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Nigerian Food Journal 33 (2015) 29–34 www.elsevier.com/locate/nifoj

The resistant starch content of some based Nigerian foods

Frank C. Ogbon, Edith N. Okafor

Department of Applied Microbiology & Brewing, Nnamdi Azikiwe University, Awka,

Available online 23 May 2015

Abstract

The resistant starch (RS) content of some Nigerian cassava varieties and staples, “”, “garri” and “abacha” processed from them were determined. Tubers of six varieties studied contained different concentrations of resistant starch, ranging from 5.70% in TMS 4(2)1425 to 7.07% in the TMS 30,572. Processing using traditional methods reduced the RS content in all cassava based foods compared with tubers from which they were processed. RS concentration was reduced by an average of 70.4% in “fufu”, 52.8% in “garri” and 35.85% in “abacha” for the four varieties of cassava tested. Cassava processing steps involving fermentation were responsible for the major reductions in concentration of RS. Steps involving cooking or frying, resulted in increase in concentrations of RS relative to other processing methods. Modifications of traditional methods of processing such as the addition of bitter leaf during retting or the addition of oil to mash during dewatering of “garri” affected RS concentrations in foods studied. Results of this work suggest that manipulation of processing methods and conditions employed during cassava processing can be used to improve RS concentration in cassava based foods, thus making them more functional.

& 2015 Association of Vice-Chancellors of Nigerian Universities. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Resistance starch; Functional food; Cassava

