The Indian gooseberry, also known as Amla (Emblica Officinalis), is a significant fruit crop widely cultivated in various regions of the Indian subcontinent. Belonging to the family Euphorbiaceae, the Amla tree is native to tropical Southeast Asia, particularly Central or Southern India, Pakistan, Bangladesh, Sri Lanka, and Southern China. Amla is an excellent source of vitamin C and pectin and is a vital component of the popular Ayurvedic preparation, 'Triphala.' It inhibits platelet aggregation and lowers cholesterol levels, functioning as a tonic with hematinic and lipolytic properties that are useful in treating scurvy and jaundice. Additionally, Amla prevents indigestion, controls acidity, and is a natural anti-aging agent that increases all-around immunity against heart and nervous disorders. However, Amla fruits are highly perishable, and their storage in atmospheric conditions after harvesting is limited to the months between October and January.

Drying is one of the traditional methods of preserving food products such as fruits, vegetables, fish, grains, meats and other agricultural products. It involves removing moisture from the food by applying heat energy either through electrical sources or the sun. The rate of drying depends upon two different parameters such as external parameters (solar radiation, ambient temperature, wind velocity, and relative humidity) and internal parameters (initial moisture content, type of crop, crop absorptivity, and mass of product per unit exposed). Therefore, various drying technologies have been utilized for drying Amla, such as those shown in Figure 1.

Open Sun Drying is one of the most adopted drying practices across the country. The practice is mostly adopted by the villagers, farmers and every household due to its simplicity and small capital investment. In the process, the cut Amla is kept on a tray made of locally available materials and kept for sun drying. This practice usually takes 5-7 days for the Amla to dry. However, there are a lot many hurdles one has to face while drying due to uncertainties caused by rain and cloudiness, engagement of one person to control drying conditions and contamination of dust, and stones brought by the speedy wind. And also, it requires large areas for the proper spreading of the Amla apart from its long duration drying time. Therefore, sometimes, in such drying practices, there is an incidence of pests, and insects and hence suffers microbial degradation.

Cabinet Tray Drying (CTD)
CTD is a technique that can be adopted by farmers and also shows better techniques than Open Sun Drying. In this technique, a control setup is made consisting of a tray, and cabinet in the control temperature using an electrical supplier. The parameters such as moisture, rate of drying, time, moisture evaporation, etc. are controlled in the system. Because of this, CTD has been adopted vastly by the scientific community and also the technology has been transferred to some parts of the country for drying Amla.

Solar Tunnel Drying (STD)
STD follows the principles of the greenhouse effect in which tunnel-type chambers are used for drying Amla. To make the insulating medium, multi-wall polycarbonate sheets are used that can absorb the heat energy and retained high temperature for a longer time.

STD helps to preserve food crops like spices crops, and Leguminacea crops (chilli, beans) apart from Amla by extending its shelf life.

In addition, the solar dryer functions as a UV filter, aiding in preserving the natural color of the products. Compared to sun-dried Amla, Amla dried in the solar tunnel dryer contains less moisture. Additionally, the use of 2% NaCl pre-treatment reduces water activity, while the most favorable rehydration ratio is observed in Amla treated with 0.1% KMS and dried in the solar tunnel dryer.

Fig 1: Drying Technologies of Amla

Solar Assisted Heat Pump Dryer (SAHPD)
It is an advanced drying method that is not commonly utilized by farmers. It necessitates the use of mechanical equipment and instruments to ensure optimal performance and high-quality results. By maintaining temperatures at 35°C for greenish-colored Amla and 45-50°C for light brownish-colored Amla, various levels of Amla quality can be achieved. Furthermore, drying Amla using this method enhances the Vitamin C content by up to 88%.

(Content shared by Moirangthem Nobinchandra Singh and Dr. Yengkhom Disco Singh, Department of Post-Harvest Technology, College of Horticulture and Forestry, Central Agricultural University, Pasighat, Arunachal Pradesh)