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Water absorption characteristics of Canarium Schweinfurthii fruits
Available at www.sciencedirect.com INFORMATION PROCESSING IN AGRICULTURE 6 (2019) 386–395 journal homepage: www.elsevier.com/locate/inpa
Water absorption characteristics of Canarium Schweinfurthii fruits James Chinaka Ehiem a,*, Victor Ifeanyichukwu Obiora Ndirika a, Udochukwu Nelson Onwuka a, Yvan Gariepy b, Vijayan Raghavan b a
Department of Agricultural and Bio-Resources Engineering, Michael Okpara University of Agriculture, Umudike, P.M.B. 7267, Umuahia, Abia State, Nigeria b Department of Bioresources Engineering, McGill University, Macdonald Campus, 21,111 Lakeshore, Ste-Anne-de-Bellevue, Quebec H9X 3V9, Canada
A R T I C L E I N F O
A B S T R A C T
Article history:
Water absorption characteristics of two varieties of Canarium Schweinfurthii engl. fruit
Received 23 February 2018
(Canarium Schweinfurthii engl. long and short) essential for predicting their suitable absorp-
Received in revised form
tion conditions was investigated at three different temperatures (35, 50, 65 °C). Increase in
7 November 2018
moisture content of the fruits was measured at one-hour interval until constant values
Accepted 18 December 2018
were obtained after five successive intervals of moisture measurements. Loss of soluble
Available online 28 December 2018
constituents, textural and nutritive qualities of the rehydrated products and their thermodynamic behavior were also measured and calculated. The results obtained revealed that
Keywords:
saturation time for 35, 50 and 65 °C of long and short varieties are 14, 18 and 40 h and
Absorption
18, 22 and 36 h respectively. Rate of absorption of the fruits differ significantly (p > 0.05)
Canarium
with temperature and not with the variety. Water absorption rate of Canarium Schweinfurthii
Thermodynamics
engl. long and short varieties are 2.71 and 2.25 kg/h respectively. The moisture bearing
Temperature
capacity, textural, and nutritive qualities of the reconstituted products showed no signifi-
Fruits
cant difference among varieties at different temperatures used. Fruits soaked at 35 °C pro-
Moisture
duced reusable residual water, retained their nutritive values and soluble constituent more than other soaking temperatures studied. However, the absorption reaction is endothermic with negative entropy and Gibbs energy values were above zero. Midilli model had the best quality for describing the absorption characteristics of both Canarium Schweifurthii engl. fruits. Ó 2018 China Agricultural University. Production and hosting by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).
1.
Introduction
Fruits from wide tree crops are of great interest to food scientists, food producers and other scientists who work towards
achieving food security and pollution free environment in recent years especially in developing countries. This results from high rate of demand of food by the increasing population and quest for alternative source of energy other than fossil fuel. Besides, many wide economic tree crops are disappearing from the environment without being harnessed and replaced due to development and negligent. Canarium Schweifurthii engl is one of the economic forest tree crops that
* Corresponding author. E-mail address: [email protected] (J.C. Ehiem). Peer review under responsibility of China Agricultural University. https://doi.org/10.1016/j.inpa.2018.12.002 2214-3173 Ó 2018 China Agricultural University. Production and hosting by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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belongs to the family of Burseraceae and is popularly grown in the equatorial forest region of East, West and Central Africa [1,2]. In Nigeria, it is mostly grown in the south east part of the country [3]. The tree produces edible fruits that consist of mesocarp, hard spindle-like nut and kernel. The pulp of the mesocarp contain 20.43% crude protein, 23% crude fat, 0.75% crude fiber, 20.10% carbohydrate, 11.8% cellulose and 3.25% ash [4]. The fruits are also eaten fresh or boiled while the oil is used industrially to manufacture shampoo and waxes and, pharmaceutically to produce drugs for treatment of wounds and microbial infections [5]. The mesocarp is rich in edible oil (about 30–50%, [6]) but deteriorate within few days after harvest. About 40% [7] of this important oil rich fruit are wasted annually due to hardening and rotting. The challenge of extracting the mesocarp from hardened fruits is overcome by soaking the hardened fruit in water. This weakens the adhesive force between the mesocarp and the nut. More losses are associated with this practice due to vagaries of heat treatment that results in low quality end product and acidic residual soaking water. Hardened fruits absorb water during soaking and is characterized by progressive mass migration of moisture from higher concentration region to a lower one through the cell walls and intercellular spaces of the samples until saturation state is reached [8]. The rate of absorption is usually affected by the product structure, size, maturity, chemical composition, condensation of water in the capillary, surface tension in the airliquid menisci, migration of bound water through the cell walls and soaking water temperature [9,10,11]. The evaluation of water absorption characteristics of agricultural products as a function of time and temperature is very essential in predicting suitable absorption conditions as well as designing drying and storage equipment that will enhance their shelf life and improve the quality of the end product [12,13,14,15]. Different kinetic models (empirical, semi-empirical and theoretical models) have been developed and used by many researchers to express the relationship between moisture content of agricultural products and time during soaking [15,16,17]. In some water absorption cases, empirical models are mostly used because they are easy to calculate and interpret than the theoretical ones [18,19]. Ansari et al. [20] used Peleg, First-order, Weibull and exponential empirical model to study the rehydration kinetics of dried figs. Weibull, Peleg and Exponential equations were also used by Khazaei [21] to investigate the water absorption kinetics of almond kernels during soaking. Garcia-Pascual et al. [22] also reported that models derived from laws of diffusion and Peleg or Weibull models can describe the dynamic absorption of water when used to examine the hydration of air-dried morchella esculenta (morel). Thermodynamic parameters are also very important in studying water absorption process because they provide information about the affinity between water and the product which helps in the design of equipment for drying, mixing and storage of agricultural products. The aim of this study was to determine the water absorption characteristics of two Canarium Schweifurthii fruits, evaluate the quality of the reconstituted fruits and changes in their thermodynamic behavior and test the best model that will describe the absorption process.
2.
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Material and methods
Canarium schweifurthii long (CSHTL) and short (CSHTS) varieties used for this study were obtained from the local market of Ebonyi (6° 150 N 8° 050 E) State of Nigeria and the experiment was conducted in the Bioresources Engineering Department of McGill University, Macdonald campus, Canada. However, prior to taking the product to Macill University, the initial moisture content of the fruits obtained from the local market was determined at 105 °C for 24 h in the food processing laboratory of Agricultural and Bioresources Engineering Department of Michael Okpara University of Agriculture Umudike as 40.91% wet basis using a laboratory oven (Schutzart DINEN 60429, Germany). The fruits were then pretreated by drying in the sun to reduce the moisture content to safe storage moisture level until arrival in McGill for further studies. On arrival in McGill, the fruits were sorted to remove any bad fruits and the initial moisture level on arrival was re-evaluated by oven drying method at 105 °C for 24 h. Three different temperatures: 35, 50 and 65 °C were considered in the study. Airtight humidity containers containing 20 ml of distilled water were placed in a water bath at the above-specified temperatures and allowed to stabilize for several minutes before immersion of each individual fruit (6.62 g and 2.24 g of long and short varieties respectively). This volume of water was found to be enough to account for any water lost as a result of water absorption by the fruit during the soaking process. The weights of the samples were measured hourly using digital balance (APX-1502, Denver Instrument, US) of 0.01 g accuracy after removing them from the soaking water and drained with tissue paper. Measurements under each temperature were continued until no weight gain was observed after five successive intervals. Each sample variety was replicated three times for each temperature studied. Quality analysis were carried out for both reconstituted and un-reconstituted (sample not soaked in water which serves the control) samples to compare if soaking affected the quality compositions.
2.1.
Sample quality analysis
The quality of the reconstituted samples and residual water were evaluated based on level of nutritive losses and their textural characteristics (hardness, springiness, cohesion adhesion and chewiness) and, acidity and total dissolved solids of the residual water respectively. All the nutritive qualities of the reconstituted fruits were analyzed using the recommended analytical method [23]. The texture of the reconstituted samples were analyzed using a texture analyzer (Texture Analyser, TA Plus, England) with a load cell of 25 kg at the speed of 2 mm/min. Each sample for each temperature studied at every measured time under goes double compression (using 40 mm cylindrical probe) test bearing in mind the double biting of the sample during chewing. Hardness (highest force required to attain a given deformation), cohesion (level of deformation before rupture), adhesion (surface condition of the sample and the compression plate) and springiness (ability of the sample to return to its original shape when load is removed) were determined and recorded automatically by the software built in the system by the manufacturer. Chewiness (the energy needed
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to reduce the product to a swallow-able condition) was obtained by multiplying hardness, cohesion and springiness of each sample for each temperature studied. Each textural parameter was replicated three times for each experimental condition considered. The textural and nutritional analysis of un-reconstituted samples (control) were also determined in order to explain the level of change that occurred during soaking process. Conductivity meter (EC110, Fieldscout, USA) and pH meter (pH meter 25, Accumet, USA) were used to measure the total dissolved solids (TDS) and acid level of the residual water. Total dissolved solids (TDS) represent the overall mobile charged ions including minerals, salts and metals that dissolved in water during soaking operation.
2.2.
