Bean Institute

Bean Chemistry

Dr. Clifford Hall

Dr. Hall is an Associate Professor of Food Sciences at North Dakota State University, Fargo, North Dakota, and a Member of the Bean Institute Editorial Board.  He can be reached at Clifford.Hall@NDSU.edu.

Jump To:
Introduction
Changes in whole bean composition during storage
References
Processing effects on bean components
References

Introduction

Beans are considered a living seed until they have been processed in such a way that the integrity of the bean has been destroyed. Simply milling or grinding of the seed into powders eliminates the bean’s ability to germinate. However, some enzymes remain active and can impact the bean flour quality. Heat treating the bean through cooking or canning are ways to inactivate enzymes that affect quality. Extrusion processing used to make cereals and snacks is another heat process that inactivates enzymes that impact bean quality.  Other bean components such as carbohydrates and antioxidant phenolics are also affected during the storage of whole beans or through heat treatments.  This section of the website highlights the effects of storage and food processes on the basic components of beans.

Changes in whole bean composition during storage

Minimal changes occur in bean during storage of intact whole beans. The storage of intact whole beans has little impact on the protein or fat components. Berrios et al. (1999) reported a non-significant decrease in protein for black beans stored for 2 years at room temperature. Only slight reduction in lipid content were noted during bean storage (Chen, 1991).  Phytic acid  content reduction of approximately 21% was observed Nyakuni et al. (2008) after 6 months.

Pectin is part of the soluble dietary fiber and is sometime referred to as the glue that holds plant cell walls together.  As long as the pectin remains soluble it will interact with water to form a gelatinous material during cooking causing a softening.  If pectin become insoluble, the bean does not absorb as much water resulting in a bean that does not soften during cooking. This is referred scientifically as the hard to cook phenomenon. A loss of solubility of pectins was associated with the hard to cook phenomenon (Moscoso et al. , 1984; Hentges et al. 1991).  The increase in seed hardness  during storage correlated to reduced solubility of the pectins (Shiga et al. , 2004) . This suggests that some of the soluble fiber composition  converts into the insoluble form of dietary fiber during bean storage.

Antioxidant phenolics in beans can  exist in free or bound forms. These different forms can be affected by storage . Varriano-Marston and Jackson (1981) reported that as free phenolic acid content increases in the beans, seed viability decreases. Second, an increase in esterified phenolic acids in the seed coat related to bean hardening and the hard to cook phenomenon. Garcia et al. (1998)  observed that the phenolic acid content in the pectin fraction was two times higher in hard to cook beans than in normal beans.  Maurer et al. (2004) also observed an increased binding between phenolic acids and pectin in the hard to cook beans. The interactions between of the phenolic acids and pectin during storage contributes to bean hardening. Hentges et al. (1990) reported that the hard to cook defect could be reversed upon storage , at refrigerated temperatures,  of beans exhibiting this defect during cooking.  The hard to cook defect only affects a small proportion of the beans and it is not a  food safety concern.

References

Berrios, J. J., Swanson, B. G., & Cheong, A. (1999). Physicochemical characterization of stored black beans (Phaseolus Vulgaris L.). Food Research International, 32, 669-676.

Chen, M. (1991). Effect of selected storage conditions on food quality and physicochemical characteristics of dry bean (Phaseolus vulgaris) (master’s thesis). Department of Food and Nutrition. North Dakota State University, Fargo ND.

Garcia , E., Filisetti, T., Udaeta, J., & Lajolo, F. (1998). Hard-to-cook beans (Phaseolus vulgaris): Involvement of phenolic compounds and pectates.  Journal of Agricultural and Food Chemistry, 46, 2110-2116.

Hentges, D., Weaver, C., and Nielsen, S. (1990). Reversibility of the hard-to-cook defect in dry beans (Phaseolus vulgaris) and cowpeas (Vigna unguiculata). Journal of Food Science, 55, 1474-1476.

Hentges, D., Weaver, C., & Nielsen, S. (1991). Changes of selected physical and chemical components on the development of the hard-to-cook bean defect. Journal of Food Science, 56, 436-442.

Maurer, G., Ozen, B., Mauer, L.,  & Nielsen, S. (2004). Analysis of hard-to-cook red and black common beans using Fourier Transform Infrared Spectroscopy. Journal of Agricultural and Food Chemistry, 52, 1470-1477.

