Pigmented Heirloom Beans: Quality Characteristics Before and After Cooking

Abstract

The dry bean category has long been considered an important source of both macro and micronutrients in the human diet. Global usage continues to increase for many reasons; they are highly accessible to global populations due to their shelf stability and versatile growing conditions while also acting as an economical source of protein and fiber. Despite high diversity in the bean category, widespread production is limited to a relatively small set of commodity varieties. In response to the industrialization of agriculture and food production, consumers are increasingly seeking out heirloom crop varieties as a representation of small scale, sustainable food production. Heirloom crops with unique appearances, names, and historical significance are gaining popularity in many areas, including vegetables, grains, and legumes. In accordance with this trend, heirloom beans are increasingly being sought after for use in culinary applications by home cooks and restaurants as a way to reintroduce unique foods into the diet. While extensive research has been performed on the composition and cooking quality of commodity beans, relatively little is known about heirloom varieties. It is therefore advantageous to characterize the chemical composition and cooking quality of several unique heirlooms varieties in order to facilitate their adoption into everyday use. There were two main objectives of this study: (1) to characterize the composition and processing characteristics of four heirlooms varieties for comparison to a commodity control and (2) to investigate the effect of processing on antioxidant characteristics of heirloom beans in comparison to a commodity control. Four heirloom varieties (Hutterite Soup, Jacob’s Cattle, Koronis Purple, and Tiger’s Eye) were selected based on distinct physical characteristics of their shapes and seed coat colors. Pinto beans were selected as the control. Prior to processing, the composition (moisture, starch, protein, total, soluble, and insoluble dietary fiber) and antioxidant properties (including total phenolic and flavonoids content) of each bean were catalogued. Beans were then soaked in water at 25°C and time to reach 50% of maximum hydration was calculated based on hydration curves. Antioxidant testing was then repeated after soaking. Beans were cooked using a stovetop boiling method and cooking time for each bean was determined. Changes in appearance were noted after each processing stage. Cooked beans were analyzed for texture and again for antioxidant characteristics. Starch characteristics were investigated through in vitro starch digestibility of cooked beans and pasting properties of bean flours. Moisture was similar among all beans, however starch, protein, and fiber composition varied between varieties. Heirlooms tended to contain higher amounts of protein and soluble dietary fiber. Heirlooms also took significantly less time to reach 50% hydration compared to the Pinto, however cooking times for both the heirlooms and Pinto were similar. Texture analysis showed that Hutterite Soup had the least firm texture after cooking. With regard to pasting properties, heirlooms had higher swelling and retrogradation tendency while Pinto had the highest temperature of gelatinization. All heirlooms had lower digestible starch in vitro over a two hour period compared to control. Antioxidant composition varied considerably between varieties and was also affected by soaking and cooking. Hutterite Soup was the lightest colored bean and also had the lowest antioxidant values in all tests at each stage of processing. This indicates that antioxidant content can possibly be correlated to seed coat color. Soaking had a mixed effect on antioxidant content while the decrease due to cooking was universal for all heirloom varieties and the control, indicating that thermal processing has a more drastic effect on antioxidants than just hydration alone. These findings can be used to improve current knowledge of quality and composition of heirlooms beans throughout soaking and cooking.