial foliar parts of onion, white radish, red radish, beet, and carrot were used in this study. About 5 kilos of each plant was collected from the same variety and cultivated in the same area and conditions, from a local market in Riyadh, Saudi Arabia. The samples were washed, cleaned from dirt and foreign material, and dried at 40 ± 2 °C. The dried samples were packed and kept at 4 °C.

2.2. Phenolics and Antioxidant Extraction

To obtain the free phenolics, flavonoids, and antioxidants, the sample extracts were set using a ratio of 1w:25v of methanol with 24 h stirring and then filtrated through Whatman No. 1 filter paper. The final extract of each sample was desiccated at room temperature and used for further analysis. Bound phenolics and flavonoids were extracted following Finocchiaro et al.’s [13] method. The precipitate from the extraction of the free phenolic and flavonoid was blended with 2 N NaOH (40 mL) at 25 °C shaking for one hour, then neutralized with conc HCL and extracted with C₄H₈O₂ solvent. The ethyl acetate extracts were dried and kept to determine the bound phenolic and flavonoid content.

2.3. Phenolic Determination

The extracts’ free and bound phenolic content was carried out following the Flin–Ciocalteu method described by Waterhouse [14]. A mixture of sample extract (20 µL), H₂O (1.58 mL), Folin–Ciocalteu reagent (100 µL), and Na₂CO₃ (300 µL) was incubated in the dark at 20 °C for 2 h. After that, 5 mL of the solution was detected in the UV spectrophotometer (UVIKON 930, BIO-TEK Kontron, Eching, Germany) at 765 nm in contradiction to the blank solution. The phenolic content (bound, free, and total) was stated as mg gallic acid per gram of dry extract (mg GAE/g). For the standardization curve (R² = 0.9672), solutions with different gallic acid concentrations were used instead of the extract.

2.4. Flavonoids Determination

The evaluation of the free and bound flavonoid content in root sample extracts was performed according to Kim et al. [15]. An aliquot mixture of (1 mL) methanolic extract, (300 μL) 5% NaNO₂, and (300 μL) 10% AgCl₃ was incubated at 25 °C for 5 min, and then (2 mL) 0.1 N NaOH was added. The volume was then made up to 10 mL with H₂O. The extract solutions were incubated at 20 °C for 30 min, and then the absorbance was detected at 510 nm. Several concentrations of quercetin were used to create the calibration curve (R² = 0.974), and the flavonoid content was specified as mg QE/g.

2.5. Antioxidant Activity

The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) of the vegetable’s wasted part extracts was measured spectrophotometrically following the Chang et al. [16] protocol. Approximately 0.1 mL of the sample extracts mixed with 0.9 mL of a 50 mM Tris-HCl buffer (pH 7.4) and 1 mL of DPPH solutionwas incubated at 20 °C for 30 min. The absorbance was detected with a UV-spectrophotometer (517 nm), and the DPPH scavenging was quantified as mg Trolox/g sample. The method of Gulcin et al. [17] was performed to assess the ferric-reducing power (FRAP) of sample extracts. A solution of phosphate buffer (2.5 mL; 0.2 M, pH 6.6) and K₃ [Fe (CN)₆] (2.5 mL of 1%) was mixed with sample extract (1 mL). The mixtures were incubated at 50 °C for 20 min, and then TCA (2.5 mL of 10%) was added prior to the centrifugation (1038× g for 10 min). Then, the filtrate supernatant (2.5 mL) was mixed with H₂O and FeCl₃. In this assay, a UV spectrophotometer (UVIKON 930, BIO-TEK Kontron, Eching, Germany) was used to record the absorbance at 700 nm, and the FRAP was specified as mg ascorbic acid (AAE)/gram of sample. The hydrogen peroxide (H₂O₂) scavenging test was estimated following the assay of Jayaprakasha et al. [18]. About 1000 µL extract was mixed with phosphate buffer (3 mL; pH 7.4) and H₂O₂ (1 mL, 40 mM). The solution absorbance was recorded at 230 nm, and H₂O₂ scavenging was calculated as a percentage (%).

$${{\mathrm{H}}_2\mathrm{O}}_2\mathrm{s}\mathrm{c}\mathrm{a}\mathrm{v}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{g}\left(\%\right)={\displaystyle \frac{\left(Absorbancecontrol-Absorbancesample\right)}{Absorbanceofcontrol}}\times 100$$

2.6. Determination of Anthocyanin Content

Egbuna et al.’s [19] protocol determined the anthocyanin content of plant samples. The samples were extracted with methanol (70%) solution at 25 °C for 48 h. The extract (1 mL) was split into two tubes. The first extract (1 mL) reacted with ethanol-HCL (0.01%) solution and HCL (2%; pH 0.8). The second extract reacted with citric buffer (0.2 M; pH 3.5). The absorbance of the extracts was noted at 520 nm and calculated as the difference of the blank methanol (70%). The anthocyanin content was expressed as mg cyanidin/g.

