An Assessment of the Bioactive Compounds and the Antioxidant, Anti-Inflammatory, and Antidiabetic Potential of Hydro-Methanolic Extracts Derived from Fresh Noni (Morinda citrifolia L.) Fruits Growing in Sri Lanka ^†

Abstract

Morinda citrifolia L., or Noni, thrives in tropical and sub-tropical regions globally, garnering interest as a bioactive source. Despite Sri Lanka’s myths, Noni’s potential remains underutilized. The United States commercialized Noni products in the early 1990s, introducing Noni juice as a wellness drink in 1996. In this study, we assessed Sri Lankan Noni fruit’s functional properties through methanolic extraction and various assays, revealing its notable antioxidant, anti-inflammatory, and antidiabetic potential. Methanolic-extracted fresh Noni fruits may serve as natural sources of antioxidants and anti-inflammatory agents. Exploring specific bioactive compounds could yield innovative treatments for oxidative stress, inflammation, and diabetes-related conditions.

1. Introduction

Morinda citrifolia L., locally known as ‘Ahu’ or Noni in Sri Lanka, has gained global recognition for its significant role in a wide range of therapeutic activities [1]. Noni fruit has been deemed safe for human consumption by the European Union [2], and there is no established causal relationship between noni juice consumption and acute hepatitis [3]. A wide array of value-added products, encompassing Noni juice, capsules, powder, concentrates, tea, and others, derived from various components of Morinda citrifolia, have become commercially available [4], while Noni products, predominantly in the form of juices and dietary supplements [5], have achieved widespread global accessibility, and the fruit itself has been increasingly utilized for the production of dietary supplements in recent years [6]. Despite extensive global research on Noni fruits, only a limited number of interventions have been conducted in Sri Lanka [7], and in this study, we aim to evaluate the functional properties of Noni fruits cultivated in Sri Lanka.

2. Methodology

Ripened fruits were obtained from trees grown in the ‘Katugasthota’ area of Kandy District, Sri Lanka. The fruits, selected based color and shape, were vacuum-packaged in polyethylene bags and stored at −18 °C until further analysis.

For the quantitative determination of the proximate composition of the Morinda citrifolia (L.) fruit and seed samples, moisture was determined using a hot air oven (Association of Official Analytical Chemists; AOAC 930.04, 1990), in which we placed dried leaf samples at 105 °C until a constant weight was obtained. Crude protein was determined according to the Kjeldahl method (AOAC 978.04, 1990), and total nitrogen was multiplied by a protein factor of 6.25. Total fat was determined according to the acid hydrolysis method (AOAC 948.15, 1990) using a Soxhlet extractor at 60 °C until a constant weight was obtained. Dietary fiber was determined according to the enzymatic gravimetric method (AOAC 930.10, 1990). Ash was determined according to the gravimetric method (AOAC 930.05, 1990), heating the incinerated leaf samples at 550 °C until a constant weight was obtained. Total carbohydrate was determined according to the difference method through a calculation [8].

The methanolic extraction of fresh Noni fruits was carried out according to the method described in [9] with slight modifications. A total of 1 g of fresh fruit samples was weighed and mixed with 10 mL of 80% methanol, vortexed at high speed for 30 min, and then centrifuged (Hettich, EBA 20, Tuttlingen, Germany) for 10 min at 792 g. The extraction was subsequently filtered through a filter paper (Whatman No. 42; Whatman Paper Ltd., Maidstone, UK). The crude extract was desolventized in a rotary evaporator (HAHNVAPOR, Model HS-2005 V, HAHNSHIN Scientific, Gimpo-si, Republic of Korea) at 40 °C. The total polyphenol content of the methanolic extraction was estimated using the Folin–Ciocalteu method described by [10]. The total antioxidant capacity of Noni extraction was analyzed according to the modified method described by [11]. A modified thiobarbituric acid reactive substance (TBARS) assay was employed to measure the level of lipid peroxide formed in egg homogenates as lipid-rich media, following the method described by [12]. The ability of the prepared extracts to scavenge the ‘stable’ free radical DPPH was monitored according to the modified method [13]. The ABTS free radical scavenging activity was assessed using the methodology of [14] with some modifications. The antioxidant capacity of the Noni extracts was assessed using the FRAP assay, following the method of [15] with certain modifications. The Singlet Oxygen Scavenging Assay was conducted in accordance with the protocol outlined in [16]. The in vitro anti-inflammatory activity was assessed through three membrane lysis assays, namely, the preparation of an erythrocyte suspension, heat-induced hemolysis, and the effect on protein denaturation, following the methods elucidated by [9] with some modifications. Furthermore, the nitric oxide inhibition activity was examined as reported by [17].

