Moisture Sorption Isotherms and Isotherm Model Performance Evaluation for Food and Agricultural Products

Moisture sorption characteristics of agricultural and food products play important roles in such technological processes as drying, handling, packaging, storage, mixing, freeze-drying and other processes that require the prediction of food stability, shelf life, glass transition and estimation of drying time and texture and prevention of deteriorative reactions. They are useful in the computation of thermodynamic energies of moisture in the products. An understanding of moisture sorption phenomena in products, moisture sorption isotherm (MSI) determination techniques and moisture sorption isotherm model evaluation procedures would be useful in the development or selection, modeling and controlling as well as optimization of appropriate processes to make for enhanced efficiency. The phenomena addressed in this chapter are equilibrium moisture content (EMC)-water activity (aw) relationships and MSI types, temperature influence on isotherms and occurrence of moisture sorption hysteresis. MSI measurement techniques highlighted are the gravimetric, vapor pressure manometric (VPM), hygrometric and inverse gas chromatographic and the use of AquaLab equipment. Commonly used moisture sorption isotherm models (BET, GAB, modified GAB, Hailwood-Horrobin, modified Hailwood-Horrobin, modified Halsey, modified Henderson, modified Chung-Pfost and modified Oswin) were selected, and their evaluation procedures using moisture sorption data were outlined. Static gravimetric technique involving the use of saturated salt solution appears to be the most widely used and recommended method of determining the EMC of agricultural and food products. Most of the MSI models can be fitted to moisture sorption data thorough linearization by logarithmic transformation, while others can be solved using such expression as second-order polynomial. Model goodness of fit can be determined using standard (SE) error of estimate, coefficient of determination (R2), mean relative percentage deviation (P) and fraction explained variation (FEV). The acceptance of a model depends on the nature of its residual plots. A model is considered acceptable if the residual plots show uniform scatter around the horizontal value of zero showing no systemic tendency towards a clear pattern. A model is better than another model if it has lower SE, lower P, higher R2 and higher FEV. Although it appears as if a generalized MSI model is yet to exist, it is recommended that the Ngoddy-Bakker-Arkema (NBA) model should be given thorough going and extensive testing on the MSI of different categories of food as it could prove true to its generalized model posture due to the fundamental nature of its derivation

Effects of heating temperature and time on some mechanical properties of Balanites Aegyptiaca nut

Balanites aegyptiaca nuts were pretreated by heating at different temperatures in the range of 30 – 90oC for time durations in the range of 30 – 120 mins. Moisture content of the nuts prior to pretreatment was 4.7 % (d.b.). Some strength properties of the pretreated nuts namely, bioyield, yield and rupture points; bioyield, compressive and rupture strengths; and moduli of elasticity, resilience, stiffness and toughness were determined at lateral and longitudinal axial loading, using a Universal Testing Machine (UTM). Results showed that all the strength properties of the nut decreased with increase in temperature and varied significantly with heating time at different loading orientations. Temperature and heating time range existed within which the nuts exhibited the typical behavior of biomaterials when heated and subjected to compression. After these ranges were exceeded, the nuts’ behavior deviated.         The study suggests that in addition to conditioning balanites aegyptiaca nuts to a moisture level at which they could easily be cracked, further treatment by exposure to heat at a level and for a duration that would not compromise product quality, could be used to enhance energy efficiency. Loading along the longitudinal axis should be applied if the cracking of nut is to be carried out using uniaxial compression

Effect of Moisture Content on some Engineering Properties of African Mahogany (Afzelia Africana) Seed

Some engineering properties of Afzelia africana, namely axial dimensions, one thousand seed mass, surface area, particle density, bulk density, porosity, angle of repose, static and kinetic coefficients of friction, coefficient of restitution and specific heat were determined as a function of moisture content in the moisture range of 6.1 – 32.3% (d.b). Results showed that in the above moisture range, major, intermediate and minor axial dimensions of the seed increased from 25.4 – 26.2mm, 13.2 – 13.95mm and 10.2 – 11.2mm, respectively. One thousand seed mass, surface area, particle density, porosity, angle of repose, static coefficient of friction, kinetic coefficient of friction and specific heat capacity of the seeds all increased with increase in moisture content. Seed bulk density decreased with increase in moisture content and coefficient of restitution decreased as drop height and moisture content increased. The relationship existing between the engineering properties and seed moisture content, established using regression analysis showed high coefficient of determination. These properties would be useful in the design of Afzelia africana seed handling, storage and processing equipment

