Abstract

Background:

The eggplant (Solanum melongena) is a fruit of world consumption. Its processing in the form of flour is a way to avoid losses and to take advantage of its nutritional characteristics.

Objective:

This study assessed the physicochemical composition (moisture, proteins, lipids, crude fiber, carbohydrates, minerals, niacin, saponins, titratable acidity, dietary fiber, and total phenols) of eggplant flour prepared from the whole fruit dehydrated in an oven.

Methods:

In vitro antioxidant activity was assessed using the following methods: 2.2-diphenyl-1-picrylhydrazyl radical (DPPH); Ferric Reducing/Antioxidant Power (FRAP); and analysis of polyphenols using HPLC (chlorogenic acid, caffeic acid, ferulic acid, and rutin).

Results:

It was possible to observe: 23.09% carbohydrates; 13.34% proteins; 1.85% lipids; 39.19% total fibers; 1,540 mg/100 g total soluble phenolic compounds; 840 mg/100 g saponins; minerals (potassium, magnesium, copper, iron, zinc, manganese); and niacin. In vitro antioxidant activity was observed through DPPH (455.6 mg ascorbic acid/100 g) and FRAP (486.8 mg ascorbic acid/100 g). The HPLC method determined the presence of ascorbic acid, tyrosine, and phenolic acids (chlorogenic acid, caffeic acid, and ferulic acid).

Conclusion:

The eggplant flour had great fiber content in addition to good content of phenolic compounds and saponins with important antioxidant capacity observed through in vitro assays. As a result, eggplant flour is a good addition to the diet of the population, since it can bring potential health benefits.

Keywords:
Solanum Melongena; Antioxidants; Diet; Nutrition; Phenolic Compounds; Hyperlipidemias

Resumo

Fundamento:

A berinjela (Solanum melongena) é um fruto de consumo mundial. Seu processamento em forma de farinha é uma maneira de evitar perdas e aproveitar suas características nutricionais.

Objetivos:

Este estudo avaliou a composição físico-química (umidade, proteínas, lipídeos, fibra bruta, carboidratos, minerais, niacina, saponinas, acidez titulável, fibra alimentar e fenóis totais) da farinha de berinjela preparada a partir do fruto inteiro desidratado em estufa.

Métodos:

Avaliou-se a atividade antioxidante in vitro usando os seguintes ensaios: radical 2,2-difenil-1-picrilhidrazila (DPPH); poder antioxidante de redução do ferro (FRAP); e análise de polifenóis com Cromatografia Líquida de Alta Eficiência (CLAE - ácido clorogênico, ácido cafeico, ácido ferúlico e rutina).

Resultados:

Verificou-se a presença de: 23,09% de carboidratos; 13,34% de proteínas; 1,85% de lipídeos; 39,19% de fibras totais; 1.540 mg/100 g de compostos fenólicos solúveis totais; 840 mg/100 g de saponinas; minerais (potássio, magnésio, cobre, ferro, zinco, manganês); e niacina. Observou-se atividade antioxidante in vitro para DPPH (455,6 mg de ácido ascórbico/100 g) e FRAP (486,8 mg de ácido ascórbico/100 g). A CLAE determinou a presença de ácido ascórbico, tirosina e ácidos fenólicos (ácido clorogênico, ácido cafeico e ácido ferúlico).

Conclusão:

A farinha de berinjela tem alto teor de fibra além de bom teor de compostos fenólicos e saponinas com importante capacidade antioxidante observada através de ensaios in vitro. A farinha de berinjela é uma boa opção para ser adicionada à dieta da população, devido aos seus potenciais benefícios à saúde.

