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Changes of antioxidant constituents in pineapple (Ananas comosus) residue during drying process C r D M a b a A R R A K R P A 1 a w p a c j v p l h p r o m t a s h B m 0 h Industrial Crops and Product[.]
Industrial Crops and Products 50 (2013) 557–562 Contents lists available at ScienceDirect Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop Changes of antioxidant constituents in pineapple (Ananas comosus) residue during drying process Diogo I.S da Silva a , Geraldo D.R Nogueira b , Alexandra G Duzzioni b , Marcos A.S Barrozo b,∗ a b Federal Institute of Mato Grosso, Campus Rondonópolis, Brazil Federal University of Uberlândia, Chemical Engineering School, Brazil a r t i c l e i n f o Article history: Received 23 April 2013 Received in revised form 30 July 2013 Accepted August 2013 Keywords: Residue Pineapple Antioxidant activity a b s t r a c t Brazil is one of the three largest producers of fruit in the world As a consequence, it has become one of the largest producers of agricultural residues Studies have shown that the residues of certain fruits can present a higher antioxidant activity than the pulp Although these residues are usually discarded, it could be used as an alternative source of nutrients The present paper investigates the drying of pineapple residues in a fixed-bed dryer, analyzing the effect of the process variables on the antioxidant properties of the residue The content of phenolic compounds, flavonoids, and ascorbic acid were also quantified The results shown that the drying of the fruit residue in a fixed-bed was very efficient The content of some bioactive compounds was found to increase after drying Therefore, a new type of product could somehow be considered helpful to promote the nutritional value and extend the utilization of residues © 2013 Elsevier B.V All rights reserved Introduction Pineapple (Ananas comosus) belongs to the Bromeliaceae family, and is originated from South America Pineapple mainly contains water, carbohydrates, sugars, vitamins A, C and beta carotene, protein, fat, ash and fiber and antioxidants namely flavonoids in addition to citric and ascorbic acid (Wai, 2009) It is commonly consumed as fresh and as processed products such as pineapple juice, which is a popular product due to its pleasant aroma and flavor (Rattanathanalerk et al., 2005) The world-wide total pineapple production is between 16 and 19 million tons Brazil is the second largest producer of pineapple in the world (FAO, 2010) and has a huge domestic market Sixty percent of fresh pineapple is edible and average yield in processing ranges from 45% to 55% (Samson, 1986) Processing residuals ranges between 45% and 65% an indication of serious organic-side streams disposal challenges, which causes environmental pollution if not successfully utilized Studies have shown that the residues of certain fruits can present a higher antioxidant activity than the pulp (Gorinstein et al., 2001) Antioxidants are the substances that are able to prevent or inhibit oxidation processes in human body and food products (Diaz et al., 1997) as ascorbic acid, ∗ Corresponding author at: Bloco K - Santa Mônica, 38400-902 Uberlândia, MG, Brazil Tel.: +55 34 96776099; fax: +55 34 32394188 E-mail addresses: diogo.silva@roo.ifmt.edu.br (D.I.S da Silva), masbarrozo@ufu.br (M.A.S Barrozo) 0926-6690/$ – see front matter © 2013 Elsevier B.V All rights reserved http://dx.doi.org/10.1016/j.indcrop.2013.08.001 phenolics and flavonoids Thus, although these residues are usually discarded, it could be used as an alternative source of nutrients to increase the nutritive value of poor people’s diets and to help reduce dietary deficiencies Vitamin C, also known as ascorbic acid, is water soluble, meaning it will dissolve in water and is not stored in the body It is essential for collagen, l-carnitine and neurotransmitters biosynthesis (Naidu, 2003) For adults, the recommended amount of vitamin C is 60–90 mg per day (Gordon, 2005) Vitamin C is found in fruits such as oranges, lemons, acerola, pineapple and grapefruit, as well as in vegetables including tomatoes, green peppers, and potatoes Phenolic compounds, in particular, are thought to act as antioxidant, anti-carcinogenic, anti-microbial, anti-allergic, antimutagenic and anti-inflammatory, as well as reduce cardiovascular diseases (Kima et al., 2003) Flavonoids are the most abundant polyphenolic compounds present in fruits and vegetables and, mainly present as coloring pigments in plants also function as potent antioxidants at various levels Some studies showed that flavonoids could protect membrane lipids from oxidation (Terao et al., 1994) As said before, the recovery of fruit residues, to be used in food, cosmetics and in the pharmacy industry can be an important alternative for the sustainable development However, depending on the type of fruit, the residues can contain a high moisture content level (80–90%), that can contribute to the degradation at an accelerated pace (Makris et al., 