Mathematical modeling and quality properties of a

Received: 4 January 2016

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Revised: 23 August 2016

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Accepted: 8 September 2016

DOI 10.1111/jfpe.12499

ORIGINAL ARTICLE

Mathematical modeling and quality properties of a dehydrated native Chilean berry Issis Quispe-Fuentes | Antonio Vega-G
alvez | Valeria V
asquez | Elsa Uribe | Sebasti
an Astudillo Department of Food Engineering,
l Universidad de La Serena, Avenida Rau Bitr
an 1305, Box 599, La Serena, Chile Correspondence Issis Quispe-Fuentes, Department of Food Engineering, Universidad de La Serena,
l Bitr
an 1305, Box 599, Avenida Rau La Serena, Chile Email: [email protected]

Abstract Maqui (Aristotelia chilensis [Molina] Stuntz) berry dehydration, drying kinetics (40–808C), and drying temperature effects on texture profile, rehydration properties, dietary fiber, and sugar contents were evaluated. The Midilli–Kucuk model presented the best fitting to the drying curves. The effective diffusion coefficients varied from 0.34 3 10210 m2 s21 at 408C to 2.14 3 10210 m2 s21 at 808C. The texture profile analysis showed a slight difference in some parameters (springiness, gumminess cohesiveness, and chewiness). The WHC parameters had no significant differences in the range 50–808C. The insoluble dietary fiber content was greater than the soluble one in all the samples. Also, the dietary fiber, fructose, and glucose contents increased in value with an increase in temperature. The results could be used to estimate the best drying conditions for producing a dehydrated maqui product.

Practical application This native berry is categorized as a “superfruit” due to its great number of wholesome properties. However, it is highly perishable and is primarily marketed as a powder since it is stable after drying. This study is the first one that provides results on both quality changes and energy consumption of the drying process. This information, here, can help engineers and marketers to determine the best drying conditions for maqui berries so that they retain their antioxidant properties and dietary fiber contents as well as maintain proper rehydration and texture properties, all of them interesting for to functional food marketing. KEYWORDS

maqui, Aristotelia chilensis [Molina] Stuntz, convective drying, moisture diffusivity, energy consumption


spedes, Alarcon, Avila, & Nieto, 2010; Miranda-Rottmann activity (Ce

1 | INTRODUCTION

et al., 2002; Schreckinger, Wang, Yousef, Lila, & Gonzalez De Mejia, Maqui (Aristotelia chilensis [Molina] Stuntz) is a plant of the Elaeocarpaceae

2010).

family that grows in central and southern regions of Chile and pro-

A great interest in dietary fiber and antioxidants has also increased

duces a red/purple color berry about 6 mm in diameter with typically

in recent decades leading to the development of a large market for


s-Vilaplana, Mena, García-Viguera, & Moreno, 3–4 seeds (Girone

fiber and antioxidant rich products and ingredients (Ajila, Leelavathi, &

2012). Maqui berries are collected in a wild condition from December

Prasada, 2008). However, the maqui berry is highly perishable, it has

to February, despite the fact there is not a commercial production yet

high water activity and is highly susceptible to mechanical damage,

(Fredes et al., 2014). In recent years, there has been growing a commer-

microbial spoilage, and environmental conditions (Rodríguez et al.,

cial and scientific interest in these berries because they contribute to

2016). To prolong its shelf life after harvest, it is essential to preserve

many health benefits, including high anti-inflammatory activity, anti-

and stabilize their active ingredients. Convective drying can be used to

adipogenic capacity, anti-atherogenic capacity, and cardioprotective

inactivate the enzymatic activity and reduce microbial growth or

J. Food Process Eng. 2016; 01–11

wileyonlinelibrary.com/journal/jfpe

C 2016 Wiley Periodicals, Inc. V

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QUISPE-FUENTES

chemical reactions to prolong shelf life considerably (Wojdylo, Figel,

ET AL.

2 | MATERIALS AND METHODS

Lech, Nowicka, & Oszmianski, 2014). Several investigations have reported the effects of convective drying temperature on relevant quality attributes, physical and dietetic parameters of various fruits (Di Scala et al., 2011; Djendoubi Mrad, Boudhrioua, Kechaou, Courtois, &
pez et al., 2013; Rodríguez et al., 2014; Vega-G
alvez Bonazzi, 2012; Lo et al., 2015; Wojdylo et al., 2014). However, its high costs make this process economical only for the dehydration of high-value products to protect qualities such as color, flavor, nutrients, rehydration capacity, appearance, and uniformity. Also, texture is a key attribute in foods to ensure consumer acceptance. In addition, in some foods, as dry fruits for breakfast, the rehydration velocity is very important in the judgment of its quality (Ramallo & Mascheroni, 2012). Dried fruits and vegetables have been regarded as an alternative of fat-free snack for health-conscious consumers, and dried maqui berry can potentially be

2.1 | Raw material and drying experiments Maqui (A. chilensis) berries were obtained from a local market in Valdivia City (Los Ríos Region), Chile. The drying process was performed in a convective dryer designed and constructed by the Department of Food Engineering at La Serena University, Chile. The maqui berry (the whole fruit with a maturity index of 6.5 estimated by soluble solids to % acidity ratio) drying was performed at five different drying temperatures of 40, 50, 60, 70, and 808C (60.28C) under a constant air flow rate of 2.0 6 0.2 m s21. The samples were dried until a constant weight (equilibrium condition) was achieved. The dried berries were stored in vacuum-sealed, low-density polyethylene bags, and protected from sunlight until further analyses.

a good option. The health benefits of dietary fiber have led to an increase in consumption of fiber-rich products, and drying process at a high temperature could also cause a partial degradation of some soluble dietary fiber

2.2 | Determination of effective moisture diffusivity (deff)

