Enhanced antifungal activity of michelia oil on the surface of bamboo paper packaging boxes using helium-neon (HeNe) laser and its application to brown rice snack bar

Abstract

The objective of this research is to evaluate the antifungal activity of michelia oil (Michelia alba) and its main components (linalool and caryophyllene) at concentrations of 300–500 mg g−1against the growth of Aspergillus niger, Aspergillus flavus, Penicillium sp., Rhizopus sp., Fusarium sp. and Cladosporium sp. on the surface of bamboo paper packaging boxes. Next, Helium-Neon (He-Ne) laser operating at 543, 594, 604, 612, and 633 nm for 1 min was used to enhance the antifungal activity of these additives. A spore suspension of each mold (7log10 CFU ml−1) was inoculated on pieces of treated bamboo paper. Visible mycelium growth of all molds on treated bamboo paper compared to control specimens was to calculate minimum inhibitory concentration (MIC). The inhibitory period of michelia oil and linalool in a bamboo paper box with and without laser against natural mold infections on brown rice snack bars was further examined for 8 weeks at 25 °C and 100% RH. The MIC values of michelia oil and linalool with laser treatment were 300 mg g−1 and 150 mg g−1, respectively. Without laser treatment, no MICs were found at the maximum concentration (500 mg g−1). Therefore, linalool was shown to be a stronger inhibitor than the essential oil after laser treatment and should be the key factor in boosting the antifungal activity of michelia oil. In addition, the MICs showed the capability of bamboo paper boxes treated with michelia oil and linalool, with laser treatment to protect against mold growth on snack bars for at least 5–7 weeks in comparison with the control (3 days) during storage at accelerated conditions (25 °C and 100% RH).