Distribution and stability of aflatoxin M₁during production and storage of yoghurt

Abstract

Yoghurt from cow's milk artificially contaminated with aflatoxin M1 (AFM1) at levels of 0.050 and 0.100 g l(-1) was fermented to reach pHs 4.0 and 4.6. Yoghurt fermented to pH 4.6 was also used for preparing strained yoghurt. Yoghurts were stored at 4 degrees C for up to 4 weeks. Analysis of AFM1 in milk, yoghurt, strained yoghurt and yoghurt whey was carried out using immunoaffinity column extraction and liquid chromatography coupled with fluorometric detection. AFM1 levels in yoghurt samples showed a significant decrease (p < 0.01) compared with those initially added to milk. Growth of culture lactic acid bacteria was not affected in the AFM1 contaminated yoghurts, with the exception of Streptococcus thermophilus that showed a significantly (p < 0.01) lower increase in the yoghurt containing the toxin at high concentration. Following fermentation, AFM1 was significantly lower (p < 0.01) in yoghurts with pH 4.0 than in yoghurts with pH 4.6 at both contamination levels. During refrigerated storage, AFM1 was rather more stable in yoghurts with pH 4.6 than with pH 4.0. The percentage loss of the initial amount of AFM1 in milk was estimated at about 13 and 22% by the end of the fermentation, and 16 and 34% by the end of storage for yoghurts with pHs 4.6 and 4.0, respectively. The percentage distribution ratio of AFM1 in strained yoghurt/yoghurt whey of the initial toxin present in the yoghurt was about 90/10 and 87/13 for the lower and the higher contamination levels, respectively.

Carrot Yoghurt : Sensory, Chemical, Microbiological Properties and Consumer Acceptance

“…It can be phsophatized by light to form an electronic excited molecule that may react with the double bond in the terminal dihydrofuran moiety o f aflatoxin M1 leading to their transformation of aflatoxin M1 into aflatoxin M2a which is non toxic (Joseph et al, 1997;Aman 1998;Yousef, 2000;Pitt (2003) and Martins and Martins, 2004). Nearly similar findings were recorded by Wiseman and Marth (1983); Blanco et al (1993); Gourama and Bullerman, (1995); Salwa and Diekmann, (2000) and Govaris et al (2002) who found that AFM1 was relatively stable in plain yoghurt during manufacture and storage.…”

Aflatoxin M1 Contamination of Milk and Its Products in Bomet County, Kenya

“…However, some reports show that aflatoxins are stable during heat-treatments such as pasteurization and sterilization [30]. The effect of fermentation was assessed by [31]. It was reported that AFM1 levels in all yoghurt samples showed a significant decrease from those initially present in milk.…”

A Review of Aflatoxin M1, Milk, and Milk Products

“…Rasic et al (1991) found that S. thermophilus was affected by the presence of in milk during fermentation of yoghurt, exhibiting longer cell chains in the contaminated than in the uncontaminated yoghurt samples. Similarly, Govaris et al (2002) observed that the growth rate of S. Thermophilus and curdling time were affected by the higher level and not by the lower level of AFM 1 . Unlike cheese and milk samples, the presence of AFM 1 in yogurt has not frequently been studied.…”

“…Maryamma et al (1990) reported a high reduction of AFM 1 in fermented goat milk. As a result of Study by Govaris et al (2002), during refrigerated storage, AFM 1 was rather more stable in the yoghurts with pH 4.6 than with pH 4.0. The percentage loss of the initial amount of AFM 1 in milk was estimated at about 13 and 22% by the end of the fermentation, and 16 and 34% by the end of storage for yoghurts with pHs 4.6 and 4.0, respectively.…”

“…In contrast, Munksgaard et al (1987) and Bakirci (2001) detected variable increases of AFM 1 content in yogurt related to the milk. The effect of fermentation was assessed by Govaris et al (2002). They reported that AFM 1 levels in all yoghurt samples showed a significant decrease from those initially present in milk.…”