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Glycaemic response to frozen stored wheat rolls enriched with inulin and oat fibre
Journal of Cereal Science 56 (2012) 576e580
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Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs
Glycaemic response to frozen stored wheat rolls enriched with inulin and oat fibre B. Borczak a, *, E. Sikora a, M. Sikora b, C.M. Rosell c, C. Collar c a
Department of Human Nutrition, Faculty of Food Technology, Agricultural University in Krakow, 122 Balicka St, 30-149 Krakow, Poland Department of Carbohydrate Technology, Faculty of Food Technology, Agricultural University in Krakow, 122 Balicka St, 30-149 Krakow, Poland c Instituto de Agroquímica y Tecnología de Alimentos (IATA), PO Box 73, 46100 Burjassot, Valencia, Spain b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 December 2011 Received in revised form 10 July 2012 Accepted 17 July 2012
The aim of this study was to examine the effect of dietary fibre addition to partially baked and frozen wheat rolls on the glycaemic index (GI). Healthy humans volunteers (n ¼ 15) took part in the study. They were asked to attend six times in the early morning, over three weeks. Each tested four types of wheat rolls e two without dietary fibre addition: (1) fully baked, non-frozen (FBNF), (2) partially baked and frozen (PBF); and two with the addition of 10% dietary fibre: (3) fully baked, non-frozen (FBNF þ F), (4) partially baked and frozen (PBF þ F). Glucose solution was used as a reference food and tested twice. Blood glucose concentrations were measured before consumption, as well as at 15, 30, 45, 60, 90 and 120 min after the start of the meal. Dietary fibre consisted of oat fibre (75%) and of inulin (25%). It was concluded that both factors (freezing and fibre), applied to the wheat rolls at the same time, reduced statistically significantly (P 0.05) the glycaemic index by 34% e PBF þ F (GI ¼ 53 7) compared to control e FBNF roll (GI ¼ 87 11). This effect was not observed when fibre supplementation or frozen storage were applied separately. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Glycaemic index Wheat rolls Dietary fibre Frozen storage
1. Introduction Cereals constitute essential components of the human daily diet and are consumed in various forms, especially in the form of whitewheat bread, brown bread, whole bread, bran enriched bread and multi-cereal bread, among others (Fardet et al., 2006). Nutritionally, they are important sources of carbohydrates, proteins, dietary fibre, also vitamins and minerals. Depending on the flour kind and its extraction rate, bakery goods can be more or less abundant in these compounds. Hence their nutritional value may be differentiated. Glycaemic index is one of carbohydrates’ nutritional value determinants. There are evidences that low GI diets are shown to reduce the insulin resistance syndrome, cardiovascular disease, type 2 diabetes and certain cancers (Behall et al., 2006; Cleary et al., 2007; Holm and Björck, 1992). Wheat bread, commonly consumed, is classified as a high GI food (Borczak et al., 2008, 2011; Burton and Lightowler, 2007). At the same time, it is a poor source of dietary fibre, containing typically less than 2.5% of this component (Cleary
Abbreviations: BMI, body mass index; CV, coefficient of variation; FBNF, fully baked, non-frozen; F, dietary fibre; GI, glycaemic index; IAUC, incremental area under the curve; PBF, partially baked and frozen; sd, standard deviation. * Corresponding author. Tel.: þ48 12 662 48 17; fax: þ48 12 662 48 12. E-mail address: [email protected] (B. Borczak). 0733-5210/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcs.2012.07.008
et al., 2007). Improving the nutritional profile of bread, especially the value of glycaemic index has been of much attention. Several different ways have been proposed to decrease the high glycaemic response of white wheat bread, e.g. the use of high-amylose flours (Grandfeldt et al., 1991; Holm and Björck, 1992), selection of hardtype wheat (semolina) (Grandfeldt et al., 1991), incorporation of intact cereal grains into bread (Holm and Björck, 1992; Liljeberg and Björck, 1994), the addition of soluble fibre (Cavallero et al., 2002), sourdough baking technology and addition of organic acids (Borczak et al., 2011; Katina et al., 2006; Lappi et al., 2010), modification of the traditional baking technology by using freezing treatment (Borczak et al., 2008, 2011; Burton and Lightowler, 2007). Among dietary fibres, the most popular sources are oats and barley (Claye et al., 1996). Oat fibre is rich in insoluble compounds (w73.6%), especially in hemicelluloses (38.3%), cellulose (26.6%), lignin (21.4%) and insoluble pectin (8.9%). It consists also of the soluble b-glucans (w1.5%) (Claye et al., 1996). Since insoluble fibres have rather greater influence on bowel function, the gel forming soluble fibres are considered to reduce glycaemic response. Notably, there is shown that viscosity of soluble fibres (i.e. b-glucan, pectins, inulin) could influence glucose absorption by several mechanisms: slowing of gastric emptying, decrease of the accessibility of a-amylase to its substrate (starch), slowing down the glucose absorption produced from starch hydrolysis (due to
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a slowing of glucose diffusion) and increase of the unstirred water layer at the surface of the small intestine (Guillon and Champ, 2000). What’s more, the consumption of foods containing soluble fibre or resistant starch reduces the risk of chronic disease. Risk factors include reductions in blood glucose and insulin, as well as, improvement of glycaemic control in normoglycaemic and diabetic subjects (Behall et al., 2006; Cleary et al., 2007; Holm and Björck, 1992). On the other hand, there is also accepted that the insoluble dietary fibres may slow gastric emptying through their water binding capacity delaying the absorption of glucose (Asp, 1995). Taking into account the above mentioned, this paper focused on application of the freezing process to the baking technology in so-called “postponed baking” combined with the addition of dietary fibre, and the impact of these two factors on the glycaemic response of white wheat-flour rolls. Freezing and fibres applied together were not reported in the literature before so that this approach seems to be innovative. It seems to be also very useful, since white wheat-flour rolls are usually preferred by consumers. The objective of this paper was to investigate the effect of both fibre addition and freezing treatment in the white-flour rolls on postprandial blood glucose in human volunteers.
2. Materials and methods 2.1. Wheat rolls The material consisted of four types of wheat rolls: (1) fully baked, non-frozen e FBNF; (2) fully baked, non-frozen with dietary fibre e FBNF þ F; (3) partially baked and frozen e PBF; and (4) partially baked and frozen with dietary fibre e PBF þ F. The dough for the wheat rolls was prepared using the following ingredients: wheat flour, type 55 e 900 g in the case of FBNF þ F and 1000 g for the rest of the tested rolls (Moulins Soufflet, Pornic, France), salt (18 g) (Janikosoda S.A., Janikowo, Poland), yeast (10 g) (SAF e Instant red e Lesaffre Group, Strasbourg, France), dietary fibres (100 g) in which 75 g of insoluble fibre delivered from oat fibre 300 (SunOpta, Bedford MA, USA) and 25 g of soluble fibre e inulin, (RaftilineÒ HP, Orafti, Tienen, Belgium), Freshbake improver (10 g) (Puratos, Belgium), tap watere 580 g in FBNF and PBF rolls, 590 g in the case of FBNF þ F rolls and 540 g in the case of PBF þ F rolls. The ingredients were mixed for 9 min in a mixer (DIOSNA SP12, GETH, Germany), then underwent proofing (60 min, 35 C, 95% RH) and baking in an electric oven (MIWE, Germany). The FBNF rolls were baked conventionally (20 min, 230 C). The PBF rolls were partially baked (190 C, 3 min, 165 C, 14 min), frozen in a blast freezer for about 30 min at 30 C, and then stored in a freezer at 18 C in airtight containers for 14 days. At the end of the storage period, the rolls were defrosted at room temperature for about 10 min, put in the oven and fully baked (12 min at 230 C). All bakings were conducted at the Department of Carbohydrates Technology, Agricultural University in Krakow.
