Green strategies to control redox potential in the fermented food industry.

Lactic acid bacteria (LAB) are important microorganisms in the food industry as functional starters for the manufacture of fermented food products and as probiotics. Redox potential (Eh) is a parameter of the physicochemical environment of foods that influences key oxidation-reduction reactions involved in process performances and product quality. Eh can be modified by different methods, using redox molecules, catalytic activity of enzymes or LAB themselves, technological treatments like electroreduction or heating, and finally gases. Nowadays new applications for food manufacture must undertake green process innovation. This paper presents the strategies for Eh modification in a sustainable manner for production of LAB biomass (starters, probiotics) and fermented food products (fermented milks, cheeses and others). While the use of chemical or enzymes may be subject to controversy, the use of gases offers new opportunities, in combination with LAB. Protection against food-borne microorganisms, an increasing growth and viability of LAB, and a positive impact on food flavour are expected.

Aroma compounds production by solid state fermentation, importance of in situ gas-phase recovery systems.

Flavour and fragrance compounds are extremely important for food, feed, cosmetic and pharmaceutical industries. In the last decades, due to the consumer's increased trend towards natural products, a great interest in natural aroma compounds has arisen to the detriment of chemically synthesised ones. Recently, solid state fermentation (SSF) has been applied in the production of many metabolites. Aroma compounds can be produced by SSF with a higher yield compared to submerged fermentation (SmF). In SSF processes, aroma compounds can be produced in the solid matrix or in the headspace, but they can be lost or stripped when aeration is required. This review focuses on the production of aroma compounds by SSF processes with a special highlight on in situ systems to recover the volatiles released in the gaseous phase and stripped due to aeration. Following a brief presentation of specificities of SSF processes concerning the choice of microorganisms and the solid matrix used for the production of aroma compounds, bioreactor aspects, factors affecting production of aroma compounds and in situ gas phase aroma recovery systems in aerated SSF bioreactors are discussed.

Immunomodulatory Properties of Filamentous Fungi Cultivated through Solid-State Fermentation on Rapeseed Meal.

Water extracts from solid-state fermentation (SSF) on rapeseed meal using filamentous fungi exhibit interesting immunomodulatory activities in vitro. Immunomodulation was determined by the capacity of the compounds to activate blood neutrophils and to influence cytokine production in human peripheral blood mononuclear cells (PBMC) and mouse bone marrow-derived macrophages (BMDM). Among the strains tested, Aspergillus sojae mycelium and SSF extracts were the most promising in terms of enhancing the immune response. The filamentous fungus was also successfully cultivated in a pre-pilot bioreactor with forced aeration. The results indicated that the extracts not only activated blood neutrophils but also significantly modulated IL-1ß cytokine levels with lipopolysaccharide (LPS)-stimulated PBMC and BMDM without any cytotoxicity in immune cells. IL-1ß was down-regulated in a dose-dependent manner in the presence of A. sojae crude mycelium and SSF extract with PBMC, which indicated that there was an anti-inflammatory activity, whereas IL-1ß secretion was up-regulated in the presence of stimulated BMDM with the highest concentration that was tested (100 µg/mL). The non-fermented rapeseed had no effect at the same concentration. SSF culture, as a natural product, may be a good source for the development of functional feed with an immunostimulating effect or could potentially be used in medicinal applications.

Screening of lactic acid bacteria for reducing power using a tetrazolium salt reduction method on milk agar.

Reducing activity is a physiological property of lactic acid bacteria (LAB) of technological importance. We developed a solid medium with tetrazolium dyes enabling weakly and strongly reducing LAB to be discriminated. It was used to quantify populations in a mixed culture (spreading method) and screen strains (spot method).

A new alternative in vitro method for quantification of Toxoplasma gondii infectivity.

An in vitro method to determine the infectious potency of an unknown suspension of the protozoan parasite Toxoplasma gondii based on kinetics of host cells lysis was developed. Mic1-3KO a mutant strain of T. gondii RH tachyzoites was inoculated in 25-cm² flasks containing a 90% confluent monolayer of human foreskin fibroblasts. Lysis kinetics was monitored for infection ratios ranging from 1∶106 to 1∶10; we defined 106 tachyzoites/ml⁻¹ as the threshold value for parasite egress. Results allowed us to build a calibration curve relating the initial infection ratios to the time needed to reach 106 tachyzoites/ml⁻¹. Finally, we validated the method using a known mixture of dead and live parasites. This method was found to estimate with accuracy the initial ratio of infection of the unknown parasite suspension. This easy-to-use method is reproducible and can be applied to any T. gondii tachyzoite RH strain, genetically modified or not. This method is also suitable for testing promising candidates for an effective live vaccine.

Comparison of some new pretreatment methods for second generation bioethanol production from wheat straw and water hyacinth.

Pretreatment of lignocellulosic residues like water hyacinth (WH) and wheat straw (WS) using crude glycerol (CG) and ionic liquids (IL) pretreatment was evaluated and compared with conventional dilute acid pretreatment (DAT) in terms of enzymatic hydrolysis yield and fermentation yield of pretreated samples. In the case of WS, 1-butyl-3-methylimidazolium acetate pretreatment was found to be the best method. The hydrolysis yields of glucose and total reducing sugars were 2.1 and 3.3 times respectively higher by IL pretreatment than DAT, while it was 1.4 and 1.9 times respectively higher with CG pretreatment. For WH sample, CG pretreatment was as effective as DAT and more effective than IL pretreatment regarding hydrolysis yield. The fermentation inhibition was not noticeable with both types of pretreatment methods and feedstocks. Besides, CG pretreatment was found as effective as pure glycerol pretreatment for both feedstocks. This opens up an attractive economic route for the utilization of CG.

Gaseous environments modify reserve carbohydrate contents and cell survival in the brewing yeast Saccharomyces cerevisiae.

The use of H(2), He and O(2) during batch fermentation of Saccharomyces cerevisiae BRAS291 increased the final intracellular glycogen contents of the cells from 2-fold to 10-fold compared with a gas-free condition, and this depended on the gas applied. Differently, the intracellular trehalose contents increased from 2-fold to 10-fold in reducing conditions compared with more oxidizing conditions. During storage at 4 degrees C, the viability of cells cultivated with gas was twice that of cells cultivated without gas. These results could be explained by the intracellular carbohydrate contents as well as yeast ultrastructural modifications observed previously.