Moisture dependent physical properties of Detarium microcarpum seed

Physical properties of Detarium microcarpum seed were investigated as a function of moisture content with a view to exploring the possibility of developing its bulk handling and processing equipment. In the moisture range of 8.2%–28.5% (d.b.), the major, intermediate and the minor axes increased from 2.95–3.21 cm, 1.85–2.61 cm, and 0.40–1.21 cm respectively. The arithmetic mean, geometric mean and equivalent sphere effective diameters determined at the same moisture level were significantly different from each other with the arithmetic mean diameter being of the highest value. The seed can be described as an irregularly shaped spherical disc. In the above moisture range, the surface area, one thousand seed weight, particle density and porosity increased linearly with moisture content from 354.62-433.19 cm2, 3.184-3.737kg, 1060-1316 kg/m3 and 30% to 53.1% respectively, while bulk density decreased with increase in moisture content from 647.6-617.2 kg/m3. Angle of repose increased linearly with moisture content from 13.9o-28.4o. Static and kinetic coefficients of friction increased linearly with moisture content and varied with structural surface. Highest value of static coefficient of friction at each moisture level in the above range was on galvanized steel sheet, while the lowest value was on fiber glass. For the kinetic coefficient of friction, the highest values were on Hessian bag material, while the lowest values were on fiber glass

Effect of Moisture Content and Grain Variety on Frictional Properties and Specific Heat Capacity of Acha (Fonio) Grains

There are many varieties of acha, but the most prominent two are white acha (Digitaria exilis) and brown acha (Digitaria iburua). This study was undertaken to determine the static coefficient of friction, kinetic coefficient of friction and specific heat of the grains as influenced by moisture content. The moisture levels considered were 5, 11, 23 and 28% db for the white variety and 5, 9, 21 and 30% db. The study revealed that increase in moisture content resulted to increase in the value of the properties considered for both varieties, with the white acha showing the highest values. Static coefficient of friction increased linearly with moisture content and had maximum values of 0.49 - 0.62 for the brown variety and 0.52-0.66 for the white variety all on steel sheet, while the minimum values for both varieties were on glass surface. Kinetic coefficient of friction increased linearly with moisture content and the highest value was obtained on hessian bag material (0.62-0.66) with the least being on steel sheet (0.58-0.64) for the two acha grain varieties. The study further revealed that, specific heat capacity of acha grains increased with increase in moisture content from 2.93 – 11.29 kJ/kgK (5 – 28% db) for the white variety and from 2.33 – 13.88 kJ/kgK (5 – 30% db) for brown variety. This study concludes that variety and changes in moisture content significantly affected the determined properties of acha

Effect of moisture content and impact energy on the cracking of conophor nut

The cracking of conophor nut using an impact test apparatus was carried out at different moisture contents (14.9% - 50.3% (d.b.)) and impact energy levels (0.05 - 0.19J) under lateral and longitudinal loading orientations, in order to explore the possibility of developing an effective and appropriate technology equipment for cracking the nut.  The data obtained on the quantity of fully cracked nuts with unbroken kernels, fully cracked nuts with broken kernels, partially cracked and uncracked nuts were subjected to statistical analysis.  Results showed that moisture content, impact energy and loading orientation as well as their interactions significantly affected the crackability of conophor nut at 1% level of significance.  The moisture content at which a combination of high whole kernel yield and minimum kernel damage was obtained ranged from 14.9% to 31.9% (d.b.).  The impact energy range of 0.05 to 0.11 J gave the best combination of high whole kernel yield and minimum kernel damage at both lateral and longitudinal orientations.  The study shows that the development of a spinning disc cracker, which uses impact to crack conophor nut is possible.  It suggests that the radius and speed of the spinning disc should be such that would ensure that the impact energy generated and imparted on the nuts will not exceed 0.11J and nuts should be conditioned to the dry basis moisture content that does not exceed 31.9% (d.b.) prior to cracking for optimum efficiency. Keywords: crackability, impact energy, moisture content, conophor nut, kernel, cracker, cro

