Effect of Fermentation Time on the Chemical Composition of Mulberry (Morus alba L.) Leaf Teas

Morus alba (Mulberry) leaves were exposed to fermentation for varying amounts of time: no fermentation (0 min, MANF), medial fermentation (10 h, MAMF), and full fermentation (24 h, MAFF). The chemical compositions of the teas were determined and compared with those of commercial Camellia sinensis teas. The results showed that mulberry leaf teas contained significantly higher amounts of ash and fat than Camellia sinensis tea. Compared with Camellia sinensis teas, all mulberry leaf teas contained significantly more total free amino acids (24.26~54.25mg L-glutamic acid equivalent $g^{-1}$), but the concentration of caffeine was relatively low for mulberry leaf teas. High thiamine, riboflavin, and niacin contents were found in all mulberry leaf teas, but ascorbic acid and pyridoxine were found at higher levels in Camellia sinensis teas than in mulberry leaf teas. Color measurements demonstrated that mulberry leaf tea infusions generally had lower $a^*$ (greenness) and $b^*$ (yellowness) values than Camellia sinensis tea infusions. All infusions exhibited low turbidity levels (less than 10%). The contents of total phenols were measured as 71.8 and 74.9mg 100 $ml^{-1}$ infusion in MANF and MAFF, respectively, but the MAMF tea infusion showed significantly lower total phenols (64.6mg 100$ml^{-1}$ infusion). The total flavonoid contents of mulberry leaf tea infusions were lower (8.9~20.6mg 100 $ml^{-1}$ infusion) than those of Camellia sinensis teas and thus had lower antioxidant capacities (DPPH: 326.8~526.9 ${\mu}M$ trolox equivalent $g^{-1}$ and FRAP: 364.6~387.6 ${\mu}M$ trolox equivalent $g^{-1}$) than Camellia sinensis teas. The amounts of ${\gamma}$-aminobutyric acid (GABA) and rutin were higher in fermented mulberry leaf teas; the level of GABA increased with increasing fermentation time and the content was highest in MAFF, but rutin content was highest in MAMF.

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