Institute for Food, Nutrition and Well-being and Department of Consumer and Food Sciences, University of Pretoria, Private Bag X 20, Hatfield, Pretoria, 0028, South Africa.
Department of Food Science and Post Harvest Technology, Gulu University, P.O. Box 166, Gulu, Uganda.
Appl Biochem Biotechnol. 2020 Aug;191(4):1395-1410. doi: 10.1007/s12010-020-03286-x. Epub 2020 Feb 27.
To improve cassava starch extraction by wet milling, solid-state fermentation of ground roots using cellulolytic-type alkaliphilic Bacilli spp., Bacillus akibai, B. cellulosilyticus and B. hemicellulosilyticus was investigated. Enzyme assay and scanning electron microscopy indicated that Bacillus spp. production of extracellular cellulase and polygalacturonase caused the formation of micropores through the root parenchyma cell walls and exposed the embedded cellulosic network. Gas chromatography data of the cell wall constituent sugars remaining after fermentation and Fourier transform infrared data indicated that the Bacillus treatments reduced the levels of pectin and, hemicellulose and to lesser extent cellulose. Wide-angle X-ray scattering data indicated that the Bacillus spp. cell wall degrading enzymes had partially hydrolysed the amorphous fractions of the cell wall polysaccharides. All the Bacillus spp. treatments improved starch extraction by 17-23% compared to fermentation with endogenous microflora. B. cellulosilyticus was most effective in disintegration of large root particles and as result, released marginally the most starch, probably due to it having the highest cellulase activity. Solid-state fermentation using cellulolytic-type Bacillus spp. is, therefore, promising to technology to improve the efficiency of cassava wet milling cell wall disintegration and consequent starch yield without use of commercial cell wall degrading enzymes or polluting chemicals.
为了提高木薯淀粉的湿磨提取率，研究了利用产纤维素碱性芽孢杆菌、解木聚糖芽孢杆菌、解纤维芽孢杆菌和嗜热解淀粉芽孢杆菌对磨碎的木薯根进行固态发酵。酶活性测定和扫描电子显微镜分析表明，芽孢杆菌产生的胞外纤维素酶和聚半乳糖醛酸酶导致根薄壁细胞壁形成微孔，并暴露出嵌入的纤维网络。发酵后细胞壁成分糖的气相色谱数据和傅里叶变换红外数据表明，芽孢杆菌处理降低了果胶、半纤维素和纤维素的水平，但其程度较小。广角 X 射线散射数据表明，芽孢杆菌细胞壁降解酶部分水解了细胞壁多糖的无定形部分。与内源微生物发酵相比，所有芽孢杆菌处理都使淀粉提取率提高了 17%至 23%。解木聚糖芽孢杆菌在大根颗粒的崩解方面最为有效，因此释放出的淀粉略多，可能是因为它的纤维素酶活性最高。因此，利用产纤维素的芽孢杆菌进行固态发酵有望提高木薯湿磨细胞壁崩解效率，提高淀粉产量，而无需使用商业细胞壁降解酶或污染性化学物质。
