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DRYING TECHNOLOGY

Vol. 21, No. 1, pp. 147–163, 2003

TECHNICAL NOTE

Equilibrium Moisture Characteristics of High

Oleic Sunflower Seeds and Kernels

Estela M. Santalla1,* and Rodolfo H. Mascheroni2

1TECSE, Programa Tecnologıa de Semillas, Depto. de IngenierıaQuımica, Facultad de Ingenierıa, UNCPBA, Olavarrıa, Argentina

2Departamento de Ingenierıa Quımica, Facultad deIngenierıa—UNLP and CIDCA (UNLP—CONICET),

La Plata, Argentina

ABSTRACT

The equilibrium moisture content (EMC) characteristics of high oleic

sunflower seeds and kernels between 10 and 55�C were determined byequilibrating the samples to known relative humidities (RH) abovesaturated salt solutions. EMC of the kernels was lower than that of

seeds in the range of 11 to 96% ERH and at 25 and 40�C. Hysteresiseffect was found for the EMC properties of seeds and kernels at25�C. Four EMC–ERH models (modified Henderson, Chung-

Pfost, Halsey, and Guggenheim–Anderson–de Boer) and their

*Correspondence: Estela M. Santalla, TECSE, Programa Tecnologıa deSemillas, Depto. de Ingenierıa Quımica, Facultad de Ingenierıa, UNCPBA,

Av. del Valle 5737. B7400JWI Olavarrıa, Argentina; Fax: 54 2284 451055;E-mail: esantall@fio.unicen.edu.ar.

147

DOI: 10.1081/DRT-120017288 0737-3937 (Print); 1532-2300 (Online)

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estimated parameters were evaluated for goodness of fit. GAB andHalsey equations showed the best fitting of experimental data

although GAB equation adjusted for temperature described theEMC data the best. Components of the seed as oil content or hull/kernel ratio did not explain the slight differences in EMC found

between the varieties.

Key Words: Adsorption isotherms; Grains; Oil content; Sunflower(Helianthus annuus L.).

INTRODUCTION

High oleic sunflower constitutes a new crop to obtain oils that aremore stable and of better quality. The managing of high oleic sunflowerpost harvest process is based on studies done on traditional sunflower(oilseed type) because not much information is available on these newhybrids.

As it occurs with traditional sunflower, high oleic sunflower isharvested with higher moisture levels than those of the safe storagerange to avoid field losses due to shattering and bird damage. So, alater hot-air drying stage is unavoidable. Therefore data for high oleicsunflower components relating equilibrium relative humidity (ERH) andequilibrium moisture content (EMC) to temperature are necessary fordesigning postharvest processing and storage systems. As the dryingprocess is a significant operation to ensure the quality of seed andby-products until commercialization, it is important the availability ofdesorption property data.

The equilibrium moisture contents for the adsorption and desorptionprocesses—at the same RH and temperature—are not equal. Thedifference, called effect of hysteresis, is useful to know when effectsof humidification and drying of grains are possible. No references areavailable about this phenomenon in high oleic sunflower seeds.

It have been reported[1] that the modified Henderson[2,3] andChung–Pfost[4,5] equations are good models for starchy grains andfibrous materials while the modified Halsey[6,7] equation is a goodmodel for high oil and high protein products. Other report[8] notedthat the Halsey equation was a good model for describing EMC–ERHdata of sunflower seeds, hulls and kernels in spite of the fact that theGAB equation[9,10] gave the best fit to the experimental data at varioustemperatures. The same report informed values of EMC–ERH for

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sunflower seeds of different oil content and hull/kernel ratios and havefound that sunflower seeds with a higher hull/kernel ratio can be stored athigher moisture content than seeds with lower hull/kernel ratio, and thatthe seeds with high oil content require a longer drying time, drying air oflower relative humidity or a higher temperature to dry to the same finalmoisture content than seeds with lower oil content.

It have been informed[11] that the variety and the growing locationdifferences did affect the ERH property for some seeds as soybean (notincluded sunflower) and that the effect of drying temperature andhysteresis on EMC/ERH properties was significant for rough rice,brown rice, corn kernels and corn cobs.