The antidiabetic potential was evaluated using two diabetic assays: alpha-amylase inhibitory activity, following the methodology outlined by [18], and alpha-glucosidase inhibitory activity, as assessed through the methodology detailed in [19].

3. Results

A proximate chemical composition analysis of the Noni fruit was conducted, and the results for the fresh part were revealed. It was observed that the moisture content was found to be approximately 89.20 ± 1.98% per 100 g of fresh weight, indicating a high water content. In contrast, the fruit had a relatively low crude fat content, which was measured at 0.16 ± 0.01% per 100 g of fresh weight. The protein content was also relatively low, with a measurement of 0.64 ± 0.12%. The Noni fruit exhibited moderate levels of crude fiber at 1.97 ± 0.31% and a crude carbohydrate content at 6.94 ± 1.98% per 100 g of fresh weight. Additionally, the ash content was found to be 1.08 ± 0.06% per 100 g of fresh weight, indicating the mineral composition of the fruit. These findings provided insights into the nutritional composition of fresh Noni fruit.

The significant total phenolics content was determined at 198.60 ± 2.48 μmol gallic acid equivalent per 1 g of fresh weight in the methanolic extract of the fresh noni fruits. Furthermore, a series of IC50 values were obtained in various assays, demonstrating the extract’s antioxidant potential. The total antioxidant capacity was measured at 33.96 ± 0.30 µg/mL, while the IC50 value for the DPPH scavenging activity was determined as 35.87 ± 0.48 µg/mL. Additionally, the ABTS scavenging activity exhibited an IC50 value of 24.36 ± 0.42 µg/mL. The lipid peroxidation inhibition activity was notably effective, with an IC50 value of 77.42 ± 0.84 µg/mL, and the inhibition of singlet oxygen had an IC50 value of 6.91 ± 0.24 µg/mL. In the ferric reducing antioxidant power assay (FRAP assay), an IC50 value of 45 ± 0.81 µg/mL was recorded. Significant anti-inflammatory potential was also observed, with IC50 values for the nitric oxide inhibition activity measured at 73.40 ± 1.20 µg/mL, heat-induced hemolysis inhibition at 9.40 ± 0.80 µg/mL, protein denaturation inhibition at 4.81 ± 0.21 µg/mL, and proteinase inhibitory activity at 9.12 ± 0.89 µg/mL. Additionally, antidiabetic activities were evaluated, with IC50 values of 13.40 ± 0.20 µg/mL for alpha-amylase inhibitory activity and 6.92 ± 0.34 µg/mL for alpha-glucosidase inhibitory activity.

4. Conclusions

In summary, this study has confirmed that the extract from fresh noni fruits, obtained using methanol, has impressive health benefits. The extract was shown to be a powerful antioxidant, effectively combatting harmful molecules called free radicals and preventing damage to fats in our bodies. Additionally, it demonstrates an ability to reduce inflammation, which is linked to various health issues. Furthermore, it exhibits potential in managing diabetes by blocking certain enzymes involved in sugar metabolism. These findings emphasize that methanol-extracted fresh noni fruits can serve as a valuable source of natural antioxidants and anti-inflammatory substances with various health uses. Further research aiming to pinpoint the specific active compounds responsible for these effects could lead to new treatments and healthy food products for conditions related to oxidative stress, inflammation, and diabetes.