UC Davis

Chickpea (Cicer arietinum L.) is an agriculturally-important legume crop that is an excellent source of proteins, fiber, and minerals. Therefore, developing chickpea-based snacks could add value to chickpeas, as well as provide consumers with snack products rich in protein and fiber. As two main components, there are around 24% protein and 54% carbohydrate in chickpea that could be influenced by processing methods. Many studies have focused on the effect of processing on in vitro digestibility of starch and nutrient availability in legumes. Previous studies have found that the water uptake during digestion plays an important role in the breakdown of starch-based food matrices. However, the interaction between particle size, water content, and modifications in nutrient release and digestibility is not clear. The objective of this project was to investigate the effect of particle size and water content on particle breakdown and starch digestibility of chickpea-based snacks during dynamic in vitro digestion.To achieve this goal, chickpeas puree and cracker were produced with different particle size: fine puree, fine cracker, coarse puree, coarse cracker. For all treatments, chickpea samples were mixed with simulated saliva for 30 s and were incubated in the Human Gastric Simulator (HGS) for up to 180 min. Gastric digesta were removed from the bottom of HGS every 30 min to be analyzed and sample aliquots were also incubated in a shaking water bath (37℃ at 100 rpm) with simulated intestinal juice for up to 180 min. Intestinal digesta were removed from simulated intestinal juice every 30 min up to 180 min to be analyzed. For whole gastric digesta, pH, moisture content, and gastric emptying were measured. Gastric digesta were then separated into 3 phases: liquid, suspended solid, and solid phase. For the suspended solid phase, particle size was measured using laser diffraction, while image analysis was used to measure the particle size and number of particles in the solid phase. The starch hydrolysis and protein hydrolysis were measured in all three phases through analysis of reducing sugars and free amino groups, respectively. It was found that both the initial particle size and drying influenced the breakdown rate and the digestibility of starch and protein in chickpea snacks. Across the four treatments, the pH decreased from 3.38-4.00 after 30 min and to 1.61-1.14 after 180 min gastric digestion. The pH of the fine puree was the highest from 60-150 min compared with the other treatments, as it had the highest buffering capacity of the four treatments. For the gastric emptying of dry matter, the emptying rate (k) was significantly (p<0.05) higher for fine puree compared to the other treatments, which may be due to the higher pH and lower water holding capacity observed in the fine puree. The particle size of the solid phase was quantified through the x50, or median particle area. The x50 of fine puree was constant during gastric digestion due to the smallest particle size, while fine cracker and coarse cracker rapidly decreased in size from 0-30 min due to changes in the product matrix that occur during drying. The coarse puree had the largest particle size at all digestion times, due to the remaining large pieces of skin that were not broken down during milling. The hydrolysis of starch and protein in the liquid phase during gastric digestion had a similar trend: fine cracker>coarse cracker>fine puree>coarse puree, which was impacted by both initial particle size and drying. The reducing sugars and free amino groups released from fine puree were higher than coarse puree, and fine cracker was higher than coarse cracker due to the influence of initial particle size. Similarly, the water content also impacted starch and protein hydrolysis in the chickpea snacks, crackers showed higher protein and starch hydrolysis than puree. Due to their high protein content and potentially low glycemic index, developing chickpea-based snacks could result in nutritious, slowly-digestible high protein snacks. Therefore, this study is essential to understand how the properties and processing of chickpeas, such as particle size and moisture content, impact their breakdown and macronutrient digestibility. This information will help to develop chickpea-based snacks with specific functional properties to control starch and protein digestion.