Palavras-chave:
Solanum Melongena; Antioxidantes; Alimentos; Dieta; Nutrição; Compostos Fenólicos; Hiperlipidemias

Introduction

The eggplant (Solanum melongena, L.) is a fruit consumed worldwide and commonly grown in subtropical and tropical regions. It originated in India and was introduced in Brazil by the Portuguese in the 16^th century.¹1 Ribeiro, C.S.d.C. (2007) Berinjela (Solanum melongena, L). Embrapa Hortaliças. Sistemas de Produção. Versão Eletrônica; 2007.[Citado em 2015 nov 23]. Disponível: em:http://sistemasdeproducão.cnptia.embrapa.br/FontesHTML/Beringela/Beringela_Solanum_melongena_L/index.html.
http://sistemasdeproducão.cnptia.embrapa... It is currently grown by small-scale producers in practically all the Brazilian territory; however, eggplant production suffers heavy losses during the harvest period due to oversupply.²2 Finco AM, Bezerra JR, Rigo M, Córdova KR. Elaboração de biscoitos com adição de farinha de beringela. Revista Brasileira de Tecnologia Agroindustrial. 2009;3(1):49-59.

The eggplant is a good source of minerals and vitamins. In addition to being rich in fiber and having low lipid content, it contains a variety of phytochemicals, such as polyphenols, which provide important health benefits.³3 Akanitapichat P, Phraibung K, Nuchklang K, Prompitakkul S. Antioxidant and hepatoprotective activities of five eggplant varieties. Food Chem Toxicol. 2010;48(10):3017-21. One way to avoid losses and capitalize on the nutritional characteristics of eggplant is processing it into flour. Eggplant flour (EF) is a highly desirable food ingredient to enrich the diet; however, there are few data on its chemical composition.⁴4 Perez PM, Germani R. Farinha mista de trigo e berinjela: características físicas e químicas. B CEPPA (Curitiba). 2004;22(1):15-24.

Studies have shown that phenolic compounds of eggplant have the potential to reduce intestinal glucose absorption and provide cellular antioxidant protection, preventing oxidation and diabetes complications,⁵5 Kwon YI, Apostolidis E, Shetty K. In vitro studies of eggplant (Solanum melongena) phenolics as inhibitors of key enzymes relevant for type 2 diabetes and hypertension. Bioresource Technology. 2008;99(8):2981-8. especially those phenolic compounds present in eggplant peel.⁶6 Derivi SC, Mendez MH, Francisconi AD, Silva CS, Castro AF, Luz DP. Efeito hipoglicêmico de rações a base de berinjela (Solanum melongena, L.) em ratos. Ciênc Tecnol Aliment (Campinas). 2002;22(2):164-9. In addition, the eggplant peel is rich in anthocyanins and has therapeutic potential for the treatment of hyperlipidemia and prevention of atherogenic cardiovascular diseases by inhibiting lipid peroxidation.⁷7 Basuny AM, Arafat SM, El-Marzooq MA. Antioxidant and antihyperlipidemic activities of anthocyanins from eggplant peels. Journal of Pharma Research & Reviews. 2012;2(3):50-7. Gonçalves et al.⁸8 Gonçalves MC, Diniz MF, Borba JD, Nunes XP, Barbosa-Filho JM. Berinjela (Solanum melongena L.) - mito ou realidade no combate as dislipidemias? Rev Bras Farmacogn. 2006;16(2):252-7. conducted a literature review comprising 25 articles on the species S. melongena and concluded that this species has a mitigation effect on dyslipidemia, particularly hypercholesterolemia, when used in the form of juice made from the fruit with peel.

Cooking methods tend to reduce the content of polyphenols in fruits and vegetables, for example by simply removing their peel, since the higher concentrations of these substances are often present in the external parts.⁹9 Manach C, Scalbert A, Morand C, Rémèsy C, Jimenez L. Polyphenols: food sources and bioavailability. Am J Clin Nutr. 2004;79(5):727-47. Even though several studies have addressed the eggplant in its different forms (in natura, juices, teas, extracts), studies that present a broad analysis of EF produced from the whole fruit dehydrated in an oven are scarce. The authors consider that this process is more accessible to the general public than the freeze-drying process.

