Technical paper
Effect of Resistant Starch as Dietary Fiber Substitute on Cookies Quality Evaluation
2014 Volume 20 Issue 2 Pages 263-272
Details
2014 Volume 20 Issue 2 Pages 263-272
The aim of this present study was to develop and investigate the effect of different resistant starch (RS) as dietary fiber substitute on cookies quality evaluation. Mung bean resistant starch with pullulanase debranching and retrograded (DR-MB), mung bean resistant starch with heat-moisture treatment (HMT-MB), high-amylose (Hylon V) corn resistant starch with heat-moisture treatment (HMT-HV), Hi-maize@ particle resistant starch (Hi-M), and wheat dietary fiber (WDF) were replaced in 5%, 15%, and 25% of equivalent amount of low-gluten flour to compare water-holding capacity, sensory evaluation and texture analysis of cookies. Further discussion of the application was indicated that cookies added into DR-MB had the advantage of higher resistant starch content and greater water-holding capacity whereas the disadvantage of poor sensory evaluation. RS prepared by heat-moisture treatment had approximate water-holding capacity with wheat dietary fiber but was superior on sensory evaluation, especially the mass fraction of 25% with HMT-MB. Moreover, hardness as the main evaluated indicators of texture analysis was shown that cookies could be accepted for the majority consumers when the hardness value ranged from 450 g to 630 g, providing a better combination between objective quantitative identification and subjective sensory assessment.
In the current social trends, more considerable attention has been paid to the effects of foods in the diet on human health based upon the development of economy and the improvement of living and consumer demand for food nutrition (Brouns et al., 2002). Nowadays, healthier and more convenient food products that offer excellent and premium sensory qualities such as color and texture are a continuously increasing requirement especially for the new generation (Wang et al., 2008). Exactly, cookies as one type of valuable supplementation means for nutritional improvement have appeared in people’ s sight and are widely being accepted and popularly consumed in plenty of many countries. Consequently, more and more customers have regarded cookies as a better application of composite flour than other foods, not only because of their ready-to-eat form and wide consumption, but also their relatively long shelf-life (Lorenz et al., 1979). However, cookies are defined as a kind of high-fat biscuits for forming irregular corrugated or dimensional pattern (Barak et al., 2013). It is well known that they are prepared and manufactured by wheat flour, fats, sugar and dairy products as the main raw material with some and other accessories such as bulking agent (Aparicio-Saguilan et al., 2007). Therefore, cookies are still contributing to the high sugar and high calorie food though they are being as a widely welcomed by consumers and common food. Hence, it is extremely necessary to legitimately add dietary fiber into cookies in order to cater to the needs of the modern healthy diet and the value of market application.
Dietary fiber is regularly worked as a species of food nutrition ingredient mixed into cookies to improve food function (Threapleton et al., 2013). Dietary fiber is described as the material that has the ability to be resistant to digestion and absorption in the human small intestine along with absolute or segmental fermentation (Camire et al., 2001; Tabung et al., 2012). It has been illustrated that numerous researchers have offered more detailed information and showed that dietary fiber as an important functional food is capable of absorbing some of the human bodies' harmful substances, strengthening the immune systems and helping prevent some diseases such as high blood pressure and heart disease & Clydesdale (Behall et al., 2006; Bourdon et al., 2001; Pandolf & Clydesdale, 1992). Simultaneously, it has been confirmed adding a certain amount of dietary fiber into daily food products is secure and beneficial in recent years. For example, Arshad et al. (2007) reported that wheat flour with defatted wheat germ at levels of 0 – 25% as replacement was investigated for its impacts on functional and nutritional properties of cookies, revealing that 15% was the best acceptable level for cookies. However, on the other hand, some traditional dietary fibers may influence the taste and flavor of food on account of the limitations of its own characteristics (Gómez et al., 2003). Subsequently, there are some challenges and opportunities for researchers to focus on the substitutes for dietary fiber adding into cookies.
Resistant Starch (RS) has been classified as a new type of dietary fiber by the Food and Agriculture Organization (FAO). RS also as the so-called enzyme-resistant starch is a kind of starch which cannot be digestive and absorptive for human. In the small intestine, RS cannot be hydrolyzed by the enzyme solution, but in the colon, part of the RS would be fermented by the intestinal bacteria and short chain fatty acid was produced (Fuentes-Zaragoza et al., 2010). The distinguishing feature of RS is not as same as the ordinary starch quickly digested providing biological benefits. Compared with traditional fiber, some of the benefits of RS can be obtained (Haralampu, 2000). For instance, Sajilata et al. (2006) pointed out that RS could offer a number of superiorities over cellulosic sources of fiber such as colorless, inoffensive flavor, fine particle size, reduced caloric content, low water-holding capacity and minimal swelling, those characters of which minimize the effects of RS incorporation on processing and consumer properties of base foods. So RS can be comprehensively used in food industry as dietary fiber substitute to be applied to different cereal baked products such as cookies.
