Use of gamma-irradiation and sulphur dioxide to improve storability of two Syrian grape cultivars (Vitis vinifera)

The feasibility of using gamma-irradiation and sulphur dioxide to control post-harvest diseases and to extend the shelf-life of table grapes in cold storage (1–2 °C) was studied using two cultivars of grapes local to Syria (Baladi and Helwani). The experiment took 2 years. In the first year the clusters of both cultivars were subjected to one of the following treatments, irradiation with 1.0 kGy of gamma-rays, sulphur dioxide (3 g of Na₂S₂O₅ per 5-kg cluster) or a combination of both 1.0 kGy of gamma-irradiation and sulphur dioxide. In the second year clusters of Baladi cv. were treated with 1.5 kGy of gamma-radiation, sulphur dioxide, and a combination of 1.5 kGy of gamma-radiation and sulphur dioxide, whereas clusters of Helwani cv. were treated with 0.5 kGy of gamma-radiation, sulphur dioxide, and a combination of 0.5 kGy of gamma-irradiation and sulphur dioxide. Treated and untreated clusters were kept in cold storage. With the exception of Helwani cv. produced in the first year and treated with sulphur dioxide, the results indicated that separate application of sulphur dioxide and gamma-radiation reduced the rotting induced by Botrytis cinerea . Gamma-irradiation in combination with sulphur dioxide was the best method of preserving the two varieties of table grapes.     

Changes on Enological Parameters of White Wine Packaged in Bag-in-Box during Secondary Shelf Life

ABSTRACT:  This study investigated the effects of temperature (22, 35, and 45 °C), storage time (48, 30, and 15 d), and packaging type on the quality of white wine in bag-in-box (BIB) during the secondary shelf life. Several enological parameters (color and contents of free and total SO₂, total aldehyde, and total phenol) were monitored and correlated with oxygen transmission rate (OTR) and Fourier transform infrared (FTIR) spectral data. Time and temperature had significant effects on color development and SO₂ depletion during storage. The increased absorbance at 420 nm was correlated with decreases of free SO₂ and total SO₂. Overall, total phenol content correlated negatively with total aldehyde content. The variance of the enological parameters can be correlated with the OTR data, indicating the barrier properties for the tested packages were different. FTIR–ATR spectra of the wine were analyzed chemometrically using PLS algorithm. The resulting models were able to predict the  A ₄₂₀, free SO₂, total SO₂, total phenol, total aldehyde, and storage time of the wines. This technique can potentially be used as an efficient tool to evaluate the quality of wine.     

Occurrence of ochratoxin A-producing fungi in grapes grown in Italy

A study was carried out to investigate fungi present on grapes grown in Italy. Aspergillus and Penicillium spp. isolates were identified and studied in vitro, and their ability to produce ochratoxin A (OA) was investigated. The survey involved nine vineyards, three located in northern Italy and six located in southern Italy. In 1999 and 2000, bunches of grapes at different growth stages were collected from all nine vineyards, and berry samples were placed in moist chambers and incubated. The resultant fungal colonies were then transferred to petri dishes containing Czapek yeast agar and incubated at 25 degrees C for 7 days; the fungal isolates were identified and then cultivated in liquid Czapek yeast medium and evaluated for their ability to produce OA. During the survey, 508 isolates were collected, with 477 belonging to Aspergillus spp. and 31 belonging to Penicillium spp. Among the aspergilli, species of the Fumigati, Circumdati, and Nigri sections were identified, with species of the Nigri section (464 isolates) largely predominating; for species of the Nigri section, 108 isolates were uniseriate, 270 were biseriate, and 86 were identified as Aspergillus carbonarius. Black aspergilli isolated over the 2 years of the study showed a very similar pattern. On average, the biseriates represented about 60% of the isolates collected in both years and were followed by uniseriates (21%) and A. carbonarius (19%). The most toxigenic strains proved to be those of A. carbonarius; about 60% of these isolates were OA producers and produced the highest levels of OA. A. carbonarius was more frequent in the south, but in both areas the percentages of OA-producing isolates remained the same.     

