Introduction
The edible wild fruit species are those that are neither produced nor domesticated but are available in their natural environment and used as food and socioeconomic wellbeing sources, particularly by rural impoverished communities.1,2 Botanical investigations and literature emphasize the abundance, diversity, and economic worth of wild edible fruit species throughout the world. In Cameroon, edible wild fruits are valued and regularly sold in markets3 throughout the year. The indigenous populations realize and use their nutritional, medicinal, therapeutic, and industrial possibilities. They also feed on small local businesses and generate the income needed for survival in many households.3 Edible fruits, in general, are important for a balanced diet, because they serve as food supplements and provide humans with very essential nutrients such as dietary fibers, proteins, sugars, and vitamins (particularly Vitamin C in some fruits), as well as health-promoting phytochemicals and major minerals constituents.4
Carissa edulis Vahl (Apocynaceae) is a multi-stemmed, much-branched prickly evergreen shrub or small tree, that may grow up to 6 m tall and produce a dense canopy. Because of its tiny size, seedless/small seed, and ability to be eaten whole, this plant is sometimes referred to as a berry. Its fruits are fleshy, oval, 6–11 mm in diameter, with red to purple blackberries and two- to four-seeded.5C. edulis fruits are vibrantly colored, becoming red, purple, and purplish-black when ripe. Furthermore, due to their nutritional content, therapeutic value, and application in many processing commodities, such as drinks, jellies, and syrup,6,7 these wild fruits are usually harvested and consumed uncooked fresh in most rural areas. Indeed, these wild fruits consumed by locals are a good source of nutrients, and given their low cost and widespread availability, they should be promoted for commercial exploitation. In Sudan and Kenya, the fruits of C. edulis are used to make vinegar through fermentation and jam. The intense red-purple and purple coloration of these berries indicate the richness of their fruits in anthocyanins which are natural antioxidants.8 Aside from flavonoids, fruits, and vegetable coloring, it can also be caused by the presence of other chemicals such as carotenoids and chlorophylls.9 Several investigations conducted on C. edulis fruits have shown a variety of bioactive phytochemicals including polyphenolic antioxidants, vitamins, minerals, and a variety of nutraceutical, and biological effects including antioxidant properties.10–12 Thus, consuming nutritious components is a critical approach for regulating and avoiding various diseases as well as boosting the usage of natural substances. Nonetheless, to the best of our knowledge, no research has been undertaken on the nutritional value, phenolic and antioxidant characteristics of C. edulis fruit processed goods. Although these fruits are regularly processed into juice and cake, an investigation of the physicochemical, antioxidant properties, as well as phenolic contents of the fruit juice and cake, will undoubtedly provide insight into their nutritional and medicinal potential. The current study solely looked at the nutritional value, bioactive components, and antioxidant properties of juice and cake made from fruits of C. edulis fruits taken in the dark red stage.
Discussion
This study aimed to assess the nutritional value, phenolic content, and antioxidant properties of cake and juice made from Carissa edulis fruit. It appears from Table 1 that the fruits of C. edulis were juicy, and their measured juice contents were 60.64 ± 1.59%. Some previous studies on other wild fruits reported a close value of juice content such as pomegranate (50.25–64.17%);27 or Purnima granatum (35.4–74.3%).28 The values obtained were twice higher than those reported in conventional fruits like pineapple (36%);29 black cherry (31.6%),30 and cherry (30%).31 However, they were lower than those found by Dossou et al. (2019)32 with Anacardium occidentale (56.77–69.46%). The extraction yield varied between 40 and 50.8% fresh fruits in Citrus reticulata fruits.33 The reported extraction yield of 23–49% fresh fruits on 72 varieties of Citrus satsuma and Citrus reticulate fruits.34 The variability of juice extraction content is generally linked to certain parameters such as the extraction process used, the type of press, the maturity of fruits, their water content, etc.35 The high juice extraction yields observed on the fruits studied suggest industrial production of these juices. Seeds represent 13.90 g/100 g of fruits of the mass of C. edulis fruits, the results confirm that these fruits are as highly juicy as mangoes (78.9%), apples (84.2%), or grapes (81.6%).36 Dry matter, which refers to the material that remains after the removal of water, is an indication of the number of nutrients accessible to the organism in a given meal.37 The cake of these fruits has higher dry matter content (64.14 g/100 g fresh cake weight) than those of their juices (09.28 g/100 g fresh cake weight). This observation is normal because the juices have higher water content. The cake obtained after extraction of juice can also be revalorized in animal feed or other food formulations according to its nutritional and biological properties such as antioxidant activity.
