Amino acid profile and oxidizable vitamin content of
Synsepalum dulcificum berry (miracle fruit) pulp
Njideka E. Njoku, Collins N. Ubbaonu, Serah O. Alagbaoso, Chioma N. Eluchie &Munachiso C. Umelo
The amino acid profile of the Synsepalum dulcificum berry was studied. Among the essential amino acids observed, leucine which was the highest while methionine which was the lowest. The nonessential amino acids were also discovered, with glutamic acid being the highest and glycine being the lowest. The study of the oxidizable vitamins revealed that vitamin C was more abundant than vitamin A and vitamin E. This information will hopefully enhance the fruits acceptability by more people and thus, generally promote its utilization and appreciation in our diets.
Synsepalum dulcificum is a tropical fruit, native to West Africa. The plant belongs to the family – Sapotaceae. Although it can grow up to 20 feet high, its predominant form is shrubby. The plant first bears fruits after growing for approximately 2–3 years. The berry has a unique effect on the taste buds, such that flavours of fruits (citrus fruits), consumed after eating the fruit are generally enhanced and their delicate flavours, formerly masked by natural acids, are released, hence the name ‘miracle fruit’. A new class of sweeteners from proteins found in the fruits of tropical plants has been discovered, and Synsepalum dulcificum is one of them. The taste modifying principle was found to be miraculin where scientists have confirmed. Miraculin, a glycoprotein consisting of 191 amino acids and some carbohydrate chains found in the pulp of the berry. An evaluation of the amino acid profile of the yellow variety of Synsepalum dulcificum, therefore, becomes necessary to identify and quantify some of these amino acids. The vitamins content was investigated to determine if the pulp can provide additional benefits. This natural sweetener may be exploited especially by dieters and diabetes, who need more protein and vitamins in their diet.
Materials and Methods
Fresh mature berries of Synsepalum dulcificum (miracle fruit). The pulp of these freshly harvested and cleaned Synsepalum dulcificum berries was extracted by scraping the fruits with a clean stainless spatula. It was oven-dried and used for the vitamins and amino acid profile analysis.
Determination of oxidizable vitamins content
The vitamins A, E, and C contents of the pulp sample were determined.
Preparation of sample for vitamins determination
The sample was oven-dried using a Baird and Tatlock oven BS2648 at a temperature of 50°C for 24 h.
Determination of vitamin A content
One gram of the sample was macerated with 30 mL of absolute alcohol. Three millilitres of 50% potassium hydroxide was added. The solution was boiled for 30 min and cooled. Thirty millilitres of distilled water was added. The mixture was transferred to a separating funnel and washed with 10 mL of petroleum ether. The lower layer was discarded while the upper layer evaporated to dryness. The residue was dissolved with 10 mL of isopropyl alcohol. The absorbance was taken at 334 nm using a spectrum 21D PEC spectrophotometer. The vitamin A content was extrapolated from a vitamin A standard curve (Fig. 1). Alternatively, using the formula given below
Determination of vitamin E content
One gram of the pulp sample was macerated with 20 mL of ethanol. The solution was filtered with Whatman No 1 filter paper. One millilitre of the filtrate was pipetted out and 1 mL of 0.2% ferric chloride in ethanol was added. One millilitre of 0.5% a-dipyridyl solution was also added. The solution was diluted to 5 mL with water and the absorbance read at 520 nm using a spectrum 21D PEC spectrophotometer. The vitamin E content was extrapolated from a vitamin E standard curve.
Determination of vitamin C content
One gram of the sample was macerated with 20 mL of 0.4% oxalic acid. It was filtered with Whatman No 1 filter paper. One millilitre of the filtrate was pipetted out and 9 mL of indophenol reagent added to it. The absorbance was read at 520 nm (using a spectrum 21D PEC spectrophotometer). The vitamin C content was extrapolated from a vitamin C standard curve
Amino acid profile determination
The amino acid profile in the sample was determined. The sample was dried to constant weight. A known weight (300 mg) of the dried sample was put into an extraction thimble and the fat was extracted using Soxhlet extraction apparatus. A small amount (200 mg) of ground fat-free sample was weighed, wrapped in Whatman No 1 filter paper, and put in a Kjeldahl digestion flask. It was digested and distilled.
The distillate was then titrated with standardized 0.01 N hydrochloric acids to a gray-colored endpoint and the percentage nitrogen in the sample was calculated using the formula. Seven millilitres (7 mL) of 6 N hydrochloric acids (HCl) was added and oxygen was expelled by passing nitrogen into the ampoule (this is to avoid possible oxidation of some amino acids such as methionine and cystine during hydrolysis). The glass ampoule was then sealed with Bunsen burner flame and put in an oven preset at 105°C 5°C for 22 h. The ampoule was allowed to cool before breaking it open at the tip and the content was filtered to remove the humins. The filtrate was then evaporated to dryness at 40°C under vacuum in a rotary evaporator. The residue was diluted with 5 mL acetate buffer (pH 2.0) and stored in plastic specimen bottles, which were kept in the freezer. It was noted that tryptophan was destroyed by hydrolysis with 6 N hydrochloric acid. Between 5 and 10 µL of the buffered residue was dispensed into the cartridge of the analyzer and analyzed with the TSM analyzer to acidic, neutral, and basic amino acids.
The period of an analysis lasted for 76 min. A constant ‘S’ was calculated for each amino acid in the standard mixture using the formula, Finally, the amount of each amino acid present in the sample was calculated.
Results and Discussion
From Table 1, it was observed that although fruits are known as important sources of vitamins especially vitamins A and C, the pulp of yellow Synsepalum dulcificum was found to be very low in vitamin C.
The vitamin A value in the pulp was also very low.
The vitamin E in the pulp of Synsepalum dulcificum was higher.
This berry is primarily consumed for its taste-modifying effect and not necessarily for its nutrients. As such, it is only eaten when there is a need for its sweetening function, making it highly underutilized. This investigation aims to change this by identifying its nutritional benefits. However, from the results below, it is observed that to adequately provide needed vitamins, in comparison with other berries and fruits, more quantity of the berry pulp may be consumed.
All the essential amino acids were detected in the test. The highest value was from leucine followed by Lysine and the lowest from methionine. Leucine, isoleucine, and valine are oxidized in the muscle and the nitrogen used for the formation of alanine. All the analysed amino acids in miracle fruit are higher in quantity than the amino acids in Pyrus communis pear pulp.
The nonessential amino acids were also detected as shown in the table. Glutamic acid had the highest value while glycine had the least value. This implied that the amino acids in the pulp of miracle fruit had high biological values and could contribute in meeting the human requirements of these essential amino acids especially if the commercial potential of this berry or its processed by-products is exploited.
Table 1. Mean values of the vitamins identified in the pulp of Synsepalum dulcificum berry.
Vitamin A (lg) 2.54
Vitamin C (mg/100 g) 1.33
Vitamin E (mg/100 g) 0.78
Values are means of triplicate determinations.
Table 2. Amino acid profifile of Synsepalum dulcifificum berry pulp.
Amino acid Amount g/100 g protein Chemical score (%)
Glutamic acid 3.43
Aspartic acid 1.76
The research revealed that the berry’s pulp had more vitamin C than vitamins A and E. The oxidative vitamin content (vitamin C, A, and E) of the pulp was generally lower than that of other berries. The berry also had varying amounts of all the essential amino acids, with leucine having the highest amount and methionine the least value. This investigation on the yellow variety of the miracle berry has revealed the amino acid profile of the pulp. This study has also provided information on vitamin contents of the berry with respect to their identity and quantity in the pulp.