Cold and ambient deck storage prior to processing as a critical control point for patulin accumulation

Efficacy and Mechanisms of Action of Essential Oils' Vapours against Blue Mould on Apples Caused by Penicillium expansum

Biofumigation with slow-release diffusers of essential oils (EOs) of basil, oregano, savoury, thyme, lemon, and fennel was assessed for the control of blue mould of apples, caused by Penicillium expansum. In vitro, the ability of the six EOs to inhibit the mycelial growth was evaluated at concentrations of 1.0, 0.5, and 0.1%. EOs of thyme, savoury, and oregano, at all three concentrations, and basil, at 1.0 and 0.5%, were effective in inhibiting the mycelial growth of P. expansum. In vivo, disease incidence and severity were evaluated on 'Opal' apples artificially inoculated with the pathogen and treated at concentrations of 1.0% and 0.5% of EOs. The highest efficacy in reducing blue mould was observed with EOs of lemon and oregano at 1.0% after 60 days of storage at 1 ± 1 °C (incidence of rot, 3 and 1%, respectively) and after a further 14 days of shelf-life at 15 ± 1 °C (15 and 17%). Firmness, titratable acidity, and total soluble solids were evaluated at harvest, after cold storage, and after shelf-life. Throughout the storage period, no evident phytotoxic effects were observed. The EOs used were characterised through GC-MS to analyse their compositions. Moreover, the volatile organic compounds (VOCs) present in the cabinets were characterised during storage using the SPME-GC-MS technique. The antifungal effects of EOs were confirmed both in vitro and in vivo and the possible mechanisms of action were hypothesised. High concentrations of antimicrobial and antioxidant compounds in the EOs explain the efficacy of biofumigation in postharvest disease control. These findings provide new insights for the development of sustainable strategies for the management of postharvest diseases and the reduction of fruit losses during storage.

Predictive growth kinetic parameters and modelled probabilities of deoxynivalenol production by Fusarium graminearum on wheat during simulated storing conditions

AIMS

Mathematical models were employed to predict the growth kinetic parameters of F. graminearum and the accumulation of deoxynivalenol (DON) during wheat storage as a function of different moisture contents (MCs) and temperatures.

METHODS AND RESULTS

The colony counting method was used to quantify F. graminearum growth under different environmental conditions, and kinetic and probability models were developed to describe the effect of different MCs and temperatures on fungal growth and DON production during wheat storage. Among the employed secondary models (Arrhenius-Davey, Gibson, and Cardinal), the general polynomial best predicted the fungal growth rate under varying temperature and MC during wheat storage. According to the logistic model, DON contamination was correctly predicted in 96.5% of cases.

CONCLUSIONS

The maximum growth rate of fungi was 0.4889±0.092 Log CFU g^-1 d^-1 at 25°C and 30% moisture according to the polynomial model. At below 17°C and ≤15% moisture, no fungal growth was observed. The probability model of toxin production showed no toxin production at less than 15% moisture (a_w ≤ 0.76) and below 15°C.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first application of a probability model of DON production during wheat storage, providing a reference for preventing fungal growth and mycotoxin accumulation by F. graminearum during wheat storage and guaranteeing food product safety.

Ecophysiology of Penicillium expansum and patulin production in synthetic and olive-based media

Olives and their derivatives, in particular olive oil, represent one of the most significant agricultural products in the Mediterranean basin. Storage under inadequate conditions poses serious problems concerning fungal contamination, with consequent defects and potential mycotoxin production in olives and olive oils. Penicillium expansum represents one of the most significant postharvest pathogens in several fruits, including olives. Not only it causes blue mold but also is one of the most relevant patulin producing species of the genus Penicillium. The aim of this research was to evaluate the ecophysiological conditions governing growth and PAT production by P. expansum strains previously isolated from Tunisian olives. For this purpose, four P. expansum isolates were tested in a synthetic medium (Czapek Yeast Autolysate, CYA) and in olive-based medium (OM) for their ability to grow and produce PAT under different temperatures (4 °C, 15 °C and 25 °C) for 10 and 20 d. The mycotoxin was analysed by HPLC-UV. Results showed that all isolates were able to grow on tested media at different temperatures. Different PAT production profiles were found, showing that at 25 °C P. expansum isolates were able to produce PAT on CYA and OM medium. At 15 °C the production of PAT was only detected on CYA medium, while no PAT production was detected at 4 °C for the two media.

