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Fresh catfish (Clarias gariepinus) is highly perishable. This paper aims to investigate the drying characteristics and quality of body-mass dehydrated catfish to determine the effective dehydration parameters for preservation.

Brine concentration (3-9 per cent), brining time (30-90 min) and drying temperature (90-130°C) interacted using the response surface methodology. Preliminary experiments were conducted to select treatments. Moisture content and ratio and drying rate were determined and fitted into five thin-layer drying models; the goodness of fit was evaluated by average grade ranking of the regression parameters. Proximate compositions and microbial load of dehydrated catfish were determined using standard methods.

Treatments with 110°C gave initial higher drying rate (0.034-0.043 kg H₂O/kg solid/h) and shorter drying time (20-21 h). Drying occurred at two falling rate periods. Midilli model ranked first in fitting the drying data. It explained up to 99.6-99.7 per cent of the total variations in the independent variables with low values of error terms; RMSE was 0.02131-0.01794 and χ² was 0.00037-0.00043, indicating good predictive quality. Processing parameters positively and significantly (p < 0.05) influenced the proximate compositions of dehydrated catfish. Treatment: 6 per cent brine, 90 min and 110°C presented the most effective dehydration parameters for quality preservation of body-mass catfish.

The dehydration technique used in this study could enhance nutritive quality and storage stability of body-mass dehydrated catfish that could serve as a useful and convenient tool for commercial application.

Hygienically processed dehydrated catfish of good quality could be used as a source of nutrients to ameliorate malnutrition and reduce post-harvest losses of catfish.

The effective processing parameters established is an important step to harness the high nutrients and economic values embedded in catfish.

It is only fair to say that this work is backed by a larger basis of research than exists in most countries. For nearly twenty years, that is since the formation of the “Dehydration Committee” by the Department of Agriculture in 1923, experiments have been carried on to determine the best methods of dehydrating Canadian apples, and the experience gained is now being applied to the dehydration of vegetables. One point which has been emphasised consistently throughout the work of the Committee is that high quality and fine flavour are essential for fruit or vegetables to be processed. During the past winter the Canadian Government was informed that the British Government was interested in dehydrated vegetables to an amount of approximately 1,000 tons. While the Canadian industry was not equipped to handle on short notice such a large order, immediate steps were taken in the establishment of test plants and the speeding up of experimentation. At that time representatives from the United Kingdom pointed out that no commercial samples of dehydrated vegetables from any country had been considered entirely satisfactory from the point of view of nutrition. The Canadian tests indicate that dehydrated vegetables can be of fine flavour and retain from 50 to 75 per cent. of the original vitamin content. Five experimental dehydration plants have been operating for some months, processing potatoes, carrots, turnips and cabbages from the 1941 crop. These are being held as a reserve supply for the Canadian Army. On the basis of these results, Canada should be able to supply large quantities of high‐quality dehydrated vegetables. The actual methods of dehydration employed vary according to the product. The simplest is that applied to the drying of fruits. Many of these, such as dates, figs, raisins, are dried in the whole state; others, apricots for example, are halved and pitted, while apples should be peeled, cored and sliced. Cut fruits, such as apricots and apples, are treated with sulphur dioxide, which acts as a steriliser and prevents discolourisation. Such fruits must be cooked before using in order to drive off the sulphur, but other dried fruits can be used without soaking or cooking. The moisture is removed by natural drying in the sun or by artificial evaporation. Many of the dehydration processes lie in the realm of chemical