2.2. Chemical analyses of fresh and frozen stored wheat rolls Chemical analyses (dry matter, protein, lipid, dietary fibre, resistant starch and ash content) of wheat rolls were performed using AOAC standard methods (AOAC, 2006). The content of available carbohydrates (total carbohydrates minus dietary fibre) was evaluated according to FAO/WHO (Table 1). Total carbohydrates (TC) were calculated using the formula: TC ¼ 100 (proteins þ fat þ water þ ash content) (Cichon and Wa˛ do1owska, 2010).
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Table 1 Chemical composition of fresh and frozen stored wheat rolls enriched with dietary fibre. Components [% f.m.]
FBNF
Dry matter Protein Fat Total carbohydrates Available carbohydrates
70.2 8.8 0.8 58.6 55.9
FBNF þ F 0.0a 0.0a 0.1a 0.1a 0.1a
68.5 7.2 1.0 58.7 50.9
0.0b 0.2b 0.0b 0.2a 0.3b
PBF þ F
PBF 70.6 8.9 0.4 59.2 56.0
0.0c 0.7a 0.0c 0.6a 0.6a
69.0 9.3 1.0 57.2 49.3
0.0d 0.3a 0.0b 0.1b 0.1c
Dietary fibre Total Soluble Insoluble
2.9 0.0a 1.2 0.0a 1.7 0.1a
7.8 0.0b 1.4 0.0b 6.4 0.0b
3.2 0.0c 1.1 0.1a 2.1 0.1c
7.9 0.0d 1.7 0.0c 6.6 0.0d
Resistant starch Ash
1.3 0.0a 2.0 0.2ab
1.1 0.2ab 1.6 0.0ac
1.5 0.0b 2.0 0.1b
1.3 0.1ab 1.5 0.1c
FBNF e fully bakedenon frozen, FBNF þ F fully bakedenon frozen with fibre, PBF e partially baked and frozen, PBF þ F e partially baked and frozen with fibre, f.m. e fresh matter. Different letters in rows show significantly different values at P 0.05.
Values are obtained by means of duplicate analysis and are expressed as g per 100 g of fresh sample. The weight of the rolls and the content of the portion given to each participant were calculated on the basis of the chemical composition thus obtained. Thus, the weight of rolls that contained 50 g of available carbohydrates was 88 g, 93 g, 86 g and 94 g for FBNF, FBNF þ F, PBF and PBF þ F, respectively. 2.3. Subjects Fifteen healthy volunteers (non-smoking, restricted alcohol consumption, aged between 18 and 40, normal activity) according to FAO/WHO criteria (Brouns et al., 2005; FAO/WHO, 1998), two men and thirteen women, aged (mean sd) 23.1 1.2 years, with an average body mass index (BMI) (mean sd) of 21.8 2.70 kg/ m2, height (mean sd) 1.68 0.1, weight (mean sd) 61.8 9.2, took part in the test. They were recruited from among students of the Agricultural University in Krakow. The Regional Chamber of Bioethics Committee approved the experimental procedure and the participants signed their consent to attending. Each volunteer was medically examined before the tests. 2.4. Evaluation of glycaemic index (GI) Subjects were asked to attend six times in the morning over a period of three weeks (on Mondays and Thursdays). In order to reduce intra- and inter-individual variability, the volunteers were instructed to fast for 10e12 h before the test, as well as to avoid intense physical activity, and alcohol consumption, and to restrict the time spent ingesting the test food. Every participant tested once the four different wheat rolls and twice the reference food, as recommended by FAO/WHO (1998). Each roll was tested on a separate day in a random order, with at least a two-day gap between each glycaemic index evaluation, in order to minimize carry-over effects. The rolls were served with 250 ml of lowmineralized water. Subjects were asked to eat the test wheat rolls within 15 min and to consume the reference food in 10 min (Brouns et al., 2005). Pure glucose was used as the reference food. The amount of 50 g of glucose was dissolved in 250 ml of lowmineralized water, just before the start of the test, and served to the volunteers. Blood glucose concentrations were measured before consumption as well as at 15, 30, 45, 60, 90 and 120 min after the start of the meal. Finger-prick blood samples were taken for capillary blood glucose analysis. Glucose concentration was measured by
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glucose hexokinase enzymatic assay (Olympus Glucose OSR6121, Beckman Coulter Polska, Warszawa, Poland). The results were given in mmol/l. 2.5. Calculation of glycaemic index (GI) The incremental area under the glycaemic curve (IAUC) was measured using the trapezoidal method (FAO/WHO, 1998). The glycaemic index (GI) was calculated as the IAUC of the blood glucose response curve of a test roll containing 50 g of carbohydrate and expressed as a percentage of the response to the same amount of carbohydrate from the reference food (glucose). 2.6. Statistical analysis The results were given as a mean value standard deviation of two repetitions for chemical composition, and in order to assess the impact of the freezing process and the addition of dietary fibre, multivariate analysis of variance was applied. Significance of differences was calculated based on the Duncan test at a significance level of P 0.05. Levels of intra-individual variation to the two reference (glucose) tests were assessed by determining the coefficient of variation (CV % ¼ 100 standard deviation/mean). 3. Results and discussion The results of the chemical analyses of rolls prepared both traditionally and with the application of postponed baking showed their concordance, except one case, with the data presented in the literature (Table 1) (Marques et al., 2005). Namely, the fat content in PBF roll was lower than the range presented in the literature. It was probably the freezing process that reduced the total fat content in the roll, as a result of physical deterioration of the structure of the and Misniakiewicz, 2007). The addition of fibre powder fat (Cichon led to decreased protein content in the case of FBNF þ F roll and, increased fat content in rolls (FBNF þ F and PBF þ F). Increased fat content may be explained by the presence of fat in the fibre powder added to roll (0.2% fat). All analyzed fibre fractions, i.e. soluble, insoluble and total fibre increased significantly upon an addition of inulin and oat fibre independently on the baking technology (P 0.05). The ash content was significantly lower in rolls with inulin and oat fibre, independently on the baking technology (P 0.05). Observed phenomenon was not supported by the and Misniakiewicz (2007) ascertained that either literature. Cichon fibre addition or freezing treatment did not lead to ash content loss. The amount of resistant starch was significantly higher in roll subjected to frozen storage (PBF) (P 0.05), which has been also documented in the literature (Borczak et al., 2011; Niba, 2003) (Table 1). One of the main objectives of this study was to examine the glycaemic index of roll obtained by applying the freezing process at various stages of production. The mean intra-individual variation in glycaemic response to the two reference tests in the volunteers was 24% CV. This value is consistent with data in normal subjects (Brouns et al., 2005).
