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We determined the optimum amount of ground flaxseed substitution for flour in bakery products and evaluated the effect of flaxseed on sensory and nutritional qualities of those bakery products using a consumer panel (n = 45). Flaxseed was added to yeast breads at 15, 25 and 30% and to muffins at 33, 50 and 66% substitution levels for flour on a weight for weight basis. Breads containing 30% and muffins containing 50% flaxseed were rated better than their counterparts regarding overall acceptability scores. Linolenic acid, fiber and folate contents were improved by 28 g, 16 g and 387-µg dietary folate equivalents (DFE), respectively, in 30% flaxseed bread compared to control. In 50% flaxseed muffins compared to control, linolenic acid, fiber and folate contents were improved by 21 g, 17 g and 341-µg DFE, respectively. Flaxseed at 30–50% substitution for flour greatly enhanced the nutritional qualities of some nutrients without affecting the overall acceptability of bakery products.
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Flaxseed (Linum usitatissimum) has been used for centuries as a food ingredient with medicinal properties (Carter 2008). It is widely used as a bakery ingredient and has gained popularity in North America (Fitzpatrick 2007), and has prompted investigators to study the versatility, stability and acceptability of flaxseed in foods. Flaxseed is classified as a functional food (Carter 1993; Lee 2006) because of its high fiber (27.3/100 g); protein (18.3/100 g); potassium (813 mg/100 g); linolenic acid, an n-3 fatty acid (22.8/100 g) (United States Department of Agriculture 2007); and lignan content (6.1 to 13.3 mg/g) (Johnsson et al. 2000). Flaxseed can be incorporated into the diet through oil, milled or ground flaxseed or through eggs and meats produced by animals fed flax meal (Vaisey-Genser & Morris 1997).
Flaxseed has been found to be stable under normal processing and storage conditions, and Manthey et al. (2002) reported that linolenic acid remained stable during processing and cooking of spaghetti fortified with ground flaxseed. Also, lignan in flaxseed was found to be stable in bakery (Hyvarinen et al. 2006a) and dairy products (Hyvarinen et al. 2006b). Flaxseed lignan content was unaffected by baking temperature and storage temperature at −25°C when tested after incorporating flaxseed into rye breads, graham buns and muffins (Hyvarinen et al. 2006a). Similarly, flaxseed lignan was stable when subjected to high-temperature pasteurization, fermentation and milk renneting (Hyvarinen et al. 2006b). There are no clear guidelines with regard to the optimum amounts of flaxseed to be incorporated into products without affecting the physical or sensory properties of food.
The objective of this study, therefore, was to determine the optimum amounts of ground flaxseed to be incorporated into bakery products and to evaluate the effect of ground flaxseed on sensory and selected nutritional characteristics of those bakery products. In this study, ground flaxseed was incorporated into yeast breads and muffins because these foods are commonly consumed in the USA.
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Yeast bread and muffins containing flaxseed were prepared using standard recipes (Table 1). Bread recipe modifications included a control and test samples containing 15, 25 and 30% substitutions with ground flaxseed for wheat flour on a weight for weight basis. Recipe modifications for muffins included a control and test samples containing 33, 50 and 66% substitutions on a weight for weight basis with ground flaxseed for wheat flour. Prior to selecting these formulations, several yeast bread and muffin recipes were prepared and evaluated for physical properties of those products. Briefly, yeast breads with 50, 60, 75 and 80% and muffins with 75, 80 and 90% flaxseed substitution for wheat flour yielded too dense/chewy and too dark-colored products. After testing these preformulations, it was decided to use 15, 25 and 30% flaxseed substitutions for yeast bread and 33, 50 and 66% flaxseed substitutions for muffins. As the purpose of this project was to incorporate flaxseed into bakery products, it was decided not to test the products with low levels of flaxseed.
Table 1. Ingredient formulations of yeast bread and muffin recipes utilizing ground flaxseed as a substitution for wheat flour
|Ingredient||Ground flaxseed substitution level in yeast breads*|
|Flour, bread (g)||320||271||238.5||222|
|Flour, whole wheat (g)||170||145.5||129||121|
|Flaxseed, ground (g)||–||73.5||122.5||147|
|Vegetable oil, canola (mL)||16||16||16||16|
|Yeast, active dry (g)||6||6||6||6|
| ||Ground flaxseed substitution level in muffins‡|
|Flour, all purpose (g)||247||164.5||123.5||82.5|
|Flaxseed, ground (g)||–||82.5||123.5||164.5|
|Baking powder (g)||12.4||12.4||12.4||12.4|
|Vegetable oil, canola (mL)||27||–||–||–|
Although flaxseed contains 42/100 g of fat, no adjustment was made to the bread formulation because breads prepared with a reduced added fat recipe yielded dry products. Also, reduced fat bread mixtures were too stiff to be kneaded. However, the muffin recipe was adjusted to compensate for the high fat content of flaxseed by eliminating the 27 g of canola oil in flaxseed formulations (Table 1) because muffins made with added fat yielded very oily and moist products.