technology, but a short sketch of the principles involved may be of interest. The dehydration process used in the case of vegetables involves careful cleaning and cutting into small pieces, shreds or flakes. These are then “blanched” in steam or boiling water and placed in the dryer. While the amount of moisture which should be left varies with the particular vegetable, it should never exceed 7 per cent., and best results indicate a moisture content of 3 to 5 per cent. Substantial progress has already been made in research into the pre‐treatment of the vegetables. Cabbages, for example, should be “blanched” in steam, potatoes in plain water, and carrots in salt water. Investigation is continuing, however, into the actual drying of the vegetables and particularly as to the proper stage of maturity at which dehydration should take place. So far, it appears that no vegetables which are woody or fibrous have produced satisfactory results. Soft fruits, such as raspberries or strawberries, are reduced to a pulp, after the preliminary cleaning and “blanching.” This pulp is forced out over a heated drum, and when drying is completed looks something like “coloured crepe paper.” This filmy layer is broken into small fragments for packing and storage. It is reported that the original flavour and colour of the fruit is well maintained. The handling of milk and eggs, which are very liquid in their original form, requires a different process. After testing and preliminary sterilisation, the liquid is sprayed into a drying chamber where hot air in constant motion reduces it to a powder which falls to the floor. Although dehydrated foods can be kept under conditions of ordinary storage, they do require special care in packing. Metal containers are unnecessary, but the cartons must be impervious to moisture, to changes in temperature and to the attacks of insects and rodents. Canadian experience also indicates that removal of the oxygen in the container and its replacement by an inert gas, such as hydrogen, prevents any recurrence of chemical change and retains flavour for a considerably longer period. The acceptance of any product in war‐time, even for civilian consumption is, of course, no proof of its continued acceptance under normal conditions. Shortages of supply and the exigencies of the situation necessitate strange substitutions. Sometimes these are found better than the original product, and in the post‐war period tend to replace it. But this only occurs when the new substance or material has intrinsic advantages and can compete on a basis of quality. Many of us can remember the reaction in Great Britain against Canadian bacon after the last war, resulting from war‐time shipments of a type and quality to which the British were not accustomed. Long years of effort were necessary to break down the prejudice against Canadian bacon which was built up at that time. In the present war Canadian bacon is being prepared to suit the British palate. Since dehydrated foods have not yet come into general war‐time use it is impossible to prophesy regarding post‐war markets, but there are a number of interesting sidelights on the situation. One of the industries hardest hit by the tin shortage has been the manufacture of dog food, which had been growing rapidly in the pre‐war years. These manufacturers have been the first to produce dehydrated products to be sold to the general public, truly a case of “trying it out on the dog.” While we do not attempt to draw any analogy between dog biscuits and food for human consumption, it will be interesting to watch the results of this experiment. Dogs are certainly not interested in eating things that are good for them regardless of flavour, and if our canine friends accept the new preparations it will at least indicate that a palatable product has been obtained. The palatability of food can only be determined in use. It is feared, for example, that dehydrated vegetables would tend to become monotonous in constant use. General consumer interest has, however, been aroused by the wide publicity which has been given the industry, and already commercial dehydrators in the United States are studying the possibilities of civilian markets. The future of this development would appear to depend upon the assurance of quality, as the convenience of such products is undeniable.

