Effect of multi-frequency multi-mode ultrasound washing treatments on physicochemical, antioxidant potential and microbial quality of tomato

摘要

The study investigated the effect of multi-frequency ultrasound treatments including mono-frequency ultrasound (MFU), dual-frequency ultrasound (DFU), and tri-frequency ultrasound (TFU) on the physicochemical, antioxidant potential and microbial quality of tomatoes. The results revealed that various frequencies and modes presented significant (P0.05) differences in measured parameters including total soluble solids, colour, texture, lycopene content, total phenolic content, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, microstructure, pigment reflectance and microbial inactivation. However, ultrasound treatments did not significantly affect the pH and titratable acidity of the tomato. The TFU treatment led to a higher retention of total soluble solids, tomato colour indices, total phenolic content and 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of the sample, with a significant reduction in natural microbiota. The best treatment for natural microbiota reduction and enhancement of microbial safety was TFU, which in general reduced in decimal terms1.5 log CFU/g of bacteria, yeast and molds. In general, lycopene content, total colour difference, pigment reflectance, texture, microstructural integrity, and microbial load of tomato decreased in the order of MFUDFUTFU due to the increasing cavitation and possible additive effect of multi-frequency ultrasound. Results of the investigation recommend that multi-frequency multi-mode ultrasound washing could retain the quality of tomato. It could effectively be employed for postharvest processing of tomato leading to improvement in physicochemical, antioxidant potential and microbial safety.