(SDF) components (Chantaro, Devahastin, & Chiewchan, 2008), and

The moisture ratio (MR) was calculated according to Equation 1,

therefore, it would be interesting to investigate. So, maqui berry can be

where the average moisture content of each sample during drying

a good raw material to produce an antioxidant dietary fiber powder,

was calculated from the sample weight recorded during the process.

because in a previous study it has been reported about its high antioxi-

Fick’s second law of diffusion (Equation 2) was used to model the

dant activity and bioactive compound contents at different convective

drying process, because moisture diffusion is one of the major mass

drying temperatures and based on this study, the highest total phenolic

transport mechanisms in this process. From Puente-Díaz et al.

content was found at 608C, whereas the highest total flavonoid con-

(2012), the following assumptions were made: (i) maqui berries has a

tent was at 708C with a better correlation to 1,1-diphenyl-2-picryl-

spherical shape with radius of 0.025 m; (ii) effective moisture diffu-

hydrazyl (DPPH) than to oxygen radical absorbance capacity (ORAC)

sivity is a homogeneous process throughout the whole fruit; (iii)

values (Rodríguez et al., 2016). Therefore, this new contribution would

moisture moves radially from inside of the fruit and through its sur-

complement the previous one, since there are no other studies on this

face; (iv) shrinkage during drying is negligible; and (v) mass transfer

dehydrated berry.

is symmetric. The moisture distribution was also considered initially

The main technological variable involved in the final product features is addressed to drying process time. To minimize the operative problems of a drying process (product damage, excessive energy consumption, among others) in the food industry, drying process simulations can be performed by mathematical models using empirical models derived from Fick’s second law of diffusion for different geo€ro, Vega-G
alvez, & Lemus-Mondaca, metries (Ah-Hen, Zambra, Ague

uniform in the whole fruit. Considering these assumptions, Equation 3 was obtained: Xwt 2Xwe ; Xw0 2Xwe " # oMR o2 MR 2 o MR 5Deff ; 1 ot or2 r or MR5

(1)

(2)

dration and are applied to simulate drying curves under similar condi-

  6 2Deff p2 t ; exp p2 r2

tions (Puente-Díaz, Ah-Hen, Vega-G
alvez, Lemus-Mondaca, & Di Scala,

where Xwt is the moisture content (g water g21 dry matter (d.m.)) at

2012). Drying kinetics of different fruits and vegetables have been

any drying time t (s), Xw0 is the initial moisture content (g water g21

obtained by several authors, strawberry (Doymaz, 2008), murta berries

d.m.), Xwe is the equilibrium moisture content (g water g21 d.m.), Deff

(Ah-Hen et al., 2013), tomatoes (Doymaz, 2007), among others.

is the effective moisture diffusivity (m2 s21), and r is the mean radius

2013). These models allow a prediction of mass transfer during dehy-

MR5

(3)

The objectives of this research were to determine the kinetic

of the berries (m). The effective moisture diffusivity at each temper-

parameters involved in the convective drying of maqui berries (40, 50,

ature was calculated by plotting the experimental drying data in

60, 70, and 808C) by simulating the experimental drying data with both

terms of ln (MR) as a function of drying time and the Deff value

diffusional and empirical mathematical models, as an alternative pro-

obtained from the slope of the straight line.

cess for a Chilean native fruit. Also, the effect of air temperature on

The effective moisture diffusivity can be related to temperature by

texture profile, rehydration properties, dietary fiber, and sugar contents

an Arrhenius-type relationship, as given in Equation 4. Activation

of maqui berries was evaluated. In addition, the energy consumption

energy (Ea) was calculated by plotting ln (Deff) as a function of the recip-

during drying was calculated.

rocal of absolute temperature

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ET AL.

 Deff 5D0 exp

 2Ea ; RT

(4)

where D0 is the pre-exponential factor of the Arrhenius equation (m2 21

s

21

), Ea is the activation energy (kJ mol

), R is the universal gas con-

3

included in Equation 13, v is the air velocity (m s21), qa is the air density (kg m23), Ca is the air specific heat (kJ kg218C21), DT is the temperature difference (8C), t is the total drying time of each sample (h), d is the load density (kg m22), and DX is the moisture content difference (kg kg21).

stant (8.314 J mol21 K21), and T is the absolute temperature (K)

2.5 | Texture profile analysis (TPA)

(Ah-Hen et al., 2013).

TPA was performed by a TA-XT Plus texture analyzer (Stable Micro

2.3 | Mathematical modeling of drying kinetics

Systems Ltd., YL, UK) and a Texture Exponent Program. All experi-

Different mathematical models have been proposed to describe the

ments were performed at a room temperature of 208C on 10 rehy-

drying kinetics of food and bioproducts (Doymaz & Ismail, 2011). The

drated samples of maqui berries for each treatment group. A double

equilibrium moisture contents of maqui berries at different tempera-

compression cycle test was performed to 50% compression of the orig-

tures were obtained by the desorption isotherm at 608C from the Hal-

inal portion thickness using a stainless steel plate (10-mm diameter).

sey equation (A 5 0.1160, B 5 2.0145, and R2 5 0.987). The equilibrium

The compression plate (P-10) with a stroke distance of 2 mm and

moisture contents at different temperatures (40, 60, and 708C) were

1.0 mm s21 test speed was used. From the resulting force–time curves,

obtained using saturated salt solutions at relative humidity of 10–90%

the following parameters were obtained: hardness (N), springiness

(a standard gravimetric method recommended by the COST 90 Project)

(mm), cohesiveness (dimensionless), gumminess (N) (hardness 3 cohe-

(Vega-G
alvez, Tello, & Lemus, 2007). The mathematical models used to

siveness), chewiness (N 3 mm) (gumminess 3 springiness), resilience

fit the experimental drying data of maqui berries are the following

(dimensionless), and adhesiveness (N s21).