Other concentrated milk products are evaporated or condensed milks. These do serve as direct substitutes for the original, simply by the restoration of the original amount of water content. Large shipments of these products are going forward regularly from Canada and the United States to Great Britain. The next logical step in the process is the complete dehydration into powdered form. This has been an expanding industry in recent years. Milk in powdered form occupies only about one‐quarter of the space taken by evaporated milk and approximately one‐eleventh of the volume of the original fluid milk. Experiments are now under way in Canada to make further economies. Dried milk is usually packed in tins or small containers, in loose powder form. Half a ton of milk was recently sent from Ontario to Great Britain in the form of solid blocks, packed in large cartons. If these experiments are successful further important economies in shipping space will result. The drying of eggs has until last year only been incidentally carried on in this continent, and industries using dried eggs have depended upon China for their supply. The cutting off of this source and spectacular demand for military use and overseas shipment have resulted in a tremendous increase in output. In 1939 the United States egg‐drying industry prepared only 10 million pounds of dried egg products. By 1941 this had been increased to 45 million pounds, and it has been estimated that output in 1942 will reach 150 million pounds. Some fear has been expressed that the present expansion in the industry will have severe repercussions, when conditions of normal supply and demand are restored after the war. It should be noted, however, that production of this year's quota will involve operation of the plants twenty‐four hours a day throughout the year and that the industry can go back to a peacetime operation with an eight‐hour day and a four‐month season. On this basis output would be only 17 million pounds per annum, or slightly larger than pre‐war consumption in the United States. Egg drying in Canada has also begun to expand. During 1941 we delivered 15 million dozen eggs to Great Britain. These eggs were shipped in the shell, and owing to shipping delays their condition upon arrival was not always satisfactory. Egg deliveries to Great Britain in 1942 are expected to reach 45 million dozen eggs, and since February 7th all of these have been shipped in the dried form. Although the drying capacity in Canada has been sharply increased it is not yet capable of handling all the eggs available at the period of peak production and the surplus eggs are being packed for future processing. While there has been a substantial growth in the processing of milk and eggs by dehydration, the industry which has received the greatest publicity and aroused most public interest is the dehydration of vegetables. During the World War of 1914–18 a substantial quantity of dehydrated vegetables was prepared and shipped to Europe, primarily for the use of United States armed forces. These were not popular; in general they tasted like anything but vegetables, and the kindest description of their flavour was that it resembled hay. The industry died away at the end of the war almost as rapidly as it had risen. The last few years, however, have seen a revival of interest and of operation in the dehydrated vegetable industry. This revival has, curiously enough, been based upon discoveries made in research for a rival, the quick‐frozen food industry. In the earlier days of the latter industry the same problem of hay‐like flavour arose. Research indicated that this was due to activity of enzymes—those curious biological catalysts present in all living matter without which the chemical changes necessary for its existence could not take place. It was discovered by pioneers in the frozen food industry that a pre‐heating or “blanching” process immediately prior to freezing prevented activity of the enzymes during the period when the food remained frozen. As a result of the lack of chemical change the flavour remained unaffected. It is thus against the background of this research rather than as a result of immediate war demands that the dehydrated vegetable industry has so far had its development. For a number of years the industry in the United States has been slowly growing, and a survey conducted last year by the United States Department of Commerce indicated that fifteen commercial plants produced slightly less than 5 million pounds of dehydrated vegetables in 1940. Nearly two‐thirds of the output was in the form of powders to be used for seasoning, including such highly flavoured vegetables as onions, celery and red peppers. The remainder of the output was either in the form of mixed vegetables which, combined with animal protein and flavourings, make up the now familiar packaged soups. There has also been, however, a relatively substantial volume of production for dehydration and use in the form of the original vegetable. One company in fact has specialised in the production of potato shreds which permit the preparation of mashed potatoes in five minutes. The greater part of the output was purchased by hotels, restaurants and other large organisations where convenience in use was a major factor. The direct sale to individual consumers was only in the preliminary stages. The increased demand for food products in the United States, both for the armed forces and for shipment abroad under “lease‐lend,” has aroused an intense interest in the industry. The United States Department of Agriculture announced at the beginning of June a programme of technical assistance and priorities on materials for food processors desirous of converting their plants. Compared with the fifteen plants producing 5,000,000 pounds in 1940, there are now reported to be 113 companies operating dehydration plants, with an aggregate annual production of 125,000,000 pounds. Potential demand may be measured by the fact that if dehydrated potatoes were served to the men in the United States army only once a week it would require 7 million pounds of finished product per annum of this vegetable alone. The types of dehydrated vegetables most in demand are potatoes, onions, cabbages, carrots, beets and tomatoes. The important factor in all these products is quality. Dehydration is not a process for getting rid of second‐grade products. One successful operator has found that green peas for dehydration should be of approximately the same quality as those used for quick‐freezing, and must be better than the average quality of peas canned. If the product is to be restored to anything like palatable flavour and texture the flavour must be there to begin with. During recent months the Canadian Government has been actively encouraging experimental work in the dehydration of vegetables.