2007) One of the methods to conserve the sensorial properties and the bioactive compounds present in these residues is the drying (Barrozo et al., 2001) 558 D.I.S da Silva et al / Industrial Crops and Products 50 (2013) 557–562 The copper-constantan thermocouples used for measuring of the dry and wet bulb temperatures were calibrated by means of a thermostatic bath and a mercury thermometer with precision of 0.05 ◦ C (Felipe and Barrozo, 2003) The thermocouples were positioned in the tube of the air feeding 2.4 Experimental procedure Fig Experimental apparatus The present paper investigates the effects of the variables in the drying process to define the best drying conditions in a fixedbed, bearing in mind the final quality of the product, regarding the changes in the content of citric acid, ascorbic acid, of total phenolics and flavonoids, present in residue of pineapple taken after processed juice These bioactive compounds contents are compared with the values obtained from the fresh pineapple pulp and skin Materials and methods 2.1 Material The residues of pineapple taken from the industrial processing of juices and pastes, used in the experiments, were given away by the Lotus Solutions Company, located in the state of Minas Gerais in mid-southern Brazil The residues were separated in small portions, labeled and then frozen in a freezer Before the analysis took place, the frozen samples were taken out and put in fridges until completely defrosted 2.2 Drying conditions The study of the drying process of the pineapple residue took place in a fixed-bed dryer The independent variables studied were air velocity and air temperature The experimental conditions were chosen based on an experimental design of two levels of each variable (2k ) 2.3 Experimental apparatus A scheme of the fixed bed in thin layer (Barrozo et al., 2005) and the experimental apparatus is shown in Fig The unit is composed, basically, of a blower type fan radial (2), an electric heater (3) provided with a variable voltage (4), thermocouples (6), gate valves to control flow (1), a flowmeter type hot wire anemometer (5) and a measuring cell The cell consists of a cylindrical tube of diameter 8.1 × 10−2 m and length 3.0 × 10−2 m, having metallic screens at the two extremities (details in Fig 1) The system is thermally isolated Initially the system was adjusted to the requested operating conditions An auxiliary cell, identical to the measuring cell, was connected to the equipment Next, the dry and wet bulb temperatures were measured As soon as the desired conditions were reached, the measuring cell was inserted into the equipment, initiating the experiment (zero time) The measuring cell was periodically withdrawn (to each 0.5, 1.0, 2.0, and 5.0 in the beginning, to each 10 until the first hour and in the sequence to each 20 min) and its mass determined on an analytical balance with a precision of × 10−5 kg At the times of sample mass determination, which took about s, the auxiliary cell was connected to the unit in order to maintain thermal and fluid-dynamic equilibrium in the system (Barrozo et al., 2006) The drying time was maintained constant and equal to 27,000 s (7.50 h) for all the experiments in order to maintain the standard for the analysis of the bioactive compounds at the end of each experiment At the end of experiment, the dry mass of the residues was determined by oven method 105 ± ◦ C/24 h The moisture ratio was obtained as a function of the time The equilibrium moisture has been obtained by dynamic method (Arnosti Jr et al., 1999) The moisture ratio (MR) has been calculated according to Eq (1): MR = M − Meq M0 − Meq (1) where MR is the moisture ratio, M is the moisture content (dry basis) at any time, Meq is the equilibrium moisture content (dry basis) and M0 is the initial moisture content (dry basis) 2.5 Quality parameters 2.5.1 Analysis of titratable citric acid (CA) and ascorbic acid (AA) Acidity content of the samples was titrated with 0.1 N NaOH and the results were expressed as the percentage of citric acid The titration method was based on the reduction of the sodium salt of the blue dye 2,6-dichlorophenolindophenol by ascorbic acid (AOAC, 1995) The results are expressed as milligrams of ascorbic acid 100 g−1 samples (dry matter) 2.5.2 Determination of total phenolics content (TPC) Total polyphenols were determined by the Folin Ciocalteu method (Singleton and Rossi, 1965), using gallic acid as the standard The linear reading of the standard curve was from 0.2 to 2.0 mg gallic acid per milliliter Total phenolics were expressed as milligrams of gallic acid equivalents (GAE) 100 g−1 samples (dry matter) 2.5.3 Determination of total flavonoids content (TFC) Total flavonoids content were determined using a colorimetric method described by Zhishen et al (1999) The linear reading of the standard curve was from 20 to 80 g rutin acid per milliliter Total flavonoids were expressed as milligrams of rutin 100 g−1 samples (dry matter) D.I.S da Silva et al / Industrial Crops and Products 50 (2013) 557–562 1.0 Table Drying kinetics models Equation References MR = exp(− kt) MR = Aexp(− kt) Lewis (1921) Brooker et al (1974) exp(−9kt) MR = exp(− ktn ) MR = exp − (kt)n 0.8 Henderson and Henderson (1968) Page (1949) Overhults et al (1973) V = 1,0 m s-1 T = 46 ° C T = 60 ° C Overhults 0.6 MR MR = A exp(−kt) + 559 0.4 2.6 Statistical treatment 0.2 Table shows the drying kinetics models analyzed in this work The parameters of these models were estimated by nonlinear regression (Barrozo et al., 1996) The selection of the model that best predicted the drying kinetics considered: the significance of the parameters; residues distribution and the correlation coefficient (Duarte et al., 2004) All analyses of antioxidant compounds were performed in triplicate and the results expressed in mean value ± standard deviation (SD) 0.0 2000 4000 6000 20000 24000 8000 12000 16000 28000 22000 26000 10000 14000 18000 Time (s) Fig Drying kinetics v = 1.0 m s−1 and experimental data and simulated by Overhults model 1.0 Results and discussion V = 1,5 m s-1 T = 46 ° C T = 60 ° C Overhults 0.8 3.1 Drying kinetics Table Parameters found for the kinetic model evaluated V (m s−1 ) T (◦ C) 1.0 1.0 1.5 1.5 46 60 46 60 R2 (Average) Parameters of Overhults model k n 0.000239 ± 0.000008 0.000460 ± 0.000012 0.000395 ± 0.000011 0.000698 ± 0.000010 0.6608 ± 0.011662 0.5377 ± 0.010975 0.7419 ± 0.014611 0.8201 ± 0.009941 0.9965 MR 0.6 In the statistical discrimination of rival models (Table 1), considering all the statistical aspects, the kinetic model that showed better results was the Overhults model The quadratic correlation coefficient (R2 ) obtained with Overhults model was 0.997; while for the other models the R2 were 0.948 (Lewis), 0.983 (Brooker), 0.996 (Page) and 0.991 (Henderson and Henderson) The Overhults model also showed the best results to describe the drying of the organic solid wastes from citrus juice industry, as showed by Perazzini et al (2013) Table shows the parameters of Overhults model for each operating conditions considering the experimental design of two levels of each variable (2k ) Figs and show the experimental data and the prediction by the Overhults model for the moisture ratio (MR) as a function of the drying time (t) These figures show that Overhults equation could well describe the drying kinetics of the pineapple residues and that the water removal during drying of this material occurs mainly in the falling-rate period, conform also observed for ginger by Gouveia et al (1997) and for kiwi by Simal et al (2005) The results of the Figs and show that the drying kinetics of the residues of pineapple is clearly influenced by air velocity and temperature The experimental drying results also show that the time of 7.25 h was adequate to dehydrate the residue of pineapple For the extreme conditions (60 ◦ C and 1.5 m s−1 ) occurred a moisture reduction from 83.4% to 1.42% (Table 3) 0.4 0.2 0.0 2000 4000 6000 8000 12000 16000 20000 24000 28000 10000 14000 18000 22000 26000 Time (s) Fig Drying kinetics v = 1.5 m s−1 and experimental data and simulated by Overhults model 3.2 Physical–chemical analysis The temperature and the drying conditions can affect the activity and stability of the bioactive compounds caused by chemical and enzymatic degradation, by volatilization and/or thermic decomposition (Dorta et al., 2012) Thus, in this work, we evaluated the effect of temperature and drying air velocity on the content of citric acid, ascorbic acid, total phenolics and total flavonoids present in the sample after drying The citric acid content (CA) obtained in the different samples of pineapple was 6.72 ± 0.49 g citric acid 100 g−1 samples (dry base), while for the dried samples the value obtained varied between 0.67 ± 0.03 g citric acid 100 g−1 samples and 0.39 ± 0.03 g citric acid Table Moisture (%) residue of pineapple before and after drying Drying kinetics variables −1 V (m s 1.0 1.0 1.5 1.5 ) ◦ Moisture T ( C) Before drying (%) After drying (%) 46 60 46 60 82.240 82.670 83.170 83.396 5.012 2.724 3.123 1.419 560 D.I.S da Silva et al / Industrial Crops and Products 50 (2013) 557–562 Fig Citric acid contents (CA) of fresh and dried pineapple residue Fig Acid contents (AA) of fresh and dried pineapple residue Fig Total phenolic contents (TPC) of fresh and dried pineapple residue D.I.S da Silva et al / Industrial Crops and Products 50 (2013) 557–562 561 Fig Total flavonoids contents (TFC) of fresh and dried pineapple residue 100 g−1 samples (dry base) at 60 ◦ C and 1.5 m s−1 and 46 ◦ C and 1.0 m s−1 , respectively (Fig 4) The experimental results show that the highest value of the ascorbic acid content (AA) was 84.27 ± 8.31 mg 100 g−1 for pineapple pulp (dry base), while for the fresh residue we found 21.84 ± 2.67 mg 100 g−1 (dry base) and for the pineapple skin we found 56.17 ± 6.40 mg 100 g−1 (Fig 5) The higher values of the ascorbic acid content (AA) for the dry residue were obtained with the drying temperature of 60 ◦ C, with values close to the fresh residue In particular, vitamin