1. Introduction microorganisms such as bifidobacteria, which exert a lot of beneficial effects on human body. Butyrate, a short chain fatty Resistant starch is defined as that fraction of starch, which acid (SCFA) produced as a result of fermentation of RS has escapes digestion in the small intestine and passes into the been hypothesized to reduce the risk of colon cancer and to large intestine where it is more or less fermented by gut benefitinflammatory bowel disease (Sajilata et al., 2006). microflora. It is considered a functional component of food due These properties make RS an important functional fiber to the health benefits it confers following its consumption. component of food, which can be exploited in the prevention Many studies suggest that resistant starch (RS) intake and management of chronic non communicable diseases. decreases postprandial glycaemic and insulinemic responses The nature of RS in foods is variable and is classified on the (Bodinham et al., 2008; Brown, 1996; Li et al., 2010), lowers basis of its botanical source and processing. Resistant starch (RS) is plasma cholesterol and triglyceride concentrations (Liu and naturally found in starchy foods such as potato, corn and rice and is Ogawa, 2009), increases satiety and decreases fat storage classified into four subtypes based on its physicochemical proper- (Chiu and Stewart, 2013). Its beneficial effect on human type ties. Type 1 (RS1) is physically unavailable starch. Amylolytic 2 diabetes has also been proposed (Bodinham et al., 2014). enzymes have no access to starch accumulated in undamaged plant The prevalence of diabetes in Nigeria is expected to grow from cells as the gastrointestinal tract lacks enzymes capable of 1,707,000 in the year 2000 to 4,835,000 in 2030 (WHO, 2015) degrading the components of plant cell walls. Type 2 (RS2) is RS as a prebiotic can promote the growth of beneficial native granular starch, such as that found in potato and banana. Type 3 (RS3) is retrograded starch made by cooking/cooling processes on starchy materials occurring in the form of water- n þ Corrresponding author. Tel.: 234 8035642014. insoluble semi-crystalline structures. As a result of retrogradation, E-mail address: [email protected] (F.C. Ogbo). Peer review under responsibility of Association of Vice-Chancellors of more thermostable structures are formed by amylose rather than by Nigerian Universities. amylopectin. The amount of resistant starch produced this way http://dx.doi.org/10.1016/j.nifoj.2015.04.007 0189-7241/& 2015 Association of Vice-Chancellors of Nigerian Universities. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 30 F.C. Ogbo, E.N. Okafor / Nigerian Food Journal 33 (2015) 29–34 increases along with the increasing amylose content of starch. Type The method described by Ogbo (2006) was adopted for the 4 (RS4) is chemically modified starch (Waclaw, 2004). processing of "fufu". Cassava roots were peeled, washed, cut According to the FAO (2013), Nigeria is the world's largest into pieces of approximately 10 cm length 5 cm diameter producer of cassava (about 54 million metric tons per annum), and soaked in plastic containers. The container was left under 95% of which is also consumed in the country. Major staple room temperature to ferment until tubers retted. The resulting cassava based foods consumed in Nigeria are “garri”, “fufu” retted roots were hand pulverized, wet sieved and dewatered in and “abacha”. "Garri" is granular flour with a sticky sour a clean sack. Modifications of this method used by some fermented flavor made from gelatinized fresh cassava tubers. processors were performed by the addition of 10 g mild steel "Fufu" is sticky dough made by pounding cooked fermented nails and 5 g of bitter leaves/L of steep water. roots into a paste. "Abacha" is sun dried fermented cooked The method of Ogbo et al. (2004) was employed to process cassava chips. "abacha". The cassava roots were washed, boiled for 10 mins, Current methods of processing cassava into these foods peeled and sliced as thinly as possible using a hand held shredder. remain essentially traditional and targeted at detoxifying The slices were soaked in water for 48 h, washed, drained and cyanogenic glycosides and development of aroma. Several spread in mats to sun dry. Modification of the process comprised research studies have elucidated the biological and chemical boiling the cassava root for 20 instead of 10 min. mechanisms involved in these processes and considerable The schematic diagram of the methods for processing of the effort has been directed towards methods for the improvement cassava based foods is presented in Fig. 1. of the nutritional value of these foods. However, as far as we know, very little attention has been paid to the processing of 2.2.1. Determination of resistant (RS) and digestible (DS) cassava for the purpose of improving its functional character- starch istics. Functional foods are foods that not only provide Samples used for the determination of resistant and diges- nutritional value but also provide health benefits when con- tible (non-resistant) starches were prepared as follows. Cassava sumed in a regular diet tubers were diced, and the various processed samples of foods This study is intended to draw attention to this area of need, broken up as appropriate and then dried in the oven (Gallen- provide some baseline data about the occurrence of RS in kamp) at 50 1C until they attained less than 15% moisture. cassava and to highlight the existence of the possibility of Moisture content of the samples was determined by method exploiting processing methods to improve the functional 967.03, AOAC (2005). The dried samples were subsequently characteristics of our cassava based foods. ground into fine powder using a hand operated grinder. Resistant starch was determined using a kit assay (K- RSTAR, Megazyme Bray, Co. Wicklow, Ireland). This kit 2. Materials and methods follows the protocols of the AOAC method 2002.02 (2003) procedures explicated by Niba and Hoffman (2003). Samples 2.1. Cassava varieties (10070.5 mg) prepared as already described were incubated with pancreatic α-amylase (10 mg/ml) solution containing Six improved cassava varieties of the Tropical Manihot amyloglucosidase (AMG) for 16 h at 37 1C with constant Species (TMS); TMS 30,555, TMS 117, TMS 693, TMS shaking. After hydrolysis, samples were washed thrice with 30,572, TMS98/0505 and TMS 4(2) 1425, as identified by the ethanol (99% v/v and 50% ethanol) followed by centrifugation. International Institute for Tropical Agriculture (IITA) Ubiaja The separated pellet from supernatant was further digested field, Edo State, were used for this study. Cassava roots were with 2 M KOH. Digested pellet and supernatant were sepa- harvested from nine-month old plants. rately incubated with AMG. Glucose released was measured using a glucose oxidase-peroxidase (GOPOD) reagent kit (K- 2.2. Processing of cassava roots into cassava based food GLOX, Megazyme Bray, Co. Wicklow, Ireland) by absor- products bance at 510 nm against the reagent blank. The glucose content of the supernatant and digested pellet were used in Traditional methods, which have been extensively studied calculation of digestible starch (DS) and Resistant Starch (RS) and widely reported in literature, were used to process the respectively by applying the factor of 0.9. various cassava based foods. "Garri" was processed using the method reported by Oluwole et al. (2004). Cassava roots were 2.2.2. Determination of cyanide content of the cassava based peeled, washed and grated into a mash. The mash was stuffed foods into a clean sack. The cassava mash filled sack was left to Total cyanides in dried food samples were analyzed spectro- stand under the weight of a solid slab at room temperature for photometrically using the picrate paper method of Bradbury 72 h to achieve both dewatering and fermentation. The et al. (1999). The method involved the immobilization of dewatered mash was sieved using a sieve to break the mash linamarase in a round filter paper disc containing phosphate cake into smooth granules and then fried to obtain "garri" buffer at pH 6.0. The disc was placed in a flat bottomed plastic granules. Oil "garri" was prepared by a modification of this bottle. A 100 mg portion of the powdered food sample was process, which comprised the addition of palm oil (10 g/kg) to added to the filter paper and 0.5 ml of distilled water was grated cassava mash before dewatering and garrification. added. This was followed immediately by the addition of a F.C. Ogbo, E.N. Okafor / Nigerian Food Journal 33 (2015) 29–34 31