RS has a wide variety of sources that can be obtained from both processed and raw food materials (Sajilata et al., 2006). According to different indigestible starch fractions, RS can be subdivided into five types: RS1, physically inaccessible starch; RS2, native granule or ungelatinized starch; RS3, starch that has been retrograded; RS4, formed by chemical modification of starch; RS5, containing complexes with amylose and polar lipids (Brown et al., 2006; Englyst et al., 1992). The formation and properties of RS can be affected by different processing methods and conditions (Li et al., 2011a). Various findings were presented that enzyme hydrolysis and heat-moisture treatments (HMT) are both effective methods to help produce resistant starch (Khamthong & Lumdubwong, 2012; Puncha-arnon & Uttapap, 2012). As to the former method, the means of enzyme hydrolysis is usually adopted by pullulanase debranching. It is well documented that the starch slurry will become starch gel when it is heated and cooked. And then adding pullulanase, amylopectin molecules are cut into short chain amylose and amylose is reassociated that leads to a new and strong crystalline structure, finally RS is formed (Shi & Gao, 2011). With respect to the second method, HMT is defined as a physical modification that requires the treated condition at a low moisture content (< 35% w/w) for a certain period of time (15 min–16 h) and at elevated temperatures above the glass transition temperature (Tg) but below gelatinization temperature (Gunaratne & Hoover, 2002). In order to avoid traditional chemical means to modify starch and comply with the requirements of green chemistry, HMT is quite receptive to the consumer as well as the food industry.
However, there is little information on the use of RS prepared by enzyme hydrolysis or heat-moisture treatment in cookie-making. Therefore, in this study, mung bean starch and high-amylose (Hylon V) corn starch are imported to prepare the resistant starch with the two methods before adding into cookies. Mung bean starch as a member of the legume family has not been largely investigated and is potential for producing a higher resistant starch. And it is well known that Hylon V consists of 50% amylose and 50% amylopectin, which is the common starch source to yield a higher resistant starch by HMT (Lin et al., 2011). Moreover, three modified starch and Hi-maize@ particle resistant starch were attempted to look for the optimum formula of consumer acceptance compared with dietary fiber and the aim of this study was to mainly assess the suitability and acceptability of addition of RS as dietary fiber substitute for cookies application by the means of water-holding capacity, sensory evaluation and texture analysis.
Materials Low-gluten flour was obtained from Nanfang flour Corporation (Guangdong Province, China). Native mung bean starch (amylose contents of 29.7%) was purchased from Hada Starch Factory (Harbin, China), and high-amylose corn starch (Hylon V, amylose contents of 50.5%) and Hi-maize@ particle resistant starch were obtained from Corn Products and National Starch. Wheat dietary fiber was bought from the local supermarket (Guangdong Province, China). The Anchor butter was supplied from Fonterra Brands (GZ) Ltd, which was applied for a condiment and rich in nutrition. Frosting as a sweetener to a food stuff was acquired from Taikoo Sugar Limited to enhance food flavor. For the purpose of producing the unique aroma of cookies while roasted, milk powder provided from Nestle Food Co., Ltd. was added into this production process. In addition, salad oil was gotten from Shuangma dedicated baking oil (Shenzhen, China) with the power of reducing the flexibility and toughness of dough, increasing the plasticity of the dough in order to make dough easy stereotypes and improve the products apparent nature. Pullulanase (E.C.3.2.1.41, 1000 ASPU/g, 1.15 g/mL) was provided by Danisco Company (Diazyme® P10) (USA). All other chemicals and solvents were all of analytical grade.
Preparation of resistant starch
Preparation of resistant starch with pullulanase debranching and retrograded On the grounds of previously published literature on the preparation of resistant starch (Li et al., 2011a), a certain amount of starch was weighed to compound the 8% starch slurry (w/w, dry basis) with diluted pH 4.6 buffer solution containing 0.2 M acetic acid and 0.2 M sodium acetate and then was cooked in water bath at 95°C for 30 min. After natural cooling to 55°C, the gelatinized starch was added in pullulanase at 50 ASPU/g dry starches and debranched for 24 h. After that, the solution was treated with 100°C for 10 min in order to inactivate the enzyme and then was retrograded at 20°C for 24 h. Finally the starch obtained was dried at 45°C in the oven and was adequately grinded to screen by 80 mesh sieve. According to this method, mung bean resistant starch was prepared with pullulanase debranching and retrograded.
