Control of citrinin and pigments produced by Monascus purpureus during the fermentation of red fermented rice : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatu Campus, New Zealand
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Date
2024
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Massey University
Figures 2.2 (=Chen et al., 2015 Fig 1) and 6.3 (=Mou et al., 2023 Fig 3) were removed for copyright reasons. Figures 2.3, 2.4, 5.11, 5.12, and 7.2 are reused under a Creative Commons Attribution 4.0 International (CC BY 4.0) license.
Figures 2.2 (=Chen et al., 2015 Fig 1) and 6.3 (=Mou et al., 2023 Fig 3) were removed for copyright reasons. Figures 2.3, 2.4, 5.11, 5.12, and 7.2 are reused under a Creative Commons Attribution 4.0 International (CC BY 4.0) license.
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Abstract
Monascus spp. is a fungal starter used to produce red fermented rice (RFR). This product has some health benefits and contains pigments that can act as natural colour and flavouring agents. However, Monascus spp. can also produce the mycotoxin, citrinin (CIT) which is believed to have adverse effects on human health. CIT in RFR has been reported worldwide by using different methods of detection. In this current research, Coconut Cream Agar (CCA) was developed as a simple and rapid semiquantitative method to screen CIT–producing Monascus spp. isolates from RFR. Two Monascus purpureus isolates, MF1 and MS1, were isolated. These isolates were identified based on the macroscopic and microscopic observations, and deoxyribonucleic acid (DNA) sequencing [internal transcribed spacer (ITS) and beta–tubulin (β–tubulin) genes]. Further analysis showed that these isolates contained polyketide synthase (pksCT) and ctnA genes, which are CIT biosynthesis genes. These isolates exhibited fluorescence on CCA and were confirmed as CIT producers by Ultra–high performance liquid chromatography with a fluorescence detector (UHPLC–FLD). A toxicity test was conducted using Artemia salina to determine the toxicity of CIT. The results showed that LC50 was 66 µg/mL. The fungal growth, CIT, pigments production, and pH of M. purpureus isolates were characterized on CCA for 30 days. Decreasing CIT levels were observed after incubation of MF1 and MS1 on CCA for 8 and 7 days, respectively. The pigments increased during this incubation time. There were similar trends for CIT and pigments observed during the production of RFR. CIT increased to a maximum level after 5 days of incubation and pigments increased from 5–9 days. There appears to be a relationship between pigments production and CIT levels during the growth of M. purpureus. Mixing CIT and pigments extracted from MF1 and MS1 resulted in a reduction of CIT by 26–68% and 16–45%, respectively. The results on specific pigments and their effect on CIT showed that ankaflavin, monascin, monascorubrin, rubropunctatin, and monascorubramine significantly reduced CIT, with the highest reduction produced by ankaflavin. The findings of this study suggest pigments production could be optimized to control CIT levels in Monascus–fermented products.
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Food contamination, Prevention, Fermented foods, Microbiology, Monascus purpureus, Mycotoxins, fungi, Monascus spp., pigments, fermentation, Coconut Cream Agar, fluorescence, UHPLC-FLD, brine shrimp lethality test