Wheat products, such as white roll are characterized by the high glycaemic index which is ascribed to the high content of easily digestible starch (Burton and Lightowler, 2007; Liljeberg and Björck, 1994; Marques et al., 2005). During cooling starch molecules link together by hydrogen bonds, forming highly packed structures (retrogradation). Retrograded amylose which is not susceptible to enzymatic digestion belongs to a type 3 resistant starch. Processing and storage conditions influence the retrogradation, increasing the amount of resistant starch (Niba, 2003). Rosin et al. (2002), among others, observed an 8% increase in the resistant starch in wheat bread stored at 20 C for 30 days. In this study, it was shown a significantly higher amount of resistant starch in the partially baked and frozen rolls wihout fibres (PBF). This confirmed the phenomenon of the formation of resistant starch type 3 (Table 1) by the action of alternating cycles of high and low temperatures (Borczak et al., 2011; Niba, 2003). At the same time wheat rolls prepared with fibres (FBNF þ F; PBF þ F) independently on the baking technology had a resistant starch content at the same level as control roll (FBNF). The impact of fibre on the formation of retrograded starch is documented in the literature. In the process of amylose recrystallization and resistant starch formation, the availability of water is essential (Niba, 2003). Dietary fibre has an ability to bind water molecules (Guillon and Champ, 2000; Rosell et al., 2009) and thus may contribute to reducing the amount of water needed in the process of recrystallization (Katina et al., 2006). Binding of water by the fibre can therefore be used as an explanation of reduced resistant starch content in the rolls with fibres (FBNF þ F, PBF þ F). As seen in Table 2, the areas under the glycaemic response curves (IAUC, mmol/l min) were significantly lower for all types of rolls as compared to the area under the curve of glucose (IAUC ¼ 187 16), (P 0.05). The exception was the area under the curve of fully baked, non-frozen rolls (FBNF), which was not statistically significant. Significantly lowest IAUC value had PBF þ F rolls (IAUC ¼ 106.09 14) (P 0.05). The data in Fig. 1 show that in the case of glucose and the rolls containing fibres (PBF þ F), the maximum value of blood glucose occurred at 30 min after the start of the meal, while for the FBNF, FBNF þ F and PBF it occurred at 45 min. Moreover, the blood glucose level in participants’ serum in the 90th minute was significantly lower in the case of partially baked frozen fibres rolls (PBF þ F) than for the PBF rolls (P 0.05), (Fig. 1). The glycaemic indices of the tested rolls are presented in Table 2. The rolls prepared without the addition of fibres (FBNF and PBF) have glycaemic indices of 87 11% and 67 3%, respectively, while the relevant figures for the rolls prepared with added fibres were 72 6% (FBNF þ F) and 53 7% (PBF þ F). On the basis of the calculated average GI values, fully baked, non-frozen rolls (FBNF) and FBNF þ F were classified as the products with high glycaemic indices (>70%), while partially baked, frozen rolls (PBF) were characterized by a medium glycaemic index value (56% GI 69%). Partially baked and frozen rolls with fibres (PBF þ F) were classified as the products with low glycaemic index (55%). Studies in vivo have shown that the application of either freezing or the addition of dietary fibre could affect the metabolism of
Table 2 Postprandial glucose characteristics (average values with standard errors of the mean). Glucose
FBNF
FBNF þ F
PBF
PBF þ F
161 19bc 87 11a
130 16bd 72 6ab
123 15bd 67 6ab
106 14d 53 7b
Mean SEM IAUC [mmol/l min] GI value [%]
187 16c e
IAUC, incremental area under the blood glucose curve; GI, glycaemic index; FBNF e fully bakedenon frozen; FBNF þ F e fully bakedenon frozen with fibre; PBF e partially baked and frozen; PBF þ F e partially baked and frozen with fibre. Data are shown as a mean SEM. Different letters in lines show significantly different values at P 0.05.
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Fig. 1. Blood glucose response curve for fresh- and frozen stored wheat rolls enriched with fibres: Glucose (C); FBNF e fully bakedenon frozen (6); FBNF þ F fully bakede non frozen with fibre (:); PBF e partially baked and frozen (,); PBF þ F e partially baked and frozen with fibre (-).
glucose and the degree of starch hydrolysis (Borczak et al., 2011; Burton and Lightowler, 2007; Lappi et al., 2010). A 22% significant reduction in glycaemic index has been reported by Borczak et al. (2008) in the study of partially baked, frozen white wheat rolls without fibres. Burton and Lightowler (2007) observed a similar tendency. In the present study, a 15% non-significant reduction was observed in PBF white wheat rolls in comparison to the control rolls (FBNF) (P > 0.05). However, the glycaemic index of partially baked, frozen rolls enriched with fibres (PBF þ F) was 34% significantly lower than in the control rolls (FBNF) (P 0.05). So far, the reduced glycaemic response as presented in the literature upon addition of fibres has in most cases been explained by an ability to increase the viscosity of the digestive medium, especially the thickness of the unstirred layer at the level of the intestinal mucosa, limiting the diffusion and thus the absorption of glucose through epithelial cells (Guillon and Champ, 2000). The mobility of the digestive fluids at the level of intestinal microvilli is thus greatly reduced (Fardet et al., 2006). These properties are mainly linked to soluble fractions: oat fibre (Holm and Björck, 1992), barley fibre rich in b-glucans (Liljeberg and Björck, 1994), inulin (Brennan et al., 2004; Rumessen et al., 1990), arabinoxylans (Lappi et al., 2010) or the use of cereal varieties naturally rich in soluble fibre (Holm and Björck, 1992). In order to have such positive effect, soluble fibres must be incorporated into the food or consumed at the same time as the tested food. Moreover, the fibre must not be destructed, since there is a risk that its rheological properties (especially viscosity) will be modified in the intestine, thus decreasing the GI reduction (Wood et al., 1994). On the other hand, insoluble fractions like cellulose, hemicellulose, lignin or resistant starch influence mainly the proper functioning of the colon and surround the starch granules, limiting the degree of starch gelatinisation and forming physical barrier to a-amylases (Holm and Björck, 1992; Liljeberg et al., 1996). In this study, oat fibre and chicory inulin were used. Dietary fibre from oats is rich mainly in the insoluble fraction (w73.6%). According to Claye et al. (1996) it also contains soluble fraction in the form of b-glucans, although in small amounts (w1.5%). Inulin is a compound of plant origin, occurring mainly in artichoke, chicory, garlic and onion. In the studies conducted on diabetic rats, a significant reduction in fasting glucose and glycated haemoglobin level (HbA1c) was reported after feeding the rich in fibre diet for 9 months (Li et al., 2003). In the people suffering from diabetes type 2, an increasing intake of dietary fibre (especially the soluble fraction) significantly improved glucose and lowered high blood insulin levels (Chandalia
579