Effect of some thermal and chemical pre-treatments on smoked oyster mushroom quality

The effect of different thermal and chemical pre-treatments on quality and enzyme activities of smoked mushroom was investigated. Mushrooms were blanched (water and steam) and dipped in different concentrations of SO₂, H₂O₂, ethylenediaminetetraacetic acid (EDTA) and citric acid for 10 min before smoking. Enzyme activities, colour characteristics, microbiological and sensory examinations were carried out every 2 weeks up to 8 weeks of storage at 4 °C. Smoked mushroom pre-treated with sulphites (SO₂), H₂O₂ and steam blanching had the best colour values, better scores for all sensory characteristics and lower non-enzymatic browning compared with the other pre-treatments. Pre-treatment against total aerobic bacteria, yeast and moulds was the most effective when using citric acid, EDTA and steam, followed by smoking of mushroom. The most effective pre-treatments on quality and safety of smoked mushrooms were those using H₂O₂ and steam. It can be concluded that thermal and chemical treatments followed by smoking of mushroom reduce enzyme activities and are suitable for preserving mushrooms.     

Ochratoxin A-producing fungi from grapes intended for liqueur wine production

The ochratoxigenic mycobiota of grapes intended for liqueur wines from four Spanish vineyards were studied. The specific wine-making technology of these wines requires overripening of the grapes on the vine or extended post-harvest exposure of the grapes in the sun. In every vineyard, samples were taken at three different developmental stages: veraison, harvesting time and after over-ripening. With the maturation of the berries there was a clear increase of Aspergillus spp. In the last sampling time studied, they were isolated from the 90.3% of the plated berries. Black aspergilli (mainly A. niger aggregate and A. carbonarius) were predominant among the different Aspergillus spp. isolated and constituted 98.5% of the total Aspergillus strains isolated. At harvesting time and after over-ripening, the percentage of colonized berries with A. carbonarius exceeded that of Aspergillus niger aggregate. Due to their low frequency of isolation, Penicillium spp. and Aspergillus spp. outside black aspergilli are not an important source of ochratoxin A in grapes for liqueur wine production. On the contrary, 98.5% of the A. carbonarius isolates screened were able to produce ochratoxin A. Although the possible participation of different ochratoxin A-producing species may occur, our results confirm that A. carbonarius is the most important source of ochratoxin A in liqueur wines, increasing its occurrence along the ripening of grapes.     

Effects of Hot Rehydration in the Presence of Hydrogen Peroxide on Microbial Quality, Texture, Color, and Antioxidant Activity of Cold-stored Intermediate-moisture Sun-dried Figs

ABSTRACT: Pectin methylesterase (PME) causes considerable softening in intermediate-moisture (IM) figs rehydrated at 30°C and cold stored at 28% to 29% moisture content. Rehydration of figs at 80°C for 16 min inactivated PME partially (25–30%), but this did not prevent the softening over 3 mo of cold storage. Also, heating did not reduce the microbial load of figs significantly and increased their browning. In contrast, rehydration of figs 1st in 2.5% H₂O₂ at 80°C for 8 min and then in water at 80°C for 8 min reduced the microbial load of IM figs significantly, turned their brown color to yellow-light brown, and maintained their desired textural properties. The residual H₂O₂ in IM figs decomposed in 3 or 1.5 wk by the in situ catalase or by application of the iron (II) sulfate-ascorbic acid residue elimination method, respectively. Hot rehydration did not affect the antioxidant activity of IM figs, but treatment of figs with H₂O₂ increased their antioxidant activity slightly. These results indicate that the hot rehydration of figs in the presence of H₂O₂ and cold storage may be applied to obtain safe and SO₂-free light-colored IM fig products.     

