# Experimental Verification of Yam (_Dioscorea rotundata_) Drying with Solar Adsorption Drying
## 1 Introduction  
Yam (from the _Dioscoreaceae_ family) is a perennial tuber crop from a climbing plant. Some species (_Dioscorea_) contain toxic or bioactive chemicals, while others are cultivated for pharmaceutical purposes [1]. Yams vary in appearance between and within species, however all yams have common growth habit of thin, twinning vines and a shallow wide radiator root system. White yam ('Pona', 'Lilli' and 'Dente') tubers are long cylindrical and tapering in shape with rough scaly brown, firm exterior texture and white flesh. White yam (_Dioscorea rotundata_) is the most widely grown and preferred yam species in Ghana, especially the 'Pona' cultivar for both the domestic and export market. The other important cultivars are 'Dente' and 'Lilli'. The fresh product is eaten when boiled or fried. The cooked yam is bounded into a dough-like paste called futu is eaten with soup which is a delicacy in Ghana [2]. Fried yam involves frying after cutting yam chips in vegetable or palm oil and is usually consumed with pepper, fried fish and or stew. On the other hand, the differences in morphology, texture, functional, rheological and their effect on drying characteristics are yet to be given attention. Yam is highly perishable due to its high moisture content about 70% [3]. This makes fresh yams susceptible to microbial spoilage. This phenomenon has challenged scientists and product developers to engineer novel approaches to address the challenge. Notable among them is drying technology [4]. Solar energy which is free, abundant and safe will not only help meet the energy needs of the farmer but will also help remove potential roadblocks for processing agricultural products. Energy from the sun has been used in the drying and preservation of agricultural products for a long time. According to [PERSON] et al. [5], most agricultural surpluses are preserved using energy from the sun. [PERSON] et al. [6] reported that in developing countries over 90% of agricultural products are sun dried. Although open sun drying requires little capital and work force, it is associated with many problems and shortcomings. Besides longer drying periods and the possibility of contact with contaminants such as stones and dirt, the crops dried along roadsides stand the risk of contamination with exhaust gases from traffic or moving vehicles, which denatures their nutritional value [7]. [PERSON] et al. [8] reported that vitamin C has a high sensitivity to light and, therefore, the exposure to solar radiation increased the vitamin C loss during drying. In order to minimize or prevent the shortcomings of open-air drying, the use of dryer equipment driven by solar energy has been investigated and proven to be a better alternative. A reliable supply of energy is one of the important prerequisites for the growth of Africa's agricultural industry. Access to fossil fuels such as coal and petroleum or electricity for farm operations or crop processing is expensive and mostly unreliable, while that of fuel wood is not sustainable. Solar energy is an alternative source of energy which has an advantage over other alternative sources of energy such as wind and shale because of its abundant, inexhaustible, renewable and non-polluting nature. The method of drying affects the rate of drying and the quality of the product. Air drying in general enhances the drying rate, while direct exposure to the sun can have a deleterious effect on the quality of the dried product. Changes of vitamin C content during drying have been affected by drying time, drying air temperature and moisture content [9; 10]. Yam contains vitamin C as a bioactive compound, which has strong antioxidant activity. It plays an important role in human nutrition due to free radical scavenging activities [11; 12]. Vitamin C is degraded by irreversible oxidative reactions during air drying [13]. [PERSON] and [PERSON] [14] mentioned that a high oxygen concentration around the drying environment may lead to an increase in vitamin C degradation in the dried product.