(Ah-Hen et al., 2013; Doymaz, 2007; Doymaz, 2008; Doymaz & Ismail, 2011; Lemus-Mondaca, Vega-G
alvez, Moraga, & Astudillo, 2015; Vega-G
alvez, Puente-Díaz, Lemus-Mondaca, Miranda, & Torres, 2014):

2.6 | Rehydration properties: rehydration ratio (RR) and water holding capacity (WHC)

Midilli–Kucuk MR5aexp ð2ktn Þ1bt;

(5)

The dehydrated maqui berries were soaked in distilled water at 208C

Logarithmic MR5aexp ð2ktÞ1c;

(6)

for 6 hr, using a solid to liquid ratio of 1:50 according to Vega-G
alvez

Page MR5exp ð2kt Þ;   Modified Page MR5exp ð2ktÞn ;

(7)

et al. (2015) with some modifications. The samples were then removed,

Two2term MR5aexp ð2k1 tÞ1bexp ð2k2 tÞ;

(9)

expressed as grams of water absorbed per gram of dry matter. The

(10)

WHC was determined by centrifuging rehydrated samples at

n

Two2term exponential MR5aexp ð2ktÞ1ð12aÞexp ð2katÞ; Verma MR5aexp ð2ktÞ1ð12aÞexp ð2ctÞ;   a  t Weibull MR5exp 2 : b

drained for 30 s, and weighed. This process was done in triplicate for (8)

(11) (12)

each treatment. The RR was calculated according to Equation 14 and

4,000 rpm (Eppendorf, 5804 R, Hamburg, Germany) for 10 min at 58C in tubes fitted with a centrally placed plastic mesh to allow water to drain freely from the sample during centrifugation. WHC was calculated from the amount of water removed according to Equation 15. Wreh 3 Xreh 2 Wdried 3 Xdried ; Wdried 3 ð12 Xdried Þ

(14)

Wreh 3 Xreh 2 Wdripped Wreh 3 Xreh

(15)

it has been successfully used to model the drying characteristics of sweet cherries (Doymaz & Ismail, 2011). Another model is the Logarith-

where Wreh is the weight of the rehydrated sample (g), Xreh is the mois-

mic model, which is widely used for thin-layer drying studies and has

ture content of the rehydrated sample (wet matter), Wdried is the

These models are generally derived by simplifying the general series

RR5

solution of Fick’s second law. For example, the Page model is an empirical modification of the Lewis model to overcome its shortcomings, and

WHC5

3 100;

been used to describe the drying characteristics of mulberries (Doymaz,

weight of the dried sample (g), Xdried is the moisture content of the

2004). The Weibull and Midilli–Kucuk models have also been used for

dried sample (wet matter), and Wdripped is the weight of the dripped liq-

murta berries (Ah-Hen et al., 2013).

uid after centrifugation.

2.4 | Energy consumption in a convective dryer

2.7 | Total dietary fiber (TDF)

The specific energy consumption required for drying 1 kg of maqui ber-

The maqui berry samples were analyzed for soluble and insoluble die-

ries is calculated using Equation 13 according to the work of Uribe

tary fiber (IDF) fractions according to a gravimetric-enzymatic method

et al. (2013).

(No. 991.43, AOAC, 1990) by using a total dietary fiber assay kit m qa Ca DT t Et 5 ; d DX

(13)

(TDF100A; Sigma-Aldrich, Missouri, USA). Briefly, the samples were suspended in MES-Tris buffer pH 8.2 and digested sequentially by heat

where Et is total energy consumption under each drying condition (kW

stable a-amylase at 95–1008C, protease at 608C, and amyloglucosidase

h kg21), also considered as a specific energy consumption since mass is

at 608C (Velp Scientifica GDE and CSF6, filtration system, Usmate,

4

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"

Italy). The enzyme digestate obtained was filtered through tarred fritted glass crucibles. Crucibles containing the IDF were rinsed with dilute

RMSE5

alcohol and then with acetone, and dried overnight in an oven at 1058C. The filtrates were then mixed with 4 volumes of ethanol to precipitate materials that were soluble in the enzyme digestate fraction. The samples were allowed to stand overnight and the precipitates were filtered through tarred fritted glass crucibles, weighed previously (SDF). One set of insoluble and soluble fiber residues was ashed in a

ET AL.

SSE5

#1 N  2 2 1X MRcalc;i 2MRexp;i ; N i51

N  2 1X MRexp;i 2 MRcalc;i ; N i51

(16)

(17)

N  2 P MRexp;i 2MRcalc;i

v2 5 i51

N2m

;

(18)

muffle furnace at 5258C for 5 hr. Another set of residues was used to

where MRexp is the experimental moisture ratio, MRcalc is the calcu-

determine protein content by the Kjeldahl method (N 3 6.25) (Velp

lated moisture ratio, N is the number of datum values, m is the number

Scientifica DK 20 and UDK 129, Usmate Italy). TDF was calculated as

of constants, and i is the number of terms.

the sum of SDF and IDF, and expressed as g 100 g21 d.m.

