Bacillus mojavensis enhances the antioxidant defense mechanism of soursop (Annona muricata L.) fruits during postharvest storage.

Rapid softening of soursop (Annona muricata L.) fruit results in postharvest losses. Bacillus genus is one of the most studied antagonistic biological control agents against postharvest diseases. Nevertheless, information about how this bacterium acts on the fruits is still not understood. The objective of this study aims to gain an insight into the effect of Bacillus mojavensis on the activity and gene expression of antioxidant defense enzymes in soursop fruits during postharvest storage. Our findings indicate different responses in the fruits inoculated with B. mojavensis at biochemical and molecular levels. On day one, fruits inoculated with B. mojavensis presented a mean value of 79.09 GAE/100 gFW in total phenols, and higher superoxide dismutase (SOD) and catalase (CAT) activities (1.35 and 1.78-fold higher, respectively). On the other hand, on the third day of storage, the ferric reducing/antioxidant power (FRAP) reached its highest level, including an increase in the expression of SOD, and PPO genes by 18.7-fold and 4.5-fold in fruits inoculated with B. mojavensis. Finally, on the fifth day of storage, soursop fruits inoculated with B. mojavensis had the highest mean values for 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH·), 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonate (ABTS· +), with values of 194.68 EAA/100 gFW, and 172.33 EAA/100 gFW, respectively. Indeed, higher polyphenol oxidase (PPO), and peroxidase (POD) activities (2.17-fold and 1.27-fold higher, respectively) were recorded compared to the control fruits. We show that depending on the stage of ripening, the antagonist bacteria B. mojavensis enhanced the antioxidant capacity, enzymatic activity, and gene expression of soursop fruits.

Differential Responses of Antioxidative System during the Interaction of Soursop Fruits (Annona muricata L.) and Nectria haematococca at Postharvest Storage.

Soursop fruit (Annona muricata L.) production is diminished by the attack of pathogens such as Nectria haematococca. However, the fruit-pathogen interaction at the biochemical and molecular levels is still unknown. The objective of this study was to analyze the response of the soursop fruit to the presence of N. haematococca during postharvest storage. Soursop fruits were inoculated with the pathogen and total phenolic compounds, antioxidant capacity by Ferric reducing/antioxidant power (FRAP), 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS•+), and 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH•), as well as enzymatic activity and transcript levels of polyphenol oxidase (PPO) and superoxide dismutase (SOD), were evaluated at 1, 3, and 5 days of storage. The noninoculated fruits were the controls of the experiment. The highest total phenol content was recorded on day one in the inoculated fruits. FRAP, ABTS, and DPPH activity presented the highest values on day three in the control fruits. Inoculated fruits recorded the highest PPO activity on day five and a five-fold induction in the PPO transcript on day three. SOD activity showed a decrease during the days of storage and 10-fold induction of SOD transcript on day three in the inoculated fruits. Principal component analysis showed that total phenols were the variable that contributed the most to the observed variations. Furthermore, a positive correlation between total phenols and SOD activity, PPO expression, and SOD expression, as well as between DPPH and FRAP, was recorded. The results showed a differential response in antioxidant capacity, enzymatic activity, and gene expression during the interaction of soursop fruits-N. haematococca at postharvest storage.

Cold Plasma Treatment as an Alternative for Ochratoxin a Detoxification and Inhibition of Mycotoxigenic Fungi in Roasted Coffee.

Ochratoxin A (OTA) produced by mycotoxigenic fungi (Aspergillus and Penicillium spp.) is an extremely toxic and carcinogenic metabolite. The use of cold plasma to inhibit toxin-producing microorganisms in coffee could be an important alternative to avoid proliferation of mycotoxigenic fungi. Roasted coffee samples were artificially inoculated with A. westerdijikiae, A. steynii, A. versicolor, and A. niger, and incubated at 27 °C over 21 days for OTA production. Samples were cold plasma treated at 30 W input power and 850 V output voltage with helium at 1.5 L/min flow. OTA production in coffee was analyzed by high performance liquid chromatography coupled to a mass spectrometer (HPLC-MS). After 6 min of treatment with cold plasma, fungi were completely inhibited (4 log reduction). Cold plasma reduces 50% of OTA content after 30 min of treatment. Toxicity was estimated for extracts of artificially contaminated roasted coffee samples using the brine shrimp (Artemia salina) lethality assay. Toxicity for untreated roasted coffee was shown to be "toxic", while toxicity for cold plasma treated coffee was reduced to "slightly toxic". These results suggested that cold plasma may be considered as an alternative method for the degradation and reduction of toxin production by mycotoxigenic fungi in the processing of foods and feedstuffs.

Determination of potentially mycotoxigenic fungi in coffee (Coffea arabica L.) from Nayarit.

A total of fourteen roasted coffee samples were collected from different local markets in Nayarit, Mexico. Twenty-two fungi isolates were related to the genera Aspergillus (54.54%) and Penicillium (4.5%). The strains R16 (0.33 µg/kg), 6N (1.16 µg/kg) and 11 (0.36 µg/kg) tested positive for OTA (ochratoxin A) production in PDA, the other fungi samples were not toxigenic. According to the sequence analysis of their ITS1-5.8S-ITS2 rDNA region, fungi OTA producers correspond to A. niger, A. versicolor and Byssochlamys spectabilis. These three strains were able to produce OTA when inoculated in roasted coffee in concentrations ranging from 75 to 90 µg/kg, after 21 days. Different production stages of roasted coffee (crop management, postharvest practices and storage) along with environmental conditions do not ensure mycotoxigenic fungi free products. This is the first report of OTA natural occurrence in roasted coffee from Nayarit.