Effect of carbon monoxide on browning of fresh-cut lotus root slice in relation to phenolic metabolism

Active Packaging Film Developed by Incorporating Starch Aldehyde-Quercetin Conjugate into SPI Matrix

In this study, soy protein isolate (SPI) films incorporating quercetin-grafted dialdehyde starch (DAS-QR) and DAS/QR, respectively, were developed. The structural, physical, and functional properties of the composite films were determined. The results suggested that DAS-QR and DAS/QR formed hydrogen bonding with the SPI matrix, which improved the structural properties of the films. The light-blocking capacity, thermal stability, hydrophobicity, tensile strength, elongation at break, and antioxidant and antibacterial abilities of SPI films were improved by DAS-QR and DAS/QR. Notably, SPI films incorporated with DAS-QR exhibited better performance than those with DAS/QR in terms of antioxidant (SPI/DAS-QR: 79.8% of DPPH and 62.1% of ABTS scavenging activity; SPI/DAS/QR: 71.4% of DPPH and 56.0% of ABTS scavenging activity) and antibacterial abilities against S. aureus (inhibition rate: 92.7% for SPI/DAS-QR, 83.4% for SPI/DAS/QR). The composite coating film SPI/DAS-QR effectively maintained appearance quality, delayed the loss of weight and total soluble solids, postponed malondialdehyde accumulation, and decreased peroxidase activity and microbial contamination in fresh-cut potatoes. These good performances highlight SPI/DAS-QR as a promising active packaging material for fresh-cut product preservation.

Cactus polysaccharides enhance preservative effects of ultrasound treatment on fresh-cut potatoes

The shelf life of fresh-cut fruits and vegetables is affected by microbial growth, enzymatic browning, and loss of flavor. Although ultrasound (US) treatment is often used in the preservation of fresh-cut fruits and vegetables, it has limited antibacterial and preservative effects. Here, we used cactus polysaccharides (CP) to enhance the preservative effect of ultrasound treatment and extended the shelf life of fresh-cut potatoes. The results showed that combined treatment (CP + US) exerted better antimicrobial and anti-browning effects than individual treatments (either US or CP alone). In addition, CP + US has no adverse effect on texture and quality properties, as well as reduced the mobility of internal water. Combination treatment not only significantly decreased the activities of polyphenol oxidase and peroxidase (P < 0.05), but also maintained a high level of phenylalanine ammonia lyase activity and total phenol content during storage. It also maintained the integrity of cell membrane and reduced its permeability by inhibiting the peroxidation of membrane lipids. In addition, CP + US treatment significantly inhibited the activity of antioxidant enzymes and maintained a high DPPH scavenging ability. GC-IMS technology was used to evaluate the flavor of fresh-cut potatoes. The results showed that CP + US treatment reduced the production of a peculiar smell during storage and maintained a good flavor by inhibiting the production of aldehydes. Taken together, these results indicate that the effective preservation method of CP + US treatment can be utilized to increase the shelf life of fresh-cut potatoes.

The mechanism of interaction between lotus rhizome polyphenol oxidase and ascorbic acid: Inhibitory activity, thermodynamics, and conformation analysis

In this study, the interaction between lotus rhizome polyphenol oxidase (PPO) and ascorbic acid (AA) was discussed from the aspects of inhibitory activity, thermodynamics, and conformation. Results showed that PPO was purified from lotus rhizome by DEAE-52 anion exchange chromatography and Sephadex G-100 gel filtration chromatography, with its optimum substrate being determined as pyrogallic acid. Spectrophotometric and polarographic assays demonstrated that AA exhibited strong inhibitory activity against PPO. Thermodynamics, fluorescence, and circular dichroism spectral analysis showed that hydrophobic interactions caused the formation of AA-PPO complex, leading to the remarkable fluorescence quenching and conformational change of PPO. Atomic force microscopic analysis revealed that binding to AA induced significant changes in the surface morphology and molecular aggregation of PPO molecules. In this study, the interaction mechanism between PPO and AA was proposed for the first time, which provided a theoretical basis for AA to inhibit lotus rhizome browning. PRACTICAL APPLICATIONS: Lotus rhizome, an aquatic vegetable, is prone to enzymatic browning in processing operations, which leads to a decrease in market value and economic loss. At present, ascorbic acid (AA) is widely used in industries as an excellent antioxidant because of its good antibrowning effect and relatively low cost. However, the interaction between the enzymatic browning-related polyphenol oxidase (PPO) from lotus rhizome and ascorbic acid has not been clearly studied. Understanding the mechanism of inhibiting PPO will help to prevent vegetable browning, especially fresh-cut products. The inhibitory effect of AA on PPO in lotus rhizome favors simultaneous use with other types of PPO inhibitors because of their likely synergistic effects.