Development of a Guna Seed Extractor

Guna seed extraction presents an onerous task and has been the labour and time consuming operation that militates against the large scale production and processing of this important oil crop. To overcome this problem, a guna seed extractor that works on the principle of impact from breaker arms and macerators was developed. The seed extractor consists of a hopper equipped with flow rate control device, a seed extraction unit, winnowing unit and power system. Performance tests were conducted on the seed extractor using the fruits of two varieties of guna crop namely citrullus colocynthis and citrullus lanatus in the moisture ranges of 87.21-92.45% (wb) and 85.07-89.74% (wb) respectively, obtained by varying the fruit storage duration. Result of tests and analyses showed that the performance indicators (percentage effective seed extraction, cleaning efficiency, cleaning loss, percentage seed loss at concave, material retention and percentage seed retention) were significantly affected by fruit moisture content (storage duration), material feed rate and machine speed at 1 and 5% levels. Percentage effective seed extraction and percentage seed loss at concave increased with increase in fruit moisture content, material feed rate and machine speed Maximum percentage effective seed extraction of 95.1% at the moisture content of 92.45% for the colocynthis fruit, and 96.0% at 89.74% moisture content for the lanatus, was obtained at the material feed rate of 375 kg/h and machine speed of 939 min – 1. Maximum percentage seed loss at concave was less than 5%. Cleaning efficiency, cleaning loss and material retention in the seed extraction chamber, decreased with the increase in the fruit moisture content for both varieties of guna fruits, but increased with increase in material feed rate and machine speed, while percentage seed retention decreased with increase in moisture content, material feed rate and machine speed. Maximum cleaning efficiency of 94.15% and 91.28% for the colocynthis and lanatus varieties respectively, was obtained at the material feed rate of 375 kg/h, machine speed of 939 min -1, and fruit moisture contents of 87.21% and 85.07%. Maximum cleaning loss was less than 30% and percentage seed retention was high at low fruit moisture content, material feed rate and machine speed. Practically no seed damage was recorded. Regression models that could be used to express the relationship existing between the seed extractor performance indices and fruit moisture content, material feed rate and machine speed were established for each variety of guna crop

Physicochemical properties of sorghum (sorghum bicolor l. Moench) starch as affected by drying temperature

 N. A. Aviara1, J. C. Igbeka2, L. M. Nwokocha3(1. Department of Agricultural and Environmental Resources Engineering, University of Maiduguri, Maiduguri, Nigeria;2. Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria;3. Department of Chemistry, University of Ibadan, Ibadan, Nigeria) Abstract: Starch was isolated from sorghum (white) grains and its proximate composition determined.  Scanning electron micrograph and x-ray diffraction pattern of the starch were obtained using scanning electron microscope and x-ray diffractometer, respectively.  The effect of drying temperature in a tray dryer on starch physicochemical and pasting properties was investigated.  The open air dried starch had a composition of 10.73% moisture, 0.30% ash, 1.06% protein and 1.07% fat.  Amylose content was 21.08% and it had an average granule size and pH of 18.59 μm and 5.45, respectively.  The starch exhibited the A-type crystalline diffraction pattern, which was not altered by drying in a tray dryer at the temperature range of 40 to 60℃.  Water binding capacity and swelling power of the open air dried starch were not significantly different from those of starch dried at 40℃ (p<0.05).  Water binding capacity increased from 79.63 to 88.5%, while swelling power, solubility and percentage syneresis decreased from 12.01 to 8.96 g/g, 7.08 to 2.85% and 14.00 to 10.80%, respectively as the drying temperature increased from 40 to 60oC.  Paste clarity was low (22.50%–26.20%) but increased with an increase in drying temperature up to 50℃ and decreased with a further increase in temperature.  Pasting properties of open air dried starch differed significantly from those of starch dried at different temperatures.  Peak viscosity decreased from 398.75 to 325.25 RVU as the drying temperature increased from 40 to 60℃.  Setback viscosity increased with an increase in drying temperature up to a point and decreased with a further increase in temperature.  Final and breakdown viscosities as well as pasting temperature and peak time had polynomial relationships of the third order with drying temperature.  Regression equations that could be used to adequately express the relationships existing between the physicochemical and pasting properties of sorghum starch and drying temperature were established.  These models could be used to select the drying temperature that would yield starch of desired physicochemical properties for a functional application.Keywords: sorghum starch, degree of crystallinity, physicochemical properties, pasting properties, drying temperature, tray dryer Citation: Aviara N. A, J. C. Igbeka, and L. M. Nwokocha.  Physicochemical properties of sorghum (sorghum bicolor l. Moench) starch as affected by drying temperature.  Agric Eng Int: CIGR Journal, 2010, 12(2): 85-94. &nbsp

