Fresh-cut Lotus Root Research Articles

Varying concentrations of ethephon induce antioxidant defences and cell wall degradation to regulate storage quality of fresh-cut lotus root

This study examined the impact of varying concentrations of ethephon (ET) immersion on the storage quality of fresh-cut lotus root. Compared to the 0.1%, the 0.8% and 1.6% ET groups inhibited phenolic oxidation and showed stronger antioxidant and reactive oxygen species balancing capacity during early storage, which led to better browning inhibition. During the early storage period, varying concentrations of ET treatments were inversely associated with microbial growth, and Pseudomonas as the major microorganism was significantly inhibited. During the post-storage period, the ET group exacerbated cell wall metabolism, contributed to the softening of lotus root slices. Additionally, ET stimulated enhanced respiration and reduced total soluble solids content as ET concentration increased. The heightened expression of NnERF in the late storage stage suggested a potential link to the regulation of root quality deterioration. Both browning inhibition and quality deterioration promotion exhibited gradient shifts in accordance with ET concentration. Combined with DNA affinity purification sequencing technology to identify the presence of motifs that bind specifically to ERF1B in lotus root, and screening for the possible target genes NnPL18 and NnACO that may be regulated by NnERF1B-like (104610030), it further suggests that NnERF1B-like (104610030) may mediate the process of lotus root flake softening and ethylene biosynthesis.

Multi-frequency thermosonication washing treatments of fresh-cut lotus root: Effect on the accumulation of phenolics and storage quality characterization evaluation

The effects of thermosonication (TS) washing at varying multi-frequencies in comparison to ultrasonication (US) and water washing (as a control) on the fresh-cut lotus root phenolics accumulation and the storage quality characteristics were explored. The relationships between free phenols (FPs), bound phenols (BPs), total phenolic content (TPC), and total antioxidant capacity were also revealed. Thermosonication increased the free phenols and total phenolic content, with the thermosonication of 20 + 40 + 60 kHz showing the most significant effect, and TS predominantly improved the total antioxidant capacity. Thermosonication promoted phenylalanine ammonia-lyase (PAL) activity and inhibited polyphenol peroxidase (POD) activity. The color analysis showed the thermosonicated samples exhibited the lowest value of ΔE and the browning degree. Thermosonication substantially increased weight loss and firmness, while reducing the levels of malondialdehyde (MDA) and Vitamin C (VC) compared to control. Overall, TS washing can increase the phenolic content of fresh-cut lotus root while preserving its antioxidant capacity and qualitative characteristics.

Melatonin-induced myeloblastosis viral oncogene homologs alleviate fresh-cut lotus root browning during storage by attenuating flavonoid biosynthesis and reactive oxygen species.

Lotus roots (Nelumbo nucifera Gaertn.) are rich in nutrients and have ornamental and food value. However, browning has caused huge economic losses and security risks during the storage and harvesting of fresh-cut lotus. This study investigated the role of melatonin in inhibiting lotus browning, and illustrates its molecular mechanism. The application of melatonin effectively retarded the process of lotus browning, enhanced reactive oxygen species (ROS) scavenging enzyme activity, and inhibited the activity of polyphenol oxidase (PPO), and peroxidase (POD). Melatonin reduced flavonoid content, and decreased enzymatic activity in flavonoid biosynthesis. Transcriptome Sequencing (RNA-seq) was used to screen the genes regulated by exogenous melatonin when defending against fresh-cut lotus browning. Gene co-expression analysis (GCN) indicated that the transcription factors MYB5, MYB6, and MYB308, activated by melatonin, were negatively related to the expression of PPO and the genes related to flavonoid and phenylpropanoid biosynthesis. These myeloblastosis viral oncogene homologs (MYBs) were positively related to the expression of genes encoding the enzymes in glutathione metabolism. Melatonin retarded lotus browning by transcriptional suppression of key genes associated with flavonoid and phenylpropanoid biosynthesis through the stimulation of MYB5, MYB6, and MYB308. © 2023 Society of Chemical Industry.

