Formula optimization and verification of mould inhibitor for southern rice by Design-Expert response surface method

Abstract

[Objective] The mould inhibitor formula for southern rice during storage was selected so as to provide technical support for the rice storage.

[Method] The main rice mold contaminants were determined from two indica rice varieties stored for 3-6 months and 12-24 months. The total mold counts and the mildew proof effects of five plant extracts, including leaf extracts from ampelopsis, tea, and mulberry, essential oils of orange peel and clove, on Aspergillus flavus growth in stored rice were analyzed. Finally, inhibition zone diameters achieved against A. flavus was used as an index and combined with the Design Expert response surface method to obtain an optimized compound formulation of the plant extracts.

[Result] The microbial presence in grain stored for 3-6 months was 1.1×10 ³-9.2×10 ³ CFU/g, while that in rice stored for 12-24 months was significantly greater at 8.1×10 ³-2.2×10 ⁵ CFU/g. Aspergillus and Penicillium were the main contaminating molds in southern rice, followed by Mucor and Fusarium. The inhibition zone diameter of A. flavus is between 8.4-11.1 mm, and the minimum inhibitory (%) and bactericidal concentrations were between 0.0125%-0.0500% and 0.0500%-0.1000%, respectively. All five plant extracts were effective as independent fungicides, the most effective of which was the leaf extract of ampelopsis. The prediction and simulation equation of mold inhibitor is as follows: Y=10.34A+10.06B+7.18C+8126.84D-10096.90E+11.97AB+ 12.18AC-8236.89AD+10212.4AE+10.74BC-8245.77BD+10084.50BE-8149.38CD+10357.06CE+6202.14DE. Where Y represents the diameter of the antifungal zone and A, B, C, D and E represent the proportions of extracts of ampelopsis, tea, mulberry, orange peel and clove in the mold inhibitor formulation respectively. The optimal proportion of leaf extracts and essential oils was as follows: 55.00% ampelopsis, 22.12% tea, 22.56% mulberry, 0.10% orange peel and 0.21% clove. The inhibition of mildew development by the compound fungicidal formula was clearly more effective than individual extracts or essential oils and the inhibition zone diameter of 25 combinations against A. flavus was between 11.30-13.90 mm. The safe grain storage time after spraying with the best compound fungicide on rice could be extended for about 60-120 d.

[Conclusion] The compound fungicide composed of five natural plant extracts described above could inhibit the reproduction of microorganisms and extend the safe storage period for grain.

Abstract

摘要：【目的】筛选适合南方稻谷贮藏要求的防霉剂配方, 为南方稻谷贮藏提供技术支持。 【方法】以当年收储、入 库贮藏3~6个月的籼稻稻谷 (新粮) 和入库贮藏12~24个月的籼稻稻谷 (陈粮) 为试验材料, 分析稻谷带菌总量、主要污 染菌种类以及藤茶提取物、茶叶提取物、桑叶提取物、陈皮精油和丁香精油等5种植物提取物对稻谷中黄曲霉的抑制 效果; 以黄曲霉的抑菌圈直径为考察指标, 通过Design-Expert响应面法进行南方稻谷复合防霉剂最佳配方设计。 【结果】新粮稻谷样品带菌量为1.1×10 ³~9.2×10 ³ CFU/g, 陈粮样品带菌量为8.1×10 ³~2.2×10 ⁵ CFU/g, 陈粮样品的带菌总量 明显高于新粮样品; 南方稻谷的主要污染菌属以曲霉属和青霉属为主, 其次是毛霉属和镰刀菌属; 5种植物提取物对 黄曲霉的抑菌圈直径在8.4~11.1 mm, 最低抑菌浓度 (MIC) 和最低杀菌浓度 (MBC) 分别为0.0125%~0.0500%和 0.0500%~0.1000%, 5种植物提取物均可作为单独的防霉剂使用, 以藤茶提取物的抑制效果最好。复合防霉剂预测模 拟方程为: Y=10.34A+10.06B+7.18C+8126.84D-10096.90E+11.97AB+12.18AC-8236.89AD+10212.40AE+10.74BC-8245.77BD+10084.50BE-8149.38CD+10357.06CE+6202.14DE (其中Y代表抑菌圈直径, A、B、C、D和E分别代表藤茶 提取物、茶叶提取物、桑叶提取物、陈皮精油和丁香精油在复合防霉剂中的比例), 拟合后得到的复合防霉剂最优配方 比例为: 55.00%藤茶提取物、22.12%茶叶提取物、22.56%桑叶提取物、0.10%陈皮精油和0.21%丁香精油; 复合防霉剂 的防霉效果明显优于单一防霉剂, 25个组合对黄曲霉的抑菌圈直径在11.30~13.90 mm; 稻谷表面喷洒最优复合防霉 剂后的安全贮藏时间可延长60~120 d。 【结论】由藤茶提取物、茶叶提取物、桑叶提取物、陈皮精油和丁香精油等5种植 物提取物组成的复合型稻谷防霉剂可抑制稻谷中微生物的繁殖, 延长稻谷安全贮藏时间。