3 | RESULTS AND DISCUSSION 2.8 | Determination of sugar contents The extractions to determine sugars were performed according to Djendoubi Mrad, Bonazzi, Boudhrioua, Kechaou, and Courtois (2012) with some modifications. Two grams (triplicate) of finely milled fruit sample was dissolved in 6 mL of methanol (80%, v/v) and was agitated on an orbital shaker at 200 rpm for 30 min and then centrifuged at 5,000 rpm for 3 min. An aliquot (350 mL) of supernatant was passed through a reverse phase (RP) C18 cartridges (Sep-pak, Waters, Ireland) previously activated with MeOH/HCl (10%). In this way, anthocyanins were adsorbed onto the column, whereas sugars and water soluble compounds were washed and recovered using ultra-pure water. The collected volume was adjusted to 5 mL, followed by filtration through a 0.45 mm membrane filter. A 10 mL sample was injected into the HPLC (Perkin Elmer Flexar LC model) with a refraction index (RI) detector,

3.1 | Determination of effective moisture diffusivity Figure 1a shows the experimental drying curves of maqui at a temperature range of 40–808C (curves are from Rodríguez et al. (2016)). A moisture content decreases with an increase in temperature and drying time was observed. As can be seen in Figure 1b, a period of constant drying rate was not observed in the range of drying temperatures. Consequently, the entire drying process occurred in the falling-rate period, where water mass transfer was considered as the predominant mechanism by internal molecular diffusion (Uribe et al., 2013). In comparison, during a constant drying rate period, the moisture removal rate is mainly depended on the surrounding conditions and not on the nature of the product. The falling-rate period essentially depended on the moisture diffusion rate from the product to the surface and also on the moisture removal from the surface (Koyuncu, Tosun, & Pinar, 2007). Furthermore,

including a Flexar binary LC Pump, a Flexar LC autosampler, and a

the time needed to reach a specific final water content decreased as

Flexar column oven. The separation of sugars was carried out using

drying temperature increased. Higher temperatures promoted faster

a Phenomenex Luna 5m NH2 100A (250 mm 3 4.6 mm) column at a

water loss in maqui berry. For example, the time required to achieve a

temperature of 258C. The mobile phase was acetonitrile:water

moisture content lower than 0.33 g water g21 d.m. at 508C was 540

(82.5:17.5, v/v; pH 6), the flow rate was at 1 mL min21, and an iso-

min, whereas the time necessary to reach the same moisture content at

cratic elution was applied. Sugars (fructose, glucose, and sucrose) were

^a, Resende, 808C was 300 min. This behavior was also observed by Corre

identified by their retention times compared to those of standards.

and Menezes (2006), Vega-G
alvez et al. (2014), and Ah-Hen et al. (2013)

Data were processed by using TotalChrom software. Sugar contents

for coffee berry, uchuva fruit, and murta berry, respectively.

were expressed as g 100 g21 d.m.

To estimate the effective moisture diffusivity (Deff), Equation 3 was applied to each set of experimental drying data at different air-drying

2.9 | Statistical analysis

temperatures. Thus, the effective moisture diffusivity values for maqui berry samples were calculated from drying curves, yielding values of

The fit quality of models proposed for drying kinetic models was eval-

0.34, 0.62, 0.89, 1.51, and 2.14 (310210) m2 s21 at 40, 50, 60, 70, and

uated using the root mean square error (RMSE, Equation 16), sum

808C, respectively. The results showed the effects of drying tempera-

squared error (SSE, Equation 17), and Chi-square (v2, Equation 18) sta-

ture on effective moisture diffusion coefficients since an increase in

tistics. The effect of convective drying temperatures on quality param-

this operative variable led to an increase in the Deff. Several investiga-

eters studies was performed in triplicate. The design of experiments

tions showed similar values of Deff: 1.89 2 3.30 3 10210 m2 s21 for

used was nk with one factor to study (k 5 1) corresponding to the tem-

cherry laurel (Kaya & Aydin, 2008) and 0.97 2 8.65 3 10210 m2 s21

perature at six levels (n 5 6). Statgraphics® Centurion XVI was used to

for murta berry (Rodríguez et al., 2014). Also, maqui berry had lower

analyze the results by the analysis of variance (ANOVA). The difference

diffusivity values compared to those of sour cherry, strawberry, and

between the mean was analyzed using the least significant difference

sweet cherry from different drying processes (Doymaz, 2007; Doymaz,

(LSD) test with a significance level of a 5 0.05 and a confidence interval

2008; Doymaz & Ismail, 2011). The ANOVA determined that drying

of 95%. In addition, the multiple range test included the existence of

temperature was highly significant (p < 0.05) regarding to its influence

homogeneous groups within each of the parameters

on moisture diffusion during drying process in maqui berries.

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ET AL.

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F I G U R E 1 (a) Drying curves of maqui berry at temperature 40, 50, 60, 70, 808C and modeling by Midilli–Kucuk and (b) experimental drying rate curves of maqui berry

The Arrhenius equation (Equation 4) was applied to study the influ-

Regarding to the kinetic parameters (a, k, b, n) shown in Table 2, for

ence of temperature on diffusion coefficients. The plot of the natural

the Midilli–Kucuk model, it was observed a decrease on “a” and “k” val-

logarithm of Deff as a function of the reciprocal of temperature resulted

ues when increasing drying temperature. In contrast, the “n” parameter

in a linear relationship (R2 5 0.996), indicating a clear effect of tempera-

increased in value with an increase in temperature. A similar tendency

ture on moisture diffusion. An activation energy value of 42.00 kJ

was observed for these kinetic parameters in another murta berry study

mol21 was obtained from the plot which corresponded to the energy

(Puente-Díaz et al., 2012). It is known that the parameters that do not

required for the water diffusion process to occur. Similar values were

show any tendency to the drying conditions being applied, it probably

found by Doymaz and Ismail (2011) in sweet cherry (43.05 kJ mol21)

depend on other variables such as the initial moisture, shape, size, and

and Ah-Hen et al. (2013) in murta berries (59.27 kJ mol21) during con-

seed content as in the case of maqui berry. However, the results indi-

vective drying processes.

cate that differences are slightly significant (p < 0.05) among the drying temperatures as to the kinetic parameters being studied. The “n” parameter showed a linear correlation with the temperature (R2 5 0.95). For

3.2 | Drying kinetic mathematical modeling

the “a” parameter, a lower correlation (R2 5 0.48) was obtained.