2.7. Determination of γ-Aminobutyric Acid Content

The protocol of Zhang et al. [20] was followed in measuring the contents of γ-Aminobutyric acid (GABA) in root samples. Briefly, 1 g of sample was extracted with 15 mL of H₂O, for 1 h. The supernatant was filtered by using filter paper and syringe filter (0.45 µm), and then 0.5 mL was mixed with borate buffer (0.2 mL; 0.2 M pH 9.0), phenol (1 mL of 6%), and NaClO (0.4 mL of 9%). The reaction mixture was then boiled in a water bath for 10 min, followed by cooling for 30 min. The GABA content was estimated by spectrophotometry (645 nm). The standard curve was set from the different concentrations of GABA with R-squared value of 0.994.

2.8. Vitamin C Measurement

Vitamin C was estimated following the 2,6-dichloroindophenol [21]. About 5 g of the samples was mixed with oxalic acid (30 mL; 0.4%), and then the filtered volume was made up of oxalic acid to 100 mL. Then, 10 mL of the filtrate was mixed with 5 mL of oxalic acid (10%) and followed by titration against the dye.

2.9. HPLC Analysis of Phenolic Compounds

The profile of the phenolic compounds in the extracts was analyzed using the HPLC apparatus. The HPLC (SCL-10A VP Shimadzu, Kyoto, Japan) is equipped with a PDA detector and an Inertsil ODS-3 (5 µm; 4.6 × 250 mm) column. A mixture of acetic acid (0.05%) in water (A) and acetonitrile (B) acted as the mobile phase with a 1 mL/min flow rate at 30 °C (20 µL). The recorded peaks were detected at 280 and 330 nm. The gradient programme was as follows: 0–0.10 min 8% B; 0.10–2 min 10% B; 2–27 min 30% B; 27–37 min 56% B; 37–37.10 min 8% B; 37.10–45 min 8% B. The total running time per sample was 60 min.

2.10. Antimicrobial Activity

The antimicrobial activity of the extracts was assessed against the following food spoilage microorganisms Klebsiella pneumoniae, E. coli, Yersinia enterocolitica, S. typhimurium, S. aureus, and B. cereus following Brandt et al.’s [22] protocol. The antimicrobial agent was estimated to be a result of pure zones of inhibition of the growth culture of each microorganism. About 10 µL of the methanolic extract for each sample was released on the growth culture. The existence of inhibition zones was observed after incubation at 37 °C. Extraction solvents were served as blanks. The width of the clear zones was used to assess the antimicrobial activity of each extract.

2.11. Total and Available Mineral Determination

The total mineral content of samples was assessed using the atomic absorption spectrophotometer method [23]. Samples of ash were incubated (37 °C; 3 h) in HCl (5 mL; 5 N). The bioavailability of minerals of samples (1 g) was performed after dissolving in HCl (10 mL; 0.03 M) following Chauhan and Mahjan’s [24] protocol. The available mineral extracts were then dried at 60 °C and then acid-digested following the method of Chapman and Pratt [23]. The bioavailability of the mineral was determined and expressed as a percentage.

2.12. Statistical Analysis

The number results of three replicates were analyzed and then averaged. Data were evaluated by analysis of variance (ANOVA) and by LSD test with a significance level of p < 0.05. Multivariate analysis was performed using MultBiplot software (https://www.researchgate.net/publication/236143127_MultBiplot_Jose_Luis_Vicente_Villardon (accessed on 22 March 2025) incorporated into MATLAB r2024a software (MathWorks Inc., Natick, MA, USA) as described in the instruction manual.

3. Results and Discussion

3.1. Free, Bound, and Total Phenolic and Flavonoid Contents of Aerial Parts of Selected Root Vegetables

The results of free, bound, and total phenolic and flavonoid contents of radish (white and red types), onion, beetroot, and carrot are shown in

Table 1. Total phenolic content (mg GAE/g) and total flavonoid content (mg QE/g) of aerial part of selected root vegetables.

Root Vegetables	Free Phenolic	Bound Phenolic	Total Phenolic
Onion	16.9 ± 0.65 e	2.7 ± 0.16 b	19.6 ± 0.41 d
White radish	29.5 ± 0.36 d	3.8 ± 0.25 a	33.3 ± 0.30 c
Red radish	37.1 ± 0.36 b	3.8 ± 0.40 a	40.9 ± 0.38 b
Beetroot	31.7 ± 0.95 c	2.6 ± 0.33 b	34.3 ± 0.64 c
Carrot	66.3 ± 1.49 a	2.2 ± 0.28 b	68.8 ± 0.89 a
Root Vegetables	Free flavonoids	Bound flavonoids	Total flavonoids
Onion	30.9 ± 0.78 b	7.4 ± 0.23 b	38.3 ± 0.51 b
White radish	26.3 ± 0.72 b	5.3 ± 0.68 c	31.6 ± 0.71 c
Red radish	27.8 ± 0.93 b	1.1 ± 0.36 e	28.9 ± 0.65 c
Beetroot	24.3 ± 1.05 b	8.6 ± 0.88 a	32.9 ± 0.97 c
Carrot	59.8 ± 0.72 a	3.7 ± 0.79 d	63.5 ± 0.76 a

Values are means (±SD) of triplicate samples. Means not sharing a common superscript letter in the same column are significantly (p < 0.05) different as assessed by LSD.