Moscoso, W., Bourne, M., & Hood, L. (1984). Relationship between hard-to-cook phenomenon in red kidney beans and water absorption, puncture force, pectin, phtyic acid and minerals. Journal of Food Science, 49, 1577-1583.

Nyakuni, G., Kikafunda, J., Muyonga, J., Kyamuhangire, W., Nakimbugwe, D., & Ugen, M. (2008). Chemical and nutritional changes associated with the development of the hard-to-cook defect in common beans. International Journal of Food Sciences and Nutrition, 59, 652-659.

Shiga, T.M., Lajolo, F.M., & Filisetti, T.M.C.C. (2004). Changes in the cell wall polysaccharides during storage and hardening of beans. Food Chemistry, 84, 53-64.

Varriano-Marston, E., & Jackson, G. M. (1981). Hard-to-cook phenomenon in beans:  structure changes during storage and imbibition. Journal of Food Science, 46, 1379-1385.

Processing effects on bean components

Phytic Acid
Chang et al. (1977) reported that phytic acid could be removed by simply soaking beans at 60 ˚C for 10 hrs. In her method, elimination of 90% of the phytic acid occurred. El-Hady and Habiba (2003) observed a 36% reduction in phytic acid in kidney beans after an overnight soaking in water at room temperature. Morris and Hill (1996) and Chen (2004) reported a loss of phytic acid in cooked beans. They noted approximately 30, 27, 29, 30, 32 % reductions in phytic acid for cooked black, great northern, navy, pinto, and kidney beans, respectively. Nergiz and Gokgoz (2007) also reported 57-58% reduction in phytic acid after cooking beans that had been soaked 12 hours prior to cooking. Rehman and Salariya (2005) also noted cooking reduced phytic acid contents by 21 and 24 % in red and white kidney beans. Theses authors also observed  greater reductions of phytic acids in kidney beans exposed to 121 ˚C (pressure cooking conditions). The reduction in phytic acid increased as the length of processing time increased. After 90 minutes at 121 ˚C, 48-50% of the phytic acid remained in the kidney beans.

Alonso et al (2001) reported that extrusion reduced phytic acid content by 27 %, with a concomitant increase in the inositol tetrakisphosphate and inositol pentakisphosphate contents. El-Hady and Habiba (2003) also reported that phytic acid content decreased significantly for kidney beans processed at 180˚C and a bean feed moisture of 22%. In both of these studies, protein content was not affected indicating that reduction in phytic acid can be achieved without the destruction of protein.

Phenolic Compounds
Data suggests that much of the phenolics in beans are in the hull. Treatments that involve removal of the hull (i.e. dehulling) or manipulation of the hull such as soaking will affect phenolic content. Processes involving heat may also reduce phenolic compounds.

Dehulling legumes substantially reduces the polyphenolic content in beans of P. vulgaris L. For example, Deshpande et al. (1982) reported that tannin content was reduced by 68.0 to 94.6%  (Figure 1) using a dehulling process.  Anton et al. (2008) reported that total phenolic content was substantially higher in the isolated seed coats of navy and pinto beans than in the whole bean. The high concentration of phenolic components in the bean hull was likely responsible for the increased antioxidant activity of th hull fraction observed by Anton et al. (2008).

Figure 1. Tannin Content (mg equivalent catechin/100 g sample (dry weight basis)) of Whole and De-hulled Beans. (Adapted from Deshpande et al., 1982)

El-Hady and Habiba (2003) reported that total phenolics and tannin contents were reduced significantly by a 16 hour soaking of kidney beans. The reduction was as much as 17%. Boateng et al. (2008) also observed as slight decrease in total phenolic content and tannin levels in soaked kidney and pinto beans.  However, higher flavonoids levels were observed in the soaked pinto beans (Boateng et al.  2008). Xu and Chang (2008) reported that the soak time affected the loss of phenolic compounds. Up to approximately 52% of the total phenolic content in the black beans was lost to the soak water. Luthria and Pastor-Corrales (2006) reported that only 1 and 2% of the phenolic acids were found in the water used for soaking Great Northern and black beans, respectively. In their particular experiment, specific phenolic acids were measure. Thus, phenolic compounds other than phenolic acid may account the high losses observed by some researchers during bean soaking. In contrast, research shows that a significant reduction in total phenolic content occurs during a process that combines soaking and cooking.

