This work investigates the production of citric acid from cashew apple juice, an abundant waste in the processing of cashew, using a local strain of Aspergillus niger and the application of the citric acid as a coagulant for the production of soy cheese. Fungal isolates were obtained from a cashew plantation in Ogbomoso, Nigeria, using potato dextrose agar. Further screening was undertaken to determine the qualitative strength of acid production by the fungi on Czapek-Dox agar supplemented with bromocresol green, with the development of yellow zone taken as an indication of citric acid production. Thereafter, the best producing strain was cultivated in a cashew apple juice medium. Out of 150 fungal isolates generated from the cashew plantation, 92 (61.3%), 44 (29.3%) and 14 (9.3%) were obtained from cashew fruits, soil and cashew tree surfaces, respectively. Different strains of fungi isolated include Aspergillus niger, A. flavus, A. foetidus, A. heteromorphus, A. nidulans and A. viridinutans. The isolates produced yellow zonation of 0.4–5.5 cm on modified Czapek-Dox agar; the highest was observed for a strain of A. niger LCFS 5, which was identified using molecular tools. In the formulated cashew apple juice medium, the citric acid yield of LCFS 5 ranged 16.0–92.8 g/l with the peak obtained on the 10th day of fermentation. The citric acid produced was recovered using the double precipitation method with Ca(OH)2 and H2SO4 having ≈ 70% purity of citric acid on HPLC. The citric acid acted as a coagulant to produce soy cheese with 66.67% acceptability by panelists. This work has extended the frontiers of valorization of cashew waste by a strain of A. niger to produce citric acid in high yield, with potential application in food industries.

中文翻译：

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腰果苹果汁通过本地黑曲霉 LCFS 5 菌株生产柠檬酸的生物技术价值

这项工作研究了从腰果苹果汁（腰果加工过程中的大量废物）中生产柠檬酸，使用当地的黑曲霉菌株，以及将柠檬酸作为凝固剂用于生产大豆奶酪。真菌分离物使用马铃薯葡萄糖琼脂从尼日利亚 Ogbomoso 的腰果种植园中获得。进行了进一步筛选以确定真菌在补充有溴甲酚绿的 Czapek-Dox 琼脂上产酸的定性强度，黄色区域的发展作为柠檬酸生产的指示。此后，最好的生产菌株在腰果苹果汁培养基中培养。在腰果种植园产生的 150 种真菌分离物中，92 (61.3%)、44 (29.3%) 和 14 (9.3%) 从腰果果实、土壤和腰果树表面获得，分别。分离的不同真菌菌株包括黑曲霉、黄曲霉、臭曲霉、异形曲霉、构巢曲霉和绿曲霉。分离株在改良的 Czapek-Dox 琼脂上产生 0.4-5.5 cm 的黄色带；观察到的最高值是使用分子工具鉴定的 A. niger LCFS 5 菌株。在配制的腰果苹果汁培养基中，LCFS 5 的柠檬酸产量范围为 16.0-92.8 g/l，峰值出现在发酵第 10 天。使用双沉淀法回收产生的柠檬酸，Ca(OH)2 和 H2SO4 在 HPLC 上的柠檬酸纯度约为 70%。柠檬酸作为凝固剂生产大豆奶酪，专家组成员的接受率为 66.67%。这项工作扩展了腰果废料价值化的前沿领域。