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 ethylene biosynthesis and signaling on oxidative stress and antioxidant defense system in Nelumbo nucifera G. under cadmium exposure

Water contamination with cadmium (Cd) is a global environmental problem and its remediation becomes urgent. Phytoremediation using ornamental plants has attracted much attention for its advantages of cost-effectiveness and beautification of the environment. Nelumbo nucifera G. is a popular ornamental aquatic macrophyte with fast growth, large biomass, and high capacities for Cd accumulation and removal. However, information about Cd resistance and defense responses in N. nucifera is rather scarce, which restricts its large-scale utilization for phytoremediation. The phytohormone ethylene plays an important role in plant resistance to Cd stress, but the underlying mechanism remains unclear. In this study, we investigated morphophysiological responses of N. nucifera seedlings to Cd stress, and focused on the effects of ethylene on oxidative damage, Cd accumulation, and antioxidant defense system at the metabolic and transcript levels in leaves under Cd stress. Our results showed that Cd exposure led to leaf chlorosis and necrosis, coupled with an increase in contents of hydrogen peroxide, electrolyte leakage, and malondialdehyde, and decrease in chlorophyll content. Exogenous ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) application intensified Cd-induced stress responses and Cd accumulation, and increased ethylene production by inducing ACC synthase (ACS) gene NnACS. Such enhanced ethylene emission inhibited catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities, and modulated ascorbate (AsA) and glutathione (GSH) accumulation through transcriptional regulation of their respective metabolic genes. After ethylene action inhibitor silver thiosulfate (STS) supplementation, Cd-induced oxidative damage was abolished, and Cd content declined but still at a relatively high level. Blocking of ethylene perception by STS inhibited ethylene biosynthesis; enhanced CAT, APX, and GR activities and their transcript levels; increased AsA accumulation via inducing its biosynthetic genes; but reduced GSH content and NnGSH2 expression level. These results suggest that ethylene biosynthesis and signaling play an important role in N. nucifera response to Cd stress, and maintaining appropriate ethylene level and low ethylene sensitivity could improve its Cd tolerance via efficient antioxidant defenses.

Effect of pre-storage ascorbic acid and Aloe vera gel coating application on enzymatic browning and quality of lotus root slices

The effect of ascorbic acid [AA (1%)] and Aloe vera gel [AVG (50%)] coating alone and in combination was investigated on enzymatic browning and quality of lotus root slices during storage at 20 ± 1°C. The combined application of AA and AVG coating delayed surface browning, reduced increase in relative electrolyte leakage (REL) and showed higher overall visual quality (OVQ). Similarly, AA and AVG combined treatment reduced superoxide anion ( O 2 - · ) and hydrogen peroxide (H₂ O₂ ) production and malondialdehyde (MDA) content, and suppressed peroxidase (POD) and polyphenol oxidase (PPO) activities. In addition, AA and AVG treatment conserved higher AA content, ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase (CAT) enzymes activities along with higher total phenolics and radical scavenging activity. In conclusion, the combined application of AA and AVG coating could be an appropriate treatment to delay surface browning and quality loss of lotus root slices. PRACTICAL APPLICATIONS: Lotus root is an aquatic rhizome vegetable. The fresh-cut slices of lotus roots are prone to post-cut enzymatic browning and quality deterioration during postharvest storage. Browning induced loss of visual quality and microbial infestations are the leading constraints in extending storage and/or shelf life of lotus root slices. Surface browning results in loss of characteristic color eventually leading to significant reduction in market potential and visual quality. However, quality deterioration and development of browning could be delayed with some suitable postharvest treatments. So, the effect of AA and Aloe vera gel based coating was investigated for quality conservation of lotus root slices. The findings of the current work are of global importance in reducing browning and conserving visual quality of lotus root slices in particular and fresh-cut produce in general.