Cassava (whole tubers)

Washing Peeling

Cooking Washing

Peeling Steeping / Fermentation Mashing

Slicing Hand grating / Sieving Fermentation/ Dewatering

Steeping / Fermentation Settling Sieving

Washing Pressing / Dewatering Dry frying

Spreading/ Sun drying FUFU (fermented mash) GARRI (granular flour)

ABACHA (cassava chips)

Fig. 1. Schematic diagram of the processing methods of cassava tubers into cassava based foods.

Table 1 Starch content of some cassava varieties cultivated in Nigeria.

Cassava variety TMS 30,555 TMS 30,572 TMS 693 TMS 98/0505 TMS 4(2)1425 TME 117

Resistant starch (g/100 g) 6.9670.9 7.0771.0 6.7671.1 6.9570.8 5.770.8 6.2170.9 Digestible starch (g/100 g) 63.471.6 56.972.1 73.572.5 68.571.8 74.472.0 73.272.0

Means in rows are not significantly different at (Po0.05). yellow picrate paper attached to a plastic strip to the bottle. starch among cassava varieties were determined by a one way The bottle was closed immediately with a screw lid and analysis of variance (ANOVA) followed by Duncan's multiple allowed to stand for 24 h at room temperature. The picrate range test (Po0.05). paper was removed and immersed in 5 ml distilled water in a test tube with occasional gentle stirring for 30 min. An unreacted picrate paper was taken as blank. The absorbance of the solution was measured against the blank at 510 nm. The 3. Results and discussion total cyanide content in ppm was calculated by multiplying the absorbance by 396. All the processed cassava based foods showed character- istics typical of their types. The result of the HCN content of 2.3. Statistical analysis the food samples showed 8 mg/kg, 5 mg/kg and 1.03 mg/kg for "garri", "fufu" and "abacha" respectively, which were Data were expressed as mean values7standard deviation of below the maximum level of tolerance (10 mg/kg) recom- three replicate measurements. Variation in levels of resistant mended by the FAO/WHO (1991). 32 F.C. Ogbo, E.N. Okafor / Nigerian Food Journal 33 (2015) 29–34

