Efficacy of gaseous ozone to counteract postharvest table grape sour rot

Temperature Requirements Can Affect the Microbial Composition Causing Sour Rot in Grapes

Sour rot (SR) is a late-season non-Botrytis rot affecting grapevines, resulting from a complex interplay of microorganisms, including non-Saccharomyces yeasts and acetic acid bacteria. Nonmicrobial factors contributing to disease development encompass vectors (e.g., Drosophila spp.), the presence of wounds or microcracks on grape berry surfaces, and environmental conditions during berry ripening. The microbial complexes within SR-affected grapes exhibit variability among different bioclimates and seasons, with certain microorganisms predominating under specific conditions. This study examined the influence of environmental conditions on the microbiome composition associated with SR-affected grape bunches, utilising data from 41 locations across three distinct Italian bioclimates. We selected nine yeast and two bacterial species frequently isolated from sour-rotted grapes for analysis. The growth responses of these microorganisms to temperature were assessed by categorising them into four ecophysiological clusters. Furthermore, we analysed the distribution of these microorganisms and their respective ecophysiological clusters across the three bioclimates. The results indicate that the microbiomes involved in SR can vary according to the bioclimatic conditions of the grape-growing area. Further research is required to comprehend the ecological requirements of these microorganisms, define their ecological niches to understand their geographical distribution and epidemiology, and enhance SR management strategies.

Knowledge gaps on grape sour rot inferred from a systematic literature review

Sour rot (SR) is one of the major diseases affecting grapevine berries, causing severe yield losses and deterioration of wine quality. SR is caused by an etiologic complex of microorganisms, including yeasts, bacteria, and filamentous fungi. This systematic review focuses on the etiology, epidemiology, and control of SR. A total of 74 papers published between 1986 and 2023 were assessed in this review. Description of disease symptoms was quite consistent across the papers, including oxidation of the grape skin, disaggregation of the internal tissues, and detachment of the rotten berries from the pedicel. The affected bunches are characterized by the smell of acetic acid and ethyl acetate that attracts fruit flies (Drosophila spp.). However, several knowledge gaps and/or inconsistencies were identified with respect to SR etiology, epidemiology, and control. Overall, 146 microorganisms were isolated from the affected berries (44.5% yeasts, 34.3% bacteria, and 21.2% filamentous fungi); however, the selected papers could not definitively clarify which species are primarily involved in the etiology of the disease. A general inconsistency was also observed in the methods used to assess the incidence and severity of SR in vineyards, making inter-study comparisons extremely challenging. Inconsistencies were also found in the methods used for pathogenicity assessment in artificial inoculation studies. Furthermore, gaps were detected in terms of SR epidemiology, with a focus on environmental conditions affecting the disease development. The SR management options are limited, and efficacy trials often result in poor, variable, and inconsistent levels of control, which might be attributed to the lack of knowledge on disease epidemiology. These knowledge gaps and inconsistencies were analyzed in this review to inform future research activities.

Antibacterial Activity of Oregano (Origanum vulgare L.) Essential Oil Vapors against Microbial Contaminants of Food-Contact Surfaces

The antimicrobial effect of eight essential oils' vapors against pathogens and spoilage bacteria was assayed. Oreganum vulgare L. essential oil (OVO) showed a broad antibacterial effect, with Minimum Inhibitory Concentration (MIC) values ranging from 94 to 754 µg cm-3 air, depending on the bacterial species. Then, gaseous OVO was used for the treatment of stainless steel, polypropylene, and glass surfaces contaminated with four bacterial pathogens at 6-7 log cfu coupon-1. No viable cells were found after OVO treatment on all food-contact surfaces contaminated with all pathogens, with the exception of Sta. aureus DSM 799 on the glass surface. The antimicrobial activity of OVO after the addition of beef extract as a soiling agent reduced the Sta. aureus DSM 799 viable cell count by more than 5 log cfu coupon-1 on polypropylene and glass, while no viable cells were found in the case of stainless steel. HS-GC-MS analysis of the headspace of the boxes used for the antibacterial assay revealed 14 different volatile compounds with α-Pinene (62-63%), and p-Cymene (21%) as the main terpenes. In conclusion, gaseous OVO could be used for the microbial decontamination of food-contact surfaces, although its efficacy needs to be evaluated since it depends on several parameters such as target microorganisms, food-contact material, temperature, time of contact, and relative humidity.