Effect of postharvest oxalic acid application on enzymatic browning and quality of lotus (Nelumbo nuciferaGaertn.) root slices

Post-cut surface browning is one of the major constraints for shelf-life extension of lotus root slices. In the present study, lotus roots slices were treated with 0, 5 and 10 mmol L^-1 oxalic acid and stored at 20 ± 1 °C for 5 days. Results showed that 10 mmol L^-1 oxalic acid treated lotus slices exhibited reduced browning, superoxide anion, hydrogen peroxide, electrolyte leakage and malondialdehyde content than control. The 10 mmol L^-1 treated slices had better visual quality and higher ascorbic acid and total phenolic contents. In addition, 10 mmol L^-1 treated slices showed reduced total bacterial count along with lower soluble quinones, peroxidase and polyphenol oxidase activities in contrast to control. Similarly, 10 mmol L^-1 treatment showed higher superoxide dismutase, catalase and ascorbate peroxidase activities as compared to control. In conclusion, 10 mmol L^-1 oxalic acid application could be considered suitable to delay post-cut browning of lotus root slices.

Orthogonal array design for optimization of phenyllactic acid-sodium alginate blend coating and its effect on the browning and quality of minimally processed lily bulbs

BACKGROUND

In order to develop active packaging of lily products, we for the first time investigated the effects of phenyllactic acid (PLA) incorporated into a sodium alginate (SA)-based coating on the quality of minimally processed lily bulbs stored at 4 °C for 15 days.

RESULTS

L9 (3⁴ ) orthogonal array design showed that the optimal concentrations of PLA, SA and glycerinum were 0.03, 0.03 and 0.05 mol L^-1 , respectively, to prepare a blend coating. It was noticed that a PLA-SA blend coating treatment could inhibit browning and maintain the firmness and ascorbic acid of minimally processed lily bulbs. Compared with the control, polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia-lyase (PAL) activities of PLA-SA blend coating treated minimally processed lily bulbs reduced by about 31%, 21% and 29% on the 15th day, respectively. Total phenolic and quinone contents decreased, respectively, by 16% and 55% at the same time. Moreover, PLA-SA blend coating treatment eliminated the accumulation of malonaldehyde (MDA) while inhibiting microbial growth of minimally processed lily bulbs.

CONCLUSIONS

These results showed PLA-SA blend coating could effectively maintain quality of minimally processed lily bulbs stored at 4 °C, and it might be a prospective technology. © 2018 Society of Chemical Industry.

Improvements on the Fluorescence Quenching/Deflection Method for Real-time in situ Simultaneous Monitoring of Dissolved Oxygen and Material Movement-induced Beam Deflection in the Vicinity of an Aquatic Plant

Although the newly developed beam deflection/fluorescence detection system for real-time in situ simultaneous monitoring of dissolved oxygen (DO) and material movements in the vicinity of aquatic plants was not only much more sensitive but also could be carried out much more closely to real time than conventional analytical methods that monitor the concentration changes at a bulk solution, it could not be applied to the photosynthesis process of aquatic plants. Here, improvements are reported to enable application of the system to the photosynthesis process. A white-light LED, which was used as a light source for photosynthesis in our previous paper, was replaced by a red-blue LED with wavelength of about 660 and 450 nm. Also, an interference filter of 589 ± 25 nm was placed in front of a photomultiplier tube (PMT). Furthermore, the LED and its electric power supply were placed outside of the dark room for preventing great temperature increases in the photosynthetic experiments. Experimental results showed the DO-quenched fluorescence could be sensitively monitored in both the respiration and photosynthesis processes, while only in the respiration process before the improvements. It is successfully demonstrated that the DO change and material movement-induced beam deflection in the vicinity of the plants in both the respiration and photosynthesis processes could be real-time in situ monitored with high sensitivity.

