## 3 Results  
### Susceptibility of PEF-Treated Oat Flour to Digestive Enzyme Action  
The susceptibility of starch in PEF-treated oat flour (as a whole) towards the action of digestive enzymes was studied using a static _in vitro_ simulated human digestion assay. Data presented in Figure 2 shows the amount of glucose released per volume of digest (mg/mL) during the small intestinal phase of oat flour digestion at different sampling times (0, 20, 60, 90, 120 min).  
Findings from this study showed the impact of varying levels of PEF treatment on the susceptibility of starch to digestive enzymes. Oat flour processed at 421 kJ/kg and 2.2 kV/cm displayed significantly higher overall starch susceptibility (2-C, Figure 2) than Control, as indicated by higher levels of glucose released. Aligned with this finding, the resulting proportion of rapidly digestible starch (RDS) for 2-C sample was the highest compared to Control and other PEF-treated oat flours (Table 1). However, it is worth noting that the estimated rate of _in vitro_ starch digestibility (\(k\)) for 2-C sample fell within the same range (3.68-3.83 \(\times\) 10\({}^{-2}\) min\({}^{-1}\)) as the Control. At lower specific energy input application of 52-218 kJ/kg at similar electric field strength level (2.2 kV/cm), PEF treatment of oat flour did not result in any significant modification in its starch susceptibility properties (2-A and 2-B, Figure 2). These samples shared similar proportion of starch fractions with the Control in terms of RDS, slowly digestible starch (SDS) and resistant (RS). However, the %SDS and %RS of these samples were significantly lower and higher than the high-energy treated 2-C sample, respectively (Table 1).  
Figure 2: Glucose released (mg/mL digest) during the _in vitro_ small intestinal digestion phase of PEF-treated oat flours (\(n=3\)). PEF treatment was applied at electric field strength levels of (**a**) 2.1–2.2 kV/cm and (**b**) 4.2–4.5 kV/cm. Specific energy input ranges from 52 to 53 kJ/kg (A), 216 to 218 kJ/kg (B), and 421 to 438 kJ/kg (C). Bars showing different letters indicate significant difference (\(p<0.05\)) between mean values of samples collected from the same time interval (e.g., Control vs. 2-A/B/C or Control vs. 4-A/B/C at time 0). Errors bars were generated using the calculated standard error of mean as positive and negative error values.  
Likewise, the application of elevated electric field strength (4.2-4.5 kV/cm) at high levels of specific energy input (421-438 kJ/kg) on oat flour led to increased starch digestibility. Compared to Control, PEF-treated oat flour at 4.2 kV/cm, 438 kJ/kg released significantly higher levels of glucose up to the 60 th min during intestinal digestion (4-C, Figure 2). Moreover, the %RDS for 4-C sample was significantly higher than Control while the %SDS was significantly lower than Control (Table 1). It is interesting to note that PEF treatment at lower specific energy input of 48-249 kJ/kg, at similar electric field strength levels (4.3-4.5 kV/cm), resulted in oat flours that are less susceptible to digestive enzymes compared to Control (4-A and 4-B, Figure 2). Lower levels of glucose released were noted for 4-A and 4-B samples from 20 min onwards during simulated human digestion. Moreover, 4-A and 4-B samples displayed significantly lower proportion of RDS and higher proportion of RS compared to Control and other PEF-treated oat flours (Table 1). In particular, the estimated rate of _in vitro_ starch digestibility (\(k\)) of 4-B sample was the lowest (1.99 \(\times\) 10\({}^{-2}\) min\({}^{-1}\)) amongst PEF-treated oat flours, in which its starch digestion was 48% slower than the Control. Overall, PEF treatment of oat flour at elevated specific energy input increases the susceptibility of starch to the action of digestive enzymes. On the other hand, increased electric field strength application leads to greater proportion of RS and effectively slowed down the starch digestion rate and thus, lowering the amount of RDS fraction.