et al., 2000). In the study on healthy humans conducted by Casiraghi et al. (2006), consumption of cookies containing barley b-glucan in an amount of 3.5 g per serving led to a significant decrease in the glycaemic index by 50% compared with whole meal biscuits, containing 0.2 g b-glucan per serving. In this study, a portion of 75 g of oat fibre was added to 900 g of white wheat flour, in which b-glucan was at the level not higher than 2.5 g. The glycaemic index of traditionally baked roll with fibres (FBNF þ F) decreased not significantly by 15%. Significant reduction was however observed in the case of partially baked and frozen roll (PBF þ F), where the GI value was by 34% lower than in FBNF roll (P 0.05). In the study of Behall et al. (2006), b-glucans and resistant starch were added separately to a muffin cakes and then together. They were consumed by women of normal weight and overweight. As a result a decrease in the incremental area under the glycaemic response curves was observed by 33% after eating cookies containing both b-glucans and resistant starch. Influence of inulin on plasma glucose was tested repeatedly by using both methods, in vitro and in vivo, demonstrating a positive effect (Brennan et al., 2004; Rumessen et al., 1990) and no effect on the postprandial blood glucose (Causey et al., 2000). In vitro study performed by Brennan et al. (2004) showed that an addition of inulin to pasta in different concentrations (2.5 g, 5.0 g, 7.5 g, 10.0 g/ 100 g flour) resulted in slower release of glucose during in vitro starch digestion. In terms of glycaemic index, this would correspond to a decrease in glycaemic index value by 2.3e15%. Increasing inulin content resulted in reducing swelling index of starch and decreased water absorption capacity compared with the control pasta without inulin. The authors speculated that higher concentrations of inulin probably inhibit starch gelatinization process and thereby reduce its digestibility. Starch was being closed in a semi-permanent gel prepared from hydrated inulin. Thus, the movement of water into starch granules was restricted as well as the access to amylolytic enzymes of human gastrointestinal tract (Brennan et al., 2004). This could explain the reduction of the glycaemic index of roll after the addition of inulin. In this study, an addition of 2.5% inulin to freshly baked and non frozen roll (FBNF), caused a 15% non-significant decrease in the GI value. At the same time, an addition of inulin to the partially baked and frozen rolls (PBF þ F) in the same amount resulted in significant decrease of this index by 34% compared to FBNF, (P 0.05). Rumessen et al. (1990) observed that after addition of fructans (10 g) to 50 g starch meal, the area under the glucose curve was reduced. In this study, a 2.5% inulin addition to fully baked and non frozen rolls (FBNF) resulted in non-significant decrease in area under the glycaemic response curve, while in the case of partially baked and frozen rolls with fibres (PBF þ F), the area has been significantly reduced by 35% compared to the control roll rolls (FBNF) and by 43% compared to glucose (P 0.05). This effect has not been confirmed by Causey et al. (2000) who served 20 g of chicory inulin with daily diet to the volunteers for 3 weeks. A possible explanation of these inconsistent results regarding the effect of inulin on glucose metabolism might be the way of processing and preparation of meals that contain this ingredient, which as a consequence determine its gel-forming properties. Thus, any action that will reduce the viscosity of inulin will also reduce its beneficial physiological effects (Guillon and Champ, 2000). Generally, the frozen storage, as well as fibres addition resulted in lower GI values compared to fresh samples (non-frozen). The addition of fibres to frozen wheat roll rolls reduced significantly the glycaemic index compared to fresh-non frozen sample (P 0.05) (Fig. 1). An addition of fibres to freshly baked wheat flour rolls slightly decreased the GI value, probably through the overwhelming amount of insoluble fraction which only marginally affected glucose metabolism. An amount of fibre was probably also too small
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to induce a desired physiological effect. Only after the use of two factors at the same time, freezing treatment and an addition of fibres resulted in wheat rolls with low glycaemic index, below 55%. Our previously published results (Borczak et al., 2008, 2011) indicated a significant influence of frozen storage of white wheat rolls on lowering the glycaemic index and the significant increase of resistant starch content in frozen stored white wheat rolls. Viewing the presented results it seems that freezing has stronger effect than fibre addition, but only with fibre addition and freezing process applied together it is possible to obtain low GI breads. The impact of both freezing process and dietary fibre powder on the glycaemic response was investigated in order to find new ways to decrease the GI value of most commonly consumed white wheatflour rolls. A significant reduction in the glycaemic index value, of 35% compared to the control roll (FBNF) (P 0.05) was found. The production of rolls by the use of freezing (PBF) is simple, and an application of fibres in powdered form additionally simplifies baking process for use in industrial conditions. The 15% reduction of GI upon addition of fibres powder and the 35% reduction on application of both fibres and freezing is an important achievement in the production of white wheat rolls. White wheat rolls seem to be the most preferred by the consumers as compared to the other less refined rolls, although it is a cereal product of poor nutrient density. It is known that GI is not the only parameter showing the nutritional quality of baked goods. However, food with a low GI seems to be advantageous for people suffering from type 2 diabetes, and for those who want to protect themselves from development of this disease. 4. Conclusions The addition of fibres together with the freezing treatment to wheat rolls decreased significantly the glycaemic index (P 0.05) as compared to fully baked non frozen rolls. The frozen storage or fibres addition applied alone to wheat rolls has not influenced significantly the glycaemic response. Acknowledgements This study has been carried out with financial support from the Commission of the European Communities, FP 6, Thematic Area “Food quality and safety”, FOOD-2006-36302 EU-FRESH BAKE. It does not necessarily reflect its views and in no way anticipates the Commission’s future policy in this area. This study was also supported by the Polish Ministry of Science and Higher Education, grant No. 162/6PR UE/2007/7. References AOAC, 2006. Official Methods of Analysis, eighth ed. Gaithersburg Association of Official Analytical Chemists International. Asp, N.-G.L., 1995. Classification and methodology of food carbohydrates as related to nutritional effects. American Journal of Clinical Nutrition 61 (Suppl.), 930Se937S. Behall, K.M., Scholfield, D.J., Hallfrisch, J.G., 2006. Barley b-glucan reduces plasma glucose and insulin responses compared with resistant starch in men. Nutrition Research 26, 644e650. Borczak, B., Pisulewski, P.M., Sikora, M., Krawontka, J., 2008. Comparison of glycemic responses to frozen and non-frozen wheat rolls in human volunteers e a short report. Polish Journal of Food and Nutrition Sciences 58 (3), 377e380. Borczak, B., Sikora, E., Sikora, M., Van Haesendonck, I., 2011. The impact of sourdough addition to frozen stored wheat-flour rolls on glycemic response in human volunteers. Starch e Stärke 63 (12), 801e807. Brennan, Ch.S., Kuri, V., Tudorica, C.M., 2004. Inulin-enriched pasta: effects on textural properties and starch degradation. Food Chemistry 86 (2), 189e193.