Patulin in Apples and Apple-Based Food Products: The Burdens and the Mitigation Strategies

Apples and apple-based products are among the most popular foods around the world for their delightful flavors and health benefits. However, the commonly found mold, Penicillium expansum invades wounded apples, causing the blue mold decay and ensuing the production of patulin, a mycotoxin that negatively affects human health. Patulin contamination in apple products has been a worldwide problem without a satisfactory solution yet. A comprehensive understanding of the factors and challenges associated with patulin accumulation in apples is essential for finding such a solution. This review will discuss the effects of the pathogenicity of Penicillium species, quality traits of apple cultivars, and environmental conditions on the severity of apple blue mold and patulin contamination. Moreover, beyond the complicated interactions of the three aforementioned factors, patulin control is also challenged by the lack of reliable detection methods in food matrices, as well as unclear degradation mechanisms and limited knowledge about the toxicities of the metabolites resulting from the degradations. As apple-based products are mainly produced with stored apples, pre- and post-harvest strategies are equally important for patulin mitigation. Before storage, disease-resistance breeding, orchard-management, and elicitor(s) application help control the patulin level by improving the storage qualities of apples and lowering fruit rot severity. From storage to processing, patulin mitigation strategies could benefit from the optimization of apple storage conditions, the elimination of rotten apples, and the safe and effective detoxification or biodegradation of patulin.

Mitigation of Patulin in Fresh and Processed Foods and Beverages

Patulin is a mycotoxin of food safety concern. It is produced by numerous species of fungi growing on fruits and vegetables. Exposure to the toxin is connected to issues neurological, immunological, and gastrointestinal in nature. Regulatory agencies worldwide have established maximum allowable levels of 50 µg/kg in foods. Despite regulations, surveys continue to find patulin in commercial food and beverage products, in some cases, to exceed the maximum limits. Patulin content in food can be mitigated throughout the food processing chain. Proper handling, storage, and transportation of food can limit fungal growth and patulin production. Common processing techniques including pasteurisation, filtration, and fermentation all have an effect on patulin content in food but individually are not sufficient safety measures. Novel methods to remove or detoxify patulin have been reviewed. Non-thermal processing techniques such as high hydrostatic pressure, UV radiation, enzymatic degradation, binding to microorganisms, and chemical degradation all have potential but have not been optimised. Until further refinement of these methods, the hurdle approach to processing should be used where food safety is concerned. Future development should focus on determining the nature and safety of chemicals produced from the breakdown of patulin in treatment techniques.

Patulin production by Penicillium expansum isolates from apples during different steps of long-term storage

Penicillium expansum is the principal cause of blue mould rot and associated production of patulin, a weak mycotoxin, in apples worldwide. P. expansum growth and patulin production is observed during improper or long-term storage of apples. We have investigated the extent to which each successive step during long-term storage contributes to patulin production in various P. expansum isolates. Fungal isolates collected on apples from several Belgian orchards/industries were identified to species level. Random amplification of polymorphic DNA (RAPD) analysis and β-tubulin gene sequencing identified P. expansum and Penicillium solitum as the most prevalent Penicillium species associated with Belgian apples. All 27 P. expansum isolates and eight reference strains were characterised for their patulin production capacity on apple puree agar medium for five days under classical constant temperature and atmosphere conditions. Under these conditions, a large range of patulin production levels was observed. Based on this phenotypic diversity, five P. expansum isolates and one reference strain were selected for in vitro investigation of patulin production under representative conditions in each step of long-term apple storage. Patulin accumulation seemed highly strain dependent and no significant differences between the storage steps were observed. The results also indicated that a high spore inoculum may lead to a strong patulin accumulation even at cold temperatures (1 °C) combined with controlled atmosphere (CA) (3% O2, 1% CO2), suggesting that future control strategies may benefit from considering the duration of storage under CA conditions as well as duration of deck storage.