The objectives of this study were: (1) to determine the EMC/ERHrelationships of high oleic sunflower seeds and kernels at four differenttemperatures, (2) to evaluate the goodness-of-fit of four of the ERHmodels recommended by ASAE Standard D245.5,[12] and to estimatethe parameters for the description of EMC/ERH equilibrium, and (3)to determine the differences between this grain and other sunflowervarieties.

EXPERIMENTAL PROCEDURE

Trisum 568 (Mycoyen-Morgan), a striated high oleic genotype ofsunflower (Helianthus annuus L.) was selected to carry out this study.Ten bulk samples, each consisting of 5 kg of seed were procured from1998/99 harvest from Oriente, Coronel Dorrego, Argentina, after 80 daysof physiological maturity stage. The seeds were cleaned manually forforeign matter, broken and immature seeds. Whole kernels and hullwere both obtained using a centrifugal machine to get higher ratio ofdehulled sample and by later manual separation of kernels from hulls.Seeds and kernels were packed separately in double-layered low-densitypolyethylene bags, sealed, and stored at low temperature (5�C). Theinitial moisture contents (percent, dry basis) were 2.6 and 3.1 for theadsorption process and 27.3 and 30.1 for the desorption process forseed and kernels, respectively. Subsamples of seeds and kernels wereobtained for adsorption process by storing samples at 10�C in a lowhumidity chamber for several weeks until low moisture content wasattained. For the desorption process the samples were obtained byadding calculated amount of distilled water, spraying it on the grainsheld in a solid mixer and by periodically mixing the contents during48 h. After this rewetting method the sub-samples were sealed in separate

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polyethylene bags. The sub-samples were kept at low temperature in arefrigerator to avoid the growth of micro-organisms. Before startinga test, the amount of sub-sample was taken out of the refrigerator andwas allowed to warm up to room temperature. The moisture content ofseeds and kernels was determined by an oven drying method.[12]

The static method with standard solutions to maintain constant vaporpressure was used to obtain equilibrium moisture content at constanttemperature.[13] Glass desiccators containing saturated salt (AR grade)solutions in the range of relative humidities between 11 and 96% werekept in temperature-controlled cabinets at 10, 25, 40, and 55�C. Thetemperature of the cabinets was controlled to an accuracy of 0.2�C.The fungal growth was avoided by adding small quantities of antifungalagent. High oleic sunflower seeds and kernels were placed on perforatedtrays above the salt solutions and weighed every third day until thechange in sample mass between two successive readings was less than0.01 g. The moisture content of the samples at this stage was defined tobe the equilibrium moisture content and was determined by the vacuumovenmethod.[14] The time for the samples to reach equilibrium varied fromone to six weeks depending on the material, relative humidity andtemperature. Triplicate determinations were made for all the conditionstested. Oil content of high oleic sunflower seed and kernel and oleiccontent of seed oil were determined by the AOCS methods[15] asdescribed previously.[16]

The procedure NonLin of Systat Statistics Software[17] was used toestimate the parameters of the proposed models and to calculatethe statistics. Residual plots and the following quantitative standardscorrelation coefficient (R2), and standard error of the estimated value(SE) are calculated as:

SE ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiPðY � Y 0Þ

2

df

sð1Þ

and mean relative percent deviation (P) calculated as:

P ¼100

N

X ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiY � Y 0

Y

rð2Þ

were used to evaluate the fit of the four models studied.Data points in a plot of residual values vs. predicted values should

tend to be a horizontal band centered around zero. If the residual plotsindicate a clear pattern, the model should not be accepted.[18]

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RESULTS AND DISCUSSION

The principal differences between high oleic seeds and traditional oneshave been reported in previous works.[19,20] The main characteristics areseed oil content 43.6%� 0.94, kernel oil content 60.13%� 0.52, hull/kernel ratio (by weight of dry matter) 0.531, and oleic acid content80.25%.

The mean values of the EMC (g water/100 g of dry matter) for seedsand kernels of high oleic sunflower at different temperatures and relativehumidities are given in Table 1.

Table 1. Mean equilibrium moisture content (g H2O/100 g dry matter of higholeic sunflower seeds and kernels) equilibrated at relative humidities in the range

of 11 to 96% at 10, 25, 40 and 55�C.

