Nagel F J, Tramper J, Bakker M S, Rinzema A
Wageningen University, Department of Food Technology and Nutritional Sciences, Food and Bioprocess Engineering Group, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
Biotechnol Bioeng. 2001 Jan 20;72(2):231-43. doi: 10.1002/1097-0290(20000120)72:2<231::aid-bit11>3.0.co;2-s.
In this study we describe a model that estimates the extracellular (nonfungal) and overall water contents of wheat grains during solid-state fermentation (SSF) with Aspergillus oryzae, using on-line measurements of oxygen, carbon dioxide, and water vapor in the gas phase. The model uses elemental balances to predict substrate dry matter losses from carbon dioxide measurements, and metabolic water production, water used in starch hydrolysis, and water incorporated in new biomass from oxygen measurements. Water losses caused by evaporation were calculated from water vapor measurements. Model parameters were determined using an experimental membrane-based model system, which mimicked the growth of A. oryzae on the wheat grains and permitted direct measurement of the fungal biomass dry weight and wet weight. The measured water content of the biomass depended heavily on the moisture content of the solid substrate and was significantly lower than the estimated values reported in the literature. The model accurately predicted the measured overall water content of fermenting solid substrate during fermentations performed in a 1.5-L scraped drum reactor and in a 35-L horizontal paddle mixer, and is therefore considered validated. The model can be used to calculate the water addition required to control the extracellular water content in a mixed solid-state bioreactor for cultivation of A. oryzae on wheat.
在本研究中，我们描述了一种模型，该模型利用气相中氧气、二氧化碳和水蒸气的在线测量值，估算米曲霉固态发酵（SSF）过程中小麦籽粒的细胞外（非真菌）水含量和总水含量。该模型利用元素平衡，通过二氧化碳测量值预测底物干物质损失，并通过氧气测量值预测代谢水生成、淀粉水解所用水以及新生物质中所含的水。蒸发造成的水分损失通过水蒸气测量值计算得出。模型参数通过基于实验膜的模型系统确定，该系统模拟了米曲霉在小麦籽粒上的生长，并允许直接测量真菌生物质的干重和湿重。所测生物质的含水量在很大程度上取决于固体底物的水分含量，且明显低于文献报道的估计值。该模型准确预测了在1.5升刮壁式鼓式反应器和35升卧式桨叶混合器中进行发酵时，发酵固体底物的实测总含水量，因此被认为经过了验证。该模型可用于计算在混合固态生物反应器中控制米曲霉在小麦上培养时细胞外水含量所需添加的水量。
