Solar Drying of Ivy Gourd: Inuence of Various Dipping Solutions on Activation Energy and Moisture Diffusivity

The study is aimed to enhance the shelf life of ivy gourd through solar drying method in open, forced and natural 9 convection mode. Ivy gourd is treated as primary agent to prepare medicines and the stems, leaves; flowers are used to 10 cure the diseases related diabetics, ulcer, skin. The normal shelf life is 2-3 days and it can be increased up to 6 months 11 with an effective drying process. The experiment is intended to find the best drying process among the open, natural and 12 forced convection mode with an initial dipping method with ascorbic acid, lemon juice, sugar solution, honey solutions 13 individually and a control sample (without dipping). A 3kg sample of ivy gourd is dipped in 10g/L of the each of the 14 solution and it is used for the three drying process individually. The obtained results are indicating that forced convection 15 method for ascorbic acid is best among the other drying method with highest moisture diffusivity is 7.88×10 -8 m 2 /s and 16 lowest activation energy 21.12 kJ/mol. It was observed that the drying kinetics of ivy gourd should be considered an 17 indicator of efficiency for solar drying technique from environmental safety perspective. The influence of dipping 18 solution and drying mechanisms on the functionalities of drying are discussed with suitable illustrations. 19


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The developing countries are experiencing food scarcity due to the inefficacy to preserve food supplies compared to low 24 production. The medicinal values existed in vegetables are partially using in the current situation due to inefficient and 25 uneconomical preservation process. Ivy gourd is one of the tropical vegetables which remain under treated though it 26 contains many nutraceutical properties. Solar drying is considered as one of the prominent food preservation techniques 27 for many years which can be supportive to maintain nutritional and medicinal benefits for long time. However this 28 process highly dependent on solar irradiation and it requires constant supply at longer duration. It is observed that the 29 developing countries are facing post-harvest losses due to inefficiency at utilizing solar dryers and the mode of drying.

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Vegetables and fruits are vital sources of necessary dietary nutrients but are characterized under perishable goods since their moisture content exceeds 80% (Changrue and Raghavan 2006). Storing the product dry and moisture-free are the 36 prominent ways to sustain its quality and nutrition, but a majority of such storage mechanisms need low-temperature 37 setups that require heavy maintenance. Around 20% of the world's perishable food supplies are subjected to drying in 38 order to expand their shelf storage span and enhance food quality (Grabowski, S., Marcotte, M. and Ramaswamy 39 2003). Important quality attributes associated with vegetables include their sensory appeal, drying characteristics, 40 microbial load, aroma, taste, retention of nutrients, and exclusion from pests and preservatives (Bhatta et al. 2020).

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A curtailment in the post-harvest losses of agricultural crops can majorly influence the economy of developing 42 countries positively (Chandra and Sodha 1991). About 80% of the agricultural products in countries like India are

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The adaption of solar thermal systems to preserve fruits, vegetables, and various other agricultural products is 58 proven to be a more efficient, cost-effective, and environmentally friendly approach. The solar drying technique is a 59 very clean and hygienic alternative that processes the vegetables and fruits in sanitary conditions. It occupies less area, 60 saves energy and time, and makes the process highly efficient concerning drying time and drying characteristics 61 (Funebo and Ohlsson 1998;Zhang et al. 2006). In comparison to conventional open sun drying techniques, solar drying 62 is highly advantageous since it mitigates several issues like contamination, the possibility of spoilage, lack of control, 63 and ambiguity over-drying conditions due to longer drying duration. The solar drying method is also economical, unlike 64 the widely used convective hot air dryer method which has a high fuel consumption rate and energy cost. As solar 65 energy is one of the prominent renewable energy sources and available abundantly, it is widely accepted for the 66 Page 4 of 29 dehydration of perishable food supplies. The main advantages of solar drying of agricultural crops include the 67 possibility of an early harvest, long-term storage without deterioration, and selling a better-quality product. As an added 68 advantage, it minimizes packaging requirements and reduces transport weight. 69 1.2. Pre-treatments before Solar Drying

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As reported by Sablani, changes are happening with the evaluation of quality and standards of nutrition of the 71 agricultural products after dehydration (Sablani 2006). The agricultural crops that are using solar drying should be 72 capable of retaining their various quality features which include colour, texture and nutritional values post dehydration or 73 drying. Quality enhancement is attained by different pre-treatment methods before drying. The application of appropriate 74 pre-treatments before drying enhances the quality of drying by minimizing the time required for drying, improving 75 drying attributes, and preserving energy-yielding higher-quality end products. Several pre-treatment methods are 76 available that are incorporated with the drying mechanism and blanching is considered as the most generalized method.

