Efficacy of Citrus aurantium L. essential oil for inhibition of inhibiting Aspergillus sp. in fresh bread products

Abstract

Citrus aurantium L. Orange peel essential oil (CaEO) is terpene and phenylpropene organic compound, which has antimicrobial activity and is safe when used as a food preservative. Therefore, CaEO was used to evaluate for its efficacy in inhibiting Aspergillus sp., cause of spoilage in fresh bread products by poisoned food technique and the antioxidant activity of CaEO was determined by spectrophotometric method using 2,2-Diphenyl-1-picrylhydrazyl radical scavenging capacity assay (DPPH assay). The results showed that CaEO at concentrations of 2.50, 5.00 and 10.00 µl/ml was able to inhibit the growth of Aspergillus sp. colony with a colony diameter of 2.68 ± 0.1, 2.40 ± 0.24 and 1.63 ± 0.09 cm, respectively, compared to the sterile distilled water used as a control (2.98 ± 0.05 cm).It was found that CaEO at a concentration of 10.00 µl/ml had an inhibitory effect  comparable to that of 0.2% calcium propionate used as a reference compound with a colony diameter of 1.50 ± 0.23 cm, which was  significantly different to the control (p ≤ 0.05). CaEO at concentrations of 5.00 and 10.00 µl/ml were used as an ingredient in fresh bread products with calcium propionate as reference compound and the sterile distilled water as control. Fresh bread kept for 1-4 days showed no changes and fewer black spots on the bread surface were found on the 5^th day as compared to the control with more black spots, while fresh bread with the reference compound showed no microorganisms on it. When fresh bread was cultured in PDA agar and incubated at 27°C, CaEO at concentrations of 5.00 µl/ml was found to have fungal growth of 8.20 colonies per 1 g of sample (CFU/g) on the 4^thday, while CaEO at a concentration of 10.00 µl/ml and calcium propionate solution showed no fungal growth. The antioxidant activity of CaEO was assessed by DPPH scavenging assay. It was found that CaEO exhibited very low antioxidant activity with EC₅₀ > 1,000 µg/ml, compared to a standard solution α-tocopherol (Vitamin E), with possesses very high radical scavenging with an EC₅₀ value of 43.47 µg/ml. Therefore, the CaEO at a concentration of 10.00 µl/ml exhibited highest inhibitory effect on Aspergillus sp Its effect was comparable to that of calcium propionate and the CaEO