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The behavior and susceptibility to degradation of high and low molecular weight barley b-glucan in wheat bread during baking and in vitro digestion. Food Chemistry 102, 889e897. FAO/WHO, 1998. Carbohydrates in Human Nutrition. Report of a Joint FAO/WHO Expert Consultation, Rome, Italy, 14e18 April, 1997, FAO Food and Nutrition Paper, vol. 66. Fardet, A., Leenhardt, F., Lioger, D., Scalbert, A., et al., 2006. Parameters controlling the glycaemic response to breads. Nutrition Research Reviews 19, 18e25. Grandfeldt, Y., Björck, I., Hagander, B., 1991. On the importance of processing conditions, product thickness and egg addition for the glycaemic and hormonal responses to pasta: a comparison with bread made from “pasta ingredients”. European Journal of Clinical Nutrition 45, 489e499. Guillon, F., Champ, M., 2000. Structural and physical properties of dietary fibers, and consequences of processing on human physiology. Food Research International 33, 233e245. Holm, J., Björck, I., 1992. Bioavailability of starch in various wheat-based bread products: evaluation of metabolic responses in healthy subjects and rate and extent of in vitro starch digestion. American Journal of Clinical Nutrition 55, 420e429. Katina, K., Salmenkallio-Marttila, M., Partanen, R., Forssell, P., Autio, K., 2006. Effects of sourdough and enzymes on staling of high-fibre wheat bread. Food Science and Technology 39, 479e491. Lappi, J., Selinheimo, E., Schwab, U., Katina, K., et al., 2010. Sourdough fermentation of wholemeal wheat bread increases solubility of arabinoxylan and protein and decreases postprandial glucose and insulin responses. Journal of Cereal Science 51, 152e158. Li, J., Kaneko, T., Qin, L., Wang, J., Wang, Y., Sato, A., 2003. Long-term effects of high dietary fiber intake on glucose tolerance and lipid metabolism in GK rats: comparison among barley, rice and cornstarch. Metabolism 52 (9), 1206e1210. Liljeberg, H., Björck, I., 1994. Bioavailability of starch in bread products. Postprandial glucose and insulin responses in healthy subjects and in vitro resistant starch content. European Journal of Clinical Nutrition 48, 151e163. Liljeberg, H., Åkerberg, A., Björck, I., 1996. Resistant starch formation in bread as influenced by choice of ingredients or baking conditions. Food Chemistry 57 (3), 389e394. Marques, C., D’auria, L., Cani, P.D., Baccelli, C., et al., 2005. Comparison of glycemic index of spelt and wheat bread in human volunteers. Food Chemistry 100, 1265e1271. Niba, L.L., 2003. Effect of storage period and temperature on resistant starch and b-glucan content in cornbread. Food Chemistry 83, 493e498. Rosell, C.M., Santos, E., Collar, C., 2009. Physico-chemical properties of dietary fibres from different sources: a comparative approach. Food Research International 42, 176e184. Rosin, P., Lajolo, F.M., Menezes, E.W., 2002. Measurement and characterization of dietary starches. Journal of Food Composition and Analysis 15 (4), 367e377. Rumessen, J.J., Bode, S., Hamberg, O., Gudmand-Hoyer, E., 1990. Fructans of Jerusalem artichokes: intestinal transport, absorption, fermentation, and influence on blood glucose, insulin, and C-peptide responses in healthy subjects. American Journal of Clinical Nutrition 52, 675e681. Wood, P.J., Braate, J.T., Scott, F.W., Riedel, K.D., Wolynetz, M.S., Collin, M.W., 1994. Effect of dose and modification of viscous properties of oat gum on plasma glucose and insulin following an oral glucose load. British Journal of Nutrition 72, 731e743.
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Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs
Glycaemic response to frozen stored wheat rolls enriched with inulin and oat fibre B. Borczak a, *, E. Sikora a, M. Sikora b, C.M. Rosell c, C. Collar c a
Department of Human Nutrition, Faculty of Food Technology, Agricultural University in Krakow, 122 Balicka St, 30-149 Krakow, Poland Department of Carbohydrate Technology, Faculty of Food Technology, Agricultural University in Krakow, 122 Balicka St, 30-149 Krakow, Poland c Instituto de Agroquímica y Tecnología de Alimentos (IATA), PO Box 73, 46100 Burjassot, Valencia, Spain b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 December 2011 Received in revised form 10 July 2012 Accepted 17 July 2012
The aim of this study was to examine the effect of dietary fibre addition to partially baked and frozen wheat rolls on the glycaemic index (GI). Healthy humans volunteers (n ¼ 15) took part in the study. They were asked to attend six times in the early morning, over three weeks. Each tested four types of wheat rolls e two without dietary fibre addition: (1) fully baked, non-frozen (FBNF), (2) partially baked and frozen (PBF); and two with the addition of 10% dietary fibre: (3) fully baked, non-frozen (FBNF þ F), (4) partially baked and frozen (PBF þ F). Glucose solution was used as a reference food and tested twice. Blood glucose concentrations were measured before consumption, as well as at 15, 30, 45, 60, 90 and 120 min after the start of the meal. Dietary fibre consisted of oat fibre (75%) and of inulin (25%). It was concluded that both factors (freezing and fibre), applied to the wheat rolls at the same time, reduced statistically significantly (P 0.05) the glycaemic index by 34% e PBF þ F (GI ¼ 53 7) compared to control e FBNF roll (GI ¼ 87 11). This effect was not observed when fibre supplementation or frozen storage were applied separately. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Glycaemic index Wheat rolls Dietary fibre Frozen storage
1. Introduction Cereals constitute essential components of the human daily diet and are consumed in various forms, especially in the form of whitewheat bread, brown bread, whole bread, bran enriched bread and multi-cereal bread, among others (Fardet et al., 2006). Nutritionally, they are important sources of carbohydrates, proteins, dietary fibre, also vitamins and minerals. Depending on the flour kind and its extraction rate, bakery goods can be more or less abundant in these compounds. Hence their nutritional value may be differentiated. Glycaemic index is one of carbohydrates’ nutritional value determinants. There are evidences that low GI diets are shown to reduce the insulin resistance syndrome, cardiovascular disease, type 2 diabetes and certain cancers (Behall et al., 2006; Cleary et al., 2007; Holm and Björck, 1992). Wheat bread, commonly consumed, is classified as a high GI food (Borczak et al., 2008, 2011; Burton and Lightowler, 2007). At the same time, it is a poor source of dietary fibre, containing typically less than 2.5% of this component (Cleary
Abbreviations: BMI, body mass index; CV, coefficient of variation; FBNF, fully baked, non-frozen; F, dietary fibre; GI, glycaemic index; IAUC, incremental area under the curve; PBF, partially baked and frozen; sd, standard deviation. * Corresponding author. Tel.: þ48 12 662 48 17; fax: þ48 12 662 48 12. E-mail address: [email protected] (B. Borczak). 0733-5210/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcs.2012.07.008
et al., 2007). Improving the nutritional profile of bread, especially the value of glycaemic index has been of much attention. Several different ways have been proposed to decrease the high glycaemic response of white wheat bread, e.g. the use of high-amylose flours (Grandfeldt et al., 1991; Holm and Björck, 1992), selection of hardtype wheat (semolina) (Grandfeldt et al., 1991), incorporation of intact cereal grains into bread (Holm and Björck, 1992; Liljeberg and Björck, 1994), the addition of soluble fibre (Cavallero et al., 2002), sourdough baking technology and addition of organic acids (Borczak et al., 2011; Katina et al., 2006; Lappi et al., 2010), modification of the traditional baking technology by using freezing treatment (Borczak et al., 2008, 2011; Burton and Lightowler, 2007). Among dietary fibres, the most popular sources are oats and barley (Claye et al., 1996). Oat fibre is rich in insoluble compounds (w73.6%), especially in hemicelluloses (38.3%), cellulose (26.6%), lignin (21.4%) and insoluble pectin (8.9%). It consists also of the soluble b-glucans (w1.5%) (Claye et al., 1996). Since insoluble fibres have rather greater influence on bowel function, the gel forming soluble fibres are considered to reduce glycaemic response. Notably, there is shown that viscosity of soluble fibres (i.e. b-glucan, pectins, inulin) could influence glucose absorption by several mechanisms: slowing of gastric emptying, decrease of the accessibility of a-amylase to its substrate (starch), slowing down the glucose absorption produced from starch hydrolysis (due to
B. Borczak et al. / Journal of Cereal Science 56 (2012) 576e580
a slowing of glucose diffusion) and increase of the unstirred water layer at the surface of the small intestine (Guillon and Champ, 2000). What’s more, the consumption of foods containing soluble fibre or resistant starch reduces the risk of chronic disease. Risk factors include reductions in blood glucose and insulin, as well as, improvement of glycaemic control in normoglycaemic and diabetic subjects (Behall et al., 2006; Cleary et al., 2007; Holm and Björck, 1992). On the other hand, there is also accepted that the insoluble dietary fibres may slow gastric emptying through their water binding capacity delaying the absorption of glucose (Asp, 1995). Taking into account the above mentioned, this paper focused on application of the freezing process to the baking technology in so-called “postponed baking” combined with the addition of dietary fibre, and the impact of these two factors on the glycaemic response of white wheat-flour rolls. Freezing and fibres applied together were not reported in the literature before so that this approach seems to be innovative. It seems to be also very useful, since white wheat-flour rolls are usually preferred by consumers. The objective of this paper was to investigate the effect of both fibre addition and freezing treatment in the white-flour rolls on postprandial blood glucose in human volunteers.