Rehman and Salariya (2005) reported tannin reductions after ordinary cooking and during canning of the beans. Nergiz and Gokgoz (2007) reported a 71-77% reduction in total phenolic content compared to the raw bean. Xu and Chang (2008, 2009) observed similar reductions in phenolic compounds under boiling water conditions. Steam processing of the beans resulted in a lower phenolic loss (Xu and Chang 2008). Luthria and Pastor-Corrales (2006) reported that over 83% of the phenolic acids were retained beans during cooking. Their method of analysis was more complex and measured specifically the phenolic acids. These results are more indicative of the phenolic acid stability and may not be a comparable measure to the loss of total phenolic compounds, which is a more generic method for measuring total phenolic compounds in beans. Regardless of the phenolic reductions, cooked beans maintained good antioxidant activity (Boateng et al. 2008; Xu and Chang 2008, 2009).

El-Hady and Habiba (2003) reported that the extrusion process reduced total phenolics and tannins. The combination of soaking followed by extrusion had a greater impact on tannin reduction than extrusion processing of the raw kidney bean flour.  Korus et al. (2007) reported that extrusion caused a reduction in the total phenolic content for several bean varieties but did cause an increase in total phenolics in one variety tested. Overall, literature suggests that extrusion causes a slight reduction, usually less than 25%, in phenolic contents of beans.

Carbohydrates
The increase in resistant starch during storage and processing has been well documented. Tovar and Melito (1996) showed a 9-fold increase in black bean resistant starch, i.e. 0.69 g / 100 g beans to 4.31 / 100 g beans after cooking. These same researchers observed a 12-fold increase in resistant starches in kidney beans. The opposite trend was observed in the available starch content where black and kidney bean available starch decreased after cooking. This is logical considering that as resistant starch increase, available starch decreases. The type of heat treatment also appears to affect significantly the resistant starch formation (Tovar and Melito, 1996).  Black beans heated using steam had the greatest impact on resistant starch formation whereas a dry heat did not affect resistant starch formation.  Carmona-Garcia et al. (2007) observed that soaking of beans in sodium bicarbonate, i.e. baking soda, prior to cooking significantly increased resistant starches over non-soaked beans or beans soaked in water or 1% salt prior to cooking.

Osorio-Diaz et al. (2002) reported commercial bean flours had significantly different resistant starch contents, i.e.  4.44-6.14 %. Canning of the flours led to an increase of resistant starches in two of the three samples. Velasco et al. (1997) reported that the percent resistant starch content increased from 6.4 to 7.0 or 7.6 %, respectively, in black beans that were first boiled and then stored and reheated either conventional or using a microwave.  Vargas-Torres et al. (2004) also noted significant increases in resistant starches in cooked beans stored under refrigeration.

Rehman et al. (2001) reported that soaking significantly reduced the total sugars and starch content of kidney beans. Kutoš et al. (2003) reported that soaking of pinto beans increased the total dietary fiber from 14.2 to 17.0 g / 100 g beans (dwb) and that further enhancement of the fiber content did not occur after heat processing. In contrast, resistant starches increased, from 3.1 to between 5 and 8 g/100 g, after soaked beans were heat processed.  The increase in fiber content may be due to leaching of non-fiber polysaccharides into the soak water. The bean fiber content also changed under different cooking methods. Cooking under pressure promoted the reduction of neutral fiber by 35 and 29% in red and white kidney beans, respectively (Rehinan et al, 2004). Microwave cooking and boiling reduced the fiber content but not to the same degree as pressure-cooking.

The processing of beans is necessary as raw beans are not consumed due to the presence of antinutrients such as trypsin inhibitors. There is overwhelming amounts of data available that demonstrates that processing destroys antinutrients. In fact, processes such as cooking improve bean protein digestion. Thus, the processing of beans should be a balance between eliminating antinutrients and preservation of the health-promoting bioactive compounds.

References

Anton, A., Ross, K., Beta, T., Fulcher,G., & Arntfield, S. (2008). Effect of pre-dehulling treatments on some nutritional and physical properties of navy and pinto beans (Phaseolus vulgaris L.) Lebensmittel Wissenschaft und Technologie (LWT) – Food Science and Technology, 41, 771-778.

