In this study TAC and TPC values of petai pods and seeds were compared to asses the antioxidant activity of pods with respect to seeds.
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ABTS DPPH FRAP FOLIN
AEAC (mg / 100 g) Seeds
Pods
Figure 3.27 The AEAC values of petai seeds and pods using different methods
Figure 3.27 shows the TAC and TPC in AEAC values of petai seeds and pods. The antioxidant capacities of seeds were found to be generally lower than that of pods. TAC values of petai pods by ABTS and DPPH assays were around 6 times higher than seeds.
The mean AEAC values for seeds using FRAP reagent was around 20 times lower than that of petai pods. These might be due to the presence of antioxidants in pods that can
effectively react with FRAP reagent and due to the presence of more electron donating antioxidants in petai pods than seeds. The mean TPC value of petai pods was around 9 times higher than seeds. There was no constant difference in the TAC values between seeds and pods except the radical scavenging assays. This may be due to the differences in the mechanisms of reaction of different reagents with antioxidants or due to the difference in the nature of antioxidants in pods and seeds. However, further investigation has to be done to find out if there are more antioxidants in pods that react more rapidly with FRAP and Folin reagents.
It is very interesting to estimate the potential of petai as a source of antioxidants by comparing the antioxidant capacities and phenolic contents of seeds and pods with the TAC and TPC of different fruits and vegetables.
Table 3.2 The antioxidant activities of petai and different fruits using ABTS assay Fruit / vegetable AEAC (mg / 100 g)
Petai seeds 556 ± 68
Petai pods 3150 ± 223
Ciku 3396 ± 387.9
Strawberry 472 ± 92.9
Plum 312 ± 23.2
Apple 78.9 ± 2.7
Kiwi 136 ± 18.2
Table 3.3 The phenolic contents of petai and different fruits by Folin assay
GAE and AEAC values of different fruits (Imeh and Khokhar, 2002; Leong and Shui, 2002) and petai are tabulated in Tables 3.2 and 3.3. From Table 3.2 it is observed that antioxidant activities (AEAC values) are high for both petai seeds and pods compared to other fruits. The antioxidant activity of petai pods is very high and is almost equal to ciku.
Table 3.3 shows high phenolic content value (GAE) for petai pods. The phenolic content of seeds is less compared with other fruits. GAE value of pods is the highest among all the fruits mentioned. This implies that petai pods are a better source of phenolic compounds than many other fruits. The information from the tables suggests presence of high amount of phenolic compounds and radical scavenging antioxidants in petai. From these comparisons (Tables 3.2 and 3.3) it is shown that petai is a good source of natural antioxidants.
Fruit / vegetable GAE FOLIN (mg / 100 g)
Petai seeds 78 ± 24
Petai pods 908.94 ±104
Apple (Braeburn cultivar) 535 ± 14.6 Pear (Conference) 302.3 ± 15.5 Plum (Royal Garnet) 534.8 ± 16
Kiwi 302.8 ± 11
3.7.4 Correlations between TAC and TPC
The antioxidant capacity of petai pods was found to be very high. In the next step to find out the nature of antioxidant compounds present in petai pods TAC of petai pods were plotted against phenolic content to find out whether there is any contribution of these antioxidants to the TAC.
y = 1.2831x - 156.13 R2 = 0.7039
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GAEABTS
GAE
Figure 3.28 The correlation between GAE values by ABTS and Folin assays
y = 2.4732x - 1523.3 R2 = 0.7125
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GAEDP P H
GAE
Figure 3.29 The correlation between GAE values by DPPH and Folin assays
y = 2.6024x - 1399.8 R2 = 0.7485
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GAEFRAP
GAE
Figure 3.30 The correlation between GAE values by FRAP and Folin assays
The antioxidant capacity (GAE) values of 20 batches of petai pods by ABTS, DPPH, and FRAP assays are plotted against phenolic content as shown in Figure 3.28, Figure 3.29 and Figure 3.30 respectively to evaluate the correlation between antioxidant capacity and phenolic content. A positive linear correlation (R2 = 0.703) was found between the GAE values by ABTS and Folin assays. Similarly, significant correlation coefficient values of R2 = 0.712 and 0.748 were obtained for plot of GAE values by DPPH and FRAP methods against Folin test respectively. The results demonstrate the contribution of phenolic compounds to the antioxidant capacity of petai. From these correlations it can be suggested that a major part of the TAC of petai pods is due to phenolic compounds and a part of the antioxidant capacity is contributed by other compounds such as sulfur compounds etc.
To further understand the importance of petai seeds and pods as sources of natural phenolic compounds the r2 values obtained on plotting the antioxidant activities with
phenolic contents for the seeds and pods are shown in comparison with the r2 values similarly obtained for several other fruits and vegetables.
Table 3.4 The correlation coefficient values (r2) for the plot between the phenolic content and total antioxidant activity of different fruits / vegetables and petai
Fruit / vegetable r2 Values Petai pods 0.74
Petai seeds 0.75
Coriander 0.83
Honey 0.86
Plum 0.938
Apple 0.942
Sweeties 0.94
Grape fruit 0.94
Table 3.4 shows correlation coefficients obtained for different fruits / vegetables (Dae-Ok et al., 2003; Shela et al., 2004; Helle et al., 2004; Aljadi and Kamaruddin, 2004) and petai on plotting the antioxidant activity values against phenolic contents. Excepting coriander and Honey all other vegetables / fruits have high r2 values. The contribution of phenolic compounds to the total antioxidant capacity for petai seeds and pods is less than most of the other vegetables and fruit. Around 75 % of the total antioxidant capacity is contributed by the phenolic compounds in pods and seeds. The rest of the antioxidant capacity may be contributed by non-phenolic antioxidants.