61C-30

The inhibitory effects of various concentrations of lemon (Citrus limon) extract exposed or not to UVA (365 nm) on the growth of Aspergillus niger in two fruit (peach and plum) based agars at pH 3.5 and 35°Brix (a_w, 0.97) were evaluated.

Freeze-dried lemon peel (10g) was extracted with ethyl acetate (150 mL), filtered and concentrated by vacuum evaporation. The concentrated extract was dissolved in 100 ml of ethanol. Mold was cultivated on potato-dextrose agar slants and spores harvested (10⁶ spore/ml). Fruits were hand peeled, cut into cubes and blanched. Each blanched fruit was aseptically homogenized in a warring blender with 1% w/w of agar-agar, sucrose and citric acid. The fruit based agars were heated (10 min, 110°C) cooled, and 0, 1000, 2000, up to 5000 ppm lemon extract were incorporated. Triplicate plates of every combination were inoculated with the spore suspension, exposed or not to UVA (60 s), incubated for 20 days (25°C), observed and the colony diameter recorded.

The increase in extract concentration, exposure to UVA, and the type of fruit used in agar preparation significantly (p<0.05) affected radial growth rate and lag time. Extract inhibitory concentrations were in general higher than 2,000 ppm when expossed to UVA, suggesting that furocoumarins from lemon were photoactivated which resulted in a delay in growth for 20 days. The inoculated molds grew faster and in higher concentrations on plum fruit based agars.

The results obtained suggest that lemon extract - UVA could be used as an antimicrobial system to prevent mold spoilage in fruit purées. The inhibitory concentrations of lemon extract may be compatible with the fruit characteristics.