Influences of modified atmosphere and drying conditions on qualities of mulberry leaf powder

The present research was conducted to investigate effects of controlled atmosphere conditions on postharvest qualities of fresh mulberry leaves prior to mulberry leaf dry, and antimicrobial activity of extracts obtained from dried mulberry leaf powder against Erwinia carotovora, a key postharvest horticultural pathogen. There were 3 main experiments undertaken. The first experiments were conducted to study effects of modified atmosphere storage, i.e. 100% O2(v/v) controlled concentration, on total phenolic content (TPC) of fresh mulberry leaf, at 5C for 9 d, in comparisons to the effects of an ambient air condition. Experimental results indicated the controlled atmospheric condition tested did not have significant effects on increasing TPC values. The mulberry leaf accordingly was kept in the ambient air prior being dried. The second experiments were to investigate effects of drying processes (40-70 C) on dried mulberry leaf which was later processed into the powder form (70 mesh). Experimental findings highlighted thermal degradations of dried leaf parameters including TPC, antioxidant activity (AA) and ascorbic acid content and these were well described by the first-order fractional conversion model. An optimal drying condition was 60 C for 4 h due to its effects on those parameters and consumer acceptance. The third experiment was undertaken to investigate processes of mulberry leaf powder extraction and antimicrobial effects of the extract against Erwinia caratovora. The optimal extraction condition was mixing 10 g powder with 90 ml distilled water for 1 h. Experimental findings on in vitro antimicrobial tests showed that the powder extract had potentials to delay proliferations of Erwinia caratovora. Its antimicrobial activities positively increased with increases in extract solution concentrations. Overall the present research contributes new knowledge on processing of mulberry leaf powder and its extract. The methodologies developed in this work can be further utilized and applied to suit with other plant leaves such as Cratoxylum formosum dryer or, in Thai, Teaw leaves.