C (ascorbic acid) is considered to be a quality indicator of processed food due to its low stability during heat treatments (Podsedek, 2007) Hence, the drying method studied in this paper can be considered effective as the dried product showed similar content of ascorbic acid compared to the fresh residue As regard to content of phenolic (TPC), the experimental results show that the highest value was found at 60 ◦ C and 1.5 m s−1 (13.79 ± 0.26 mg of gallic acid 100 g−1 samples, dry base) For the fresh residue the content found was 1.41 ± 0.06 mg of gallic acid 100 g−1 sample, dry base (Fig 6) The same trend was found by Chang et al (2006), which evaluated the content of phenolic compounds in tomatoes after drying and obtained higher values than the fresh tomatoes According to the authors, this behavior can possibly be explained by the liberation of phenolic compounds during the drying process Chism and Haard (1996) has mentioned that fruits and vegetables normally contain high contents of phenolic compounds in the outer parts, in other words, total phenolics including all the phenolic acid compounds occur in plants as the metabolic intermediates and usually accumulate in the vacuoles It is assumed that food processes might accelerate more bound phenolic compounds releasing from the breakdown of cellular constituents Although, disruption of cell walls may also trigger the release of oxidative and hydrolytic enzymes that would destroy the antioxidants in fruits, however, high temperature processing would deactivate these enzymes and avoid the loss of phenolic acids and, therefore, lead to the increase of total phenolics It is also worth noting that the drying caused a more pronounced increase in the total phenolic of the pineapple residue (13.79 ± 0.26 mg of gallic acid 100 g−1 sample, dry base) when compared with fresh pineapple pulp (2.71 ± 0.13 mg of gallic acid 100 g−1 sample, dry base) and skin (4.16 ± 0.24) Therefore we can realize the importance of recycling the residue of this fruit The total flavonoids content for pineapple residue after drying and for fresh pineapple pulp and skin can be seen in Fig It can be observed that at 46 ◦ C and 1.5 m s−1 , the content of this compound was at its highest level (580.70 ± 20.46 g of rutin 100 g−1 sample) For the fresh residue, we found 114.40 ± 11.82 g of rutin 100 g−1 sample (dry base) The effect of the drying on the content of flavonoids was similar to that observed on content of phenolic (Fig 6) The content of flavonoids compounds in pineapple residue after drying was higher than fresh pineapple pulp (197.10 ± 2.60 g of rutin 100 g−1 sample, dry base) and skin (76.93 ± 11.85 g of rutin 100 g−1 sample) The same behavior was found by Chang et al (2006) in their studies with tomatoes in which the dried samples contained higher levels of total flavonoids compared to fresh samples Thus, the drying conditions play an important role in determining the final quality of the product mainly in terms of antioxidant constituents Conclusions The drying kinetics of pineapple residues showed to be consistent in the range studied It was observed that the behavior was similar to other studies in the literature using similar fruit as study material The statistical discrimination of rival models shows that the Overhults model (Overhults et al., 1973) was the kinetic model that better represented the experimental data of the residues of pineapple The drying kinetics was clearly influenced by air velocity and temperature As for the content of bioactive compounds analyzed in this work, drying in a fixed-bed was very efficient The content of some bioactive compounds was found to increase after drying Higher values of total phenolic and flavonoids content were found compared with the same fresh residue It can be explained by the fact that these compounds in plants act as metabolic intermediates and normally accumulate in vacuoles, and that the drying process accelerates the release of these compounds by breaking down the cellular constituents The results presented in this paper indicated the drying process could enhance the nutritional value of pineapple residue Thus, once handled correctly, the residue from the extraction of pineapple pulp and juice industry can be reused for various purposes, considering it as a source of bioactive compounds, thereby avoiding the discharge to the environment Therefore, a new type of product 562 D.I.S da Silva et al / Industrial Crops and Products 50 (2013) 557–562 could somehow be considered helpful to promote the nutritional value and extend the utilization of pineapple residues Acknowledgments The authors gratefully acknowledge the financial support of the Brazilian research funding agencies FAPEMIG (Foundation for Research Support of the State of Minas Gerais), CAPES (Federal Agency for the Support and Improvement of Higher Education, PNPD–National Postdoctoral Program) and CNPq (National Council for Scientific and Technological Development) 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