2. Materials and methods 2.1. Wheat rolls The material consisted of four types of wheat rolls: (1) fully baked, non-frozen e FBNF; (2) fully baked, non-frozen with dietary fibre e FBNF þ F; (3) partially baked and frozen e PBF; and (4) partially baked and frozen with dietary fibre e PBF þ F. The dough for the wheat rolls was prepared using the following ingredients: wheat flour, type 55 e 900 g in the case of FBNF þ F and 1000 g for the rest of the tested rolls (Moulins Soufflet, Pornic, France), salt (18 g) (Janikosoda S.A., Janikowo, Poland), yeast (10 g) (SAF e Instant red e Lesaffre Group, Strasbourg, France), dietary fibres (100 g) in which 75 g of insoluble fibre delivered from oat fibre 300 (SunOpta, Bedford MA, USA) and 25 g of soluble fibre e inulin, (RaftilineÒ HP, Orafti, Tienen, Belgium), Freshbake improver (10 g) (Puratos, Belgium), tap watere 580 g in FBNF and PBF rolls, 590 g in the case of FBNF þ F rolls and 540 g in the case of PBF þ F rolls. The ingredients were mixed for 9 min in a mixer (DIOSNA SP12, GETH, Germany), then underwent proofing (60 min, 35 C, 95% RH) and baking in an electric oven (MIWE, Germany). The FBNF rolls were baked conventionally (20 min, 230 C). The PBF rolls were partially baked (190 C, 3 min, 165 C, 14 min), frozen in a blast freezer for about 30 min at 30 C, and then stored in a freezer at 18 C in airtight containers for 14 days. At the end of the storage period, the rolls were defrosted at room temperature for about 10 min, put in the oven and fully baked (12 min at 230 C). All bakings were conducted at the Department of Carbohydrates Technology, Agricultural University in Krakow.
2.2. Chemical analyses of fresh and frozen stored wheat rolls Chemical analyses (dry matter, protein, lipid, dietary fibre, resistant starch and ash content) of wheat rolls were performed using AOAC standard methods (AOAC, 2006). The content of available carbohydrates (total carbohydrates minus dietary fibre) was evaluated according to FAO/WHO (Table 1). Total carbohydrates (TC) were calculated using the formula: TC ¼ 100 (proteins þ fat þ water þ ash content) (Cichon and Wa˛ do1owska, 2010).
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Table 1 Chemical composition of fresh and frozen stored wheat rolls enriched with dietary fibre. Components [% f.m.]
FBNF
Dry matter Protein Fat Total carbohydrates Available carbohydrates
70.2 8.8 0.8 58.6 55.9
FBNF þ F 0.0a 0.0a 0.1a 0.1a 0.1a
68.5 7.2 1.0 58.7 50.9
0.0b 0.2b 0.0b 0.2a 0.3b
PBF þ F
PBF 70.6 8.9 0.4 59.2 56.0
0.0c 0.7a 0.0c 0.6a 0.6a
69.0 9.3 1.0 57.2 49.3
0.0d 0.3a 0.0b 0.1b 0.1c
Dietary fibre Total Soluble Insoluble
2.9 0.0a 1.2 0.0a 1.7 0.1a
7.8 0.0b 1.4 0.0b 6.4 0.0b
3.2 0.0c 1.1 0.1a 2.1 0.1c
7.9 0.0d 1.7 0.0c 6.6 0.0d
Resistant starch Ash
1.3 0.0a 2.0 0.2ab
1.1 0.2ab 1.6 0.0ac
1.5 0.0b 2.0 0.1b
1.3 0.1ab 1.5 0.1c
FBNF e fully bakedenon frozen, FBNF þ F fully bakedenon frozen with fibre, PBF e partially baked and frozen, PBF þ F e partially baked and frozen with fibre, f.m. e fresh matter. Different letters in rows show significantly different values at P 0.05.
Values are obtained by means of duplicate analysis and are expressed as g per 100 g of fresh sample. The weight of the rolls and the content of the portion given to each participant were calculated on the basis of the chemical composition thus obtained. Thus, the weight of rolls that contained 50 g of available carbohydrates was 88 g, 93 g, 86 g and 94 g for FBNF, FBNF þ F, PBF and PBF þ F, respectively. 2.3. Subjects Fifteen healthy volunteers (non-smoking, restricted alcohol consumption, aged between 18 and 40, normal activity) according to FAO/WHO criteria (Brouns et al., 2005; FAO/WHO, 1998), two men and thirteen women, aged (mean sd) 23.1 1.2 years, with an average body mass index (BMI) (mean sd) of 21.8 2.70 kg/ m2, height (mean sd) 1.68 0.1, weight (mean sd) 61.8 9.2, took part in the test. They were recruited from among students of the Agricultural University in Krakow. The Regional Chamber of Bioethics Committee approved the experimental procedure and the participants signed their consent to attending. Each volunteer was medically examined before the tests. 2.4. Evaluation of glycaemic index (GI) Subjects were asked to attend six times in the morning over a period of three weeks (on Mondays and Thursdays). In order to reduce intra- and inter-individual variability, the volunteers were instructed to fast for 10e12 h before the test, as well as to avoid intense physical activity, and alcohol consumption, and to restrict the time spent ingesting the test food. Every participant tested once the four different wheat rolls and twice the reference food, as recommended by FAO/WHO (1998). Each roll was tested on a separate day in a random order, with at least a two-day gap between each glycaemic index evaluation, in order to minimize carry-over effects. The rolls were served with 250 ml of lowmineralized water. Subjects were asked to eat the test wheat rolls within 15 min and to consume the reference food in 10 min (Brouns et al., 2005). Pure glucose was used as the reference food. The amount of 50 g of glucose was dissolved in 250 ml of lowmineralized water, just before the start of the test, and served to the volunteers. Blood glucose concentrations were measured before consumption as well as at 15, 30, 45, 60, 90 and 120 min after the start of the meal. Finger-prick blood samples were taken for capillary blood glucose analysis. Glucose concentration was measured by
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glucose hexokinase enzymatic assay (Olympus Glucose OSR6121, Beckman Coulter Polska, Warszawa, Poland). The results were given in mmol/l. 2.5. Calculation of glycaemic index (GI) The incremental area under the glycaemic curve (IAUC) was measured using the trapezoidal method (FAO/WHO, 1998). The glycaemic index (GI) was calculated as the IAUC of the blood glucose response curve of a test roll containing 50 g of carbohydrate and expressed as a percentage of the response to the same amount of carbohydrate from the reference food (glucose). 2.6. Statistical analysis The results were given as a mean value standard deviation of two repetitions for chemical composition, and in order to assess the impact of the freezing process and the addition of dietary fibre, multivariate analysis of variance was applied. Significance of differences was calculated based on the Duncan test at a significance level of P 0.05. Levels of intra-individual variation to the two reference (glucose) tests were assessed by determining the coefficient of variation (CV % ¼ 100 standard deviation/mean). 3. Results and discussion The results of the chemical analyses of rolls prepared both traditionally and with the application of postponed baking showed their concordance, except one case, with the data presented in the literature (Table 1) (Marques et al., 2005). Namely, the fat content in PBF roll was lower than the range presented in the literature. It was probably the freezing process that reduced the total fat content in the roll, as a result of physical deterioration of the structure of the and Misniakiewicz, 2007). The addition of fibre powder fat (Cichon led to decreased protein content in the case of FBNF þ F roll and, increased fat content in rolls (FBNF þ F and PBF þ F). Increased fat content may be explained by the presence of fat in the fibre powder added to roll (0.2% fat). All analyzed fibre fractions, i.e. soluble, insoluble and total fibre increased significantly upon an addition of inulin and oat fibre independently on the baking technology (P 0.05). The ash content was significantly lower in rolls with inulin and oat fibre, independently on the baking technology (P 0.05). Observed phenomenon was not supported by the and Misniakiewicz (2007) ascertained that either literature. Cichon fibre addition or freezing treatment did not lead to ash content loss. The amount of resistant starch was significantly higher in roll subjected to frozen storage (PBF) (P 0.05), which has been also documented in the literature (Borczak et al., 2011; Niba, 2003) (Table 1). One of the main objectives of this study was to examine the glycaemic index of roll obtained by applying the freezing process at various stages of production. The mean intra-individual variation in glycaemic response to the two reference tests in the volunteers was 24% CV. This value is consistent with data in normal subjects (Brouns et al., 2005).
