Rhizopus stolonifer and related control strategies in postharvest fruit: A review.

Rhizopus stolonifer is one of the main pathogens in postharvest storage logistics of more than 100 kinds of fruit, such as strawberries, tomatoes and melons. In this paper, the research on the morphology and detection, pathogenicity and infection mechanism of Rhizopus stolonifer was reviewed. The control methods of Rhizopus stolonifer in recent years was summarized from three dimensions of physics, chemistry and biology, including the nanomaterials, biological metabolites, light control bacteria, etc. Future direction of postharvest Rhizopus stolonifer infection control was analyzed from two aspects of pathogenic mechanism research and new composite technology. The information provided in this review will help researchers and technicians to deepen their understanding of the pathogenicity of Rhizopus stolonifer, and develop more effective control methods in the future.

Ultrasonic-Microwave extraction of glucoside alkaloids from potato peel residue and its antibacterial activity.

A new extraction and bacteriostatic ability of glucoside alkaloids in potato peel. To make better use of glucoside alkaloids, this experiment adopted ultrasonic microwave combined extraction of glucoside alkaloids from potato peel; then, the extracts of potato peel were subjected to bacteriostatic assays. The optimum experimental condition of response surface method was that the solid-liquid ratio was 1:18.00 g/mL, the ultrasonic power 505.00 W, the microwave time was 6.10 min and the ultrasonic time was 10.70 min. Under those conditions, the extraction amount of glucoside alkaloids was 292.91 mg/kg, which increased by about 28% compared with the QUEChERS method. The antibacterial activity of the obtained glucoside alkaloids was tested using five kinds of strains, and the results showed that Penicillium and Colletotrichum gloeosporioides were more sensitive. The results indicated that Ultrasonic-Microwave combined extraction was more efficient and convenient than that of QuEChERS method for glucoside alkaloids and related antibacterial compounds from potato peel.

Preparation of a multilayer antibacterial film and its application for controlling postharvest disease in temperate fruit (including apple, pear, and peach) under ambient storage.

The objective of this study was to provide formulation of a new multilayer antibacterial film and to investigate the optimal use concentration of chitosan and carboxymethyl cellulose in the range from 0.5% to 2%, as well as its application for controlling postharvest disease in temperate fruit (apple, pear, and peach). The multilayer antibacterial film used chitosan (CS) and carboxymethyl cellulose (CMC) as polysaccharide macromolecule, lemon essential oil (LEO) as active agent, and ε-polylysine (ε-PL) as the main antibacterial ingredient. The results showed that the physical properties of the self-assembled film were adjusted by the electrostatic layer-by-layer (LbL) deposition. Fourier transform infrared (FT-IR) analysis and thermogravimetric (TGA) revealed that hydrogen bonds were generated during the self-assembly of CS-LEO/CMC-ε-PL film, resulting in changes in intermolecular interactions and thermal stability. Furthermore, compared with CS-LEO single-layer film, the multilayer film exhibited higher retention rate of LEO. In vivo test, the self-assembled film significantly inhibited the infection of postharvest pathogenic fungi including Penicillium expansum (P. expansum) and Alternaria alternata (A. alternata) on fruit. To summarize, the CS-LEO/CMC-ε-PL LbL self-assembly coating notably controlled postharvest pathogen rot on fruit, and reduced the loss of fruit during storage and transportation. Our results suggest that the polysaccharide-based edible coating prepared in this work may offer an alternative to synthetic waxes.

Organic acid, a virulence factor for pathogenic fungi, causing postharvest decay in fruits.

Decay due to fungal infection is a major cause of postharvest losses in fruits. Acidic fungi may enhance their virulence by locally reducing the pH of the host. Several devastating postharvest fungi, such as Penicillium spp., Botrytis cinerea, and Sclerotinia sclerotiorum, can secrete gluconic acid, oxalic acid, or citric acid. Emerging evidence suggests that organic acids secreted by acidic fungi are important virulence factors. In this review, we summarized the research progress on the biosynthesis of organic acids, the role of the pH signalling transcription factor PacC in regulating organic acid, and the action mechanism of the main organic acid secreted via postharvest pathogenic fungi during infection of host tissues. This paper systematically demonstrates the relationships between tissue acidification and postharvest fungal pathogenicity, which will motivate the study of host-pathogen interactions and provide a better understanding of virulence mechanisms of the pathogens so as to design new technical strategies to prevent postharvest diseases.

Chlorine Dioxide Controls Green Mold Caused by Penicillium digitatum in Citrus Fruits and the Mechanism Involved.

