Changes in tocopherol concentrations during the heating process were also considered, and a significant decrease was observed in all treatments as heating time increased. Barrera-Arellano et al. reported that after 10 h of heating, significant reductions of tocopherols were found in polyunsaturated oils, with a 40% loss in soybean oil, and with a-tocopherol being the least stable. The addition of antioxidants strongly influenced the retention of tocopherols present in soybean oil subjected to heating. There was a higher degradation of tocopherols in oils free from rosemary extract at the end of the heating, which may have favored a lower oxidative stability of these oils. The a-tocopherol was strongly protected by the use of rosemary, which is in agreement with the results obtained by Rizner-Hras et al. In the current study, the presence of rosemary increased the retention of a-, g- and d-tocopherol, respectively, from 4 to 76%,
from 4 to 40%, and from 45 to 83% after 20 h of heating
and when compared with the SO treatment. There was no
synergistic effect between TBHQ and rosemary extract to
prevent the loss of tocopherols in soybean oil that underwent thermoxidation, because for all fractions of tocopherols, except b-tocopherol, retention after 20 h of heating
was higher in the RE sample, which was the soybean oil that
contained only rosemary extract.
Changes in tocopherol concentrations during the heating process were also considered, and a significant decrease was observed in all treatments as heating time increased. Barrera-Arellano et al. reported that after 10 h of heating, significant reductions of tocopherols were found in polyunsaturated oils, with a 40% loss in soybean oil, and with a-tocopherol being the least stable. The addition of antioxidants strongly influenced the retention of tocopherols present in soybean oil subjected to heating. There was a higher degradation of tocopherols in oils free from rosemary extract at the end of the heating, which may have favored a lower oxidative stability of these oils. The a-tocopherol was strongly protected by the use of rosemary, which is in agreement with the results obtained by Rizner-Hras et al. In the current study, the presence of rosemary increased the retention of a-, g- and d-tocopherol, respectively, from 4 to 76%,from 4 to 40%, and from 45 to 83% after 20 h of heatingand when compared with the SO treatment. There was nosynergistic effect between TBHQ and rosemary extract toprevent the loss of tocopherols in soybean oil that underwent thermoxidation, because for all fractions of tocopherols, except b-tocopherol, retention after 20 h of heatingwas higher in the RE sample, which was the soybean oil thatcontained only rosemary extract.
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