The purpose of this paper is to analyze the nutritional composition and the acceptability of value-added products prepared from the dehydrated leaf mixture of underutilized green leafy vegetables (GLVs). GLVs are dense in micronutrients and are of great importance to the nutrition of population in developing countries. Nutritive value of commonly consumed GLVs has been studied extensively, but there is limited information available on nutritive value and acceptability of unconventional leafy vegetables.

The nutritional potential and acceptability of leaf mixtures (LMs) prepared from the less-utilized leaves of beet root (Beta vulgaris), carrot (Daucus carota), cauliflower (Brassica oleracea) and turnip (Brassica rapa) which are usually discarded or are used as animal fodder were analyzed in the present study. The LM was prepared by mixing the powders of above-mentioned greens in a definite ratio (1:2:1:1). The LM was analyzed for the proximate, mineral composition (Ca, P, Fe, Cu, Zn, Mn and Mg) and antinutritional factors (oxalate and phenols). In total, 20 different recipes with different levels (0, 5, 10, 15 and 20 per cent) of LM incorporation were prepared and were assessed for quality on the basis of sensory attributes.

The LM contains appreciable amount of proteins, fat, fiber, carbohydrate and calorific value, mineral elements and generally low levels of antinutrients. Products were well-accepted to the level of 10 per cent. Protein, iron and calcium content was significantly (p < 0.05) higher in the LM-incorporated recipes, and the increase was directly proportional to the level of LM incorporated.

Dehydrated GLVs are concentrate source of micronutrients and can be used in product formulation. Value addition of traditional products with dehydrated GLVs can be advocated as a feasible food-based approach to combat micronutrient deficiencies.

Dehydrated bacterial cellulose’s (BC) intrinsic rigidity constrains applicability across textiles, leather, health care and other sectors. This study aims to yield a novel BC modification method using glycerol and succinic acid with catalyst and heat, applied via an industrially scalable padding method to tackle BC’s stiffness drawbacks and enhance BC properties.

Fabric-like BC is generated via mechanical dehydration and then finished by using padding method with glycerol, succinic acid, catalyst and heat. Comprehensive material characterizations, including international testing standards for stiffness, bending properties (cantilever method), tensile properties, moisture vapor transmission rate, moisture content and regain, washing, thermal gravimetric analysis, derivative thermogravimetry, Fourier-transform infrared spectroscopy and colorimetric measurement, are used.

The combination of BC/glycerol/succinic acid dramatically enhanced porous structure, elongation (27.40 ± 6.39%), flexibility (flexural rigidity of 21.46 ± 4.01 µN m; bending modulus of 97.45 ± 18.20 MPa) and moisture management (moisture vapor transmission rate of 961.07 ± 86.16 g/m²/24 h; moisture content of 27.43 ± 2.50%; and moisture regain of 37.94 ± 4.73%). This softening process modified the thermal stability of BC. Besides, this study alleviated the drawbacks for washing (five cycles) of BC and glycerol caused by the ineffective affinity between glycerol and cellulose by adding succinic acid with catalyst and heat.

The study yields an effective padding process for BC softening and a unique modified BC to contribute added value to textile and leather industries as a sustainable alternative to existing materials and a premise for future research on BC functionalization by using doable technologies in mass production as padding.