Green mold caused by Penicillium digitatum is the main postharvest disease in citrus fruits. The goal of this study is to evaluate the antifungal activity of chlorine dioxide (ClO2) against P. digitatum both in vivo and in vitro and to elucidate the underlying mechanism using flow cytometry and scanning electron microscopy. The results showed that 200-1800 mg/L of ClO2 significantly inhibited the incidence of green mold on kumquats, mandarins, Peru's oranges, and grapefruits caused by P. digitatum. Additionally, 200 mg/L of ClO2 significantly induced cell apoptosis of P. digitatum by increasing the fluorescence intensity of the mitochondrial membrane potential from 118 to 1225 and decreased the living cell rate from 96.8 to 6.1%. Further study demonstrated that the content of malondialdehyde and nucleic acid leakage (OD260) of P. digitatum markedly increased, and the mycelial morphology was seriously damaged with increased ClO2 concentration. These results indicated that ClO2 could inhibit fungal growth by destroying the membrane integrity of P. digitatum, and the use of ClO2 may be an alternative strategy to control green mold in postharvest citrus fruits.

Analysis of flavor and taste attributes differences treated by chemical preservatives: a case study in strawberry fruits treated by 1-methylcyclopropene and chlorine dioxide.

Flavor and taste attributes of fruits varied by different preservatives treatments. Changes in sugars, organic acids, amino acids as well as volatiles of strawberries treated with 1-methylcyclopropene (1-MCP) and/or chlorine dioxide (ClO2) were evaluated during storage period in this study. Our results revealed that the decreases of tartaric acid, malic acid, citric acid, titratable acidity (TA), sucrose and soluble sugar contents were significantly inhibited by 1-MCP + ClO2. The fructose and glucose contents of all groups remained stable and slightly increased at the last period of 10 days. However, different treatments had no influence on content of succinic acid. Moreover, the highest sweet taste (77.37 mg 100 g-1 fresh weight) and lowest bitter taste (3.44 mg 100 g-1 fresh weight) free amino acids (FAA) were observed in the strawberries treated by 1-MCP combined with ClO2 treatment as compared to other treatments and control. (E)-2-hexenal was the most abundant volatile and showed a significant increase trend during strawberry storage. More interestingly, ethyl butyrate, fruit-like aroma, could be recovered in content by 1-MCP, ClO2 alone and their combination treatment. Compared with other treatments, the significant different flavor in ClO2 treatment was identified by principle component analysis. In addition, methyl hexanoate and 4-methoxy-2,5-dimethylfuran-3(2H)-one (DMMF) were the major factors that affected the volatile organic compounds (VOCs) of strawberries through the whole storage. Taken together, 1-MCP coupled with ClO2 could be a complex preservative to maintain strawberries quality by regulating the flavor and taste attributes.

Sucrose transportation control mediates the fresh-keeping effects of burdock fructooligosaccharide in 'Crimson Seedless' grapes.

In 'Crimson Seedless' grapes, the appearance of senescence caused by abnormal dark red color, the loss of crisp taste caused by the decrease in firmness, and the fading of sweetness caused by the decrease in total soluble sugar (TSS) are the main problems affecting its edible qualities after storage. In the mesocarp, burdock fructooligosaccharide (BFO) restricted sucrose export; therefore, more carbohydrates were retained directly leading to higher TSS and sweetness, and cell osmotic pressure and firmness were retained indirectly. In the exocarp, BFO restricted sucrose import; therefore, the signal molecule sucrose was reduced and the senescence-related processes were inhibited. The downregulation of SUC12 and SUC27 by BFO may play an important role in restricting sucrose transportation. The opposing effects exhibited by exogenous sucrose treatments compared to those of BFO further verified these mechanisms. Based on the above mechanisms, sucrose transportation mediates the fresh-keeping effects of BFO in 'Crimson Seedless' grapes.

Application of antagonist Bacillus amyloliquefaciens NCPSJ7 against Botrytis cinerea in postharvest Red Globe grapes.

We investigated the effects and possible mechanisms of Bacillus amyloliquefaciens NCPSJ7 against the gray mold caused by Botrytis cinerea in the postharvest Red Globe grapes. The disease incidence, lesion diameter, decay index, and some resistance-related enzymes were evaluated. The antioxidant capacity of grape treated with 1 × 104 CFU/ml B. cinerea alone and combined with 1 × 107 CFU/ml NCPSJ7 was also determined. The results showed that NCPSJ7 + B. cinerea reduced the disease incidence, lesion diameter, and decay index of postharvest grapes and enhanced the activities of polyphenol oxidase, peroxidase, chitinase, and ß-1,3-glucanase during different storage periods. Furthermore, the oxidative resistance, demonstrated by an escalating trend in the total phenolic content, DPPH free radical clearance rate, reducing power, and superoxide anion clearance rate after lesion presence, was improved. However, NCPSJ7 showed an inhibitory effect on gray mold, but resulted in the reduced antioxidant capacity in the grapes.

Effect of chlorine dioxide (ClO2 ) on patulin produced by Penicillum expansum and involved mechanism.