Water absorption models
Five empirical models (Peleg, Midilli, Weibull, exponential and logarithmic models) were used to describe the dynamics of water absorption characteristics of canarium schweifurthii engl. fruits. A simple, two parameter non-exponential equation developed by Peleg [24] has been used successfully to describe the absorption behavior of many agricultural products [25,19,26,27,28] It is given as Eq. (1): Mt ¼ Mo t=kt k2 t
where; a = shape factor; b = scale parameter (minutes) Exponential model is based on the assumption that the water absorption rate is directly proportional to the difference between moisture content at saturation and at any given level. It is given as, Eq. (10), [25,31,32]: Mt Me =Mo Me ¼ expðktÞ
ð10Þ
where Me = saturated moisture content %wb; Mt = moisture content at time t %wb; Mo = Initial moisture content %wet basis; k = rate constant (%h1). Logarithmic model, Eq. (11) [33]: MR ¼ a expðktÞ þ c
ð11Þ
where; a, k and c are absorption constants
2.3.
Thermodynamic evaluations
ð13Þ
DG ¼ DH TDS ðJ=KÞ
ð14Þ
ð5Þ
Rearranging and plotting Eq. (2), the values of kt and k2 will be obtained as intercept and slope of the straight line respectively. In estimating the dependence of Peleg rate constant (k1) on temperature, k1 can be assumed to vary according to Arrhenius equation as, Eq. (6): ð6Þ
where: R is the universal gas constant, kref = intersection of the line obtained by linear regression to calculate Ea, hb = Boltzmann’s constant (1.38 10–23 J K1), hp = Planck’s constant (6.626 10–34 J s), and T = absolute temperature. The fitness of the models were tested using the statistical equations shown in Eqs. (15) and (16): " #12 N X 2 RMSE ¼ 1=N Xpredt Xexpt ð15Þ i¼1
x2 ¼
n X 2 Xexpt Xpredt =N n
ð16Þ
i1
The data generated from the experiment was analyzed using GenStat, SPSS and Microsoft excel statistical packages.
3.
Results and discussions
3.1.
Water absorption
1
where: kt = constant (h % ), Ea = activation energy (kJ mol ), Tref = average of the used temperatures, R = universal gas constant (8:314 kJmol1 K1), and T is the absolute temperature (K). Taking the plot of ln (1/kt) against (1/Tref 1/T), kref becomes the intercept while Ea can be calculated from the slope (S) of the graph as shown in Eq. (7): Ea ¼ RS
ð9Þ
ð12Þ
As t ? 1, Eq. (2) gives the relationship between equilibrium moisture content (Me) and k2 as Eq. (5):
1
MR ¼ exp½ðt=bÞa
DS ¼ R ln kref ln hb =hp ln T ðJ=KÞ
ð4Þ
1=kt ¼ kref expðEa =Rð1=Tref 1=TÞÞ
where k and b = absorption constants Weibull model is given as, Eq. (9), [30]:
DH ¼ Ea RT ðJÞ
At t = 0, Sorption rate (R) relates to k1 as:
Me ¼ Mo þ 1=k2
ð8Þ
ð2Þ
ð3Þ
R0 ¼ dM=dt ¼ 1=kt
MR ¼ expðktn Þ þ bt
ð1Þ
where: Mt = moisture content at the time, t (% wet basis); Mo = initial moisture content of the dried sample (% wet basis); soaking time, h; kt = Peleg rate constant (h%1); k2 = Peleg capacity constant (%1). Differentiating Eq. (2) gives sorption rate (R) as: dM 2 ¼ kt =ðkt þ k2 tÞ ¼ R dt
Midilli model is given as, Eq. (8), [29]:
The thermodynamic properties: enthalpy (DH), entropy (DS) and Gibbs free energy of canarium schweifurthii engl fruits were calculated using activation energy values. The equations are, Eqs. (12)–(14) [34,14]:
Rearranging Eq. (1); Mt Mo ¼ t=kt k2 t
6 ( 2 0 1 9 ) 3 8 6 –3 9 5
ð7Þ
Water absorption of Canarium Schweinfurthii engl. fruits in relation to temperature and time is shown in Fig. 1. The fruits absorbed water faster at the beginning of absorption process and reduced gradually until saturation is attained. Botswana Bambara variety, lupin seed, guar seed were reported to behave the same way [34,27,35] respectively. The fruits saturation time correlated negatively with temperature. The rate of water absorption by the fruits at different temperature is
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Fig. 1 – Moisture content relationship with soaking time for Canarium Schweinfurthii engl. (a) Long and (b) short varieties.
significant (p > 0.05) while variety is not. This observation has also been reported to be due to softening and expansion of the fruit cells caused by temperature, which created more moisture gradient and enhanced migration of water molecules into inner capillaries and intercellular spaces [31,36]. However, the similarity of behavior for short variety at 35 and 50 °C observed at 1 h interval could be the existence of similar reaction time for both due to low temperature. Long and short varieties had an asymptotical change at 67.32% and 56.13% dry basis respectively and could be assumed as the points where the samples transition from glass to plastic state took place.
6 ( 2 0 1 9 ) 3 8 6 –3 9 5
389
Fig. 2 – Experimental moisture ratio in comparism with the predicted moisture ratio from five different models at 35 °C for (a) long and (b) short varieties of Canarium Schweinfurthii engl.fruits. the highest R2 value and lowest root mean square error (RMSE) and chi square x2. Among the models tested for describing the water absorption characteristics of the fruits at 35 °C, Midili models had the highest coefficient of determination (R2) and lowest root mean square error (RMSE) and chi square x2 for long and short varieties (Table 1). Regression equations for predicting the moisture content of the fruits at any given temperature and absorption time is given below: %MCðlongÞ ¼ 0:2692A þ 1:39B þ 0:0186AB 0:4386
ð17Þ
%MCðshortÞ ¼ 0:3178A þ 1:52B þ 0:0158AB 2:92
ð18Þ
where A = temperature; B = absorption time
3.2.
Water absorption models 3.3.
The comparism of the experimental moisture ratio with the predicted moisture ratio is shown in Fig. 2. The best models describing the absorption characteristics was the one with
Peleg rate constant
The rate constant (kt) of Canarium Schweinfurthii engl. fruits presented in Table 2 decreased with increase in temperature
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Table 1 – Statistical models and constants applied to absorption characteristics of Canarium Schweifurthii engl. fruits. Long variety
Models a Peleg Midili Weibul Exponential Logarithmic
b
c
0.0289
a
k
n
0.0293
0.0519 0.0032
72.23
73.27
b
Kt
k2
R2
RMSE
X2
0.7031
0.0015
0.99 0.99 0.89 0.89 0.99
0.9633 0.0107 0.0985 0.0971 0.0107
0.2425 0.0038 0.3297 0.3297 0.0038
0.3945
0.0076
0.98 0.99 0.99 0.94 0.99
2.69 0.0112 0.0112 0.0766 0.0230
0.4287 0.0045 0.0046 0.2232 0.0191
0.0714
0.0444 0.0004 Short variety
Peleg Midili Weibul Exponential Logarithmic
0.0002
0.0124
1.53 1.55
0.2397
1.37
17.48
0.0586 0.0454
Table 2 – Peleg constants and sample quality parameters. Varieties
Temp °C
Kt h%1
K2 %1 a
Me g
Ro
R2
TDS
pH a
(CSHTL)
35 50 65
0.7721 ± 0.0113 0.4249 ± 0.0833b 0.2703 ± 0.0079c
0.0023 ± 0.0005 0.0086 ± 0.0026h 0.0127 ± 0.0083m
163.47 ± 18.16 134.41 ± 37.08 120.15 ± 76.24
1.051 ± 0.0383 1.31 ± 0.3261 1.55 ± 0.7657
0.89 0.95 0.91
413.00 582.67b 546.67bc
6.21 5.31 4.77
(CSHTs)
35 50 65
0.5255 ± 0.0107d 0.4727 ± 0.0974e 0.2069 ± 0.0217f
0.0080 ± 0.0044q 0.0079 ± 0.0023q 0.0083 ± 0.0003q
166.68 ± 90.94 142.47 ± 38.11 130.25 ± 4.61
0.9223 ± 0.3268 1.26 ± 0.3069 1.88 ± 0.1029
0.77 0.73 0.89
164.67d 209.67e 290.67f
6.66 6.52 4.97
TDS (mg/L).
for both varieties studied. Contraction of the fruits surface at higher temperature (resulting in surface pore shrinkage) where the fruits surface interfaced with water could be responsible for the reduced mass transfer. High rate of loss of soluble solids at high temperature could also block the surface pores of the sample and thereby resulting in low rate constant. Long and short varieties of the fruits decreased by 63.58 and 57.37% respectively as temperature rises from 35 to 65 °C. Negative correlation of temperature and rate constant has been reported for milk powder and rice, wheat products, amaranth and barley [24,37,38,39,14]. Temperature and varietal influence on the rate constant of the fruits are not significant (p < 0.05).
3.4.
