Variability in the fermentation index, polyphenols and amino acids of seeds of rambutan (Nephelium lappaceum L.) during fermentation

The variability in the fermentation index, polyphenols, and amino acids of rambutan seeds was investigated during fermentation. Results revealed that fermentation index (FI) value ≥1 was achieved on the 4th day of fermentation. While fermentation significantly reduced the levels of total polyphenols (59%), tannin (60%), and saponins (33%), it seems to have a moderate effect on geraniin, corilagin, and a much stronger effect on ellagic, and gallic acids. During fermentation, variability in gallic acid, geraniin, corilagin, and ellagic acid did not show a consistent trend. In contrast, amino acids significantly decreased up to the second day of fermentation. Importantly, amino acids (phenylalanine, tyrosine and leucine) with characteristic bitter taste showed reductions of 20%, 30%, and 40%, respectively after 10 days of fermentation. Sucrose, which was the only sugar present in significant concentrations in unfermented seed, was significantly reduced by fermentation.