Comparison of antifungal effects of nigella sativa oil and extract with imazalil on two apple cultivars in cold storage

Apple and its products play a major role in the Iranian agricultural economy. Apple fruit, after grapes, is the most important product of the country. Iran is ranked fourth in the global production of apple. After harvesting, to maintain the quality of apples, the cold stores are used. Molds like penicillium expansum causes significant damage to the quality and the quantity of apples and fungicides such as imazalil are used to control them. These fungicides usually decompose in nature slowly, and the residue of them, compromise the health of consumers and the environment. Scientists try developing new antifungal environment friendly materials.  Nigella Sativa oil and extract contain compounds such as Caron, Alfa-pinene, Sopinen, Beta-pinene and P-cimen. Alpha-pinene is a disinfectant material. Antimicrobial and antioxidant properties of Nigella Sativa have been reported in several studies. In this study, the possibility of replacing chemical fungicides such as Imazalil with Nigella Sativa oil and extract for extending the storage life of two apple varieties was investigated.

The preservative effects of Nigella Sativa oil and extracts as an antimicrobial agent was compared with Imazalil fungicide for two cultivars of apples, Red and Golden Delicious. Nigella Sativa oil and extract were extracted by solvent extraction and they were sprayed at two concentrations (0.1 and 0.2%) on Red and Golden Delicious apple cultivars. The sprayed apples and the controls (samples containing imazalil without any additives) were kept in a cold store at 0°C for 6 months. During 6 months, total microbial count, mold and yeast, tissue hardness, brix, acidity, sensory, percentage of waste, moisture and vitamin C were tested each month.

The results showed that Golden delicious variety with 8.16×103 had better bacterial properties, Brix (17.5), Moisture (80.07%) and Vitamin C (2.02 mg/100g) than that of Red Delicious. However, the texture of the Red Delicious variety (3.01N) showed more hardness than Red Delicious, less waste (3.63%) and higher overall acceptance (3.72). The effects of anti-microbial agents on the texture and acidity of apple cultivars were not significant, but it was significant on vitamin C (P<0.05). During storage for six months, all samples experienced a decrease in quality. In addition, there were increases in the total count of microbes (from 2.11×103 at first month to 15.33×103 at sixth month, mold and yeast (from 111 at first month to 6.25×103 at sixth month, and a significant decrease in other qualitative parameters. The effect of anti-microbial agents used in this research on mold and yeast was higher than that of total microbial count. Anti-microbial agents, especially Nigella Sativa oil and extract, had much lower mold and yeast content during the six months, than the control. The qualitative characteristics of the apple were also maintained. Therefore, Nigella sativa oil and extract are introduced as alternative to Imazalil that can prevent the microbial decay of apple.