The Department of Scientific and Industrial Research has released an account of the preparation of emergency rations in the form of dehydrated foodstuffs. These rations were designed and made when the result of a forced landing of an aircraft flying over polar regions may have to be faced. Having regard to the special circumstances for which the method described by the Department was designed it is perhaps not too much to say that it introduces as great a change in feeding the crews of airships as did Appert in feeding the crews of sailing ships a hundred and thirty‐five years ago. Appert's method did much to eliminate scurvy. This to prevent starvation and loss of life which the accounts of Polar expeditions have too often recorded. Dried fruits and dried vegetables have long been known and used. Milk powder and egg powder are now as well known. If these and tinned foods be regarded as ordinary rations they are too heavy and too bulky to be of use in an emergency such as may arise when a Polar flight ends in an unpremeditated grounding and the crew are left in a Polar desert to make the best they can of the conditions. It will be remembered that in May last the “Aries,” a British Lancaster airship, made a trip of some 17,000 miles. Much of this trip was in the Polar regions. The g eographical North Pole was visited and in the return journey the true position of the magnetic North Pole was ascertained in a 4,000 mile non‐stop return journey from White Horse, Yukon, to Shrewsbury. In view of possibilities an emergency ration had to be designed in which most of the food was in the form of hydrostatically compressed blocks of compounded and dehydrated foods. The compression reducing bulk; dehydration, weight; compounding ensuring variety. The rations so prepared had to be sufficient to feed nine men for twenty‐eight days. An account of the rations so prepared forms the subject of the report issued by the Department. These blocks consist of mixtures of dehydrated foods with added sweetening and flavouring materials where appropriate, so that each is a ready‐made meal requiring only the addition of water. They are fabricated into tablets of standard size (usually 2in. by 2in. by 0·9in.). They need only to be wrapped in high grade waxed films or papers and their standard size facilitates the assembly of mixed rations whilst very little space is wasted as compared for instance with circular cans. They are made by one of two processes—those containing dried foods of large particle size such as dehydrated meat or vegetables are made by compressing the mixture in a hydraulic press. The pressed block can be broken down easily in the hand. Where the particle size of the material is much finer, as with spray dried powders such as milk or egg, such compressed blocks would be very difficult to crumble, and furthermore lumps escaping crumbling would remain as unreconstituted lumps and mar the smoothness of the product. Thus they are prepared by casting the mixture hot into moulds with added molten fat. The block can be dissolved by boiling water. Many of the blocks containing milk powder may be eaten as sweets. Four kinds of menus from these blocks were prepared to relieve monotony of diet. Details of these are given in the report for four days. The total number of calories for each day ranges from 3,550 to 3,380. The weight of food per man in grammes from 715 to 704. Fat in grammes 213 to 177. Percentage of fat 30 to 25. The computed total nett weight was 393 lbs. Rations for two days can be packed in a standard four‐gallon can—gas packed if necessary—as a master container. Fourteen such cans would be necessary. These, together with immediate wrappings, would make a gross weight of 435 lbs. A most important consideration is weight. It is pointed out that the water extracted during the dehydration process would fill another seventeen cans! If light metal alloys instead of tin plate were used for the master cans a reduction of weight would be possible, but even a total weight of 435 lbs. is “very modest” compared with the weight of most emergency rations, even when the weight of master containers is excluded for the rations as drawn up provide for each man three normal meals per day. The Department refers to the theoretical aspect of the provision of a calorific level of 3,400 per day, with a total weight of 704 gms. per man. If the diet were made up of pure carbohydrate, pure fat and pure protein alone, then, using the factors 4·9 and 4 respectively as the number of calories derived from each gramme of food, a diet containing 25 per cent. fat would have an overall calorific value of 5·25 Cals/gm. a diet giving 3,400 calories, as in Day 3, would therefore weigh 647 gms. This is an absolute minimum below which it would be impossible to go. This figure takes no account of the residual water content of dehydrated foods of salt or minerals or roughage. The weight of 715 gms. achieved in practice includes, in addition to water and roughage, some 8 gms. of salt and 13 gms. of tea. It is therefore considered that, for a ration which gives three normal meals a day, it would be virtually impossible with the materials available at present to reduce the weight of the ration further. It may be added that a stove has been designed to burn motor spirit should it be possible to salvage any after a forced landing. It is considered that this type of food may be of great value for future polar expeditions. This is undoubtedly true whether aeroplanes be used as part of the equipment or not. It may be permissible to suggest that rations such as these would prove useful in land expeditions at a pinch. While in the case of a ship having to be abandoned in mid ocean the crew's chance of survival would obviously be bettered by having a supply of such concentrated rations in the ship's boats.

This study aims to have a product with enhanced shelf stability from the Kadaknath bird. It is localized to its native tract in India and is unknown to a major part of the world. As in tropical countries, the meat products prepared have limited shelf-life and restricted market access, hence, the pickle was developed to enhance its access to areas other than a native tract of Kadaknath.

The product was developed to assess the effect of cooking and dehydration on sensory and microbial features while enhancing shelf stability. A comparison between cooking methods i.e. steam cooking (SC) and microwave cooking (MC) followed by dehydration to get steam cooked + dehydration (SCD) and microwave cooked + dehydration (MCD) were subjected for the study.

The study revealed that sensory evaluation, from 0 to 100 days, for all the sensory parameters indicated that SC and MC samples scored more values than SCD and MCD, however, with the storage the values increased initially on the 20th day followed by a gradual decrease. The total plate count (colony forming unit) on 0 day for SC and MC were 2.51 and 2.46, whereas for SCD and MCD the values were 1.94 and 1.98, respectively, indicating significantly (P = 0.01) lower values in dehydrated meat pickle preparations (SCD and MCD) in comparison to samples prepared without dehydration (SC and MC). Similarly, on the 60th day, the meat pickle treatments mentioned as SC and MC had the yeast and mold counts (colony forming unit) detected as 1.79 and 1.88, respectively, however, the organisms were not detectable in treatments SCD and MCD.

Developed product may be suitable for long distance marketing and making the local delicacy available to distant places.

The literature review indicated that though meat pickles have been prepared earlier most of the preparations involved chemical preservatives/antioxidants and trials with hurdles such as dehydration and cooking variations were scanty.