Moisture levels ranged from 5.67% for cake powder to 14.40% for juice powder on a wet basis. This result is equivalent to the moisture content of previously reported Bus mango cake (8.4%), Pumpkin blended cake (6.01%), and Phoenix dactylifera cake (6.07%).38,39 Powder stability, storage qualities, and other technical features are affected by the humidity content and water activity of powder samples.40 It is well known that a moisture level less than 14% ensures powder stability during storage, whereas greater moisture content greater promotes the growth of microorganisms and product degradation.41 The increased moisture content of juice and cake powder might be attributed to their hygroscopic properties. The capacity of materials to absorb moisture in the environment is referred to as hygroscopicity. According to some authors, the hygroscopic index of a powder is acceptable when lower than 20 g/100 g DW.42 Furthermore, the presence of protein might be connected to the high moisture content of powder, because protein has a greater water-holding capability inside its amorphous state.43
Fat contents are presented in Table 2. The cake powder included substantially (p < 0.05) more fats (22.68%) than the juice (5.06%). These results are comparable to recent studies on Phoenix dactylifera cake (5.37%),39 and Mangifera indica juice (25.57%).44 These findings imply that fruit cakes might be a good source of vegetable oil. In this investigation, the fat contents of Mangifera indica (0.7%)38 and Citrus maxima juices (0.83%) were considerably (p < 0.05) greater than those of other typical fruits juices (0.83%).45 As previously demonstrated, the low-fat level of fruit juice makes it an appropriate component of weight-loss programs.45
The ash contents in juice powders were 0.31% and were 0.28% for the cakes. Ash is a good predictor of the mineral concentration in a sample. From a comparative point of view, our results are similar to those obtained previously on lyophilized C. edulis pulps (0.21%),46 and the Anacardium occidentale fruits (0.25%).47 However, the ash value found here was lower compared to previous values found on the Citrus maxima juice (0.7%),45 and the Rhus coriaria fruits pulps (2.87%).48
The carbohydrates contents were ranged from 19.29 g/100 g DW for the juice to 39.25 g/100 g DW for the cake. Carbohydrate was the most abundant macronutrient as in the majority of fruits. This conforms with other studies45,49,50 which found higher carbohydrates contents in citrus pulps. The carbohydrates content obtained in our study is higher than those obtained on Carissa macrocarpa pulps (21.57 g/100 g DW).51 Compared with juices of conventional fruits, our results are 1.5 times as high as those obtained on Citrus maxima fruit juice (16.79 g/100 g DW),45 and three times higher than those obtained on Anacardium occidentale fruits juice (9.9 g/100 g DW).52 Juice and cakes of C. edulis fruits might be considered as a source of carbohydrates particularly in animal feed production. Carbohydrate is energy-producing food that provides readily available fuel for physical and other bodily activities.
The juice and cake of the studied fruit contain low protein. Protein contents of juice powders were lowest with the values 0.23, while protein contents of the cake powders were 1.32 g/100 g DW. The diversity in protein concentration might be attributable to the diverse varieties of fruits utilized, most likely owing to the fruits’ varying nitrogen-containing components. The protein content reported in this study coincides with the values obtained with the Mangifera juice (1.1 g/100 g DW),38Citrus maxima juice (1.76 g/100 g DW),45 and H. barteri pulps53 (1.5 g/100 g DW) and by Amouzou et al., 2013 (0.813 g/100 g DW).
