Characterisation of nutritional, physiochemical, and mineral compositions of aril and seed of longan fruit (Dimocarpus longan L.)

Longan (Dimocarpus longan L.) seeds are usually discarded without further utilisation in food production. In the present work, to determine the food resource value of longan seeds, their nutritional components, bioactive materials, and antioxidant activity were compared with those of the longan aril, the edible portion. The dried longan aril and seeds produced in Thailand were examined for their primary nutritional composition, organic acid composition, phenolic contents (gallic acid and ellagic acid), and antioxidant activity; including the DPPH radical-scavenging activity, superoxide dismutase (SOD)-like activity, and reducing power. Based on the proximate composition, the longan aril had higher moisture (9.85%) and crude ash (4.07%) contents, whereas the seed had higher crude protein (7.38%), crude lipid (4.91%), and carbohydrate (83.63%) contents. Among the minerals, calcium (122.60 mg/100 g), potassium (2053.50 mg/100 g), phosphorus (191.21 mg/100 g), and sodium (25.24 mg/100 g) contents were higher in the longan aril, whereas magnesium (69.83 mg/100 g) and iron (2.97 mg/100 g) contents were higher in the seed. The contents of most free sugars and organic acids were higher in the longan aril than in the seed. UHPLC-MS/MS analysis showed the contents of gallic acid and ellagic acid were higher in the seed (1.54 and 1249.50 µg/g, respectively) than in the aril. The total phenolic and total flavonoid contents, which indicate the antioxidant activity, were higher in the longan seed (248.42 mg GAE/g and 6.37 mg CAE/g, respectively) than in the longan aril, whereas the seed showed higher values for all the antioxidant activities than the aril. Our findings suggest that the longan seed exhibits not only high contents of nutrients but also an outstanding antioxidant activity, thereby verifying the high value of longan seeds as a potential food resource.