. The highest (p < 0.05) levels of free (66.3 ± 1.49 mg GAE/g) and total phenolic (68.8 ± 0.89 mg GAE/g) content were noted in green waste of carrot followed by that of red radish (37.1 ± 0.36 mg GAE/g free phenolic and 40.9 ± 0.38 mg GAE/g total phenolic). In contrast, the lowest values were seen in green waste of onion (16.9 ± 0.65 mg GAE/g free phenolic and 19.6 ± 0.41 mg GAE/g total phenolic). The highest amount (p < 0.05) of bound phenolic contents was seen in the white and red radish aerial parts. The highest (p < 0.05) levels of free and total flavonoids were found in carrot aerial parts, followed by onion aerial parts. The lowest (p < 0.05) values of free and total flavonoids were seen in beetroot aerial parts and red radish aerial parts, respectively. The highest levels of bound flavonoids were found in the aerial parts of beetroot, followed by that of onion, whereas the lowest value was observed in the aerial parts of red radish.

In this study, the phenolic and flavonoid contents are comparable to previous reports on aerial parts of different vegetables. Mohammed et al. [5] studied the effects of various solvents on the total phenolic and total flavonoids of aerial parts of carrot, onion, white radish, red radish, and beetroot. They revealed that the TPC, TFC, and antioxidant activity of wasted parts of the root vegetables were relatively high, particularly in the absolute methanolic and ethanolic extracts. In another study, Khan et al. [25] reported higher amounts of total phenolics (125.3 mg GAE/g) in radish leaves, whereas the levels of total flavonoids (44.5 mg QE/g) were comparable to that of our study. In addition, Gawlik-Dziki et al. [26] reported that the total polyphenol and flavonoid content of leaves of white and red beetroot ranged between 8.15 and 16.55 mg GAE/g and 1.31 and 1.6 mg QE/g, which was lower than our results. Moreover, Bardakçi et al. [27] stated that the total phenolic content of carrot leaves was 9.17 mg GAE/g, which was lower than that determined in this study. Yuasa et al. [28] reported that the total polyphenol of onion and fresh onion leaves was 0.31 to 0.57 mg GAE/g, which was lower than our results. The differences in the total phenolic and total flavonoid contents in the aerial parts of root vegetables are likely due to the variation in the environmental conditions, genotypes, cultivation and harvesting conditions, postharvest processing, and extraction conditions. However, the obtained results revealed that the aerial parts of the root vegetables could be considered as a rich source of phenolics and flavonoids, which explore their potential utilization in food and feed applications.

3.2. Antioxidant Activity and Vitamin C, GABA, and Anthocyanin Contents of Aerial Parts of Selected Root Vegetables

The results on the antioxidant activity in terms of as assessed by DPPH radical scavenging activity, ferric reducing antioxidant power (FRAP) and H₂O₂ scavenging activity, vitamin C, GABA, and anthocyanin contents, and aerial parts of root vegetables (onion, white radish, red radish, carrot, and beetroot) are displayed in

Table 2. DPPH scavenging activity, ferric reducing power (FRAP), and H₂O₂ scavenging activity and vitamin C, GABA, and anthocyanin content of the aerial part of selected root vegetables.

Root Vegetables	DPPH (mg Trolox/g)	FRAP (mg AAE/g)	H2O2(%)
Onion	4.4 ± 0.337 c	0.5 ± 0.08 c	76.1 ± 0.20 b
White radish	5.3 ± 0.250 ab	2.7 ± 0.33 bc	80.6 ± 1.04 a
Red radish	5.2 ± 0.083 b	4.0 ± 0.11 b	75.3 ± 0.94 b
Beetroot	5.7 ± 0.087 a	9.7 ± 0.09 a	82.5 ± 1.10 a
Carrot	4.98 ± 0.105 b	9.9 ± 0.11 a	81.1 ± 0.19 a
Root Vegetables	Vitamin C (mg/g)	GABA (mg/g)	Anthocyanin (mg/g)
Onion	2.9 ± 0.69 c	2.0 ± 0.040 c	14.4 ± 0.06 d
White radish	9.7 ± 0.23 b	13.6 ± 0.09 b	29.5 ± 0.00 b
Red radish	17.6 ± 0.70 a	13.6 ± 0.09 b	23.7 ± 0.11 c
Beetroot	2.4 ± 0.11 c	30.1 ± 0.05 a	9.35 ± 0.09 e
Carrot	7.1 ± 0.23 bc	13.8 ± 0.24 b	40.9 ± 0.11 a

Values are means (±SD) of triplicate samples. Means not sharing a common superscript letter in the same column are significantly (p < 0.05) different as assessed by LSD.