Preparation of resistant starch with heat-moisture treatment The moisture content of starch samples was adjusted as 20% on the basis of the pre-determined moisture level of native starch by distilled water. All the starch specimens were subsequently placed in sealed stainless containers and balanced 24 h at room temperature. The sealed containers were placed in a thermostatically controlled convection oven to heat 12 h at 120°C and then were cooled to the room temperature. The dealt starch samples were taken out from the containers and dried at 45°C in the oven overnight. According to the method from (Li et al., 2011b), mung bean resistant starch and high-amylose (Hylon V) corn resistant starch were obtained.
Resistant starch determination Resistant starch content based on the Megazyme Resistant Starch Assay Kit was determined by AOAC 2002.02. Official methods of analysis (McCleary et al., 2002). In simple terms, the samples (100 mg, dry basis) mixed with 4.0 mL mixture of pancreatic α-amylase (10 mg/mL) and amyloglucosidase (3 U/mL) were incubated in a shaking water bath at 37°C for 16 h (200 strokes/min) in order to confirm the non-resistant starch digested and hydrolyzed to glucose. The reaction was stopped with 4 mL of 95% ethanol (v/v) and the solution was treated by centrifugation (1500 × g, 10 min). The supernatant was removed and the residue was washed with 50% ethanol twice. And then the rest of portion was put in a magnetic stir bar and dissolved with 2 mL of 4 M potassium hydroxide solution in an ice bath. After stirring 20 min, the resulting solution was neutralized with 8 mL of 1.2 M sodium acetate buffer (pH 3.8) to beneficially add into amyloglucosidase (0.1 mL, 3300 U/mL) at 50°C for 30 min. After the samples were centrifuged (3000 × g, 10 min), 3 mL of glucose oxidase/peroxidase reagent (GOPOD) was added in aliquots (0.1 mL) of the diluent and the compound was reacted at 50°C for 20 min. Absorbance was determined by using a spectrophotometer under 510 nm and resistant starch content of the sample was calculated through a specific formula.
Preparation of cookies In order to prepare better cookies, raw materials were required to store in glass/plastic containers at ambient temperature, or under refrigeration based on the stored requirements (Aparicio-Saguilan et al., 2007). In the preparation of dietary fiber cookies, the equivalent amount of low-gluten flour was replaced in the mass fraction of 5%, 15%, and 25% with cookies added into wheat dietary fiber (WDF), mung bean resistant starch with pullulanase debranching and retrograded (DR-MB, amylose contents of 57.6%), mung bean resistant starch with heat-moisture treatment (HMT-MB, amylose contents of 35.0%), high-amylose (Hylon V) corn resistant starch with heat-moisture treatment (HMT- HV, amylose contents of 58.5%), or Hi-maize@ particle resistant starch (Hi-M). These doses and the procedure were referred by formerly published literature (Arshad et al., 2007). The total amount of flour used was 118.8 g, together with such food ingredients as 28.0 g of crystalline frosting, 0.5 g of salt, 7.2 g of milk powder, 7.2 g of salad oil, 60.0 g of Anchor butter, 16.8 g of the edible pure water. The butter was whipped mildly with an electric mixer before blending, and added with sifted powdered sugar and salt while the butter turned white. And then the mixture was constantly stirred to prevent oil-water separation while slowly poured into salad oil, the solution of milk powder and water in order to mix well and obtain the uniform condition. Biscuit machine was brought in the next step to extrude homogeneous pattern. The dough was preliminary formed and baked 15 min in the baking oven maintaining a temperature of 175°C. By doing so, not only the moisture within cookies could be evaporated at high temperature, but also the starch ought to be richly gelatinized with the leavening agent decomposed and dough volume enlarged. At the same time, the gluten protein turned coagulated because of heating leading to denaturation. Due to the different temperature between the surface layer and the center of the cookies, the temperature of cookies was cooled slowly. The porous crisp cookies ultimately achieved must be cooled down to room temperature before packaging for the sake of preventing contraction of shape and rupture of the finished product. Eventually, the cookies were sealed in store for later analysis using. Sixteen different cookie samples were labeled as follows: (1) Control sample: whole low-gluten flour, (2) WDF5, (3) WDF15, (4) WDF25, (5) HMT- HV5, (6) HMT- HV15, (7) HMT- HV25, (8) HMT-MB5, (9) HMT-MB15, (10) HMT-MB25, (11) DR-MB5, (12) DR-MB15, (13) DR-MB25, (14) Hi-M5, (15) Hi-M15, (16) Hi-M25.