Advances in gas fumigation technologies for postharvest fruit preservation

This work summarizes the application of gas fumigation technology in postharvest fruit quality management and related biochemical mechanisms in recent years. Gas fumigants mainly include SO2, ClO2, ozone, NO, CO, 1-MCP, essential oils, H2S and ethanol. This work indicated that gas fumigation preservatives can effectively improve postharvest fruit quality, which is mainly manifested in delaying senescence, inhibiting browning, controlling disease and alleviating chilling injury. Gas preservatives are mainly involved in postharvest fruit quality control in the roles of antifungal agent, anti-browning agent, redox agent, ethylene inhibitors, elicitor and pesticide remover. Different gas preservatives have different roles, but most of them have multiple roles at the same time in postharvest fruit quality management. In addition, the role of some gas preservatives with direct antifungal activity in the control of postharvest fruit diseases can also activate defense systems to improve fruit resistance. It should be noted that some gas fumigation treatments with slow-release effects have been developed recently, which may allow gas fumigation gases to perform better. Moreover, some gas fumigants can cause irrational side effects on the fruit and some combined treatments need to be found to counteract such side effects.

Effect of Gaseous Citral on Table Grapes Contaminated by Rhizopus oryzae ITEM 18876

Rhizopus oryzae is responsible for rapidly producing a deliquescent appearance in grape berries, generally favoured by cold chain interruptions. To counteract fruit spoilage and to meet consumer acceptance, innovative strategies based on the application of natural compounds are ongoing. Due to their biological activities, including antimicrobial ones, natural flavour compounds extend the shelf life and improve the nutritional value as well as the organoleptic properties of foods. Thus, in this work, the application of the antimicrobial citral, a flavor component of monoterpenes identified in plant and fruit essential oils, was developed and validated against one spoiler of R. oryzae. Citral, as pure compound, was first investigated in vitro against R. oryzae ITEM 18876; then, concentrations equal to the minimal inhibitory concentration (MIC) and 4-fold MIC (4MIC) value were applied on the table grape cv Italia infected with this strain and stored. The MIC value was equal to 0.0125 μL/cm3; both citral concentrations (0.0125 and 0.05 µL/cm3) were effective in counteracting the microbial decay of infected table grapes over the storage period. The HS-SPME/GC-MS method showed citral persistence in the head space of plastic trays with the infected samples; as expected, a higher content of citral isomers was found in the sample treated with 4MIC value. In conclusion, citral revealed its efficacy to counteract the onset of soft rot by R. oryzae ITEM 18876 under storage conditions. Thus, it could be successfully exploited to develop an active packaging or natural preservatives to extend table grape shelf life without affecting its quality and sensory characteristics, whilst also satisfying the consumer demand for natural preservative agents.

Ozone in wineries and wine processing: A review of the benefits, application, and perspectives