Table 1 shows the average values of kinetic parameters obtained for each proposed model. All proposed models were evaluated statistically to determine the ones that showed better fits to the data. The criteria

3.3 | Energy consumption

to evaluate the quality of fit included low values of SSE (0.009),

The drying rate, energy consumption, and quality of dried products con-

RMSE (0.090), and v2 (0.009) (Ah-Hen et al., 2013). The results

stitute the three most important criteria for assessing drying effective-

showed that the convective drying process of maqui berry samples

ness (Kowalski, Rybicki, & Rajewska, 2014). The energy needed to dry

from an initial moisture content of 2.14 g water g21 (d.m.) to 0.3 g

1 kg of fruits can be seen from Figure 2, where it shows the influence

water g21 d.m. can be approximated by an exponential curve. Accord-

of temperature on specific energy consumption during the convective

ing to these results, all models fit the experimental data well. However,

drying of maqui berry. Et for the convective drying ranged from 65.00

the Midilli–Kucuk model showed the lowest statistical values over the

to 112.77 kW h kg21. It can be observed that Et decreased in value for

drying temperature range studied. The same model was found to be

an increase in air temperature, with the lowest energy consumption

most suitable in describing the drying characteristics of murta berry

occurring at 808C. By increasing the process temperature, the drying

(Ah-Hen et al., 2013; Puente-Díaz et al., 2012) and sour cherry

time to reach a final MR 5 0.1 has been reduced. The specific energy

(Doymaz, 2007). Therefore, this model can be the most appropriated

consumptions in maqui berry are higher than those reported by

one to simulate the complete drying process of maqui berry. Figure 1a

Koyuncu et al. (2007) for cornelian cherry fruits at different tempera-

shows both the experimental data and those predicted MRs from the

tures and air velocities. However, this values were lower than those of

Midilli–Kucuk model. The experimental data agreed with the predicted

berberis using the same air velocities (Aghbashlo, Kianmehr, & Samimi-

values (RMSE 5 0.00289 2 0.01205) indicating that the Midilli–Kucuk

Akhijahani, 2008). A maximum specific energy of 112.77 kW h kg21

model could be used to characterize the drying process of maqui berry

was determined at 408C. Therefore, the choice of a drying temperature

from an initial moisture content until the final drying stage.

has an important role on dryer efficiency and drying time.

6

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TA BL E 1

QUISPE-FUENTES

ET AL.

Statistical test for each model at different drying temperatures

Model Midilli–Kucuk

Statistical test

40

50

60

70

80

RMSE

0.00289

0.00956

0.01054

0.01205

0.00889

SSE

0.00001

0.00009

0.00011

0.00015

0.00008

v

0.00001

0.00010

0.00013

0.00017

0.00009

RMSE

0.00518

0.01044

0.02328

0.02434

0.03739

2

Logarithmic

Verma

SSE

0.00003

0.00011

0.00054

0.00059

0.00140

v2

0.00003

0.00012

0.00061

0.00068

0.00161

RMSE

0.00486

0.01986

0.03724

0.03629

0.05133

SSE

0.00002

0.00039

0.00139

0.00132

0.00263

v

0.00003

0.00044

0.00156

0.00151

0.00304

RMSE

0.01790

0.02374

0.02139

0.02309

0.01858

2

Weibull

Two term

SSE

0.00032

0.00056

0.00046

0.00053

0.00035

v2

0.00035

0.00063

0.00051

0.00061

0.00040

RMSE

0.00485

0.01919

0.03175

0.03190

0.04145

SSE

0.00002

0.00037

0.00101

0.00102

0.00172

v

0.00003

0.00041

0.00113

0.00116

0.00198

RMSE

0.01790

0.02374

0.02139

0.02309

0.01858

2

Page

Two-term exp.

SSE

0.00032

0.00056

0.00046

0.00053

0.00035

v2

0.00035

0.00063

0.00051

0.00061

0.00040

RMSE

0.00490

0.05661

0.10922

0.09158

0.12147

SSE

0.00002

0.00320

0.01193

0.00839

0.01475

v

0.00003

0.00358

0.01342

0.00958

0.01702

RMSE

0.01790

0.02374

0.02139

0.01645

0.01858

2

Modified Page

Temperatures (8C)

SSE

0.00032

0.00056

0.00046

0.00027

0.00035

v2

0.00035

0.00063

0.00051

0.00031

0.00040

3.4 | Texture profile analysis

The TPA parameters, fruit hardness, cohesiveness, chewiness, and

The texture of a fruit is related to the cellular wall structure and its

resilience decreased in value, whereas springiness and adhesiveness

composition. The most important physical changes taking place during

increased in value during drying process at each temperature. It has to

fruit dehydration involve tissue microstructure modification and chemi-

be highlighted that some parameters such as springiness, cohesiveness,

cal changes affecting saccharides and proteins. These can negatively

and gumminess have very similar values at 808C in comparison to fresh

affect the rehydration ability of dehydrated fruits and their texture

fruit. This might be due to the lower-drying time at 808C as compared


rez, Gamboa-Santos, Soria, Villamiel, & Montilla, attributes (Megías-Pe

to the other treatments. Fresh maqui berry is a very labile fruit and

2014). Table 3 shows the parameters of texture analyzed, such as

undergoes a quick fermentation process after harvest. Water loss in

hardness (N), which corresponds to the maximum force required to

fresh fruit causes surface damages (fading and dehydration) and

compress the sample; springiness (mm), which is the ability of a sample

reduces texture quality, such as softening and juiciness, affecting fresh

to recover its original shape after removal of the deformation force;

fruit texture quickly. This might explain why there were no significant

cohesiveness (dimensionless), which is the extent of sample deformed

differences (p < 0.05) between the fresh samples and the samples sub-

prior to rupture; gumminess (N), which is the force needed to

jected at 808C for springiness, cohesiveness, and gumminess; so, recov-

disintegrate a semisolid sample at a steady state of swallowing;

