Herbal smoke fumigation for controlling Penicillium crustosum in fresh walnuts

Fresh walnuts have a high water content and are susceptible to decay, and controlling fungal contamination during storage is vital to walnut marketing. In this research, the dominant pathogenic fungus of fresh walnuts was first identified as Penicillium crustosum by morphological and molecular methods. The antifungal effect of herbal smoke fumigation was tested in vitro and in vivo, including Myristica fragrans Houtt., Aucklandia lappa Decne., Eugenia caryophyllata Thunb., Atractylodes lancea (Thunb.) DC., Shiraia bambusicola Henn., Artemisia argyi Lévl. et Vant. The results demonstrated that smoke from all six herbs successfully inhibited P. crustosum growth, and A. argyi smoke produced the best antifungal effect, which contained higher contents of phenol (17.1%), eugenol (13.7%), hexacosane, tetracontane, heneicosane, linolenic acid and other antimicrobial components by gas chromatography-mass spectrometry. Interestingly, optical transmittance data were found to correlate with antifungal capacity, revealing that a formed physical barrier combined with the above antimicrobial compositions, to participate in mold controlling together. Finally, fumigation with A. argyi smoke was tested in a real storage situation at proper dose, which not only dramatically controlled fungal contamination (>70%), but also maintained better odor and taste without oxidative rancidity or other adverse effects. This is the first report in which herbal smoke fumigation was adopted to preserve fresh walnut, providing a new way to reduce mold contamination and maintain quality of fresh walnuts in a natural and safe manner. More research on the application of herbal smoke fumigation to agricultural products in post-harvest storage is needed to explore the conditions and products for which it can be used successfully.