Effectiveness of synthetic and potential natural antioxidants in improving the stability of sheep's anhydrous butter fat during long-term storage

Sheep's anhydrous butter fat was prepared by including separately wheat grits, turmeric, rosemary, sage, rue and fennel at a level of 75 g dry matter kg-1 butter. The product was stored at room temperature in clear glass jars for a period of one year. The storage stabilities of the anhydrous butterfat samples were compared with a control and with a sample treated with a 1:1 mixture of BHA and BHT at a level of 0.25 g kg-1. Both storage time and type of treatment had highly significant effects (P less than or equal to 0.01) on the peroxide value and free fatty acid content of the product. None of the treatments succeeded in keeping the peroxide value below 5 mEq O2 kg-1 beyond the fourth month of storage. The BHA-BHT mixture and rosemary helped extend the peroxide induction period to 10 and 6 months respectively. Turmeric and wheat grits were as effective as BHA-BHT in controlling the oxidative rancidity during the first four months of storage. The rest of the herbs exhibited a pro-oxidant effect throughout the study when they were used separately. In a second experiment, some cases of positive synergistic interactions were observed between turmeric and wheat grits on one hand and the herbs used in the study on the other. This pattern was not regular as negative interactions were also observed in some other cases. Free fatty acid content of all the samples remained below 10 g kg-1 as oleic acid; however, fennel had a significant (P less than or equal to 0.05) effect on controlling the evolution of free fatty acids.