No abstract

Tomato fruits can be contaminated by saprophytic strains of Alternaria alternata which is the reason for the frequent occurrence of Alternaria toxins like alternariol, alternariol monomethylether or tenuazonic acid in these types of products. It was shown earlier that alternariol is a colonization factor for tomatoes. In the current analysis two different tomato genotypes were analysed by untargeted comprehensive twodimensional gas chromatography mass spectrometry (GC×GC-MS). This analysis revealed clear differences in the metabolic profiles which were paralleled by differences in resistance towards Alternaria colonization. One of the genotypes was more resistant against A. alternata infection and contained high amounts of chlorogenic acid in contrast to the other genotype which was sensitive against infection. In in vitro analysis, chlorogenic acid reduced alternariol biosynthesis during the first days of growth of A. alternata. Expression analysis of the alternariol polyketide synthase gene, a key gene in the biosynthesis of alternariol, also revealed a temporal reduction in its expression in the first phases of growth. However by chromatographic analysis it could be demonstrated that chlorogenic acid was degraded over time. This degradation leads to a relief of inhibition resulting in an only temporal inhibition of alternariol biosynthesis. In vivo colonization experiments revealed that chlorogenic acid reduces colonization of tomatoes by A. alternata in a concentration dependent manner, which however is partly counteracted by the addition of alterariol.

A rich variety of indigenous fruits and vegetables grow in Africa, which contribute to the nutrition and health of Africa’s populations. Fruits and vegetables have high moisture and are thus inherently prone to accelerated spoilage. Food fermentation still plays a major role in combating food spoilage and foodborne diseases that are prevalent in many of Africa’s resource disadvantaged regions. Lactic acid fermentation is probably the oldest and best-accepted food processing method among the African people, and is largely a home-based process. Fermentation of leafy vegetables and fruits is, however, underutilized in Africa, although such fermented products could contribute toward improving nutrition and food security in this continent, where many are still malnourished and suffer from hidden hunger. Fermentation of leafy vegetables and fruits may not only improve safety and prolong shelf life, but may also enhance the availability of some trace minerals, vitamins and anti-oxidants. Cassava, cow-peas, amaranth, African nightshade, and spider plant leaves have a potential for fermentation, as do various fruits for the production of vinegars or fruit beers and wines. What is needed to accelerate efforts for production of fermented leaves and vegetables is the development of fermentation protocols, training of personnel and scale-up of production methods. Furthermore, suitable starter cultures need to be developed and produced to guarantee the success of the fermentations.

Background: Ethiopian kale (Brassica carinata) is a horticulturally important crop used as leafy vegetable in large parts of East and Southern Africa. The leaves are reported to contain high concentrations of health-promoting secondary plant metabolites. However, scientific knowledge on their health benefits is scarce. Objective: This study aimed to determine the cancer preventive potential of B. carinata using a human liver in vitro model focusing on processing effects on the pattern of secondary plant metabolites and bioactivity. Design: B. carinata was cultivated under controlled conditions and differentially processed (raw, fermented, or cooked) after harvesting. Human liver cancer cells (HepG2) were treated with ethanolic extracts of raw or processed B. carinata leaves and analyzed for their anti-genotoxic, anti-oxidant, and cytostatic potential. Chemical analyses were carried out on glucosinolates including breakdown products, phenolic compounds, carotenoids, and chlorophyll content. Results: Pre-treatment with B. carinata extracts concentration dependently reduced aflatoxin-induced DNA damage in the Comet assay, reduced the production of reactive oxygen species as determined by electron paramagnetic resonance spectroscopy, and induced Nrf2-mediated gene expression. Increasing extract concentrations also promoted cytostasis. Processing had a significant effect on the content of secondary plant metabolites. However, different processing methodologies did not dramatically decrease bioactivity, but enhanced the protective effect in some of the endpoints studied. Conclusion: Our findings highlight the cancer preventive potential of B. carinata as indicated by the protection of human liver cells against aflatoxin in vitro. In general, consumption of B. carinata should be encouraged as part of chemopreventive measures to combat prevalence of aflatoxin-induced diseases.

Plant cultivation and processing may impact nutrient and phytochemical content of vegetables. The present study aimed at determining the influence of cultivation and processing on the health promoting capacity of African nightshade (Solanum scabrum Mill.) leaves, an indigenous vegetable, rich in nutrients and phytochemicals. Anti-genotoxicity against the human liver carcinogen aflatoxin B1 (AFB1) as determined by the comet assay and radical oxygen species (ROS) scavenging capacity of ethanolic and aqueous extracts were investigated in human derived liver (HepG2) cells. ROS scavenging activity was assessed using electron paramagnetic spin resonance and quantification of ARE/Nrf2 mediated gene expression. The cultivation was done under different environmental conditions. The processing included fermentation and cooking; postharvest ultraviolet irradiation (UV-C) treatment was also investigated. Overall, S. scabrum extracts showed strong health promoting potential, the highest potential was observed with the fermented extract, which showed a 60% reduction of AFB1 induced DNA damage and a 38% reduction in FeSO4 induced oxidative stress. The content of total polyphenols, carotenoids and chlorophylls was indeed affected by cultivation and processing. Based on the present in vitro findings consumption of S. scabrum leaves could be further encouraged, preferentially after cooking or fermentation of the plant.