ering ability to its original shape, deformation resistance and the force

chewiness (N 3 mm), which is the work needed to chew a solid sample

to disintegrate the fruit seem to have no significant effect when a dry-

at a steady state of swallowing (Chen & Opara, 2013); resilience

ing treatment has been applied to this berry. It was observed that at

(dimensionless), which reflects the redeformation capacity of fruit

the temperature of 508C, springiness, gumminess, and chewiness

tissue after penetration (Yang et al., 2007); and adhesiveness, which is

parameters had no significant difference with respect to the fresh

a surface characteristic that depends on the adhesive and cohesive

berry. Also, at 50 and 808C, three of the seven of the evaluated param-

forces and other authors include even viscosity and viscoelasticity as

eters presented no significant differences compared to the fresh berry.

well (Rahman & Al-Farsi, 2005).

In addition, the remaining treatments, only two of the seven

QUISPE-FUENTES

TA BL E 2

|

ET AL.

7

Kinetics parameters of each model at different drying temperatures (initial moisture content 2.14 g water g21 d.m.)

Final moisture content (g water g21 d.m.)

0.382 6 0.012

Model

Temperatures (8C)

Parameters

0.321 6 0.020

40 Midilli–Kucuk

Logarithmic

Verma

Weibull

Page

Two-term exp.

Modified Page

50

a

0.995 6 0.004

k

0.005 6 0.001a 205

60

0.987 6 0.008

a

6 1.5E

0.002 6 0.001a

6 5.8E

206a

0.986 6 0.007ab

b

0.004 6 0.001a

0.004 6 0.004a 23.24E205 6 1.6E205ab

1.274 6 0.087bc

1.268 6 0.043bc

1.482 6 0.262c

a

0.998 6 0.012

1.049 6 0.018

1.094 6 0.018

1.080 6 0.023

1.100 6 0.042c

k

0.005 6 0.001a

c

20.012 6 0.004

a

0.018 6 0.014a

0.002 6 0.002b

0.003 6 0.002b

0.005 6 0.003b

0.008 6 0.005ab

k

0.137 6 0.027

0.074 6 0.003

0.008 6 0.000

0.013 6 0.001

b

0.017 6 0.002b

c

0.004 6 0.000a

0.074 6 0.003b

0.008 6 0.004b

0.012 6 0.000c

0.017 6 0.001d

a

0.977 6 0.044

1.070 6 0.061

1.175 6 0.034

1.154 6 0.060

1.266 6 0.111c

0.007 6 0.000b

a

a

224.787 6 8.458a

20.049 6 0.006

0.007 6 0.000c bc

b

ab

20.066 6 0.012

6 8.2E

207b

1.081 6 0.031ab

bc

23.0E

205

0.951 6 0.034a

a

6 1.6E

205b

n

b

23.0E

205

80

0.977 6 0.007

ab

23.0E

a

25.0E

205

0.332 6 0.019

70

0.983 6 0.006

ab

0.005 6 0.001a 205ab

0.322 6 0.025

b

b Two term

0.332 6 0.001

bc

0.011 6 0.001cd 20.055 6 0.009

d

b

bc

124.878 6 6.472b

115.5 6 4.866b

0.003 6 0.005

2.1E206 6 2.8E206

0.017 6 0.002d 20.038 6 0.012b

cd

bc

77.135 6 5.785c

0.019 6 0.014

k1

0.138 6 0.026a

1.026 6 1.764a

0.016 6 0.003a

0.016 6 0.003a

0.019 6 0.001a

B

0.982 6 0.014

1.009 6 0.015

1.034 6 0.014

1.034 6 0.014

b

1.039 6 0.033b

k2

0.004 6 0.000a

0.008 6 1E204b

0.013 6 0.001b

0.013 6 0.001c

0.018 6 0.001d

n

0.977 6 0.044

1.070 6 0.061

1.175 6 0.034

1.154 6 0.060

1.266 6 0.111c

k

0.005 6 0.001a

0.006 6 0.002a

0.004 6 0.001a

0.007 6 0.003a

0.006 6 0.004a

a

0.017 6 0.016

0.004 6 0.003

0.001 6 0.003

0.002 6 0.000

0.002 6 0.001b

k

0.431 6 0.380a

2.408 6 1.263a

6.049 6 0.465b

7.204 6 0.457b

11.790 6 2.926c

n

0.977 6 0.044

1.070 6 0.061

1.175 6 0.034

1.154 6 0.060

1.266 6 0.111c

k

0.004 6 0.000a

a

a

a

a

a

ab

ab

b

ab

0.008 6 0.000b

b

bc

b

bc

0.009 6 0.000b

a

6.5E205 6 9.9E205

59.069 6 5.293d

a

a

bc

b

bc

0.013 6 0.001c

a

0.023 6 0.038a

0.017 6 0.002d

parameters did not differ with respect to the fresh. After a rehydration,

ucts. Drying can diminish the osmotic properties of cell walls, leading

the cellular structure presented an irregular shape and an intercellular

to increased water absorption (Kaymak-Ertekin, 2002). Figure 3 shows

integrity loss as a result of the thermal process (Vega-G
alvez et al.,

the WHC and RR results for each of the rehydrated samples. The maxi-

2015). Yang et al. (2007) mentioned that the temperature effect on a

mum WHC was 64.6 6 5.1 g retained water 100 g21 water at 708C,

berry fruit may be due to solubilization and depolymerization of cell

however, no significant differences in the range 50–808C, which indi-

wall constituents including pectins located in the middle lamella that

cated that these drying temperatures cause a tissue structure damage,

caused a decrease in cell–cell adhesiveness, resulting in a fruit soften-

but the WHC values obtained in this range were significantly (p < 0.05)

