In vitro starch digestion and cake quality: Impact of the ratio of soluble and insoluble dietary fiber
Introduction
Concerns of healthy diets have focused on low-calorie and nutritionally balanced foods containing dietary fiber (DFs). DFs have been recognized for their health benefits and have been applied in a wide variety of food applications. Moreover, DFs have been well known for their effects regarding the prevention of constipation, the regulation of serum cholesterol, the reduction of the risk of diabetes and intestinal cancer, and the stimulation of beneficial microorganisms [1], [2], [3], [4], [5]. The potential of using DFs for food applications is strongly related to their functional properties such as their fiber source, type, and degree of processing [6], [7]. DFs have been classified into soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) based on their solubility in water. Specifically, SDF and IDF exhibit unique components, structures, and physiological effects [8]. SDFs have been linked to the reduction of cholesterol in blood and the decrease in the intestinal absorption of glucose, whereas IDFs are associated with water absorption and intestinal regulation [9]. These physiological effects of SDFs and IDFs depend on their structural and physical properties, which can result in behavior such as hydration, swelling, and enzymatic attack [10].
DFs can also influence the digestion of starch by reducing the rate of starch degradation and preventing excess glucose absorption [11]. DFs incorporated into starch-based foods can entrap starch granules and restrict the availability of water during gelatinization. As a result, the accessibility of starch granules to digestive enzymes is limited under human digestion, which results in the lowering of the glycemic index [12]. Furthermore, these factors affecting the digestion of starch are known anti-nutrients including amylase inhibitors (such as phytate and polyphenolics), high amylose contents, and high contents of viscous soluble dietary fiber [13]. The impact of DFs on the degree of starch digestion and the predicted glycemic index (pGI) under in vitro digestion models have been reported for various food items including pasta, biscuits, and bread [12], [14], [15], [16], [17]. However, many studies of the correlation between DF and pGI have been conducted, the results are still not certain. Also no clear trend could be defined the ideal type and the amount of dietary fiber in vitro starch digestion. The results showed a very wide range depending on the various kinds of dietary fiber and starch source (cereal, legume). In addition, these previous studies are not fully explored the effect of the ratio of SDF and IDF on the digestion pattern and the quality of fiber-enriched cakes.
Therefore, the aim of the present work was to evaluate the effect of a blended ratio of SDF and IDF on in vitro starch digestion and the pGI in a model food (cake). The cake-making performance of selected cakes was subsequently evaluated by textural (volume, texture, and color) and nutritional analysis.
Section snippets
Materials
Commercial dietary fibers were used inulin (Orafti GR, Beneo-Orafti, Belgium) as SDF and soy fiber (Fibrim 2000, Solae, USA) as IDF, respectively. The blend mixtures were prepared with SDF/IDF ratios as follows: 100/0 (SDF 100), 75/25 (SDF 75), 50/50 (SDF 50), 25/75 (SDF 25), and 0/100 (SDF 0). The total dietary fiber assay kit (TDF-100A), pancreatin from porcine pancreas (P7545, activity 8XUSP/g), and amyloglucosidase (A9913) were obtained from Sigma–Aldrich (St Louis, MO, USA). The total
Hydration and pasting properties of the DF blend mixtures with various SDF/IDF ratios
The water hydration properties were investigated as a function of the ratio of SDF and IDF. As shown in Fig. 1, the reduction of SDF ratio decreased WS (water solubility) and improved WAI (water absorption index), while did not show significant differences in SP (swelling power). The decreased WS can be explained by the highly hydrophilic characteristics of soluble dietary fiber. Inulin preferentially is dissolved in water (not viscous) and inhibited the water absorption and swelling of the
Conclusions
Under in vitro starch digestion, decreasing levels of the SDF ratio in cakes resulted in a decrease in RDS values. With the exception of the 3 g SDF 100 and 3 g SDF 75, all of the fiber-enriched cakes showed a lower pGI than the control cake. Additionally, adding to the IDF ratio in the 3 g fiber-enriched cakes increased volume index and hardness. In particular, the cakes with SDF 75 and SDF 50 were of similar volume and texture as compared to the control. The color values of crumb also increased
Acknowledgment
This work was supported by the Mid-career Researcher Program through a NRF grant funded by the MEST (2011-0017002).
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