The investigation here reported was undertaken to determine certain physical principles and their application to dehydration problems in general. The project was not carried to the point where it was possible to consider the modifications necessary for the different varieties of fruits and vegetables. Factors leading to the deterioration of dehydrated products and the relation which the condition of the fresh material may bear to this deterioration are important phases of the problem not here considered. Spoilage of raw food is due principally to the growth of moulds and bacteria. This growth does not occur when the soluble solids are sufficiently concentrated through the reduction, by drying or by other means, of the water present in foods. Even if they are not killed, the moulds and bacteria remain dormant and harmless in the absence of a suitable medium for their growth. Changes in composition, flavour and appearance, however, may also be brought about by the action of the enzymes present in practically all foodstuffs. As these natural catalytic bodies are not always inactivated by the treatment which stops mould and bacterial action they must be considered in working out methods of dehydration. The outstanding advantage of drying as a method of preserving foods is that the weight and bulk of the products are greatly reduced, thus making possible economy in storage and transportation. The production cost of dehydration compares favourably with that of canning. Dried fruits and vegetables are almost as convenient for use in the home as the fresh products. They need no peeling or other preliminary treatment, and soaking and cooking can often be combined. Only the quantity required need be used when the package is opened; the rest will keep in good condition for a reasonable time. “Dried,” “sun‐dried,” “evaporated” and “dehydrated” are the terms most commonly used to describe dried products. Dried indicates drying by any means; sun‐dried indicates drying without artificial heat; and evaporated implies the use of artificial heat. Evaporated refers more particularly to the use of artificial heat in driers depending for their air circulation on natural draught, while dehydrated implies mechanical circulation of artificial heat. The commercial dehydration of fruits has reached a more advanced stage of development than has the commercial dehydration of vegetables, owing largely to the fact that the public is familiar with sun‐dried and evaporated fruits, whereas it knows comparatively little about dried vegetables. During the World War 8,905,158 lbs. of dehydrated vegetables, divided as follows, were shipped to the United States Army overseas: Potatoes, 6,437,430lbs.; onions, 336,780; carrots, 214,724; turnips, 56,224; and soup mixture, 1,860,000. In the years immediately following 1919 the drying of vegetables declined rapidly, and for the last 10 years or more production has been compartively small. To be successful, a dehydration plant must be built where fresh materials are plentiful and reasonable in price. A diversity of products makes possible an operating season long enough to keep the overhead expenses down to the minimum. The products dried, however, should be limited to those for which a ready market exists. The only satisfactory method of operating is to contract for a sufficient acreage to take care of the needs of a plant at a price which will permit both the grower and the drier to make a profit. Material to be dried must be carefully sorted so as to be free of mould, decay and other defects that would lower the grade of the finished product. The stone fruits (apricots, peaches, cherries and plums) must be sufficiently firm to permit mechanical pitting without tearing. Where they are prepared by manual labour they must not be so soft as to stick to the trays. Apples and pears must not be so soft as to crush in the coring and peeling machines. Berries, cranberries and grapes are usually dried whole. Fruit that needs trimming must be avoided, as it not only adds to the cost of operation, but also lowers the grade of the final product. Vegetables, such as beans (snap), cabbage, carrots, celery, corn, parsnips, potatoes, pumpkin, spinach, squash and turnips, are sliced, shredded, diced or cut in desired pieces before drying. Dehydration does not improve the quality of fresh fruits or vegetables, nor does it provide for the satisfactory use of unsound products. At best the process can only conserve the original constituents of the foods, minus replaceable water. Careful handling reduces labour and waste. Bruised tissue is especially susceptible to discolouration and decay. Individual pieces prepared from good stock are more uniform and attractive than those from heavily trimmed stock. Raw materials should be as carefully washed and cleaned for dehydration as for table use. Much of the washing machinery used in canning is suitable for use in dehydration plants. A rotary cylindrical washer equipped with a water‐spraying system is very satisfactory for washing many types of products. Soft or easily broken fruits and vegetables may be washed by passing the trayed material between several sprays of cold water. The segregation of fresh fruits and vegetables according to size facilitates both the preparatory handling and the drying. One type of grader consists of a perforated metal plate, 3 by 10 feet, or larger. The perforations are in sections of varying size, and the plate is inclined and mechanically agitated in order to insure an even flow of the material in one direction. The product is separated according to size by being passed through the perforations. Perforated plates are also used in stacks. Several plates, each stamped with holes of a uniform size, the holes varying in size with each plate, are set one above the other, with 6 inches or more between plates. They are arranged so that the holes are progressively smaller from top to bottom. Another grader sorts out easily rolling materials according to diameter. As a mechanically driven cable rolls the materials along an opening that increases in width, the product falls through and is collected according to size. A grader based on the same principle passes the product down a chute the floor of which consists of rollers placed at increasingly greater distances apart. As the product rolls along the chute it is separated in progression according to size.

