Miracle fruit: An Alternative Sugar Substitute in Sour Beverages

Jessica Ferreira Rodrigues, Rafaela da Silva Andrade, Sabrina Carvalho Bastos,

Sandra Bragança Coelho, Ana Carla Marques Pinheiro

High sugar consumption has been related to several chronic diseases and thus, many alternative sweeteners have been extensively researched. However, there is still controversy regarding the harmful effects of their consumption, mainly regarding the use of artificial sweeteners, a controversy which increases the demand for natural sweeteners, such as miracle fruit. This tropical plant grows in West Africa is named for its unique ability to change sour taste into sweet.

Therefore, this study aimed to characterize the temporal profile of miracle fruit and assess its sugar substitute power in sour beverages through time-intensity and temporal dominance of sensations tests. For this, unsweetened lemonade and lemonades with sugar, sucralose and previous miracle fruit ingestions were evaluated. We noted that the dynamic profile of lemonade ingested after miracle fruit ingestion indicates that it seems to be a good sugar substitute since it provides high sweetness intensity and persistence, reduced product sourness and an absence of aftertastes.

The miracle fruit also provided a sensory profile similar to that of sucralose, an established and recognized sugar substitute. The results of this study provide important information for future applications of miracle fruit as a sugar substitute in sour beverages, providing an alternative use for a natural substance as a sweetening agent.

INTRODUCTION

The harmful effects related to high sugar consumption has been a matter of great public and scientific interest. These adverse effects have been associated with the development of obesity and the risk of several chronic diseases, like Type 2 diabetes and cardiovascular diseases. As a result, many alternative sweeteners have been extensively researched and their consumption has gained much popularity due to their reduced costs.

Miracle fruit (Synsepalum dulcificum) has been studied as a sweetness enhancer. It is an indigenous tropical plant growing in West Africa, named for its unique ability to change a sour taste into sweet. The active compound in miracle fruit is Miraculin, a single polypeptide chain having a molecular weight of 24,600 kDa and two sugars linked to two amino acid residues that bind adjacently to sweet receptor cells on the tongue, activating them in response to a low pH. This effect lasts until the miraculin is diluted and eliminated by saliva.

Miraculin, itself, has no taste but stimulates a sweet taste estimated to be 400,000 times sweeter than sucrose on a molar basis.

Therefore, in assessing miracle fruit as a sugar substitute, it is interesting to compare its sensory profile with sucrose and sucralose profiles. Temporal methodologies such as Time Intensity (TI) and Temporal Dominance of Sensations (TDS) have proven to be efficient techniques to characterize and monitor the sensory profile of different products with substituted ingredients (i.e. sugar or salt), providing information about the temporal evolution and intensity of different sensations and off-flavours developed during food consumption. Thus, the aim of this study was to characterize the temporal profile of miracle fruit and assess its sugar substitute power in sour beverages.

EXPERIMENTAL

The study was reviewed and accepted by the Ethics Committee in Human Research of the Federal University of Lavras and it was performed in accordance with the Declaration of Helsinki.

2.1. Materials

The following is a list of materials used for sample preparation in this study: lemons, sucrose, sucralose (Nutramax ® ) and Frooties ® brand dried miracle fruit.

2.2. Preparation of lemonade

Lemonades were prepared in a proportion of 3:1 (water: lemon). The lemons were squeezed using a Walita RI2745 ® brand juicer. Thereafter, water and the sweetener (in the case of the treatments with sucrose or sucralose) were added. The lemonade was then stirred with a glass rod for 5 min. The prepared lemonade was standardized at a pH ¼ 2.43 ± 0.20 and solid soluble (SS) ¼ 2.1 ± 0.25 Brix.

2.3. Sensory analysis

Sensory analysis with subjects that did not have any restriction to the products analyzed and they did not use nose clips during the sensory tests.

2.4. Ideal test

The ideal sugar concentration in lemonade was determined using sensory tests with an ideal scale, using a linear scale with 9 cm, anchored by “less sweet than ideal” and “sweeter than ideal” at the endpoints and “just right” in the centre.

During the analysis, 75 consumers with a minimum lemonade consumption frequency of once a week evaluated the samples and recorded their responses. The tested samples were determined by pre-test, in which the sucrose concentrations were defined varying from 0 to 30% sucrose (0%, 7.5%, 15%, 22.5%, 30%).