. The DPPH antiradical activity was high (p < 0.05) in the aerial parts of beetroot, followed by that of white and red radish, whereas it was low in onion aerial parts. The highest (p < 0.05) FRAP levels were observed in the carrot and beetroot aerial parts, while the lowest value was seen in the aerial parts of the onion. The scavenging activity of H₂O₂ was high in the aerial parts of beetroot, followed by that of carrot and white radish, onion, and then red radish.

It was clearly observed that the antioxidant activity varied among the aerial parts of different root vegetables as assessed by DPPH, FRAP, and H₂O₂ scavenging activity. In a previous study which assessed the antioxidant activity of the aerial parts of the same root vegetables, the findings showed great variations in the antioxidant activity due to the variation of the samples and extraction solvents [5]. Similarly, Yuasa et al. [28] reported that the DPPH radical scavenging activity of onion and fresh onion leaves was in the range of 3.9–5.4 µmol TE/g, similar to our results. Khan et al. [25] reported a lower amount of DPPH antiradical activity (0.39 mg TE/g) in radish leaves than in this study. Moreover, Bardakçi et al. [27] stated that carrot leaves’ total antioxidant activity (ABTS) was 5.56 mg/g. Gawlik-Dziki et al. [26] reported that the antioxidant capacities as assessed by ABTS, OH, and chelating power of leaves of white and red beetroot were 41.65 mg FW/mL, 50.0 mg/mL, and 111.05 mg/mL, respectively. The differences between these studies could be due to the variations in the genotypes, environment, cultivation practices, pre- and postharvest processing methods, and antioxidant extraction and assessment methods. However, the wasted aerial parts of these root vegetables are considered a rich source of phenolic and flavonoid content, which highlights their potential to improve food quality and serve as a natural alternative to synthetic additives.

Regarding vitamin C, the highest (p < 0.05) level of vitamin C was observed in the aerial parts of red radish (17.6 mg/g), followed by that of white radish (9.7 mg/g), whereas the lowest (p < 0.05) value was evident in aerial parts of onion and beetroot 2.9 and 2.4 mg/g, respectively (Table 2). The GABA content was found to be significantly varied among the root vegetable types. It ranged between 2.0 and 30.1 mg/g. The highest level of GABA was shown in the aerial parts of beetroot (30.1 mg/g), whereas the lowest value (2.0 mg/g) was recorded in the onion. Likewise, the anthocyanin content was significantly (p < 0.05) varied among the different crops. It was found to be 40.9, 29.5, 23.7, 14.4, and 9.35 (mg/g) in the aerial parts of carrots, white radish, red radishes, while, onion, and beetroot, respectively (Table 2).

In this study, the variation in these antioxidant compounds among the root vegetable types might be associated with several factors such as growing environment (temperature, light exposure time, soil type and fertility, relative humidity, etc.), cultivating conditions, harvesting season, and postharvest handling. Similar findings were also stated by several studies. Bardakçi et al. [27] reported that the vitamin C content of fresh carrot leaves was 186 mg/100 g. Yuasa et al. [28] reported that the total vitamin C content of onion and fresh onion leaves was in the range of 29.25–40.32 mg/100 g. Rubóczki and Hájos [29] stated that the vitamin C content of the leaves of different beetroot cultivars is between 5.94 and 7.90 mg/100 g. Khazail and Asadi-Gharneh [30] and Goyeneche et al. [31] reported that radish leaves are rich in vitamin C, recording about 34.25 mg/100 g and 38.69 mg/100 g, respectively. Despite the variation in the antioxidant capacity among the studied root vegetables, these wasted parts could play a vital role in food manufacturing as sustainable natural additives.

3.3. Phenolic Compounds of Aerial Parts of Selected Root Vegetables

The results of phenolic compounds of aerial parts of selected root vegetables are shown in

Table 3. Phenolic compounds (mg/100 g) of aerial part of selected root vegetables.