Water-holding capacity determination The water-holding capacity (WHC), was expressed by Iyengar et al. (1991) and made some moderate modifications according to the practical test need. 1.000 g samples sieved by the 60-mesh were weighted and transferred into the undefiled 100 mL beaker. Each blend mixed with 10 mL distilled water was evenly oscillated in every 5 min at room temperature until up to obtain the uniform compound. And then, all the mixtures were diverted to the specified centrifugal cup and centrifuged at 3000 × g for 30 min. After centrifugation, the supernatant was abandoned and the precipitate was weighted. Thus, water-holding capacity (WHC) was calculated according to the following formula.
 |
where W, the wet basis weight of starch samples, g; D, the dry basis weight of starch samples, g.
Sensory evaluation of cookies A panel of 17 testers who were good at food sensory analysis and experienced in sensory evaluation was selected in cookies assessment. To put it simply, these testers must be in good health and maintain an objective and impartial ratings attitude under a quiet environment. The samples were randomly numbered and kept in secret to all the testers. Edible pure water was provided to testers to cleanse their gestations in case that they would be harassed by the taste from different samples. The testers were instructed not to discuss with each other or look around. After tasting analysis, the forms contained scoring criteria were timely handed in and were subject to data processing and statistics. The scoring criteria were shown in Table 1. In short, cookies were evaluated by two aspects, that is to say, exterior features and internal structure, according to the preference method of Ihekoronye & Ngoddy (1985) and McWatters et al. (2003) with slight modification. The exterior features consisting of appearance, color, surface and flavor were determined by intuitive point of view to study consumers' preference, while the internal structures composed of sweetness, cross section structure, taste and smoothness were measured by degustation to obtain consumers' acceptability. And then the overall was calculated for the benefit of further analysis.
| Evaluation indicators | Scoring criteria and level | |||
|---|---|---|---|---|
| Exterior features | Appearance (9) | Complete Uniform Not broken (7 ∼ 9) | Less complete Less uniform Less broken (4 ∼ 6) | Incomplete Non-uniform Broken (1 ∼ 3) |
| Color (9) | Whole golden yellow Uniform Not burnt (7 ∼ 9) | Light golden or light coffee Less uniform Partial burnt (4 ∼ 6) | Coffee Non-uniform Burnt (1 ∼ 3) | |
| Surface (9) | Flat Uncracked bottom (7 ∼ 9) | Partial flat Slightly crached bottom (4 ∼ 6) | Non-flat Cracked bottom (1 ∼ 3) | |
| Flavor (9) | Obvious fragrance (7 ∼ 9) | Slight fragrance (4 ∼ 6) | No fragrance (1 ∼ 3) | |
| Internal structures | Sweetness (9) | Harmonious Acceptable (7 ∼ 9) | Less harmonious Moderate sweetness (4 ∼ 6) | Disharmonious Too sweet or insipidness (1 ∼ 3) |
| Cross section structure (9) | Small and even hole (7 ∼ 9) | Medium and slightly even hole (4 ∼ 6) | Big and uneven hole (1 ∼ 3) | |
| Taste (9) | Crispy Not rough Better (7 ∼ 9) | Slightly crispy Slightly rough Good (4 ∼ 6) | Not crispy Rough Bad (1 ∼ 3) | |
| Smoothness (9) | Swallow much easily No sense of particles No viscous (7 ∼ 9) | Swallow easily Slight sense of particles Viscous (4 ∼ 6) | Swallow difficultly Serious sense of particles Obviously viscous (1 ∼ 3) | |
Texture analysis of cookies The TA-XT2i Texture Analyzer (Stable Micro Systems Ltd, UK) suited with P/45 cylindrical probe was carried out to measure the texture of cookies. The basic set parameters were based on the method of three point bending test in this work, where the pre-test speed was 5.0 mm/s, and the test speed was 1.0 mm/s, and the post-test speed was 10 mm/s. After the strain was set as 40%, the cookies samples were fixed between horizontal brackets in certain distance and were not suspended until broken in half under pressure by a blade-type probe. The texture profile analyzer (TPA) test was performed for every sample in triplicate.
Statistical analysis One-way analysis of variance (ANOVA) and multiple comparisons were conducted using SPSS 17.0, SPSS Inc. IL, USA for expression of the obtained results. The differences between the means were compared to test for significant differences (p < 0.05). The test data with a p < 0.05 was considered as statistically significant. Every trial was determined by triplicate measurement to calculate the average and standard error. Origin 8.0 software was also applied for statistical treatment.
