Shelf-life Studies on Osmo-Air Dried White Button Mushroom (Agaricus Bisporus L.)

introduction Mushrooms are edible fungi of commercial importance and their cultivation and consumption has increased substantially due to their nutritional value, delicacy and flavor1. White button mushroom Abstract White button mushroom (Agaricus bisporus L.) was subjected to osmotic dehydration at different concentrations of common salt (sodium chloride) i.e. 10, 15, 20 and 25% and sugar solution i. e. 50, 60 and 70°B and dried in hotair oven at 55 ± 2 °C. There were about 31.2, 29.4, 27.2 and 24.4% reduction in weight with 10, 15, 20 and 25% salt solutions and 35.4, 38.3 and 38.8% with 50, 60 and 70°B sugar solution respectively. It took about 240, 220, 200 and 180 minutes to dry samples after osmotic treatment with 10, 15, 20 and 25% salt concentration and 240, 220 and 220 minutes with 50, 60 and 70°B sugar solution respectively. The untreated samples took about 340 minutes for complete drying. The colour was brighter for samples dried after OT with 25% salt and 70°B sugar concentrations having lowest optical density (OD) values. The dried products were packed in 200 gauge polypropylene bags and stored at ambient condition for one year. The chemical, microbial and organoleptic changes were monitored for one year. Storage study showed that there was marginal increase in moisture content and decrease in organoleptic quality of osmoa-air dried (OAD) mushroom slices. The samples dried after osmosis with 25% salt and 70°B sugar concentrations were found microbiologically safe and organoleptically acceptable up to one year of storage at ambient condition. Article history

white button mushroom, osmosis, drying, organoleptic, optical density.phosphorous, potassium, selenium.It is highly perishable and has a short shelf life of 3-5 days at 2°C and around 1-2 days under ambient (Temp.25 ± 2°C, RH 70%) conditions 2 .These can serve as a functional foods and as a source of drugs and nutraceuticals due to their antioxidant, antitumor and antimicrobial properties 3 .Because of their short shelf-life under normal ambient conditions of temperature and humidity, their preservation is of most importance 4 .Much work has been done on processing aspects of white button mushroom such as drying 5 , preparation of soup powder 6 , pickle 7 , chutney 8 , bakery products such as bread 9 , biscuits 10 and its incorporation with other fruits and vegetables such as tomato-mushroom mixed ketch-up 11 and tomato-mushroom mixed soup 12 .Osmotic dehydration has received greater attention in recent years as an effective method for fruits and vegetables preservation.Being a simple process, it facilitates processing with retention of initial characteristics of fruits and vegetables viz.colour, aroma and nutritional compounds 13 .It is a technique of production of shelf-stable foods by placing the solid food in sugar or salt solution of high osmotic pressure and removal of moisture.It applies hurdle technique to solid foods without affecting their structural integrity 14 .Due to high concentration of TSS (Total soluble solids), dried product becames chemically stable.The other advantages include lower cost of packaging, storage and transport, decrease in bulk, so easy handling and availability in off-season 15 .Bchir, Besbes 16 reported that among all the preservation techniques osmotic dehydration is an economical and efficient from nutritional point of view.Yadav and Singh 17 concluded that it is one of the best and economical method for preservation because it does not deteriorate the nutritional ingredients and sensory characteristics such as flavor, color, and texture etc. also being preservative free, it does not adversely affect the human body.During peak season, there is glut of mushrooms in the market but due to its perishable nature, it can not be stored for a longer period.Therefore, in order to minimize wastage and maximize its use, an effort has been made for development of osmo-air dried (OAD) mushroom slices.The study was undertaken to study the effect of different concentrations of osmotic agents i.e. salt (sodium chloride) and sugar on physico-chemical, organoleptic and microbial quality of OAD slices.Products were stored at room temperature (21-35°C) and changes in keeping quality were observed upto one year at 2 months interval.

