Inhibition Of Postharvest Pathogens By Essential Oils And Their Effect On Storage Physiology Of Blackberry

Blackberry fruit has been a part of man’s diet for centuries. This berry, like other berries, is an important dietary source of fiber, essential vitamins (ascorbic and folic acids) and minerals, which are very important for health. Blackberry fruit is one of the most perishable berries because of its thin and fragile skin and high water content of flesh. At present, refrigerated storage combined with synthetic chemical fungicides are the most commonly used method of storage for blackberry fruit, but chemical fungicides will create problems about food safety and environmental pollution. Threrfore, the search for a safe and effective alternative or partial substitute to chemical fungicides is very important. According to the experiment design, the antifungal activities of four essential oils (Carvacrol, Allyl isothiocyanate [AITC], Linalool and P_Cymene) against two phytopathogenic fungi (Alternaria, Fusarimn) were tested at different concentrations in vitro. Preliminary results showed that carvacrol and AITChad strong antifungal activity against some phytopathogenic fungi.Therefore, the effect of these two essential oils in combination with other control measures on postharvest storage of blackberry was studied. We also investigated the mechanisms of antioxidation and fruit disease resistance to provide the theoretical basis for preservation of berries. The results were as follows:(1) This research has been conducted to study effects of different temperatures (5,10and20℃) on storage quality and physiology of’Hull’blackberry fruit during storage.5℃storage reduced the decay rate, delayed the decline in TSS and TA content, inhibited the increase of LOX activity in fruit, and kept the activities of PPO, POD, CAT at a high level. This low storage temperature also maintained good quality and the integrity of cell membrane of blackberry and delayed fruit senescence.(2) According to the colony and microscopic morphology, there were four isolated fungal strains from postharvest blackberry fruit, including Penicillium, Aspergillus, Alternaria and Fusarimn. Fusarimn was the dominant fungus in the storage. All four kinds of essential oils tested could inhibit fungus in vitro, but carvacrol and AITC had the best results. The higher the concentration of oil, the stronger the inhibition. In the experiment, we found that carvacrol and AITC could significantly reduce fruit rot and inhibit the growth of pathogenic fungi in fruit.(3) Carvacrol and AITC reduced decay of fruit, delayed decline of fruit firmness, had higher TSS and TA content, and maintained the quality of the fruit. However, high concentrations of essential oils might have phytotoxicity. When the concentration of carvacrol reached10μL·L-1; the blackberry decay rate was higher than those in control. When the concentration AITC reached15μL·L-1, serious discoloration of fruit occurred. Apparently, anthocyanin in berries might have been damaged by the high concentration of AITC.For blackberry preservation, suitable concentrations of AITC and carvacrol were10μL·L-1and2μL·L-1, respectively.(4) Carvacrol increased the content of total phenol and anthocyanin, enhanced the PAL, SOD, POD,CAT and β-1,3-glucanase and chitinase related enzyme activities, improved the antioxidant activity and disease resistance ability of the fruit, reduced the accumulation of reactive oxygen species (ROS) and pathogenic fungus, thereby, maintained the quality of fruit. AITC treatment did not improve the antioxidant activity and disease resistance ability of the fruit, but AITC enhanced higher amounts of H2O2and O2-. radicals than untreated fruit in blackberries. The DPPH radical scavenging capacity in AITC treatment was also lower than those in the control. It is possible that AITC might have directly interfered the growth of fungi by ROS accumulation and higher free radical activities, resulting in less fruit decay.