Ozone (O₃ ) is an emerging eco-friendly technology that has been widely used in the beverage industry due to its broad spectrum of usages, such as fermentation, microbial inactivation, Clean-in-Place (CIP) systems, and postharvest treatment. Wine is among the most financially profitable sectors of the beverage industry. Ozone technology as an alternative approach to conventional methods to inhibit microbes in wine processing and wineries has attracted researchers' attention as this emerging technology will probably play important roles in wineries in the future. This review discusses the prospective applications of ozone in winemaking and wineries and elaborates on ozone's antimicrobial effects on the control of the broad spectrum of microorganisms during wine processing. Also, this paper provides discussions on its effects of O₃  on wine quality and the benefits this emerging technology can bring to wineries. Ozone treatments can improve yeast fermentation by impacting the yeast ecology of postharvested wine grapes, mainly by affecting apiculate yeasts and adjusting the population of undesirable yeasts, such as Brettanomyces spp., during the fermentation process. Furthermore, ozone treatment may enhance wine's anthocyanin concentration, physicochemical properties, color, pH, oxidative stability, and concentration of pleasant volatile compounds and esters. This article presents important information to have a better understanding of the impact of ozone treatment on different stages of wine preparation.

Effects of Gaseous Ozone on Microbiological Quality of Andean Blackberries (Rubus glaucus Benth)

Andean blackberries are highly perishable due to their susceptibility to water loss, softening, mechanical injuries, and postharvest diseases. In this study, the antimicrobial efficacy of gaseous ozone against spoilage (mesophiles, psychrotrophs, and yeasts and molds) and pathogenic (E. coli, S. enterica, and B. cinerea) microorganisms was evaluated during 10 days of storage at 6 ± 1 °C. Respiration rate and mass loss were also determined. Ozone was applied prior to storage at 0.4, 0.5, 0.6, and 0.7 ppm, for 3 min. The best results were observed with the higher ozone dose, with initial maximum reductions of ~0.5, 1.09, and 0.46 log units for E. coli, S. enterica, and B. cinerea, respectively. For the native microflora, maximum reductions of 1.85, 1.89, and 2.24 log units were achieved on day 1 for the mesophiles, psychrotrophs, and yeasts and molds, respectively, and this effect was maintained throughout storage. In addition, the lower respiration rate and mass loss of the blackberries ozonated at 0.7 ppm indicate that this treatment did not induce physiological damage to the fruit. Gaseous O₃ could be effective in maintaining the postharvest quality of blackberries throughout refrigerated storage but higher doses could be advisable to enhance its antimicrobial activity.

D-Fructose Assimilation and Fermentation by Yeasts Belonging to Saccharomycetes: Rediscovery of Universal Phenotypes and Elucidation of Fructophilic Behaviors in Ambrosiozyma platypodis and Cyberlindnera americana

The purpose of this study was to investigate the ability of ascomycetous yeasts to assimilate/ferment d-fructose. This ability of the vast majority of yeasts has long been neglected since the standardization of the methodology around 1950, wherein fructose was excluded from the standard set of physiological properties for characterizing yeast species, despite the ubiquitous presence of fructose in the natural environment. In this study, we examined 388 strains of yeast, mainly belonging to the Saccharomycetes (Saccharomycotina, Ascomycota), to determine whether they can assimilate/ferment d-fructose. Conventional methods, using liquid medium containing yeast nitrogen base +0.5% (w/v) of d-fructose solution for assimilation and yeast extract-peptone +2% (w/v) fructose solution with an inverted Durham tube for fermentation, were used. All strains examined (n = 388, 100%) assimilated d-fructose, whereas 302 (77.8%) of them fermented d-fructose. In addition, almost all strains capable of fermenting d-glucose could also ferment d-fructose. These results strongly suggest that the ability to assimilate/ferment d-fructose is a universal phenotype among yeasts in the Saccharomycetes. Furthermore, the fructophilic behavior of Ambrosiozyma platypodis JCM 1843 and Cyberlindnera americana JCM 3592 was characterized by sugar consumption profiles during fermentation.

