Valorization of African indigenous leafy vegetables: The role of phyllosphere microbiota.

In sub-Saharan Africa, malnutrition occurs in various forms going from micronutrient deficiency (MND) to severe malnutrition. In this scenario, African indigenous leafy vegetables (AILVs) could help in alleviating hunger and food insecurity. Principally used by smallholder farmers as subsistence crops thanks to the ease of growing, AILVs have been reported to have valuable nutrient content. Nevertheless, rough handling coupled with microbial activities could lead to phyllosphere deterioration, hence leading to spoilage events that make the sustainable supply and consumption of AILVs difficult. Reviewing the literature regarding AILVs' phyllosphere microbiota, some bacteria such as Pseudomonadaceae, Enterobacteriaceae, and lactic acid bacteria (LAB) were commonly found. Their ability to deteriorate vegetables is known, thus stressing the necessity to valorize these commodities. In this review, fermentation was deepened as an inexpensive form of food processing to valorize AILVs, modulating the phyllosphere microbiota in favor of fermenting microorganisms. The literature review revealed that traditional methods implying alkaline fermentation lower the levels of toxigenic compounds in AILVs such as cyanhydric acid. Methods involving lactic acid bacteria (LAB) fermentation with beneficial LAB were able to control the fermentation, hindering the proliferation of spoilage (i.e. Pseudomonadaceae) and potentially pathogenic bacteria (i.e. Enterobacteriaceae). Aside, the improvement of nutritional content is achieved, obtaining increased levels of B-group vitamins, carotenoids, and the reduction of antinutrient and toxic compounds for certain AILVs. Furthermore, the AILVs' shelf life is also prolonged, thus further confirming that the final products are valorized by the fermentation processes. Howbeit, this review also points out some weaknesses in the methods. Indeed, alkaline fermentation can allow the growth of toxin-producing Bacillus spp. that can jeopardize the consumers' health. While the unpredictability of spontaneous LAB fermentation caused in some cases the resilience of certain pathogens such as Enterobacteriaceae. More studies involving alternative ways to inoculate LAB starters such as back slopping might be useful to perfect the fermentation methods and finally valorize AILVs.

Rigid bioplastics shape the microbial communities involved in the treatment of the organic fraction of municipal solid waste.

While bioplastics are gaining wide interest in replacing conventional plastics, it is necessary to understand whether the treatment of the organic fraction of municipal solid waste (OFMSW) as an end-of-life option is compatible with their biodegradation and their possible role in shaping the microbial communities involved in the processes. In the present work, we assessed the microbiological impact of rigid polylactic acid (PLA) and starch-based bioplastics (SBB) spoons on the thermophilic anaerobic digestion and the aerobic composting of OFMSW under real plant conditions. In order to thoroughly evaluate the effect of PLA and SBB on the bacterial, archaeal, and fungal communities during the process, high-throughput sequencing (HTS) technology was carried out. The results suggest that bioplastics shape the communities' structure, especially in the aerobic phase. Distinctive bacterial and fungal sequences were found for SBB compared to the positive control, which showed a more limited diversity. Mucor racemosus was especially abundant in composts from bioplastics' treatment, whereas Penicillium roqueforti was found only in compost from PLA and Thermomyces lanuginosus in that from SBB. This work shed a light on the microbial communities involved in the OFMSW treatment with and without the presence of bioplastics, using a new approach to evaluate this end-of-life option.

Evolution of microbial communities and nutritional content of fermented Amaranthus sp. leaves.