Biochemical Mechanism of Fresh-Cut Lotus (Nelumbo nucifera Gaertn.) Root with Exogenous Melatonin Treatment by Multiomics Analysis

Browning limits the commercial value of fresh-cut lotus root slices. Melatonin has been reported to play crucial plant roles in growth and development. However, the mechanisms in repressing the browning of fresh-cut lotuses are still unclear. In this study, fresh-cut lotus root slices were treated with melatonin, the physical signs of browning were tested, and then the selected samples (0 d, 6 d, 12 d) were used in multiomics analysis. Fresh-cut lotus root slices with a thickness of 4 mm were soaked in a 40 mmol/L melatonin solution for 10 min; then, the slices were packed in pallets and packages and stored at 10 ± 1 °C. The results show that the 40 mmol/L melatonin selected for repressing the browning of lotus roots significantly delayed the decrease in water, total soluble solid content, and Vitamin C, decreased the growth of microorganisms, enhanced total phenolic content, improved total antioxidant capacity, and decreased ·OH, H2O2, and O2-· contents. Moreover, this treatment enhanced phenylalanine ammonialyase, polyphenol oxidase, superoxide dismutase, and catalase activities and reduced peroxidase activities and soluble quinones. NnSOD (104590242), NnCAT (104609297), and some NnPOD genes showed a similar transcript accumulation pattern with enzyme activity. It can be seen from these results that exogenous melatonin accelerated an enhancement in the antioxidant system and AsA-GSH cycle system by regulating ROS-metabolism-related genes, thereby improving the capacity to withstand browning and the quality of lotus root slices. The microbiome also showed that melatonin suppressed the fertility of spoilage organisms, such as Pseudomonas, Tolumonas, Acinetobacter, Stenotrophomonas, and Proteobacteria. Metabonomics data uncovered that the metabolites of flavonoid biosynthesis, phenylpropanoid biosynthesis, tyrosine metabolism, and phenylalanine metabolism were involved in the process.

Effects of Precise Temperature Treatment on the Browning, Physiological and Quality of Fresh Cut Lotus Root

Effects of Precise Temperature Treatment on the Browning, Physiological and Quality of Fresh Cut Lotus Root

Optimization of Pretreatment for Prevention of Enzymatic Browning of Fresh-Cut Lotus (Nelumbo nucifera) Root Slices

The experiments were carried out optimized the chemical concentration as pre-treatments prior to drying of fresh-cut lotus root slices. The lotus root slices were pretreated by chemicals with Potassium metabisulphite (0.1, 0.2, and 0.3 % (w/v)), sodium bicarbonate (2, 4, and 6 % (w/v)), and ascorbic acid (0.5, 1 and 1.5 % (w/v)). The quality parameters of lotus root slices were taken as color parameters such as lightness (L*), redness (a*), and (b*) along with the browning index. The best treatment was decided based on the browning index. The experimental results indicated that the color parameters of fresh-cut lotus root slices and chemicals deteriorate over the time span of 0h to 5h. Besides that, chemically treated samples were improved over the fresh-cut lotus root slices. The lightness (L*), redness (a*), and yellowness (b*) of 0.30% potassium metabisulphite samples varies from 136 to 116, 1.17 to 248, and 2.87 to 5.34 for a period of time 0h to 5h, respectively. Which is the lowest as compared to all other samples. The browning index pre-treated samples was much lower than samples without treatment. The browning index increased with elapsed time and highly increase in untreated (fresh-cut lotus root slices) samples than pre-treated samples (chemicals treated). The optimized browning index was minimum (1.498 to 4.963) for 0.3 % KMS as compared to 5.337 to 16.02 and 2.73 to 9.227 for 6 % (w/v) sodium bicarbonate and 1.5 % (w/v) ascorbic acid solutions, respectively.