Carbon Monoxide in Meat and Fish Packaging: Advantages and Limits

Due to increased demands for greater expectation in relation to quality, convenience, safety and extended shelf-life, combined with growing demand from retailers for cost-effective extensions of fresh muscle foods’ shelf-life, the food packaging industry quickly developed to meet these expectations. During the last few decades, modified atmosphere packaging (MAP) of foods has been a promising area of research, but much remains to be known regarding the use of unconventional gases such carbon monoxide (CO). The use of CO for meat and seafood packaging is not allowed in most countries due to the potential toxic effect, and its use is controversial in some countries. The commercial application of CO in food packaging was not then considered feasible because of possible environmental hazards for workers. CO has previously been reported to mask muscle foods’ spoilage, and this was the primary concern raised for the prohibition, as this may mislead consumers. This review was undertaken to present the most comprehensive and current overview of the widely-available, scattered information about the use of CO in the preservation of muscle foods. The advantages of CO and its industrial limits are presented and discussed. The most recent literature on the consumer safety issues related to the use of CO and consumer acceptance of CO especially in meat packaging systems were also discussed. Recommendations and future prospects were addressed for food industries, consumers and regulators on what would be a “best practice” in the use of CO in food packaging. All this promotes high ethical standards in commercial communications by means of effective regulation, for the benefit of consumers and businesses in the world, and this implies that industrialized countries and members of their regulatory agencies must develop a coherent and robust systems of regulation and control that can respond effectively to new challenges.

The application of carbon monoxide in meat packaging needs to be re-evaluated within the EU: An overview

Carbon monoxide (CO) has many value-added benefits in meat packaging due to its colour stabilising effects and enhancement of meat quality attributes. The regulation of CO within meat packaging varies worldwide and remains a topical and controversial issue. CO is prohibited in the EU for use in meat packaging mainly due to fears it may mask spoilage therefore misleading consumers. The issue of consumer acceptance of CO was not considered. This article reviews the most pertinent literature to assess if the problems associated with the prohibition have been addressed. Applying CO pretreatments prior to vacuum packaging enhances colour while allowing discolouration to occur by the use-by-date, thereby addressing concerns about safety. Recent work showing European consumer acceptance of CO in meat packaging demonstrates its future potential within the EU. The information provided may support framing future policies intended to assure consumer protection, safety, choice and interest. Re-evaluation of permitting CO as a packaging gas within the EU may be warranted.

Oxyresveratrol and ascorbic acid O/W microemulsion: Preparation, characterization, anti-isomerization and potential application as antibrowning agent on fresh-cut lotus root slices

The purpose of this study is to prepare an oxyresveratrol (Oxy) microemulsion (ME) with improved Oxy's solubility and stability and to investigate its antibrowning effects on fresh-cut lotus root slices. The formula of OxyME consisted of ethyl butyrate, Tween 80, PEG400, and water with w/w of 4%, 10.67%, 5.33%, and 80%, respectively. Encapsulating Oxy into OxyME greatly increased its solubility and stability compared with that of in water. Strong antibrowning effects were observed on fresh-cut lotus root slices treated with OxyME, even better than 4-hexylresorcinol. The addition of ascorbic acid (VC) into OxyME greatly improved the Oxy stability in long-term storage and antibrowning effects on fresh-cut lotus root slices. However, the simultaneous addition of calcium chloride and VC did not obviously improve the antibrowning effects compared with the addition of VC alone. These results indicated that Oxy+VCME may be suitable as an antibrowning agent for fresh-cut vegetables.

Phenolic Profiles and Antioxidant Activity of Lotus Root Varieties

Lotus root attracts increasing attention mainly because of its phenolic compounds known as natural antioxidants. Its thirteen varieties were systematically analyzed on the content, distribution, composition and antioxidant activity of phenolic compounds for a better understanding of this aquatic vegetable. The respective mean contents of total phenolics in their flesh, peel and nodes were 1.81, 4.30 and 7.35 mg gallic acid equivalents (GAE)/g fresh weight (FW), and those of total flavonoids were 3.35, 7.69 and 15.58 mg rutin equivalents/g FW. The phenolic composition determined by a high-performance liquid chromatography method varied significantly among varieties and parts. The phenolics of flesh were mainly composed of gallocatechin and catechin; those of peel and node were mainly composed of gallocatechin, gallic acid, catechin and epicatechin. The antioxidant activities of phenolic extracts in increasing order were flesh, peel and node; their mean concentrations for 50% inhibition of 2,2-diphenyl-1-picrylhydrazyl radical were 46.00, 26.43 and 21.72 µg GAE/mL, and their mean values representing ferric reducing antioxidant power were 75.91, 87.66 and 100.43 µg Trolox equivalents/100 µg GAE, respectively. “Zoumayang”, “Baheou”, “No. 5 elian” and “Guixi Fuou” were the hierarchically clustered varieties with relatively higher phenolic content and stronger antioxidant activity as compared with the others. Especially, their nodes and peels are promising sources of antioxidants for human nutrition.