Carotenoids are the primary pigments of plants that give them distinctive hues such as yellow and orange.54 Total carotenoid concentration in the studied fruits was substantially (p < 0.05) higher in juice extract than in cakes. Also, total carotenoid content was dramatically lower within the cake than in the juice, as indicated in Table 3. These variations might be connected to the color of the peels of the fruit. Carotenoids concentrations in this study were similar to that found in orange juice (0.81 mg/100 g DW)54 but much lower than the carotenoid content of other fruits such as pomegranate juice (23 mg/100 g DW) observed in the same study.54 However, the carotenoid levels found in this study were significantly greater than that found in Anacardium occidentale fruits (0.39 mg/100 g DW).55
Vitamin C is an antioxidant compound that neutralizes the effects of free radicals and prevents diseases. The high Vitamin C content of the juice compared with the cake powder may be due to their hydro-solubility character. A similar observation was reported on the Vitamin C content between juice (26.36 mg/100 g DW) and peel (19.34 mg/100 g DW) of Citrus maxima.54 The concentration of Vitamin C found in our samples was lower compared to those found in some conventional fruits such as strawberry juice (49 mg/100 g DW).56 The quantity of Vitamin C detected in this study was higher than that found in the orange (18.9 mg/100 g DW)57 and Cherry juices (16 mg/100 g DW).58 These authors did, however, observe greater Vitamin C concentration in Anacardium occidentale (86.22 mg/100 g DW) and Mangifera indica (67 mg/100 g DW) juices.
Minerals are essential for appropriate nutrition and metabolism, and their importance cannot be overstated. Many variables influence the mineral content of fruits, including soil type, maturity stage, cultivar variety, terrain, and other geographical considerations. Iron is the third most abundant mineral in our samples study after calcium and copper. As shown in the table of mineral content, the iron content of juice was 1.34 mg/100 g DW vs 1.47 mg/100 g DW for cake. There was no notable change (p < 0.05) between the two samples. Other research on wild fruits discovered comparable results with Prunus domestica (1.08 mg/100 g DW),55 and Prickly pear juices (1.36 mg/100 g DW).45 In comparison, the iron value measured here has been higher than that published on other traditional fruits like dates (0.9 mg/100 g DW).39 Iron is a trace metal that functions as a cofactor of catalase.59 It also participates in the formation of hemoglobin by combining with porphyrin to generate heme.60
Zinc is an important micronutrient that protects the body against oxidative stress and stimulates immune mechanisms.60 The cake of C. edulis fruit presented a higher content in this mineral as compared to the juice (Table 3). Significantly (p < 0.05) higher zinc concentrations were noted in C. edulis cake (4.28 mg/100 g DW). The C. edulis juice (1.88 mg/100 g DW) had the lowest concentration of this element (1.88 mg/100 g DW). The zinc value obtained was comparable to those described by Amouzou et al. (2006) on H. barteri pulps (2.2 mg/100 g DW)61 but lower than previously discovered by Liu et al. (2020) (14 mg/100 g DW) on the same pulps.60 The result found here are ten times more than those obtained by earlier authors on typical fruits such as Prunus domestica fruits (0.2 mg/100 g DW)60 or the date spam fruits juices (0.21 mg/100 g DW).39
The copper levels in the cake (1.12 ± 0.84 mg/100 g DW) were significantly (p < 0.05) greater than in the juice powders (0.44 ± mg/100 g DW). Copper concentrations values consistent with those published in the apple juice (0.58–0.76 mg/100 g DW)62 and pulps of H. barteri fruits (0.7 mg/100 g DW).11 However, they are ten times higher than those found in Phoenix dactylifera fruit juice (0.07 mg/100 g DW).39 Copper is a cofactor of superoxide dismutase, and hence has a function in erythropoietic production.63 As a result, the C. edulis fruit cake may be effective as an anti-anemic or antioxidant agent.