Regulations and mechanisms of 1-methylcyclopropene treatment on browning and quality of fresh-cut lotus (Nelumbo nucifera Gaertn.) root slices

The quality of fresh-cut lotus root slices is greatly affected by enzymatic browning. In this study, we investigated the effects of 1-methylcyclopropene treatment on browning and quality deterioration of lotus root slices. When fresh-cut lotus root slices were immersed in 0.1 mg L−1 1-MCP for 1 h and stored at 10 ℃ for twelve days, microbial growth, respiration, total phenolic content, phenylalanine ammonia lyase activity, polyphenol oxidase activity, and soluble quinone levels in fresh-cut lotus root slices were suppressed. Furthermore, 1-MCP treatment improved the antioxidant capacities, peroxidase activities, superoxide dismutase activities, catalase activities, and DPPH free radical scavenging rates in fresh-cut lotus root slices. In addition, 1-MCP treatment inhibited the production of reactive oxide species, which delayed quality deterioration of fresh-cut lotus root slices. Based on transcriptomics and real-time quantitative PCR results, gene expression levels of NnmetK2, NnACO, NnETR2, NnEIN3, and NnERF1 were up-regulated while expression levels of NnEBF1 were down-regulated. These findings indicate that 1-MCP inhibits ethylene biosynthesis and signal transduction, which suppresses a series of ethylene-induced physiological and biochemical reactions. Based on our findings, we propose a new strategy for inhibiting enzymatic browning in fresh-cut lotus root slices.

Effects of low temperature on browning and NAC gene expression of fresh cut lotus root

Effects of low temperature on browning and <i>NAC</i> gene expression of fresh cut lotus root

Structure Analysis and Study of Biological Activities of Condensed Tannins from Bruguiera gymnorhiza (L.) Lam and Their Effect on Fresh-Cut Lotus Roots.

Bruguiera gymnorhiza (L.) Lam is a mangrove plant that spread in many parts of the world. Though mangrove plant polyphenols have been reported to exhibit many biological activities, little is known about mangrove plant tannins. To explore the application value of tannins from B. gymnorhiza, analyses on the structure and biological activity of condensed tannins (CTs) from Bruguiera gymnorhiza (L.) Lam were carried out. The results from 13C nuclear magnetic resonance (13C-NMR) and reversed-phase, high-performance liquid chromatography (RP-HPLC) showed that the CTs were dominated by procyanidins, with a small quantity of prodelphinidins and propelargonidins; and that the monomeric constituents of B. gymnorhiza tannins were catechin/epicatechin, gallocatechin/epigallocatechin and afzelechin/epiafzelechin. The CTs were reversible and mixed competitive inhibitors of tyrosinase and the 50% inhibiting concentration (IC50) was estimated to be 123.90 ± 0.140 μg/mL. The antioxidant activities of CTs from B. gymnorhiza leaves were evaluated, the IC50 for 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzo-thiazoline-6-sulfonic acid diammonium salt) (ABTS) scavenging activities were 88.81 ± 0.135 and 105.03 ± 0.130 μg/mL, respectively, and the ferric ion reducing antioxidant power (FRAP) value was 1052.27 ± 4.17 mgAAE/g. In addition, the results from fresh-keeping assays on fresh-cut lotus root reveal that CTs from B. gymnorhiza had excellent effects on inhibiting the activities of polyphenol oxidase (PPO) and peroxidase (POD), protecting fresh-cut lotus root from the oxidation of total phenolics and malondialdehyde (MDA) content and slowing the increase in total phenol content (TPC) at 4 °C during the whole storage period. Therefore, CTs showed good effects against the browning of fresh-cut lotus root. Together, these results suggested that B. gymnorhiza CTs are promising antibrowning agents for fresh-cut fruits.

Combination of sodium alginate-based coating with L-cysteine and citric acid extends the shelf-life of fresh-cut lotus root slices by inhibiting browning and microbial growth

The effects of a sodium alginate (SA) coating combined withl-cysteine (L-cys) and citric acid (CA) on browning and microbial growth in fresh-cut lotus root slices during storage at 4 °C were investigated. The SA + L-cys + CA treatment was more efficient than separate SA andl-cys + CA treatments in the maintenance of visual appearance and flavour quality. The SA + L-cys + CA coating improved the ability of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase) to scavenge reactive oxygen species, including O2·− and H2O2. In comparison to the control, the SA + L-cys + CA treatment lowered the activity of phenylalanine ammonia lyase, peroxidase, and membrane lipid-degrading enzymes (phospholipase D, lipase and lipoxygenase) and furthermore, maintained high amounts of unsaturated and saturated fatty acids as well as low levels of phenolics and malondialdehyde. The bacterial diversity in lotus root slices was also determined and discussed. The SA + L-cys + CA treatment could maintain the shelf-life of fresh-cut lotus root slices for 14 d at 4 °C, which provides a theoretical basis for commercial application.

