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Cuban Journal of Agricultural Science

Print version ISSN 0864-0408On-line version ISSN 2079-3480

Cuban J. Agric. Sci. vol.54 no.2 Mayabeque Apr.-June 2020  Epub June 01, 2020



Effect of different dehydration methods on physicochemical properties of Roystonea regia nuts

O.G. Pérez-Acosta1  *

Madeleidy Martínez-Pérez1

Laisury Díaz Mora1 

Lucía R. Sarduy García1 

Lázara Ayala González1

1Instituto de Ciencia Animal, Apartado Postal 24, San José de Las Lajas, Mayabeque, Cuba


To study the effect of different dehydration methods on physicochemical properties of Roystonea regia nuts (royal palm nuts), three treatments were established, consisting of three methods for drying seeds: in an oven at 45ºC, open air and in a solar dryer. The fresh sample constituted the control. Physical properties like sphericity, weight of 1,000 nuts, apparent and real density, as well as porosity, were studied. The content of dry matter, ash, crude protein, ether extract and fiber fractionation were determined. For the variables weight loss and bed temperature, the mixed generalized linear model was used, with repeated measurements over time. Analysis of variance was applied for analyzing physicochemical properties, according to a completely randomized design. Interaction in temperature (sampling hours x treatment) was observed, and there was no effect on weight loss. This last indicator decreased as drying time increased (0.92, 0.79, 0.64, 0.48 kg for 0, 24, 48 and 72 h, respectively, P <0.0001). There were no differences among treatments for physical properties, but there were differences regarding the fresh sample. However, crude protein, ether extract, acid detergent fiber and lignin varied. Results allowed to conclude that the dehydration method did not influence on weight loss nor on palm nuts properties. However, it was found that, out of the three studied methods, the use of solar dryer favors chemical composition of the grain.

Key words: chemical composition; dehydration; royal palm; gravimetric properties

The use of seeds in animal species of zootechnical interest, allows to fulfill a balanced diet, since they constitute a source of macro and micronutrients, necessary for optimal growth, development and animal production. After harvesting, so that the seeds do not lose their quality, it is necessary to reduce the moisture content to minimize the risk of deterioration due to fungi and mycotoxins (Sánchez et al. 2020). Physical and chemical properties of the grain and its relationship with the water content can be modified in the drying and conservation process of the seed (Ordóñez et al. 2012). Therefore, the study of these variables is essential for the proper design of the equipment required for its management, transport and storage.

Dehydration or drying is one of the oldest methods for processing and preserving food. It constitutes the main transformation that takes place in the seed after its harvest. This process requires great attention so that grain quality is not affected, since its objective is that the chemical characteristics are maintained for as long as possible during the storage period (Fernández-Gómez et al. 2019).

Drying is carried out by applying heat, specifically hot air (Espinoza 2016). Drying methods range from mechanical to thermal with hot air, natural or forced. These last include open air drying and the use of solar dryers or industrial ovens (forced air ovens), and some others (Tinoco and Ospina 2010).

Royal palm nuts are the fruit of royal palm (Roystonea regia H.B.K. Cook), which represents an important source of fiber and fat. Traditionally, it is used for animal feed (Caro et al. 2015) and inclusion levels of up to 30% in the diet have been reported in pigs (Oliva et al. 2018). However, little research has been carried out on drying methods, as well as their influence on physicochemical indicators of the grain. Therefore, the objective of this study was to analyze the effect of different dehydration methods on the physicochemical properties of royal palm nuts.

Materials and Methods

Location. The experiment was conducted at the Institute of Animal Science. During the research, records of climate variables were obtained, which were kept between 22-24 ºC minimum temperature, 32-33 ºC maximum and 65-70% of relative environmental humidity.

Study material. Royal palm nuts were obtained in Mayabeque province, Cuba. Two days after cutting the clusters, nuts were collected at random after they separated from the inflorescence. They were stored indoors, in bags, for two days until the experiment began.