Calcium was the first most abundant mineral identified in the cake and juice of the tested fruits and its content was significantly (p < 0.05) greater in the cake powders. The values ranged from 43.78 ± mg/100 g DW for the juice to 80.52 ± mg/100 g DW for the cake. These results are in close line with those found in the H. barteri (80 mg/100 g DW),61 and Mangifera indica pulps (40–49 mg/100 g DW),64 and the Prickly pear juice (83–89 mg/100 g DW).65 Furthermore, they were much greater than those obtained with Prunus domestica (12 mg/100 g DW),66 and Anacardium occidentale (12 mg/100 g DW). Calcium is essential in many biological functions (cardiac automatism, in the contraction of smooth and striated muscles, nerve conduction, coagulation, and endocrine and exocrine hormonal secretions).67 This calcium decreases the bioavailability of dietary iron by competition at the site of absorption and therefore can lead to iron-deficiency anemia.68
Phytochemicals are important bioactive molecules that have been linked to a variety of health benefits. Polyphenols are abundant in the cake extract, trailed by tannin, flavonoids, and anthocyanins. These antioxidants were also found in significant quantities in the juice.
It should be noted that the concentration of polyphenolic compounds varied significantly between liquid fruits versus cake powders made from the same fruits. Fruit cake powder (16.12 ± 0.63 mg GAE/g DW) had a considerably (p < 0.05) greater total phenolic content than juice powder (14.10 ± 0.65 mg GAE/g DW). Similar findings were observed by previous authors on C. edulis fruit pulps69 (9.54 mg GAE/g DW) and 27 citrus cultivars (2.6–10.45 mg GAE/g DW).70 Our results also outperform those of orange juice (3.29 mg GAE/g DW),57Citrus maxima juice (1.8 mg GAE/g DW),45 and pomegranate juice (5–8 mg GAE/g DW).50 These findings indicate that C. edulis juices and cakes have vital biological qualities, as evidenced by multiple recent studies demonstrating the advantages of these secondary metabolites.71
The highest contents of flavonoids were observed in the cake compared to the juice. Flavonoid content ranged from 4.65 mg RE/g DW for the juice to 5.02 mg RE/g DW for cake powder of C. edulis fruits. The results of this study are comparable with the quantities found in the juice of Citrus maxima.45 However, these flavonoid contents are four times lower than those obtained in the cake of Citrus fruits (16.42 mg RE/g DW),70 and the juice of pomegranate fruits.50 Flavonoids are an important group of phenolic compounds in plants with a wide range of biological properties such as antioxidant, anti-inflammatory, anticancer hypoglycaemic, and hypocholesterolemic activities.72
In addition to polyphenols and flavonoids, the greatest (p < 0.05) tannin concentration (Table 4) was found in the cake powders when compared to the juice powders. In this analysis, the cake sample had a higher (p < 0.05) tannin concentration (5.97 ± 0.19 mg GAE/g DW). The tannin level in juice samples was lower (2.56 ± 1.14 mg GAE/g DW). The tannin level of the juice is commensurate with the tannin content of H. barteri fruit pulp (2.13 mg GAE/g DW),73 and the Anacardium occidentale juice (2.05–6.6 mg GAE/g DW).32 Besides, pomegranate juice has a greater tannin concentration (6.6 mg GAE/g DW).50
Anthocyanins levels of powder samples are presented in Table 4 The value of these beneficial substances ranged from 0.20 mg/g DW to 2.13 mg/g DW for the juice and cake of C. edulis fruits, with significant variations (p < 0.05). These results are comparable to the Anthocyanin contents of blackberry juice (0.7–1.34 mg/g DW)74 and pomegranate juice (0.9–1 mg/g DW) reported previously.50 Anthocyanins are the chemical substances that give the juices and fruits of H. barteri and C. edulis their purplish-red color.75 However, the current study results are 10 times higher than those reported in Anacardium occidentale fruits juice.55