Occurrence of fruit rot fungi (Aspergillus section Nigri) on some drying varieties of irrigated grapes

The occurrence of Aspergillus section Nigri on certain varieties of grapes used for dried vine fruit (and especially on Sultana), was surveyed extensively during three harvest seasons (1998, 1999 and 2000). Members of Aspergillus section Nigri were enumerated and identified in a total of 806 samples comprising both fresh fruit as well as partially-dried and fully-dried grapes. Aspergillus aculeatus , A. carbonarius and A. niger were commonly isolated. Of those three species, A. niger showed the highest optimum temperature for growth, as well as highest thermal tolerance. That combination of properties probably accounts for the occurrence of A. niger in over 80% of fruit samples in all three seasons. A. carbonarius was also prevalent on fruit surveyed for fungal rots. Severity of infection with this group of fungi was highest in the seasons when grape berries were rain-damaged. Typically, the Aspergillus count increased during the initial stages of drying. Growth of these moulds while grapes are either still on the vine or during drying carries important implications for human consumption due to the potential for certain strains of these fungi to produce ochratoxin A. Fungal cultures on coconut cream agar plates were screened for production of ochratoxin A via fluorescence emission under UV light. Such fluorescence was observed in all isolates of A. carbonarius , but was not observed in any isolates of either A. aculeatus or A. niger .     

Microbiological, physicochemical and organoleptic changes in dry-salted olives of Thassos variety stored under different modified atmospheres at 4 and 20 °C

Microbiological, physico-chemical and organoleptic changes were studied in dry-salted olives, cv. Thassos, stored under different atmospheres (100% carbon dioxide and nitrogen, 40% CO₂/30%O₂/30%N₂ and air) at 4 and 20 °C for 180 days. The initial microbial flora comprised of yeasts, no lactic acid bacteria, enterobacteria, pseudomonads or Staphylococcus aureus were detected, as the low water activity/high salt content does not favour their growth. At 4 °C, the population of yeasts declined steadily throughout storage but to a different extent depending on the gaseous atmospheres. At 20 °C, there was an initial decline in yeast counts in all samples followed by a steady increase until the end of the storage period. The CO₂ atmosphere was most effective at keeping the number of yeasts low at both storage temperatures. All gas atmospheres prevented fungal growth at both temperatures apart from the samples stored in air. The pH, a_w and salt content of the olives did not change significantly throughout the storage period. The prevailing yeast species was the salt tolerant Candida famata . The organoleptic characteristics did not differ significantly among differently treated olives. However, increased rancidity and reduced fruit colour was observed in the samples stored at 20 °C.     

EFFECT OF GAMMA IRRADIATION ON AFLATOXIN B1 PRODUCTION BY ASPERGILLUS FLAVUS IN GROUND BEEF STORED AT 5C

The effect of γ-irradiation for controlling the production of aflatoxin B₁ by Aspergillus flavus in ground beef stored at 5C for 2 weeks was investigated. Aspergillus, Penicillium, Cladosporium, Mucor, Scopulariopsis, Candida and Rhodotorula were the most common fungal genera contaminating ground beef. A. flavus and A. niger were the most common Aspergillus spp. Aspergillus flavus isolates were able to produce aflatoxin B₁ in ground beef. Only 3 (20%) samples of ground beef were contaminated with aflatoxin B₁ (25–45 μg/Kg). Gamma irradiation dose levels resulted in an immediate reduction in the total numbers of A. flavus. No growth or aflatoxin B₁ production occurred at 1.50 kGy during storage.     

An ITS-RFLP method to identify black Aspergillus isolates responsible for OTA contamination in grapes and wine

Ochratoxigenic mycobiota in grapes from representative wine regions in Valencia was identified. Black aspergilli were predominant among the different Aspergillus spp. isolated. Restriction digestion analysis of the ITS products was tested as a rapid method to identify isolates of black Aspergillus species from grapes. Restriction endonuclease digestion of the ITS products using the endonucleases HhaI, NlaIII and RsaI, distinguished five types of restriction fragment length polymorphism (RFLP) corresponding to Aspergillus niger, Aspergillus tubingensis, Aspergillus carbonarius and Aspergillus aculeatus species. In addition, a new RFLP type in the A. niger aggregate was identified. The fragments obtained by digestion with the endonuclease NlaIII could be used to identify these new isolates. Black Aspergillus isolates were tested for their ability to produce OTA. Most of the isolates that produced ochratoxin A in YES medium belonged to A. carbonarius species. These results support evidence that A. carbonarious greatly contributes to OTA contamination in grapes and consequently in wine. The ITS-RFLP assay is proposed as a rapid and easy method to identify black Aspergillus species isolated from grapes, especially in studies that involve a large number of isolates.     