Drying methods. Three methods were used: in a forced air oven at 45 ºC, open air and in a direct solar dryer.

Experimental procedure. Six trays were used for each drying method, in which the nuts were placed (2.51kg of initial weight), at a bed height of 3 cm. They were weighed on a Royal brand technical balance (± 5 g precision) before beginning the experiment, and after 24, 48 and 72 h, to determine weight loss. At these times, temperature was determined with a 100 ºC thermometer in each of the trays, inside the bed, at three different points, and they were averaged.

Humidity. It was determined in the fresh sample and after completing the experiment, according to AOAC (2019).

Weight of a thousand nuts. A total of 100 nuts were weighed on a Royal electronic scale, and then extrapolated to 1,000 grains (Kachru et al. 1994 and Vilche et al. 2003). Six experimental determinations were performed per treatment.

Geometric diameter. To determine the average dimensions of nuts, 20 units per treatment were randomly taken. Its three main dimensions were measured using a Vernier caliper, with an accuracy of 0.005 mm: length (a), width (b) and thickness (c). Mean geometric diameter (Dg) was calculated as the geometric mean of the three dimensions using the expression of Ordóñez et al. (2012):

Dg= abc1/3

Apparent density. It was calculated by the standard weight test procedure (Ghodki and Goswami 2016). For this, a 250 mL graduated test tube was used, in which royal palm nuts were dropped at a constant speed, at a height of 10 cm from its upper edge. This process was carried out until the line representing 200 mL was reached. The mass of royal palm nuts in the container was divided by the volume of the cylinder represented by the graduated test tube. Calculation was made using the following equation:




- full container mass


- empty container mass


- container volume

Real density. It was quantified by liquid pycnometer (MC-type pycnometer, 50 mL) in a 0.0001 g precision analytical balance. The equation described by Cerón Cárdenas et al. (2015) was applied:




- pycnometer mass with sample


- mass of the empty pycnometer


- pycnometer mass with the liquid


- pycnometer mass with sample and liquid


- density of the liquid

Porosity calculation. It was calculated from the values of real density and apparent density, according to Mohsenin (1970):




- porosity, %

δ apparente

- apparent density in g/mL


- real density in g/mL

Chemical composition. Content of dry matter (DM), ash, crude protein (CP) and ether extract (EE) was determined, according to the methodology of AOAC (2019). The method of van Soest et al. (1991) was used for performing fiber fractioning: neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin and hemicellulose. Six experimental determinations were made per treatment.

Statistical analysis. For data analysis, the methodology proposed by Gómez (2019) was used. Assumptions of normality of errors were demonstrated using Shapiro and Wilk (1965). Pearson correlation analysis and Mauchly (1940) sphericity analysis were applied for weight loss and temperature. These did not fit with the assumptions, so the mixed generalized linear model was used, with repeated measures over time, with the help of SAS Proc Glimmix procedure. Both variables were fitted to Gamma distribution, with logarithmic link function. Treatment, times and treatment x time interaction were considered as fixed effects, and repetitions were stated as random effect. Different variance-covariance structures were tested. The best fit for weight loss variable was composite symmetry (CS), and Toeplitz (Toep) for temperature. In the necessary cases, the comparison between means was made with the fixed range test (Kramer 1956) for P <0.05. For data processing, SAS (2013) statistical program, version 9.3, was used.

For the physicochemical variables, analysis of variance was performed, according to a completely randomized design, with four treatments and six repetitions. A tray was considered as the experimental unit. Means were compared according to Duncan (1955) for P <0.05, in the necessary cases. Data processing was performed using Infostat statistical program, according to Di Rienzo et al. (2012).