Peleg capacity constant
Capacity constant is an indication of maximum amount of moisture a given product can hold and is usually dependent on type of soaking and loss of soluble solids during absorption process [24,19,40]. The water absorption process of Canarium Schweifurthii fruits involves loss of soluble solids and differences in saturation levels, at different temperatures for both varieties studied (Table 2). This revealed that k2 of the fruits are temperature-dependent. Various authors [14,39,27] in their hydration studies for barley, amaranth and lupin seeds observed similar trend. Capacity constant for long variety increased significantly (p > 0.05) as temperature rises from 35 to 65 °C while no significant changes occurred for short
variety. Besides, moisture bearing capacity of short variety was not significantly (p < 0.05) higher than the long ones. The increase in capacity constant observed could be because the water bearing cells in the fruits expands with temperature and thereby accommodating more moisture. Chickpea and lupin seeds have shown similar behavior [19,27]. At higher temperature (65 °C), maximum absorption capacity was attained at reduced time when compared with other temperatures which could also be related to the increase in loss of dissolvable solids with higher temperature.
3.5.
Activation energy
The result of activation energy of two varieties of Canarium Schweinfurthii engl. fruits is shown in Table 3 and the plot of ln 1/kt against (1/Tref 1/T) from which Ea was calculated is also presented in Fig. 3. The Ea of long and short varieties are low when compared with that of lupin seeds, barley and, three bean varieties (Talash, Sadri and Mahali khomein) and chickpea [27,14,26]. Meanwhile, their values are relatively similar to that of guard seed and unhulled splits and, blanched soya bean [32, 25 respectively]. Low activation energy observed revealed that the fruits are not heat sensitive meaning that heat was gained during absorption process. The Ea of long variety was higher by 17.82% than short variety meaning that the rate of absorption was faster in short than long variety. This could also mean that short variety has more pore spaces than the long variety.
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Table 3 – Thermodynamic properties of Canarium Schweifurthii engl. fruits. Varieties
Temperature °C
Ea kJ/mol
Kref
R2
DH
DS
DG
(CSHTL)
35 50 65
29.57
0.9159
0.78
25.58 25.36 25.23
222.89 225.86 227.37
94.13 98.31 102.08
(CSHTs)
35 50 65
24.30
0.8387
0.82
14.99 14.86 14.74
220.13 223.09 224.61
82.79 86.92 90.66
DH (kJ); DS (J/K); DG (kJ/K).
65 °C respectively. This observation agrees with the finding of Eugene et al. [42] for African elemi (canarium schweifurthii engl. fruits) and negates the behavior of crude protein with temperature for African walnut. The decrease could be attributed to denature characteristic of protein at temperature above 41 °C. Soaking temperature of 35 °C had the least loss of nutritive values for both short and long fruit variety, hence it provides the best reconstitution environment for better retention of the nutritive value of canarium schweifurthii engl. fruits during soaking process.
3.7.
Fig. 3 – The dependence of Peleg rate constant on Temperature (K).
3.6.
Quality of reconstituted fruits
The nutritive composition of the reconstituted canarium schweifurthii engl. fruits soaked at different temperatures as shown in Table 4 revealed that all the proximate and vitamin composition of the fruits decreased with increase in temperature (35 °C–65 °C) except carbohydrate that increased. The increase in carbohydrate with temperature could be due to destruction of the cell wall that caused increase in solubility of the carbohydrate (Reid et al. [41]). Temperature and variety had no significant different (p < 0.05) on the changes in the nutritive values of the reconstituted fruits especially when compared with control. For instance, crude protein for both short and long variety decreased by 7.98%, 19.61% and 29.01% and, 10.78%, 21.76% and 27.94% at 35 °C, 50 °C and
Quality of residual water
Total dissolve solids (TDS) and acidity level of the soaking medium during soaking process of Canarium Schweinfurthii engl. fruits increased by 24.45% and 43.35% and, from 4.77 to 6.21 and 4.97 to 6.66 pH for long and short varieties respectively, Table 2. These show the level of loss of soluble constituents of the fruit which reduce the quality of the soaked product. Loss of soluble solids during soaking process for barley, wheat and rice grains have been reported by Montanuci et al. [14], Maskan [37] and Marcelo et al. [43] respectively. This result is attributed to the dependence of cations and anions production on temperature [44]. Among the temperatures studied, 35 °C had the least TDS and highest pH values indicating that at lower temperature, the level of loss of soluble solids of soaked product would be less and environmental friendly residual soaking water would be assured. Low pH values (acidic state) especially from by-product of postharvest processing of agricultural products encourages health hazards, material loses due to corrosion and lower agricultural production. ANOVA at 5% level of probability showed that the variety and temperature had high significant effect on total dissolved solids and pH levels, except varietal influence
Table 4 – The nutritional composition of the reconstituted fruits at different soaking temperatures. Variety
Short
Long
Temp
% Crude fibre
% Crude protein
% Crude fat
% Carbohydrate
Vitamin A (lg/g)
Vitamin B1 (lg/g)
Vitamin B2 (lg/g)
Vitamin C (lg/g)
Control 35 50 65
0.3201 0.3104 0.3002 0.2891
19.58 18.02 15.74 13.9
24.42 23.38 21.00 18.55
67.94 69.00 73.45 89.86
141.02 137.00 131.10 118.11
10.61 8.75 4.63 3.35
5.03 3.82 2.66 1.34
26.30 19.08 13.54 8.52
Control 35 50 65
0.4800 0.4698 0.4708 0.4449
20.98 17.47 15.32 14.11
24.47 23.78 22.05 19.14
40.64 41.61 46.40 51.89
188.23 181.15 162.02 141.45
13.77 12.33 9.26 5.35
5.38 5.01 3.71 2.98
28.65 23.53 17.29 10.32
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on pH. The value of TDS of Canarium Schweinfurthii engl. fruit fall within the range (<1000 mg/L; [45]) is recommended as fit for human use, Ela [46].
3.8.
Textural quality of the reconstituted fruits
The mean values of textural qualities of the reconstituted canarium schweifurthii engl fruits is presented in Table 5. From the table, the hardness of canarium schweifurthii engl fruits decreased by an average of 93.87% as moisture content increased from 11% to 66% dry basis for bot varieties when
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compared with control. [47,48,49] observed the same decrease behaviour with cucumber fruit, fig fruit and date fruits respectively. This could be due to negative influence (weaken) of water to the cell structure [50]. The observed decrease in hardness with moisture content was gradual for all the temperatures of both varieties and can be related to softening of the tissue with high moisture content. The changes in the hardness of all the temperatures for both varieties are not significant (p < 0.05) except 35 °C of long variety. This means that softening the fruits is independent of temperature. Similar trend was reported of fig fruits by [48].
Table 5 – The effect of soaking temperature on the textural quality of reconstituted Canarium Schweifurthii engl. fruits. Variety
Temperature
35 °C
50 °C Long
65 °C
35 °C
Short 50 °C
65 °C
The values with (*) are the controls.