Isoepoxydon dehydrogenase (idh) gene expression in relation to patulin production by Penicillium expansum under different temperature and atmosphere

Penicillium expansum growth and patulin production occur mainly at post-harvest stage during the long-term storage of apples. Low temperature in combination with reduced oxygen concentrations is commonly applied as a control strategy to extend apple shelf life and supply the market throughout the year. Our in vitro study investigated the effect of temperature and atmosphere on expression of the idh gene in relation to the patulin production by P. expansum. The idh gene encodes the isoepoxydon dehydrogenase enzyme, a key enzyme in the patulin biosynthesis pathway. First, a reverse transcription real-time PCR (RT-qPCR) method was optimized to measure accurately the P. expansum idh mRNA levels relative to the mRNA levels of three reference genes (18S, β-tubulin, calmodulin), taking into account important parameters such as PCR inhibition and multiple reference gene stability. Subsequently, two P. expansum field isolates and one reference strain were grown on apple puree agar medium (APAM) under three conditions of temperature and atmosphere: 20 °C - air, 4 °C - air and 4 °C - controlled atmosphere (CA; 3% O2). When P. expansum strains reached a 0.5 and 2.0 cm colony diameter, idh expression and patulin concentrations were determined by means of the developed RT-qPCR and an HPLC-UV method, respectively. The in vitro study showed a clear reduction in patulin production and down-regulation of the idh gene expression when P. expansum was grown under 4 °C - CA. The results suggest that stress (low temperature and oxygen level) caused a delay of the fungal metabolism rather than a complete inhibition of toxin biosynthesis. A good correlation was found between the idh expression and patulin production, corroborating that temperature and atmosphere affected patulin production by acting at the transcriptional level of the idh gene. Finally, a reliable RT-qPCR can be considered as an alternative tool to investigate the effect of control strategies on the toxin formation in food.

Risk analysis of main mycotoxins occurring in food for children: An overview

Mycotoxins are secondary metabolites produced by fungi contaminating the food chain that are toxic to animals and humans. Children up to 12 years old are recognized as a potentially vulnerable subgroup with respect to consumption of these contaminants. Apart from having a higher exposure per kg body weight, they have a different physiology from that of adults. Therefore they may be more sensitive to neurotoxic, endocrine and immunological effects. For these reasons, a specific and up-to-date risk analysis for this category is of great interest. In this review, an accurate analysis of the main mycotoxins occurring in food intended for children (deoxynivalenol, aflatoxins, ochratoxins, patulin and fumonisins) is presented. In particular, known mechanisms of toxicity and levels of exposure and bioaccessibility in children are shown. In addition, recent discoveries about the strategies of mycotoxins managing are discussed.

Investigation of the interaction between patulin and human serum albumin by a spectroscopic method, atomic force microscopy, and molecular modeling