According to the results, as compared to the contents of bioactive components in the cake, tested juice samples contained lower amounts of phenolic compounds as compared to the fruit’s cake and considering that most of these compounds remained in the pomace during the typical extraction technique.76,77
The cake had the highest antioxidant activity (lowest IC50) in the DPPH experiment when compared to the juice. This shows that phenolic compounds had a substantial role in the antioxidant activity of the fruit powders studied. This is consistent with the fact that plant products’ antioxidant activity is often attributed to the radical scavenging activity of phenolic components such as flavonoids, polyphenols, and tannins.58,78 The antioxidant activity of phenolic compounds is mostly owing to their redox characteristics, which can be useful in scavenging free radicals, quenching singlet and triplet oxygen, and degrading peroxides.79 Indeed, phenolic compounds with multi hydroxyl (OH) group moieties and unsaturation centers can promote DPPH neutralization.80 The high bioactive content of the examined fruits powders is most likely responsible for their strong antioxidant action. Previous studies have demonstrated the in vitro antioxidant properties of various solvent extracts obtained from C. edulis fruits. For instance, Fowsiya and Madhumitha (2017) found that the ethanol extract of C. edulis exhibited the best DPPH scavenging activities compared to the water, petroleum, ethyl acetate, chloroform extracts respectively.81 Likewise, Ojerinde et al. (2021) revealed that the methanol extract of fruits displayed strong antioxidant activities with the following efficient concentrations (DPPH, IC50 = 87.98 µg/ml; FRAP, EC50 = 464.33 µg/ml & Ferrous chelating, EC50 = 294.55 µg/ml).82 In addition, Woode et al. (2008) showed a lower antioxidant activity of the ethanolic extract of roots compared to fruits (IC50: 210 vs 71 µg/mL).83 On contrary to these studies, Fanta et al. (2019) showed that leaves aqueous extracts displayed stronger DPPH scavenging effects compared to organic extracts with an IC50 of 0.304 µg/mL.84
Because the presence of antioxidants in the fruit juice and cake induces the conversion of the Ferric cyanide complex into ferrous form, the ferrous iron complex may be measured by monitoring the production of Perl’s Prussian blue powder at 700 nm. The higher the absorbance value, the greater the reduction power of the samples (Fig. 3). In this investigation, fruit cakes outperformed juice in terms of lowering power, with a statistically significant difference (p < 0.05). The antioxidant potential of the fruits studied is determined by their phenolic content. Previous research has found a link between decreasing power and plants’ phenolic chemicals.85 According to other studies, substances with reducing power can diminish the oxidized intermediates of lipid peroxidation processes.86,87
The TAC is an in vitro test that gives an overall estimate of the antioxidant power of all the bioactive compounds (phenolic compounds, vitamins) present in a given sample. It can either use a single-electron transfer method monitored spectrophotometrically by a color change, or a hydrogen atom transfer reaction measured by the elimination of peroxyl radicals.88 In the present study, the obtained findings showed that cakes had a better TAC compared to juice which is consistent with the previous effects observed on DPPH and the ferric reducing power. These results tend to prove that the concurrent presence of bioactive ingredients in a sample could be seen as a factor that boosts biological activity. Indeed, Patil et al. (2016) demonstrated that piperine which is a natural alkaloid compound found in pepper could increase the bioavailability of curcumin (flavonoid compound) when mixed with it and this, through intercalation mechanisms including the intermolecular bonding formation.89 Also, Duan et al. (2004) found that polyphenolic compounds contained in the ethyl acetate extract of Galla chinese might separately exert strong inhibitory activity on the hepatitis C virus protease conferring thereby strong antiviral activity to this extract.90