M. C.
Hardness
Cohesion
Adhesion
Springiness
Chewiness
11.87 15.12 25.24 36.75 45.68 54.85 62.39 66.67 11.87 25.64 37.04 45.69 50.89 55.83 64.50 67.90 11.87 27.92 34.00 41.78 49.32 55.13 62.14 66.75 11.02 19.34 32.70 45.28 55.20 61.42 64.46 66.90 11.02 27.05 34.16 40.86 51.50 55.11 60.48 66.11 11.02 30.17 42.18 59.36 61.59 63.87 65.03 66.79
27.73* 19.27 9.94 4.08 2.76 1.96 1.70 1.70 27.73* 16.23 9.02 5.29 3.13 2.24 1.64 1.63 27.73* 18.86 11.42 6.48 3.57 2.15 1.79 1.77 24.65* 16.07 8.61 5.11 3.50 2.35 1.95 1.70 24.65* 13.62 11.60 8.18 4.28 3.13 2.06 1.70 24.65* 11.78 6.97 2.76 2.13 1.85 1.73 1.70
0.8367* 0.6109 0.8308 0.8230 0.5887 0.7810 0.5356 0.8535 0.5319* 0.7448 0.8391 0.8459 0.7280 0.5781 0.7773 0.5643 0.7336* 0.7741 0.6094 0.8246 0.7923 0.7075 0.8550 0.8285 0.5921* 0.5520 0.7125 0.7067 0.5318 0.6437 0.6869 0.6332 0.5921* 0.7448 0.6831 0.7280 0.8576 0.5643 0.7698 0.5881 0.5922* 0.7004 0.5928 0.6653 0.5982 0.5656 0.8514 0.6981
0.0625* 0.2355 0.2072 0.4206 0.4727 0.5509 0.6366 0.6525 0.0625* 0.3504 0.4984 0.5484 0.5846 0.6246 0.6582 0.6647 0.0625* 0.4629 0.4186 0.3482 0.4802 0.5192 0.5557 0.5596 0.0144* 0.1392 0.0548 0.2082 0.2401 0.2481 0.2072 0.4072 0.0144* 0.1298 0.5089 0.3572 0.2930 0.5419 0.3280 0.3704 0.0144* 0.0683 0.1393 0.2600 0.4015 0.6094 0.5835 0.6391
0.3739* 0.3150 0.0763 0.2366 0.1356 0.2410 0.4335 0.2009 0.3739* 0.2978 0.3208 0.4376 0.1604 0.3514 0.2900 0.3064 0.1510* 0.2616 0.3195 0.2108 0.1913 0.4100 0.3755 0.4242 0.1074* 0.2329 0.2634 0.3569 0.2897 0.2127 0.2010 0.1864 0.1474* 0.2884 0.2474 0.2185 0.3255 0.2223 0.3527 0.3334 0.1474* 0.2730 0.3502 0.2826 0.3981 0.3297 0.2545 0.3868
8.68* 3.71 0.6301 0.7945 0.2203 0.3689 0.3947 0.2915 5.52* 3.59 2.43 1.96 0.3655 0.4550 0.3697 0.2818 3.07* 3.82 2.22 1.13 0.5411 0.6237 0.5747 0.6221 1.57* 2.07 1.62 1.29 0.5392 0.3218 0.2692 0.2006 2.15* 2.93 1.96 1.30 1.19 0.3926 0.5593 0.3333 2.15* 2.25 1.45 0.5189 0.5072 0.3450 0.3749 0.4590
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The change in reduction behaviour of hardness started at 36.09%, 50.89% and 55.13% dry basis (long variety) and 61.20%, 55.11% and 61.59% dry basis (short variety) for 35 °C, 50 °C and 65 °C respectively. These points are taken as the transition moisture contents from glassy to plastic state from which no appreciable change in hardness with moisture content was recorded. The variations could be due to differences in fruits composition. The springiness of the fruits ranged from 0.2198 to 0.3692 and 0.1292 – 0.4318 (mean values) for short and long varieties respectively as temperature increased from 35 °C to 65°C. Non-linear behaviour of springiness with moisture content observed showed that the cell structure in the fruits that compresses and releases energy under off-load condition is heterogeneously distributed, and the tissue experienced damage (permanent deformation) during compression. [49] also reported similar trend for date fruit. Varietal and temperature differences of the fruits springiness are not significant (p < 0.05). The table also revealed that the chewiness of each fruit variety for the temperature range considered had non-linear relationship with moisture content. Both varieties had low mean values that ranged from 6.01 to 0.3625 and 6.01 – 0.4553 for short and long varieties respectively as temperature increased from 35 °C to 65°C. This could be attributed to low hardness, springiness and cohesive characteristics of the product. Decrease in chewiness with moisture content have also been reported for dried fig and date fruits by [48,49]. This result showed that at higher moisture content, very low energy would be required to reduce the size of canarium schweifurthii engl fruits for easy swallow or further processing. Both temperature and varietal differences had no significant (p < 0.05) difference on the chewiness of the rehydrated fruits. The cohesion characteristics of long and short varieties of canarium schweifurthii fruits differ significantly (p > 0.05) and the mean values ranged from 0.5589 to 0.8515 (36.60%) and 0.5539–0.8072 (31.38%) respectively at the temperature range of 35 °C–65°C. [51] observed 21.88% increase in cohesiveness of candy at the 1.3%3.1% moisture range. The difference between the two products could be due to structural and experimental condition differences used. Besides, soaking temperatures had no significant (p < 0.05) effect on the cohesion of both fruits. Long and short fruit varieties had cohesion values above critical point (0.5) at all level of moisture content hence, they are cohesive. Elasticity of the fruit cellular structure (cellulose and hemicellulose) could be responsible for this attribute [48,52,53]. This means that the fruits will manifest high level of deformation during chewing before rupture. Adhesion result as shown in Fig. 2a and b had negative values for all the considered temperature which could be due to high moisture and oil at the fruits interface with water. [48] observed the same trend with fig fruits while the report of [49] is on the contrary for date fruit. The oil may result from ruptured oil bearing sells due to shrinkage during drying. The erratic behaviour of adhesiveness with moisture content as seen in the figure is an indication that the surface grains of the fruits are not uniformly formed. The adhesion of 50 °C was higher than that of 35 °C and 65 °C by 6.40% and 44.52% (short variety) respectively while that of 35 °C was 19.49% and 5.12% higher than 50 °C
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393
and 65 °C respectively for long variety. Besides, the mean value for short variety was more than long variety by 34.79% (not significant, p < 0.05). This could be because of viscous attribute of the fruits and glass to plasticity transition of the fruits during soaking.
3.9.
Thermodynamic evaluation
Thermodynamic properties (enthalpy, entropy and Gibb’s free energy) of Canarium Schweinfurthii engl. fruits at a temperature range of 35–65 °C is presented in Table 3. Enthalpy which reveals the reaction heat occurring in a system under constant pressure had positive values and increase with increase in temperature for both varieties. This could be attributed to increase in rate of reaction of hydrophilic constituents of the samples with high temperature of soaking medium. This result is not in line with the findings of Montanuci et al. [14] for barley, which could be due to differences in their structural and chemical compositions. Entropy of long variety is significantly (p > 0.05) higher than the short variety. Negative values of entropy observed in all the studied temperature decreased with increase in temperature indicating that the absorption process was orderly. The negative trend could be attributed to the possible disruption of sample structure during drying [54]. Decrease in entropy with temperature increase may be due to water molecules being withheld in the micro capillaries and porous matrix of the sample [55]. Gibb’s free energy values are positive, above zero and increased as temperature increases, which means that energy was absorbed from the surrounding during water absorption process. Besides, less energy would be required for interaction of water molecules and the hydrophilic constituents of the sample. The absorbed energy is responsible for softening the water bearing cells of the fruits, aids its expansion and thereby increase the size of the fruits. This process helps in separation and digestion of the mesocarp for oil extraction. Varietal and temperature influence on enthalpy and Gibb’s energy are also highly significant (p > 0.05) except with entropy. Low activation energy and negative values of entropy indicates that the fruits are thermally stable and had less dependent on temperature. Barley cultivars have also shown the same trend [14].
4.
Conclusion
Water absorption characteristics of two varieties of Canarium Schweinfurthii engl fruits were investigated. The investigation showed that the water absorption of the fruits depends significantly (p > 0.05) on temperature and not on variety. However, absorption reaction was well orderly and not spontaneous for the two varieties. Soaking the fruits at 35 °C was the best temperature for obtaining minimum loss of the fruits soluble solids, nutritive quality of the fruits and environmental friendly residual water. The textural attributes of the reconstituted sample were independent of water soaking temperature. The Midili model was found to be the best-fitted model to describe the absorption characteristics for the two varieties of Canarium Schweinfurthii engl. fruits in all temperature tested.
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Conflict of interest We hereby submit that there is no conflict of interest over this manuscript either among the authors or the sponsors.
Acknowledgement The authors wish to thank Tertiary Education Trust Fund (TET Fund) through Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria, for all the financial support. R E F E R E N C E S
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[18] Nussinovitch A, Peleg M. An Empirical model for describing weight changes in swelling and shrinking gels. Food Hydrocolloids 1990;4(1):69–76. [19] Turhan M, Sayar S, Gunasekaran S. Application of Peleg’s modelto study water absorption in chickpea during soaking. J Food Eng 2002;53(2):153–9. [20] Ansari S, Maftoon-Azad N, Hosseini E, Farahnaky A, Asadi GH. Modeling rehydration behavior of dried figs. J Agric Sci Technol 2015;17:133–44. [21] Khazaei J. Characteristics of mechanical strength and water absorption in almond and its kernel. Cerceta˘ri Agronomice in Moldova 2008;41(1):133. [22] Garcia-Pascual P, Sanjuan N, Bon J, Carreres J, Mulet A. Rehydration process of boletus edulis mushroom: characteristics and modeling. J Sci Food Agric 2005;85:1397. [23] AOAC (Association of Official Analytical Chemists). Official Method of Analysis of the AOAC (W. Horwitiz Editor) Eighteenth Edition, Washington, D.C; 2006. [24] Peleg M. An empirical model for the description of moisture sorption curves. J Food Sci 1988;53(4):1216–7. [25] Gowen AA, Abu-Ghannam A, Frias J, Oliveira J. Influence of pre-blanching on the water absorption kinetics of soyabean. J Food Eng 2007;78(3):965–71. [26] Shafaei SM, Masoumi AA, Roshan H. Analysis of water absorption of bean and chickpea during soaking using Peleg model. J Saudi Soc Agric Sci 2014:1–10. [27] Solomon WK. Hydration kinetics of lupin (lupinus albus) seeds. J Food Eng 2007;30(1):119–30. [28] Singh V, Vishwanathan KH, Aswathanarayana KN, Indhudhara SYM. Hydration behavior of food grains and modelling their misture pick up as per Peleg’s equation: part 1Cereals. J Food Technol 2010;47(1):34–41. [29] Midilli A, Kucuk H. Mathematical modelling of thin layer drying of pistachio by using solar energy. Energy Convers Manage 2003;44(7):1111–22. [30] Vega Galvev A, Lemus-Mondaca R, Tello-Ireland C, Miranda M, Yagnam F. Kinetic study of convective drying of blueberry variety o’neil (Vaccinium corymbosum L.). Chilean J Agric Res 2009;69:171–8. [31] Kashaninejad M, Maghsoundlou Y, Rafiee S, Khomeiri M. Study of hydration kinetics and density changes of rice (Tarom Mahali) during hydraothermal processing. J Food Eng 2007;79:1383–90. [32] Rajesh KV, Uma SS, Saroj KN. Water absorption kinetics of guar seeds and unhulled guar splits. Food Bioprocess Technol 2013;6:1355–64. [33] Yaldiz O, Ertekin C, Uzun HB. Mathematical modelling of thin layer solar drying of sultana grapes. Energy 2001;26:457–65. [34] Jideani VA, Mpotokwana SM. Modeling of water absorption of Botswana Bambara variety using Peleg’s equation. J Food Eng 2009;92:182–8. [35] Vishwakarm RK, Shivhare US, Nanda SK. Water absorption kinetics of guar seeds and unhulled guar splits. Food Bioprocess Technol 2013;6(2):1355–64. [36] Botelho FM, Correa PC, Martins AR, Botelho SCC, Oliveira GHH. Effect of mechanical damage on water absorption process by corn kernel. J Food Sci Technol (Campinas). 2013;33(2):119–25. [37] Maskan M. Effect of processing on hydration kinetics of three wheat products of the same variety. J Food Eng 2002;52 (4):337–41. [38] Bilbao-Sainz C, Andres A, Fito P. Hydration kinetics of dried apple as affected by drying conditions. J Food Eng 2005;68:369–76. [39] Resio AC, Aguerre RJ, Suarez C. Hydration kinetics of amaranth grain. J Food Eng 2006;72(3):247–53.