Occurrence of ochratoxigenic fungi and ochratoxin A in grapes from a Tunisian vineyard

The occurrence of ochratoxin A (OTA) and the identification of the ochratoxigenic microbiota in Tunisian grapes were studied for the first time. Black aspergilli were the dominant genus among the filamentous fungi isolated from grapes and were the only potential OTA-producing fungi found. The most abundant species were member of Aspergillus niger aggregate (63%) and Aspergillus carbonarius (36%). Uniseriate aspergilli were rarely present (1%). Of the A. carbonarius isolates, 97% were OTA positive but only 3% of the A. niger aggregate isolates were OTA positive. During grape maturation, the frequency of black aspergilli increased due to increase of the numbers of A. carbonarius. Musts (n=24) obtained from grapes collected at the different sampling times were analyzed for their OTA content. Up to 37% of the musts contained OTA at levels varying between 0.59 and 2.57 microg/l. The amounts of OTA in musts increased as grapes matured. These results indicate that A. carbonarius is the main cause of OTA contamination of Tunisian grapes.     

Enhancement of Fermentation Process in Pu-Erh Tea by Tea-Leaf Extract

ABSTRACT:  Pu-erh tea is known as a fermented tea and longer storage enhances its flavor and taste. Recently,  Aspergillu s,  Blastobotrys , and  Streptomyces  are found to play important roles in nutritional enhancement of Pu-erh tea by fermentation. Since water and temperature affect the microbial growth, we therefore explored the factors that might enhance the Pu-erh tea fermentation. The results showed that the addition of fresh tea-leaf extract (TLE) enhanced the withered tea fermentation (at 37 °C, 80 to 85% RH) as compared with the water only. Contents of statin, GABA, gallic acid, DPPH scavenging and polyphenol oxidase (PPO) activities were increased, whereas polyphenols and caffeine were decreased over 6 mo. TLE dose-dependently enhanced some of the qualities (that is, statin, PPO) of Pu-erh tea significantly as compared with the water only. The effect was related to the increase population of  A. niger  and  A. carbonarius  at 6 mo (from 7.6 ± 1.2 × 10¹ and 3.2 ± 1.3 × 10¹ to 3.1 ± 1.2 × 10⁶ and 2.4 ± 1.1 × 10⁵ colony forming units [CFU]/g, respectively). After drying process (90 °C, 30 min), the total microbial count from these samples returned to background level (3 ± 0.5 × 10² CFU/g). None of ochratoxin and fumonisin, toxins from  Aspergillus , was detected in the final products. The flavor and taste were also enhanced by treatment with TLE. The inoculation with  S. cinereus  Y11 with 2% TLE further enhanced these functional contents (about 2-fold increase of statin level) in the experimental Pu-erh tea. Therefore, this result may add a new process for Pu-erh tea manufacture.     

What is the source of ochratoxin A in wine?

During a microvinification trial using natural mouldy grapes from a research experimental vineyard, ochratoxin A (OTA) contaminated white wine was obtained. Potential OTA-producing mycobiota of grape samples used in this microvinification process was assessed. Only Aspergillus carbonarius isolates were detected as producers of OTA. Our report is a strong evidence of the contribution of A. carbonarius in the OTA contamination in wine.     

Effect of different extraction and precipitation methods on yield and quality of pectin

An experimental study has been conducted to determine the combined effects of different extraction conditions and precipitation method on the yield and quality of high methoxyl pectin from lemon peels. Pectin was extracted using different mineral acids (HCl, HNO₃ and H₂SO₄) at four concentration levels (0.025; 0.05; 0.1 and 0.2  m ), at 70 °C for 4 h. The soluble pectin was precipitated by iso-propanol or by an aluminium sulphate, Al₂(SO₄)₃, solution at pH 4. The extraction with HCl and HNO₃, at the highest concentrations investigated, followed by aluminium precipitation led to the best results in terms of yield (22–25%), quality and gelling power of pectin with a remarkable decrease of alcohol consumption as compared to the alcoholic precipitation under the same extracting conditions.     