This article aims to focus on the food value of the mushroom. Because of its low calorific value and very high content of proteins, vitamins and minerals, mushrooms may contribute significantly in overcoming protein deficiency in developing countries like India.

Oyster (Pleurotus sajor caju) mushroom cultivated on two substrates i.e. wheat straw and brassica straw were procured. Freshly harvested and washed mushrooms were cut into small pieces. Sliced mushrooms were divided into four portions. Two portions were left untreated and dried using sun and oven drying methods. The third portion was blanched in boiling water at 100 °C for two mins, cooled immediately and drained. The blanched samples were divided into two portions. One portion was sun dried and another was oven dried. The fourth portion was soaked in solution of citric acid (0.25 percent) for 30 mins and drained. The steeped samples were divided into two portions. One portion was sun dried and another was oven dried. Each sample was dried from initial moisture content of 91 percent on fresh weight basis of the final moisture content 10 percent on dry weight basis. All the samples were ground to make fine powder. The untreated and treated samples were analysed for physico‐chemical properties and sensory evaluation by using standard methods.

Treated and untreated powders prepared from oyster (Pleurotus sajor caju) mushrooms grown on two substrates i.e. wheat and brassica straw were analysed for physical and chemical characteristics. Among the powders, T₆ (steeped in 0.25 percent citric acid and oven dried) powder exhibited highest yield followed by untreated and blanched powders. On the other hand, untreated samples T₁ (sun dried) and T₄ (oven dried) showed higher browning index as compared to pretreated powders. Steeped samples (T₃ and T₆) from both type of mushrooms, irrespective of drying methods exhibited higher values of water retention capacity and swelling index as well as sensory attributes (colour, aroma and texture) In terms of chemical analysis, steeped samples from both types of mushrooms, irrespective of drying methods, exhibited higher contents crude protein, crude fibre and ash as compared to blanched powders. Blanching in hot water may cause leaching out of nutrients.

With regard to healthy benefits and medicinal value of mushroom, its production and consumption should be increased. However, mushroom production does not demand land, but helps in the bioconversion of potential pollutants like agro‐wastes to useful and nutritive food for human consumption, which is essential to a developing country like India.

The findings of this article may contribute significantly in overcoming protein deficiency in developing countries like India. Mushrooms have a low carbohydrate content, no cholesterol and are almost fat free. Therefore, they form an important constituent of a diet for a population suffering from atherosclerosis.