Amaranth (Amaranthus sp.) is a promising indigenous leafy vegetable plant capable of contributing to food security in sub-Saharan Africa, thanks to its adaptability to diverse soils and its drought tolerance. Its edible parts such as leaves are characterized by high nutrient content. Food losses along the supply chain due to spoilage, however, especially of fresh produce is a challenge facing most of the sub-Saharan African countries in tackling food insecurity in the region. This calls for innovative yet inexpensive solutions such as natural fermentation to preserve the quality and safety of the commodity. To demonstrate the feasibility of natural fermentation in the preservation of vegetable amaranth, leaves were submerged (1:0.5 w/v) in distilled water with 3% sucrose and 3% NaCl dissolved. Control batches were prepared using only distilled water (1:0.5 w/v) with amaranth leaves. Samplings of both treated leaves and controls occurred at 0, 24, 48, 72, and 168 h to measure the pH and determine microbial population changes using culture and molecular-based techniques. Furthermore, the effects of treatment on nutritional content were assayed at the end of the process to determine the levels of B-group vitamins, ß-carotene, lutein, and anti-nutrient phytic acid from unfermented fresh air-dried and 3% sucrose and 3% NaCl treated amaranth leaves. Finally, a visive and olfactive analysis was carried out to evaluate the acceptability of the final product. The significant drop of pH and the correct growth of Lactobacillaceae occurred only in treated batches, although Lactococcus was found in both treated and control samples. Furthermore, mean counts observed on selective media for controls and molecular high-throughput sequencing (HTS) analyses confirmed that in control samples, the undesired bacteria represented more than 60% of the microbial population. In treated amaranth leaves the amount of thiamin, riboflavin, vitamin B6, ß-carotene and lutein content were higher compared to the fresh unfermented air-dried leaves, and phytic acid content diminished after 7-days treatment. These findings suggest that treatment of amaranth leaves using 3% sucrose and 3% NaCl does not only preserve the commodity by arresting the growth of undesired microorganisms involved in spoilage and fosters the lactic acid bacteria but also improves the nutritional content of the fermented end product that has been warmly welcomed by panelists.

Fermentation as a tool for increasing food security and nutritional quality of indigenous African leafy vegetables: the case of Cucurbita sp.

Sub-Saharan region is often characterized by food and nutrition insecurity especially "hidden hunger" which results from inadequate micronutrients in diets. African indigenous leafy vegetables (AILVs) can represent a valid food source of micronutrients, but they often go to waste resulting in post-harvest losses. In an attempt to prolong AILVs shelf-life while enhancing their nutritional quality, fermentation was studied from a microbiological and nutritional point of view. Pumpkin leaves (Cucurbita sp.) were spontaneously fermented using the submerged method with 3% NaCl and 3% sucrose. Controls were set up, consisting of leaves with no additions. During fermentation, samples of both treatments were taken at 0, 24, 48, 72 and 168 h to monitor pH and characterize the microbial population through culture-based and molecular-based analyses. Variations between fresh and treated leaves in B-group vitamins, carotenoids, polyphenols, and phytic acid were evaluated. Data revealed that the treatment with addition of NaCl and sucrose hindered the growth of undesired microorganisms; in controls, unwanted microorganisms dominated the bacterial community until 168 h, while in treated samples Lactobacillaceae predominated. Furthermore, the content in folate, ß-carotene and lutein increased in treated leaves compared to the fresh ones, while phytic acid diminished indicating an amelioration in the nutritional value of the final product. Thus, fermentation could help in preserving Cucurbita sp. leaves, avoiding contamination of spoilage microorganisms and enhancing the nutritional values.

Combined Impact of No-Till and Cover Crops with or without Short-Term Water Stress as Revealed by Physicochemical and Microbiological Indicators.

Combining no-till and cover crops (NT + CC) as an alternative to conventional tillage (CT) is generating interest to build-up farming systems' resilience while promoting climate change adaptation in agriculture. Our field study aimed to assess the impact of long-term NT + CC management and short-term water stress on soil microbial communities, enzymatic activities, and the distribution of C and N within soil aggregates. High-throughput sequencing (HTS) revealed the positive impact of NT + CC on microbial biodiversity, especially under water stress conditions, with the presence of important rhizobacteria (e.g., Bradyrhizobium spp.). An alteration index based on soil enzymes confirmed soil depletion under CT. C and N pools within aggregates showed an enrichment under NT + CC mostly due to C and N-rich large macroaggregates (LM), accounting for 44% and 33% of the total soil C and N. Within LM, C and N pools were associated to microaggregates within macroaggregates (mM), which are beneficial for long-term C and N stabilization in soils. Water stress had detrimental effects on aggregate formation and limited C and N inclusion within aggregates. The microbiological and physicochemical parameters correlation supported the hypothesis that long-term NT + CC is a promising alternative to CT, due to the contribution to soil C and N stabilization while enhancing the biodiversity and enzymes.

Smallholder Farmers' Practices and African Indigenous Vegetables Affect Soil Microbial Biodiversity and Enzyme Activities in Lake Naivasha Basin, Kenya.