Occurrence of ochratoxin A producing fungi in wine and table grapes in Israel

A 3-year survey was conducted to assay the number of Aspergillus Section Nigri isolates and in vitro ochratoxin A (OTA) production capacity in 10 vineyards in Israel. The survey included field sampling of two wine cultivars, 'Sauvignon Blanc' and 'Cabernet Sauvignon' as well as the table grape cultivar 'Superior'. A total of 2114 isolates were analyzed and of those 161 isolates were shown to produce OTA. The major finding was that Aspergillus carbonarius (336 tested strains) is the most consistent producer of OTA, with approximately 35% of the isolates identified as positive in vitro. In comparison, 3.1% of other isolates from the Aspergillus niger aggregate (of 1432 strains) produced OTA in vitro. In contrast, none of the 346 tested strains with a uniseriate head morphology produced OTA. The incidence of infected berries was very low before veraison, while at harvest, this frequency was twice as high. In general, the composition of black Aspergilli did not differ during berry development. Generally, more OTA-producing isolates were isolated from the surface of table grapes cv. 'Superior' compared to 'Sauvignon Blanc'. None of the samples collected at harvest contained traces of OTA in the juice. This study shows that grapes in Israel are contaminated with ochratoxigenic species which represent a risk of OTA contamination.     

Maintaining Quality of Fresh-cut Tomato Slices through Modified Atmosphere Packaging and Low Temperature Storage

ABSTRACT: Quality of fresh-cut tomato slices was compared during cold storage under various modified atmosphere packaging conditions. Chilling injury of slices in containers sealed with Film A was higher than with Film B; these films had oxygen transmission rates of 87.4 and 60.0 ml · h^-1· m^-2· atm^-1 at 5 °C and 99% RH, respectively. While slices in containers with an initial atmospheric composition of air, 4% CO₂+ 1 or 20% O₂, 8% CO₂+ 1 or 20% O₂, or 12% CO₂+ 20% O₂ showed fungal growth, slices in containers with 12% CO₂+ 1% O₂ did not. Low ethylene in containers enhanced chilling injury. Modified atmosphere packaging provided good quality tomato slices with a shelf life of 2 w or more at 5 °C.     

Real-time PCR based procedures for detection and quantification of Aspergillus carbonarius in wine grapes

Aspergillus carbonarius is the main species responsible for ochratoxin A accumulation in wine grapes and consequently, its rapid and sensitive detection is increasingly investigated. A new real-time PCR (RTi-PCR) based procedure was developed for the rapid and specific detection and quantification of A. carbonarius in wine grapes. The procedure includes the use of the pulsifier equipment to remove conidia from grapes which prevents releasing of PCR inhibitors, and DNA extraction with the EZNA Fungal DNA kit. It reduced the time for A. carbonarius DNA extraction from grapes to 30 min. Two specific primers (AcKS10L/AcKS10R) delimiting a 161 bp fragment, and a probe were designed and directed to the beta-ketosynthase domain of a polyketide synthase from A. carbonarius. Specificity was confirmed by testing primers towards purified DNA from 52 fungal strains, including reference and food isolates. Quantification was linear over at least 5 log units using both serial dilutions of purified DNA and calibrated conidial suspensions from A. carbonarius. The SYBR-Green I and TaqMan RTi-PCR approaches established were able to detect at least 2.4 and 24 genomic equivalents, respectively, using purified DNA. Results obtained from conidial suspensions, after DNA extraction, showed that at least 5 conidia per reaction should be present for a positive result with SYBR-Green I and 50 in the case of TaqMan. The quantification of fungal genomic DNA in artificially inoculated wine grapes performed successfully, with a minimum threshold of 10(3) conidia mL(-1) for accurate quantification. The developed RTi-PCR assay is a promising tool in the prediction of potential ochratoxigenic risk, even in the case of low-level infections, and suitable for a rapid, automated and high throughput analysis.     

