Monique Berger

Effects of fermentation on the phytochemical composition and antioxidant properties of soy germ.

Soy germ is a remarkable source of bioactive phytochemicals offering an interesting alternative as starting ingredient for fermented food. This work aimed to determine whether lactic acid bacteria fermentation of soy germ induces changes on its phytochemical composition. The antioxidant properties of fermented soy germ samples periodically taken during the fermentation process were evaluated and correlated with the concentration and structural modifications of isoflavones, saponins, phytosterols and tocopherols. Fermented soy germ extracts exhibited a higher inhibition effect against the superoxide anion radical, and lesser but significant ferric-reducing and DPPH radical scavenging effects compared with raw soy germ. By comparison to the traditional whole seed-based products, soy germ exhibits higher levels of isoflavones, saponins, phytosterols and tocopherols. All these phytochemicals contributed to the antioxidant capacity of soy germ and were conserved under lactic acid bacteria fermentation.

Response to low temperature in dinitrogen fixing soybeans

Abstract Dinitrogen fixation is an energy intensive process and photosynthesis in soybean (Glycine max L.) adapts to the carbon requirements of the nodules. Chlorophyll fluorescence measurements were used to assess the photochemical response of soybean (cv. Maple Arrow) fed exclusively on either mineral or symbiotic nitrogen, to a 12-day-long low temperature stress. In the nodule bearing plants, N2 fixation resulted in an earlier decrease in the photochemical efficiency of open reaction centers, F v F m (dark-adapted leaves), and in the photochemical efficiency of PSII at actual closure of reaction centers (Φ PSII), which reflected the occurrence of earlier leaf senescence. As a result of the specific effect of the low temperature stress, the nitrogen fixing plants exhibited a stronger decrease in F v F m ratio, with a higher increase in F0 (minimum chlorophyll fluorescence yield) than the plants supplied with nitrate. The lack of enhancement of the non-photochemical quenching NPQ with the low-temperature treatment and the persistance of high F0 values after return to optimum growth temperature suggested the occurrence of a low photoprotective ability accompanied by photodamage in the N2 fixing plants. The application of oversaturating irradiance during the low temperature treatment corroborated the greater susceptibility of the N2 fixing plants to photoinhibition. If the energy cost of symbiosis can be met by improved photosynthesis, accelerated leaf ageing and higher susceptibility to photoinhibition under stress reduce N2 fixation-related plant performances.

Response of Photochemical Processes of Photosynthesis to Dinitrogen Fixation in Soybean.

Symbiotic N2 fixation activity brings about changes in the photochemical processes of photosynthesis in soybean (Glycine max L. Merr.). For a potential photochemical efficiency ([phi]Po) similar to that obtained with an exclusively mineral nutrition, soybean, at full bloom stage (R2) with a moderate N2 fixation activity, had a better electron transfer quantum yield ([phi]PSII) and a higher photochemical quenching. At the beginning seed stage (R5), corresponding to more intense N2 fixation, the same phenomena were enhanced; in addition, an effect on the photochemical (k2b) and nonphotochemical (Kn-k22) transfer rates and an earlier activation of the electron transfer chain were characterized using a new parameter, the relative induction time of PSII fluorescence (Ap/Fm). The response of the photochemical parameters was related to the N2 fixation level (performance of the host plant-microsymbiont association): the energetic cost of symbiotic N2 fixation appeared to be met by a better photochemical efficiency of photosynthesis coupled with a decrease in thermal dissipation (kn - k22), by faster thylakoid energization, and by faster reopening of photosystem II centers at the time of fluorescence induction, as shown by decreased Ap/Fm.