A description of the preparation of control and test bakery products is provided in Table 1 with ingredients being purchased together from a local grocery store for the entire study in order to reduce any variability in composition. Yeast bread was prepared using an automatic bread machine (Hitachi Home Bakery Bread Machine, HB-B101, Norcross, GA) set to a ‘light bread cycle’. Individual bread loaves took 4 h, 10 min to prepare; they were removed from the bread pan and cooled at room temperature for 4 h to allow evaporation of excess moisture. Loaves were triple bagged in freezer bags and frozen at 0°C for 4 days prior to the sensory evaluation.
Muffins were made using muffin mixing method (dry and liquid ingredients were added and stirred with a wooden spoon to make a lumpy batter). Muffins were baked for 20 min at 190°C until the tops were lightly browned. Samples were removed and cooled on a rack for 45 min, triple bagged and stored at 0°C in a freezer for 4 days prior to the sensory evaluation. Samples were removed on the fifth day to be thawed in the refrigerator at 10°C for 14 h prior to the sensory evaluation. Samples were prepared by sectioning into ≈10-g servings. Bakery products preserved well after freezing and thawing. This evaluation was carried out by investigators by comparing the freshly prepared products with frozen samples after thawing for flavor, color, chewiness and moistness. Because of limited facilities, product preparation and sensory evaluation were conducted at different times; thus, the evaluation was carried out on frozen samples rather than on fresh samples.
The study protocol and consent form were approved by the Human Subjects Committee. A convenience sample of 45 college students was selected randomly during the time of the sensory evaluation (between 11 am and 4 pm). Participant eligibility included being free of allergies to listed ingredients, nonsmoking, free of sinus conditions, nondiabetic, nonpregnant and over the age of 18 years. Of the 45 panelists who completed the evaluation, 29 were women and 16 were men. Mean ages for women and men were 28.0 ± 7.4 years and 25.9 ± 7.0 years, respectively.
An instruction session was organized for the panel prior to the evaluation of sensory properties during which an explanation was provided regarding sensory evaluation procedures. Bread and muffin samples were presented simultaneously on separate serving plates, labeled with three-digit random codes in black ink on outer edges, corresponding to containers holding samples in an unranked random order. Water and crackers were provided and their consumption encouraged between samples for palate cleansing and to reduce/eliminate the carryover taste from the previous sample. Swallowing of samples was optional and all sensory evaluations were conducted at one session. Panelists sat around the table and performed the evaluations without any interaction or discussion between them. Sensory evaluation was conducted under the conditions of ambient temperature and fluorescent light.
The panel evaluated flaxseed and control recipe products based on characteristics of overall acceptability (1 = very poor; 3 = poor; 5 = average acceptability; 7 = good; 9 = very good), tenderness (1 = very dense/chewy; 3 = little dense/chewy; 5 = optimum tenderness; 7 = little fluffy; 9 = very fluffy), color [1 = too pale; 3 = little pale; 5 = optimum color (neither dark nor pale); 7 = lightly dark; 9 = too dark], moistness [1 = soggy (too much moisture); 3 = little moisture; 5 = optimum moistness (neither dry nor soggy); 7 = little drier; 9 = too dry], nuttiness (1 = too nutty; 3 = little nuttier; 5 = optimum nuttiness; 7 = little bland; 9 = too bland) and sweetness [1 = not sweet at all (no sugar); 3 = light sweetness; 5 = optimum sweetness; 7 = very sweet; 9 = too much sweetness]. These characteristics were selected because they are commonly used attributes for the acceptance of bakery products (Alpers & Sawyer-Morse 1996; Szafranski et al. 2005).
Recipes of all formulations of yeast breads and muffins were analyzed for nutrient content (Nutritionist V for Windows, First Data Bank, San Bruno, CA, USA). Sensory characteristics and overall acceptability scores from the panel were analyzed using analysis of variance (ANOVA) to determine the effects of the addition of flaxseed in breads and muffins. If significant difference was found in ANOVA, Newman–Keuls multiple comparison tests were used to determine which two means differed significantly. (Number Cruncher Statistical Systems for Windows, 1997, Kaysville, UT, USA). Statistical significance was set at P < 0.05.
