Antioxidants 2019, 8, 22 6 of 10 are summarized in Figure 3. The Students t-test for paired means was used to test for signicant differences between the kernels and popped samples. Figure 3. Average total phenolic content by Folin and antioxidant capacity by FRAP (mg catechin/g) of hydrolyzed raw and popped popcorn kernels. There are no signicant differences between the popped and raw kernels. (n = 3, p > 0.05). 3.3. Folin and FRAP Assays after In Vitro Digestion

An in vitro digestion simulation was performed to understand how efciently bound polyphenols in popcorn could be liberated through gastric digestion. Both raw kernels and popped kernels were analyzed to see if the popping process made any difference to the efciency of the digestion process. The results of this study are summarized in Figure 4. Among the digested samples, the paired t-test shows a signicant difference between popped and raw kernel samples for antioxidant capacity (p < 0.05) with the popped digested samples having a higher antioxidant capacity. The average antioxidant capacity is 0.76 0.33 mg catechin equiv/g corn for raw kernels and 1.25 0.12 mg catechin equiv/g corn for popped. For total phenolic content there does not seem to be a signicant difference between popped and raw kernel samples (p > 0.05). The average total phenolic content is 2.57 0.91 mg catechin equiv/g for raw kernels and 2.66 0.15 mg catechin equiv/g for popped.

Antioxidants 2018, 7, x FOR PEER REVIEW 7 of 10 Figure 4. Average total phenolic content by Folin and antioxidant capacity by FRAP (mg catechin/g) of samples processed through in vitro digestion. *For antioxidant capacity, there is a significant increase in iron reducing power (n = 3, p<0.05). 4. Discussion. 4.1. Quantity of Antioxidants Among the different grains (oats, wheat and rice), corn has been shown to contain the greatest amount of antioxidant activity due to phenolic acids . However, most of the phenolic acids are bound in insoluble fiber. Dewanto et al. reported the free total phenolic content of raw sweet corn to be 0.250 2.0 mg/g while a total phenolic content of 2.64 0.10 mg gallic acid equiv/g was reported for corn samples extracted by basic hydrolysis (based on dry weight) [11,19]. This compares favorably with our average value of 5.93 0.92 mg catechin equiv/g for basic hydrolysis and 2.66 0.15 mg catechin equiv/g for in vitro digestion and supports our low valu

· for free phenolic content. The varieties of corn used for popcorn seem to have an equal, if not slightly greater total dry phenolic content compared to other studied corn varieties. Popcorn can be consumed with little processing or preparation. According to a recent review, thermal treatments such as cooking or drying can have mixed results on the phenolic content of food depending on the cooking method and species . With regard to thermal treatments, the phenolic content of grains seems to be largely unaffected by baking and the phenolic content of cooked sweet corn increases by 54% after baking [19,21]. In this work, the antioxidant capacity and total phenolic content were shown to not be significantly affected by popping in a microwave oven when the phenolics were extracted with chemical hydrolysis (p > 0.05) Thus, the popping process does not appear to degrade the phenolic compounds originally present in the kernel. However, when extracted through in vitro digestion, the popp