Determination of the adsorption isotherms of two flour formulations based on plantain (Musa x paradisiaca) and cassava (Manihot esculenta) intended for the preparation of Foutou | IJAAR

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Int. J. Agron. Agri. R.IntroductionPlantain (Musa spp.) is a widely consumed product inCentral and West Africa. It makes an essentialcontribution to food security, job creation, incomediversification in rural and urban areas, grossdomestic product (GDP) and, in so doing, to the fightagainst poverty. In Ivory Coast, plantains play animportant role not only in feeding populations butalso in cropping systems (Thiémélé et al., 2017).because they allow knowing its domain of stabilityafter drying by determining the final water content.During the last two decades, a significant number ofworks have focused on the study of sorptionisotherms of food products, the influence oftemperature on isotherms and the study ofmathematical models describing sorption isotherms(Koko et al., 2018).Ivory Coast, located in West Africa, is self-sufficient inyams, cassava and plantains. In Ivory Coast, annualplantain production was 1,600,000 tonnes in 2012(FAO, 2012). It is the most consumed food crop with53.4% in urban areas and 46.6% in rural areas(BNETD, 1998). These fruits are most often used forthe preparation of certain traditional dishes such asfoutou, aloco, claclo, apiti, etc. and other foodproducts including among others protein flour. Manystudies undertaken over the past twenty years havefocused on the transformation of plantains intobaking flour, pastry flour and drinks (juice, beer andwine). In addition, formulated feeds in the form offlour or pulp are also made from plantains to expandthe field of use of this commodity (Yao et al., 2019).Despite the importance of this food in diets,producers face problems of post-harvest lossesrelated to the moisture content of the product. Toreduce losses, extend shelf life and add value to theproduct, conventional drying is adopted. It is anoperation widely used both in the agri-food industryand on an artisanal basis by farmers. This processstabilizes the product by lowering the water activity.However, very little work has been devoted todetermining the isotherms of sorption of plantainflour and cassava. And yet, this is an essential step inoptimizing the storage and drying conditions of thesefood products.In order to contribute to the reduction of post-harvestlosses of plantain in Ivory Coast by the developmentof new products, we have proposed in this work tostudy the adsorption isotherms of flour formulationsbased on plantain (musa x paradisiaca) of the Corne1and FHIA 21 varieties and cassava roots of theBonoua variety.Material and methodsPlant materialThe plant material of the present study consists offlour formulations based on two varieties of plantain(corne1 and FHIA 21) composed of green (stage 1 or2) and ripe (stage 4 or 5) fingers and cassava roots ofthe bonoua variety (Fig.1).Furthermore, to optimize the storage conditions of aproduct so as to ensure its physicochemical andmicrobiological stability, the determination ofsorption isotherms is a necessity. In addition, thestudy of sorption isotherms is a privileged means ofunderstanding the distribution of the intensity ofwater bonds, as well as its functional availability inpoorly or moderately hydrated agrifood products.These isotherms are curves which give preciseinformation on the hygroscopic balance of a productFig. 1. foutou flour made from plantain and cassava.Scale: 1 / 3cmMethodsSamplingPlantains and cassava were collected in the localitiesof Agboville, Tiassalé and Abidjan (Gonzagueville).Yao et al. Page 47
Int. J. Agron. Agri. R.Banana bunches with known maturity periods wereharvested randomly from a one hectare (1 Ha) plotassigned to each variety. The number of bananas ofthe Corne1 variety was 10 bunches and that of theFHIA 21 variety 7 bunches. That of cassava was 25tubers. These bananas and cassava roots have beentransformed into flour.For each sample of foutou flour, the requiredproportions of plantain and cassava cosettes areweighed. The various weighed chips are then mixedand then crushed with a hammer mill. The mixture ofcrushed chips is ground with a miller (forplex,France) containing a 50 μm sieve to obtain the flour.Determination and modeling of absorptionisothermal curves of different composite flours forconservationThe FC2 (60% ripe banana + 40% cassava) and FH2(60% ripe banana + 40% cassava) flour formulationsrespectively for the Corne1 and FHIA 21 varieties, themost appreciated by the panelists for each cultivarresulting from the sensory analyzes been used for thedetermination of the experimental adsorption isothermcurves. These absorption curves were modeled by theGAB equation (Guggenheim, Anderson and de Boer).All the measurements were repeated twice and theexperiment was performed once.Preparation of saturated saline solutionsSaturated saline solutions are prepared by addingdifferent salts to 100 mL of distilled water withstirring using a magnetic stirrer (Selecta, Spain) witha bar magnet until supersaturation. Each solution isplaced inside a tightly closed jar for 48 hours to fixthe expected relative humidity before placing thesamples (Garcia-Pérez et al., 2008). The differentsaturated saline solutions set the respective relativehumidities from 0.11 to 0.90. So, LiCl (aw = 0.11),MgCl2 (aw = 0.32), K2CO3 (aw = 0.43), Ca(NO3)2 (aw =0.56), SrCl (aw = 0.69), NaCl (aw = 0.75), KCl (aw =0.85), BaCl2 (aw = 0.90) (Greenspan, 1977). Theverification of these relative humidities (RH) is madewith the thermohygrometer which indicates therelative humidity and the temperature inside the jar.For the water activity of 0 desiccants (silica gels) areused. The jars are exposed to the ambienttemperature of 28.2 ± 1.3°C.Determination of experimental absorptionisothermal curvesThe method used for determining the adsorptioncurves is the static gravimetric method or themicroclimate method (Lang et al., 1981). This methodwas recommended by the European COST 90 projectgroup using desiccators or jars (Wolf et al., 1985). Itconsists of determining the kinetics of water uptakeand determining the maximum adsorption capacity ofeach sample as a function of the different equilibriumrelative humidities (RH). Therefore, the torque (HR,X) constitutes a point of the sorption isotherm. Thegraphic representation of the sorption isotherm curveis made up on the abscissa of the different aw or RHequilibrium of saturated saline solutions and on theordinate the water content (X) in grams (g) of waterper 100 g of dry matter.Modeling of absorption isotherms of differentsamplesThe most widely used model of GAB (Guggenheim,Anderson and de Boer) with a large area of validity isused in this study. This model is one of the besttheoretical models for the characterization of foodsorption curves. It is used and accepted in foodtechnology by most researchers (Ferradji et al., 2008a & b). This model is used in this study because it hasa wide range of validity where the relative humidity isbetween 10 to 95% (Tonon et al., 2009). The GABequation looks like this (Labuza et al., 1985 andOluwamukomi, 2009) :X =X0 × C ×K × aw(1-K × aw) (1- K × aw + C × K × aw) (1)X = equilibrium water contentX0 = water content of the monolayeraw = water activityC and K are the constants of the GAB model.Smoothing assessment criteriaThe applicability of this model was assessed by thecriteria of the correlation coefficient (R), the meansquare error (MSE) and the relative mean error ofdeviation (RMED).Yao et al. Page 48
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Determination of the adsorption isotherms of two flour formulations based on plantain (Musa x paradisiaca) and cassava (Manihot esculenta) intended for the preparation of Foutou | IJAAR

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