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Sensory evaluation ratings are presented in Table 2. Overall acceptability of yeast breads was similar for control and 15 and 30% flaxseed samples (≈6.0 rating). The control bread was perceived as pale (3.4 rating), differing significantly from all other breads (P < 0.05). Moistness of breads was significantly different between control and flaxseed-enriched samples, with no differences between flaxseed breads. The control bread was rated as dry (6.9) compared with flaxseed breads. Bread without flaxseed was rated as bland (6.2). Conversely, with flaxseed had a stronger nutty flavor compared with the control bread (P < 0.05).
Table 2. Acceptability ratings of yeast bread and muffin recipes utilizing ground flaxseed as a substitution for wheat flour*
|Flaxseed substitution (%)||Acceptability†||Tenderness‡||Color§||Moistness¶||Nuttiness**||Sweetness††|
|Yeast bread|| || || || || || |
| 0 (Control)||5.6 ± 2.1a||5.3 ± 2.4a,b||3.4 ± 1.1a||6.9 ± 1.7a||6.2 ± 1.7a||4.4 ± 1.9a|
| 15||5.8 ± 1.6a||4.7 ± 2.2a,b||4.4 ± 1.4b||5.6 ± 1.5b||5.4 ± 1.8a,c||4.5 ± 1.6a|
| 25||4.7 ± 1.8b||5.7 ± 2.2a||4.8 ± 1.1b,c||6.2 ± 1.8b||5.4 ± 2.1c||3.8 ± 1.8a|
| 30||5.9 ± 1.8a||4.3 ± 2.0b||5.2 ± 1.2c||5.8 ± 1.7b||4.6 ± 1.4c||4.8 ± 1.4a|
|Muffin|| || || || || || |
| 0 (Control)||4.9 ± 2.0a||5.5 ± 1.9a||2.8 ± 1.7a||6.1 ± 1.8a||6.5 ± 1.8a||3.6 ± 1.9a|
| 33||5.0 ± 1.7a||4.8 ± 1.5a,b||4.8 ± 1.1b||5.0 ± 1.9b||4.8 ± 1.8b||3.5 ± 1.3a|
| 50||5.1 ± 1.6a||4.8 ± 1.7a,b||5.6 ± 1.3c||4.8 ± 1.7b,c||5.2 ± 1.8b||3.1 ± 1.5a|
| 66||4.8 ± 1.7a||4.6 ± 1.5b||6.6 ± 1.5d||4.1 ± 1.7c||5.2 ± 2.1b||3.3 ± 1.7a|
The overall acceptability of flaxseed-enriched muffins and control was similar. Control muffins were rated as pale compared with other flaxseed variations. Dark color increased in direct relation to the amount of flaxseed added. Overall, scores for moistness for flaxseed muffins differed significantly from control muffins (P < 0.05). Moistness of 33 and 50% flaxseed muffins was rated as optimum (≈5.0 rating). However, no difference was perceived in moistness of 50 and 66% control muffins and 50 and 66% flaxseed muffins. Flaxseed muffins were near optimum in nuttiness (≈5.0 rating), while the control was perceived as bland (6.5 rating). Scores of sweetness for all the muffins were less than 5, indicating muffins were not sweet enough, with no significant difference between treatments.
The nutrient composition of the control and test bakery products is presented in Table 3. Analysis of recipes showed significant improvements in the nutritional value of flaxseed products compared with controls. In 15 and 30% flaxseed breads, protein content was increased by 6.3% (4 g) and 13% (8 g), respectively, while carbohydrate content was decreased by 6.5% (26 g) and 13% (53 g) reduction, respectively, compared with control. A 15-fold increase in linolenic acid (28 g), a 100% increase in linoleic acid (7 g) and a 70% (16 g) increase in dietary fiber were observed in 30% flaxseed bread compared with control bread. In 30% flaxseed bread compared with control, folate and potassium contents were improved by 387-µg dietary folate equivalents (DFE) and 1597 mg, respectively. Protein content in muffins with 33 and 66% flaxseed had an increase of 17% (7 g) and 33% (13 g), respectively, compared with control sample. Carbohydrate content was decreased by as much as 150 g and linolenic acid was improved by 21 g in muffins with 50% flaxseed compared with control. In muffins, potassium content was increased by 129–263% (958–1957 g) in graduation with flaxseed substitution levels (33, 50 and 66%), and folate content was increased from 216 to 435% (223–448-µg DFE) in the same succession.
