Antifungal and Aflatoxin-Reducing Activity of β-Glucan Isolated from Pichia norvegensis Grown on Tofu Wastewater

Yeast can be isolated from tofu wastewater and the cell wall in the form of β-glucan can act as a natural decontaminant agent. This study aimed to isolate and characterize native yeast from tofu wastewater, which can be extracted to obtain β-glucan and then identify the yeast and its β-glucan activity regarding antifungal ability against Aspergillus flavus and aflatoxin-reducing activity towards aflatoxin B1 (AFB1) and B2 (AFB2). Tofu wastewater native yeast was molecularly identified, and the growth observed based on optical density for 96 h and the pH also measured. β-glucan was extracted from native yeast cell walls with the acid-base method and then the inhibition activity towards A. flavus was tested using the well diffusion method and microscopic observation. AFB1 and AFB2 reduction were identified using HPLC LC-MS/MS. The results showed that the native yeast isolated was Pichia norvegensis with a β-glucan yield of 6.59%. Pichia norvegensis and its β-glucan showed an inhibition zone against Aspergillus flavus of 11.33 ± 4.93 and 7.33 ± 3.51 mm, respectively. Total aflatoxin-reducing activity was also shown by Pichia norvegensis of 26.85 ± 2.87%, and β-glucan of 27.30 ± 1.49%, while AFB1- and AFB2-reducing activity by Pichia norvegensis was 36.97 ± 3.07% and 27.13 ± 1.69%, and β-glucan was 27.13 ± 1.69% and 32.59 ± 4.20%, respectively.