Schutyser M A I, de Pagter P, Weber F J, Briels W J, Boom R M, Rinzema A
Wageningen Centre for Food Sciences, P.O. Box 557, 6700 AN Wageningen, The Netherlands.
Biotechnol Bioeng. 2003 Sep 5;83(5):503-13. doi: 10.1002/bit.10693.
Solid-state fermentation (SSF) is prone to process failure due to channeling caused by evaporative cooling and the formation of an interparticle mycelium network. Mixing is needed to break the mycelium network and to avoid such failure. This study presents the first attempt to quantify and predict the effect of mycelium bonds on particle mixing and vice versa. We developed a novel experimental set-up to measure the tensile strength of hyphal bonds in SSF: Aspergillus oryzae was cultivated between two wheat-dough disks and the tensile strength of the aerial mycelium was measured with a texture analyzer. Tensile strength at different incubation times was related to oxygen consumption, to allow a translation to a rotating drum with A. oryzae cultivated on wheat grain. We performed several discontinuously mixed solid-state fermentations in the drum fermentor and measured the number and size of grain-aggregates remaining after the first mixing action. We integrated data on mycelium tensile strength into a previously developed two-dimensional discrete-particle model that calculates forces acting on individual substrate particles and the resulting radial-particle movements. The discrete-particle model predicted the quantity and size of the aggregates remaining after mixing successfully. The results show that the first mixing event in SSF with A. oryzae is needed to break mycelium to avoid aggregate formation in the grain bed, and not to distribute water added to compensate for evaporation losses, or smooth out temperature gradients.
固态发酵（SSF）容易因蒸发冷却导致的沟流和颗粒间菌丝体网络的形成而出现过程故障。需要进行混合以打破菌丝体网络并避免此类故障。本研究首次尝试量化和预测菌丝体键对颗粒混合的影响，反之亦然。我们开发了一种新颖的实验装置来测量固态发酵中菌丝键的拉伸强度：在两个小麦面团圆盘之间培养米曲霉，并用质构分析仪测量气生菌丝体的拉伸强度。将不同培养时间的拉伸强度与氧气消耗相关联，以便将其转化为在小麦颗粒上培养米曲霉的转鼓情况。我们在鼓式发酵罐中进行了几次不连续混合的固态发酵，并测量了第一次混合作用后剩余的谷物聚集体的数量和大小。我们将菌丝体拉伸强度的数据整合到一个先前开发的二维离散颗粒模型中，该模型计算作用于单个底物颗粒上的力以及由此产生的径向颗粒运动。离散颗粒模型成功预测了混合后剩余聚集体的数量和大小。结果表明，在米曲霉固态发酵中，第一次混合操作是为了打破菌丝体，以避免在谷物床中形成聚集体，而不是为了分布为补偿蒸发损失而添加的水分，或消除温度梯度。
