DEVELOPMENT OF A SWEETENER FROM BLACK PLUM (VITEX DONIANA) FRUIT

Abstract

The Black plum (Vitex doniana) fruit was studied in respect of the chemical composition of its edible pulp, and syrup produced by concentration of extracted juice. Organoleptic evaluation was also conducted on the developed syrup. The results show that the edible pulp of the fruit is acidic (PH 5.20), high in moisture (67.9%), sucrose (12.5%) and reducing sugar (7.3%), and fairly rich in vitamin C (28.5 mg/100 g). Temperature of water used for extracting juice from the pulp correlated positively with soluble solids (r=0.86), titratable acidity (r=0.91) and negatively with vitamin C (r=−0.61). The syrup contained higher reducing sugars (51.7%), lower moisture (25.0%), but similar sucrose (12.9%) content compared to the pulp. The soluble solids of the extracted juice and consequently the yield of the syrup varied with water temperature. An optimum temperature of 80°C gave 20% (w/w) syrup per pulp. The syrup compares favorably with sucrose in sensory properties in model foods.

Keywords:

• Product development
• Sweetener
• Black plum syrup
• Chemical composition
• Sensory properties

INTRODUCTION

The Black plum (Vitex doniana) grows wildly in the middle belt and savanna regions of Nigeria [7], [14], [5]. The fruit is a drupe and has a sweet mesocarp. The mesocarp accounts for about 20–25% of the weight of the whole fruit. Some researchers on forest resources have described Vitex doniana as an untapped forest resource that deserves to be better known [10], [8].

Due to its high sugar content attempts have been made in local environments to obtain some food products from Black plum fruit. However, most of this information has not been published. [4] produced a local form of candy called ‘Alewa’. This is a boiled and supercooled syrup from Vitex doniana fruit juice. A study on the production of stable local drink called ‘madi’ from Black plum fruit juice and extraction of sugar was carried out by [6]. The physicochemical and sensory properties of a syrup formulated from Black plum fruit juice and sugar was reported by [9].

Local production of this sugar, which is regarded as a conventional sweetener has failed to keep pace with demand resulting in high cost. This inadequacy has been accentuated by nutritional awareness by consumers that intense sweeteners like saccharin and cyclamate which are other well-known sweeteners possess possible hazardous effects on health [11]. Coupled with these developments is the fact that there is an increasing range of manufactured foods that require the use of one or other form of sweetener. Consequently, a substantial quantity of sweeteners used domestically and industrially in Nigeria is imported [1]. Therefore, the need for research in developing fruit-base sweeteners with desirable functional properties that could serve as a substitute for sucrose could be worthwhile.

Syrups find wide application in the food industry and in the home as nutritive sweeteners. No published information is available detailing the utilization of Black plum fruit solely as a syrup. In this paper, syrup was processed from Black plum fruit and evaluated for chemical and sensory properties.

MATERIALS AND METHODS

Source of Raw Materials

Matured and unriped Black plums detached from the plants were collected from several randomly selected trees in Idah, Nigeria. Fruits were kept under atmospheric conditions (29±1°C, 72–84% relative humidity) in the laboratory and allowed to ripe.

Production of Syrup

The processing involved sorting of fresh and ripe fruits, washing with potable water, removal of the thin epicarp, and scraping of the pulp from the stony endocarp with a knife. The pulp was blended in a waring blender for a few seconds and mixed with two parts of water heated to respective temperature of 20°, 40°, 60°, 80° and 100°C. The mixtures were stirred continuously for five minutes with a wooden paddle. The juices obtained were filtered through a muslin cloth approximately equal to an international standard of 200 nm pore sized sieve and concentrated in a stainless open-pan evaporator to 74°Brix. The black colored syrups obtained were bleached with 0.01% hydrogen peroxide at 70°C for 10–15 min [15] and packaged in glass bottles.

To estimate the yield of syrup, the extracted juices obtained at different temperatures were separately concentrated to 74° Brix by evaporation in weighed beakers. The mass of the syrups was expressed per 100 g of pulp.

Chemical Analysis

[2] standard methods were used for determinations of moisture content (14.084), crude fat (14.089), crude fiber (14.087), ash (14.085) and crude protein (14.086). Total carbohydrates were derived by difference. The moisture content of syrup was determined by the standard method of pearson (1976) for evaluation of water content of honey. An Abbe refractometer (Officine Galileo RG701, Italy) calibrated against distilled water (1.333) was used for refractive index and soluble solids evaluation. Sucrose, reducing sugars and vitamin C were determined by standard procedures of pearson (1976). A PH meter (Toptronic, Milano, Italy) set at ambient temperature (29±1°C) was used for PH measurement. Filtrates of 10% sample solution were used for titratable acidity determination by titrating against 0.1 M sodium hydroxide using phenolphihalien as indicator and calculated as anhydrous citric acid. Results were expressed on a wet basis as averages of at least triplicate measurements.

Product Organoleptic Evaluation

Ten untrained panelists evaluated the sensory characteristics of the Black plum syrup in a warm (50°C) corn pap of medium consistency prepared from the yellow variety of maize. A reference sample of corn pap sweetened with sucrose was used for comparison. Degrees of preference for taste, color, flavor and overall acceptability were tested using a nine point preference scale. Ratings were statistically analyzed using the t-test [12].