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[40] Toma M, Vinatoru M, Paniwnyk L, On TJ. Investigation of the effects of ultrasound on vegetal tissues during solvent extraction. Ultrason Sonochem 2001;8(2):137–42. [41] Reid T, Munyanyi M, Mduluza T. Effect of cooking and preservation on nutritional and phytochemical composition of the mushroom Amanita Zambiana. J Food Sci Nutr 2017;5:538–44. [42] Eugene NO, Ernest AA, Michael OM. Effect of heat processing on the proximate composition and energy values of African walnut (plukenetiaconophora) and African elemi (canarium schweinfurthii) consumed as Masticatories in Nigeria). Int J Sci Technol Res 2015;4:295–301. [43] Marcelo B, Marcela PT, Constantino S. Factors affecting water uptake of rice grains during soaking. Lebensm Wiss Technol 2004;37:811–6. [44] Licht S 4635. Chem Commun 2004. [45] Boyd CE. Water quality; an introduction. The Netherland: Kluwer academic publisher group; 1999. [46] Ela WP. Introduction to environmental engineering and science. 3rd ed. Prentice Hall; 2007. [47] Okeoghene E, Hilary U, Prosper OO. Moisture-dependent mechanical and textural properties of intact cucumber fruit. Int J Eng and Tech Res (IJETR) 2018;8:24–39. [48] Ansari S, Maftoon-Azad N, Farahnaky A, Hosseini E, Badii F. Effect of moisture content on textural attributes of dried figs Int. Agrophys 2014;28:403–12.
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Water absorption characteristics of Canarium Schweinfurthii fruits James Chinaka Ehiem a,*, Victor Ifeanyichukwu Obiora Ndirika a, Udochukwu Nelson Onwuka a, Yvan Gariepy b, Vijayan Raghavan b a
Department of Agricultural and Bio-Resources Engineering, Michael Okpara University of Agriculture, Umudike, P.M.B. 7267, Umuahia, Abia State, Nigeria b Department of Bioresources Engineering, McGill University, Macdonald Campus, 21,111 Lakeshore, Ste-Anne-de-Bellevue, Quebec H9X 3V9, Canada
A R T I C L E I N F O
A B S T R A C T
Article history:
Water absorption characteristics of two varieties of Canarium Schweinfurthii engl. fruit
Received 23 February 2018
(Canarium Schweinfurthii engl. long and short) essential for predicting their suitable absorp-
Received in revised form
tion conditions was investigated at three different temperatures (35, 50, 65 °C). Increase in
7 November 2018
moisture content of the fruits was measured at one-hour interval until constant values
Accepted 18 December 2018
were obtained after five successive intervals of moisture measurements. Loss of soluble
Available online 28 December 2018
constituents, textural and nutritive qualities of the rehydrated products and their thermodynamic behavior were also measured and calculated. The results obtained revealed that
Keywords:
saturation time for 35, 50 and 65 °C of long and short varieties are 14, 18 and 40 h and
Absorption
18, 22 and 36 h respectively. Rate of absorption of the fruits differ significantly (p > 0.05)
Canarium
with temperature and not with the variety. Water absorption rate of Canarium Schweinfurthii
Thermodynamics
engl. long and short varieties are 2.71 and 2.25 kg/h respectively. The moisture bearing
Temperature
capacity, textural, and nutritive qualities of the reconstituted products showed no signifi-
Fruits
cant difference among varieties at different temperatures used. Fruits soaked at 35 °C pro-
Moisture
duced reusable residual water, retained their nutritive values and soluble constituent more than other soaking temperatures studied. However, the absorption reaction is endothermic with negative entropy and Gibbs energy values were above zero. Midilli model had the best quality for describing the absorption characteristics of both Canarium Schweifurthii engl. fruits. Ó 2018 China Agricultural University. Production and hosting by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).
1.
Introduction
Fruits from wide tree crops are of great interest to food scientists, food producers and other scientists who work towards
achieving food security and pollution free environment in recent years especially in developing countries. This results from high rate of demand of food by the increasing population and quest for alternative source of energy other than fossil fuel. Besides, many wide economic tree crops are disappearing from the environment without being harnessed and replaced due to development and negligent. Canarium Schweifurthii engl is one of the economic forest tree crops that
* Corresponding author. E-mail address: [email protected] (J.C. Ehiem). Peer review under responsibility of China Agricultural University. https://doi.org/10.1016/j.inpa.2018.12.002 2214-3173 Ó 2018 China Agricultural University. Production and hosting by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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belongs to the family of Burseraceae and is popularly grown in the equatorial forest region of East, West and Central Africa [1,2]. In Nigeria, it is mostly grown in the south east part of the country [3]. The tree produces edible fruits that consist of mesocarp, hard spindle-like nut and kernel. The pulp of the mesocarp contain 20.43% crude protein, 23% crude fat, 0.75% crude fiber, 20.10% carbohydrate, 11.8% cellulose and 3.25% ash [4]. The fruits are also eaten fresh or boiled while the oil is used industrially to manufacture shampoo and waxes and, pharmaceutically to produce drugs for treatment of wounds and microbial infections [5]. The mesocarp is rich in edible oil (about 30–50%, [6]) but deteriorate within few days after harvest. About 40% [7] of this important oil rich fruit are wasted annually due to hardening and rotting. The challenge of extracting the mesocarp from hardened fruits is overcome by soaking the hardened fruit in water. This weakens the adhesive force between the mesocarp and the nut. More losses are associated with this practice due to vagaries of heat treatment that results in low quality end product and acidic residual soaking water. Hardened fruits absorb water during soaking and is characterized by progressive mass migration of moisture from higher concentration region to a lower one through the cell walls and intercellular spaces of the samples until saturation state is reached [8]. The rate of absorption is usually affected by the product structure, size, maturity, chemical composition, condensation of water in the capillary, surface tension in the airliquid menisci, migration of bound water through the cell walls and soaking water temperature [9,10,11]. The evaluation of water absorption characteristics of agricultural products as a function of time and temperature is very essential in predicting suitable absorption conditions as well as designing drying and storage equipment that will enhance their shelf life and improve the quality of the end product [12,13,14,15]. Different kinetic models (empirical, semi-empirical and theoretical models) have been developed and used by many researchers to express the relationship between moisture content of agricultural products and time during soaking [15,16,17]. In some water absorption cases, empirical models are mostly used because they are easy to calculate and interpret than the theoretical ones [18,19]. Ansari et al. [20] used Peleg, First-order, Weibull and exponential empirical model to study the rehydration kinetics of dried figs. Weibull, Peleg and Exponential equations were also used by Khazaei [21] to investigate the water absorption kinetics of almond kernels during soaking. Garcia-Pascual et al. [22] also reported that models derived from laws of diffusion and Peleg or Weibull models can describe the dynamic absorption of water when used to examine the hydration of air-dried morchella esculenta (morel). Thermodynamic parameters are also very important in studying water absorption process because they provide information about the affinity between water and the product which helps in the design of equipment for drying, mixing and storage of agricultural products. The aim of this study was to determine the water absorption characteristics of two Canarium Schweifurthii fruits, evaluate the quality of the reconstituted fruits and changes in their thermodynamic behavior and test the best model that will describe the absorption process.
2.