3.1. Resistant starch content of different varieties of cassava days) and "abacha" (2 days). The role of microbial activity in the loss of RS during the processing of cassava is further Table 1 shows that all the cassava varieties tested contained demonstrated in the modifications of retting by the addition of resistant starch (RS) and digestible starch (DS). Moongngarm nails, used by processors to shorten retting time and bitter leaf (2013) in a study in Thailand had reported similar values of RS (Vernonia amygdalina) to reduce odor. The enhancement of for cassava (RS, 9.6971.28 and DS, 55.9974.92). Statistical microbial activity by the addition of nails (Ogbo, 2006), analysis of the data showed no significant differences in RS or resulted in greater loss of RS when compared with normally DS contents at (Po0.05) among the different varieties. processed fufu while bitter leaf on the other hand, known to However, TMS 30,572 showed nominally, the highest RS possess anti-microbial potentials (Oboh and Masodje, 2009) and lowest DS concentrations, when compared with the other inhibited some microbial activities thus permitting retention of varieties. higher levels of RS in this sample compared with normally processed "fufu". Decreases in RS concentration following 3.2. Resistant starch content of cassava based foods fermentation have also been observed in other foods such as sorghum flour (AbdElmoneim et al., 2004) and legume based RS content in foods is influenced by intrinsic and extrinsic fermented foods (Yadav et al., 2007). factors as well as processing techniques (Alsaffar, 2011). Modification of the traditional processing method by the Processing of cassava into the various Nigerian staples, "fufu", addition of oil to mash was observed to result in an increase in "garri" and "abacha" resulted in decreases in concentrations of the RS content of "garri". Generally, the presence of other RS relative to the tubers they were processed from (Tables 2– ingredients in the food matrix such as protein, fat, dietary fiber 4). No significant differences (Po0.05) were observed in the and minerals are known to affect the formation of RS in food. rate of RS loss among the four varieties of cassava tested Presence of lipids specifically results in the formation of following processing into all three types of foods. However, starch–lipid complexes, which resist enzymatic digestion of processing of cassava into the different foods resulted in losses starch (Sharma et al., 2008). Furthermore, the presence of oil of RS to significant degrees (Tables 2–4). The average loss in in the fermenting mash may have affected microbial activity RS for the four varieties of cassava processed into “fufu” was adversely. 70.4%, while average losses for “garri” and “abacha” were Cooking and frying are processes well known to play 52.8% and 35.85%, respectively. significant roles in the formation or depletion of RS in foods The major unit operations employed in the processing of depending on how they are applied. Boiling is believed to cassava can be subdivided into two groups for the purpose of induce gelatinization, thereby permanently disrupting the this report. Operations such as size reduction, soaking or amylose–amylopectin structure of the starch complex and thus steeping and dewatering may enhance conditions for chemical making it more readily accessible by digestive enzymes. and physical reactions, which occur during processing. How- However, as these foods cool, the possibility of forming R3- ever, it is the second group of operations involving fermenta- resistant starches (retrograded starches) increases. This occurs tion, cooking/frying, and drying that are most likely to define as the starches undergo re-crystallization due to the formation the influence of processing on the RS content of foods. of intermolecular hydrogen bonds. Furthermore, boiling also The fermentation of cassava is generally considered a lactic results in the leaching of free sugars, thus resulting in relative acid fermentation, but which also involves the activity of increases of overall RS concentration in such foods (Englyst sundry Gram positive bacteria as well as yeasts and molds. and Cummings, 1982; Englyst and Cummings, 1987). Fried Several microorganisms including the lactic acid bacteria are potato products, especially French fries, have been shown to known to possess the ability to ferment RS. Fermentation contain more resistant starch than cooked potatoes (Garcia- would therefore represent a major process of loss of RS during Alonso and Goni, 2000). However, Nigudkar (2014) working the processing of cassava. Loss of RS was highest in "fufu", with various rice and wheat flour menus has noted that dry heat which was fermented 4–6 days when compared with "garri" (3 treatment decreased RS content of a food preparation.

Table 2 Starch content of "fufu" processed from different cassava varieties.

Cassava variety TMS 30,555 TMS 30,572 TMS 693 TMS 98/0505

"Fufu", processed normally Resistant starch (g/100 g) 2.2170.07 2.3970.09 1.5970.06 1.9170.08 Average% loss in RS due to processing relative to tuber 68.2 66.2 76.5 72.5 Digestible starch (g/100 g) 56.172.0 53.671.8 61.772.1 58.471.7 Average% loss in DS due to processing relative to tuber 11.5 5.8 16.1 14.7 "Fufu", processed with nail added during retting Resistant starch (g/100 g) 1.6470.09 "Fufu", processed with bitter leaf added during retting Resistant starch (g/100 g) 2.4070.14

Means in rows are not significantly different at (Po0.05). F.C. Ogbo, E.N. Okafor / Nigerian Food Journal 33 (2015) 29–34 33

Table 3 Starch content of ""garri"" processed from different cassava varieties.

