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Present study, consisting of two experiments, aims to modify chemical composition and structure and improve the nutritional value of rapeseed cake by solid-state fermentation of combined Geotrichum candidum,Aspergillus niger, Bacillus subtilis. Fermentation variables such as temperature, fermentation time, and the changes of chemical composition and structure of the rapeseed cake were measured. Under the optimal fermentation conditions,the nutrients content, morphological structure and its nutritional value of fermented rapeseed cake in growing pigs were evaluated.Exp.l Effect of microbial solid-state fermentation on chemical composition of rapeseed cakeThe aim of this study was to optimize technological parameters of solid-state fermentation for modifying chemical composition and structure of rapeseed cake. Parameters such as material to water ratio, inoculation amount, inoculation order, inoculation ratio were examined. The resulting modification of biochemical constituents were measured. The results showed that:(1) The best fermentation conditions were:1:1.5of material to water ratio,16%inoculated amount,l:1:3of combination proportion for Aspergillus niger:Geotrichum candidum:Bacillus subtilis, and4days of fermentation time.(2) As fermentation time increased, small peptide and free amino acid contents increased linearly, antinutritional factors conten such as glucosinolate decreased linearly.(3) Pilot fermentation showed a similar results as the above. Protein morphological structure was modified. Small peptide content was increased by409.7%, free amino acid content was increased by309.5%, total glucosinolate content was decreased by93.4%, and the isothiocyanate disappeared. It is concluded that protein structure and anti-nutritional factor contents were changed obviously at the optimal fermentation conditions.Exp.2Nutritional evaluation of fermented rapeseed cake in growing pigs24crossbred (Duroc×Landrace×Large White) barrows with an initial body weight of26.56±0.76kg were used to study the digestibility data of FRSC and unfermented rapeseed cake(RSC). Basal corn-soybean diet, N-free diet, RSC-diet and FRSC-diet, in which35%protein of basal diets were substituted by FRSC or RSC were designed.24pigs were randomly allotted to the four diets with6replicates per diet. The digestive and metabolic trial consisted of a4-d diet adaptation and a4-d feces and urine collection. Then all piglets were slaughtered after intravenous anesthesia to collect ileal digesta. Nutrient apparent total tract digestibility coefficients (CATTD), ileal apparent digestibility (AID) and standardized ileal digestible (SID) of amino acids were measured and calculated for RSC and FRSC. The experimental results showed that apparent total tract digestibility of energy, dry matter and crude protein were81.15%,82.36%,70.00%respectively; nitrogen true digestibility, nitrogen apparent availability, nitrogen true availability, DE were65.18%,65.78%,72.35%,12.98MJ/kg (in DM) respectively for FRSC. Compared with RSC,FRSC had higher AID of AAs except for Met,Ile,Phe,Trp,Tyr. SID values for N and AA followed a similar pattern as AID values. Overall, the nutrient digestibility and availability of rapeseed cake were improved by solid-state fermentation with multi-strains.In conclusion, the optimal solid-state fermentation conditions for rapeseed cake were1:1.5of material to water ratio,16%inoculated amount,l:1:3of proportion for Aspergillus niger.Geotrichum candidum.Bacillus subtilis, and4days of fermentation time. Under such conditions, the structure of protein was changed, small peptide and free amino acid content were increased, anti-nutritional factor contents were decreased, and nutritional values were improved obviously for RSC. The results indicated that microbial solid-state fermentation could modify chemical compositions and improve the nutritional value of rapeseed cake.
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