Taro Leaves Drying Kinetics and Monolayer Moisture Content

cocoyam Leaves Drying Kinetics and Monolayer Moisture Content portal 1A study on the drying kinetics and monolayer wet field of dalo leavesThis research was aimed to progress dehydrated harvest-feasts institute on Taro leaves and finding out the effect of drying parameters such as loading parsimony and temperature on that control the drying kinetics. To determine the end point of drying studies on the sorption is oppositem was conducted. From the moisture sorption isotherm info, the monolayer moisture study was estimated by Braunauer-Emmett-Teller ( estimate) comparison using info up to a peeing bodily function (aw) of 0.52 and monolayer moisture depicted object was found to be 8.92 g irrigate per 100 g solid for taro leaves. By using another more or less more or less-valuable model, rumormonger (Guggenheim-Anderson-DeBoer) model, using data up to aw=0.9, the monolayer moisture issue of taro leaves was found to be 19.78g piddle per 100 gm solid.INTRODUCTI ONIt is estimated that by 2020, the population of Bangladesh impart be as high as 200 million, which means that there is a need to produce more pabulum from the limited land resources. In this context, there is a need to explore alternate fodder crops, which could proviso solid food in food insecurity situations. Taro brook be the alternative to the other veggies for developing and down the stairs developed state. Apart from performing as cheap energy and dietetic source, this crop pull up stakess other microsolid foods, vitamins and dietary fiber as good.In Bangladesh, taro is apply as vegetable throughout the country. Corms and cormels ar used as starchy vegetables whereas leaves and leaf stalks atomic number 18 used as shak. During famine, a large number of people reportedly survive simply on food materials made by boiling the corms, cormels, stolons, leaf stalks and leaves of different varieties of Taro.The subfamily Colocasioideae of family Araceae consists of th ree edible tubercrops, that is to say taro (Colocasia esculenta Schott), tannia (Xanthosoma spp.) and giant Taro (Alocasia spp.). Among these crops, taro and tannin atomic number 18 polite to a larger extent, while giant taro is not as common as commercial crop like the other two. In general, these argon crops of third world countries, particularly grown in Africa and Asia. roughly 88 % of the total world acreage is in Africa which produces roughly 80% of total production (Onwueme, 1978). Among the three crops, taro is more common in South-East Asia. It is oneness of the ancient crops with an interesting history blending with the phylogeny of agricultural systems (Gopalan et al., 1974).A large number of horticultural varieties of taro are widely cultivated in Bangladesh and still larger varieties grow wild. During the wet season when other vegetables are in scarcity in Bangladesh this taro goes a long way to meet the demand for vegetables. The leaves, petioles, stolons, cor ms and cormels, and indeed altogether the parts of some taro are taken as food in large quantities by the countrified population in our country. wherefore the use of Taro as vegetables, both leaves and roots, in the diets of the people of our country assumes special and added importance.The taro has also medicinal value. Processed Bishknchu is used in Ayurvedic medicine for the treatment of rheumatism. Juice from petioles and whole leaves are used as antiseptic to check bleeding from minor injury in the rural areas of Bangladesh (Chowdhury, 1975).The possibility of wider use of the Taro leaves as vegetables crops in our country whitethorn be ascribed to their unusual environmental adaptability and ease of cultivation. The lowland types grow in standing peeing which is rarely possible for other crops. The taro brook be produced with minimum capital investment. Growing of this crop does not rent any special technological skill. Their keeping quality in roughly cases is excelle nt.The best way of preserving the leasfy vegetables is drying or dehydration. This process costs less, then other preserving methods and require simple instrument. The type and conditions of the blanching treatment prior to drying affect the natural rubberkeeping of ascorbic acid, carotene, and ash in the dried vegetables. The sun-dried vegetables had inferior color, texture and acceptableness compared to the vegetables dried in the cabinet dryer.In the windup(prenominal) dryer, desired temperature and airflow could be maintained. Compared to sun/solar drying, higher(prenominal) airflow and temperature can be used in mechanical drying. This leads to high production rates and ameliorate quality products due to shorter drying time and reduction of the risk of insect plague and microbial spoilage as well as minimum nutrient impairment. Since mechanical drying is not dependent on sunlight so it can be done as and when necessary.Based on the above information, the insert experime nt was broadly aimed to study on development of shelf invariable taro (Colocassia esculenta) leaves product. The specific objectives of this study are as followsTo determine the stem of fresh and processed Taro leavesTo develop the isothermTo study the drying characteristics of taro leaves during mechanical and vacuum dryingTo study the reposition stability of processed taro leavesMaterials and methods3.2.3 Sorption isotherm studiesThe moisture sorption properties of dried Taro leaves were determined at room temperature under conditions of conglomerate relative humidity (11-93% RH) in the vacuum desiccators. The discordant RH conditions were achieved in vacuum desiccators using hard saltiness solutions.The following salt solutions (Table. 