Recent advances in biocontrol and other alternative strategies for the management of postharvest decay in table grapes.

During postharvest, table grapes are often spoiled by molds. Aspergillus sp., Alternaria sp., Botrytis sp., Cladosporium sp. and Penicillium sp. are different mold genera frequently related to table grape rot. Fungal spoilage affects nutritional value and organoleptic properties while also producing health hazards, such as mycotoxins. Traditionally, synthetic fungicides have been employed to control fungal diseases. However, possible negative effects on health and the environment are a serious concern for consumers and government entities. This review summarized data on innovative strategies proposed to diminish postharvest losses and extend table grape shelf life. Among physical, chemical, and biological strategies, either alone or in combination, the integrated management of fungal diseases is a sustainable alternative to synthetic fungicides. However, to date, only a few alternative technologies have succeeded on a commercial scale. Recent research aimed at increasing the competitiveness of alternative technologies has led to the development of integrated management strategies to prevent postharvest decay and increase the safety and quality of table grapes.

Biocontrol of Alternaria alternata in cold-stored table grapes using psychrotrophic yeasts and bioactive compounds of natural sources.

Alternaria alternata is a common fungal pathogen causing postharvest decay in table grapes. This study addressed the potential of autochthonous yeasts and bioactive compounds of natural sources to act as biocontrol agents (BCAs) against A. alternata in cold-stored table grapes. With this purpose, 19 yeast capable of growing at 0-1 °C were isolated from the surface of Red Globe table grapes. These isolates, along with the pre-isolated strain Metschnikowia pulcherrima RCM2, were evaluated as BCAs in wounded berries. From these results, six yeast isolates were pre-selected to be combined with bioactive compounds of natural sources, like phenolic compounds (PCs) of side streams of wine industry, including bunch stem extract (BSE) (5-25 %), and cane extract (CE) (5-25 %), and functional polysaccharides from shrimp waste such as chitosan (CH) (0.5 %). Then, the biocontrol efficacy of combined treatments beyond individual ones was compared. The results revealed that 4 yeast isolates, namely M. pulcherrima RCM2 and ULA146, and Aureobasidium pullulans FUL14 and FUL18, were the most effective. However, when combined with the natural bioactive compounds, their efficacy against A. alternata did not increase significantly. Notably, ULA146 and FUL18 demonstrated a biocontrol efficacy of 36-37 %, comparable to that of the treatment with commercial doses of SO2, which only showed a 27 % reduction in the lesion diameter. These findings highlight the potential of using psychrotrophic yeasts as BCAs against A. alternata in cold-stored table grapes. Combining these yeast strains with BSE, CE and CH did not increase BCAs efficacy against this pathogen at the concentrations tested. The development of effective biocontrol strategies for A. alternata could contribute to reducing reliance on chemically synthesized fungicides, promoting sustainable practices, aiming to improve the quality and safety of cold-stored table grapes.

Evaluation of different nitrogen sources on growth and fermentation performance for enhancing ethanol production by wine yeasts.

The utilization of grape juice from low oenological value grape varieties for bioethanol production represent an alternative for diversification and value addition in viticulture. Optimizing Very High Gravity (VHG) fermentation can significantly increase ethanol productivity while reducing water and energy consumption. In this study, the impact of different nitrogen sources on growth and fermentative performance of locally selected yeast strains was investigated. Five yeast strains of species Saccharomyces cerevisiae and Zygosaccharomyces rouxii were cultured in both synthetic culture media and natural grape juice supplemented with ammonium sulfate (NH), yeast extract (YE), Fermaid K (FERM), and urea (U) at varying concentrations. Due to the very low fermentation rate, the Z. rouxii strain was excluded from the selection. The results obtained in synthetic medium showed that nitrogen sources that promoted growth (NH and YE) had minimal effects on fermentative performance and were highly dependent on the specific yeast strain. However, the combination of urea and ammonium favored the rate of sugar consumption. When validated in natural grape juice, urea combined with ammonium (U + NH 300 + 75 mg/L) improved both growth parameters and ethanol yield. Doubling the concentration (U + NH 600 + 150 mg/L) further enhanced sugar consumption and ethanol production while reducing unwanted by-products. The combined use of urea and ammonium exhibited a synergistic effect, making it a cost-effective nitrogen supplement for VHG fermentations.

Control of ochratoxin A production in grapes.

