Unripe Fruit's Extract of Quince (Cydonia oblonga Miller) as a Potent Alpha-amylase Inhibitor

The use of alpha-amylase inhibitors has recently gained in popularity with the success and growth of carbohydrate restricted diets. In this study, two different stages from the unripe fruits of quince (Cydonia oblonga Miller) have been tested for their potentiality in alpha-amylase inhibition as a key enzyme in carbohydrates assimilation. Our results revealed that addition of different concentrations from extracts (0, 2, 4, 6, 8mg) of dry mass of each stage of unripe fruits resulted in drastically decrease in the enzymatic activity of alpha-amylase by the percent of (0%, 42.6%, 21%, 26.3%, and 16.9%) for the stage 1. Extracts from the stage 2 were more effective in enzymatic inhibition (0%, 26.9%, 3.8%, 0.2%, and 0.4%). The GC/MS analysis revealed that quince extract contains (sorbitol, quinic acid, p-vinylphenol and cyclopropane carboxylic acid). To explore which components are involved in the inhibition process, two pure components of the quince extract (sorbitol and quinic acid) were used in inhibition assay. Neither sorbitol nor quinic acid shows any significant inhibition; therefore, these two components could be excluded from the inhibition process. Our current study suggested that p-vinylphenol and cyclopropane carboxylic acid might act as -amylase inhibitors in vitro separately or synergistically. The possible explanation for the presence of cyclopropane carboxylic acid (CPCA) in this critical phase of the unripe fruit will be discussed. This study suggests that the unripe fruits of quince can be used as a natural starch blocker containing alpha-amylase inhibitors which would be of interest for people requiring carbohydrate restricted diets.