Phenolic Compound	Onion	White Radish	Red Radish	Beetroot	Carrot
Phenolic acids
Gallic acid	0.2 ± 0.02 c	0.5 ± 0.02 b	0.1 ± 0.00 d	0.7 ± 0.08 a	0.6 ± 0.05 a
Protocatechuic acid	0.6 ± 0.04 c	0.6 ± 0.05 c	0.8 ± 0.01 b	1.1 ± 0.10 a	1.2 ± 0.03 a
Chlorogenic acid	0.1 ± 0.03 a	Nd	Nd	Nd	Nd
Caffeic acid	0.1 ± 0.01 b	0.1 ± 0.01 b	0.3 ± 0.01 a	Nd	0.3 ± 0.00 a
Coumaric acid	0.1 ± 0.00 b	0.1 ± 0.00 b	0.1 ± 0.00 b	0.1 ± 0.01 b	0.2 ± 0.01 a
Ferulic acid	1.2 ± 0.14 b	2.7 ± 0.08 a	0.2 ± 0.06 c	0.2 ± 0.04 c	1.1 ± 0.09 b
Cinnamic acid	1.0 ± 0.04 d	4.0 ± 0.09 b	2.4 ± 0.17 c	0.4 ± 0.03 e	9.9 ± 0.07 a
Flavonoids
Catechin	5.6 ± 0.17 a	1.9 ± 0.08 b	0.9 ± 0.06 c	0.4 ± 0.05 d	0.6 ± 0.07 d
Rutin	16.5±0.03 a	1.0 ± 0.07 b	0.9 ± 0.04 c	0.4 ± 0.04 d	0.9 ± 0.03 c
Hesperidin	3.7 ± 0.58 a	0.5 ± 0.03 d	0.8 ± 0.04 c	0.8 ± 0.07 c	1.9 ± 0.04 b
Quercetin	7.7 ± 0.27 c	15.9 ± 1.23 b	14.0 ± 1.17 b	3.4 ± 0.28 d	24.7 ± 1.67 a
Kaempferol	6.2 ± 0.95 c	0.1 ± 0.01 d	13.8 ± 0.89 a	7.7 ± 0.62 c	10.1 ± 0.21 b

Values are means (±SD) of triplicate samples. Means not sharing a common superscript letter in a row are significantly (p < 0.05) different as assessed by LSD. Nd; not detectable.

. The most abundant phenolic compound in the aerial part of onion was rutin, followed by quercetin, kaempferol, catechin, and hesperidin. Quercetin is the most abundant phenolic compound in aerial parts of red radishes and carrots, followed by kaempferol and cinnamic acid. It is also the major phenolic compound in white radish’s aerial parts, followed by cinnamic acid and ferulic acid. In contrast, kaempferol and quercetin are the most abundant compounds in beetroot. Among the assessed aerial parts, the highest (p < 0.05) level of gallic and protocatechuic acids was observed in aerial parts of beetroot and carrot, and the least was found in aerial parts of onion. Chlorogenic acid was only detected in trace amounts in aerial parts of the onion and not in all other samples. The highest level of ferulic acid was in the seed in the aerial parts of white radish, followed by that of onion and carrot, and the lowest was observed in the aerial parts of beetroot and red radish. The highest level of cinnamic acid was seen in the aerial parts of the carrot, followed by that of white and red radish, whereas the lowest value was seen in beetroot. The highest (p < 0.05) amounts of catechin and rutin were noted in the aerial parts of onion, followed by white radish, while the lowest amounts were found in the aerial parts of beetroot. The highest (p < 0.05) amount of hesperidin was seen in the aerial parts of onion, followed by that of the carrot, and the lowest was found in the aerial parts of the white radish. The highest (p < 0.05) amount of quercetin was observed in the aerial parts of the carrot, followed by white and red radish, onion, and then beetroot. The highest levels of kaempferol were evident in the aerial parts of red radish, followed by that of carrot, and the lowest level was seen in the aerial parts of white radish. Overall, there are variations in the contents of phenolic compounds among the aerial parts of the selected root vegetables.

The phenolic compound profile of aerial parts of onion, white radish, red radish, beetroot, and carrot extracts was varied among the sample types; however, the major phenolic compound was quercetin, followed by kaempferol. Previous reports showed different phenolic profiles of aerial parts of root vegetables. In radish aerial parts, the major phenolic compounds were reported as p-coumaric acid [32], vanillic acid, catechin and sinapic acid [10], epicatechin, p-coumaric acid, and vanillic acid [31], and rosmarinic acid and chlorogenic acid [33]. In beetroot aerial parts, the most abundant phenolic compounds were salicylic and sinapic acids [26], quercetin, rosmarinic acid, and gallic acid [33], and ferulic acid [34]. The major phenolic compounds in carrot aerial parts were reported as chlorogenic acid, rosmarinic acid, o-coumaric acid [33], and chlorogenic acid [35]. All aforementioned studies showed great variability in the types and quantities of phenolic compounds of the aerial parts of root vegetables, likely due to the variation in the genetics, environmental conditions, postharvest processing conditions, and experimental conditions.

3.4. Antimicrobial Activities of Aerial Part of Root Vegetables Extracts Against Different Bacterial Species

The antimicrobial activity of the extracts of aerial parts of selected root vegetables was assessed against six pathogenic microorganisms, namely Bacillus cereus, Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Salmonella typhimurium, and Yersinia enterocolitica, and the results are displayed in

Table 4. Antimicrobial activities of aerial part of selected root vegetable extracts (100 μg/ML) against different bacterial species.

