Shelf-life Study and Antioxidant Capacity
The most accepted samples of the dried longan were packed in 190-ml polypropylene plastic
boxes (100 g per box) and kept at room temperature (25.46C) for 12 months. Their water activity,
moisture content and antioxidant capacity during storage were determined. The antioxidant capacity
was measured by 3 different methods, namely ferric reducing/antioxidative power (FRAP) assay
[23], improved ABTS radical-cation decolourisation assay [24] and DPPH free radical scavenging
activity [25] with some modification as previously described [26]. Vitamin C was used as a standard
for all methods and results were reported as mg vitamin C equivalent/ g dry sample. The change of
water activity and moisture content was used to predict the shelf life of the products by the following
linear equation [27]:
ln [(me - m0)/(me - mc) = [K / ] t
where me = Equilibrium moisture content of product (% dry basis)
m0 = Initial moisture content of product (% dry basis)
mc = Moisture content of product at the end of acceptance point (% dry basis)
K = Moisture transmission rate (g water/ g solid.time)
= Slope of liner regression (g water/ g solid)
t = Shelf life of product (time)