Resistant starch content Resistant starch contents of mung bean starch and high-amylose (Hylon V) corn starch before and after modified were obtained in Fig. 1. It has been observed that the RS contents all have widely been improved in contrast with native starches both the treatment with enzyme hydrolysis and heat-moisture treatment (HMT), which is also indicated that the two methods could be an effectively practicable way to enhance the RS contents. And the results were consistent with more than one research conclusion from numerous researchers (Li et al., 2011a; Li et al., 2011b).
RS contents of starches before and after being modified.
The RS content of mung bean starch treated with pullulanase was 56.6%. Compared to that of native starch (10.9%), the RS content of mung bean was raised by 45.7%. The difference in RS contents between starches treated with pullulanase and native starch was statistically significant. Leong et al. (2007) proposed that the pullulanase could catalyze not only hydrolysis of α-D-glucosidic linkages of pullulan, but also cleave α-1, 6 branch linkages of amylopectin and glycosidic bond. And then part of amylose was produced. The increase in the number of amylose was conducive that amylose molecules were approached with each other in the amorphous region and sequentially were combined into the solid crystal (Perera et al., 1997). Meanwhile, the double helix structure of the crystallization region could induce the crystal more orderly arranged. Thus, it has been predicted that treatment with pullulanase can be rather beneficial to prompt the formation of resistant starch and increase the resistant starch content.
At the same time, heat-moisture treatment also enabled the RS content to receive a higher value. In comparison with native starch, RS content of mung bean with HMT greatly increased from 10.9% to 44.9%, while that of Hylon V was 43.5%. These results may be explained that HMT could prompt the growth of crystal and improve the existing crystallization (Hoover & Vasanthan, 1994) and increase the interaction between amylose and amylopectin as well (Kawabata et al., 2006). Therefore, with an appropriate reaction condition of HMT, the arrangements of the starch granules would be presented in a relatively more ordered state, which was devoted to raise the resistant starch content. Nevertheless, Hylon V provided from HMT did not achieve quite high RS content. This phenomenon might suggest that the particle surfaces of Hylon V, unlike that of ordinary corn starch, were lack of some tiny holes and the interiors of the particles were without a large number of channels for amylase entering (Zhang et al., 2006). Hence, the disadvantage of the Hylon V caused some difficulties for amylase hydrolysis that occurred only on the surface of the starch granules not inside. This came to an agreement with Brewer et al. (2012). Therefore, the optimal values were obtained and the RS products were labeled as DR-MB (56.6%), HMT-MB (44.9%) and HMT-HV (43.5%) as additives into cookies for further analysis in following experiments and discussion.
Water-holding capacity Fig. 2 showed the detailed information about dietary fiber and different starches. Water-holding capacity plays an important role in the properties of starch applications. Acted as high dietary fiber food additives, the water-holding capacity of resistant starch serves as a particularly vital significance to the application of cookies (Iyengar et al., 1991). As it can be seen from Fig. 2, the DR-MB had the highest water-holding capacity (1.98 g/g) among all samples and the HMT-MB had the lowest value (0.96 g/g). And the water-holding capacity (1.06 g/g) of WDF was equal with that of HMT-HV. The Hi-M, which played the part of common resistant starch, showed the water-holding capacity of 1.20 g/g. Based on the results obtained, it was noted that ordinary resistant starch like Hi-M commercial produced may hold higher level than wheat dietary fiber, while it might not the most appropriate additive to meet the requirements of special products such as cookies. Furthermore, the DR-MB possessed quite greater water-holding capacity than any other ordinary resistant starch or dietary fiber, corresponding to the main reason that the amylopectin of the enzymatic starch was debranched by pullulanase so as to increase the content of the short straight chain (Kotoki & Deka, 2010). Thereby, when added into the low moisture products, the enzymatic starch such as DR-MB might compete with the other ingredients for moisture so fiercely that a more excellent organizational structure would not be formed easily (Kaur et al., 2011). It can thus be obtained that the starch samples processed by the heat-moisture treatment may possess lower water holding capacity compared with others and may be more suitable for contributing to low moisture content of foods.
Water-holding capacity of dietary fiber and starches.
Sensory evaluation of cookies Sensory evaluation as one of the most important methods for evaluating food quality has been widely applied in recent years (García-Segovia et al., 2007). Only in this way, can it be described that any functional food must be safety, healthy and tasty. In other words, sensory evaluation is an important means of cookies on applied research. Sensory scores of cookies added into different resistant starch were displayed in Table 2.