The goal of the present study was to assess the physicochemical composition of EF prepared from the whole fruit dehydrated in an oven, characterizing qualitatively and quantitatively phenolic compounds, niacin, and saponins, in addition to assessing in vitro antioxidant activity using 2.2-diphenyl-1-picrylhydrazyl radical (DPPH) and Ferric Reducing/Antioxidant Power (FRAP) assays.

Material and Method

Standards and reagents

High-Performance Liquid Chromatography (HPLC) reagents and standard chlorogenic acid 3878, caffeic acid 0625, ferulic acid 12.870, and rutin 5143 were purchased from Sigma Chemical Co. (St. Louis, MO, USA). The samples were analyzed using a Varian HPLC system, with a tertiary gradient pump, variable-wavelength UV/VIS absorbance detector, and an automatic sampler with a refrigerated compartment (Varian Canada Inc., Mississauga, ON, Canada). The Folin-Denis reagent (Fluka) was purchased from Sigma-Aldrich Brazil LTDA.

Preparation of samples

The samples of EF used for analysis were purchased in stores of Rio de Janeiro, Brazil. According to the manufacturer, the eggplants produced in the State of Rio de Janeiro had originally been sanitized, sliced, and dehydrated in an oven at a temperature between 62°C and 70°C for approximately ten hours. Subsequently, they were placed in containers, sealed until complete cooling and the next day they were ground and packaged immediately. The final result was a dark beige thick powder. Samples from different lots were homogenized and the analyses were performed in triplicate.

Physicochemical Analysis

Moisture content was determined by weight loss in an oven set at 105°C until constant weight.¹⁰10 Instituto Adolfo Lutz (São Paulo). Métodos físico-químicos para análise de alimentos/coords.Odair Zenebon, Neus S Pascuet, Paulo Tiglea. ed.digital São Paulo;2008. The determination of fixed mineral residue (FMR) was based on the burning of organic matter in a muffle furnace at 550ºC until the ashes were white or slightly grey. The ashes allowed the analysis of specific minerals since they were composed of macro-and micronutrients-and trace elements.¹⁰10 Instituto Adolfo Lutz (São Paulo). Métodos físico-químicos para análise de alimentos/coords.Odair Zenebon, Neus S Pascuet, Paulo Tiglea. ed.digital São Paulo;2008.

Proteins were determined through Kjeldahl digestion process, by which organic matter was decomposed by sulfuric acid and nitrogen was transformed into ammonia.¹⁰10 Instituto Adolfo Lutz (São Paulo). Métodos físico-químicos para análise de alimentos/coords.Odair Zenebon, Neus S Pascuet, Paulo Tiglea. ed.digital São Paulo;2008.

Lipids were determined through continuous diethyl ether extraction in a Soxhlet apparatus, followed by the removal of the ether through evaporation.¹⁰10 Instituto Adolfo Lutz (São Paulo). Métodos físico-químicos para análise de alimentos/coords.Odair Zenebon, Neus S Pascuet, Paulo Tiglea. ed.digital São Paulo;2008.

The analysis of crude fiber content was conducted in an industrial digester (Marconi MA-444/CI) subjecting the samples to acid digestion with 1.25% sulfuric acid solution, followed by alkaline digestion with 1.25% sodium hydroxide.¹⁰10 Instituto Adolfo Lutz (São Paulo). Métodos físico-químicos para análise de alimentos/coords.Odair Zenebon, Neus S Pascuet, Paulo Tiglea. ed.digital São Paulo;2008.

Total carbohydrates were estimated by difference, subtracting the values obtained for moisture, proteins, lipids, ashes, and fibers from 100.

Total titratable acidity (TTA) was determined by titration with 0.1 N NaOH, using alcoholic solution of phenolphthalein to determine color change.¹⁰10 Instituto Adolfo Lutz (São Paulo). Métodos físico-químicos para análise de alimentos/coords.Odair Zenebon, Neus S Pascuet, Paulo Tiglea. ed.digital São Paulo;2008.