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Dipping treatment which involves the dipping or soaking of an agricultural product mainly in organic acids (Karapinar 78 and Gönül 1992) serves as an alternative to blanching which helps in reducing the quantity of conventional flora and 79 pathogenic species and, some of them like acetic acid reportedly mitigate the activity of enzymes responsible for

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Moisture diffusivity of the drying product should be high which in turn increases the drying rate reducing drying time.

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Whereas activation energy should be less in order to initialize the drying task with less amount of energy maintaining 102 very minimum drying time. An ideal range of moisture diffusivity lies between 10 -9 to 10 -11 m 2 /s and activation energy is 103 better to be below 35kJ/mol to have an effective drying process (Mirzaee et al. 2009).  and increases the moisture removal rate. Also, a sustainable forced convection method using a fan running with the help 114 of electricity produced by photovoltaic panels gives out forced air circulation and increases the moisture removal rate.

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The usage of concentrators results in increased air temperature inside the dryer which helps in decreasing the drying 116 time. Saxena and Gaur (2020) introduced a novel solar-assisted greenhouse type dryer integrated with an evacuated tube 117 solar collector to regulate and maintain the greenhouse conditions. It also consists of flow regulating devices, solar PV 118 modules for providing forced circulation of solar-heated water, and a drying bed with water flow arrangement. The

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The following research gaps have been identified from the cited research literature:

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(i) The influence of pretreatment of the samples on the overall drying period is not investigated.

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(ii) The pretreated drying characteristics of Ivy gourd have been not analyzed.

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(iii) Sensory appeal such as aroma, taste, color, shrinkage and texture after the drying is not estimated.

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Page 6 of 29 The current research is aimed to enhance the shelf life of ivy gourd through solar drying after pretreatment with 127 different solutions. Section-2 presents the research design, experimental setup and mathematical equations to support the 128 investigational study. Section-3 presents the obtained results and the relevant discussions performed through the 129 observation. Section-4 concludes the article by presenting the overview and future scope of the research.

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The experimental procedure starts with preparing the sample. 15 kg of fresh ivy gourd is purchased from the market.

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Washing, peeling, and slicing of ivy gourd to the required size is done. Dipping pre-treatment is performed by immersing

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The dryers were designed in a way that the heat gets trapped within the drying chamber effectively. In order to insulate 143 the setup, coconut husk and thermocol are used with the GI sheets which act as an insulating medium and prevent heat

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The process drying of food material is mostly governed by diffusion mechanism as the rate of falling period.

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Therefore, Fick's 2 nd law of diffusion is applied to find the effective moisture diffusion and is governed by (Elangovan

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Page 10 of 29 Similarly, for a natural convection dryer, the moisture content reaches the minimum value in 9hrs for control sample, 206 ascorbic acid, and lemon juice. Whereas it takes 10hrs for sugar solution and 11hrs for honey sample. For forced 207 convection dryer, the duration was less, and the moisture content was reduced to minimum value in 7hrs for control 208 sample, ascorbic acid, and lemon juice and in 8hrs for sugar solution and honey sample. It was also observed from the 209 results that forced convection dryer reduce the moisture content faster compared to other two methods. There exists a 210 non-linear relationship between moisture content and drying time since the moisture content reduces with the increase in

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The effective moisture diffusivity of the ivy gourd dipped in ascorbic acid is observed to have highest value (7.88×10 -8 233 m 2 /s) when dried under forced convection dryer (Table 1)      Page 18 of 29

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The analysis of effective moisture diffusivity of drying ivy gourd is given as:

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The uncertainty analysis during drying experiment of ivy gourd is illustrated in Table 5.

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• In open sun drying, control samples are exhibited higher moisture diffusivity whereas the ascorbic acid samples 357 shown higher moisture diffusivity and low activation energy followed by control, sugar solution, lemon juice,

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and honey samples in natural and forced convection.

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• The highest moisture diffusivity and the lowest activation energy are observed in ascorbic acid based samples 360 compared to other in three different drying processes.

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• The sensory appeal is found best in Lemon juice sample in terms of colour (darkness) and shrinkage whereas the 362 honey-dipped sample has better aroma compared to other samples.

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• It can be declared that the ascorbic acid is the best dipping solution for the pre-treatment of ivy gourd in terms of 364 drying characteristics whereas lemon juice is best choice if sensory appeals are given as priority.

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• Forced convection drying is found as best method to observed better increment in shelf life of ivy gourd. Thus, 366 solar drying of food products to be cost effective, environmentally safe and sustainable for food industries 367 Further investigation on the nutritional and physicochemical properties of the pre-treated solar dried ivy gourd samples is 368 required since the drying process and conditions significantly influence the chemical composition and nutritional values.

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The influential factors include the type of food, drying method, dipping solution, operating conditions, and storage 370 conditions. The dipping pre-treatment mainly affects the nutritional values which is out of the scope of this paper and 371 requires future work.     Moisture content of ascorbic acid sample