| Cookies type | Sensory cores | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Appearance | Color | Surface | Flavor | Sweetness | Cross section structure | Taste | Smoothness | Overall | |
| Control | 7.5 ± 0.3a | 6.7 ± 0.2a | 6.6 ± 0.5a | 6.7 ± 0.3a | 5.9 ± 0.4a | 6.2 ± 0.3a | 6.2 ± 0.4a | 5.8 ± 0.3a | 51.6 ± 0.4a |
| WDF5 | 6.2 ± 0.5b | 4.8 ± 0.3c | 5.9 ± 0.7b | 6.8 ± 0.5a | 6.2 ± 0.3a | 5.9 ± 0.4a | 6.6 ± 0.3a | 6.6 ± 0.3b | 49.2 ± 0.3b |
| WDF15 | 5.5 ± 0.4c | 5.8 ± 0.3b | 4.6 ± 0.5c | 6.7 ± 0.4a | 5.8 ± 0.5a | 5.8 ± 0.4a | 6.0 ± 0.2a | 5.0 ± 0.4b | 45.3 ± 0.3e |
| WDF25 | 4.9 ± 0.2d | 4.5 ± 0.1c | 3.8 ± 0.4d | 7.1 ± 0.3a | 5.9 ± 0.3a | 5.3 ± 0.3b | 5.5 ± 0.4b | 4.4 ± 0.3b | 41.4 ± 0.5g |
| HMT-HV5 | 7.6 ± 0.4a | 7.1 ± 0.5a | 7.5 ± 0.3b | 6.1 ± 0.3b | 5.8 ± 0.4a | 6.7 ± 0.5a | 7.0 ± 0.3a | 6.2 ± 0.2a | 54.1 ± 0.3b |
| HMT-HV15 | 7.6 ± 0.3a | 6.8 ± 0.3a | 6.8 ± 0.4a | 6.5 ± 0.2a | 6.3 ± 0.3a | 7.0 ± 0.4b | 6.7 ± 0.2a | 6.3 ± 0.3a | 53.9 ± 0.4b |
| HMT-HV25 | 6.8 ± 0.1b | 6.9 ± 0.3a | 7.5 ± 0.5b | 6.4 ± 0.3a | 5.5 ± 0.4a | 6.3 ± 0.2a | 6.2 ± 0.3a | 6.4 ± 0.4b | 52.0 ± 0.4a |
| HMT-MB | 5.5 ± 0.2a | 6.9 ± 0.4a | 7.3 ± 0.3b | 7.0 ± 0.5a | 6.1 ± 0.3a | 6.5 ± 0.3a | 6.6 ± 0.4a | 6.4 ± 0.3b | 54.3 ± 0.3c |
| HMT-MB15 | 7.5 ± 0.2a | 5.8 ± 0.3b | 6.8 ± 0.2a | 6.5 ± 0.4a | 6.1 ± 0.4a | 6.8 ± 0.4b | 7.0 ± 0.3b | 6.7 ± 0.4b | 53.2 ± 0.5b |
| HMT-MB25 | 7.9 ± 0.3a | 6.9 ± 0.2a | 7.9 ± 0.5b | 6.8 ± 0.5a | 6.3 ± 0.2a | 6.7 ± 0.3a | 7.1 ± 0.3b | 6.9 ± 0.3b | 56.6 ± 0.2d |
| DR-MB5 | 7.4 ± 0.7a | 6.2 ± 0.7a | 7.2 ± 0.3b | 6.3 ± 0.3a | 6.1 ± 0.3a | 6.0 ± 0.3a | 6.8 ± 0.5b | 5.9 ± 0.5a | 51.8 ± 0.3a |
| DR-MB15 | 7.3 ± 0.4a | 6.2 ± 0.3a | 7.1 ± 0.4a | 6.2 ± 0.5a | 5.9 ± 0.4a | 6.2 ± 0.2a | 5.8 ± 0.4a | 4.7 ± 0.5b | 49.4 ± 0.4b |
| DR-MB25 | 7.1 ± 0.6a | 5.2 ± 0.2b | 7.1 ± 0.3a | 5.0 ± 0.6c | 4.7 ± 0.4b | 6.6 ± 0.3a | 4.4 ± 0.3c | 3.8 ± 0.4c | 43.9 ± 0.3f |
| Hi-M5 | 7.8 ± 0.2a | 7.1 ± 0.3a | 7.4 ± 0.3b | 6.6 ± 0.3a | 6.5 ± 0.3b | 6.9 ± 0.4b | 6.5 ± 0.4a | 6.6 ± 0.3b | 55.4 ± 0.5c |
| Hi-M15 | 7.4 ± 0.4a | 5.9 ± 0.5b | 6.9 ± 0.4a | 5.9 ± 0.4b | 6.2 ± 0.3a | 6.9 ± 0.5b | 6.1 ± 0.3a | 6.4 ± 0.2b | 51.7 ± 0.3a |
| Hi-M25 | 7.0 ± 0.3a | 6.1 ± 0.4b | 6.9 ± 0.3a | 6.7 ± 0.3a | 5.9 ± 0.5a | 5.9 ± 0.3a | 5.6 ± 0.2b | 6.0 ± 0.3a | 50.2 ± 0.5b |
Average values in the column with different superscripts are significantly different (p < 0.05).