Total dietary fiber was determined using the method proposed by Prosky et al.,¹¹11 Prosky L, Asp NG, Furda I, DeVries JW, Schweizer TF, Harland BF. Determination of total dietary fiber in foods, food products and total diets: International study. J Assoc Off Anal Chem.1985;68(4):677-9. in addition to soluble and insoluble dietary fiber.¹²12 Horwitz W, Latimer GW Jr. Official methods of analysis of AOAC International. 18th ed : Current Through Revision 3; 2010.^,1313 Prosky L, Asp NG, Furda I, DEeVities JW, Schweizer TF, Harland BF. Determination of total dietary fiber in foods, food products and total diets: International study. J assoc Off Anal Chem.1985;68(4):677-9.

The determination of minerals (K, Ca, Na, Mg, Cu, Fe, Mn, and Zn) was performed through atomic absorption spectrophotometry, using an Analytik Jena spectrophotometer (Model ContrAA® 700).

Niacin concentrations were determined using the method proposed by Horwitz et al.¹⁴14 Horwitz W (ed.) Official methods of analysis of the Association of Official Analytical Chemists. 18th ed Gaitersburg(Maryland): AOAC;2010.p.61-2

Total phenols were determined using Folin-Ciocalteu reagent.¹⁵15 Shetty K, Curtis OF, Levin RE, Wikowsky R, Ang W. Prevention of verification associated with in vitro shoot culture of oregano (Origanum vulgare) by Pseudomonas spp. J Plant Physiol. 1995;147:447-51.

Saponins content was determined using the double-solvent extraction gravimetric method described by Harborne.¹⁶16 Harborne JB. Phytochemical methods: a guide to modern techniqus of plant analysis. London:New York: Chapman and Hall; 1973.^,1717 Edeoga HO, Osuagwu GG, Omosun G, Mbaebie BO, Osuagwu AN. Pharmaceutical and therapeutic potential of some wild cucurbitaceae species from South- East - Nigeria. Recent Research in Science and Technology. 2010;2(1):63-8.

In vitro antioxidant activity

Sample extraction¹⁸18 Singh AP, Luthria D, Wilson T, Vorsa N, Singh V, Banuelos GS, et al. Polyphenols content and antioxidant capacity of eggplant pulp. Food Chemistry. 2009;114:955-61.

The EF was weighted (500 mg) and placed in 15-mL plastic tubes to which 10 mL of 80% methanol were added. The mixture was vigorously shaken using a vortex mixer for two minutes. The samples were then centrifuged at 5000 rpm for 15 minutes and the supernatant was filtered using Whatman filter paper (0.45 µm). The waste was re-extracted two more times with additional 10 mL of 80% methanol. The three extracts were combined to carry out the DPPH and FRAP assays and the analysis of phenolic acids through HPLC assay.

Scavenging method of DPPH free radical¹⁹19 Burits M, Bucar F. Antioxidant activity of Nigella sativa essential oil. Phytother Res. 2000;14(5):323-8.

Ferric reducing/antioxidant power²⁰20 Pulido R, Bravo L, Saura-Calixto F. Antioxidant activity of dietary polyphenols as determined by a modified ferric reducing/antioxidant power assay. J Agric Food Chem. 2000;48(8):3396-402.

Analysis of phenolic acids and flavonoids through HPLC

The samples were analyzed using a Gemini-NX reverse-phase (RP)-HPLC column (100 x 4.5 mm) (Phenomenex, CA, USA), using 1 mL/min solvent flow rate, and detection was at 215 nm. Gradient elution was carried out with a mixture of the following solvents: Solvent A: 0.05% trifluoroacetic acid (TFA) in 10% aqueous acetonitrile (ACN); and solvent B: 0.05% TFA in 60% aqueous ACN (v/v), starting with 100% solvent A and reaching 40% solvent A and 60% solvent B in 30 minutes.

Phenolic acids and flavonoids were identified through comparisons with the retention time (RT) and UV spectra of authentic standards analyzed under identical analytical conditions. Ascorbic acid, tyrosine, chlorogenic acid, caffeic acid, ferulic acid, and rutin were analyzed. The same standards were used for calibration curves to quantify these substances in the EF. The results are presented as mean and standard deviation.

