In-vitro antifungal activity of leaf, stem bark and root extracts of Irvingia gabonensis against fungi associated with its seed deterioration

Irvingia gabonensis (Aubry-Lecomte ex O'Rorke) Baill seeds are often contaminated in storage by postharvest spoilage fungi. This study investigated the nutritional contents of the seeds, phytochemical contents and antioxidant activity of different parts of the plant as well as their antifungal effects against fungi isolated from the deteriorated seeds. Proximate, mineral and phytochemical analyses were carried out using standard laboratory techniques. The antioxidant activity was against DPPH radicals. Ethanol extracts (100 and 200 mg/ml) of the various parts were screened against the isolates using pour plate method in Potato Dextrose Agar (PDA) plates. The plates were examined for growth daily for 10 days. Data were statistically analysed. The healthy seeds contained higher protein (13.73%), fat (58.73%) and fibre (2.50%), whereas, higher content of moisture (10.17%) and carbohydrate (15.47%) were observed in the spoilt seeds. The leaf had highest contents of alkaloids (1228.3 mg/100 g), flavonoids (1345.9 mg/100 g), tannins (1345.9 mg/100 g), saponins (578.3 mg/100 g) and carotenoids (2348.3 μg/100 g). The antioxidant activity of the leaf (50.30%) was the highest. Fungi isolated from the deteriorated seeds were Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus and Curvilaria lunata. The leaf was most effective against A. niger, A. flavus and C. lunata whereas the stem bark extract was most effective against A. fumigatus. The F-values were significant for model, treatment, concentration and number of days for the leaf and root. This study confirmed the antifungal activity of extracts of various parts of the plant against isolates implicated in the deterioration of its seeds. The extracts could be used as preservative to enhance the shelf-life and nutritional quality of the seeds. Keywords: Irvingia gabonensis, Spoilage of seeds, Antifungal activity, Free radical scavengers, Preservatives

Technological, functional and safety properties of lactobacilli isolates from soft wheat sourdough and their potential use as antimould cultures

Bakery products are a common medium for fungal growth due to their high-water activity and nutrients availability. The application of lactic acid bacteria (LAB) isolated from wheat bran or other cereals has shown great potential in controlling the growth of spoilage fungi, guarantee quality and prolong the shelf life of bakery products. This study outlines the antifungal, technological, functional and safety properties of autochthonous LAB microbiota isolated from type 0 soft wheat sourdough fermentation. Antifungal activity of 77 LAB belonging to Lactiplantibacillus plantarum and Lacticaseibacillus casei species isolated from spontaneous sourdough fermentation was tested in vitro against 16 spoilage fungi. Our findings demonstrated that the antifungal activity, enzymatic and safety properties of LAB isolates vary strain-dependently. Four LAB isolates (Lp. plantarum A16, A25, B11, and B15) showed the best traits, in particular strong antifungal activity and good capabilities to produce exopolysaccharides from different carbon sources in vitro. Care should be taken when using Lp. plantarum A310 and B18 and Lc. casei A23, as starter cultures, since these isolates exhibited a multiple antibiotic-resistance. Here we showed the promising potential of different LAB isolates as bio-preservative agents and to provide new insights regarding their prospective use as starter cultures to guarantee safety and palatability. Graphic abstract

Comparative Growth Inhibition of Bread Spoilage Fungi by Different Preservative Concentrations Using a Rapid Turbidimetric Assay System

Bread and intermediate moisture bakery products are mainly spoiled by yeasts and filamentous fungi. The inoculum load and preservation system used determines their shelf life. To extend the shelf life of such commodities, the use of chemical preservatives is the most common way to try and control the initiation of mold spoilage of bread. This study has utilized a rapid turbidimetric assay system (Bioscreen C) to examine the temporal efficacy of calcium propionate (CP) and potassium sorbate (PS) for controlling the growth of important bread spoilage fungi. The objectives were to compare the temporal growth of strains of three important spoilage fungi Hyphopichia burtonii (HB17), Paecilomyces variotii (PV11), and Penicillium roqueforti (PR06) isolated from visibly molded bread to (a) different concentrations of CP and PS (0–128 mM), (b) temperatures (25°C, 30°C), (c) water activity (aw; 0.95, 0.97), and (d) pH (5.0, 5.5). All three abiotic factors, pH, aw, and temperature, and preservative concentrations influenced the relative growth of the species examined. In general, PS was more effective than CP in inhibiting the growth of the strains of these three species. In addition, the Time to Detection (TTD) for the efficacy of the preservatives under the interacting abiotic factors was compared. The strain of Paecilomyces variotii (PV10) was the most tolerant to the preservatives, with the shortest TTD values for both preservatives. P. roqueforti was the most sensitive with the longest TTD values under all conditions examined. These results are discussed in the context of the evolution of resistance to food-grade preservatives by such spoilage fungi in bakery products.

Impacts of Climate Change Interacting Abiotic Factors on Growth, aflD and aflR Gene Expression and Aflatoxin B1 Production by Aspergillus flavus Strains In Vitro and on Pistachio Nuts

Pistachio nuts are an important economic tree nut crop which is used directly or processed for many food-related activities. They can become colonized by mycotoxigenic spoilage fungi, especially Aspergillus flavus, mainly resulting in contamination with aflatoxins (AFs), especially aflatoxin B1 (AFB1). The prevailing climate in which these crops are grown changes as temperature and atmospheric CO2 levels increase, and episodes of extreme wet/dry cycles occur due to human industrial activity. The objectives of this study were to evaluate the effect of interacting Climate Change (CC)-related abiotic factors of temperature (35 vs. 37 °C), CO2 (400 vs. 1000 ppm), and water stress (0.98–0.93 water activity, aw) on (a) growth (b) aflD and aflR biosynthetic gene expression and (c) AFB1 production by two strains A. flavus (AB3, AB10) in vitro on milled pistachio-based media and when colonizing layers of shelled raw pistachio nuts. The A. flavus strains were resilient in terms of growth on pistachio-based media and the colonisation of pistachio nuts with no significant difference when exposed to the interacting three-way climate-related abiotic factors. However, in vitro studies showed that AFB1 production was significantly stimulated (p < 0.05), especially when exposed to 1000 ppm CO2 at 0.98–0.95 aw and 35 °C, and sometimes in the 37 °C treatment group at 0.98 aw. The relative expression of the structural aflD gene involved in AFB1 biosynthesis was decreased or only slightly increased, relative to the control conditions at elevated CO, regardless of the aw level examined. For the regulatory aflR gene expression, there was a significant (p < 0.05) increase in 1000 ppm CO2 and 37 °C for both strains, especially at 0.95 aw. The in situ colonization of pistachio nuts resulted in a significant (p < 0.05) stimulation of AFB1 production at 35 °C and 1000 ppm CO2 for both strains, especially at 0.98 aw. At 37 °C, AFB1 production was either decreased, in strain AB3, or remained similar, as in strain AB10, when exposed to 1000 ppm CO2. This suggests that CC factors may have a differential effect, depending on the interacting conditions of temperature, exposure to CO2 and the level of water stress on AFB1 production.