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387
Material and methods
Canarium schweifurthii long (CSHTL) and short (CSHTS) varieties used for this study were obtained from the local market of Ebonyi (6° 150 N 8° 050 E) State of Nigeria and the experiment was conducted in the Bioresources Engineering Department of McGill University, Macdonald campus, Canada. However, prior to taking the product to Macill University, the initial moisture content of the fruits obtained from the local market was determined at 105 °C for 24 h in the food processing laboratory of Agricultural and Bioresources Engineering Department of Michael Okpara University of Agriculture Umudike as 40.91% wet basis using a laboratory oven (Schutzart DINEN 60429, Germany). The fruits were then pretreated by drying in the sun to reduce the moisture content to safe storage moisture level until arrival in McGill for further studies. On arrival in McGill, the fruits were sorted to remove any bad fruits and the initial moisture level on arrival was re-evaluated by oven drying method at 105 °C for 24 h. Three different temperatures: 35, 50 and 65 °C were considered in the study. Airtight humidity containers containing 20 ml of distilled water were placed in a water bath at the above-specified temperatures and allowed to stabilize for several minutes before immersion of each individual fruit (6.62 g and 2.24 g of long and short varieties respectively). This volume of water was found to be enough to account for any water lost as a result of water absorption by the fruit during the soaking process. The weights of the samples were measured hourly using digital balance (APX-1502, Denver Instrument, US) of 0.01 g accuracy after removing them from the soaking water and drained with tissue paper. Measurements under each temperature were continued until no weight gain was observed after five successive intervals. Each sample variety was replicated three times for each temperature studied. Quality analysis were carried out for both reconstituted and un-reconstituted (sample not soaked in water which serves the control) samples to compare if soaking affected the quality compositions.
2.1.
Sample quality analysis
The quality of the reconstituted samples and residual water were evaluated based on level of nutritive losses and their textural characteristics (hardness, springiness, cohesion adhesion and chewiness) and, acidity and total dissolved solids of the residual water respectively. All the nutritive qualities of the reconstituted fruits were analyzed using the recommended analytical method [23]. The texture of the reconstituted samples were analyzed using a texture analyzer (Texture Analyser, TA Plus, England) with a load cell of 25 kg at the speed of 2 mm/min. Each sample for each temperature studied at every measured time under goes double compression (using 40 mm cylindrical probe) test bearing in mind the double biting of the sample during chewing. Hardness (highest force required to attain a given deformation), cohesion (level of deformation before rupture), adhesion (surface condition of the sample and the compression plate) and springiness (ability of the sample to return to its original shape when load is removed) were determined and recorded automatically by the software built in the system by the manufacturer. Chewiness (the energy needed
388
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to reduce the product to a swallow-able condition) was obtained by multiplying hardness, cohesion and springiness of each sample for each temperature studied. Each textural parameter was replicated three times for each experimental condition considered. The textural and nutritional analysis of un-reconstituted samples (control) were also determined in order to explain the level of change that occurred during soaking process. Conductivity meter (EC110, Fieldscout, USA) and pH meter (pH meter 25, Accumet, USA) were used to measure the total dissolved solids (TDS) and acid level of the residual water. Total dissolved solids (TDS) represent the overall mobile charged ions including minerals, salts and metals that dissolved in water during soaking operation.
2.2.
Water absorption models
Five empirical models (Peleg, Midilli, Weibull, exponential and logarithmic models) were used to describe the dynamics of water absorption characteristics of canarium schweifurthii engl. fruits. A simple, two parameter non-exponential equation developed by Peleg [24] has been used successfully to describe the absorption behavior of many agricultural products [25,19,26,27,28] It is given as Eq. (1): Mt ¼ Mo t=kt k2 t
where; a = shape factor; b = scale parameter (minutes) Exponential model is based on the assumption that the water absorption rate is directly proportional to the difference between moisture content at saturation and at any given level. It is given as, Eq. (10), [25,31,32]: Mt Me =Mo Me ¼ expðktÞ
ð10Þ
where Me = saturated moisture content %wb; Mt = moisture content at time t %wb; Mo = Initial moisture content %wet basis; k = rate constant (%h1). Logarithmic model, Eq. (11) [33]: MR ¼ a expðktÞ þ c
ð11Þ
where; a, k and c are absorption constants
2.3.
Thermodynamic evaluations
ð13Þ
DG ¼ DH TDS ðJ=KÞ
ð14Þ
ð5Þ
Rearranging and plotting Eq. (2), the values of kt and k2 will be obtained as intercept and slope of the straight line respectively. In estimating the dependence of Peleg rate constant (k1) on temperature, k1 can be assumed to vary according to Arrhenius equation as, Eq. (6): ð6Þ
where: R is the universal gas constant, kref = intersection of the line obtained by linear regression to calculate Ea, hb = Boltzmann’s constant (1.38 10–23 J K1), hp = Planck’s constant (6.626 10–34 J s), and T = absolute temperature. The fitness of the models were tested using the statistical equations shown in Eqs. (15) and (16): " #12 N X 2 RMSE ¼ 1=N Xpredt Xexpt ð15Þ i¼1
x2 ¼
n X 2 Xexpt Xpredt =N n
ð16Þ
i1
The data generated from the experiment was analyzed using GenStat, SPSS and Microsoft excel statistical packages.
3.
Results and discussions
3.1.
Water absorption
1
where: kt = constant (h % ), Ea = activation energy (kJ mol ), Tref = average of the used temperatures, R = universal gas constant (8:314 kJmol1 K1), and T is the absolute temperature (K). Taking the plot of ln (1/kt) against (1/Tref 1/T), kref becomes the intercept while Ea can be calculated from the slope (S) of the graph as shown in Eq. (7): Ea ¼ RS
ð9Þ
ð12Þ
As t ? 1, Eq. (2) gives the relationship between equilibrium moisture content (Me) and k2 as Eq. (5):
1
MR ¼ exp½ðt=bÞa
DS ¼ R ln kref ln hb =hp ln T ðJ=KÞ
ð4Þ
1=kt ¼ kref expðEa =Rð1=Tref 1=TÞÞ
where k and b = absorption constants Weibull model is given as, Eq. (9), [30]:
DH ¼ Ea RT ðJÞ
At t = 0, Sorption rate (R) relates to k1 as:
Me ¼ Mo þ 1=k2
ð8Þ
ð2Þ
ð3Þ
R0 ¼ dM=dt ¼ 1=kt
MR ¼ expðktn Þ þ bt
ð1Þ
where: Mt = moisture content at the time, t (% wet basis); Mo = initial moisture content of the dried sample (% wet basis); soaking time, h; kt = Peleg rate constant (h%1); k2 = Peleg capacity constant (%1). Differentiating Eq. (2) gives sorption rate (R) as: dM 2 ¼ kt =ðkt þ k2 tÞ ¼ R dt
Midilli model is given as, Eq. (8), [29]:
The thermodynamic properties: enthalpy (DH), entropy (DS) and Gibbs free energy of canarium schweifurthii engl fruits were calculated using activation energy values. The equations are, Eqs. (12)–(14) [34,14]:
Rearranging Eq. (1); Mt Mo ¼ t=kt k2 t
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ð7Þ
Water absorption of Canarium Schweinfurthii engl. fruits in relation to temperature and time is shown in Fig. 1. The fruits absorbed water faster at the beginning of absorption process and reduced gradually until saturation is attained. Botswana Bambara variety, lupin seed, guar seed were reported to behave the same way [34,27,35] respectively. The fruits saturation time correlated negatively with temperature. The rate of water absorption by the fruits at different temperature is
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Fig. 1 – Moisture content relationship with soaking time for Canarium Schweinfurthii engl. (a) Long and (b) short varieties.
significant (p > 0.05) while variety is not. This observation has also been reported to be due to softening and expansion of the fruit cells caused by temperature, which created more moisture gradient and enhanced migration of water molecules into inner capillaries and intercellular spaces [31,36]. However, the similarity of behavior for short variety at 35 and 50 °C observed at 1 h interval could be the existence of similar reaction time for both due to low temperature. Long and short varieties had an asymptotical change at 67.32% and 56.13% dry basis respectively and could be assumed as the points where the samples transition from glass to plastic state took place.
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389
Fig. 2 – Experimental moisture ratio in comparism with the predicted moisture ratio from five different models at 35 °C for (a) long and (b) short varieties of Canarium Schweinfurthii engl.fruits. the highest R2 value and lowest root mean square error (RMSE) and chi square x2. Among the models tested for describing the water absorption characteristics of the fruits at 35 °C, Midili models had the highest coefficient of determination (R2) and lowest root mean square error (RMSE) and chi square x2 for long and short varieties (Table 1). Regression equations for predicting the moisture content of the fruits at any given temperature and absorption time is given below: %MCðlongÞ ¼ 0:2692A þ 1:39B þ 0:0186AB 0:4386
ð17Þ
%MCðshortÞ ¼ 0:3178A þ 1:52B þ 0:0158AB 2:92
ð18Þ
where A = temperature; B = absorption time
3.2.
Water absorption models 3.3.