Apparently, when cookies were prepared by adding into wheat dietary fiber ranging from 5% to 25%, overall appearance became increasingly rough and also made a terrible influence on the scores. Not surprisingly, the lowest score of the color among all cookie samples was that of WDF products. However, the satisfaction of cookies containing a small amount of wheat dietary fiber (for example, WDF5), was even higher than the control sample on flavor, sweetness, taste and smoothness, indicating that moderate WDF could be conducive to the optimization of the cookies (Gómez et al., 2003). Due to its lower water-holding capacity (Fig. 2) and rough fiber texture, WDF as adding ingredients of dietary fiber was performed obscure taste and charred color after baking, which therefore led to the rather lower scores occurring in all three WDF products than the control sample (51.6). This characteristic may be responsible for affecting consumers' sensory evaluation as it is essentially not as popular as ordinary cookies. Comprehensively speaking, WDF should be limited additive dosage in case of easily influencing the shape, color, structure. The WDF5 would be the optimization to be chosen if the suitable amount was added.
On the other hand, with the amount of addition of HMT-HV increasing, the taste and sweetness of cookies declined instead. Compared to the control, the flavor was poor, but the color and surface were more superior. It could be considered that the HMT-HV had a contribution to the color and surface except for flavor. Among all influencing factors in HMT-HV cookies, smoothness was particularly significantly refined in comparison with ordinary cookies. This might be ascribed that on one hand, high-amylose (Hylon V) corn starch had high amylopectin and much viscosity that was beneficial to improve smoothness; on the other hand, starches went through heat-moisture treatment still retained birefringence of native starches and had little impact on starch granule structure. HMT-HV5 (54.1) and HMT-HV15 (53.9) had close total score. However, since the cross section structure of HMT-HV15 was the best in all sixteen samples, 15% can be considered optimal addition in the HMT-HV products.
With respect to the HMT-MB cookies, the overall scores of these three cookies were all higher than control cookies. Moreover, the HMT-MB25 product had the best scores in the ratings among sixteen samples. It is fully suggested that the sensory evaluation of HMT-MB cookies was gradually enhanced along with the increase of HMT-MB content, showing that HMT-MB was suitable for being substituted largely to cookies (e.g. 25%). Similarly, HMT-MB and HMT-HV both experienced heat-moisture treatment and did not affect the particle structure of the starch, and this evaluation was closer to the consumers' palate. Meanwhile, the amylopectin content of mung bean starch owning medium viscosity was less than that of high-amylose corn starch, so HMT-MB products could never appear not enough crispness like corn products. Besides, smoothness and taste of HMT-MB were also superior to the HMT-HV (Nasir et al., 2010). It can be seen that HMT-MB25 is the most outstanding product in the congeneric cookie samples.
As to the DR-MB samples, it was found that the overall of all indicators but cross section structure decreased significantly with DR-MB increasing in the proportion, especially less harmonious sweetness, rough taste, and worse smoothness. Though the content of mung bean resistant starch with enzyme hydrolysis was highest (56.6%), it was observed that DR-MB cookies were serious sense of particles and not smooth during tasting. This was possibly attributed that the particle integrities of the mung bean resistant starch were damaged after the starch was treated with gelatinization, enzymatic hydrolysis, and retrogradation (Chudik et al., 2011), and the recrystallized starch granules became tough. In this way, even if starch products were grinded and sieved, they still held obvious sense of particles to difficultly swallow after baking, which significantly affected the sensory evaluation. It was well proved that the added amount of 5%, DR-MB5, was the preferable addition ratio by the comprehensive comparison and discussion.
Besides, the characteristics of cookies adding into ordinary RS products such as Hi-maize@ particle resistant starch performed distinctly diminishing trend with modified starch rising, especially appearance, surface, sweetness, taste, and smoothness. Among these three samples, Hi-M5 sample manifested most excellent, followed by Hi-M15 sample, with Hi-M25 sample located in the back. On the basis of these results, it can be argued that ordinary resistant starch was perhaps unsuited to bring in a lot otherwise the senses of samples would be affected. And because of the higher water-holding capacity (1.20 g/g), Hi-maize@ particle resistant starch might be not conducive to the formation of crispness and hardness of cookies.