Loss of soil biodiversity and fertility in Sub-Saharan Africa (SSA) may put the food security of smallholder farmers in peril. Food systems in SSA are seeing the rise of African indigenous vegetables (AIVs) that are underexploited but locally consumed without being considered a primary source of food and income. Here we present a field study, a first of its kind, in which we investigated the effects of different cropping systems and inclusion of AIVs in the farming approach on bacterial and fungal biodiversity and community structures, enzymatic activity, and the alteration status of soils of the smallholder farmers in Kenya. When compared to mainstream farming approaches, the composition and biodiversity of bacteria and fungi under AIV cultivations was significantly different. Tillage had a significant impact only on the fungal communities. Fertilization and soil amendments caused shifts in microbial communities towards specialized degraders and revealed the introduction of specific microorganisms from amendments. Traditional homemade plant protection products did not cause any disturbance to either of soil bacteria or fungi. The soil alteration index based on enzyme activity successfully differentiated the alteration status for the first time in SSA. These findings could be useful for farmers to integrate AIVs with correct sustainable practices for a sustainable future.

Biopolymers modulate microbial communities in municipal organic waste digestion.

The development of biopolymers has raised issues about their recalcitrance in the environment. Their disposal is mainly carried out with the organic fraction of municipal solid waste (OFMSW) through thermophilic anaerobic digestion and aerobic composting, bioprocesses aimed at turning organic matter into biogas and compost. However, the effects of biopolymers on OFMSW treatment, on the final compost and on the microbial communities involved are partly unexplored. In this study, the OFMSW treatment was reproduced on a laboratory-scale respecting real plant conditions and testing the impacts of mixing polylactic acid (PLA) and starch-based bioplastic (SBB) separately. The dynamics of bacterial, archaeal and fungal communities during the process was screened by high-throughput sequencing (HTS) of phylogenetic amplicons. Starch-based bioplastic showed a minor and heterogeneous microbial diversity between the anaerobic and aerobic phases. Contrariwise, PLA treatment resulted in wider and more diverse bacterial and fungal communities for the compost and the aerobic biofilm. Since the biodiversity in compost may play a crucial role in its stability and safety, the modulation of environmental microbial communities induced by higher concentrations of PLA in OFMSW treatment can pose relevant issues.

Sustainability Perspectives of Vigna unguiculata L. Walp. Cultivation under No Tillage and Water Stress Conditions.

Nowadays, agriculture is facing the great challenge of climate change which puts the productivity of the crops in peril due to unpredictable rain patterns and water shortages, especially in the developing world. Besides productivity, nutritional values of the yields of these crops may also be affected, especially under low mechanization and the low water availability conditions of the developing world. Conservation agriculture (CA) is a topic of emerging interest due to the provision of adequate yields and reduced environmental impact, such as greenhouse gas emissions, by being based on three main principles: minimum soil disturbance (reduced or no tillage), cover crop maintenance, and crop rotation. The aim of this study was to assess the impact of CA management on the growth performance and the nutritional profile of cowpea (Vigna unguiculata L. Walp), a pulse of African origin, commonly known as black eye bean under field conditions. A field experiment was designed to assess the effect of conventional tillage (CT) and no-tillage (NT) combined with the usage of a set of cover crops, coupled to normal and deficient water regimes. Cowpea was revealed to be able to grow and yield comparably at each level of the treatment tested, with a better ability to face water exhaustion under CA management. After a faster initial growth phase in CT plots, the level of adaptability of this legume to NT was such that growth performances improved significantly with respect to CT plots. The flowering rate was higher and earlier in CT conditions, while in NT it was slower but longer-lasting. The leafy photosynthetic rate and the nutritional profile of beans were slightly influenced by tillage management: only total starch content was negatively affected in NT and watered plots while proteins and aminoacids did not show any significant variation. Furthermore, significantly higher carbon and nitrogen concentration occurred in NT soils especially at the topmost (0-5 cm) soil horizon. These findings confirm the capability of CA to enrich soil superficial horizons and highlight that cowpea is a suitable crop to be grown under sustainable CA management. This practice could be pivotal to preserve soils and to save agronomical costs without losing a panel of nutrients that are important to the human diet. Due to its great protein and aminoacidic composition, V. unguiculata is a good candidate for further cultivation in regions of the word facing deficiencies in the intake of such nutrients, such as the Mediterranean basins and Sub-Saharan countries.