The interaction of patulin with human serum albumin (HSA) was studied in vitro under normal physiological conditions. The study was performed using fluorescence, ultraviolet-visible spectroscopy (UV-Vis), circular dichroism (CD), atomic force microscopy (AFM), and molecular modeling techniques. The quenching mechanism was investigated using the association constants, the number of binding sites, and basic thermodynamic parameters. A dynamic quenching mechanism occurred between HSA and patulin, and the binding constants (K) were 2.60 × 10(4), 4.59 × 10(4), and 7.01 × 10(4) M(-1) at 288, 300, and 310 K, respectively. Based on fluorescence resonance energy transfer, the distance between the HSA and patulin was determined to be 2.847 nm. The ΔG (0), ΔH (0), and ΔS (0) values across various temperatures indicated that hydrophobic interaction was the predominant binding force. The UV-Vis and CD results confirmed that the secondary structure of HSA was altered in the presence of patulin. The AFM results revealed that the individual HSA molecule dimensions were larger after interaction with patulin. In addition, molecular modeling showed that the patulin-HSA complex was stabilized by hydrophobic and hydrogen bond forces. The study results suggested that a weak intermolecular interaction occurred between patulin and HSA. Overall, the results are potentially useful for elucidating the toxigenicity of patulin when it is combined with the biomolecular function effect, transmembrane transport, toxicological, testing and other experiments.

Modeling kinetics of aflatoxin production by Aspergillus flavus in maize-based medium and maize grain

Predictive mycology has dealt mainly with germination, growth and inactivation of fungi while the issue of mycotoxin production remains relatively unexplored. Very few studies provide biomass dry weight/colony size data along with mycotoxin data for the same sample times, thus the ratio mycotoxin accumulation per fungal biomass dry weight/colony size has rarely been reported. For this reason, the objective of the present study was to model the kinetics of mycotoxin production under the assumption of existing both no-growth-associated and growth-associated production. Aspergillus flavus was chosen as a model mycotoxigenic microorganism, and it was grown in maize agar medium and maize grain at 0.90 and 0.99 aw at 25°C. A significant positive correlation (p<0.05) was observed among the biomass responses (colony radius and biomass dry weight) in agar medium and colony radius in maize at both aw levels assayed. The Luedeking-Piret model was used to model AFB1 production and reasonable percentages of variability were explained. Moreover, AFB1 production was in general slightly better predicted through colony area. As conclusion, aflatoxin production may follow a mixed-growth associated trend, confirming that toxin formation does not present a clear delay in relation to growth under certain conditions.

Risk assessment of patulin intake from apple containing products by young children

Patulin is a mycotoxin for which a provisional maximum tolerable daily intake (PMTDI) of 400 ng/kg bodyweight/ day has been set based on its most sensitive toxic effect, growth retardation. Apple containing products are the major source for patulin exposure, with major intake differences according to age and living region. Young children are most at risk of patulin intoxication, because they consume much higher amounts of apple products than adults. In this study, the patulin intake was calculated for Dutch children of 8 to 48 months and the risks of patulin intoxication were assessed. In addition, the bioaccessibility of patulin from apple containing products was investigated for a more refined risk assessment of patulin. The bioaccessibility of patulin was high, varying between 55 and 100%, and, consequently, no refinement of the risk assessment was possible. Based on the probabilistic intake calculations, children are exposed to levels below the PMTDI. Children aged 13-20 months with a high organic apple product intake have the highest patulin exposure, 342 ng/kg bodyweight/day at the upper confidence interval of the P95. No harmful effects are expected with the current patulin intake in young children. No concentration data are available for baby food (organic and conventional) and, therefore, concentrations were set at half the legal limit for intake calculations. Concentration data are needed for a more refined intake calculation for children younger than one year to estimate the actual risk in these children, because baby food comprises 23% of their diet.

Study on the role of patulin on pathogenicity and virulence of Penicillium expansum