Temperature (�C)

10 25 40 55

Mean Mean Mean Mean

ERH EMC SDa ERH EMC SD ERH EMC SD ERH EMC SD

Seeds11.2 2.11 0.06 11.2 1.98 0.02 11.2 1.42 0.26 11.0 1.37 0.2635.0 5.19 0.39 33.2 4.15 0.13 32.1 2.91 0.31 31.4 2.61 0.41

57.0 6.70 0.09 53.5 5.90 0.09 49.0 4.17 0.50 45.0 3.72 0.2062.0 7.28 0.11 57.8 6.38 0.41 53.7 4.69 0.25 52.0 4.23 0.6867.0 8.10 0.37 64.3 7.08 0.89 61.8 5.83 0.15 59.0 4.85 0.46

75.6 9.33 0.22 75.5 8.42 0.11 75.4 6.93 0.42 74.7 6.40 0.1787.0 13.03 0.17 84.0 11.69 0.17 82.0 9.22 0.28 81.0 8.18 0.0295.5 23.81 0.22 92.0 20.46 0.95 87.9 19.67 0.41 85.0 14.21 0.81

Kernels11.2 2.32 0.12 11.2 2.19 0.25 11.2 1.88 0.09 11.0 1.777 0.29

35.0 4.03 0.26 33.2 2.45 0.42 32.1 2.09 0.16 31.4 2.063 0.1457.0 5.02 0.12 53.5 3.76 0.29 49.0 3.58 0.09 45.0 2.815 0.3862.0 6.23 0.07 57.8 4.39 0.59 53.7 3.73 0.99 52.0 3.460 0.37

67.0 6.71 0.12 64.3 5.12 0.43 61.8 4.01 0.21 59.0 3.937 0.2775.6 7.35 0.11 75.5 6.61 0.21 75.4 6.35 0.09 74.7 5.827 0.5087.0 11.48 1.34 84.0 8.54 0.16 82.0 9.48 0.39 81.0 7.057 0.0995.5 21.72 1.11 92.0 14.30 0.72 87.9 14.32 0.66 85.0 14.17 1.88

aStandard deviation of EMC.

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The seeds equilibrated at 10 and 25�C at relative humidities lower than23% and those equilibrated at 40 and 55�C at a relative humidity lowerthan 34% reached equilibrium by desorption, whereas at higher relativehumidities equilibrium was attained by adsorption. In the same way,kernels equilibrated by desorption at relative humidities lower than35–49%. As adsorption theory predicts, the amount of sorbed water ata given relative humidity decreased as the temperature increased (Fig. 1).

The values of equilibrium moisture content obtained for high oleicseeds were compared with those of traditional sunflower seeds of differentoil content and hull/kernel ratio.[8] The maximum difference in the datapoints for different oil content and hull/kernel ratio was 3.4% of EMC ata similar RH environment. The lower differences were detected betweenhigh oleic seeds (present study) and sunflower hybrids of higher oilcontent (and lower hull/kernel ratio). Agreement among data was goodexcept for the range above 80% RH. Considering the differences in H/Kratio, the EMC values from the present study resulted lower (except athigh RH values) than the trend showed for sunflower seed oil[8] (Fig. 2).

EMC of kernels of high oleic sunflower resulted lower than that ofseeds (Fig. 3) according with their higher oil content, as had beenreported previously.[8]

A hysteresis phenomenonwas observed when seeds of low or high initialmoisture content were equilibrated with saturated salt solutions at 25�C(Fig. 3). The behavior was accentuated for relative humidity rangingbetween 60 and 90%. In kernels this phenomenon was relevant only at

Figure 1. Equilibrium moisture content of high oleic sunflower seeds in the rangebetween 10 and 55�C and relative humidities ranging between 0.11 and 0.96.

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relative humidities over 75%. To adequately take into account this effectwe suggest to consider the use of specific constants in the sorptionisotherms, according to the adsorption or desorption process.

Four sorption isotherm models were used for the analysis ofthe EMC–ERH data for sunflower seeds and kernels (Table 2).

Figure 2. Equilibrium moisture content of seeds with different oil contents andhull/kernel ratios (given in parentheses). White and black symbols represent EMCvalues at 25�C and 55�C, respectively. Cross-lined circles represent the data from

the present study.

