*3.2. Analysis of the Effect of γ-Irradiation on the Functional Properties of Pea Fiber* 3.2.1. Analysis of Oil-Holding Capacity

The oil-holding capacity of dietary fiber can significantly improve the sensory characteristics of food, and help to prolong the shelf life of food [12]. Meanwhile, the high oil-holding capacity of dietary fiber can reduce the absorption of lipids in the intestinal tract [39]. According to Figure 4, the oil-holding capacity of pea fiber increased first and then decreased with the increase in γ-irradiation dose. When the γ-irradiation dose was 2 kGy, the oil-holding capacity of pea fiber was the highest. This may be because the γ-irradiation treatment can increase the porosity and specific surface area of pea fibers by destroying the microstructure. This is helpful for powering more oil droplets to contact and embed in pea fibers, thereby improving the oil-holding capacity of pea dietary fibers [25]. However, when the irradiation dose was greater than 2 kGy, the pores on the microstructure surface of pea fiber decreased, and the specific surface area decreased; therefore, that the oil-holding capacity decreased.

**Figure 4.** Effect of γ-irradiation on oil-holding capacity of pea fiber. Note: Different lowercase letters indicate significant differences in oil-holding capacity (*p* < 0.05).

#### 3.2.2. Analysis of Swelling and Water-Holding Capacity

The water swelling capacity is a functional characteristic in food processing, which is used to evaluate the hydration properties of dietary fiber [12]. The swelling properties and water-holding capacity of dietary fiber are beneficial to intestinal function by increasing chyme bulk and enhancing peristalsis. According to Figure 5, compared with the untreated sample, the swelling capacity and water-holding capacity of pea fiber were significantly increased (*p* < 0.05). With the increase in γ-irradiation dose, the swelling capacity and waterholding capacity increased first and then decreased. Additionally, when the irradiation dose was 2 kGy, the swelling capacity and water-holding capacity were highest. It shows that the appropriate irradiation dose can significantly improve the swelling capacity and water-holding capacity of dietary fiber. Alam reported in his study that particle size can affect the swelling capacity of dietary fiber, and the smaller the particle size, the higher the swelling capacity of dietary fiber [40]. This is consistent with the results in Section 3.1.2. Furthermore, the moderate irradiation could break some fibers, thereby loosening the dense network structure of dietary fibers and increasing the specific surface area. This is also one of the reasons for the increased swelling capacity of dietary fiber. Irradiation treatment can break the glycosidic bond of dietary fiber, and the microstructure of fiber has obvious pores and honeycomb structure at 2 kGy. This provides more space for the storage of water molecules, thereby enhancing the water-holding capacity of the pea fibers [41,42]. However, when the irradiation dose was too high, the swelling and water-holding capacity of pea fiber decreased significantly (*p* < 0.05). This may be because the swelling capacity is related to the crystallinity. Studies have shown that the crystallinity of γ-irradiated potato starch is reduced, which leads to a reduction in its swelling capacity [43]. At the same time, high-dose irradiation will lead to the destruction of the network structure of the fibers, resulting in a decrease in water-holding capacity [12].

**Figure 5.** Effects of γ-irradiation on the swelling and water-holding capacity of pea fiber. Note: Different uppercase letters indicate significant differences in swelling capacity (*p* < 0.05), and different lowercase letters indicate significant differences in water-holding capacity (*p* < 0.05).