Quality Changes of Highbush Blueberries Fruit Stored in CA with Different CO2 Levels

ABSTRACT:  Quality changes of blueberries ( Vacccinium corymbosum L. cv Brigitta) were evaluated during CA storage (0 °C) with different concentrations of CO₂ (5%, 10%, and 15%) combined with 5% O₂, respectively. Atmospheric air (20.9% O₂+ 0.03% CO₂) was used as control. From samples taken at 0, 24, and 48 d of storage, unmarketable fruits and weight loss were recorded as well as color ( h ), firmness ( g ), soluble solid content (%), titratable acidity (% citric acid), ratio, and the monomeric anthocyanin content (ppm). At each sampling time, additional units were kept for 3 d at 10 °C to simulate retail holding conditions. Irrespective of gas concentration, 0.9% of the initial fresh weight was lost after 48 d at 0 °C. CA fruit had better quality than control at the 24 d sampling but due to the high number of unmarketable fruits, this advantage was not observed at 48 d at 0 °C. After 24 d of storage, fruits for CA treatments were more firm and had better color, with higher anthocyanin and acidity levels. Soluble solid content showed no significant differences throughout the cold storage period. Residual effect of CA storage was observed at the retail holding condition yielding better firmness, acidity, and ratio. However, the CO₂ level tested increased the number of unmarketable fruit in long-term storage (48 d). Response of "Brigitta" blueberries to the different CO₂ levels studied was moderate and could be related to the high storage potential of this cultivar.     

Effects of Reducing Agent Concentration on Soy Protein Fractionation and Functionality

ABSTRACT: The concentration of the reducing agent SO₂ significantly affected fraction yields, purities, and compositions during soy protein fractionation, especially the purity of the glycinin-rich fraction. The optimum amount of reducing agent was 5 m M SO₂ based on protein yields, purities, and functional properties. With no SO₂, the glycinin-rich fraction contained 29% of the total protein with only 63% glycinin, and the β-conglycinin-rich fraction contained 10% of the total protein with 94%β-conglycinin; whereas, by adding 5 m M SO₂, the glycinin-rich fraction contained 23.4% of total protein with 81.5% glycinin, and the β-conglycinin-rich fraction contained 16.8% of the total protein with 83.7%β-conglycinin. Increasing amounts of storage proteins were lost in the whey fraction as SO₂ concentration increased. The functional properties of the 2 major fractions were greatly influenced by the addition of SO₂. The thermal behaviors of the fractions were only slightly affected by using higher amounts of SO₂. The solubility and hydrophobicity of the glycinin-rich fraction decreased with increasing SO₂ concentration, whereas the solubility of the β-conglycinin-rich fraction increased. Emulsification properties of the glycinin-rich fraction were adversely affected by higher SO₂ concentrations, whereas, those of the β-conglycinin-rich fraction were improved. The β-conglycinin-rich fractions had better emulsification properties than did the glycinin-rich fractions. The best foaming properties were achieved at 5 m M SO₂.     

Using Dimethyldicarbonate to Minimize Sulfur Dioxide for Prevention of Fermentation from Excessive Yeast Contamination in Juice and Semi-Sweet Wine

ABSTRACT: Sulfur dioxide (SO₂) at 0, 10, 25, and 50 mg/L and/or dimethyldicarbonate (DMDC) at 0, 50, 100, and 200 mg/L at different pH levels (3.0, 3.2, 3.4, and 3.6) in juice and semi-sweet wine were evaluated by monitoring yeast growth and visible fermentation at 20 °C after excessive yeast contamination (500 to 700 colony forming units/mL), using Saccharomyces bayanus. The treatments with the least preservatives that prevented yeast growth and visible fermentation at all pH levels in juice were 50 mg/L SO₂+ 100 mg/L DMDC and in wine were 10 mg/L SO₂+ 50 mg/L DMDC. DMDC and minimal SO₂ levels prevented fermentation in juice and semi-sweet wine with excessive yeast contamination.