Effects of 405 nm light‐emitting diode treatment on microbial community on fresh‐cut pakchoi and antimicrobial action against Pseudomonas reinekei and Pseudomonas palleroniana

Abstract

Pakchoi (Brassica rapa L. Chinensis) is an important cruciferous vegetable crop in East and Southeast Asia. This research aimed to investigate the change of microbial community and antibacterial effect of 405 nm light-emitting diode (LED 405 nm ) illumination (15 μ mol/(m 2 Á s)) against spoilage bacteria on the surface of agar media and fresh-cut pakchoi. High-throughput community sequencing was used to quantify bacterial abundance and 16S rRNA was used to analyze the bacterial community composition on fresh-cut pakchoi treated with or without LED 405 nm storage at 4 C. And alkaline phosphatase (AKP) activity and metabolic inhibition assays were selected to measure the mechanism of bacterial inhibition. The results showed that Pseudomonas spp. were able to multiply and cause spoilage of fresh-cut pakchoi at 4 C. Nevertheless, the majority of Pseudomonas spp. isolated from spoilage pakchoi were Pseudomonas reinekei and Pseudomonas palleroniana which were considered as representative specific spoilage microorganisms in pakchoi. Furthermore, 405 nm light treatment retarded sensory deterioration, inhibited microbial growth. AKP activity and metabolic inhibition assays confirmed the inhibitory effect of light treatment. In brief, 405 nm LED illumination has potential as a preservative to maintain quality, extend the shelf life for 6 days of fresh-cut pakchoi and abled to control P. reinekei and P. palleroniana growth on fresh-cut pakchoi at 4 C. | INTRODUCTIONFresh-cut vegetables refer to vegetables processed by washing, sorting, peeling, and slicing (Pan & Sasanatayart, 2016). However, during the processing of fresh-cut vegetables, because the phenols are oxidized by polyphenol oxidase reaction, it is easy to turn brown, red, and black (Chisari, Barbagallo, & Spagna, 2008). Different from enzymatic browning of vegetables, Pseudomonas spp. mainly causes tissue rot of fresh-cut vegetables, and has been proved to result in rapid browning reaction on cut surface of pakchoi (Wu et al., 2019).Research studies revealed that Pseudomonas spp. was correlated with the deterioration of lettuce (Federico et al., 2015), whereas Pseudomonas cichorii caused quality decline of head lettuce such as dark-brown and necrotic spots on leaves (Grogan, 1977). Moreover, pectolytic enzymes produced in Pseudomonas viridiflava and Pseudomonas chlororaphis caused organoleptic properties' decline and spoilage in fresh-cut vegetables (Lee et al., 2013;Liao, 1988).Studies have revealed that 405 nm visible light is effective to eliminating various bacterial strains (

Metabolic Effects of Violet Light on Spoilage Bacteria from Fresh-Cut Pakchoi during Postharvest Stage

“…For instance, discovered that LED 405 nm illumination significantly reduced populations of Salmonella on fresh-cut papaya by 0.3-1.3 log CFU/cm 2 at 4 • C for 36-48 h (1.3-1.7 kJ/cm 2 , p < 0.05) [11]. Meanwhile, our previous study showed that LED 405 nm light can not only inhibit the level of spoilage bacteria on fresh-cut pakchoi during the storage stage but also prolong the shelf life of fresh-cut pakchoi [10]. With regard to the mechanism of the bacteriostatic method of visible light, several scholars believe that reactive oxygen species (ROS) are generated inside cells and destroy the bacterial structure, resulting in a sublethal state or even cell death, which is called photodynamic inactivation (PDI) [12][13][14].…”

“…In our previous work, Pseudomonas palleroniana CFBP 4389 samples were isolated from spoiled pakchoi and were identified by 16S rRNA gene sequencing using a VITEK ® 2 CompactA system (BIOMÉRIEUX, France) [10]. Bacterial stock cultures contained 25% glycerine and were stored at −80 • C. The accession number of NCBI of Pseudomonas palleroniana CFBP 4389 is NR_029050.1.…”

“…The results of our previous study showed that Pseudomonas palleroniana is one of the specific spoilage organisms (SSOs) of fresh-cut pakchoi, which causes pakchoi to decline in quality during the storage stage [7]. Nonetheless, previous studies revealed that LED 405 nm light effectively reduced bacterial levels on the surface of fresh-cut fruits or vegetables during the storage stage [8,9] and extended their shelf life [10]. For instance, discovered that LED 405 nm illumination significantly reduced populations of Salmonella on fresh-cut papaya by 0.3-1.3 log CFU/cm 2 at 4 • C for 36-48 h (1.3-1.7 kJ/cm 2 , p < 0.05) [11].…”

Chlorophyllin-Based 405 nm Light Photodynamic Improved Fresh-Cut Pakchoi Quality at Postharvest and Inhibited the Formation of Biofilm

“…Another example of Pseudomonas spp.-caused spoilage was when pectolytic enzymes produced by Pseudomonas viridiflava and Pseudomonas chlororaphis accelerated the rate of rot and caused soft rot of vegetables [ 7 , 8 ]. Our previous work found that Pseudomonas reinekei and Pseudomonas palleroniana showed highly the dominant decaying bacteria of fresh-cut pakchoi [ 9 , 10 ]. Moreover, Morris et al [ 11 ] found that bacteria formed biofilms easily on the surface of vegetables, such as parsley and lettuce, and that the bacterial biofilms formed on the surface of vegetables are difficult to remove, which adversely affects the freshness storage of vegetables.…”

“…However, the excessive use of chlorine can be carcinogenic [ 13 ] and is forbidden in food industries in Sweden, Germany, Belgium, and other European countries [ 14 ]. Additionally, excessive UV exposure is harmful to human skin and eyes and 405 nm light sterilization efficiency is low [ 10 ]. Hence, there is a need to develop a new sterilization technology for the fresh-cut vegetable industry.…”