Background and methodology:
The objective of this study was to investigate the seasonal variation in the stable isotope composition of light elements (carbon, nitrogen and sulphur) of organic and conventional retail Irish beef. Organic beef samples were collected from two large supermarkets and two certified butcher shops dealing exclusively with organic beef. All sources were approved either by the Irish Organic Farmers’ and Growers’ Association or the Organic Trust of Ireland, as certified organic beef retailers. Conventional beef samples were collected from the same supermarkets and three further butcher shops dealing only with conventional beef produced in Ireland. A total of 242 beef samples (127 organic, 115 conventional) was collected in a one-year survey and analyzed by isotope ratio mass spectrometry.
Findings:
The carbon time series in conventional beef was significantly non-random, with a pronounced seasonal positive shift between December and June, while carbon in organic beef was less variable and significantly more negative. In conventional beef, nitrogen was remarkably invariant (throughout the year, while organic beef was more variable and also significantly lower in nitrogen. The sulphur isotope composition exhibited a complex seasonal pattern in both types of beef. These results show that seasonal patterns can occur in the isotopic composition of beef, probably reflecting seasonality in animal feeding practices modulated by tissue turnover rates. Such seasonal variation needs to be considered in the isotopic authentication of beef and other animal-derived products.
Reference:
Bahar, B., Schmidt, O., Moloney, A. P., Scrimgeour, C. M., Begley, I. S., & Monahan F. J., (2007). Seasonal variation in the C, N and S stable isotope composition of retail organic and conventional Irish beef. Food Chemistry, 106(3), 1299-1305.