Though the processed food industry in India has grown by leaps and bounds, it is still a long way from achieving its full potential. Taking into account the growing demand for food, India will soon require a strong food industry, which calls for added vigour in food science and technology. The pressing need will be concerted effort to transfer modern food technology to small and medium-sized enterprises (SMEs). In this regard, the cultivation of highly nutritious food products such as mushrooms, which are in high demand, can be a great investment opportunity for the rural farming population. However, mushroom cultivation is a technically sophisticated farming process which further extends to complex mushroom processing and preservation techniques.



Mushroom Production
Mushroom farming is practised in more than 100 countries and production is increasing at the rate of 7 per cent per annum. The production of mushrooms in the world has already crossed 5 million metric tonne annually and is expected to reach around 7 million metric tonne in the next ten years. India is known worldwide for its exotic mushrooms, with total mushroom production in excess of 48,000 tonne. Punjab alone produces 20–25 per cent of the total production in India.

There are around 38,000 mushroom varieties known to exist but only 100 of these are edible. The variety which is exported in dried form, i.e. morel (Morchella) or black mushrooms (Morchella spp) commonly known as ‘Guchhi’ are collected as wild growth from the coniferous forests of Himachal Pradesh, Jammu and Kashmir, and Uttar Pradesh. The most acceptable varieties among the cultivated types are Agaricus Bisporus., Auricularia spp., Flemulina Velutipes., Lentinus edodes, Tramella spp., Volvariella spp., Plerotus spp.

The Food and Agriculture Organisation (FAO) has recognised mushrooms as a food. Mushrooms contribute protein nutrition to countries which depend largely on cereals as food staples. In addition, folic acid and vitamin B12, which are absent in most vegetables, are present in mushrooms. Mushrooms are praised and priced for their characteristic meaty texture and flavour. Mushroom cultivation is now a big industry in the industrialised countries of the west. However, quality starts declining soon after harvesting, rendering the produce unsalable. There is considerable export potential for mushrooms, and climatic conditions in various states offer congenial environments for cultivation, if modern technology is adopted. Hence, the development of appropriate storage and processing technology in order to extend the marketability and availability of mushrooms—in fresh or processed form—is of great significance. Drying, canning and freezing are the accepted methods of mushroom preservation. Drying, being cheaper, can be employed on a commercial scale.

Mushroom Processing
Freshly harvested mushrooms are highly perishable because of their high moisture content, metabolism and susceptibility to enzymatic browning (which develops very fast around the bruised portions caused during handling). Due to their high respiration rate, there is a build-up of temperature, which adversely affects the delicate flavour principles in mushrooms, ultimately resulting in a short post-harvest life. There is also grey colour formation due to polyphenoloxidase enzymes which are quite active in mushrooms. Hence, the preservation and processing of mushrooms has received considerable attention over the years. Freshly harvested mushrooms should be immediately processed by any of the following techniques.
• Short-term storage
• Long-term storage

Short-term Storage
The shelf life of mushrooms may vary from one day to two weeks at 1–4°C. Low temperature is effective in short-term preservation because it retards the growth of microorganisms. It helps in reducing the rate of post-harvest metabolic activities of the mushroom tissues, and also minimises moisture loss.

For example, straw mushrooms, a species widely cultivated for food across Asia, may be packed in wooden cases and transported by road, rail or sea. The case is divided into three compartments: ice is placed in the central compartment and the mushrooms are packed in the two other sections. The mushrooms may also be packed in bamboo baskets and transported by airfreight. An aeration channel is formed at the centre of the basket, and dry ice, wrapped in paper, is placed above the mushrooms.

Storage of straw mushrooms in a closed plastic box with 95 per cent carbon dioxide accelerates deterioration even at 15–20°C, the temperature range most suitable for their storage under normal circumstances. On the other hand, mushrooms stored in a perforated plastic box at 10–15°C have excellent keeping quality for up to four days and the loss of moisture is less than 5 per cent. When straw mushrooms are stored at 3°C, under similar conditions, the veils are fully open and vegetative mycelias develop after only two days. In closed bags, liquefaction and microbial spoilage may occur rapidly.

Straw mushrooms can be stored more effectively at the button stage than at any other stage. At temperatures below 10°C, however, the mushrooms liquefy rapidly, irrespective of type of packaging and stage of development (button or umbrella stage) due to the injury caused by chilling.



Long-term Storage
Canning, pickling, and drying processes are employed for long-term storage. These processes are not always suitable for all types of mushrooms. The quality of the finishedproduct is rarely comparable with that of fresh mushrooms.

Canning: Canning is the most common process for preserving mushrooms, particularly Agaricus mushrooms. Canning is divided into six basic operations—cleaning, blanching, canning, sterilisation, cooling, labelling and packing.