Materials And Methods
Freshly harvested mushrooms (Agaricus bisporus L.) were obtained from a local mushroom farm, Hisar.Osmotic agents like sugar and salt were purchased  1).
Osmotically dehydrated mushrooms (ODM) after draining were dried in hot air oven at 55 ± 2°C.Weight reduction during drying was noted at 15 min interval till the mushroom is completely dried.Loss in weight was plotted against time to get drying curve for mushrooms (Fig. 2).After complete drying mushrooms were taken out in desiccators and cooled.Thereafter, samples were finely packaged in 200 gauge polypropylene bags for further use in the study.Mushrooms dried in air without osmosis were taken as control.The dried products were stored at ambient condition (21-35°C) for one year.Dehydration ratio which is the ratio of weight of fresh mushrooms to the weight of dried mushrooms was determined 18 .Osmotic solutions were reused after concentration for fresh lot of mushrooms.Bolin, Huxsoll 19 reported that osmotic syrups could be re-concentrated and reused for osmotic water removal through at least five complete cycles without adversely affecting the quality of product.
For rehydration, OAD mushrooms were immersed in cold distilled water and allowed to get rehydrated.The rehydration ratio, which is the ratio of weight of sample after rehydration to the initial weight of dry matter, was determined 18 .The colouring matter in mushrooms was extracted with 60% ethanol and absorbance was measured at 440 nm using spectrophotometer 20 .Organoleptic evaluation of osmodehydrated slices was done using 9-point hedonic rating scale as described by Ranganna 18 .The data was tabulated and statistically analysed as per the method described by Snedecor and Cochran 21 using factorial CRD (Complete Randomized Design).1).Rehydration ratio was recorded higher in case of sugar than salt OAD product which was mainly due to less shrinkage during drying in sugar OAD thereby resulting in higher uptake of water during rehydration.Further, rehydration ratio of all OAD slices was higher than that of control samples dried only by hot air oven method.Madan and Dhawan 15 also reported higher rehydration ratio of 3.28 in OAD carrot slices than 2.79 in hot air dried slices.Organoleptic evaluation of OAD mushroom slices treated with different sugar and salt is presented in Table 2.There was significant difference in colour, flavour, texture and overall acceptability of products.Significant increase in overall sensory score of osmo-dehydrated products was observed with higher concentration of sugar and salt in osmotic solutions.Values for salt treated samples increased from 2.56 for control to 6.07,During storage, there was slight but non-significant decrease in overall organoleptic score of products (Table 3).This may be due to slight browning of the products during storage.Changes in values for organoleptic characteristics were, statistically nonsignificant.Narayana et al 14 reported no significant variation in the scores of colour, flavour, texture, taste and overall acceptability of osmo-dehydrated banana during storage.Madan and Dhawan 15 also reported non-significant decrease in the acceptability of dehydrated carrot slices during storage.However, slight decrease in colour/appearance was noticed during storage.
There was decrease in optical density (OD) values of products with increase in concentration of osmotic agents which was statistically significant (Table 4).
Values decreased from 0.35 in control sample to 0.23, 0.18, 0.16 and 0.10 in samples treated with 10, 15, 20 and 25 % salt solutions respectively.In case of osmosis with sugar solutions OD value changed from 0.35 in control samples to 0.18, 0.14 and 0.12 in samples treated with 50, 60 and 70 °B sugar solutions respectively.Amuthan et al [22] reported that mushroom samples (Calocybe indica L.) treated with 25 % salt concentration had lower value for OD compared to other samples.During storage, there was significant increase in values for OD of OAD mushroom slices.Values increased from 0.20-0.37 for salt and 0.20-0.41for sugar treated samples after one year of storage.Suguna, Usha [20] reported that OD value for fluidized bed dried mushroom (Pleurotus citrinopileatus) increased continuously during storage for five months.Changes in total plate count of products during storage are depicted in Table 4. Microbial count was nil in all treatments on zero day except for control where microbial count was 0.30 CFU × 10/g.Due to hygroscopic nature of products, there was slight increase in moisture content of samples which resulted in significant increase in total plate count of osmo-dehydrated products during storage.Values for microbial count increased from 0.30 CFU × 10/g on zero days to 6.34 CFU × 10/g after 12 months of storage in case of salt OAD products.In sugar OAD products, values increased from 0.30 CFU × 10/g to 7.93 CFU × 10/g which were statistically significant.Microbial growth was found less in samples treated with higher concentration of sugar and salt in comparison to control samples.Similar results were

Conclusion
It can be concluded that osmotic dehydration of mushrooms is an energy saving and quality improvement process.Mushroom slices could be successfully osmo-air dried using 25% salt and 70 °B sugar solution after giving a combined treatment with 0.5% Potassium metabisulphite + 0.2% citric acid for 30 min for inactivation of enzyme polyphenol oxidase.Osmo-dehydrated samples consumed less time and energy as compared to control samples during drying drying process as about 40% of moisture was removed during osmotic dehydration.Therefore, OAD saved time of about 100-160 minutes in drying mushrooms than air drying method.As osmotic agents i. e. salt and sugar can be reused, it is a cost effective process.OAD products showed better appearance, flavour, texture, taste and overall acceptability and could be stored for one year at ambient condition without any appreciable deterioration in quality.

Fig. 1 (
Fig. 1 (a-b):Weight reduction during osmosis of mushroom slices with different concentrations of salt (a) and sugar (b) solution