Figure 3. Hysteresis phenomenon at 25�C in seeds and kernels.

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As have been reported,[1] modified Halsey equation is a good model fordescribing EMC–ERH data for high oil and high protein products,as occurs with sunflower seeds. It has been reported[10] that there is aconsensus of the superiority of the Guggenheim–Anderson–de Boer(GAB) equation for the prediction of the water activity of food materials.This was verified for different foods.[21–23] Modified Henderson,Chung–Pfost and Halsey equations are three-parameter equationsand the parameters of the GAB equation may each be a function oftemperature. Therefore, direct statistical comparison of the GABequation with the other three ones was not possible. The coefficientsfor each equation were determined using the Nonlin model of Systat.The equations were compared using the standard error of the parameterestimate (SE), the relative percent error (P), residual plots, and thecorrected regression coefficient of the adjusted model (R2).

Figure 4 shows the experimental data at 25�C for high oleic sunflowerseeds and the predicted equilibrium moisture contents calculated usingthe four equations. The coefficients, the standard error of the equilibriummoisture content, the corrected regression coefficient of the adjustmentmodel, the mean relative percentage deviation and the residual plots ofthe modified Henderson, modified Chung–Pfost, and Halsey equationsare given in Table 3. Halsey equation resulted in a better adjustment ofthe experimental data for seeds and kernels according to the lower valuesobtained of the standard error of EMC and the mean relative percenterror, the higher regression coefficient of the adjustment model and therandom distribution of the residual plots.

The coefficients, standard deviation and mean relative percent error ofGAB equation are shown in Table 4 for each temperature. As can be seenthe percentage of water content corresponding to saturation of allprimary adsorption sites by one water molecule (A) decreased whentemperature increased. These values resulted lower than those reportedpreviously.[8]

Table 2. EMC–ERH relationships used to analyze EMC–ERH data of high

oleic sunflower seeds and kernels.

Modified Henderson equation[2,3]: 1�RH¼ exp[�A (TþC)MB]Modified Chung–Pfost equation[4,5]: RH¼ exp[�A/(TþC)exp(�B M/100)]Modified Halsey equation[6,7]: RH¼ exp[�exp(AþB T) M�C]

Guggenheim–Anderson–de Boer(GAB) equations[9,10]:

M¼ABCRH/[(1�BRH)(1�BRHþB C RH)]

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Figure 4. Equilibrium moisture content of high oleic sunflower seeds andpredicted values obtained using modified Henderson, Chung–Pfost, Halsey andGAB equations at 25�C.

Table 3. Coefficients of modified Henderson, Chung–Pfost, and Halseyequations for Trisum 568 seedsa and kernels.a

Seeds Kernels

Coefficient Henderson Chung–Pfost Halsey Henderson Chung–Pfost Halsey

A 0.000449 236.19032 2.180812 0.000380 267.514147 1.637428

B 0.897153 19.746799 0.000201 0.843200 23.88945 0.002006

C 388.6192 85.493196 1.606955 633.6807 100.979042 1.524335

SE of

moistureb1.69 2.17 1.63 1.38 1.96 1.17

Pc 10.8 10.7 8.2 11.8 4.39 4.0

R2 d 0.907 0.846 0.914 0.915 0.829 0.939

Residual plot Pattern Pattern Random Pattern Pattern Random

aEquilibrated at 11 to 96% relative humidity and at 10, 25, 40, and 55�C.bStandard error of the estimate parameter.cMean relative percent error.dCorrected regression coefficient of the adjustment model.

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From the analysis of Tables 3 and 4, Halsey and GAB equationsshowed the better adjustment of experimental data. Individual plots foreach temperature for seed and kernel evidenced a superior adjustment ofGAB equation at higher temperatures as shown in Fig. 5.

Based on the superiority of the adjustment of GAB equation respectmodified Halsey one for experimental data, a further improvement is toconsider the effect of temperature on the monolayer water content.

