In this study, the technological parameters of solid-state fermentation for producing lipid by Mor-tierella isabellina and the variation of substrate composition before and after fermentation were explored. Single factor trial design and orthogonal trial design were conducted to optimize the substrate composition and fermentation conditions, respectively. Then, the methods of chemical assay, scanning electron microscope (SEM) and X ray diffraction (XRD) were taken to detect physicochemical properties of substrate and products, in order to compare the variation of substrate composition. The results showed that the optimal substrate was mixture of corn starch and wheat bran. The optimal fermentation conditions were corn starch and wheat bran at the proportion of 1:3, 30% inoculation amount of Mortierella isabellina, 60% moisture content, and 60 g fermentation substrate per 250 mL volume. In addition, the last two factors had a significant effect on the lipid production (P <0. 01). Under the optimal fermentation conditions, lipid production reached 102 g/kg DM of fermentation products, and the contents of C18:3 and C22:6 in lipid were 4. 03% and 1. 70% , respectively. Meanwhile, the gross energy of fermentation substrate was increased (15.81 MJ/kg DM vs. 20.44 MJ/kg DM). The results of chemical analysis showed that the contents of neutral detergent fiber, acid detergent lignin, total starch and amylose of substrate were decreased, and the concentrations of reducing sugar and protein of substrate were increased by fermentation. The results of SEM analysis showed that after fermentation, granule of corn starch was eroded, and proportion of small starch granule increased. The results of XRD analysis showed that the crystal type of corn starch was disappeared after the fermentation. These results suggest that solid-state fermentation on the mixture of corn starch and wheat bran by Mortierella isabellina can produce lipid containing high level of unsaturated fatty acids. The probable lipid-producing reason is that physical structure of substrate is altered, and its hydrolysates are used to mycelial growth and lipid production.%本试验旨在探讨深黄被孢霉固态发酵生产油脂的工艺参数及发酵前后底物组成变化规律.分别采用单因素试验设计与正交试验设计优化发酵底物组成及发酵条件,采用化学分析以及扫描电镜分析、X射线衍射分析方法检测发酵前后底物的理化性质,以比较发酵前后底物组成变化规律.结果表明,最适的发酵底物为玉米淀粉和麸皮的混合物；最佳发酵条件为玉米淀粉:麸皮为1:3、深黄被孢霉接种量30％、含水量60％、250 mL装料量60 g,其中含水量和装料量这2个因素对油脂产量的影响极显著(P＜0.01).此条件下,发酵产物中油脂含量可达102 g/kg DM,其中C18:3和C22:6含量分别占油脂含量的4.03％和1.70％；总能从发酵前的15.81 MJ/kg DM提高到了20.44 MJ/kg DM.化学分析结果表明,发酵降低了底物中中性洗涤纤维、酸性洗涤木质素、总淀粉和直链淀粉含量,提高了底物中还原糖和蛋白质浓度；扫描电镜分析结果表明,发酵后玉米淀粉颗粒被腐蚀,小颗粒淀粉增多；X射线衍射分析结果表明,发酵使得玉米淀粉晶型结构消失.综上所述,利用深黄被孢霉固态发酵玉米淀粉和麸皮的混合物可生产含高不饱和脂肪酸的油脂,其原因可能与发酵使底物结构改变而利于微生物利用有关.
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