Texture analysis of cookies The Texture Analyzer which could make a data representation of the physical properties of the sample is recognized as the industry standard testing equipment. Thus it is used to analyze the texture effect of resistant starch and dietary fiber added into cookies in this study. The test was to simulate the chewing action by compressing the bite size of food twice (Sozer et al., 2007). And the textural parameters were shown in Table 3.
| Cookies type | Force/g | Time/s | Distance/mm |
|---|---|---|---|
| Control | 421.5 ± 3.4 | 0.960 ± 0.070 | 0.477 ± 0.017 |
| WDF5 | 599.4 ± 5.8 | 1.405 ± 0.091 | 0.700 ± 0.023 |
| WDF15 | 383.5 ± 4.7 | 1.285 ± 0.065 | 0.642 ± 0.018 |
| WDF25 | 536.4 ± 2.3 | 1.150 ± 0.088 | 0.572 ± 0.034 |
| HMT-HV5 | 546.9 ± 4.2 | 1.450 ± 0.043 | 0.725 ± 0.042 |
| HMT-HV15 | 403.2 ± 1.9 | 1.670 ± 0.032 | 0.832 ± 0.014 |
| HMT-HV25 | 348.1 ± 3.3 | 0.970 ± 0.021 | 0.482 ± 0.011 |
| HMT-MB5 | 337.0 ± 4.1 | 0.970 ± 0.054 | 0.485 ± 0.016 |
| HMT-MB15 | 616.2 ± 3.8 | 1.815 ± 0.073 | 0.905 ± 0.027 |
| HMT-MB25 | 461.5 ± 5.2 | 0.730 ± 0.026 | 0.363 ± 0.009 |
| DR-MB5 | 430.0 ± 2.8 | 0.930 ± 0.017 | 0.465 ± 0.012 |
| DR-MB15 | 630.7 ± 4.4 | 1.315 ± 0.022 | 0.655 ± 0.013 |
| DR-MB25 | 312.7 ± 2.6 | 0.690 ± 0.034 | 0.345 ± 0.010 |
| Hi-M5 | 437.1 ± 1.8 | 1.190 ± 0.037 | 0.595 ± 0.018 |
| Hi-M15 | 235.4 ± 4.5 | 0.755 ± 0.012 | 0.377 ± 0.021 |
| Hi-M25 | 174.9 ± 3.6 | 0.960 ± 0.046 | 0.480 ± 0.009 |
Textural parameter, especially hardness, is important for the cooking quality of cookies. The hardness is regarded as the main evaluated indicators for soft cookie texture and is defined that samples require how much force values to reach a certain deformation. In general, the extrusion peak was on behalf of the hardness of cookies and turned greater with the more resistance. The data obtained indicated that the hardness of samples varied from different types to different contents. However, except for Hi-M cookies as desired, it was suggested that the hardness posed a negative correlation with the content of resistant starch. Nonetheless, other high content of resistant starch added could not necessarily improve the hardness, depending on resistant starch varieties (Civille, 2010). Combined with sensory evaluation, it was well discovered that the hardness values below 450 g of cookies demonstrated poor taste and softly friable. Taking the factors of transportation and storage into account, a low hardness cookies samples might be difficult to be preserved in the transport and be not suitable as a market-oriented products to be promoted. In addition, when the hardness value increased to more than 630 g, the degree of hardening of cookies was also beyond the acceptable range of consumers. That is to say, cookies could be preferred for the majority consumers when the hardness value ranged from 450 g to 630 g.
It has been proved that resistant starch, being a new type of dietary fiber, was a good alternative to apply in cookies. During the preparation of dietary fiber cookies, four resistant starch types and wheat dietary fiber were respectively appended to cookies looked upon as the equivalent amount of low-gluten flour ranged from 5%, 15% to 25%, and took on different properties. Even though DR-MB might possess higher RS content but greater water-holding capacity, poor sensory evaluation and less-than-ideal hardness values could prove that starch experienced enzyme hydrolysis might be unable to work well compared to dietary fiber, so it was with ordinary resistant starch such as Hi-M. Contrasted with wheat dietary fiber, resistant starch with heat-moisture treatment could exhibit dissimilarly between mung bean resistant starch and high-amylose (Hylon V) corn resistant starch. This difference may be attributed to the particular characteristic of mung bean resistant starch, which was more easily to cater to the taste of the public. Not only subjective assessment such as sensory evaluation but also objective appraisal such as hardness analysis was combined to confirm HMT-MB25 best to add into cookies replacing wheat dietary fiber. Meanwhile, it has been drawn a conclusion that the hardness value from 450 g to 630 g would be better recognized by most consumers.
Acknowledgement The study was carried out with financial support of the State Key Program of National Natural Science of China (Grant No. 31230057), and Guangdong Province Program of China (Grant No. 2012B091100291).