Spray technology applications of xanthan gum-based edible coatings for fresh-cut lotus root (Nelumbo nucifera)

In this study, the effect of spraying method as an application technique for xanthan gum-based edible coatings was investigated, based on its barrier and microbial properties on fresh-cut lotus root. Xanthan gum solutions (0.1%, 0.3%, and 0.5%) were prepared and incorporated with 2% (w/w) citric acid as an anti-browning agent and 1% (w/w) glycerol as plasticizer. The coatings were then sprayed using a pilot spray system to 5 mm-thick slices of fresh-cut lotus root for 20 s, packed in polyethylene bags, stored for 16 d at 5 °C and analyzed for color, pH, morphology and microbial counts. It was found that spray-coated fresh-cut lotus root samples had significant reduction in the total color changes as compared to non-coated samples. The experimental results suggested that the spray coating treatments were effective in decreasing the enzymatic browning of fresh-cut lotus root during storage which could potentially increase its shelf-life in the market. In addition, we have also found that the xanthan gum-based spray coated treatments were also effective against inhibiting the growth of Bacillus subtilis during 24 h of incubation which were indicated by the lower microbial counts recorded as compared to non-coated fresh-cut lotus root samples. In this part of the work, the author highlighted the spray coating technique of xanthan gum-based edible coatings as a promising strategy in improving the storage stability of fresh-cut lotus root during post-harvest storage. Overall, the application of edible coatings is a promising strategy in extending the shelf life of fresh-cut lotus root. In the future, the author aims to widen the scope of the application of these coatings to other agricultural products which are prone to degradation during storage in the market.

Effects of pulsed electric field pretreatment on frying quality of fresh-cut lotus root slices

This study aimed to compare the effects of pulsed electric field (PEF) pretreatment on fresh-cut lotus root and its frying quality with those under blanching (80 °C, 3 min). The lotus root slices were treated by 10,000 pulses at different electric field strength (0.5, 1.0 and 1.5 kV/cm) with specific energy levels (5.56, 22.20 and 50.00 kJ/kg). PEF treatment decreased the reducing sugar content in fresh samples and then diminished the Millard reaction, including lower browning index and 25.9% reduction in acrylamide content. Besides, membrane disintegration occurred when the cells were subjected to PEF, resulting in soft tissue structure and a reduction of oil inhalation of 15%. Results imply that PEF treatment can be used as a viable alternative to blanching to pretreat lotus root slices, effectively saved thermal energy required for industrial production and delivered more positive effects on quality of fried slices.

Layer-by-Layer Electrostatic Deposition of Edible Coatings for Enhancing the Storage Stability of Fresh-Cut Lotus Root (Nelumbo nucifera)

Various strategies have been employed to improve the storage stability of fresh-cut lotus root, which is prone to undesirable changes such as enzymatic oxidation. In our research, we targeted the formulation of polysaccharide-based edible coatings with different ionic charges from natural gum sources, such as guar gum, xanthan gum, and chitosan, due to the limited information regarding its application as coating material for fresh-cut lotus root. We have also compared the effect of single layer coatings versus layer-by-layer deposition as edible coating techniques for fresh-cut lotus root. Our results have shown that layer-by-layer coatings consisting of xanthan gum and chitosan were the most effective among all treatments, thereby reducing whiteness color (L*) changes and weight loss up to 60% and 86%, respectively. Overall, the layer-by-layer coating technique was more effective than single layer coating, which shows a promising strategy to increase the storage stability of fresh-cut lotus root especially during transport and distribution.

Expression Analysis of ERFs during Storage under Modified Atmosphere Packaging (High-concentration of CO2) of Fresh-cut Lotus Root

Ethylene response factor (ERF) genes have been characterized in numerous plants, where they are associated with responses to biotic and abiotic stress. Modified atmosphere packaging (MAP) is an effective treatment to prevent lotus root browning. However, the possible relationship between ERF transcription factors and lotus root browning under MAP remains unexplored. In this study, the effects of phenol, phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) enzyme activities; and PPO, PAL, POD, and ERF gene expression on fresh-cut lotus root browning were studied with MAP. The expression pattern of ERF2/5 correlated highly with the degree of browning. It is suggested that NnERF2/5 can be used as an important candidate gene for the regulation of fresh-cut lotus root browning under MAP, and the correlation of each gene should be studied further.

