Effects of electrolyzed water combining with ultrasonic wave on fusarium oxysporum and escherichia coli control in turmeric (Curcuma longa L.) after harvest

Abstract

The major problem during postharvest of Zingiberaceae is microbial contamination. Fusarium oxysporum and Escherichia coli had been reported to cause soft rot. In this study, it was a study on the use of acidic electrolyzed water (electrolyzed oxidizing: EO) and alkaline electrolyzed water (electrolyzed reducing: ER). Electrolyzed water was generated by electrolysis from 5% NaCl solution. The spore suspensions were soaked with EO water at free chlorine concentrations of 100, 200, 300, and 400 mg/L and ER water at NaOH concentrations of 125, 250, 500 and 750 mg/L for 10 min; after that dropped on PDA plate, then incubated at room temperature (28±2°C) for 72 hr. The abnormality of mycelial was observed under compound microscope. The results showed that EO water at 300 and 400 mg/L and ER water at 500 and 750 mg/L had affected on abnormal mycelial of F. oxysporum. When combining electrolyzed water with an ultrasonic (US) wave at 43 and 1,000 kHz for 10 min, it was found that EO water at 200 mg/L combined with US at 43 kHz gave the best inhibition of microbial growth. The cell structure of F. oxysporum and E. coli was observed with a scanning electron microscope (SEM), which demonstrated that they represented abnormal cells after being treated with EO and ER water. The morphological damage of all treatments showed the mycelial of F. oxysporum was contorted and uneven, which decreased bacterial cell viability. In the case of E. coli, cells showed rupture and collapse, especially at the damage site of the surface bacterial cells. In addition, the use of electrolyzed water (EO and ER) combined with ultrasonic waves on the control of postharvest pathogens, it was found that the application of EO water at 400 mg/L combined with US wave at 43 kHz for 10 min gave the best inhibition of microbial growth. Moreover, the study of total curcuminoid contents, which important factor to determine the quality and marketability of fresh and commercial dried turmeric. The result showed that total curcuminoid contents of fresh turmeric after treated with EO and ER water combined US wave trended to decrease after storage for 28 days, it varied between 3.36–4.33 mg/g fresh weight and significantly different when compared with control treatment (3.38 mg/g fresh weight), while the commercial dried turmeric treated with EO and ER water combined with the US wave of all treatments had no effect on the total curcuminoid contents throughout the storage period when compared with the control treatment. From the analysis of moisture and ash percentages in fresh and commercial dried turmeric, it was found that the moisture contents of all treatments of fresh turmeric increased over the storage period of 28 days, and the ash contents of all treatments were higher than in the control treatment after storage for 21 days, which was not statistically different. After 7 days of storage, it was demonstrated that the commercial dried turmeric had a slowly declining moisture percentage, which was not statistically different. The ash contents of commercial dried turmeric in each treatment were not different after storage for 14 days. Therefore, the application of acidic and alkaline water (EO and ER water) combined with ultrasonic wave. It has the potential to be used as a disease control for both fresh and commercial dried turmeric and could have further agricultural and other food industry applications.