The comparism of the experimental moisture ratio with the predicted moisture ratio is shown in Fig. 2. The best models describing the absorption characteristics was the one with
Peleg rate constant
The rate constant (kt) of Canarium Schweinfurthii engl. fruits presented in Table 2 decreased with increase in temperature
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Table 1 – Statistical models and constants applied to absorption characteristics of Canarium Schweifurthii engl. fruits. Long variety
Models a Peleg Midili Weibul Exponential Logarithmic
b
c
0.0289
a
k
n
0.0293
0.0519 0.0032
72.23
73.27
b
Kt
k2
R2
RMSE
X2
0.7031
0.0015
0.99 0.99 0.89 0.89 0.99
0.9633 0.0107 0.0985 0.0971 0.0107
0.2425 0.0038 0.3297 0.3297 0.0038
0.3945
0.0076
0.98 0.99 0.99 0.94 0.99
2.69 0.0112 0.0112 0.0766 0.0230
0.4287 0.0045 0.0046 0.2232 0.0191
0.0714
0.0444 0.0004 Short variety
Peleg Midili Weibul Exponential Logarithmic
0.0002
0.0124
1.53 1.55
0.2397
1.37
17.48
0.0586 0.0454
Table 2 – Peleg constants and sample quality parameters. Varieties
Temp °C
Kt h%1
K2 %1 a
Me g
Ro
R2
TDS
pH a
(CSHTL)
35 50 65
0.7721 ± 0.0113 0.4249 ± 0.0833b 0.2703 ± 0.0079c
0.0023 ± 0.0005 0.0086 ± 0.0026h 0.0127 ± 0.0083m
163.47 ± 18.16 134.41 ± 37.08 120.15 ± 76.24
1.051 ± 0.0383 1.31 ± 0.3261 1.55 ± 0.7657
0.89 0.95 0.91
413.00 582.67b 546.67bc
6.21 5.31 4.77
(CSHTs)
35 50 65
0.5255 ± 0.0107d 0.4727 ± 0.0974e 0.2069 ± 0.0217f
0.0080 ± 0.0044q 0.0079 ± 0.0023q 0.0083 ± 0.0003q
166.68 ± 90.94 142.47 ± 38.11 130.25 ± 4.61
0.9223 ± 0.3268 1.26 ± 0.3069 1.88 ± 0.1029
0.77 0.73 0.89
164.67d 209.67e 290.67f
6.66 6.52 4.97
TDS (mg/L).
for both varieties studied. Contraction of the fruits surface at higher temperature (resulting in surface pore shrinkage) where the fruits surface interfaced with water could be responsible for the reduced mass transfer. High rate of loss of soluble solids at high temperature could also block the surface pores of the sample and thereby resulting in low rate constant. Long and short varieties of the fruits decreased by 63.58 and 57.37% respectively as temperature rises from 35 to 65 °C. Negative correlation of temperature and rate constant has been reported for milk powder and rice, wheat products, amaranth and barley [24,37,38,39,14]. Temperature and varietal influence on the rate constant of the fruits are not significant (p < 0.05).
3.4.
Peleg capacity constant
Capacity constant is an indication of maximum amount of moisture a given product can hold and is usually dependent on type of soaking and loss of soluble solids during absorption process [24,19,40]. The water absorption process of Canarium Schweifurthii fruits involves loss of soluble solids and differences in saturation levels, at different temperatures for both varieties studied (Table 2). This revealed that k2 of the fruits are temperature-dependent. Various authors [14,39,27] in their hydration studies for barley, amaranth and lupin seeds observed similar trend. Capacity constant for long variety increased significantly (p > 0.05) as temperature rises from 35 to 65 °C while no significant changes occurred for short
variety. Besides, moisture bearing capacity of short variety was not significantly (p < 0.05) higher than the long ones. The increase in capacity constant observed could be because the water bearing cells in the fruits expands with temperature and thereby accommodating more moisture. Chickpea and lupin seeds have shown similar behavior [19,27]. At higher temperature (65 °C), maximum absorption capacity was attained at reduced time when compared with other temperatures which could also be related to the increase in loss of dissolvable solids with higher temperature.
3.5.
Activation energy
The result of activation energy of two varieties of Canarium Schweinfurthii engl. fruits is shown in Table 3 and the plot of ln 1/kt against (1/Tref 1/T) from which Ea was calculated is also presented in Fig. 3. The Ea of long and short varieties are low when compared with that of lupin seeds, barley and, three bean varieties (Talash, Sadri and Mahali khomein) and chickpea [27,14,26]. Meanwhile, their values are relatively similar to that of guard seed and unhulled splits and, blanched soya bean [32, 25 respectively]. Low activation energy observed revealed that the fruits are not heat sensitive meaning that heat was gained during absorption process. The Ea of long variety was higher by 17.82% than short variety meaning that the rate of absorption was faster in short than long variety. This could also mean that short variety has more pore spaces than the long variety.
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Table 3 – Thermodynamic properties of Canarium Schweifurthii engl. fruits. Varieties
Temperature °C
Ea kJ/mol
Kref
R2
DH
DS
DG
(CSHTL)
35 50 65
29.57
0.9159
0.78
25.58 25.36 25.23
222.89 225.86 227.37
94.13 98.31 102.08
(CSHTs)
35 50 65
24.30
0.8387
0.82
14.99 14.86 14.74
220.13 223.09 224.61
82.79 86.92 90.66
DH (kJ); DS (J/K); DG (kJ/K).
65 °C respectively. This observation agrees with the finding of Eugene et al. [42] for African elemi (canarium schweifurthii engl. fruits) and negates the behavior of crude protein with temperature for African walnut. The decrease could be attributed to denature characteristic of protein at temperature above 41 °C. Soaking temperature of 35 °C had the least loss of nutritive values for both short and long fruit variety, hence it provides the best reconstitution environment for better retention of the nutritive value of canarium schweifurthii engl. fruits during soaking process.
3.7.
Fig. 3 – The dependence of Peleg rate constant on Temperature (K).
3.6.
Quality of reconstituted fruits
The nutritive composition of the reconstituted canarium schweifurthii engl. fruits soaked at different temperatures as shown in Table 4 revealed that all the proximate and vitamin composition of the fruits decreased with increase in temperature (35 °C–65 °C) except carbohydrate that increased. The increase in carbohydrate with temperature could be due to destruction of the cell wall that caused increase in solubility of the carbohydrate (Reid et al. [41]). Temperature and variety had no significant different (p < 0.05) on the changes in the nutritive values of the reconstituted fruits especially when compared with control. For instance, crude protein for both short and long variety decreased by 7.98%, 19.61% and 29.01% and, 10.78%, 21.76% and 27.94% at 35 °C, 50 °C and
Quality of residual water
Total dissolve solids (TDS) and acidity level of the soaking medium during soaking process of Canarium Schweinfurthii engl. fruits increased by 24.45% and 43.35% and, from 4.77 to 6.21 and 4.97 to 6.66 pH for long and short varieties respectively, Table 2. These show the level of loss of soluble constituents of the fruit which reduce the quality of the soaked product. Loss of soluble solids during soaking process for barley, wheat and rice grains have been reported by Montanuci et al. [14], Maskan [37] and Marcelo et al. [43] respectively. This result is attributed to the dependence of cations and anions production on temperature [44]. Among the temperatures studied, 35 °C had the least TDS and highest pH values indicating that at lower temperature, the level of loss of soluble solids of soaked product would be less and environmental friendly residual soaking water would be assured. Low pH values (acidic state) especially from by-product of postharvest processing of agricultural products encourages health hazards, material loses due to corrosion and lower agricultural production. ANOVA at 5% level of probability showed that the variety and temperature had high significant effect on total dissolved solids and pH levels, except varietal influence
Table 4 – The nutritional composition of the reconstituted fruits at different soaking temperatures. Variety
Short
Long
Temp
% Crude fibre
% Crude protein
% Crude fat
% Carbohydrate
Vitamin A (lg/g)
Vitamin B1 (lg/g)
Vitamin B2 (lg/g)
Vitamin C (lg/g)
Control 35 50 65
0.3201 0.3104 0.3002 0.2891
19.58 18.02 15.74 13.9
24.42 23.38 21.00 18.55
67.94 69.00 73.45 89.86
141.02 137.00 131.10 118.11
10.61 8.75 4.63 3.35
5.03 3.82 2.66 1.34
26.30 19.08 13.54 8.52
Control 35 50 65
0.4800 0.4698 0.4708 0.4449
20.98 17.47 15.32 14.11
24.47 23.78 22.05 19.14
40.64 41.61 46.40 51.89
188.23 181.15 162.02 141.45
13.77 12.33 9.26 5.35
5.38 5.01 3.71 2.98
28.65 23.53 17.29 10.32
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on pH. The value of TDS of Canarium Schweinfurthii engl. fruit fall within the range (<1000 mg/L; [45]) is recommended as fit for human use, Ela [46].
3.8.
Textural quality of the reconstituted fruits
The mean values of textural qualities of the reconstituted canarium schweifurthii engl fruits is presented in Table 5. From the table, the hardness of canarium schweifurthii engl fruits decreased by an average of 93.87% as moisture content increased from 11% to 66% dry basis for bot varieties when
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compared with control. [47,48,49] observed the same decrease behaviour with cucumber fruit, fig fruit and date fruits respectively. This could be due to negative influence (weaken) of water to the cell structure [50]. The observed decrease in hardness with moisture content was gradual for all the temperatures of both varieties and can be related to softening of the tissue with high moisture content. The changes in the hardness of all the temperatures for both varieties are not significant (p < 0.05) except 35 °C of long variety. This means that softening the fruits is independent of temperature. Similar trend was reported of fig fruits by [48].
Table 5 – The effect of soaking temperature on the textural quality of reconstituted Canarium Schweifurthii engl. fruits. Variety
Temperature
35 °C
50 °C Long
65 °C
35 °C
Short 50 °C
65 °C
The values with (*) are the controls.
