Sensory evaluation results of off-odor and discoloration of beef patties throughout storage are presented in Table 1.
Results showed that off-odor intensity increased (p < 0.05) along storage in all samples,
though not with the same intensity.
Sensory panel scores revealed that beef patties treated with either rosemary (alone or with ascorbic acid) or borage (1 and 2%) maintained fresh beef odor for a longer time (p < 0.05, except patties with rosemary alone at d 20) than those treated with oregano, and these longer than the controls.
These results exhibited a good correspondence with those of TBARS values.
In fact, panelists identified the predominant off-odor as that of deterioration related to oxidative processes, and not as that of spoilage due to microorganism growth.
Several researchers have suggested maximum acceptable TBA values in relation with off-odor formation.
In a study to determine the relationship between TBA values and inexperienced taste panel assessments of oxidized lipid flavor,Greene and Cumuze (1982) reported a TBA range of 0.6 to 2.0 as the minimum detectable level for ground beef. According to them, even though the methods used for TBARS determination are not readily comparable, our results suggest that control patties were unacceptable after 8 d of storage, while those treated with oregano would be unacceptable after 16 d, and those treated with either rosemary or borage, after 20 d of storage.
Regarding the sensory evaluation of discoloration, all the samples showed color fading throughout storage, which was delayed to a varying extent by treatment with the different antioxidants.
The most effective treatment was the combination of rosemary and ascorbic acid, which had significantly lower (p < 0.05) discoloration scores than any other treatment even at d 20 of storage.
It was followed by those of either oregano, borage, or rosemary alone, which were given scores < 3 until d 12 of storage. Both control and ascorbic acid-treated samples were given scores > 3 at this same time.
These results showed a good agreement with those of CIE a* values and surface metmyoglobin percentage; a score of 3 ( > 10% discoloration) appeared to correspond approximately to a CIE a* value of 10 and a metmyoglobin percentage of 40%.
Therefore, according to Greene and others (1971), who reported that a consumer panel rejected samples of fresh beef having a percentage of metmyoglobin greater than 40%, control and ascorbic acid-treated patties would be acceptable for only 8 d, while patties treated with rosemary
and ascorbic acid would be acceptable for 16 d, and all other patties for 12 d.