Effects of Vacuum Packaging on NAC Gene Expression in Fresh-cut Lotus Root

NAC transcription factors have been characterized in numerous plants, and the NAC gene has been shown to be involved not only in plant growth and development, but also in plant responses to abiotic and biological stresses, such as drought, high salinity, low temperature, and anaerobic/hypoxic stress. Creating an environment of anaerobic/hypoxic stress has been shown to be one of the effective storage methods for delaying the browning of fresh-cut lotus (Nelumbo nucifera) root. However, whether NAC is associated with lotus root browning under anaerobic stress has not been studied. In this study, vacuum packaging (VP; anaerobic/hypoxic stress) effectively delayed the browning of fresh-cut lotus root. The changes in the expressions of NnPAL1, NnPPOA, and NnPOD2/3 were consistent with phenylalanine aminolase, polyphenol oxidase (PPO), and peroxidase (POD) enzyme activity changes and lotus root browning. Using RNA sequencing, five NnNAC genes were isolated and studied. Transcriptional analysis indicates that the NnNAC genes showed different responses to VP. The expressions of NnNAC1/4 were inhibited by VP, which was consistent with the observed change in the degree of fresh-cut lotus root browning. However, NnNAC2 messenger RNA (mRNA) levels were upregulated, and the expressions of NnNAC3/5 showed no clear differences under different packaging scenarios. Thus, NnNAC1/4 were identified as promising candidates for further transcriptional regulation analysis in lotus root to understand more fully the molecular mechanism of browning under anaerobic/anoxic stress.

Effects of Vacuum Packaging on Enzymatic Browning and Ethylene Response Factor (ERF) Gene Expression of Fresh-cut Lotus Root

Ethylene response factor (ERF) genes have been involved in responses to biotic and abiotic stress, including hypoxia and anaerobic stress. Vacuum packaging (a typical anaerobic stress) is an effective storage method used to delay browning of fresh-cut lotus root (Nelumbo nucifera). In model plants, ERF genes have been identified as responsive to hypoxia. Whether ERF is associated with browning of vacuum-packaged lotus root has not been studied. The effects of vacuum packaging on browning, phenolic content, the enzyme activity of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD), and PPO, PAL, POD, and ERF genes expression in fresh-cut lotus root were studied. Downregulation of NnPAL1, NnPPOA, and NnPOD2/3 attributable to vacuum packaging coincided with increased related enzyme activities and the degree of browning of fresh-cut lotus root. The expression patterns of NnERF4/5 were consistent with the changes in NnPAL1, NnPPOA, and NnPOD2/3 gene expression. It has been proposed that NnERF4/5 could have be important regulators of fresh-cut lotus root browning, and that the relationships of NnERF4/5 and NnPAL1, NnPPOA, and NnPOD2/3 should to be studied further.

Effect of UV-C treatment on the quality of fresh-cut lotus (Nelumbo nucifera Gaertn.) root.

The effect of shortwave ultraviolet (UV-C) radiation on the quality, especially browning of fresh-cut lotus (NelumbonuciferaGaertn.) root in relation to enzymes and phenolic metabolism was investigated. Fresh-cut lotus roots were exposed to UV-C lamp (75 W) at a distance of 30 cm above the produce tray for 1, 5, 10, 20, and 40 min, and then stored for 8 days at 4 °C. Results showed that UV-C treatments for 5 and 10 min exhibited significantly low browning degree, soluble quinone content and inactivation of polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase activities, while other qualities including soluble solids content and hardness had no difference with other treatments. Prolonging treatment time had less effect on inhibiting the browning since a long time of UV-C radiation increased cell damage. In summary, UV-C treatment has the potential to maintain quality of fresh-cut lotus root.