M. C.
Hardness
Cohesion
Adhesion
Springiness
Chewiness
11.87 15.12 25.24 36.75 45.68 54.85 62.39 66.67 11.87 25.64 37.04 45.69 50.89 55.83 64.50 67.90 11.87 27.92 34.00 41.78 49.32 55.13 62.14 66.75 11.02 19.34 32.70 45.28 55.20 61.42 64.46 66.90 11.02 27.05 34.16 40.86 51.50 55.11 60.48 66.11 11.02 30.17 42.18 59.36 61.59 63.87 65.03 66.79
27.73* 19.27 9.94 4.08 2.76 1.96 1.70 1.70 27.73* 16.23 9.02 5.29 3.13 2.24 1.64 1.63 27.73* 18.86 11.42 6.48 3.57 2.15 1.79 1.77 24.65* 16.07 8.61 5.11 3.50 2.35 1.95 1.70 24.65* 13.62 11.60 8.18 4.28 3.13 2.06 1.70 24.65* 11.78 6.97 2.76 2.13 1.85 1.73 1.70
0.8367* 0.6109 0.8308 0.8230 0.5887 0.7810 0.5356 0.8535 0.5319* 0.7448 0.8391 0.8459 0.7280 0.5781 0.7773 0.5643 0.7336* 0.7741 0.6094 0.8246 0.7923 0.7075 0.8550 0.8285 0.5921* 0.5520 0.7125 0.7067 0.5318 0.6437 0.6869 0.6332 0.5921* 0.7448 0.6831 0.7280 0.8576 0.5643 0.7698 0.5881 0.5922* 0.7004 0.5928 0.6653 0.5982 0.5656 0.8514 0.6981
0.0625* 0.2355 0.2072 0.4206 0.4727 0.5509 0.6366 0.6525 0.0625* 0.3504 0.4984 0.5484 0.5846 0.6246 0.6582 0.6647 0.0625* 0.4629 0.4186 0.3482 0.4802 0.5192 0.5557 0.5596 0.0144* 0.1392 0.0548 0.2082 0.2401 0.2481 0.2072 0.4072 0.0144* 0.1298 0.5089 0.3572 0.2930 0.5419 0.3280 0.3704 0.0144* 0.0683 0.1393 0.2600 0.4015 0.6094 0.5835 0.6391
0.3739* 0.3150 0.0763 0.2366 0.1356 0.2410 0.4335 0.2009 0.3739* 0.2978 0.3208 0.4376 0.1604 0.3514 0.2900 0.3064 0.1510* 0.2616 0.3195 0.2108 0.1913 0.4100 0.3755 0.4242 0.1074* 0.2329 0.2634 0.3569 0.2897 0.2127 0.2010 0.1864 0.1474* 0.2884 0.2474 0.2185 0.3255 0.2223 0.3527 0.3334 0.1474* 0.2730 0.3502 0.2826 0.3981 0.3297 0.2545 0.3868
8.68* 3.71 0.6301 0.7945 0.2203 0.3689 0.3947 0.2915 5.52* 3.59 2.43 1.96 0.3655 0.4550 0.3697 0.2818 3.07* 3.82 2.22 1.13 0.5411 0.6237 0.5747 0.6221 1.57* 2.07 1.62 1.29 0.5392 0.3218 0.2692 0.2006 2.15* 2.93 1.96 1.30 1.19 0.3926 0.5593 0.3333 2.15* 2.25 1.45 0.5189 0.5072 0.3450 0.3749 0.4590
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The change in reduction behaviour of hardness started at 36.09%, 50.89% and 55.13% dry basis (long variety) and 61.20%, 55.11% and 61.59% dry basis (short variety) for 35 °C, 50 °C and 65 °C respectively. These points are taken as the transition moisture contents from glassy to plastic state from which no appreciable change in hardness with moisture content was recorded. The variations could be due to differences in fruits composition. The springiness of the fruits ranged from 0.2198 to 0.3692 and 0.1292 – 0.4318 (mean values) for short and long varieties respectively as temperature increased from 35 °C to 65°C. Non-linear behaviour of springiness with moisture content observed showed that the cell structure in the fruits that compresses and releases energy under off-load condition is heterogeneously distributed, and the tissue experienced damage (permanent deformation) during compression. [49] also reported similar trend for date fruit. Varietal and temperature differences of the fruits springiness are not significant (p < 0.05). The table also revealed that the chewiness of each fruit variety for the temperature range considered had non-linear relationship with moisture content. Both varieties had low mean values that ranged from 6.01 to 0.3625 and 6.01 – 0.4553 for short and long varieties respectively as temperature increased from 35 °C to 65°C. This could be attributed to low hardness, springiness and cohesive characteristics of the product. Decrease in chewiness with moisture content have also been reported for dried fig and date fruits by [48,49]. This result showed that at higher moisture content, very low energy would be required to reduce the size of canarium schweifurthii engl fruits for easy swallow or further processing. Both temperature and varietal differences had no significant (p < 0.05) difference on the chewiness of the rehydrated fruits. The cohesion characteristics of long and short varieties of canarium schweifurthii fruits differ significantly (p > 0.05) and the mean values ranged from 0.5589 to 0.8515 (36.60%) and 0.5539–0.8072 (31.38%) respectively at the temperature range of 35 °C–65°C. [51] observed 21.88% increase in cohesiveness of candy at the 1.3%3.1% moisture range. The difference between the two products could be due to structural and experimental condition differences used. Besides, soaking temperatures had no significant (p < 0.05) effect on the cohesion of both fruits. Long and short fruit varieties had cohesion values above critical point (0.5) at all level of moisture content hence, they are cohesive. Elasticity of the fruit cellular structure (cellulose and hemicellulose) could be responsible for this attribute [48,52,53]. This means that the fruits will manifest high level of deformation during chewing before rupture. Adhesion result as shown in Fig. 2a and b had negative values for all the considered temperature which could be due to high moisture and oil at the fruits interface with water. [48] observed the same trend with fig fruits while the report of [49] is on the contrary for date fruit. The oil may result from ruptured oil bearing sells due to shrinkage during drying. The erratic behaviour of adhesiveness with moisture content as seen in the figure is an indication that the surface grains of the fruits are not uniformly formed. The adhesion of 50 °C was higher than that of 35 °C and 65 °C by 6.40% and 44.52% (short variety) respectively while that of 35 °C was 19.49% and 5.12% higher than 50 °C
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393
and 65 °C respectively for long variety. Besides, the mean value for short variety was more than long variety by 34.79% (not significant, p < 0.05). This could be because of viscous attribute of the fruits and glass to plasticity transition of the fruits during soaking.
3.9.
Thermodynamic evaluation
Thermodynamic properties (enthalpy, entropy and Gibb’s free energy) of Canarium Schweinfurthii engl. fruits at a temperature range of 35–65 °C is presented in Table 3. Enthalpy which reveals the reaction heat occurring in a system under constant pressure had positive values and increase with increase in temperature for both varieties. This could be attributed to increase in rate of reaction of hydrophilic constituents of the samples with high temperature of soaking medium. This result is not in line with the findings of Montanuci et al. [14] for barley, which could be due to differences in their structural and chemical compositions. Entropy of long variety is significantly (p > 0.05) higher than the short variety. Negative values of entropy observed in all the studied temperature decreased with increase in temperature indicating that the absorption process was orderly. The negative trend could be attributed to the possible disruption of sample structure during drying [54]. Decrease in entropy with temperature increase may be due to water molecules being withheld in the micro capillaries and porous matrix of the sample [55]. Gibb’s free energy values are positive, above zero and increased as temperature increases, which means that energy was absorbed from the surrounding during water absorption process. Besides, less energy would be required for interaction of water molecules and the hydrophilic constituents of the sample. The absorbed energy is responsible for softening the water bearing cells of the fruits, aids its expansion and thereby increase the size of the fruits. This process helps in separation and digestion of the mesocarp for oil extraction. Varietal and temperature influence on enthalpy and Gibb’s energy are also highly significant (p > 0.05) except with entropy. Low activation energy and negative values of entropy indicates that the fruits are thermally stable and had less dependent on temperature. Barley cultivars have also shown the same trend [14].
4.
Conclusion
Water absorption characteristics of two varieties of Canarium Schweinfurthii engl fruits were investigated. The investigation showed that the water absorption of the fruits depends significantly (p > 0.05) on temperature and not on variety. However, absorption reaction was well orderly and not spontaneous for the two varieties. Soaking the fruits at 35 °C was the best temperature for obtaining minimum loss of the fruits soluble solids, nutritive quality of the fruits and environmental friendly residual water. The textural attributes of the reconstituted sample were independent of water soaking temperature. The Midili model was found to be the best-fitted model to describe the absorption characteristics for the two varieties of Canarium Schweinfurthii engl. fruits in all temperature tested.
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Conflict of interest We hereby submit that there is no conflict of interest over this manuscript either among the authors or the sponsors.
Acknowledgement The authors wish to thank Tertiary Education Trust Fund (TET Fund) through Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria, for all the financial support. R E F E R E N C E S
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