Natural sun drying is one of the most common ways to preserve agricultural product. the most purpose in drying farm manufacture is to reduce its water activity from the harvest level to the safe storage level in order to increase its shelf life. Once the product has been dried, its rate of deterioration because of respiration, insects, and microbial activity and biochemical reactions should diminish resulting in maintenance of quality of the stored product. It does improve bargaining position of the farmer to keep up comparatively constant value of his product. Drying reduces post-harvest losses and transportation prices since most of the water are taken out from the product throughout the drying method. In India, sun drying is the most typically used technique to dry the agricultural material like grains, fruits and vegetables. In sun drying, the garlic is spread in a very skinny layer on the bottom and exposed on to solar radiation, ambient temperature, wind velocity, relative humidity, initial moisture content, absorptive, exposure time and mass of product per unit exposed area.
Garlic is a bulbous perennial vegetable spice. The bulb is composed of pungent bolblets, commonly known as cloves. Garlic is a semi-perishable product. Due to lack of suitable storage and transportation facilities, about 30% of fresh crop is wasted by respiration and microbial spoilage. At times of shortages, India imports garlic of Chinese origin from Taiwan or via Nepal. Fresh garlic, dehydrated garlic flakes, dehydrated garlic powder and garlic oil is exported from India. India was once a leader in this field but is losing out to China in the overseas market. China has an edge over India in terms of both quality and quantity.
Food drying is one of the oldest methods of preserving food for later use. Food drying is a very simple, ancient skill. It is one of the most accessible and hence the most widespread processing technology. Sun drying of fruits and vegetables is still practiced largely unchanged from ancient times. Traditional sun drying takes place by storing the product under direct sunlight. Sun drying is only possible in areas where, in an average year, the weather allows foods to be dried immediately after harvest. The main advantages of sun drying are low capital and operating costs and the fact that little expertise is required. The main disadvantages of this method are as follows: contamination, theft or damage by birds, rats or insects; slow or intermittent drying and no protection from rain or dew that wets the product, encourages mould growth and may result in a relatively high final moisture content; low and variable quality of products due to over-or under drying; large areas of land needed for the shallow layers of food; laborious since the crop must be turned, moved if it rains; direct exposure to sunlight reduces the quality (colour and vitamin content) of some fruits and vegetables. Moreover, since sun drying depends on uncontrolled factors, production of uniform and standard products is not expected. The quality of sun dried foods can be improved by reducing the size of pieces to achieve faster drying and by drying on raised platforms, covered with cloth or netting to protect against insects and animals. In open sun drying, there is a considerable loss due to various reasons such as rodents, birds, insects and microorganisms. The unexpected rain or storm further worsens the situation. Further, over drying, insufficient drying, contamination by foreign material like dust dirt, insects, and micro-organism as well discolouring by UV radiation are characteristic for open sun drying. In general, open sun drying does not fulfil the quality standards and therefore it cannot be sold in the international market.
The major quality issues faced throughout garlic drying loss of flavour, discoloration and poor rehydration characteristics of the dried garlics. Garlic flavour and colour are usually perceived as important quality attributes. In drying, diffusivity is employed to indicate the flow of moisture from the material. in the filling rate amount of drying moisture removed is controlled mainly by molecular diffusion. Diffusivity is influenced by shrinkage, case hardening throughout drying, moisture content and temperature of the material.
Methods of Drying:
Hot air drying
Hot-air drying of garlic slices in a common fixed bed method is unfortunately not suitable due to a significant decrease in the quality of dried product related to the fresh one. Applying high temperature (about 60°C) in a fixed bed drying causes an increase in drying period, energy consumption, color degradation and mass transfer.
Solar and Open sun drying
Recent efforts to enhance on sun drying have led to solar drying. Solar drying additionally uses the sun because the heat source. A foil surface within the dehydrator helps to extend the temperature. Ventilation speeds up the drying time. Shorter drying times reduce the risks of food spoilage or mold growth. it’s a complex operation involving heat and mass transfer which can cause changes in product quality. Physical changes which will occur include shrinkage, puffing and crystallization.
Infra-Red drying
Microwave and infrared (IR) drying are studied for achieving quick drying and reducing quality loss of fruits and vegetables. a mixture of hot air and microwave drying of osmotic dehydrated blueberries had similar or higher product quality compared with freeze-dried product with a lot of reduced drying time.
Fluidized bed drying
Thin layer drying properties of high moisture garlic sheets under semi fluidized and fluidized bed conditions with high initial moisture content (about 154.26% d.b.) were studied. Air temperatures of 50, 60, 70 and 80°C were applied to garlic samples. Among the applied models, Page model was the best to predict the thin layer drying behavior of garlic sheets.
Dried garlic Products
Garlic Powder: In Asian country thanks to lack of appropriate storage, transport and process facilities, significant losses are incurred both in terms of quality and quantity thanks to respiration, transpiration and microbiological spoilage. Through garlic is made abundantly and consumed as such, little efforts have so far been made to supply dehydrated garlic and garlic powder.
Conclusion
To obtain the dehydrated product of prime quality, the drying method should be specified it allows effective retention of colour appearance, flavour, taste and nutritive value, comparable to recent vegetables. The technique of drying is perhaps the oldest technique of food preservation practiced by human race for the extension of food period. The utilization of artificial drying to preserve agricultural commodities is increasing, making a requirement for a lot of fast drying techniques and ways that reduce the big quantity of energy needed in drying processes. Just in case of garlic is an antioxidant product used for many medicative purposes. New and innovation techniques that increase drying rates and enhance dried garlic quality are receiving substantial attention.
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