EFFECT OF PRETREATMENTS AND DRYING TEMPERATURES ON THE QUALITY OF DRIED PLEUROTUS MUSHROOM SPP.

Abstract

This study was carried out to evaluate the effect of pretreatments prior drying as well as drying temperature on quality of the dried mushroom. Rehydration ratio and color of the dried product are the most effective parameter for judging and evaluating the drying process. Pleurotus ostreatus and Pleurotus eryngii samples were pretreated by different solutions (NaCl, citric acid and sodium metabisulfite) at room temperature and at 96± 2 oC. Pretreated and control mushroom samples were dried by hot air at 50, 60 and 70 oC until reached to constant weight. The dried product was evaluated immediately after drying. P. ostreatus required from 7-12 hr, while P. eryngii required 6.5- 11 hr to reach moisture content around 7% depending on pretreatment and drying temperature. Control sample dried by using any tested drying temperature recorded the highest rehydration ratio compared to other pretreated samples dried at the same drying temperature. Also, steeped dried samples had higher rehydration ratio than blanched ones. Samples steeped in sodium metabisulfite (SMS) prior drying had the lowest browning index, while those blanched in NaCl or citric acid had the highest browning index values. Drying process caused a considerable decrement in protein content and a severe reduction in total microbial counts of mushroom samples. Sensory evaluation revealed that control and samples steeped in SMS or NaCl prior drying at 50 oC got higher scores than the others. According to the results obtained it could be clearly concluded that, steeping P. ostreatus and P. eryngii samples in NaCl, citric acid or Sodium metabisulfite (0.1% each at room temperature) for 10 min. prior drying at 50 oC prevented browning especially with SMS. Also, steeping treatment resulted satisfactory rehydration ratio for dried products even they were lower than the untreated (control) sample.