Pterostilbene emulsion preparation and its control effect on superficial scald in Dangshansuli pear

Abstract:【Objective】Dangshansuli pear is one of the most widely grown varieties of pear and one of the main fruits exported from China. Dangshansuli pear is always affected by the superficial scald disorder, causing serious economic losses. Superficial scald, a physiological disorder that causes the appearance of irregular browning or black patches on the skin of some pear and apple cultivars, generally occurs after several months of cold storage and rapidly worsens when fruits are transferred to room temperature. Although superficial scald does not affect fruit flesh, it severely affects the appearance quality and commodity value. The post-storage quality of fruit must be maintained or enhanced to meet the increasing demands of consumers and market competition. The natural antioxidant pterostilbene (Pte) in plants plays an important role in inhibiting fruit disorders, but due to the lack of emulsifiers when fruits are treated, it is difficult to spread fully on and adsorb by the fruit, thus affecting its medicinal effect. This study aims to explore the optimal formulation of pterostilbene emulsifiable (Pte EC), and find theeffects of it, Pte and Diphenylamine (DPA) on the post-harvest pear fruit storage quality and superficial scald control to explore whether Pte EC can improve the efficacy and replace the application of DPA in production, and provide a certain theoretical basis for the prevention of superficial scald in the future. 【Methods】In this study, the solvent and emulsifier of the preparation were screened with pterostilbene as the active ingredient, and then the emulsion quality was determined. Finally the optimum formula of 10% pterostilbene emulsifiable (Pte EC) was determined. On this basis, the Dangshansuli pear fruits were used as the experimental materials, which were harvested in September 2020 in the commercial orchard of Tongchuan county, Shaanxi province. Fruits with the same maturity and similar size, as well as without pests, diseases and mechanical damage were selected during harvesting, and transported back to Shaanxi Huasheng Fruit Industry on the same day. The next day, each of the treatments was carried out: In 2500 μL·L^-1 DPA aqueous solution, fruits were soaked for 2 minutes; In 10 mg·L^-1 Pte aqueous solution, fruits were treated for 2 min; In 10% Pte EC diluted into 10 mg · L^-1 aqueous solution, fruits were treated for 2 min. After processing, the fruits were packed in a carton with a plastic foam screen and stored in a cold storage [storage temperature: (-1.0±0.5) ℃, RH 90%-95%]. Twelve fruits were randomly selected every 30 days during cold storage, and each treatment was repeated for three times. Immediately after taking pears back to the laboratory to determine the fruit quality index, the peel and pulp were ground with liquid nitrogen and stored at -80 ℃ for further analysis. The indicators included hardness, soluble solids content, titrable acid content, malondialdehyde content, DPPH free radical scavenging capability and hydrogen peroxide content. In addition, superficial scald related indicators also included superficial scald incidence, disease index, α- fanneene and conjugated triene contents. Then the effects of diphenylamine (DPA), Pte and Pte EC were studied on the fruit quality after refrigeration and shelf life.【Results】(1) In the current research, the best combination of absolute ethanol and Tween 20 were selected from 6 solvents and 10 emulsifiers that could meet the requirements of food safety. When Tween 20 was used as the emulsifier to prepare Pte EC, the solution was automatically dispersed in a mist. And after stirring, it became a blue and clear emulsion, without floating oil on the top and sediment on the bottom. The emulsification dispersion effect was perfect and could meet the national standards. The emulsion stability, heat storage stability and cold storage stability were also qualified. (2) DPA, Pte, and Pte EC treatments could delay the decline of pear fruit firmness during cold storage and had the effect of maintaining the freshness of fruits. (3) DPA, Pte and Pte EC treatments can effectively inhibit the accumulation of H2O2, MDA and conjugated triene in pear peel during cold storage, thereby inhibiting the occurrence of superficial scald of Dangshansuli pear (p＜0.05). When pear fruits were stored up to 210 days, the incidence of fruit with three treatments was 28.69%, 12.19% and 15.32% lower than that of the control, respectively. (4) The controlling effect of Pte EC on pear superficial scald was second only to the DPA level, which was better than that of Pte treatment.【Conclusion】The preferred formula of 10% Pte EC finalized in this study is 10% pterostilbene + 10% Tween 20 + 80% absolute ethanol, and the performance of this formulation meets the national pesticide formulation standards. The formula is green environmental protection and safe, and improves the efficacy of Pte, which can improve the fruit quality and delay the fruit senescence to a certain extent. Simultaneously, Pte EC can effectively control the superficial scald of Dangshansuli pear. This study provides not only a new idea for the prevention of superficial scald, but also a theoretical basis for further Pte EC commercial application.