Native Vineyard Non-Saccharomyces Yeasts Used for Biological Control of Botrytis cinerea in Stored Table Grape

Postharvest spoilage fungi, such as Botrytis cinerea, are considered the main cause of losses of fresh fruit quality and vegetables during storage, distribution, and consumption. The current control strategy is the use of SO₂ generator pads whose application is now largely under observation. A high quantity of SO₂ can be deleterious for fresh fruits and vegetables and it is not allowed in organic agriculture. For this reason, great attention has been recently focused on identifying Biological Control Agents (BCA) to implement biological approaches devoid of chemicals. In this direction, we carried out our study in isolating five different non-Saccharomyces yeast strains from local vineyards in the South of Italy as possible BCA. We performed both in vitro and in vivo assays in semi-commercial conditions on detached grape berries stored at 0 °C, simulating the temperature normally used during cold storage, and obtained relevant results. We isolated three M. pulcherrima strains and one L. thermotolerans strain able to largely antagonize the development of the B. cinerea, at both in vitro and in vivo conditions. In particular, we detected the ability of the three isolates of M. pulcherrima strains Ale4, N20/006, and Pr7 and the L. thermotolerans strain N10 to completely inhibit (100% in reduction) the mycelial growth of B. cinerea by producing fungistatic compounds. We found, using an extracellular lytic enzymes activity assay, that such activity could be related to lipid hydrolyzation, β-1,3-glucanase and pectinase activity, and pectinase and protease activity, depending on the yeasts used. Results from our in vitro assays allowed us to hypothesize for M. pulcherrima strains Ale4 and N20/006 a possible combination of both the production of soluble metabolites and volatile organic compounds to antagonize against B. cinerea growth. Moreover, in semi-commercial conditions, the M. pulcherrima strain N20/006 and L. thermotolerans strain N10 showed relevant antagonistic effect also at low concentrations (with a significantly reduction of ‘slip skin’ incidence of 86.4% and 72.7%, respectively), thus highlighting a peculiar property to use in commercial development for organic agriculture and the handling process.

Health Promoting Properties of Cereal Vinegars

Vinegar has been used for its health promoting properties since antiquity. Nowadays, these properties are investigated, scientifically documented, and highlighted. The health benefits of vinegar have been associated with the presence of a variety of bioactive components such as acetic acid and other organic acids, phenolic compounds, amino acids, carotenoids, phytosterols, vitamins, minerals, and alkaloids, etc. These components are known to induce responses in the human body, such as antioxidant, antidiabetic, antimicrobial, antitumor, antiobesity, antihypertensive, and anti-inflammatory effects. The diversity and levels of bioactive components in vinegars depend on the raw material and the production method used. Cereal vinegars, which are more common in the Asia-Pacific region, are usually made from rice, although other cereals, such as millet, sorghum, barley, malt, wheat, corn, rye, oats, bran and chaff, are also used. A variety of bioactive components, such as organic acids, polyphenols, amino acids, vitamins, minerals, alkaloids, melanoidins, butenolides, and specific compounds such as γ-oryzanol, tetramethylpyrazine, γ-aminobutyric acid, etc., have been associated with the health properties of cereal vinegars. In this work, the bioactive components and the related health effects of cereal vinegars are reviewed, and the most recent scientific literature is presented and discussed.

Plasma-Activated Water (PAW) as a Disinfection Technology for Bacterial Inactivation with a Focus on Fruit and Vegetables

Plasma-activated water (PAW) is generated by treating water with cold atmospheric plasma (CAP) using controllable parameters, such as plasma-forming voltage, carrier gas, temperature, pulses, or frequency as required. PAW is reported to have lower pH, higher conductivity, and higher oxygen reduction potential when compared with untreated water due to the presence of reactive species. PAW has received significant attention from researchers over the last decade due to its non-thermal and non-toxic mode of action especially for bacterial inactivation. The objective of the current review is to develop a summary of the effect of PAW on bacterial strains in foods as well as model systems such as buffers, with a specific focus on fruit and vegetables. The review elaborated the properties of PAW, the effect of various treatment parameters on its efficiency in bacterial inactivation along with its usage as a standalone technology as well as a hurdle approach with mild thermal treatments. A section highlighting different models that can be employed to generate PAW alongside a direct comparison of the PAW characteristics on the inactivation potential and the existing research gaps are also included. The mechanism of action of PAW on the bacterial cells and any reported effects on the sensory qualities and shelf life of food has been evaluated. Based on the literature, it can be concluded that PAW offers a significant potential as a non-chemical and non-thermal intervention for bacterial inactivation, especially on food. However, the applicability and usage of PAW depend on the effect of environmental and bacterial strain-based conditions and cost-effectiveness.