Results and Discussion

There was no significant interaction for weight loss among the studied treatments and drying time. Tables 1 and 2 show the effects separately, in which there were no differences between treatments for weight loss, while this indicator decreased with the increase of drying time. According to Tinoco and Ospina (2010), water of the sample linearly decreases, since there is a direct relationship for its extraction from the solid, according to the humidity content of the nut. The extraction speed will depend on temperature, relative humidity and air speed (Prada et al. 2019). Humidity content tends to stabilize over time. However, in this experiment, the limits were not reached for this indicator to remain constant, so further studies are required to achieve optimal storage humidity.

Table 1 Weight loss, according to drying method  

Indicator Treatments SE ± Sign
Open air Oven 45 ºC Solar dryer
Weight loss, kg 0.72 (2.05) 0.70 (2.01) 0.70 (2.01) 0.02 P = 0.6873

( ) Means fitted from link function

Table 2 Weight loss, according to drying time 

Indicator Times, h SE± Sign
0 24 48 72
Weight loss, kg 0.92a (2.51) 0.79b (2.20) 0.64c (1.89) 0.48d (1.61) 0.02 P < 0.0001

a,b,c,d Different letters in lines differ at P < 0.05 (Kramer 1956)

() Means fitted from link function

Studies carried out in Cuba on the performance of royal palm described that its flowering and fruiting occurs throughout the year. However, those that take place in the periods from April to August and from October to February are the most significant (Ly 2010). This experiment was carried out in the first period, in which, in addition, relative environmental humidity was high (67%). This could influence on results, since drying time takes longer as the air is close to saturation. According to Fernández-Gómez et al. (2019), one of the essential conditions for grain drying is the relationship between humidity content of the product and relative humidity of the air.

Regarding bed temperature, there was an interaction between drying method and sampling time. An increase in the indicator was observed with the increase of drying time in the three methods (table 3). However, the highest values ​​were with the solar dryer. Similar results were obtained by Prada et al. (2019), when drying coffee beans. According to these authors, as the temperature is higher, the kinetic energy of water molecules located on the surface of the grain increases and, as a consequence, water evaporates because it overcomes the intermolecular forces of liquid phase. In this process, it is important to pay attention to drying temperature, since it has a decisive influence on nut temperature, because, depending on its value and exposure time, it can become inadequate and negatively influence on mill quality, which affects quality grain availability and their chemical composition (Fernández-Gómez et al. 2019).

Table 3 Temperature variation, according to drying method and sampling time  

Times (h) Treatments SE ± Sign
Open air Oven 45 ºC Solar drying

  • 3.24g

  • (25.52)

  • 3.27g

  • (26.22)

  • 3.31f

  • (27.49)

  • 0.01

  • P < 0.0001


  • 3.39e

  • (29.58)

  • 3.43cd

  • (31.01)

  • 3.57a

  • (35.45)


  • 3.39de

  • (29.70)

  • 3.43cd

  • (31.00)

  • 3.51b

  • (33.55)


  • 3.45c

  • (31.61)

  • 3.42cde

  • (30.49)

  • 3.55ab

  • (34.67)

a,b,c,d,e,f,g Different letters differ at P < 0.05 (Kramer 1956)

() Means fitted from link function

Figure 1 shows the geometric diameter and weight of 1,000 nuts. There were no differences among methods. However, both indicators decrease with respect to fresh sample. Ordóñez et al. (2012) suggested that humidity content influences on these physical properties, so it was logical to observe the superiority of control regarding the rest of treatments. Values obtained in this study were in the range reported by the cited authors, who worked with hard red corn. They also coincided with Cerón Cárdenas et al. (2015), with Pisum sativum L. seeds. These results can be related to those observed in tables 1 and 2, because, although the method did not influence, drying time did, since moisture remained in the seed, and this may be the reason why differences in both indicators were not observed.

a,b Different letters differ at P < 0.05 (Duncan 1955)

Figure 1 Geometric diameter (SE ± 0.076, P = 0.0001) and weight of 1,000 nuts (SE ± 0.013, P<0.0001), according to drying method and fresh sample 

