Investigating carotenoid loss after drying and storage of

157
7. Involvement of enzymes
Table 7-3: Degradation rate* and mean percentage of !-carotene retained** at
450nm after 30 min incubation at 40ºC at pH 7.4 with various enzymes and/or
substrates
Subset**
Enzyme LA H2O2 k* (min -1 ) R 2 1 2 3 4 5 6
LOX x - 0.035 (0.013) 0.997 (0.001) 63.9
POD x x 0.023 (0.005) 0.990 (0.005) 72.5
POD x - 0.022 (0.003) 0.994 (0.003) 73.2
- x x 0.017 (0.003) 0.996 (0.001) 78.7
- x - 0.015 (0.002) 0.992 (0.007) 81.4
POD - x 0.009 (0.001) 0.993 (0.004) 86.9
POD - - 0.008 (0.001) 0.978 (0.020) 88.4 88.4
S x - 0.007 (0.002) 0.989 (0.006) 90.6 90.6 90.6
S x x 0.006 (0.002) 0.983 (0.009) 91.1 91.1
Blank - - 0.005 (0.000) 0.976 (0.018) 93.8
S - - 0.004 (0.000) 0.991 (0.009) 94.3
S - x 0.004 (0.001) 0.985 (0.006) 94.4
Sigma 1.00 1.00 0.54 0.10 0.50 0.09
*First order kinetic; mean (standard deviation) of triplicate trial; **Two- way ANOVA;
Univariate. Tukey HSD; p< 0.05. Factors: enzyme and/or substrate; time of incubation. n= 21 (7
collections (every five minute) x 3 replication trials). x indicates addition of 5% substrate.
Substrates: LA: Linoleic acid 0.2mM; H2O2 1mM. Enzymes (5% of solution): POD:
Horseradish peroxidase; LOX: Soybean lipoxygenase; S: filtered extract from sweet potato flour.
At pH= 7.4, POD activity = 0.386±0.013 mmol ABTS min -1 .ml -1 ; LOX activity = 0.141±0.005
mmol conjugated diene min -1 .ml -1
In all cases degradation of !-carotene followed a first order kinetics in accordance with
Galan and Minguez-Mosquera (1997) working in a liquid medium. All coefficients of
correlation R 2 fitted well the first order reaction with values comprised between 0.975
and 0.997.
Oxidation by commercial enzymes (Horseradish peroxidase and Soybean lipoxygenase)
was significant as compared with the control (ANOVA; p