Root Vegetables	Inhibition Zone (mm)
	Klebsiella pneumoniae	Yersinia enterocolitica	E. coli	S. typhimurium	S. aureus	B. cereus
Onion	12.7 ± 0.58 a	11.0 ± 1.00 a	12.3 ± 0.58 b	13.0 ± 0.00 b	9.3 ± 0.58 b	8.0 ± 0.00 d
White radish	11.7 ± 0.50 ab	9.0 ± 0.00 b	10.3 ± 0.58 d	15.7 ± 1.015 a	8.0 ± 0.00 c	11.0 ± 1.00 b
Red radish	12.0 ± 0.00 ab	9.0 ± 0.00 b	13.3 ± 0.58 a	12.0 ± 0.50 c	10.3 ± 0.29 a	10.0 ± 0.00 c
Beet	8.0 ± 0.00 c	11.5 ± 0.50 a	10.0 ± 0.00 d	10.0 ± 1.00 d	9.0 ± 0.50 b	12.0 ± 0.00 a
Carrot	11.0 ± 0.00 b	11.0 ± 0.00 a	11.0 ± 0.00 c	9.0 ± 0.00 e	7.7 ± 0.58 c	11.0 ± 1.00 b

Values are means (±SD) of triplicate samples. Means not sharing a common superscript letter in the same column are significantly (p < 0.05) different as assessed by LSD.

. The extracts had different antimicrobial impacts as the inhibition zones varied among the used strains and extracts. Generally, greater zones were observed in Gram-negative strains compared to those of Gram-positive strains, with some exceptions. For K. pneumoniae, the more extensive (p < 0.05) inhibition zone was observed when using extracts of aerial parts of onion followed by red and white radishes. In contrast, the lowest zone was seen when this strain was treated with beetroot extract. The inhibition zone of Y. enterocolitica was high (p < 0.05) using the extracts of aerial parts of beetroot, carrot, and onion. Extracts of aerial parts of red radish possessed a high inhibition zone against E. coli and S. aureus followed by onion and carrot aerial parts. Salmonella typhimurium was more sensitive to most of the extracts, with the highest inhibition zone among all extracts observed with white radish extract, followed by that of onion and red radish, and the lowest was recorded by carrot. Beetroot aerial parts extract possessed a high inhibition zone against B. cereus, followed by that of white radish and carrot, whereas onion aerial part extract showed a low inhibition zone against this strain.

Antimicrobial activity of aerial parts extracts of root vegetables showed variations based on the type of the extracts and targeted strains. Similar trends of antimicrobial activity were reported in aerial parts of root vegetables. The previous reports demonstrated that the green part of the carrot showed great inhibition against Salmonella enterica, followed by Escherichia coli [36]. In addition, broad inhibition zones (17 mm) were reported to inhibit E. coli and Vibrio parahaemolyticus with onion green parts demonstrating great antimicrobial activity [37]. Moreover, the aerial parts of radish possessed higher antibacterial activity against the Gram-negative strain Morganella morganii and the Gram-positive strain Listeria monocytogenes than other tested strains [32]. Furthermore, the methanolic extracts of beetroot leaves displayed antimicrobial activity against Escherichia coli, Salmonella enteritidis, Bacillus cereus, and Staphylococcus aureus with different affinities [38]. Our study noted that the aerial part extracts of root vegetables possessed greater antimicrobial activity against Gram-negative strains than Gram-positive ones. This could be because natural phenolic compounds initially target the bacterial cell wall, thereby causing structural damage to the cell walls and cellular components, condensing cellular materials, and promoting the leakage of the cellular components by increasing membrane permeability [39,40]. In addition, high antimicrobial activity might also be associated with the high content of some phenolic and flavonoid compounds such as quercetin and kaempferol, which are high in aerial part extracts of selected root vegetables. It was well recognized that these compounds are capable of inhibiting lactamase activity and thereby stopping bacterial resistance to antibiotics, inhibiting RNS synthesis, and negatively affecting the fluidity of external and internal bacterial membranes [39].

3.5. Mineral Content and Availability of Aerial Parts of Root Vegetables

Table 5. Total (mg/100 g) and available (%) macro and micro elements of aerial parts of selected root vegetables.