Expression of Ethylene Response Factor Genes during Fresh-cut Lotus Root Storage and Browning

Ethylene response factor (ERF) genes have been characterized in numerous plants in which they are involved in responses to biotic and abiotic stress, including cold and heat stress. Cool temperatures is one of the most effective storage methods for delaying browning of fresh-cut lotus (Nelumbo nucifera) root. In model plants, ERF genes have been identified as being responsive to cold and heat stress. Whether ERF is associated with lotus root browning in cooler temperatures has not been studied. In this research, low-temperature storage (4 °C) effectively delayed browning of fresh-cut lotus root. Using RNA sequencing, seven Nelumbo nucifera ERF (NnERF) genes were isolated and studied. Transcriptional analysis indicated NnERF genes responded differently to temperature. NnERF3/4/5 were reduced continuously by a low temperature (4 °C) and NnERF5 was the most strongly downregulated. In contrast, transcripts of NnERF1/2/7 were increased at a low temperature (4 °C). The expression of NnERF6 showed no obvious difference between the two different temperatures. It is proposed that NnERF3/4/5 could be important candidates as regulators of fresh-cut lotus root browning. The roles of other members are also discussed.

Mild concentration of ethanol in combination with ascorbic acid inhibits browning and maintains quality of fresh-cut lotus root

Aqueous solutions of ethanol and ascorbic acid alone and in combination were compared to a commonly used sanitizer, sodium hypochlorite, and a leading commercial antibrowning agent containing calcium ascorbate (CA) for their efficacy to inhibit microbial growth and browning on fresh-cut lotus root. Fresh-cut lotus root slices were immersed in one of 7 treatment solutions including water (control), 30% ethanol (v/v), 30% ethanol (v/v) plus 30gL−1 ascorbic acid (AA), 30% ethanol (v/v) plus 30gL−1 CA, 30gL−1 AA, 30gL−1 CA and 100mgL−1 sodium hypochlorite for 2min, and then packaged in polyethylene bags and stored for 28d at 4°C. Packages were monitored for headspace gas composition, color, texture, aerobic mesophilic bacteria, and yeast and mold populations, electrolyte leakage and sensory attributes. The results indicate that all ethanol treatments, with and without added AA or CA, not only inhibited microbial growth, but also delayed browning more effectively than either AA or CA alone. The combined treatments of Ethanol 30% (v/v) along with 30gL−1 AA or 30gL−1 CA were even more effective than ethanol alone in maintaining quality of fresh-cut lotus slices during cold storage. Increasing ethanol concentration within the range of 5–30% (v/v) when accompanied by 30gL−1 AA, decreased microbial populations and had little effect on quality maintenance of fresh-cut lotus root during cold storage. Ethanol concentrations of 20–30% (v/v) in conjunction with 30gL−1 AA have the potential to inhibit browning and maintain quality of fresh-cut lotus root slices for more than 14d when stored at 4°C. This is the first use of ethanol as a dual control for both browning and microbial growth in fresh-cut lotus root.

The effect of different temperatures on browning incidence and phenol compound metabolism in fresh-cut lotus (Nelumbo nucifera G.) root

Lotus root (Nelumbo nucifera G.) is an important aquatic vegetable in China. Browning easily during the processing and storage reduces the value of lotus root. Therefore, browning is an important issue for the lotus root industry. PAL, PPO and POD genes were reported as being involved in fruit and vegetable tissue browning, and PAL, PPO and POD enzymes have long been associated with lotus root browning. However, the molecular mechanism of PAL, PPO and POD involved in fresh-cut lotus root browning is poorly understood. This paper analyses the effect of different temperatures on the phenolic content, browning, PPO, PAL and POD enzyme activity and the expression pattern of PPO, PAL and POD genes in fresh-cut lotus root. The results show that the change of PAL, PPO and POD enzymatic activity occurs in parallel with the increase in browning degree in storage at different temperatures. Furthermore, the total phenol content and PAL enzyme activity changes are basically identical, suggesting that PAL might be the key genes involved in the synthesis of total phenol content. Two NnPAL, 2 NnPPO and 7 NnPOD genes were isolated using RNA-seq, and the upregulation of NnPAL1, NnPPOA, NnPOD1, NnPOD2, NnPOD3, NnPOD4, NnPOD5 and NnPOD6 by high temperature coincided with the increase in related enzyme activities and the browning degree of fresh-cut lotus root, which should be considered the most important candidates for fresh-cut lotus root browning.