Low‐temperature drying characteristics of mint leaves in a continuous‐dehumidified air drying system

Abstract

Low‐temperature drying seems a better alternative option for drying heat labile products, especially leafy vegetables. In this article, the thin layer drying characteristics of mint leaves are studied using a continuous‐dehumidified air produced by molecular sieve 13X based heatless pressure swing adsorption (PSA) system. The PSA system consists of an air compressor with after cooler, two adsorber towers, and drying chamber. The optimum process parameters of adsorption system are identified through Box Wilson Central Composite experimental design to produce continuous‐dehumidified air suitable for low‐temperature drying applications ranging from 35 to 37°C dry bulb temperature and 0.1% rh. The performance indices of the PSA system such as thermal effectiveness and dehumidification efficiency at optimal conditions are observed as 0.884 and 96.40%, respectively. The effect of the volume flow rate of continuous‐dehumidified air on mint leaves drying characteristics is also studied, and the initial moisture content of leaves is reduced from 83.45% (wb) to less than 10% (wb) in 6 hr at the volume flow rate of 0.160 m3/min. The effective moisture diffusivity value for varied volume flow rates of air is varying from 2.07534 × 10−11 to 3.45817 × 10−11 m2/s. The ascorbic acid retention percentage in dried mint leaves is increased with increase in volume flow rate of dehumidified air, and the maximum of 70.11% is achieved at 0.160 m3/min. Based on the regression analysis, the most suitable drying model to describe the low‐temperature drying characteristics of mint leaves is the Midilli and Kucuk model. It is noted that the low‐temperature drying is the most appropriate drying method for retaining the good amount of ascorbic acid. Practical applications Highly suitable for heat‐sensitive products' drying especially medicinal herbs, spicy (leafy) vegetables. Production of continuous‐dehumidified air (with ultra‐low dew point) for sensitive applications like pharmaceutical, lithium battery manufacturing, defense, chemicals, electronics, leather, and so forth.

Multi‐objective optimization of drying conditions for the Olea europaea L. leaves with NSGA‐II

“…Very high and low hot air temperatures are not desirable. Because, in very hot temperatures, leaves can be hardened and burned, color loss occurred, and contrary to this in low temperatures increased enzyme activity can resulted decomposition and the need of more time arises for drying (Ataei et al, 2014;Dwivedy, 2012;Jeni et al, 2010;Venkatachalam et al, 2020). Therefore, optimum hot air input temperature needs to be selected carefully for the behalf of quality.…”

Parametric study on pressure-based packed bed adsorption system for air dehumidification

“…Apart from these initial design parameter assumptions, the adsorption uptake rate of adsorbate by the adsorbent in the system mainly depends on the operational parameters namely, (i) absolute feed air pressure, (ii) Feed air linear velocity, and (iii) purge air flow rate percent. [33][34][35][36] The first important parameter that influences the performance of the pressure-based adsorption system is absolute feed air pressure. The system is developed to produce product dry air to the lowest possible dew point, and it also must be able to supply the required product airflow rate from the system with allowable pressure drop as needed for the application.…”

Review on low‐temperature heat pump drying applications in food industry: Cooling with dehumidification drying method

“…Costa and others (Costa et al, 2016) have found that the drying operation of microalgae using a heat pump (30-50 C) can Goh et al (2011) Green sweet pepper 30 to 40 India Pal, Khan, and Mohanty (2008) Red pepper −3 to 20 Thailand Prasertsan and Saen-saby (1998) Red pepper −3 to 20 Norway Alves-Filho, Eikevik, Mulet, Garau, and Rossello (2007) Rice 30.8 Mexico Best, Cruz, Gutierrez, and Soto (1996) -Filho (2002) Pet food Bovine intestine −10 to 25 Norway Senadeera et al (2013) retain bioactive compounds (phyco-cyanin) in the dried product (nutritional supplement) because of the regulated conditions (temperature and humidity). Most recent research studies on drying mint leaves through low-temperature (30-37 C) had shown that this method had retained the ascorbic acid content in the dried product (Venkatachalam et al, 2020). Moringa (M. olifera) leaves which are higher in nutrients and phytochemicals have been dried using a heat pump dryer at 40-50 C (Potisate et al, 2014;Rathnayake, Navaratne, & Uthpala, 2019 an efficient, eco-friendly method to obtain high-quality pet food products (bovine intestine) at a lower cost (Senadeera et al, 2013).…”

“…Costa and others (Costa et al, 2016) have found that the drying operation of microalgae using a heat pump (30–50°C) can retain bioactive compounds (phyco‐cyanin) in the dried product (nutritional supplement) because of the regulated conditions (temperature and humidity). Most recent research studies on drying mint leaves through low‐temperature (30–37°C) had shown that this method had retained the ascorbic acid content in the dried product (Venkatachalam et al, 2020). Moringa ( M. olifera ) leaves which are higher in nutrients and phytochemicals have been dried using a heat pump dryer at 40–50°C (Potisate et al, 2014; Rathnayake, Navaratne, & Uthpala, 2019).…”