Abstract
Both XTT (3'-[1-(phenylamino)-carbonyl]-3, 4-tetrazolium)-bis (4-methoxy-6-nitro) benzenesulfonic acid hydrate) assay and ferricyanide assay systems were applied to the evaluation of heattreated milk samples which depend on reducibility of heat induced substances in milk. Although the both values were similar in magnitude immediately after the heat treatment, apparent differences were observed in their values measured after storage. The protein reducing substance value (PRS) by ferricyanide assay was almost constant during the storage, but XTT reducibility decreased gradually depending on the storage conditions. It was revealed that aminoreductones, which are the XTT-reducing substances, did not contribute to the reaction with ferricyanide, suggesting that XTT assay differs from ferricyanide assay in the principle of the method. The data obtained by XTT method are applicable to the estimation of the storage conditions of the sample. The XTT assay is another useful method for evaluation of heattreated and further stored milk products, as more convenient and faster than the ferricyanide assay.