Cassava variety TMS 30,555 TMS 30,572 TMS 693 TMS 98/0505

White "garri", processed normally Resistant starch (g/100 g) 3.2970.05 3.5570.08 3.0570.07 3.1870.07 Average% loss in RS due to processing relative to tuber 52.7 49.8 54.8 54.2 Digestible starch (g/100 g) 39.570.09 34.870.06 40.570.07 39.870.09 Average% loss in DS due to processing relative to tuber 37.7 38.8 44.9 41.9 Oil "garri", processed with oil added to mash Resistant starch (g/100 g) 5.0570.16 5.0970.16

Means in rows are not significantly different at (Po0.05).

Table 4 Starch content of "abacha" processed from different cassava varieties.

Cassava variety TMS 30,555 TMS 30,572 TMS 693 TMS 98/0505

"Abacha" processed normally, tuber boiled for 10 mins Resistant starch (g/100 g) 4.5370.1 4.7970.09 4.3570.08 4.1370.1 Average% loss in RS due to processing relative to tuber 34.9 32.2 35.7 40.6 Digestible starch (g/100 g) 30.271.8 28.171.6 31.672.0 32.471.7 Average% loss in DS due to processing relative to tuber 52.3 50.6 57.0 52.7 "Abacha" processed with modification, tuber boiled for 20 mins Resistant starch (g/100 g) 4.6370.12

Means in rows are not significantly different at (Po0.05).

The two cassava based food products, "garri" and "abacha", heat treatments received by these foods. Heat gelatinizes which received these treatments showed higher RS values than starch, thus improving its water solubility. "Abacha", which "fufu", which did not (Tables 3 and 4). The higher values of received a fermentation and then a washing step after cooking RS observed in "abacha" compared with "garri" may have expectedly showed the lowest content of DS. The lower the been on account of the shorter duration of fermentation DS level of food, the lower is the risk that its consumption will received by this product. Modification of "abacha" processing elicit diseases associated with diabetes. by boiling for a longer (20 min) did not result in a significant change of RS concentration. Observations similar to these have 4. Conclusion been reported with potatoes (Kingman and Englyst, 1994; Gormley and Walshe, 1999) and various rice and wheat menus This study has shown that cassava varieties cultivated in (Nigudkar, 2014). Nigeria contain some quantities of RS like cassava and other Drying, particularly under the sun as in the processing of tubers in other parts of the world. Generally, processing of "abacha" is akin to storage, which is associated with increases cassava into "fufu", "garri" and "abacha" using traditional in RS concentration in foods. The transformation of RS during methods result in losses of some quantities of both RS and DS storage appears to be affected by temperature. Cooked potato originally present in the tuber. These losses occur to different storage at a temperature approximating 0 1C led to the extents because of the differences in processing treatments formation of more resistant starch than at room temperature employed to make these foods. Additionally, modifications of (Gormley and Walshe, 1999). Drying may have contributed to the traditional process used by local processors may reduce or the higher levels of RS in "abacha" compared with "garri". exacerbate losses of RS and DS during processing. These observations suggest that manipulation of processing methods and conditions can be used to increase RS and reduce DS, thus 3.3. Digestible starch content of cassava based foods making cassava based foods more functional. Availability of more functional cassava based foods to Nigerians will con- The levels of DS in the various foods were also affected by tribute to efforts by authorities to reduce the prevalence of fi processing as shown by its losses to signi cantly different diabetes. extents (Tables 2–4). Average loss of DS in "fufu", "garri" and "abacha" were 12%, 40.6% and 53.2% respectively. The References implication of this is that "fufu" contained 57.4%, while "garri" and "abacha" contained respectively, 38.7% and AbdElmoneim, O., Elkhalifa, B.S., Bernhard, R., 2004. Effect of fermentation 30.6% of digestible starch. The lower levels of DS in "garri" on the starch digestibility, resistant starch and some physicochemical and "abacha" are attributable to enhanced losses of DS due properties of sorghum flour. Food/Nahrung 48, 91–94. 34 F.C. Ogbo, E.N. Okafor / Nigerian Food Journal 33 (2015) 29–34

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