Wheat products, such as white roll are characterized by the high glycaemic index which is ascribed to the high content of easily digestible starch (Burton and Lightowler, 2007; Liljeberg and Björck, 1994; Marques et al., 2005). During cooling starch molecules link together by hydrogen bonds, forming highly packed structures (retrogradation). Retrograded amylose which is not susceptible to enzymatic digestion belongs to a type 3 resistant starch. Processing and storage conditions influence the retrogradation, increasing the amount of resistant starch (Niba, 2003). Rosin et al. (2002), among others, observed an 8% increase in the resistant starch in wheat bread stored at 20 C for 30 days. In this study, it was shown a significantly higher amount of resistant starch in the partially baked and frozen rolls wihout fibres (PBF). This confirmed the phenomenon of the formation of resistant starch type 3 (Table 1) by the action of alternating cycles of high and low temperatures (Borczak et al., 2011; Niba, 2003). At the same time wheat rolls prepared with fibres (FBNF þ F; PBF þ F) independently on the baking technology had a resistant starch content at the same level as control roll (FBNF). The impact of fibre on the formation of retrograded starch is documented in the literature. In the process of amylose recrystallization and resistant starch formation, the availability of water is essential (Niba, 2003). Dietary fibre has an ability to bind water molecules (Guillon and Champ, 2000; Rosell et al., 2009) and thus may contribute to reducing the amount of water needed in the process of recrystallization (Katina et al., 2006). Binding of water by the fibre can therefore be used as an explanation of reduced resistant starch content in the rolls with fibres (FBNF þ F, PBF þ F). As seen in Table 2, the areas under the glycaemic response curves (IAUC, mmol/l min) were significantly lower for all types of rolls as compared to the area under the curve of glucose (IAUC ¼ 187 16), (P 0.05). The exception was the area under the curve of fully baked, non-frozen rolls (FBNF), which was not statistically significant. Significantly lowest IAUC value had PBF þ F rolls (IAUC ¼ 106.09 14) (P 0.05). The data in Fig. 1 show that in the case of glucose and the rolls containing fibres (PBF þ F), the maximum value of blood glucose occurred at 30 min after the start of the meal, while for the FBNF, FBNF þ F and PBF it occurred at 45 min. Moreover, the blood glucose level in participants’ serum in the 90th minute was significantly lower in the case of partially baked frozen fibres rolls (PBF þ F) than for the PBF rolls (P 0.05), (Fig. 1). The glycaemic indices of the tested rolls are presented in Table 2. The rolls prepared without the addition of fibres (FBNF and PBF) have glycaemic indices of 87 11% and 67 3%, respectively, while the relevant figures for the rolls prepared with added fibres were 72 6% (FBNF þ F) and 53 7% (PBF þ F). On the basis of the calculated average GI values, fully baked, non-frozen rolls (FBNF) and FBNF þ F were classified as the products with high glycaemic indices (>70%), while partially baked, frozen rolls (PBF) were characterized by a medium glycaemic index value (56% GI 69%). Partially baked and frozen rolls with fibres (PBF þ F) were classified as the products with low glycaemic index (55%). Studies in vivo have shown that the application of either freezing or the addition of dietary fibre could affect the metabolism of
Table 2 Postprandial glucose characteristics (average values with standard errors of the mean). Glucose
FBNF
FBNF þ F
PBF
PBF þ F
161 19bc 87 11a
130 16bd 72 6ab
123 15bd 67 6ab
106 14d 53 7b
Mean SEM IAUC [mmol/l min] GI value [%]
187 16c e
IAUC, incremental area under the blood glucose curve; GI, glycaemic index; FBNF e fully bakedenon frozen; FBNF þ F e fully bakedenon frozen with fibre; PBF e partially baked and frozen; PBF þ F e partially baked and frozen with fibre. Data are shown as a mean SEM. Different letters in lines show significantly different values at P 0.05.
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Fig. 1. Blood glucose response curve for fresh- and frozen stored wheat rolls enriched with fibres: Glucose (C); FBNF e fully bakedenon frozen (6); FBNF þ F fully bakede non frozen with fibre (:); PBF e partially baked and frozen (,); PBF þ F e partially baked and frozen with fibre (-).