Statistical analysis

Data are expressed as mean ± standard deviation for continuous variables. The linear regression analysis was performed to estimate ascorbic acid, tyrosine and phenolic acids in EF, after analysis of assumptions for the use of the regression analysis. The statistical analysis was performed using the Statistical Package for Social Sciences, version 21 (SPSS Inc., Chicago, IL, USA).

Results

The results of the centesimal composition are shown in Table 1 and the results of minerals, niacin, soluble phenolic compounds, and saponins are shown in Table 2.

In vitro antioxidant activity

Activity of DPPH free radical elimination

The increase in DPPH radical scavenging in a dose-dependent manner due to the elimination of the methanolic extract of EF is 455.6 ± 3.27 ascorbic acid equivalent (mg). The results of the determination of antioxidant activity performed using the FRAP 486.8 ± 86.8 ascorbic acid equivalent (mg).

The following compounds were detected through HPLC assay: ascorbic acid (RT = 1.06 min); tyrosine (RT = 1.68 min); chlorogenic acid (RT = 7.36 min); caffeic acid (RT = 8.57 min); and ferulic acid (RT = 9.24 min) (Figure 1). Calibration information and estimation of phenolic compounds and antioxidants present in EF are shown in Table 3.

Discussion

The Brazilian Government Health Authority has shown a growing interest in the development and promotion of strategies for the prevention of cardiovascular diseases, mainly for a better control of the known risk factors, such as smoking, obesity, sedentary lifestyle, hyperglycemia, hypertension, and hypercholesterolemia.²¹21 Cipriano G Jr, Neves LM, Cipriano GF, Chiappa GR, Borghi-Silva A. Cardiovascular disease prevention and implications for worksite health promotion programs in Brazil. Prog Cardiovasc Dis. 2014;56(5):493-500. Thus, the search for healthy and low-cost alternatives that can contribute to the health of the population becomes imperative.

A study conducted by Perez and Germani⁴4 Perez PM, Germani R. Farinha mista de trigo e berinjela: características físicas e químicas. B CEPPA (Curitiba). 2004;22(1):15-24. showed that EF had high fiber content (44%). A similar result was obtained by Possetti and Dutra (2011),²²22 Possetti T, Dutra MB. Produção, composição centesimal e qualidade microbiológica de farinha de berinjela (Solanum melongena, L.). Enciclopédia Biosfera. 2011;7(13):1514-8. who found 45% fibers. In addition to low content of lipids (1.99%), there were 6.2% ashes, 25.54% carbohydrates, and 8% proteins. Even though fibers do not supply nutrients to the body, they are essential in the diet. They promote a number of health benefits in view of which the use of EF is considered a potential food ingredient.

In the present study we found 39.2% total fibers, 1.85% lipids, 4.7% ashes, 23.1% carbohydrates, and 13.34% proteins, in addition to a good mineral content, highlighting manganese, zinc, and copper. It is observed that, although there are small variations between the different studies, the EF features around 40% fibers and low lipid content. When compared with wheat flour, it was observed that EF featured higher levels of protein, ashes, total dietary fiber, and total sugars, whereas carbohydrate content was lower. In this way, the high dietary fiber content, the high water absorption capacity, and the ease of grinding make EF a good alternative to be mixed with wheat flour. This mixed flour can be used in the preparation of bakery products (cookies, breads, cakes, and pasta), expanding the number of products to supplement the daily fiber intake.⁴4 Perez PM, Germani R. Farinha mista de trigo e berinjela: características físicas e químicas. B CEPPA (Curitiba). 2004;22(1):15-24.