ing. The lowest values in the texture parameters (cohesiveness, gummi-

higher than those at 408C. That is to say, the differences were particu-

ness, chewiness, and resilience) were observed at 608C. Such results

larly significant at temperature 408C in comparison to the remaining

are in agreement with those of Russo, Adiletta, and Di Matteo (2013)

processed samples. Consequently, an increase in air-drying tempera-

where it was concluded that such a temperature (in eggplant) increased

ture did not cause a clear decrease in the WHC values. These WHC

the porosity of fruit and therefore springiness also increased. Other

values were higher than those for Cape gooseberry (Vega-G
alvez et al.,

authors had also found similar texture properties for convective drying


, & Femenia, 2015) and Citrus aurantium v. canoneta (Garau, Simal, Rossello


, of Cape gooseberry (Vega-G
alvez et al., 2015) and apples (Cruz, Guine & Gonçalves, 2015). Dehydrated maqui berry had significantly lower hardness values (p < 0.05) than that of the fresh sample.

3.5 | Rehydration properties

2007). Dehydrated maqui berry samples in the rehydration water seem to be leading to a good water interchanging to this berry, when compared to other fruits, thus reaching a recovery close to 60% from its initial water content for all the drying treatments. Regarding to RR drying temperature had no significant effect (p > 0.05). The drying process changed the structure and composition of plant tissue which

A rapid and complete rehydration is important for dried products.

results in damaged reconstitution properties as rehydration degree

Rehydration capacity is significantly affected by drying conditions, pre-

(Ramallo & Mascheroni, 2012). This agreed with the results obtained

treatments prior to drying and textural characteristics of dried prod-

on texture profile, where the hardness loss occurred in all treatments.

8

|

QUISPE-FUENTES

Effect of drying temperature on total energy consumption in each drying condition and drying time of maqui berry (air velocity 2.0 m s21 and load density of 3.4 kg m22). Different letters above the bars indicate significant differences (p < 0.05) FIGURE 2

ET AL.

F I G U R E 3 Effect of air-drying temperature on WHC and RR of maqui berry. Identical letters above the bars indicate no significant difference (p > 0.05)

decreases LDL (low-density lipoprotein) cholesterol and blood glucose levels; and the IDF, which stimulates intestinal functions and

These results indicated that an irreversible structural damage has

increases stool weight, preventing constipation and the develop-

taken place on maqui berry during drying, which can lead to a minor

ment of hemorrhoids, as well as decreases the risk of large intestine

rehydration ability loss, since only WHC parameter was affected.

cancer (Kosmala, Zdunczyk, Karlinska, & Juskiewicz, 2014). Fresh maqui berry (41.07 6 0.46 g 100 g21 d.m.) had higher IDF content than SDF content (3.12 6 0.12 g 100 g21 d.m.). The high content of

3.6 | TDF content

IDF was due to the skin and seeds, which are rich in nonpolysac-

A high dietary fiber intake appears to be related to a lower risk of

charide insoluble material (Colin-Henrion, Mehinagic, Renard,

developing cardiovascular disease, diabetes, obesity, and certain

Richomme, & Jourjon, 2009) and the maqui berry is characterized by

gastrointestinal diseases (Anderson et al., 2009). Consequently, new

containing 3–4 seeds. The IDF content increased value from 50 to

food sources (other than grains and cereals) providing large amounts

808C due to the presence of seeds that were not greatly affected by

of dietary fiber are becoming more attractive. Fresh maqui berries

drying temperature. However, berries dried at 408C were dried for

had a TDF content of 44.19 6 0.58 g 100 g21 d.m. (Table 4). This

the longest time and therefore, these berries suffer a damage in their

value was higher than the content reported for other fruits like

fiber content compared to the other treatments. The lower value of

mango (O’shea, Arendt, & Gallagher, 2012), but comparable to that

fresh maqui berry (IDF) can be attributed to incomplete extraction.

of dehydrated Cape gooseberry (Vega-G
alvez et al., 2015). Dietary

All samples had no significant differences in SDF content in the

fiber contains two fractions, the SDF which most effectively

whole temperature range investigated.

Effect of temperature on textural parameters of rehydrated maqui subjected to convective air drying processes

TA BL E 3

Temperatures (8C) Fresh Hardness

1 2

Springiness

Cohesiveness3 Gumminess

4

Chewiness5 Resilience

6

Adhesiveness7

40

5.095 6 0.771

a

0.648 6 0.027

a

50

3.780 6 0.814

b

0.722 6 0.047

b

60

4.029 6 1.104

b

0.668 6 0.053

ac

b

4.105 6 1.567 0.683 6 0.075

abc

80

3.897 6 0.767

b

3.287 6 1.006b

0.707 6 0.032

bc

0.645 6 0.068a

0.536 6 0.023a

0.402 6 0.034b

0.346 6 0.025c

0.321 6 0.035c

0.339 6 0.033c

0.563 6 0.062a

1.446 6 0.180

1.569 6 0.564

1.383 6 0.325

1.308 6 0.344

1.483 6 0.355

1.413 6 0.370a

a

a

a

a

a

1.397 6 0.189a

1.248 6 0.459ab

1.148 6 0.376abc

0.873 6 0.214c

1.395 6 0.649a

1.016 6 0.260bc

0.124 6 0.009

0.100 6 0.010

0.095 6 0.005

0.078 6 0.007

0.094 6 0.008

0.093 6 0.007c

a

20.013 6 0.002a

b

20.008 6 0.005b

bc

20.008 6 0.001b

d

20.008 6 0.001b

Different letters in same row indicate that values are significantly difference (p < 0.05). Hardness: Newton (N). c Springiness: millimeters (mm). d Cohesiveness: dimensionless. e Gumminess: hardness 3 cohesiveness (N). f Chewiness: gumminess 3 springiness (N 3 mm). g Resilience: dimensionless. h Adhesiveness: (N s21).

a

70 b

bc

20.008 6 0.002b

20.007 6 0.002b

QUISPE-FUENTES

TA BL E 4

|

ET AL.

