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ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #88105
Title: METHODOLOGY TO DETERMINE INDIGESTIBLE STARCH IN DRY BEAN (PHASEOLUS VULGARIS L.)

Author
item OSPINA, MARIA - MICHIGAN STATE UNIVERSITY
item Hosfield, George
item BENNINK, MAURICE - MICHIGAN STATE UNIVERSITY

Submitted to: Bean Improvement Cooperative Annual Report
Publication Type: Proceedings
Publication Acceptance Date: 3/31/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: In the determination of indigestible starch (IS) in dry bean (DB) (Phaseolus vulgaris L.) particle size (PS) is important in order to obtain accurate results in both cooked and raw samples. We found that grinding raw and cooked beans with a mill and passing both samples thorough the same sized sieve, resulted in larger particles in the raw than in the cooked beans and inflated the value of the amount of IS in raw beans. To overcome this concern, we conducted a series of experiments to achieve similar PS using samples of cooked beans, simple raw beans, and raw beans that were soaked for 12 hours in distilled water and freeze-dried. All samples were ground with a mill fitted with a 40 mesh screen (MS). The PS of both the raw beans and the soaked and freeze-dried raw beans was larger than the PS of the cooked samples. However, when both types of raw bean samples were ground with a mill fitted with a 60-MS, the PS were similar to the PS of the cooked beans ground and sieved through the 40-MS. When determining IS in DB, we suggest that raw beans should be ground and sieved through a 60-MS and cooked beans should be ground and sieved through a 40-MS. Moreover, raw beans should be soaked for 12 hours in distilled water and freeze-dried before grinding. Unsoaked raw beans particles tore holes in the screen. Similar particle sizes for raw and cooked beans eliminates the problem of overestimating the amount of IS in raw beans compared to cooked beans. The accurate estimation of IS in DB will lesson errors in data and permit the plant breeder to screen breeding lines for starch digestibility with a high degree of confidence.

Technical Abstract: Methodology to determine indigestible starch (IS) in raw and cooked dry bean (Phaseolus vulgaris L.), involves 1) grinding beans to a small and homogeneous particle size (PS), 2) determining Total Dietary Fiber (TDF) content, and 3) determining the amount of undigested starch in the TDF residue. Grinding raw and cooked beans (CB) using a mill with the same size screen resulted in larger particles in the raw than in the CB and inflated the amount of IS in raw beans (RB). To counter this problem, experiments were conducted using 'Montcalm' to obtain similar particle sizes in both raw and CB samples. A 40-mesh screen (MS) was used to grind the samples from the cooked, raw and unsoaked (UNSK), raw and soaked (SK) and raw and humidified treatments. Beans from all the treatments except the raw and UNSK were freeze-dried prior to grinding. Raw, UNSK raw and SK beans were also ground and sieved (GS) through a 60-MS. PS distribution using a series of screens ranging from 26 to 120- MS was determined on the samples ground with the mills fitted with 40-MS and 60-MS. Beans representing the various treatments that were GS with 40-MS, yielded PS for the raw bean treatments (RBT) which were larger than for CB. Ninety percent of the flour from CB ground with the 40-MS, passed through a 120-MS, while flour from the RBT failed to pass through 94-MS. PS of the raw and SK beans GS with a 60-MS mill were similar in size to the CB GS with a 40-MS mill. To obtain cooked and RB with comparable PS, the cooked bean sample should be GS through a 40-MS, and RB should be SK and freeze dried before grinding and sieving through a 60-MS. Soaking and freeze drying eliminates tearing holes in the screen which happen often for UNSK RB.