Effect of red thyme oil (Thymus vulgaris L.) vapours on fungal decay, quality parameters and shelf-life of oranges during cold storage

This work has been aimed at studying the effect of red thyme oil (RTO, Thymus vulgaris L.) on the shelf-life and Penicillium decay of oranges during cold storage. RTO vapours significantly reduced (P ≤ 0.05) the percentage of infected wounds, the external growth area and the production of spores in inoculated orange fruit stored for 12 days at 7 °C in a polypropylene film selected for its appropriate permeability. Among the RTO compounds, p-cymene and thymol were the most abundant in packed boxes at the end of cold storage. The RTO vapours did not affect the main quality parameters of the oranges, or the taste and odour of the juice. The results have shown that an active packaging, using RTO vapours, could be employed, by the citrus industry, to extend the shelf-life of oranges for fresh market use and juice processing.

Diversity and spoilage potential of microbial communities associated with grape sour rot in eastern coastal areas of China

As a polymicrobial disease, sour rot decreases grape berry yield and wine quality. The diversity of microbial communities in sour rot-affected grapes depends on the cultivation site, but the microbes responsible for this disease in eastern coastal China, has not been reported. To identify the microbes that cause sour grape rot in this important grape-producing region, the diversity and abundance of bacteria and fungi were assessed by metagenomic analysis and cultivation-dependent techniques. A total of 15 bacteria and 10 fungi were isolated from sour rot-affected grapes. High-throughput sequencing of PCR-amplicons generated from diseased grapes revealed 1343 OTUs of bacteria and 1038 OTUs of fungi. Proteobacteria and Firmicutes were dominant phyla among the 19 bacterial phyla identified. Ascomycota was the dominant fungal phylum and the fungi Issatchenkia terricola, Colletotrichum viniferum, Hanseniaspora vineae, Saprochaete gigas, and Candida diversa represented the vast majority ofmicrobial species associated with sour rot-affected grapes. An in vitro spoilage assay confirmed that four of the isolated bacteria strains (two Cronobacter species, Serratia marcescens and Lysinibacillus fusiformis) and five of the isolated fungi strains (three Aspergillus species, Alternaria tenuissima, and Fusarium proliferatum) spoiled grapes. These microorganisms, which appear responsible for spoiling grapes in eastern China, appear closely related to microbes that cause this plant disease around the world.

Growth and metabolite production of a grape sour rot yeast-bacterium consortium on different carbon sources

The present study was designed to evaluate possible sugar-based trophic interactions between acetic acid bacteria (AAB) and non-Saccharomyces yeasts (NSY) involved in table grape sour rot, a disease in which berries spoilage is caused by the accumulation of several microbial metabolites. Acetobacter syzygii LMG 21419 (As) and Candida zemplinina CBS 9494 (Cz), a simplified AAB-NSY association responsible for table grape sour rot, grew differently in a minimal medium (YP) supplemented with glucose, ethanol, acetic and gluconic acid under monoculture conditions. In As -Cz co-culture media, after 24 h of incubation, As showed high relative abundance in YP-ethanol, whereas Cz was the dominant strain in YP-glucose medium. Co-culture in YP-glucose showed that glucose was converted into ethanol by Cz that, in turn, promoted the growth of As population. Gluconic acid was the main bacterial metabolite from glucose in monoculture, whereas acetic acid putatively derived from ethanol oxidation was found only in co-culture. However, gluconic acid showed inhibitory effect against As whereas acetic acid mainly inhibited Cz. Negative effects of both metabolites were mitigated in the glucose-supplemented medium. The results suggest a possible metabolic- based temporal succession between AAB and NSY during grape sour rot development. At the begin of sour rot, low glucose concentration promotes NSY producing ethanol, then, the AAB could take advantage from the oxidation of ethanol into acetic acid, becoming the dominant microbial sour rot population during the late stages of the process.