9

Dietary fiber and sugar content of dried maqui (g 100 g21 d.m.) Temperatures (8C) Fresh

40

50

60

70

80

IDF

41.07 6 0.46

SDF

3.12 6 0.12

TDF

44.19 6 0.58ab

42.70 6 0.21a

47.62 6 1.58bc

47.23 6 3.13bc

49.34 6 1.67c

46.15 6 0.05abc

Glucose

7.81 6 0.09

13.45 6 0.72

12.70 6 0.39

13.36 6 1.27

10.87 6 0.84

d

11.92 6 0.37cd

Fructose

10.48 6 0.18a

13.05 6 1.05c

13.73 6 0.08bc

Sucrose

ND

ab a

a

40.01 6 0.73

a

44.71 6 1.63

2.68 6 0.53

a

2.91 6 0.06

b

14.94 6 0.80b ND

bc a

bc

13.71 6 0.55bc ND

44.32 6 3.21 2.90 6 0.08

bc

46.07 6 1.52

c

43.23 6 0.23abc

3.26 6 0.15

a

2.92 6 0.28a

a

b

14.32 6 1.16bc ND

ND

ND

Different letters in same row indicate that values are significantly difference (p < 0.05). ND: not detected. Insoluble dietary fiber (IDF), soluble dietary fiber (SDF), and total dietary fiber (TDF).

3.7 | Sugar content The content of individual sugars for fresh and dried fruit samples is shown in Table 4. The fruit samples contained only fructose and glucose but no sucrose present, being fructose the major sugar found.
n, Alcalde-Eon, Mun ~oz, Rivas-Gonzalo, and SantosEscribano-Bailo Buelga (2006) also reported the presence of glucose in extracts of maqui berry but no fructose was found. Fresh samples contained 10.48 6 0.18 g 100 g21 d.m. and 7.81 6 0.10 g 100 g21 d.m. for fructose (Fru) and glucose (Glu), respectively, with a Glu/Fru ratio of 0.74. This ratio was similar to that reported by Boca, Skrupskis, Dimins, and Krasnova (2010) for strawberries and MikulicPetkovsek, Schmitzer, Slatnar, Stampar, and Veberic (2012) for other types of berries. The sugar composition in berries depends fruit ripe-

4 | CONCLUSIONS In this study, the convective drying of A. chilensis was investigated. Drying process took place in the falling-rate period, and the moisture transfer can be described by Fick’s second law to determine the effective diffusional coefficient. Deff varied from 0.34 to 2.14 3 10210 m2 s21 showing a dependence with drying temperature. An activation energy value of 42.00 kJ mol21 was estimated. According to these results based on the statistical test, the Midilli–Kucuk model showed the best fit to the experimental drying data of A. chilensis. Also, the drying temperature affected the energy needed for drying to take place. The texture profile analysis showed slight differences in some of their parameters between fresh and dried samples. Hot air drying at tem-

ness with fructose and glucose being predominant in very ripe fruits.

peratures between 40 and 808C caused changes in dietary fiber and

In contrast, an immature fruit has higher sucrose contents (Boca

sugar contents, but no significant differences in rehydration parame-


mez, & Robert, 2012). et al., 2010; Fredes, Montenegro, Zoffoli, Go

ters. The results from this study could be used to optimize the drying

Regarding to the effect of drying temperature on sugar content, the

process so that harmful changes in the fresh fruits could be made

fructose content of dried maqui berry varied from 13.0 to 14.9 g

minimal; however, it is necessary to consider other quality parameters

100 g21 d.m. and whereas the glucose contents varied from 10.9 to

that may affect the fresh fruit properties.

13.4 g 100 g

21

d.m. An increase is obtained in monosaccharide con-

tents in the dried fruits when comparing them to the fresh fruit

ACKNOWLEDG MENTS

(p < 0.05). These results may be due to the thermal degradation of

The authors wish to acknowledge the financial support of Depart-

polysaccharides during the hot-air drying process. It has been

ment of Food Engineering, the Program of Doctorate in Food Engi-

reported that by heat action there is an enzymatic hydrolysis of

neering and Bioprocess of Universidad de La Serena and support to

long-chain polysaccharide molecules to others of smaller size as

post-graduated thesis (PT14331).

fructose and glucose (Miranda et al., 2010). Furthermore, in dehydrated samples, there were easier to break of vegetal cell tissue than

CONFLIC T OF I NTE RE ST

in fresh sample, leading to a better sugar extraction. In general, there were slight significant differences (p < 0.05) in the experimental temperature range both on fructose and glucose contents in dehydrated

The author(s) declare(s) that there is no conflict of interest regarding the publication of this paper.

samples. When comparing the total carbohydrate content results against commercial dehydrated fruits, it is evidenced that maqui

RE FE RE NCE S

berry had a lower sugar content (glucose and fructose) as compared

Aghbashlo, M., Kianmehr, M. H., & Samimi-Akhijahani, H. (2008). Influence of drying conditions on the effective moisture diffusivity, energy of activation and energy consumption during the thin-layer drying of berberis fruit (Berberidaceae). Energy Conversion and Management, 49, 2865–2871.

to strawberry, blueberry, cranberry, cherry, among others. Also, maqui berry had no sucrose, unlike the other fruits. In addition, the Glu/Fru ratio (0.8–0.9) in the dehydrated maqui berry was comparable to those in strawberry and raspberry freeze-dried products
rez et al., 2014). (Megías-Pe

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10

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