BACKGROUND: Patulin, produced by Penicillium expansum in apple fruit, has side effects affecting human and animal health. The effect of chlorine dioxide (ClO2 ) on patulin production, and the mechanisms involved in this, were investigated. RESULTS: Patulin production by P. expansum was reduced by ClO2 treatment, both in apples and in a potato dextrose broth (PDB) medium, which was attributed to the antifungal effect of ClO2 , but not the direct reaction between ClO2 and patulin. Fumigation with ClO2 also significantly reduced disease development in apples infected with P. expansum, and inhibited mycelial growth and spore germination. After ClO2 treatment, P. expansum mycelial morphology was strongly affected, leading to the loss of plasma membrane integrity and causing cellular leakage. CONCLUSION: These data provide useful information that enables the inhibitory mechanism of ClO2 on patulin production by P. expansum to be better understood. It can also assist the development of effective methods to control patulin production in apples and other postharvest fruits. © 2018 Society of Chemical Industry.

Chlorine dioxide fumigation generated by a solid releasing agent enhanced the efficiency of 1-MCP treatment on the storage quality of strawberry.

The effect of 1-methylcyclopropene (1-MCP) and chlorine dioxide (ClO2) on fruit quality during storage was investigated. Strawberries were treated with 1-MCP alone or in combination with ClO2 gas generated by a releasing agent, and the quality, fruit decay, microbial inhibition, and enzyme activities [polyphenol oxidase (PPO), superoxide dismutase (SOD), ascorbate peroxidase (APX), and phenylalanine ammonia lyase (PAL)] at 4 °C were measured for 16 days. 1-MCP alone could maintain the fruit quality during storage but had little effect on microbial growth, resulting in quick decay during storage. ClO2 treatment effectively inhibited microbial growth during storage and improved shelf life with no visual damage. Moreover, 1-MCP in combination with ClO2 was superior in maintaining quality attributes as compared with 1-MCP alone, as significant differences were found in some indices. Furthermore, 1-MCP in combination with ClO2 maintained higher SOD, APX, and PAL activities and lower PPO activity as compared with the control and 1-MCP alone. Overall, ClO2 enhanced the effect of 1-MCP on strawberries during storage and shelf life, possibly through the inhibition of microbial growth and regulation of enzyme activity. The combination of 1-MCP and ClO2 may serve as a potential strategy with dual physiological and antimicrobial effects for the preservation of perishable products.

Ethylene inhibited sprouting of potato tubers by influencing the carbohydrate metabolism pathway.

The aim of this study was to investigate the role of ethylene to control sprouting of potatoes by observing the effect of exogenous ethylene on carbohydrate metabolism and key enzymes. The initial time of potato tuber sprouting and sprouting index were recorded, and rate of respiration, total sugar, total reducing sugar, starch, fructose, glucose, sucrose and the activities of acid invertase (AI), neutral invertase (NI), sucrose synthase (SS), sucrose phosphate synthase (SPS), starch phosphorylase and amylase during sprouting were measured. Exogenous ethylene inhibited sprouting of potato tubers. Moreover, exogenous ethylene increased respiration total sugar, AI activity, SPS activity, SS activity, and reduced sugar and assay activity. Nevertheless, starch, glucose, fructose, NI activity and starch phosphorylase activity showed lower variation. Lower sprouting resulted into potatoes with higher levels of total sugar, total reducing sugar and glucose, and lower level of fructose and sucrose. And sprouting could be inhibited by increasing the activities of SS, SPS and AI by treatment with 199.3 µl L-1 exogenous ethylene. Overall, exogenous ethylene inhibited sprouting of potato tubers by influencing its carbohydrate metabolism.

Ionic liquid-based ultrasound-assisted extraction of fangchinoline and tetrandrine from Stephaniae tetrandrae.

An ionic liquid-based ultrasound-assisted extraction method has been developed for the effective extraction of fangchinoline and tetrandrine from Stephaniae tetrandrae. The effects of some ultrasound-assisted extraction parameters including the concentration of [BMIM][BF(4)], pH, ultrasonic power and time were investigated to optimize the ultrasound-assisted extraction conditions. Compared to the regular ultrasound-assisted extraction and traditional refluent extraction, the proposed [BMIM][BF(4)]-based ultrasound-assisted extraction offered shorter extraction times (from 6 h to 40 min) and remarkable higher efficiencies (approximately 30% improved), which supported the suitability of the proposed approach. In addition, the proposed approach was confirmed by the good correlation coefficient (R(2)), recovery and reproducibility (RSD, n = 5), which were in the range of 0.9992-0.9995, 85.5-101.1%, and 1.87-4.33%, respectively.

In vitro antioxidant activities of five cultivars of daylily flowers from China.

Different cultivars of functional vegetables may vary in an antioxidant capacity. In this study, the antioxidant activity of methanol extracts from five cultivars of daylily flower grown in China was compared by various antioxidant assays, including total antioxidant activity, free radical scavenging, superoxide anion radical scavenging and reducing power, the various antioxidant activities were compared to standard antioxidants such as butylated hydroxyanisole and ascorbic acid. All the extracts showed strong antioxidant activity in all tested methods. Among the five cultivars, Panlonghua and Mengzihua were found to possess the highest antioxidant activity, while Xiye and Baihua were found to possess the lowest antioxidant activity. In addition, a high positive correlation between the antioxidant properties and total phenolic content was observed.