An analysis performed with the eggplant pulp showed a concentration of 62.5 mg gallic acid equivalent/100 g in the fresh pulp.²³23 Heras I, Alvis A, Arrazola G. Optimización del proceso de extracción de antocianinas y evaluación de la capacidad antioxidante de berenjena (Solanum melongena L.). Información Tecnológica. 2013;24(5):93-102. This value is lower than that found in the present study with EF prepared from the whole fruit, which was 1,540 mg gallic acid equivalent/100 g in the flour. This is an expected result, since eggplant skin is rich in polyphenols and 100 g EF represent 1,000 g of the fruit. Another study showed greater presence of total phenols in extracts prepared from the eggplant peel (2,200 µg/g) than in extracts made from the pulp (390 µg/g).²⁴24 Oliveira MS, Dors GC, Souza-Soares LA, Badiale-Furlong E. Atividade antioxidante e antifúngica de extratos vegetais. Alim Nutr (Araraquara). 2007;18(3):267-75.

The results of a study assessing the centesimal composition of 20% eggplant extract showed that nutrient concentrations found in the present study were much larger than those found by those authors: 0.118% proteins; 0.052% ashes; 0.0366% lipids; 0.038% insoluble fibers; 0.025% soluble fibers; and 256.66 mg/dL total polyphenols. Even though the amount of polyphenols was significant, they were not able to protect mice against the oxidation of LDL-cholesterol, probably due to the presence of biogenic amines, especially histamine. These results do not support the popular use of S. melongena extract as hypocholesterolemic agent. On the other hand, Guimarães et al.²⁵25 Guimarães PR, Galvão AM, Batista CM, Azevedo GS, Oliveira RD, Lamounier RP, et al. Eggplant (Solanum melongena) infusion has a modest and transitory effect on hypercholesterolemic subjects. Braz J Med Biol Res. 2000;33(9):1027-36. assessed S. melongena powder and found 15.09% protein, 1.42% lipids, 13.89% fibers, 0.22% calcium, and 0.31% phosphorus, and qualitative tests assessing composition showed positive results for the presence of polyphenols and saponins. These results are similar to those found in the present study regarding proteins and lipids (13.34 and 1.85%, respectively); however, far below with respect to fiber (39.19%, i.e., fiber concentration in EF was 2.8 times greater) and calcium concentrations.

A study on extracts prepared from the pulp and the peel of eggplant showed a greater presence of soluble phenolic compounds in the peel than in the pulp, and the ability to inhibit DPPH radical was greater in all the extracts prepared from the pulp of eggplant than in those prepared from the peel. These results suggest that greater phenolic content allows moderate antioxidant activity linked to free radical scavenging potential.⁵5 Kwon YI, Apostolidis E, Shetty K. In vitro studies of eggplant (Solanum melongena) phenolics as inhibitors of key enzymes relevant for type 2 diabetes and hypertension. Bioresource Technology. 2008;99(8):2981-8. The present study showed similarity between the results of DPPH and FRAP, thus revealing the antioxidant capacity of EF, possibly due to the important presence of phenolic compounds.

A comparison performed between raw, grilled for 4 to 5 minutes on both sides, and boiled in water for 10 minutes over moderate heat 100 ºC and freeze dried after the process, showed the following concentrations of total polyphenols/100 g dry matter: raw = 910 mg; grilled = 1,803 mg; and cooked = 1,991 mg. The chlorogenic acid concentrations were as follows: 154 mg; 549 mg; and 439 mg, respectively. The concentrations of caffeic acid were: 12.8 mg; 23.3 mg; and 33.9 mg, i.e., the grilling and boiling processes increased polyphenols concentrations. The authors also observed higher free radical scavenger capacity in boiled and grilled samples.²⁶26 Lo Scalzo R, Fibiani M, Mennella G, Rotino GL, Dal Sasso M, Culici M, et al. Thermal treatment of eggplant (Solanum melongena L.) increases the antioxidant content and the inhibitory effect on human neutrophil burst. J Agric Food Chem. 2010;58(6):3371-9. The amount of total polyphenols was much greater in the present study, i.e., 1,540 mg/100 g EF, probably due to the longest period during which the eggplants were exposed to heat at a constant temperature of approximately 70 ºC.