In this respect, Table 4 reveals a decrease of the monolayer moisturecontent with temperature while parameter B remained nearly constant(similar behavior was reported for corn grains[21]) and C did not showany tendency. Regressions of A vs. T (absolute) showed that an expo-nential function was the most adequate to describe this dependence:

A ¼ A0 exp ðA1=TÞ ð3Þ

By combining Eq. (3) into original GAB expression, a new four param-eters equation was obtained:

M ¼ A0 exp ðA1=TÞBCRH=½ð1� BRHÞ ð1� BRHþ BCRHÞ ð4Þ

Table 4. Coefficients of the GAB equation for high oleic sunflower hybrid seeds

and kernels.

Temperature (�C)

Coefficient 10 25 40 55

Seeds

A 3.005901 2.637182 1.590777 1.585509B 0.912894 0.944769 1.043148 1.032622C 37.31369 40.13100 0.776057� 1014 373.816229SE of moisture 1.12 0.775 1.11 1.03

P 0.06 0.41 4.35 2.66R2 corr 0.972 0.982 0.962 0.925Residual plot Random Random Random Random

KernelsA 2.302176 1.877123 1.094142 1.266925

B 0.934888 0.942955 1.095722 1.060605C 0.2251� 1014 0.1186� 1015 0.55691� 1015 0.2489� 1015

SE of moisture 0.79 0.44 1.86 1.19

P 1.649 0.115 0.145 9.60R2 corr 0.983 0.989 0.964 0.894Residual plot Random Random Pattern Random

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Equation (4) was adjusted to the whole pool of data of EMC and ERHvs. T for seed and kernel. The new fitting is shown in Table 5, where it canbe observed the higher accuracy of the adjustment respect Halseyequation (the values of standard error of EMC and mean relativepercent deviation resulted lower and the correlation coefficient resultedhigher).

Figure 5. Adjustment of experimental data with GAB and modified Halsey

equations for seed and kernel at 10, 25, 40, and 55�C.(continued)

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CONCLUSIONS

The EMC–ERH relationships of high oleic sunflower seeds andkernels were determined by the standard salt solution technique andfitted to four sorption models.

Among the equations with three temperature-independent parameters,the Halsey equation was found to be the most accurate to predict EMCfor high oleic sunflower seeds and kernels.

Figure 5. Continued.

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Guggenheim–Anderson–de Boer (GAB) predicted with slightsuperiority the EMC for high oleic seeds and kernels, specially whenthe monolayer moisture content was adjusted for temperature.

Equilibrium moisture content of the kernels was lower than that ofseeds in accordance with its higher oil content. Lower values of EMCwere found for seeds and kernels at higher temperatures. Hysteresis

Figure 5. Continued.(continued)

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phenomenon was detected at 25�C in seeds and kernels at relativehumidities higher than 60%.

No differences were observed with respect to previous results onsunflower seeds and kernels, except that at relative humidities between66 and 87% the equilibrium moisture contents obtained from the presentstudy resulted lower than those reported for other sunflower seeds.Differences in seed oil content and hull/kernel ratio did not explain the

Figure 5. Continued.

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differences in the equilibrium moisture content values (lower than 3.4%)found between varieties.

NOMENCLATURE

A, B, C, A0, A1 ConstantsM Water content, percent dry basis (kg water/kg dry

seed)RH Equilibrium relative humidity (decimal)T �CY Measured equilibrium moisture content, percent

dry basis (kg water/kg dry seed)Y Equilibrium moisture content predicted by an

equation, percent dry basis (kg water/kg dry seed)N Number of data points, dimensionlessdf Degrees of freedom of the regression model,

dimensionlessSD Standard deviation

REFERENCES

1. Chen, C.; Morey, R.V. Comparison of four EMC-ERH equations.Transactions of the ASAE 1989, 32 (3), 983–990.

2. Henderson, S.M. A basic concept of equilibrium moisture.Agricultural Engineering 1952, 2, 29–32.

Table 5. Coefficients and statistical parameters for the four-parametermodified GAB equation for whole seeds and kernels.

Coefficient Seeds Kernels

A0 1.8741 1.8735A1 114.653 27.364

B 0.9309 0.9470C 13.2049 49.094SE of moisture 1.49 1.19

P 3.21 4.56R2 0.977 0.978Residual plot random random

EMC of High Oleic Sunflower Seeds and Kernels 161

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3. Thompson, T.L.; Peart, R.M.; Forst, G.H. Mathematical simula-tion of corn drying—a new model. Transactions of the ASAE 1968,24 (3), 582–586.

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