Although the antibacterial activity and toxicity to humans and animals of the mycotoxin patulin are well known, its role in the postharvest decay of apples by Penicillium expansum has never been investigated. In the present study the gene disruption technique was used to alter the sequence of 6-methyl-salicylic acid synthase, an enzyme involved in the first committed step of patulin biosynthesis. Thirty-nine mutants were obtained, however only two of them (M5 and M21) passed the sub-cultural and molecular confirmation tests. They proved to produce 33-41% less patulin than their wild-type (WT) strain, although no difference in the growth and morphology of the colony was observed. Moreover, the mutants showed a significantly reduced pathogenicity and virulence on artificially inoculated apples. In particular, a 33-34% and 47-54% reduction of disease incidence and severity were recorded for M5 and M21, respectively. As confirmation, when the biomass of the mutants was quantified in vivo by Real-time PCR, a significant difference was recorded as compared to the WT and even between mutants. Moreover, when patulin production potential of mutants was restored by exogenous application of the mycotoxin, their ability to cause the disease was not significantly different from that of WT. Finally, mutants showed an increased susceptibility to the application of the antioxidant quercetin, their pathogenicity and virulence being significantly reduced at only 1/100 of the concentration needed for the WT. Based on these findings, patulin seems to have a role in the development of blue mold decay on apples.

Development of real-time PCR methods to quantify patulin-producing molds in food products

Patulin is a mycotoxin produced by different Penicillium and Aspergillus strains isolated from food products. To improve food safety, the presence of patulin-producing molds in foods should be quantified. In the present work, two real-time (RTi) PCR protocols based on SYBR Green and TaqMan were developed. Thirty four patulin producers and 28 non-producers strains belonging to different species usually reported in food products were used. The patulin production was tested by mycellar electrokinetic capillary electrophoresis (MECE) and high-pressure liquid chromatography-mass spectrometry (HPLC-MS). A primer pair F-idhtrb/R-idhtrb and the probe IDHprobe were designed from the isoepoxydon dehydrogenase (idh) gene, involved in patulin biosynthesis. The functionality of the developed method was demonstrated by the high linear relationship of the standard curves constructed with the idh gene copy number and Ct values for the different patulin producers tested. The ability to quantify patulin producers of the developed SYBR Green and TaqMan assays in artificially inoculated food samples was successful, with a minimum threshold of 10 conidia g(-1) per reaction. The developed methods quantified with high efficiency fungal load in foods. These RTi-PCR protocols, are proposed to be used to quantify patulin-producing molds in food products and to prevent patulin from entering the food chain.

Potential of patulin production by Penicillium expansum strains on various fruits

In this study, we investigated the pathogenicity and patulin production by ten strains of Penicillium expansum on various fruits (apples, apricots, kiwis, plums and peaches) at two (4°C and 25°C) different temperature regimes. All strains caused the infectious rots on all fruits at 4 and 25°C except one strain (PEX 09) at 4°C. Two strains (PEX 20 and PEX 12) out of ten produced the highest amounts of patulin on all fruits tested. The patulin production by P. expansum is high at 25°C compared to 4°C. All strains of P. expansum accumulated patulin ranging from 100-13,200 μg/kg and nine strains ranging from 100-12,100 μg/kg in all fruits at 25°C and 4°C, respectively. Among ten strains of P. expansum, strain PEX 20 produced the greatest amount of patulin on apricots (13,200 μg/kg of rotten fruit) and on apples (12,500 μg/kg) at 25°C after 9 days of incubation. At 4°C, this strain produced 12,100, 12,000, 2,100 and 1,200 μg/kg of patulin on apricots, apples, plums and peaches, respectively, after 45 days of incubation. Strain PEX 12 produced the highest amount of patulin on kiwis (10,700 μg/kg) at 25°C and 10,300 μg/kg at 4°C. Patulin production by P. expansum on peaches and plums at both temperatures were lower than other fruits. The results of this study showed that careful removal of rotten fruits is essential to produce patulin-free fruit juice, since high patulin levels in apricots, apples and kiwis could result in a level greater than 50 μg/kg of this mycotoxin in finished fruit juices, when one contaminated fruit occurs in 264, 250 and 214 fruits, respectively. So, the fruit processors should take care in not using rotten fruits for juice production to avoid the patulin problem worldwide, since this study proved that most important fruits being used for juice production and direct human consumption are susceptible to P. expansum and subsequent patulin production even at low temperatures. This is the first comprehensive report regarding patulin production by different strains of P. expansum on various fruits from Italy at different temperature regimes.