Physical properties of four varieties of sorghum (Sorghum bicolor L. Moench) grain at different moisture contents

This study was undertaken to determine the physical properties of four varieties of sorghum grain and investigate their variation with moisture content. The properties studied include: axial dimensions, arithmetic mean and geometric mean diameters, one thousand grain weight, particle density, bulk density, porosity and angle of repose. Each property was investigated at four moisture levels in the range of 3.5-18.25% d.b (brown variety), 3.04-25.49% d.b (red variety), 3.5-20% d.b (reddish brown variety) and 3.4-25.49% d.b (white variety). The major, intermediate and minor dimensions all increased with increase in moisture content from 4.25-5.04mm, 4.10-4.76mm and 2.80-2.99mm for brown, 3.78-4.32mm, 2.96-3.43mm and 1.95-2.85mm for red, 4.25-5.21mm, 4.11-4.99mm, 3.61-3.77mm for reddish brown, 4.0-5.38mm, 3.20-4.99mm and 3.00-3.48mm for white variety. The arithmetic mean diameter had higher values for the four varieties than the geometric mean diameter. One thousand grain weight, bulk density, true density, porosity, and angle of repose of all the varieties of sorghum studied, increased linearly with increase in moisture content. Regression models with high coefficients of determination were used to express the relationship existing between the physical properties of the grains with moisture content

Effect of moisture sorption hysteresis on thermodynamic properties of two millet varieties

Application of reversible thermodynamic principles to gain fundamental understanding of food–water interactions in foods has met with limited success due to the presence of moisture sorption hysteresis which is a manifestation of irreversibility. This study was aimed at understanding the nature and extent of influence of hysteresis on thermodynamic properties of two millet varieties namely EX-BORNO and SOSAT C88. Moisture sorption data (adsorption and desorption) in the water activity and temperature ranges of 0.07 – 0.98 and 30°C – 70°C, respectively were used. Ratio of latent heat of moisture sorption to the latent heat of pure water was determined using Clausius-Clapeyron equation. Effect of moisture content on ratio of latent heat of sorption to latent heat of pure water was determined using Gallaher model. Net integral enthalpy was determined at constant spreading pressure with monolayer moisture contents calculated using Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models. Spreading pressure was determined using an analytical procedure. Gibbs equation was used to evaluate net integral entropy. Net isosteric heat of sorption and differential entropy were evaluated and used to investigate the enthalpy‐entropy compensation theory. Latent heat of moisture sorption in the two millet varieties decreased with increase in moisture content and approached latent heat of pure water at a ‘free water’ point of between 32% and 42% moisture content (d.b.) in adsorption and desorption, respectively. Desorption latent heat of moisture was higher than the adsorption values and the difference decreased with increase in moisture content. Monolayer moisture content decreased with increase in temperature, with the GAB being higher than the BET values. Desorption monolayer moisture was higher than that of adsorption. Spreading pressure increased with increase in water activity, with adsorption isotherm being higher than that of desorption and temperature having no significant effect. Net integral enthalpy decreased with increase in moisture content with effect of hysteresis being more marked in EX-BORNO than in SOSAT C88. Net integral entropy decreased with increase in moisture content to minimum values and thereafter, maintained sinusoidal trend with adsorption curve lagging behind desorption and varnishing at 18% and 16% (db) moisture content in EX-BORNO and SOSAT C88 respectively. Net isosteric heat of sorption and differential entropy decreased with increase in moisture content with effect of hysteresis being more pronounced in EX-BORNO. Moisture sorption process in the grains was found to be enthalpy driven with differential enthalpy varying linearly with differential entropy. Inequality in isokinetic and harmonic mean temperatures confirmed the enthalpy‐entropy compensation theory. Hysteresis was found to have effect on the isokinetic temperature, causing the values of desorption isokinetic temperature to be higher than the adsorption values