3.1) of cognize water natural process were used for the study (Islam, 1980).Table 3.1 Water activeness of saturated salt solutionPetri dishes were used for preparing saturated salt solution. The various salts were put in the Petri dish an d water is added to give a saturated condition. The method involved putting a small accurately weighed about 1g essay in a previously weighed Petri dish into desiccators contained saturated salt solutions. The try and the solution was separated a perforated plate to rid of mixing. The desiccators were evacuated to less than 50 Torr. At various intervals, the vacuum was broken with air, the sample weighed and replaced in the desiccators, which was then re-evacuated. The sample was weighed daily in the initial compass point and less often, as the sample started to reach equilibrium. Weighing was continued until the sample weights were changeless two days in row.In the mid-1970s, water activity came to the forefront as a major factor in catch the control of the deterioration of reduced moisture, drugs and biological systems (Labuza, 1975). It was found that the general modes of deterioration, namely physical and physico chemic modifications, microbiological growth, and both aqueo us and lipid phase chemical reactions were all influenced by the thermodynamic availability of water (water activity) as well as the total moisture field of study of the system.Control of initial moisture field of study and moisture migration is critical to the quality and safety of foods. Ideally, food manufacturers develop products with defined moisture sums to produce a safe product with optimum shelf- life. Quality and safety factors that the manufacturer must consider are microbial stability, physical properties, sensory properties, and the rate of chemical changes leading to loss of shelf-life. Water activity or the equilibrium relative humidity of a system is defined asWhere Vapor pressure of water in equilibrium with the dry system Saturation vapor pressure of keen water at the same temperature.Sorption properties of floods (equilibrium moisture subject and monolayer moisture) are internal for the design and optimization of umpteen processes such as drying, packaging and memory board (Muhtaseb et al., 2002).The moisture sorption isotherms show the equilibrium amount of water sorbed onto a solid as a function of steady state vapor pressure at a constant quantity temperature (Bell and Labuza, 2000).There are many empirical pars that describe this behavior, but the water sorption properties at various RHs should be observationally determined for each material. The general shape of the isotherm, specific bulge area of the sample, reversibility of moisture uptake, presence and shape of a hysteresis loop provide information on the manner of interaction of the solid with water (Swaminathan and Kildsig, 2001).Sorption properties are important in predicting the physical state of materials at various conditions, because most structural transformations and phase transitions are significantly affected by water (Roos, 1995).Langmuir (1917) developed an equating based on the theory that the whits of gas are adsorbed on the active sites of the solid to f orm a layer one molecule thick (monolayer).The Brunauer-Emmett-Teller ( count) sorption model (Brunauer et al.1938) is often used in example water sorption particularly to obtain the monolayer value (Eq. 2.10) which gives the amount of water that is competent to form a layer of water molecules of the thickness of one molecule on the adsorbing surface (Bell and Labuza 2000, Roos, 1995).The BET monolayer value has been said to be best water content for stability of low-moisture materials (Labuza, 1975 and Roos, 1995). The BET comparability was developed based on the fact that sorption occurs in two distinct thermodynamic states a tightly bound portion and multilayer having the properties of bulk free water (Zografi and Kontny, 1986). The BET equation isWhere, = the measured moisture at water activity = the monolayer moisture content (the optimal moisture content for maximum storage stability of a dry food)c = the isotherm temperature dependence coefficient (energy constant)Vanchy (2002) determined the moisture sorption isotherm of unit milk powder (WMP). The WMPs were stored at 20 and 35C under 11%, 22% and 33% relative humidity . The monolayer moisture content was 4.8%, (solids not fat basis) at 0. 11 using the BET equation and 5.1 % at 0.23 according to the chin-wag equation.Nikolay et al. (2005) determined the moisture equilibrium data (adsorption and desorption) of semi-defatted (fat 10.6 % wet basis) pumpkin seed flour using the static hydrometric method of saturated salt solutions at three temperatures 10C, 25C, and 40C, found that the equilibrium moisture content decreased with the increment in storage temperature at any given water activity. They fitted the data-based data to five mathematical models (modified Oswin, modified Halsey, modified Chung-Host, modified Henderson and GAB).The GAB model was found to be the most suitable for describing the sorption data. The monolayer moisture content was estimated using the Brunauer-Emmett-Teller (BET) equation. The BET model (Brunauer et al. 1938) gives the best fit to the data at aw of up to 0.5 (Bell and Labuza 2000, Roos 1995).Guggenheim-Anderson-de Boer (GAB) sorption model (Anderson 1946, Boer 1953, Guggenheim 1966) introduces a third state of sorbed species mean(a) to the tightly bound and free states. The GAB equation has a quasi(prenominal) form to BET, but has an extra constant, K (equation 2.11). BET is actually a special case of GAB.The GAB equation isIsotherm equations are useful for predicting the