Vegetable	Macro elements
	Ca		Mg		Na		K
	Total	Available	Total	Available	Total	Available	Total	Available
Onion	37.3 ± 1.16 ab	37.1 ± 1.14 bc	11.1 ± 0.48 a	66.3 ± 0.72 c	33.0 ± 1.37 c	13.6 ± 2.15 b	133.7 ± 2.53 e	41.5 ± 1.75 c
White radish	38.0 ± 2.00 ab	31.4 ± 1.29 c	11.0 ± 0.75 a	61.2 ± 1.88 d	77.7 ± 1.63 b	12.4 ± 2.16 bc	221.3 ± 1.86 a	46.3 ± 0.28 ab
Red radish	38.7 ± 1.55 a	31.5 ± 1.41 c	9.8 ± 0.48 a	74.3 ± 1.62 a	31.6 ± 2.34 c	8.8 ± 0.76 c	175.8 ± 2.81 d	44.3 ± 2.40 bc
Beetroot	35.3 ± 1.55 ab	43.4 ± 1.09 ab	10.9 ± 0.52 a	70.3 ± 0.87 b	124.1 ± 3.85 a	45.9 ± 3.39 a	184.7 ± 2.31 c	50.2 ± 3.61 a
Carrot	34.2 ± 1.68 b	44.4 ± 0.80 a	11.2 ± 0.35 a	60.1 ± 1.53 d	66.8 ± 2.54 b	46.7 ± 1.65 a	205.1 ± 2.55 b	41.7 ± 3.08 c
Vegetable	Micro elements
	P	Fe		Zn
	Total	Available	Total	Available	Total	Available
Onion	61.2 ± 3.29 c	20.7 ± 2.79 b	11.3 ± 0.58 b	11.6 ± 2.63 c	0.5 ± 0.00 c	18.1 ± 1.39 b
White radish	154.3 ± 4.04 a	19.9 ± 2.20 b	11.0 ± 1.73 b	18.9 ± 2.42 a	1.2 ± 0.06 b	24.0 ± 1.90 a
Red radish	135.3 ± 4.62 a	29.7 ± 2.95 ab	14.7 ± 2.08 b	12.0 ± 1.38 c	0.9 ± 0.06 bc	21.4 ± 1.52 ab
Beetroot	97.0 ± 3.46 b	29.8 ± 1.28 ab	9.0 ± 1.73 b	15.6 ± 0.00 b	1.0 ± 0.06 bc	13.3 ± 1.84 c
Carrot	50.7 ± 2.31 c	36.4 ± 3.41 a	22.7 ± 2.89 a	3.9 ± 0.86 d	5.1 ± 0.98 a	7.9 ± 0.52 d

Values are means (±SD) of triplicate samples. Means not sharing a common superscript letter in the same column are significantly (p < 0.05) different as assessed by LSD.

shows the content and availability of macro and micro minerals in aerial parts of root vegetables. Generally, mineral contents and availability are significantly (p < 0.05) varied among the aerial parts of root vegetables. The highest content of Ca was seen in the aerial parts of white and red radishes, whereas the lowest one was observed in aerial parts of carrot (p < 0.05). Regarding the availability, the greatest (p < 0.05) availability of Ca was noted in the aerial parts of carrot and beetroot, whereas the least (p < 0.05) availability was found in the aerial parts of white and red radishes. There are no significant differences in Mg content in the aerial parts of the selected root vegetables, whereas there are some variations in available Mg among the aerial parts of root vegetables with the highest available Mg being observed in red radish and the lowest being carrot aerial parts. The highest content of Na was observed in aerial parts of beetroot followed by that of white radish and carrot, whereas the lowest content was seen in aerial parts of onion and red radish. High availability of Na was found in carrot and beetroot aerial parts, while aerial parts of red radish showed low Na availability. The highest content of K was seen in white radish aerial parts followed by carrot aerial parts, whereas the lowest value was noted in aerial parts of onion. Regarding availability, the highest percentage of available K was observed in the aerial parts of beetroot, whereas the lowest percentage was seen in the aerial parts of onion and carrot. The greatest (p < 0.05) P levels were observed in aerial parts of white radish followed by red radish, whereas the lowest level was noted in aerial parts of carrot. The highest level of available P was seen in aerial parts of carrot followed by beetroot and red radish, whereas the lowest P availability was evident in aerial parts of white radish and onion. The greatest Fe content was observed in aerial parts of carrot followed by that of red radish, whereas the lowest level was noted in beetroot. Regarding Fe availability, it was the highest in aerial parts of white radish followed by beetroot aerial parts, whereas it was the lowest in carrot aerial parts. The highest amounts of Zn were found in the aerial parts of carrot followed by that of white radish, whereas the lowest value was seen in onion aerial parts. The greatest Zn availability was evident in white radish followed by that of red radish, whereas the least available Zn was noted in carrot aerial parts.