Trimming the stems immediately after harvest can reduce browning and blemishing of Agaricus. If the mushrooms are not canned immediately before processing then, refrigeration at 15°C along with high relative humidity (RH) will help in retaining colour and texture. Soaking for 30 minutes prior to canning may increase canning yield and at this stage, an appropriate level of sodium metabisulphite or ascorbate is incorporated for colour retention. The mushrooms are then rinsed and blanched for 2 minutes to reduce the activity of enzymes. After blanching, the mushrooms are placed in cans containing 2.5 per cent sodium chloride and 0.25–0.5 per cent citric acid. The cans are then sealed and sterilised. Sterilisation methods vary according to the type of equipment used. The most commonly used method is the batch process. In this process, the cans are placed in an autoclave and sterilised for an hour at 120–10°C.

Drying
In India, dehydration of mushrooms is preformed directly under the sun. The products available in the market are often of sub-standard quality, or contaminated with sand, or are highly discolored. On the other hand, dried mushrooms are convenient for long-term storage and transportation. Mushrooms preserved by drying have a good flavour and the drying prevents deterioration. The moisture content of fresh mushrooms varies in the range of 70–90 per cent depending upon the harvest time and the environmental conditions, while that of dried mushrooms is about 10–13 per cent.

Mushrooms can be dried by sun drying and thermal power drying. For general drying, the picked mushrooms are cut off at the basal part of the stalk, arranged in single layers on shelves and exposed to sun or placed within a drying oven. Usually about two to four days under continuous daily sunlight is adequate for sun drying. The process of thermal power drying begins at a relatively low temperature. Mushrooms grown during sunny days are dried at an initial temperature of 35°C while mushrooms grown during damp days are dried at an initial temperature of 30°C. In addition to preserving the product, drying enhances the flavour and appearance of the mushrooms.

Dried mushrooms are highly hygroscopic and are apt to absorb moisture from the air Thus, they should be properly stored. If the moisture content of mushrooms reaches about 20 per cent, insects and mould will infest the mushrooms. The gloss of the cap surface may also fade along with development of a white powdery surface, and the gills may turn brownish from their original yellowish white. The dried mushrooms should therefore, be put into polyethylene bags, sealed, and kept in a dry, cool, and dark place. For prolonged storage, mushrooms should be packed in cartons or wooden boxes and kept at 2–5°C in a low temperature store.

Use of Chemicals
Some work has been done at the Central Food Technological Research Institute (CFTRI), Mysore, on this aspect of the preservation of mushrooms. It is reported that fresh mushrooms may be possible to preserve for about 10 days at room temperature by steeping in a solution containing 2.5 per cent common salt, 0.2 per cent citric acid, 0.1 per cent ascorbic acid, 0.1 per cent sodium bicarbonate and 0.1 per cent potassium metabisulphite. The blanched mushrooms and steeped solution of (1:2) are put into clean glass containers, which are covered with lids and sealed with paraffin wax and stored at room temperature (21–28°C). This method of preservation can be used in places where facilities for canning, freezing and dehydration do not exist.

Exploring Potential
Not only does food processing in India lag far behind the rates in developed countries but is much less than developing countries like Philippines and China where value addition is 45 per cent and 23 per cent, respectively as compared to only 7 per cent in India. Linked with the issue of fostering relationship between processor and farmer is the need to develop varieties of foods that are suitable for processing. The food processing sector has tremendous potential to promote direct and indirect employment.

The food markets in most developed economies are currently in the middle of a revolution. In general, many households today devote a large percentage of their consumer outlay on the pre-cooked and pre-packed foods, generally known as ‘convenience foods’. The share of convenience foods in a family’s total food intake is bound to increase further as households look for more nutritious foods and greater variety. Other factors which are accelerating the demand for pre-packed off-the-shelf foods include a shift in eating habits, rising personal incomes, women’s desire to spend less time in the kitchen, the growing sophistication of consumer taste and marked advances in food technology.

At the consumption end, there are two upward forces which will have a bearing on the demand for processed products. First, rural households tend to catch up with their urban counterparts in the corresponding consumer expenditure groups. Secondly, the bottom consumer expenditure group in the rural or the urban sector will tend to catch up with the adjoining higher expenditure group in its own strata till it reaches almost the same levels of consumption as the top expenditure groups. With these two factors pulling the demand for processed items, there exists a scope for a substantially large food market.

Nevertheless, the conversion of increased demand for convenience foods into an effective marketing opportunity will depend upon the weakening of several deterrents in this area. High excise duty or state taxes such as sales tax deter the growth of the market for packaged foods. Also, packaging materials are either not available or too expensive in relation to the value of the content and overall retail price. The excessive reliance on homemade foods in India is in part conditioned by a lack of trust in the quality of pre-cooked and prepacked food products available in the market. This distrust arises either from some unpleasant individual past experience or a general distrust of all foods processed by unknown persons or from inputs of unknown quality. In short, the quality of packaged foods is, as yet, not taken for granted.

In this context, producers must realise that merely producing mushrooms is of no use unless these are properly preserved, keeping in view the export objectives and domestic market demands. Mushroom production has increased manifold during the recent past And mushrooms have found a definite place in the food consumption habits of common masses. It is now up to farmers and food technologists to create and satisfy the demand for mushrooms throughout the year.

Bhupinder K is Senior Food Technologist, Department of Food Science and Technology, Punjab Agricultural University. Ibitwar BB is Senior Food Technologist, Department of Food Science and Technology, Punjab Agricultural University.