It is important to highlight that the polyphenols commonly present in the human diet are not necessarily the most active within the body. This fact is due to low bioavailability, since they are little absorbed by the intestine, highly metabolized, or eliminated quickly. Furthermore, the metabolites found in blood and specific organs, which result from a liver or digestive activity, may differ from ingested substances in terms of biological activity.⁹9 Manach C, Scalbert A, Morand C, Rémèsy C, Jimenez L. Polyphenols: food sources and bioavailability. Am J Clin Nutr. 2004;79(5):727-47. Variations in phenolic content concentrations between several studies occur due to different growing conditions.²⁷27 Luthria D, Singh AP, Wilson T, Vorsa N, Banuelos GS, Vinyard B. Influence of conventional and organic agricultural practices on the phenolic content in eggplant pulp: plant-to-plant variation. Food Chem. 2010;121:406-11.

A study assessed the hypolipidemic effect of three capsules containing 360 mg dry extract of S. melongena L. (eggplant) or 360 mg placebo/day in 28 women with dyslipidemias under nutritional control during 90 days. The authors concluded that the dry extract of S. melongena L. had a modest effect on lipid profile, with no hepatotoxic effect or adverse reactions; however, it should be noted that the clinical response found in the study did not reach the values established by the III Brazilian Guidelines on Dyslipidemias and Atherosclerosis.²⁸28 Gonçalves MC, Diniz MF, Dantas AH, Borba JD. Modesto efeito hipolipemiante do extrato seco de berinjela (Solanum melongena L.) em mulheres com dislipidemias, sob controle nutricional. Rev Bras Farmacogn. 2006;16(supl):656-63.

Freeze-dried eggplants exhibited the following phenolic acids determined through HPLC assay: caffeic; p-coumaric; ferulic; gallic; protocatechuic; and p-hydroxybenzoic. The amount of hydroxycinnamates (caffeic, ferulic, p-coumaric, and chlorogenic acids) was from 9 g/g to 12 ug/g fresh matter.²⁹29 Kowalski R, Kowalska G. Phenolic acid contents in fruits of aubergine (Solanum melongena L.) Pol J Food Nutr Sci. 2005;14(1):37-42. In the present study, the EF had the following hydroxycinnamates: caffeic, ferulic, and chlorogenic acids, totaling 1,96 mg/g flour.

The major limitation of the present study is a lack of comparison between different forms of EF preparation, to analyse how it would change the composition of EF. However, it is worth mentioning that the EF was produced by hand, thus making the procedure easier, without the need of a freeze dryer, or difficult-to-access equipment. An electric oven is sufficient, allowing low-cost access to nutrients and phenolic compounds present in this flour.

The present study demonstrates that EF is a good addition to the diet of the general population, since it is a source of fiber, minerals, phenolic compounds, saponins, ascorbic acid, tyrosine, and phenolic acids, in addition to exhibiting an important antioxidant activity observed by means of in vitro assays. However, it is observed that although several studies have assessed the eggplant in different ways, the studies on EF are limited to inserting it mixed with other flours to prepare cakes and cookies. No studies were found that had actually assessed the effect of EF on humans in order to know if it would have some hypolipidemic effect or could reduce oxidative stress. Clinical trials are needed to answer these questions.

Conclusion

The EF analyzed exhibited high fiber content and low lipid content. Also, it had good mineral content, highlighting manganese, zinc, and copper, in addition to phenolic compounds and saponins with important in vitro antioxidant capacity. In view of the results, the EF is a good addition to the diet of the population, since it enriches the diet and brings health benefits.

Acknowledgments

We are thankful to: Stan Kubow, PhD. of School of Dietetics and Human Nutrition - McGill, Montreal, Canada. Lucia Maria Jaeger, PhD. of Pharmacy College - UFRJ, Rio de Janeiro, Brazil. Anderson Junger Teodoro of the Department of Food Technology - UNIRIO, Rio de Janeiro, Brazil. Rodrigo Araújo Gonçalves of the Atomic Spectrophotometry Laboratory - PUC, Rio de Janeiro, Brazil. Longevid® Company for providing all the information related to the preparation of eggplant flour.

References

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