Boateng, J., Verghese, M., Walker, L., & Ogutu, S. (2008). Effect of processing on antioxidant contents in selected dry beans (Phaseolus spp. L.). LWT-Food Science and Technology, 41, 1541-1547.

Carmona-Garcia, R., Osorio-Diaz, P., Agama-Acevedo, E., Tovar, J., & Bello-Perez, L. (2007). Composition and effect of soaking on starch digestibility of Phaseolus vulgaris (L.) cv. ‘Mayocoba’. International Journal of Food Science and Technology, 42, 296-302.

Chen, Q. (2004). Determination of phytic acid and inositol pentakisphosphates in foods by high-performance ion chromatography. Journal of Agricultural and Food Chemistry, 52, 4604-4613.

El-Hady, E.A.A., & Habiba, R.A. (2003). Effect of soaking and extrusion conditions on antinutrients and protein digestibility of legume seeds. LWT-Food Science and Technology, 36, 285-293.

Korus, J., Gumul, D., and Czechowska, K. 2007. Effect of extrusion on the phenolic composition and antioxidant activity of dry beans of Phaseolus vulgaris L. Food Technology and Biotechnology, 45, 139-146.

Luthria, D., &  Pastor-Corrales, M. (2005). Phenolic acids content of fifteen dry edible bean (Phaseolus vulgaris L.) varieties. Journal of Food Composition and Analysis, 19, 205-211.

Morris, E.R., & Hill, D. (1996). Inositol phosphate content of selected dry beans, peas and lentils, raw and cooked. Journal of Food Composition and Analysis, 9, 2-12.

Nergiz, C., & Gokgoz, E. (2007). Effects of traditional cooking methods on some antinutrients and in vitro protein digestibility of dry bean varieties ( Phaseolus vulgaris L.) grown in Turkey.  International Journal of Food Science and Technology, 42, 868-873.

Osorio-Díaz, P., Bello-Pérez, L.,   Agama-Aceved, E.,  Vargas-Torres, A. Tovar, J,  & Paredes-López, O. (2002). In vitro digestibility and resistant starch content of some industrialized commercial beans (Phaseolus vulgaris L.). Food Chemistry, 78, 333-337.

Rehinan, Z., Rashid, M., & Shah, W.H. (2004). Insoluble dietary fibre components of food legumes as affected by soaking and cooking processes. Food Chemistry, 85, 245-249.

Rehman, Z., & Salariya, A. (2005). The effects of hydrothermal processing on antinutrients, protein and starch digestibility of food legumes. International Journal of Food Sciences and Nutrition, 30, 695-700.

Rehman, Z., Salariya, A.M., & Zafar, S.I. (2001). Effect of processing on available carbohydrate content and starch digestibility of kidney beans (Phaseolus vulgaris L.). Food Chemistry, 73, 351-355.

Tovar, J., & Melito, C. (1996). Steam cooking and dry heating produce resistant starch in legumes. Journal of Agricultural and Food Chemistry, 44, 2642-2645.

Vargas-Torres, A., Osorio-Diaz, P., Islas-Hernandez, J.J., Tovar. J., Paredes-Lopez, O., & Bello-Perez, L.A. (2004). Starch digestibility of five cooked black bean (Phaseolus vulgaris L.) varieties. Journal of Food Composition and Analysis, 17, 605-612.

Velasco, Z.I., Rascon, A., & Tovar, J. (1997). Enzymatic availability of starch in cooked black beans (Phaseolus vulgaris L.) and cowpeas (Vigna sp.) Journal of Agricultural and Food Chemistry, 45, 1548-1551.

Xu, B., & Chang, K. (2008). Total phenolic content and antioxidant properties of eclipse black beans (Phaseolus vulgaris L.) as affected by processing methods. Journal of Food Science, 73, H19-H27.

Xu, B., & Chang, K. (2009). Total phenolic, phenolic acid, anthocyanin, flavan-3-ol, and flavonol profiles and antioxidant properties of pinto and black beans (Phaseolus vulgaris L.) as affected by thermal processing. Journal of Agricultural and Food Chemistry, 57, 4754-4764.