The complex cellular structure and chemical nature of fruit and vegetable tissues retard evaporation so that under no conditions of temperature and humidity does the rate of evaporation from them equal that from a free water surface. When conditions are such that surface evaporation from the tissues exceeds the rate of moisture diffusion to the surface, the surface becomes dry and hard and seals in the moisture. This condition, known as case‐hardening, is overcome by reducing the temperature of the air or by increasing the humidity. The maximum rate of drying, then, is attained by using the highest temperature which will not injure the product, the humidity being sufficient to prevent case‐hardening. In general practice the temperature of the air entering the drying chamber should not exceed 160° to 170° F. The humidity at the air‐outlet end of the drier should not greatly exceed 65 per cent. In driers employing recirculation the conditions of temperature and humidity may be largely controlled by varying the recirculation. The velocities of air flow which produce the most efficient results in the drying chamber depend upon several conditions. In general the rate of drying increases with the velocity of air movement. Low air velocities tend to bring about slow and uneven drying. Exceedingly high velocities may not be used profitably because a point is app ched at which the materials will be blown from the trays or at which the increased speed of drying will not offset the cost of operating a larger fan. Velocities of 600 to 800 feet per minute through the drying chamber are satisfactory in tunnel driers; lower velocities are permissible in compartment driers. The most practical means of removing moisture from the air, and at the same time conserving heat, is through the steady discharge of a portion of the air leaving the drying chamber. The rest dries efficiently when mixed with fresh air from the outside and reheated. All forced‐draught driers, therefore, should be provided with recirculation ducts connecting the air‐outlet end of the drying chamber with the heaters and with dampers controlling the air discharged, recirculated, and drawn from the outside. Dehydrated fruits and vegetables should have a uniform moisture content low enough to inhibit undesirable microbic and chemical changes within the food, and they should be free from any part of the life cycle of moths or other insects. The moisture content of dehydrated foods directly controls deterioration within the food, and the protection afforded by sulphuring or blanching will not prevent insufficiently dried products from soon becoming unfit for use. Dehydrated products having a low moisture content are not readily attacked by insects. In the long run the additional protection afforded by a low moisture content will more than make up to the producer the loss resulting from the longer drying time and greater weight shrinkage involved. To assure best keeping qualities the moisture content of fruits containing much sugar should not exceed 15 to 20 per cent., while that of other fruits and vegetables should not exceed 5 to 10 per cent., the preference in both cases being for the lower percentage. The texture, or feel, of products is a guide in determining when the proper stage of dryness has been reached. At a given moisture content products usually feel softer when hot than after they have been cooled, and often they feel softer after standing until the moisture has become evenly distributed throughout the pieces than when first cooled. A rough test for moisture in dried fruits is to take up a double handful, squeeze it tight into a ball, and release the pressure. If the fruit seems soft, mushy, or wet, and sticks together when the pressure is released, the moisture content is probably 25 per cent. or more. If the fruit is springy, and, when the pressure is released, separates in a few seconds to form pieces of approximately the original size and shape, the moisture content is usually about 20 to 25 per cent. If the fruit feels hard or horny and does not press together, falling apart promptly when the pressure is released, the moisture content is probably below 20 per cent. At the proper stage of dryness vegetables look thoroughly dry and are often hard or crisp. The Association of Official Agricultural Chemists has published a method for the determination of moisture in dried fruits. In using methods of this type, care must be taken to select a composite sample from different parts of the lot, so that it will be representative of the lot as a whole, and directions for preparing the sample must be carefully followed in order to obtain dependable results. Products are never uniformly dry when removed from the drier. Large pieces and pieces not as directly exposed to the currents of heated air as most of the material contain more moisture than the rest. Products should be stored in large bins until the moisture becomes evenly distributed. This period of curing will usually take several weeks. An alternative method is to place the dried product in large friction‐top cans for curing, thus insuring complete protection from contamination and insect infestation. Leafy vegetables, like spinach, must remain in the drier until the moisture content of the stems is very low. At this point the product is bulky and the leaves are brittle. For economy in packing and handling it is desirable to reduce the bulk by compression. For this purpose the leaves are exposed to currents of cool damp air until they have reabsorbed just enough moisture to make them slightly flexible. For convenience in handling and to facilitate the application of heat or fumigation, products should be packed in the room where they were cured and stored. Such a room should be strictly clean, dry, cool and well ventilated. The doors should fit tightly, and the windows should be covered with fine‐mesh screen to exclude dust and insects. An abundance of light assists in detecting the presence of insects and in keeping the room clean. The types of containers chosen for packing will depend largely upon the severity of the storage conditions, with particular reference to the humidity and to chances of insect infestation. An ideal container would be one which, while moderate in cost, would keep the product from absorbing moisture when exposed to the most severe conditions of storage and shipment, and would be impervious to insects. Sealed tin cans and glass jars give absolute protection against moisture absorption and insect infestation. Friction‐top cans are nearly as good. Tin containers, necessary for export shipments of dehydrated foods, are more expensive than paper containers. Wooden boxes are generally used for bulk goods. Liners of heavy paper or cardboard, and sometimes additional liners of waxed paper, are used. The use of moisture‐proof cellophane packages is increasing. All types of paper containers with which experiments have been made allow the absorption of moisture when the products are stored in damp places. Also paper containers do not give perfect protection against all insects, some of which can bore holes in paper, while the larval forms of others are so small that they can crawl through the slightest imperfections at the joints where the cartons are sealed. Most products, however, keep satisfactorily in double or triple moisture‐proof cellophane or waxed‐paper bags packed in waxed, moisture‐proof cartons, provided the initial moisture content is low and no live insects in any form enter the package. Packing in insect‐proof and moisture‐proof packages cannot be too greatly stressed.