Gamma-linolenic acid production of Mucor rouxii by solid-state fermentation using agricultural by-products.

AIMS: This study aims to maximize the yield of gamma-linolenic acid by a filamentous fungus, Mucor rouxii, using low cost production by solid-state fermentation. METHODS AND RESULTS: We optimized substrate types and culture conditions including inoculum size and temperature. The optimal growth of M. rouxii was found in the cultures inoculated with 5 x 10(5) spores g(-1) substrate. The fungal cells grew well on rice bran and soy bean meal, whereas a lower biomass was found in the cultures grown on polished rice, broken rice and spent malt grain. The GLA content was highly accumulated in rice bran ferment and its maximal content of about 6 g kg(-1) fermented mass was observed in the 5th-day culture grown at 30 degrees C. However, the GLA content in the rice bran ferment was not enhanced by low temperature. CONCLUSIONS: The GLA production of M. rouxii could be enhanced by optimizing the agricultural by-product substrates and culture condition. SIGNIFICANCE AND IMPACT OF THE STUDY: Low cost GLA production process was achieved, and fermented product containing GLA can be incorporated into feed additives without further oil extraction to alternate the expensive plant oils.

Experimental and numerical study of heterogeneous pressure-temperature-induced lethal and sublethal injury of Lactococcus lactis in a medium scale high-pressure autoclave.

The present contribution is dedicated to experimental and theoretical assessment of microbiological process heterogeneities of the high-pressure (HP) inactivation of Lactococcus lactis ssp. cremoris MG 1363. The inactivation kinetics are determined in dependence of pressure, process time, temperature and absence or presence of co-solutes in the buffer system namely 4 M sodium chloride and 1.5 M sucrose. The kinetic analysis is carried out in a 0.1-L autoclave in order to minimise thermal and convective effects. Upon these data, a deterministic inactivation model is formulated with the logistic equation. Its independent variables represent the counts of viable cells (viable but injured) and of the stress-resistant cells (viable and not injured). This model is then coupled to a thermo-fluiddynamical simulation method, high-pressure computer fluid dynamics technique (HP-CFD), which yields spatiotemporal temperature and flow fields occurring during the HP application inside any considered autoclave. Besides the thermo-fluiddynamic quantities, the coupled model predicts also the spatiotemporal distribution of both viable (VC) and stress-resistant cell counts (SRC). In order to assess the process non-uniformity of the microbial inactivation in a 3.3-L autoclave experimentally, microbial samples are placed at two distinct locations and are exposed to various process conditions. It can be shown with both, experimental and theoretical models that thermal heterogeneities induce process non-uniformities of more than one decimal power in the counts of the viable cells at the end of the treatment.