Inactivation of Foodborne Bacteria Biofilms by Aqueous and Gaseous Ozone

In this study, the efficacy of treatments with ozone in water and gaseous ozone against attached cells and microbial biofilms of three foodborne species, Pseudomonas fluorescens, Staphylococcus aureus, and Listeria monocytogenes, was investigated. Biofilms formed on AISI 304 stainless steel coupons from a mixture of three strains (one reference and two wild strains) of each microbial species were subjected to three types of treatment for increasing times: (i) ozonized water (0.5 ppm) by immersion in static condition, (ii) ozonized water under flow conditions, and (iii) gaseous ozone at different concentrations (0.1-20 ppm). The Excel add-in GinaFit tool allowed to estimate the survival curves of attached cells and microbial biofilms, highlighting that, regardless of the treatment, the antimicrobial effect occurred in the first minutes of treatment, while by increasing contact times probably the residual biofilm population acquired greater resistance to ozonation. Treatment with aqueous ozone under static conditions resulted in an estimated viability reduction of 1.61-2.14 Log CFU/cm2 after 20 min, while reduction values were higher (3.26-5.23 Log CFU/cm2) for biofilms treated in dynamic conditions. S. aureus was the most sensitive species to aqueous ozone under dynamic conditions. With regard to the use of gaseous ozone, at low concentrations (up to 0.2 ppm), estimated inactivations of 2.01-2.46 Log CFU/cm2 were obtained after 60 min, while at the highest concentrations a complete inactivation (<10 CFU/cm2) of the biofilms of L. monocytogenes and the reduction of 5.51 and 4.72 Log CFU/cm2 of P. fluorescens and S. aureus respectively after 60 and 20 min were achieved. Considering the results, ozone in water form might be used in daily sanitation protocols at the end of the day or during process downtime, while gaseous ozone might be used for the treatment of confined spaces for longer times (e.g., overnight) and in the absence of personnel, to allow an eco-friendly control of microbial biofilms and consequently reduce the risk of cross-contamination in the food industry.

Survival of Listeria innocua on Fuji apples under commercial cold storage with or without low dose continuous ozone gaseous

This study evaluated the fate of Listeria innocua, a non-pathogenic species closely related to Listeria monocytogenes, on Fuji apple fruit surfaces during commercial cold storage with and without continuous low doses of gaseous ozone. Unwaxed Fuji apples of commercially acceptable maturity were inoculated with 6.0-7.0 Log₁₀ CFU L. innocua/apple, and subjected to refrigerated air (RA, 33 °F), controlled atmosphere (CA, 33 °F, 2% O₂, 1% CO₂), or CA with low doses of ozone gas (50.0 -87.0 ppb ) storage in a commercial facility for 30 weeks. A set of uninoculated apples was simultaneously subjected to the above storage conditions for total plate count and yeasts and molds enumeration. L. innocua survival under RA and CA storage was similar, which led to 2.5-3.0 Log₁₀ CFU/apple reduction during storage. Continuous gaseous ozone application decreased L. innocua population on Fuji apples to ∼1.0 Log₁₀ CFU/apple after 30-week storage, and suppressed apple native flora. CA storage delayed apple fruit ripening through reduction of apple firmness and titratable acidity loss, and low dose gaseous ozone application had no negative influence on apple visual quality, including both external and internal disorders. In summary, L. innocua decreased on Fuji apple surfaces during commercial long-term RA and CA storage. Ozone gas has the potential to be used as a supplemental intervention method to control Listeria spp. and to ensure fresh apple safety.