water sorption properties of a material, but no equation gives results accurate throughout the accurate cranial orbit of water activities. According to Timmermann (2003), the GAB monolayer value is always higher than the BET monolayer value. Prediction of water sorption is needed to establish water activity and water content relationship for materials (Roos, 1995)Wherem = the measured moisture at water activity= the monolayer moisture content (the optimal moisture conte nt for maximum storage stability of a dry food),=the GAB multi-layer constantc=the isotherm temperature dependence coefficient (energy constant).The GAB model can be used to a maximum water activity of 0.9. The following procedure is suggested by Biozt (1983) to fit data on water activities and equilibrium moisture content. compare (2.11) can be transformed as followsWhereEquation (2.12) demonstrates that GAB equation is a three-parameter model. The water activity and equilibrium moisture content engagement are regressed using equation (2.12) and determine of three coefficients, and are obtained. From these coefficients, the values of k,, and c can be calculated.To overcome this weakness of the GAB equation, modifications of the equation have been proposed (Schuchmann et al. 1990 Timmermann and Chirife 1991). Timmermann and Chirife (1991) used one additional parameter in the GAB model and studied the so-called third stage of sorption using experimental data of starch with satis factory results.Isotherm equations are useful for predicting the water sorption properties of a material, but no equation gives results accurate throughout the entire range of water activities. According to Timmermann (2003), the GAB monolayer value is always higher than the BET monolayer value. Prediction of water sorption is needed to establish water activity and water content relationship for materials (Roos, 1995).Results and discussionThe sorption isotherm is an extremely valuable tool for food scientist because it can be used to predict potential changes in food stability, for selection of packaging, for selection of ingredient and for predicting drying time. A sorption isotherm for dehydrated taro leaves obtained by Vacuum oven drying (VOD) was established to determine how the taro product will perform in a confined environment. To obtain the moisture sorption isotherm, moisture content (dry basis) versus water activity were plotted on li come near graph stem ( encounter 4.1 ).The results shown in experience 4.1 (tabulated data given in Appendix-II, Table 2.1), indicate that samples absorb little water particularly at lower aw (Figure 4.1 Graphical presentation of sorption isotherm of TaroThe water sorption isotherm of taro follows the shape of the sigmoid type isotherm. The resultant curve is caused by the combination of colligative effects (physical properties of solution), capillary effects, and surface-water interactions (Bell and Labuza, 2000). A distinct knee usually indicates a formation of a well-defined monolayer.The monolayer moisture content was estimated using the Brunauer-Emmett-Teller (BET) equation. The BET equation is an quotation of the Langmuir relationship that accounts for multilayer coverage.BET equation was used (eq. 2.10) to calculate monolayer moisture content (mo) and energy constant (C). mo represents the optimal moisture for maximum storage stability in the dry state. Results obtained from BET equation are shown in Table 4 .2.Table 4.2 Data for BET and GAB methodsFrom the slope and break of BET equation (Appendix II, Figure 2.1), monolayer moisture content and energy constant of taro leaves calculated for VOD samples. The monolayer moisture content of taro leaves was found to be 8.92g water per 100 g solid (Table 4.2). The calculated monolayer moisture content are greater than those found by Islam (1980) who reported 5.5 for potato gash and 6 for potato powder and by Kamruzzaman (2005) who reported 7.52 for aroids.Another important model of sorption isotherm behavior stated by GAB (Guggenheim-Anderson-DeBoer) in equation 2.11 and 2.12 to determine the monolayer moisture content of food products. This is very important for safe level of storage of food.Dry foods are usually considered to be most stable to chemical reactions if their moisture content is at or near the BET monolayer (Labuza et al., 1970). Usually air dried products are dried to moisture content corresponding to aw 0.6 (Nickerson and Si nskey, 1977).From this study it is seen that VOD taro leaves give 25% (Figure 4.1) moisture content at 0.6 aw. From this standpoint, freeze dried products are considered best for sorption studies (Islam, 1980). It may be mentioned here that the current study was concerned with adsorption isotherm so as to avoid risk due to hysteresis effect. At same moisture content adsorption path gives higher water activity than desorption path. consequently product dried to safe aw level according to adsorption isotherm will be even safer when it follows desorption path.After fitting data (Appendix II) the following auspicate was developed and from the developed equation the monolayer moisture content of taro leaves were found for GAB model.Fig. 4.2 Graphical presentation of GAB model of sorption isothermFrom the developed Figure (4.2) and equation (4.1) the coefficients found, and were -0.121, 0.114 and -0.003 respectively (Table 4.2). Taking k= 0.9 and found the monolayer moisture content 1 9.78gm water per 100 gm solid. It is shown that the standard GAB equation is becoming to describe experimental data for water activity values up to 0.90 but fails to adequately describe the experimental data when data in the range of aw 0.9-1.0 are included in the calculation.