Abstract
As metabolites of a wide range of fungi affecting plant materials, mycotoxins are among food contaminant groups that present major food safety issues globally. Their indispensable nature generates a plethora of problems associated with agricultural production. Taking into account animal production systems, the problem of feed contamination by mycotoxins does not only cut across food and feed value chains but compromises human and animal health, spanning well past productivity and socioeconomics, affecting farmers, traders and consumers alike. To aid in the development of a sustainable strategy for mycotoxin control in animal-based food production systems, this study focused on the often-marginalized smallholder dairy farming establishments of South Africa. With selective regional access to peri-urban and rural dairy sub-value chains, this study sought to illuminate issues surrounding the contamination of dairy cattle feeds by mycotoxins, specific dairy cattle exposure to these mycotoxins, and existing potential issues regarding farmers’ awareness and practice. Such assessment for mycotoxin risk would allow for relevant risk status to be estimated for risk management purposes. As such, twenty-eight smallholder dairy milk producers from Limpopo (Vhembe and Sekhukhune districts) and Free State (Thabo Mofutsanyane district) participated in the study across two sampling seasons between 2018 and 2019. For the establishment of mycotoxin contamination profiles, 77 dairy cattle feed samples were collected from all participating smallholder dairy establishments. Feeds collected consisted of two main classes, namely commercial feeds (dairy concentrates, dairy meals, pellets, molasses & saltlick) and forages (total mixed ration, maize stover, silages, grasses, hay, lucerne & soybean stover). Samples were analyzed using a quantitative confirmatory ultra-high-performance liquid chromatography-tandem mass spectrometric method validated for simultaneous detection of 23 mycotoxins in animal feeds. Performance characteristics for all analytes were within satisfactory limits for linearity (R2 > 0.932), with limits of detection ranging from 0.87 μg/kg (aflatoxin G1) to 190.3 μg/kg (fumonisin B1), limits of quantification between 1.7 μg/kg (aflatoxin G1) and iv 380.6 μg/kg (fumonisin B1) and mean apparent recoveries ranging from 94 % (zearalanone) to 103 % (diacetoxyscirpenol). Mycotoxins assessed were detected across samples with 86 % of samples found to contain at least one mycotoxin above respective decision limits. Data obtained revealed highest incidences for deoxynivalenol (64 %), sterigmatocystin (46 %), alternariol (44 %) and enniatin B (33%), with less prevalence patterns for 3- &15 acetyl deoxynivalenols, fumonisins B1 & B2 and zearalenone (23.4 – 9.1 %), marginal detections for nivalenol, aflatoxins, ochratoxin A, diacetoxyscirpenol, alternariol monomethyl ether and a complete absence of fusarenon-X, HT-2-toxin and neosolaniol. Isolated cases of levels above regulatory limits were noted for deoxynivalenol (maximum: 2385.4 μg/kg), aflatoxins [AFB1 (maximum: 30.2 μg/kg) & AFG1 (maximum: 23.1 μg/kg)], together with zearalenone (maximum: 1793.7 μg/kg). Kruskal−Wallis testing for pairwise comparisons of characteristics by feed type, provenance, town and season revealed significantly higher contamination profiles for deoxynivalenol and its acylated derivatives, as well as ochratoxin A and fumonisins (FB1 and FB2) in commercial feeds, significantly higher alternariol in forages, fumonisin B1 in Limpopo samples and both enniatin B and sterigmatocystin in Free State samples. Cooccurrence profiles demonstrated the presence of more than one mycotoxin in up to 70 % of all samples underlining issues on the effects of toxin interactions. Statistically significant Spearman correlations (p < 0.01) were also found apparent for ratios of deoxynivalenol/fumonisin B1 (rs = 0.587) and zearalenone/ alternariol methyl ether (rs = 0.544) across all samples...
D.Tech. (Food Technology)