Samples were served in plastic cups labelled with randomly selected 3 digit numbers, in a balanced order. The responses were converted into numerical values and analyzed by regression analysis.

2.5. Time-intensity (TI)

2.5.1. Selection We recruited seventeen individuals that were available and interested in participating in the research (individuals were part of the group of consumers that performed the Ideal test) to participate in the selection stage. The individuals had experience in sensory analysis and consumed lemonade at least once a week. The selection stage was performed in two steps. The first step was the basic tastes identification test. The second step evaluated discrimination ability applying triangular tests with two sucrose solutions at concentrations of 0.1 and 0.2% w/w.

These samples were defined in paired comparison tests in which there was a significant difference at 1%. The results were assessed from the defined parameters. Therefore, twelve panellists (nine women and two men, between 20 and 35 years of age e average ¼ 27 ± 4.6) were selected to perform the TI and TDS Tests.

2.5.2. Training session

The selected panellists were introduced to the time-intensity test procedure to become familiar with the methodology. They performed pretests with three lemonade samples with different sucrose contents in three replicates. An analysis of variance (ANOVA) was applied for each panellist.

2.5.3. Final session

Twelve selected individuals performed Time-Intensity tests in triplicate in four sections for each attribute for the four lemonade samples (unsweetened lemonade, lemonade with sugar, sucralose and miracle fruit). The attributes evaluated were sweetness and sourness and the samples were presented in a monadic way, using a balanced complete block design. The panel members were then instructed to drink the lemonade (30 ml) all at once and immediately start the evaluation for the 50s through a graphic interface in the form of a 10-point scale, with 0 meaning no perception and 10 signifying an extreme perception of the attribute. Thus, the intensity of the attribute was evaluated during and after the ingestion in order to quantify “after tastes”.

2.6. Temporal dominance of sensations (TDS)

Twelve selected panellists (the same individuals that performed TI analysis) performed the TDS tests in triplicate, totalling 36 evaluations. After the selection stage, the panel was introduced to the TDS module and instructed that the dominant sensation is perceived to have the greatest clarity and predominance. The attributes involved in the TDS sensory test were sweet, sour, bitter, unpleasant, and no taste. The samples were presented in disposable white plastic cups coded with three-digit numbers in monadic order. After instructions were presented, each panellist was asked to drink the lemonade sample (approximately 30 ml) all at once and immediately start the evaluation for 50 s, selecting the dominant sensation that was experienced during and after the lemonade ingestion (i.e over 50 s), in order to also quantify the “after tastes”.

2.7. Statistical analysis

ANOVA (sources of variation: samples, panellists and sample*-panelist interactions) was performed with all Time-intensity data and Tukey's test was applied to compare the averages of samples. The mean TI curves were also computed.

The calculations were done based on the confidence interval of a norm proportion based on a normal approximation. Three TDS parameters (DRmax - maximum dominance rate, TDRmax - time at which the maximum dominance occurs, and Plateau - duration of the attribute, i.e., the time range over which the dominance rate is equal to or higher than 90% of the maximum dominance rate.) were also computed.

RESULTS

3.1. Ideal test

The results of the ideal test showed a significant difference among the lemonade samples with different concentrations of sugar (saccharose), indicating that the samples differ in relation to the ideal sweetness. Therefore, to correlate the ideal sweetness with ideal sugar content in the lemonade, the regression model was adjusted.

The high sugar content considered ideal by consumers is one more indication of the need to reduce sugar consumption, using sugar substitutes. This information is relevant since consumers are used to eating foods with high sugar content and the consumption of sugar-sweetened beverages

Thus, to evaluate the miracle fruit powder as a sugar substitute, we established the following samples: control-unsweetened lemonade (without sweetener); lemonade at an ideal sugar content determined by Ideal test (13.4% - 134 g/L lemonade or 0.39 mol/L lemonade); lemonade with sucralose content based on the equivalence of ideal sugar content and considering its sweetness power of 600 times more than sugar (0.022% - 0.22 g/L lemonade or 5.53 10 4 /L lemonade); and 300 mg of miracle fruit ingestion before unsweetened lemonade intake.

The miracle content was determined following the producer recommendation, and performing a focus group, in which the participants evaluated different miracle fruit contents and verified which one most approached the lemonade sweetened with the optimal concentration of sucrose.