glucose and the degree of starch hydrolysis (Borczak et al., 2011; Burton and Lightowler, 2007; Lappi et al., 2010). A 22% significant reduction in glycaemic index has been reported by Borczak et al. (2008) in the study of partially baked, frozen white wheat rolls without fibres. Burton and Lightowler (2007) observed a similar tendency. In the present study, a 15% non-significant reduction was observed in PBF white wheat rolls in comparison to the control rolls (FBNF) (P > 0.05). However, the glycaemic index of partially baked, frozen rolls enriched with fibres (PBF þ F) was 34% significantly lower than in the control rolls (FBNF) (P 0.05). So far, the reduced glycaemic response as presented in the literature upon addition of fibres has in most cases been explained by an ability to increase the viscosity of the digestive medium, especially the thickness of the unstirred layer at the level of the intestinal mucosa, limiting the diffusion and thus the absorption of glucose through epithelial cells (Guillon and Champ, 2000). The mobility of the digestive fluids at the level of intestinal microvilli is thus greatly reduced (Fardet et al., 2006). These properties are mainly linked to soluble fractions: oat fibre (Holm and Björck, 1992), barley fibre rich in b-glucans (Liljeberg and Björck, 1994), inulin (Brennan et al., 2004; Rumessen et al., 1990), arabinoxylans (Lappi et al., 2010) or the use of cereal varieties naturally rich in soluble fibre (Holm and Björck, 1992). In order to have such positive effect, soluble fibres must be incorporated into the food or consumed at the same time as the tested food. Moreover, the fibre must not be destructed, since there is a risk that its rheological properties (especially viscosity) will be modified in the intestine, thus decreasing the GI reduction (Wood et al., 1994). On the other hand, insoluble fractions like cellulose, hemicellulose, lignin or resistant starch influence mainly the proper functioning of the colon and surround the starch granules, limiting the degree of starch gelatinisation and forming physical barrier to a-amylases (Holm and Björck, 1992; Liljeberg et al., 1996). In this study, oat fibre and chicory inulin were used. Dietary fibre from oats is rich mainly in the insoluble fraction (w73.6%). According to Claye et al. (1996) it also contains soluble fraction in the form of b-glucans, although in small amounts (w1.5%). Inulin is a compound of plant origin, occurring mainly in artichoke, chicory, garlic and onion. In the studies conducted on diabetic rats, a significant reduction in fasting glucose and glycated haemoglobin level (HbA1c) was reported after feeding the rich in fibre diet for 9 months (Li et al., 2003). In the people suffering from diabetes type 2, an increasing intake of dietary fibre (especially the soluble fraction) significantly improved glucose and lowered high blood insulin levels (Chandalia
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et al., 2000). In the study on healthy humans conducted by Casiraghi et al. (2006), consumption of cookies containing barley b-glucan in an amount of 3.5 g per serving led to a significant decrease in the glycaemic index by 50% compared with whole meal biscuits, containing 0.2 g b-glucan per serving. In this study, a portion of 75 g of oat fibre was added to 900 g of white wheat flour, in which b-glucan was at the level not higher than 2.5 g. The glycaemic index of traditionally baked roll with fibres (FBNF þ F) decreased not significantly by 15%. Significant reduction was however observed in the case of partially baked and frozen roll (PBF þ F), where the GI value was by 34% lower than in FBNF roll (P 0.05). In the study of Behall et al. (2006), b-glucans and resistant starch were added separately to a muffin cakes and then together. They were consumed by women of normal weight and overweight. As a result a decrease in the incremental area under the glycaemic response curves was observed by 33% after eating cookies containing both b-glucans and resistant starch. Influence of inulin on plasma glucose was tested repeatedly by using both methods, in vitro and in vivo, demonstrating a positive effect (Brennan et al., 2004; Rumessen et al., 1990) and no effect on the postprandial blood glucose (Causey et al., 2000). In vitro study performed by Brennan et al. (2004) showed that an addition of inulin to pasta in different concentrations (2.5 g, 5.0 g, 7.5 g, 10.0 g/ 100 g flour) resulted in slower release of glucose during in vitro starch digestion. In terms of glycaemic index, this would correspond to a decrease in glycaemic index value by 2.3e15%. Increasing inulin content resulted in reducing swelling index of starch and decreased water absorption capacity compared with the control pasta without inulin. The authors speculated that higher concentrations of inulin probably inhibit starch gelatinization process and thereby reduce its digestibility. Starch was being closed in a semi-permanent gel prepared from hydrated inulin. Thus, the movement of water into starch granules was restricted as well as the access to amylolytic enzymes of human gastrointestinal tract (Brennan et al., 2004). This could explain the reduction of the glycaemic index of roll after the addition of inulin. In this study, an addition of 2.5% inulin to freshly baked and non frozen roll (FBNF), caused a 15% non-significant decrease in the GI value. At the same time, an addition of inulin to the partially baked and frozen rolls (PBF þ F) in the same amount resulted in significant decrease of this index by 34% compared to FBNF, (P 0.05). Rumessen et al. (1990) observed that after addition of fructans (10 g) to 50 g starch meal, the area under the glucose curve was reduced. In this study, a 2.5% inulin addition to fully baked and non frozen rolls (FBNF) resulted in non-significant decrease in area under the glycaemic response curve, while in the case of partially baked and frozen rolls with fibres (PBF þ F), the area has been significantly reduced by 35% compared to the control roll rolls (FBNF) and by 43% compared to glucose (P 0.05). This effect has not been confirmed by Causey et al. (2000) who served 20 g of chicory inulin with daily diet to the volunteers for 3 weeks. A possible explanation of these inconsistent results regarding the effect of inulin on glucose metabolism might be the way of processing and preparation of meals that contain this ingredient, which as a consequence determine its gel-forming properties. Thus, any action that will reduce the viscosity of inulin will also reduce its beneficial physiological effects (Guillon and Champ, 2000). Generally, the frozen storage, as well as fibres addition resulted in lower GI values compared to fresh samples (non-frozen). The addition of fibres to frozen wheat roll rolls reduced significantly the glycaemic index compared to fresh-non frozen sample (P 0.05) (Fig. 1). An addition of fibres to freshly baked wheat flour rolls slightly decreased the GI value, probably through the overwhelming amount of insoluble fraction which only marginally affected glucose metabolism. An amount of fibre was probably also too small
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to induce a desired physiological effect. Only after the use of two factors at the same time, freezing treatment and an addition of fibres resulted in wheat rolls with low glycaemic index, below 55%. Our previously published results (Borczak et al., 2008, 2011) indicated a significant influence of frozen storage of white wheat rolls on lowering the glycaemic index and the significant increase of resistant starch content in frozen stored white wheat rolls. Viewing the presented results it seems that freezing has stronger effect than fibre addition, but only with fibre addition and freezing process applied together it is possible to obtain low GI breads. The impact of both freezing process and dietary fibre powder on the glycaemic response was investigated in order to find new ways to decrease the GI value of most commonly consumed white wheatflour rolls. A significant reduction in the glycaemic index value, of 35% compared to the control roll (FBNF) (P 0.05) was found. The production of rolls by the use of freezing (PBF) is simple, and an application of fibres in powdered form additionally simplifies baking process for use in industrial conditions. The 15% reduction of GI upon addition of fibres powder and the 35% reduction on application of both fibres and freezing is an important achievement in the production of white wheat rolls. White wheat rolls seem to be the most preferred by the consumers as compared to the other less refined rolls, although it is a cereal product of poor nutrient density. It is known that GI is not the only parameter showing the nutritional quality of baked goods. However, food with a low GI seems to be advantageous for people suffering from type 2 diabetes, and for those who want to protect themselves from development of this disease. 4. Conclusions The addition of fibres together with the freezing treatment to wheat rolls decreased significantly the glycaemic index (P 0.05) as compared to fully baked non frozen rolls. The frozen storage or fibres addition applied alone to wheat rolls has not influenced significantly the glycaemic response. Acknowledgements This study has been carried out with financial support from the Commission of the European Communities, FP 6, Thematic Area “Food quality and safety”, FOOD-2006-36302 EU-FRESH BAKE. It does not necessarily reflect its views and in no way anticipates the Commission’s future policy in this area. This study was also supported by the Polish Ministry of Science and Higher Education, grant No. 162/6PR UE/2007/7. References AOAC, 2006. Official Methods of Analysis, eighth ed. Gaithersburg Association of Official Analytical Chemists International. Asp, N.-G.L., 1995. Classification and methodology of food carbohydrates as related to nutritional effects. American Journal of Clinical Nutrition 61 (Suppl.), 930Se937S. Behall, K.M., Scholfield, D.J., Hallfrisch, J.G., 2006. Barley b-glucan reduces plasma glucose and insulin responses compared with resistant starch in men. Nutrition Research 26, 644e650. Borczak, B., Pisulewski, P.M., Sikora, M., Krawontka, J., 2008. Comparison of glycemic responses to frozen and non-frozen wheat rolls in human volunteers e a short report. Polish Journal of Food and Nutrition Sciences 58 (3), 377e380. Borczak, B., Sikora, E., Sikora, M., Van Haesendonck, I., 2011. The impact of sourdough addition to frozen stored wheat-flour rolls on glycemic response in human volunteers. Starch e Stärke 63 (12), 801e807. Brennan, Ch.S., Kuri, V., Tudorica, C.M., 2004. Inulin-enriched pasta: effects on textural properties and starch degradation. Food Chemistry 86 (2), 189e193.
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