The aim of this study is to propose different fed-batch strategies during the fermentation of glycerol into 1,3-Propanediol, which show the influence of the initial concentration in glycerol and the feed flow on the behaviour of Clostridium butyricum. The kinetic study of the conversion of glycerol into 1,3-Propanediol by Clostridium butyricum, showed that according to the initial concentration of glycerol and feed flow, this strain displays two different metabolic behaviours. This strain directs its metabolism towards its traditional metabolic pathways (production of 1,3-Propanediol, butyric and acetic acid), when the culture was started with a high initial concentration of glycerol and was fed with a weak rate. The high initial concentration of glycerol causes a deceleration of growth rate, which led to an increase in the growth phase duration. Feeding by a weak flow allowed maintaining the cells in full growth phase by providing the necessary substrate for its growth and its maintenance and, at the same time, to avoid the glycerol accumulation in the medium. A high feed flow involved a glycerol accumulation in the culture medium, which obliged the bacterium to direct its metabolism towards the production of acetic acid in significant quantities. The growth phase always showed the same duration, yielding similar final concentrations in biomass and metabolites, an identical metabolic behaviour was observed when the culture begin with a low initial concentration of glycerol, and whatever the flow of substrate applied. This behaviour may be explained by a growth inhibition caused by the accumulation of 1,3-Propanediol in concentrations of 20-25 g/L.

The objective of this study was the elaboration and characterization of milk-dates mixtures and utilization of this new food system for the production of steamed yoghurt. Dates at 9, 20 and 30% were mixed with milk at 30 °C and 45 °C for 2.5 hours. The addition of dates to milk increased the levels of density, viscosity, dry matter, proteins, pectin, ash and mineral salts. A certain stability of the quantity of lactose and a slight decrease in total fat were observed. The percentage of sugars increased gradually and stabilized at a value of 6% compared with the control 4.5%. All samples of milk were of satisfactory hygienic quality. Milkdates mixtures were appreciated by panelists for their best color taste and flavor. The mixture prepared at 30 °C remained stable after 19 hours while the mixture at 45 °C became a coagulum after 7 hours. The emulsifying power increased gradually with the concentration of the dates used and the foaming power of the control milk was the highest compared with the mixtures, i.e. it was 26.8% at the beginning, and then decreased to 16.6% after 45 min. Yoghurts prepared with milk-dates mixtures were marked by good biochemical, microbiological and sensory characteristics. The study found that the new milk-dates system is very rich in nutritional elements and able to produce steamed yoghurts of good quality and high acceptability to consumers.

This work was conducted to evaluate the antioxidant activity of the essential oil obtained from the aerial part of Mentha pulegium. The antioxidant power of the essential oil obtained by hydrodistillation using a Clevenger-type apparatus was evaluated by using three methods: free radical-scavenging activity, reducing power and liver lipid peroxidation assay. Results showed that Mentha pulegium oil displayed good quality according to its physicochemical characteristics, and a higher yield 5.1 ± 0.2%. The essential oil of Mentha pulegium showed a higher DPPH radical scavenging activity 90.54 ± 1.5 % at a concentration of 1000 µg/mL. This value was close to the results obtained with ascorbic acid 96.23 ± 1.2%, and catechin 94.50 ± 1.4%. This oil exhibited significant potential for reducing iron (the value observed by optical density was 1.8 ± 0.3), while ascorbic acid and catechin provided an OD of 2.069 ± 0.03 and 2.66 ± 0.016 at the same concentration of 1000 µg/mL. The tested oil protected against lipid peroxidation induced by Fe+2, and considerably increased the percentage of anti lipid peroxidation in a dose-dependent manner. The studied oil displayed a good degree of antioxidant activity and can be exploited in food and pharmaceutical industries.