Figure 2 shows apparent and real density of royal palm nuts. Differences among treatments were only observed with respect to the fresh sample for the first indicator. Apparent density represents the weight of one hectoliter of nuts, which includes the air volume enclosed by intergranular spaces (Ordóñez et al. 2012). For this reason, fresh sample, in which the seed has a larger size and humidity, has less compaction capacity, and the indicator increases with respect to the dry sample in the different methods.

a,b Different letters differ at P < 0.05 (Duncan 1955)

Figure 2 Apparent (SE ± 0.007, P < 0.0001) and real (SE ± 0.033, P = 0.8608) density, according to drying method used and fresh sample 

There was a decrease of porosity in the fresh sample with respect to the different drying methods (figure 3). This result is related to that observed in apparent density, which, in turn, varies according to nut proportion in mass with respect to total volume, as described in the calculation equations. Likewise, since fresh nuts have higher water content, their geometric diameter is higher, so this property decreases. Asoegwu et al. (2006) observed that this process occurs in the same way in the African oil bean.

a,b Different letters differ at P < 0.05 (Duncan 1955) SE ± 1.17, P < 0.0001

Figure 3 Porosity according to the drying method used and fresh sample 

Table 4 shows the chemical composition of royal palm nuts, according to the drying method used and fresh sample. Crude protein was reduced with respect to the fresh sample in the drying at open air, with intermediate values for the solar dryer, and both did not differ from the oven at 45ºC. Values are in the range reported by Caro et al. (2015) and Arias et al. (2016), who studied the chemical composition of royal palm nuts in six western and central provinces of Cuba.

Table 4 Chemical composition of royal palm nuts, according the drying method used and fresh sample 

Indicators, % Fresh sample Oven at 45 ºC Open air Solar dryer SE ± Sign
DM 97.06a 98.77b 98.82bc 99.27c 0.15 P < 0.0001
Ashes 5.24 5.55 5.56 5.67 0.11 P= 0.0591
CP 7.76c 6.97ab 6.86a 7.18b 0.10 P < 0.0001
EE 17.06ab 15.84b 17.91a 17.43a 0.44 P=0.0214
NDF 77.78 75.66 77.04 77.23 0.61 P=0.1171
ADF 58.26a 53.32b 53.36b 55.07b 0.78 P = 0.0006
Lignin 12.71a 9.08b 8.63b 10.40b 0.58 P = 0.0003
Cellulose 44.68 42.57 43.10 42.82 0.71 P = 0.1849

a,b,c Different letters in lines differ at P < 0.05 (Duncan 1955).

Ether extract increased with the solar dryer and in open air compared to the oven at 45 ºC. Fresh sample did not differ from the rest of treatments. The superiority of this fraction with both methods shows that drying process was appropriate for the source under study, since it did not allow the volatilization of these components. Values were slightly lower than those reported by Oliva et al. (2018) (20 and 26%), which can be related to the places of origin of nuts and handling process. In the current study, nuts were used after they were separated from the branch, while these authors detached them manually, so humidity was higher.

No differences were observed among treatments for NDF and cellulose. However, there was reduction of ADF and lignin content in the drying process, compared to the fresh sample. Unlike the first two, these last components are poorly digested by monogastric animals (Dihigo et al. 2008), so the used methods are beneficial for the nutritional use of this product for feeding these species, because its composition decreases.

The chemical composition was better with the use of solar dryer regarding the rest of the dehydration methods used. At the same time, higher dry matter values ​​were achieved, which contributes to a higher nutritional quality of nuts. Adding the economic and environmental benefits described by Prada et al. (2019) for this drying method, it can be considered the best option to dehydrate royal palm nuts in an alternative production system.

The results allow to conclude that the dehydration method did not influence on weight loss or physical properties of royal palm nuts. However, out of the three studied methods, the use of a solar dryer favors the chemical composition of the grain.


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Received: February 02, 2020; Accepted: March 15, 2020

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