Preparation of tyrosinase inhibitors and antibrowning agents using green technology

Chalcones and their derivatives have attracted great interests in recent years for their comprehensive biological activities. In this study, 2,4,2',4'-tetrahydroxychalcone and its two derivatives, 1,3,5-tris-(2,4-dihydroxy-phenyl)pentane-1,5-dione (new compound) and 7,2',4'-trihydroxyflavanone, were synthesized through one-pot green procedure catalyzed by boric acid in polyethylene glycol 400. Their structures were identified by ESI-MS and NMR spectral. Tyrosinase inhibitory activity and antibrowning test results showed that compounds 1-3 exhibited strong tyrosinase inhibitory activities and significant antibrowning effects on the fresh-cut lotus root slices at room temperature in 48 h. Among them, 0.01% 1,3,5-tris-(2,4-dihydroxy-phenyl)pentane-1,5-dione combined with 0.5% VC showed the best antibrowning ability. In brief, this study offers a protocol for one-pot green synthesis of high efficiency tyrosinase inhibitors which may be suitable as antibrowning agents for fresh-cut vegetables. More important, this study developed a new type of 1,5-dione derivative which may serve as new lead structures for novel tyrosinase inhibitors discovery.

Carbon Monoxide Fumigation Improved the Quality, Nutrients, and Antioxidant Activities of Postharvest Peach

Peaches (Prunus persica cv. Yanhong) were fumigated with carbon monoxide (CO) at 0, 0.5, 5, 10, and 20 μmol/L for 2 hours. The result showed that low concentration CO (0.5–10 μmol/L) might delay the decrease of firmness and titrable acid content, restrain the increase of decay incidence, and postpone the variation of soluble solids content, but treating peaches with high concentration CO (20 μmol/L) demonstrated adverse effects. Further research exhibited that exogenous CO could induce the phenylalnine ammonialyase activity, maintain nutrient contents such as Vitamin C, total flavonoid, and polyphenol, and enhance antioxidant activity according to reducing power and 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl radical scavenging activity. Treating peaches with appropriate concentration CO was beneficial to the quality, nutrients, and antioxidant activity of postharvest peaches during storage time. Therefore, CO fumigation might probably become a novel method to preserve postharvest peach and other fruits in the future.

Effects of carbon monoxide on quality, nutrients and antioxidant activity of post-harvest jujube

BACKGROUND

To effectively extend the shelf life of fresh jujube, carbon monoxide (CO), as a small molecular gas, was applied to fumigate fresh jujube. The quality and antioxidant activity of jujubes fumigated with carbon monoxide at concentrations of 0 (control), 5, 10, 20 and 40 µmol L⁻¹ for 1 h under ambient temperature were investigated.

RESULTS

The jujube fumigated with 10 µmol L⁻¹ CO showed the best preserving effect amongst all samples. At 30 days, the decay incidence of jujube fumigated with 10 µmol L⁻¹ CO is only two-thirds of that of control sample; its red index and weight loss rate were 22.8% and 19.4% lower, and its firmness, soluble solids content (SSC) and acidity were 18.7%, 5.4% and 12.2% higher than that of control samples, respectively. Its vitamin C and total flavonoid contents were also the highest. However, no significant difference in total polyphenol content was found. The jujubes treated with 10 µmol L⁻¹ CO exhibited the highest antioxidant activity in terms of reducing power and 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl radical scavenging activity. However, the jujubes fumigated with 40 µmol L⁻¹ CO showed inferior characteristics compared with the control sample.

CONCLUSION

Fumigating jujubes with proper concentration of CO probably is a potential novel method for post-harvest jujube preservation in the future.