Mineral content and bioavailability of aerial parts of root vegetables were analyzed, and the results demonstrated numerous variations in the contents and availability of the assessed wastes and mineral types. Previous studies have evaluated the contents of minerals in aerial parts of some root vegetables; however, there has been no study about the bioavailability of minerals in these valuable wastes. Biondo et al. [41] assessed the mineral contents of beetroot leaves during developmental stages. They observed decreasing and increasing trends of minerals throughout different stages, with K. Na as the major mineral and possessing increasing trends during stages. The results were higher than those in our study. They also reported that Fe is reduced during developmental stages from 34.28 mg/100 g to 18.73 mg/100 g at 80 days and then increased to 25.63 mg/100 g at 100 days of development, and the levels were slightly higher than those of our study [41]. However, similar levels of Mg and Zn were reported in beetroot leaves [41]. In addition, Mella et al. [42] reported comparable Zn and Fe levels and high Ca, Mg, P, and K levels in beetroot stems and leaves. Székely et al. [43] observed variations in mineral contents in the beetroot leaves between the cultivars and seasons and attributed that to the genotypic and environmental effects. Mineral contents of onion leaves were assessed and reported to have differed among onion cultivars and regions [44,45]. Leite et al. [7] reported the mineral contents of dehydrated carrot leaves, and the levels were somewhat similar to the amounts reported in this study. Goyeneche et al. [31] studied the mineral contents of radish leaves and roots and observed higher levels of minerals in radish leaves than in the roots. They also reported higher levels of Ca, K, Na, and Mg and lower levels of Fe and Zn compared to the findings of this study [31]. Minerals are essential nutrients in the development and metabolism of the human body and are available in sufficient amounts in aerial parts of root vegetables; however, their bioavailability is vital for proper uptake and metabolism from diets. Factors such as the presence of antinutritional factors such as phytate and tannins in green wastes might adversely affect the bioavailability of minerals. Some processing treatments, such as fermentation, must eliminate them before the utilization of these wastes in food applications. In this study, the bioavailability of the assessed minerals is excellent in all samples; hence, the utilization of plant waste rich in minerals in food processing offers a sustainable approach to enhancing nutritional value while reducing environmental waste.

3.6. Multivariate Analysis

The outcomes of the principal component analysis (PCA) and hierarchical clustering analysis (HCA) of the phenolic compound, bioactive compounds, antioxidant activity, antimicrobial activity mineral content, and bioavailability of aerial parts of elected root vegetables are shown in Figure 1a,b. The PCA revealed that the aerial parts of root vegetables were divided into four groups based on the assessed traits. There are positive, negative, and no correlations among the traits as reflected by acute, obtuse, and straight angles of the cosines between the vectors of all traits (Figure 1a). The first group is composed of onion aerial parts, which are characterized by greater levels of catechin, rutin, hesperidin, and chlorogenic acid and antimicrobial activity against E. coli and K. pneumoniae than other samples. There are positive correlations among these attributes. The second group is composed of white and red radish aerial parts and is characterized by higher levels of vitamin C, caffeic acid, ferulic acid, total Ca and P, available Zn, Mg, and Fe, and inhibition against S. aureus and S. typhimurium than other aerial part samples, and positive correlations were seen among these traits. The third cluster is composed of beetroot aerial parts, which are characterized by higher levels of bound flavonoids, GABA, antioxidant activity (DPPH, FRAP, and H₂O₂), gallic acid, protocatechuic acid, B. cereus and Y. enterocolitica inhibition, total Na, and available K and Na than other samples. The fourth group is composed of carrot aerial parts, which is characterized by greater levels of anthocyanin, TPC, TFC, free phenolics, free flavonoids, quercetin, kaempferol, p-coumaric acid, cinnamic acid, total Mg and Fe, and Zn, and available P and Ca compared to aerial parts of other samples. It is interesting to note that there are positive correlations of the bound flavonoids, gallic acid, and protocatechuic acids with DPPH, FRAP, and H₂O₂ antioxidant activity, suggesting the contribution of these compounds on the assessed antioxidant activity of aerial parts of root vegetables. Also, it could be noted that there are negative correlations between the total and available minerals, suggesting that a high mineral level does not reflect their bioavailability. HCA further supported the PCA results as the horizontal axes divide the aerial parts samples into four main clusters (Figure 1b). In the heatmap, red indicates high association and green indicates low associations between the assessed traits and aerial part samples. It is clear that most of the assessed attributes were greater in carrot aerial parts than in the other samples, followed by beetroot and red radish aerial parts.

4. Conclusions

Bioactive properties, antimicrobial activity, and mineral content and bioavailability of wasted aerial parts of onion, carrot, radish (white and red), and beetroot were assessed with the aim of paving the way for beneficial utilization of these valuable wastes in food applications. The findings demonstrated significant levels of bioactive properties, antimicrobial activity, mineral content, and bioavailability, which were highly different among the analyzed wasted green parts of these root vegetables. It is generally noted that carrot aerial parts were richer in most of the assessed attributes than other samples, followed by beetroot and red radish aerial parts. Conclusively, the aerial parts of root vegetables are rich in bioactive compounds and minerals with significant bioactivity, antimicrobial potential, and mineral bioavailability. However, further investigations are needed to improve the bioavailability of nutrients to maximize their benefits for the food industry. The application of plant waste rich in antioxidants and minerals in food manufacturing presents a useful approach to enhancing nutritional value while promoting sustainability.

Additionally, utilizing plant waste contributes to waste reduction and supports a circular economy in the food industry.