QUALITY AND MOISTURE SORPTION CHARACTERISTICS OF MICROWAVE-VACUUM, AIR AND FREEZE-DRIED BUTTON MUSHROOM (AGARICUS BISPORUS)

Abstract

ABSTRACT Button mushrooms (Agaricus bisporus) were dried by microwave-vacuum drying (MVD) technique to a moisture content of about 6% (d.b.), and the dried mushrooms were compared with hot-air and freeze-dried (FD) products on the basis of different quality attributes such as color, texture, rehydration ratio and sensory score. Statistical analysis of data revealed significant difference among the drying methods for all the attributes at P ≤ 0.05. Although FD produced the best quality dehydrated products having maximum rehydration ratio, highest instrumental color (L value) and lowest hardness, the MVD mushrooms were rated as equal to FD samples by a sensory panel in terms of appearance, color and overall acceptability. MVD mushrooms had significantly higher rehydration potential, lower density, better color and softer texture than those obtained by air drying (AD). The effect of drying methods on the water sorption properties of dehydrated products was also evaluated at 20, 30 and 40C. It was found that FD products absorbed maximum water vapor and MVD products had a higher sorption capacity than conventional AD products. PRACTICAL APPLICATIONS Microwave-vacuum drying (MVD) has been investigated as a potential method for obtaining high quality dehydrated food products including fruits, vegetables and grains. MVD combines the advantages of both microwave heating and vacuum drying. The low temperature and fast mass transfer provided by vacuum combined with rapid energy transfer by microwave heating generates very rapid, low temperature drying and, thus, it has the potential to improve energy efficiency and product quality. Several researchers have reported microwave assisted drying of foods, where considerable improvements in the drying process and product quality have been found. Good quality dehydrated button mushrooms, having properties comparable to freeze-dried products, can be obtained by MVD method within 30–40 min of drying time. The commercial application of this technology for large-scale drying of mushrooms may be examined for economic viability.