RESULTS AND DISCUSSION

The chemical composition of the pulp and syrup of Black plum (Vitex doniana) fruit is shown in Table 1. The composition of the fresh pulp varied from 67.9% moisture to 0.8% fat. Sucrose and reducing sugars contents were 12.5% and 7.3% respectively. The reducing sugars level is lower than the value of 9.4% reported for plums [13]. The appreciable quantity of sucrose and reducing sugars could account for the sweet taste of the pulp. The vitamin C (28.5 mg/100 g) content is higher than 18.5 mg/100 g report by [9]. Differences in dry matter content and preparation of sample for analysis could account for this. The PH of pulp was 5.20, and this indicates that the fruit could be classified as low acid fruit.

Table 1. Chemical Composition (%) of Black Plum (Vitex doniana) Pulp and Syrup

Components	Pulp	Syrup
Moisture	67.9	25.0
Protein	1.4	2.5
Ash	1.2	3.8
Fat	0.8	0.55
Crude fiber	2.35	ND
Carbohydrate (by difference)	26.05	67.5
Reducing sugars	7.3	51.7
Sucrose	12.5	12.9
Acidity (as citric acid)	0.28	0.52
Vitamin C (mg %)	28.5	8.8
pH	5.20	4.82
Total soluble solid (°Brix)	ND	74

ND=Not determined.

The effect of water temperature on selected chemical properties of the extracted juice is shown in Table 2. The soluble solids increased with temperature of water used and varied from 9° to 16.5°Brix at 20°C and 100°C respectively. A high positive correlation coefficient (r=0.86) was found. Similarly, there was a very high positive correlation (r=0.91) between water temperature and titratable acidity of extracted juice. This observation may be due to increased level of extraction of organic acids of the fruits as temperature increased. However, there was a negative correlation between temperature and vitamin C content probably due to the heat labile characteristics of this vitamin.

Table 2. Effects of Water Temperature on Selected Properties on Black Plum Juice (1:2 w/v Pulp/Water Ratio)

Temperature (°C)	Soluble Solids °Brix)	Vitamin C (mg/100 g)	Titratable Acidity (%)	PH
20	9.0	4.70	0.09	5.28
40	14.5	4.92	0.11	4.84
60	15.0	4.61	0.32	4.28
80	15.8	4.65	0.34	4.26
100	16.5	4.51	0.39	4.24
Correlation coefficient (r)	0.86	−0.61	0.91	−0.90

The carbohydrate, moisture, ash and protein contents of the syrup were 67.6%, 25.0%, 3.8% and 2.5% respectively (see Table 1). The sucrose (12.9%) and reducing sugars (51.7%) levels account for well over 95% of the total carbohydrate. These high values could be due to the concentration of the extracted juice by evaporation to 74°Brix. The reducing sugars level is probably due to hydrolysis of sucrose in the acidic medium during heat concentration. Consequently, the syrup could be classified as shelf-stable. Micro-organisms normally do not thrive in foods that contain above 65% level of sugars [3]. The syrup could be useful in the manufacture of pancakes and bread.

The moisture level compares with research results on honey, [16] reported the water content of honey to vary between 15.7–26.7%. Based on moisture consideration and shelf preserving potentials, the syrup of Black plum fruit, like honey is regarded as intermediate moisture food. The high ash value is most likely due to extraction of soluble minerals during processing.

The influence of temperature on the yield of the syrup is shown in Table 3. The increase in yield with increase in temperature may be due to higher extraction of water-soluble components such as sugars from the pulp. For maximum yield of syrup from Black plum fruit, water temperature of 80°C is recommend.

Table 3. Effect of Water Temperature on the Yield of Syrup from Pulp of Black Plum Fruit

Temperature (°C)	Syrup Yield (g/100 g Pulp)
20	12.00^a
40	16.82^b
60	18.70^c
80	20.00^d
100	20.80^d

Values in the same column with different superscripts differ significantly at p>0.05, LSD (0.05)=1.16.

A comparison of the sensory properties of corn pap sweetened with Black plum syrup or sucrose is shown in Table 4. Corn pap containing the syrup was significantly (P<0.05) different from that sweetened with sucrose in taste and flavor. The diminished preference for taste of the product containing the syrup might be due to confounding effects of compounds such as organic acids and salts with sugar in the syrup. However, the preference for flavor of product with syrup is probably attributable to better blend of caramel-like and fruity aroma of the syrup. The higher mean scores in terms of the overall acceptance of both types of pap may have been influenced principally by the color judgment. This implies that the 8% dispersion of the black syrup did not significantly affect the color of the yellow corn pap familiar to consumers.

Table 4. Mean Scores of Corn Pap Sweetened with Black Plum Syrup and Sugar

Attribute
Product	Taste	Flavor	Color	Overall Acceptability
Pap with syrup*	7.24^a	7.34^b	6.55^a	6.86^a
Pap with sugar*	8.15^b	6.75^a	6.73^a	7.05^a

Means with the same letter within column are not significantly different (p <0.05) by t-test. Higher score indicates greater preference (9=excellent, 1=very poor). *Syrup or sugar in pap was 8% (w/w).

CONCLUSION

The study has shown that the edible pulp of Black plum (Vitex doniana) fruit is a good source of sugars, and that acceptable syrup could be solely produced from the extracted juice. The syrup is an intermediate moisture food with total sugars accounting for about 64.0%. The syrup compares favorably with a conventional sweetener in sensory characteristics when used in model foods.

ACKNOWLEDGMENT

The author is grateful to the Federal Polytechnic, Idah, Nigeria for the research grant awarded the Post-graduate program.