3.2. Time-intensity (TI)

Sugar can influence sweetness and sourness attributes in lemonade. Thus, to evaluate the sweeteners time-intensity profiles, sweetness and sourness attributes were evaluated. Time-intensity curves for the sweetness attribute obtained for the unsweetened lemonade and lemonades with different sweeteners (sugar, sucralose and miracle fruit) shows that all the evaluated sweeteners (sugar, sucralose and miracle fruit) had an effective sweet effect on lemonade and have a similar time-intensity profile in relation to the sweet flavour.

Moreover, among the sweeteners used (sugar, sucralose and miracle fruit) after 15 s of lemonade ingestion, miracle fruit was the sweetener that reduced the intensity of lemonade sourness the most.

3.3. Temporal dominance of sensations (TDS)

TDS profiles and the graphic representation of dominance duration time for significant sensations of unsweetened lemonade and lemonade with the sugar, sucralose and miracle fruit sweeteners. The TDS parameters (DRmax - maximum dominance rate, TDRmax - time at which the maximum dominance occurs, and Plateau - duration of the attribute, i.e., the time range over which the dominance rate is equal to or higher than 90% of the maximum dominance rate) were also obtained.

DISCUSSION

4.1 Time-Intensity (TI)

The TI results demonstrated that the miracle fruit had an effective effect on sourness perception reduction, besides contributing to the sweet taste of lemonade and that the miracle fruit works by reducing the acidity and intensifies the sweetness of acid products; and that miracle fruit can successfully improve the sweetness of a low sugar popsicle to a magnitude that is similar to a sugar sweetened popsicle, without subsequent energy compensation for the absent calories.

The ability of miraculin to modify taste perception from sour to sweet depends on the pH. Miraculin is likely to be in equilibrium between being an agonist and an antagonist at acidic and neutral pH, respectively. Furthermore, commercial sour liquids that mainly contain citric acid, products like lemonade, are more effective than acetic acid-based liquids in eliciting perception of sweetness after the miracle fruit application.

4.2. Temporal dominance of sensations (TDS)

The replacement of sucrose by alternative sweeteners can produce changes in the sensory profile of the product as noted for the lemonade sweetened with sucralose and that sweetened by the effect of miracle fruit. However, similar TDS profiles were observed between them. The substitution of sucrose by other sweeteners is a challenge for the food industry and researchers, because, in addition to the sweet taste, other sensory attributes may be modified.

Bitterness and metallic off-flavours have been one of the most common problems of low-calorie sweeteners. In relation to these aspects, sucralose has been considered as the sweetener that best substitutes sucrose, since it provokes less sensory alterations in the product. However, sucralose is  among the artificial sweeteners and some toxic effects related to its heating. Moreover, a high demand for natural sweetening agents has grown. In line with that, miracle fruit also presented great results regarding the lemonade sensory profile,

Due to the relation of high sugar ingestion and chronic diseases, regulators place pressure on the food industry to decrease the sugar content in their products. A typical example of a product consumed in large volumes that contain high sugar levels are sweetened beverages. Therefore sugar alternatives, with lower caloric content, are under continuous development and scrutiny to become the ideal sugar replacement. Through this study, we observed that miracle fruit seems to be a great sugar substitute in sour beverages, as it is a natural product that confers a sweet flavor and reduces sourness, besides presenting a sensory profile similar to sucralose.

However, the product (e.g. lemonade) must not be sweetened with miracle fruit (e.g. mixing miracle fruit with the lemonade). It must always be consumed before the unsweetened beverage, once it is necessary the contact of miraculin with the membrane of taste cells, to promote a structural change in the membrane receptor, causing the sugar part of the miraculin molecule to bind to the sweet receptor site in the membrane, evoking the sweet sensation.

CONCLUSION

Time-intensity and temporal dominance of sensations profiles of lemonade ingested after miracle fruit ingestion indicate that it seems to be a good sugar substitute in sour beverages, as it presents great intensity and persistence of the sweetness, reduces the product sourness and presented no aftertaste, besides providing a sensory profile similar to that of sucralose, an established and recognized sugar substitute. However, future studies of the miracle fruit effects on different products assessing consumer perception and regarding sensory characterization by other methodologies should be conducted.

Reference:

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