Ochratoxin A (OTA) is a mycotoxin commonly present in cereals, grapes, coffee, spices, and cocoa. Even though the main objective of the food and feed chain processors and distributors is to avoid the extended contamination of plant-derived foods and animal feeds with mycotoxins, until now, complete OTA removal from foods and feedstuffs is not feasible. Prevention through pre-harvest management is the best method for controlling mycotoxin contamination. However, in the case that the contamination occurs after this stage, the hazards associated with OTA must be managed through post-harvest strategies. Due to the increasing number of fungal strains resistant to chemical fungicides and the impact of these pesticides on the environment and human health, maximum levels of chemical residues have been regulated in many products. Alternative methods are necessary to substitute or complement treatments with fungicides to control fungi under field or storage conditions. Yeasts are considered one of the most potent biocontrol agents due to their biology and non-toxic properties. Epiphytic yeasts are the major component of the microbial community on the surface of grape berries and they are evolutionarily adapted to this ecological niche. Nowadays, several yeast species included in different genera are considered as potential biocontrol agents to control both, growth of ochratoxigenic Aspergillus species and OTA accumulation.

Biocontrol as a strategy to reduce the impact of ochratoxin A and Aspergillus section Nigri in grapes.

The efficacy of two strains of Kluyveromyces thermotolerans in preventing the growth and ochratoxin A (OTA) accumulation of ochratoxigenic fungi both "in vitro" and "in situ" was evaluated. The data from this study showed that both yeast strains were able to control Aspergillus carbonarius and A. niger aggregate species growth and ochratoxin A accumulation. The inhibitory effects were dependent on the ochratoxigenic species, yeast strains, a(w) and temperature evaluated and their interactions. Over all conditions assayed, ochratoxin A accumulation was reduced from 3% to 100% and the growth rate from 11% to 82.5%, depending on conditions. These results are promising for future development of a bio-pesticide.

Natural occurrence of ochratoxin A in musts, wines and grape vine fruits from grapes harvested in Argentina.

In this study, ochratoxin A (OTA) occurrence in Argentinean musts, wines and dried vine fruits was evaluated, alongside with the performance of OchraStar(TM) columns for OTA extraction. In all the three matrices analyzed, the OchraStar(TM) columns showed good performance. The analysis of natural occurrence of OTA in the red must and the red wine samples showed low incidence with low levels of mean OTA contamination (0.12 ng/mL and 0.37 ng/mL, respectively), while 60% of the dried vine fruit samples were contaminated with OTA, in levels ranging from 0.26 to 20.28 ng/g.

Ochratoxin A and Aspergillus section Nigri in peanut seeds at different months of storage in Córdoba, Argentina.

Peanut is an important food commodity in Argentina. Last year Córdoba Province accounted for approximately 96% of the total Argentinian production. Few surveys of peanuts for the natural occurrence of ochratoxins and ochratoxin-producing fungi have been reported. The objectives of this study were to investigate the occurrence of Aspergillus section Nigri and ochratoxin A (OTA) in storage peanuts during a three-month-period. The capacity to produce OTA by Aspergillus section Nigri was also studied. A total of 100 samples were collected from May to July 2004. The frequency of contaminating fungi were determined by surface-disinfection the seeds and plating onto several agar types. Detection of OTA in seed samples was performed using an HPLC method. Strains belonging to Aspergillus section Nigri or Flavi were detected in all seeds samples. From the section Nigri, the species belonging to A. niger aggregate were isolated in 100% of the samples. The main ochratoxigenic specie, A. carbonarius, was present at low levels throughout the study period. OTA was found in 50% of the peanut samples, with mean levels ranging from 5.6 to 130 ng g(-1). The mean value of OTA obtained after the first month of storage (30 ng g(-1)) was significantly higher from those obtained after the second (6.5 ng g(-1)) and third (13 ng g(-1)) month (p<0.0001). One hundred and four (32%) of 322 strains of Aspergillus section Nigri, were OTA producers. The levels of toxin produced ranged from 2 to 24 ng ml(-1) of culture medium (mean level: 12.7 ng ml(-1)). These results indicate that humans and animals being may be frequently exposed to OTA in Argentina through the ingestion of peanut seed and foods based on peanuts. The presence of this toxin in peanuts might be an appropriate focus for future studies to estimate exposure through normal consumption of this commodity. These data are important in formulating guidelines for quality control of peanuts in Argentina.