Evaluation of resistant starch content of cooked black beans, pinto beans, and chickpeas

摘要

Highlights ? Resistant starch (RS) can vary according to the legume and the cooking/cooling. ? Pinto beans were found to be the best source of RS after an hour of cooking. ? Processed products have presented more RS content than fresh cooked legumes. ? A cooling period for legumes is advisable to increase RS consumption. Abstract Resistant starch (RS) is associated with many of the health benefits attributed to dietary fiber. In this study, RS content was determined in black beans, pinto beans, and chickpeas freshly cooked and sampled at 15-min intervals for 90 min. A second set of black bean samples, cooked identically, was held at room temperature (25?°C) for a 24-h period prior to being assayed. The analysis showed that resistant starch levels fall sharply between 15 and 30?min of cooking before achieving a steady resistant starch concentration of approximately 4?g/100?g of sample dry weight. Beans allowed to sit at 25?°C showed similar behavior, but had increased levels of resistant starch after leveling off (approximately 5?g/100?g dry weight). A texture analysis of black beans was also completed along with resistant starch analyses for pinto beans and chickpeas to provide additional results that contributed to the overall conclusions. Pinto beans had slightly higher levels of resistant starch at each time interval, but followed a pattern similar to black beans. Chickpeas had low levels of resistant starch initially and expressed little change as cooking time increased. After 60?min of cooking, all bean samples had between 3 and 5?g of resistant starch per 100?g. In order to maximize dietary consumption of RS, a cooling period for cooked legumes is advisable. Keywords Resistant starch ; Legumes ; Cooking ; Black beans ; Pinto beans ; Chickpeas prs.rt("abs_end"); 1. Introduction Legumes are an important source of proteins and complex carbohydrates. Starch is a polymeric carbohydrate that serves as a major source of energy in the human diet [1] . The two components of starch, amylose and amylopectin, both exist as polysaccharides of D-glucose residues [2] and [3] . RS is defined as the portion of starch and starch products that resist digestion, passing directly through the small intestine. The RS can be divided into four types: category one (RS1) is starch physically protected from digestive enzymes in grains that haven't been fully milled. Category two (RS2) refers to starch in less stabile, tightly packed crystalline granules that are partially resistant to hydrolysis. Category three (RS3) is starch (amylose) that has been retrograded into more highly stabile crystalline structures, and category four (RS4) refers to starch that has been modified using chemical reagents. RS3 is considered the most stable of the natural resistant starches to heat (over 100?°C) and further processing. Upon entering the colon, RS undergoes a high degree of anaerobic fermentation by local microbiota into a wide variety of products. These products include gases (hydrogen, methane, and carbon dioxide) and short-chain fatty acids (acetate, propionate, and butyrate). Butyrate is the predominate short-chain fatty acid produced from RS [4] , [5] , [6] , [7] and [8] . According to studies published over 30?years, there is no doubt of the important role that butyrate plays in maintaining intestinal homeostasis [9] . Resistant starch is associated with many of the health benefits attributed to dietary fiber, such as the reduction of type II diabetes risk, the production of short-chain fatty acid in the colon, the increase of calcium absorption and the reduction of inflammatory bowel disease [10] , [11] , [12] , [13] , [14] , [15] , [16] and [17] . It must be pointed out that resistant starch is not a precise physical entity but a concept developed to explain why some starch is not readily digested [18] . As a result, RS is characterized by analytical methods rather than a specific chemical structure. The search for an accurate analytical method for determining the RS content of food has gone on for more than 30?years. Although methods vary widely, nearly all involve mimicking the in vivo process of digestion [19] . The RS content of food therefore depends largely on the analytical method. As an example, Hughes et al. [20] found the raw starch of chickpeas contained 24–41% RS using the Englyst method [21] , while the more recent AACC approved method 32–40 [22] found 8.4–18.4% RS. Whole chickpea flour contained just 3.1–6.3% RS using the AACC method [23] and [24] . Given the interest in RS from a nutritional standpoint and availability of the approved AACC 32-40 method of analysis, a study of resistant starch levels in black beans, pinto beans, and chickpeas after cooking for increasing periods of time was performed. 2. Materials and methods 2.1. Materials and instrumentation Dry Beans: Goya Dry Black Beans, Goya Dry Pinto Beans, Goya Dry Chickpeas. Processed Beans: Goya Canned Chickpeas, Ortega No Fat Refried Beans. Chemicals: Pota