STUDIES ON THE EFFECTS OF LACTIC ACID BACTERIA FERMENTATION ON THE PROXIMATE AND MINERAL COMPOSITIONS OF Digitaria exilis

Acha (Digitaria exilis) is a cereal crop that is highly nutritious and contains carbohydrates, dietary fiber, minerals, and amino acids. It also contains antinutritional factors such as oxalate, phytate, tannin, and saponin, which can reduce the bioavailability of nutrients. The aim of this study was to evaluate the effect of lactic acid bacteria (LAB) fermentation on the proximate and mineral composition of acha flour. Acha was processed into flour and then subjected to spontaneous fermentation and fermentation using a combination of Streptococcus infantarius FDAARGOS_1019 and Limosilactobacillus fermentum SCB0035) previously isolated from cow milk. Exactly 250g of the flour was mixed with 500mL of distilled water followed by the addition of 0.02% sodium metabisulphate to inhibit the growth of microflora and other contaminating microorganisms. The same set-up was used for the spontaneous fermentation, except the addition of starter organisms and sodium metabisulphite. The proximate and mineral contents of the flours were determined using the association of official analytical chemistry (AOAC) and atomic absorbance spectroscopy (AAS) methods respectively. The result shows a significant (p < 0.05) increase in the moisture, ash, lipid and protein contents of the fermented flour when compared to the unfermented flour with the higher values occurring in the samples fermented with the LAB consortium. The carbohydrate and fiber content decreased significantly (p < 0.05) after fermentation. The result of the mineral contents of both unfermented and fermented acha flours demonstrated that magnesium, copper, iron, zinc, sodium, phosphorus, and calcium levels significantly increased (p≤0.05) through LAB fermentation, while potassium levels remained unchanged. This observation shows that LAB fermentation has the potential to enhance nutritional quality of acha flour more than spontaneous fermentation and can be applied in microbial food fortification.

阿恰（Digitaria exilis）是一种营养丰富的谷类作物，富含碳水化合物、膳食纤维、矿物质及氨基酸。它还含有草酸、植酸、单宁及皂苷等抗营养因子，这些物质会降低营养素的生物利用度。本研究旨在评估乳酸菌（LAB）发酵对阿恰面粉常规营养成分及矿物质组成的影响。阿恰经加工制成面粉后，分别进行自然发酵，以及采用先前从牛乳中分离得到的婴儿链球菌FDAARGOS_1019与发酵乳杆菌SCB0035复合菌株的发酵处理。精确称取250g面粉与500mL蒸馏水混合，随后添加0.02%焦亚硫酸钠以抑制微生物区系及其他污染微生物的生长。自然发酵采用相同的实验装置，但不添加发酵剂菌株及焦亚硫酸钠。面粉的常规营养成分及矿物质含量分别采用官方分析化学协会（AOAC）方法与原子吸收光谱法（AAS）测定。结果显示，与未发酵面粉相比，发酵面粉的水分、灰分、脂质及蛋白质含量均显著增加（p < 0.05），且采用LAB复合菌株发酵的样品中上述成分含量更高。发酵后，碳水化合物及膳食纤维含量显著降低（p < 0.05）。未发酵与发酵阿恰面粉的矿物质含量分析结果表明，经LAB发酵后，镁、铜、铁、锌、钠、磷及钙的含量显著增加（p≤0.05），而钾含量保持不变。上述观察结果表明，LAB发酵提升阿恰面粉营养品质的效果优于自然发酵，且可应用于微生物食品强化领域。