Table 3. Nutrient composition of yeast bread and muffin recipes utilizing ground flaxseed as a substitution for wheat flour at various levels*
|Ground flaxseed substitution in bakery products*|
|Nutrient||Yeast bread (10 portions)||Muffin (8 portions)|
|0%† (Control)||15%||25%||30%||0%† (Control)||33%||50%||66%|
|Energy (kcal)||2090 (240)||2210 (254)||2286 (263)||2331 (268)||1481 (232)||1496 (234)||1503 (235)||1509 (236)|
|Protein (g)||64 (7.4)||68 (7.8)||71 (8.2)||72 (8.3)||41 (6.4)||48 (7.5)||51 (8.0)||54 (8.4)|
|Carbohydrate (g)||403 (46)||377 (43)||358 (41)||350 (40)||232 (36)||202 (32)||186 (29)||170 (27)|
|Total fat (g)||25 (2.9)||48 (5.5)||64 (7.4)||72 (8.3)||43 (6.7)||55 (8.6)||62 (9.7)||68 (10.6)|
|Linolenic acid (g) (n-3 fatty acid)||2 (0.23)||16 (1.84)||25 (2.9)||30 (3.4)||3 (0.47)||16 (2.5)||24 (3.8)||32 (5.0)|
|Linoleic acid (g) (n-6 fatty acid)||7 (0.8)||10 (1.15)||13 (1.49)||14 (1.61)||7 (1.09)||6 (0.94)||8 (1.25)||10 (1.56)|
|Dietary fiber (g)||31 (3.6)||38 (4.4)||44 (5.1)||47 (5.4)||7 (1.09)||18 (2.8)||24 (3.8)||30 (4.8)|
|Folate (µg-DFE)||312 (36)||502 (58)||633 (73)||699 (80)||103 (16)||326 (51)||444 (69)||551 (86)|
|Potassium (mg)||1170 (134)||1942 (223)||2489 (786)||2767 (318)||745 (116)||1703 (266)||2227 (348)||2702 (422)|
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In this study, 30% flaxseed bread and 50% flaxseed muffins were rated as the most acceptable products based on the overall acceptability ratings. The gum fraction of flaxseed enhances foam stability and improves volume, and keeping quality and the gum-like behavior exhibited by flaxseed allows for greater amounts to be added to muffins than yeast breads (Carter 1993). Yeast breads with 30% flaxseed were slightly chewy, which is likely due to the gum fraction of flaxseed. In fact, certain sensory properties (color and nuttiness) improved with addition of flaxseed to bakery products. Alpers & Sawyer-Morse (1996) reported that substituting flaxseed at 30 and 50% levels for wheat flour yielded a more acceptable product. The formulation for the present study differed from that of Alpers & Sawyer-Morse's (1996) study in that it was specific to flaxseed distinction in bakery products. Purposeful omission of additional ingredients such as pecans or bananas avoided masking or altering the distinct flavor and textural properties imparted by the flaxseed.
There was no significant negative impact of flaxseed on tenderness. Because flaxseed contains 42 g fat/100 g (United States Department of Agriculture 2007), one might expect that the addition of flaxseed would improve tenderness. Fat has been considered a tenderizing agent in baked goods, imparting an improved mouthfeel and tenderness (Ganji & Kies 1993). However, our consumer panel was unable to detect any improvement in tenderness compared with the control. Previously, the effect of flaxseed on tenderness of muffins was described as crumbly or fluffy to tough or dense (Alpers & Sawyer-Morse 1996). In this study, the tenderness of 33 and 50% flaxseed muffins was rated as optimum (≈5.0 rating), although 66% flaxseed muffin was rated as more dense/chewy (4.6 rating) compared to the wheat-based control product (5.5 rating). This is not surprising given the differences in protein and fiber content between control and flaxseed products. Increased protein and fiber in flour mixture make baked goods heavy and dense (Brewer et al. 1992).
Ratings for color were improved with the addition of flaxseed in both breads and muffins. Color was adversely affected in breads when the substitution with flaxseed reached 66%. Consumers initially assess the quality of food on the basis of color (Lawless & Heyman 1999). It is expected that the addition of flaxseed would make bakery products noticeably darker than control samples, which was more likely due to the presence of pigments such as leutin/zeaxanthin in flaxseed (United States Department of Agriculture 2007). Maillard reaction may have also contributed to the darker color of bakery products due to the high protein content of flaxseed (Borrelli et al. 2003).
The nuttiness was used as an independent flavor descriptor for bakery products because of flaxseed's pronounced nutty flavor (Vaisey-Genser & Morris 1997). The rating of nuttiness profile indicated that bakery products made with 100% wheat flour (control) were somewhat bland compared with flaxseed products. Flaxseed addition contributed to nutty flavor but there was no difference in nutty flavor among muffins with flaxseed; however, a slight difference between levels of enrichment was apparent, with 30% bread having the strongest nutty profile.
Evaluation of moistness in test samples was directly related to flaxseed content. Improved moistness in flaxseed products can be attributed to the water-binding capacity of gum mucilage fractions and the high fat content of flaxseed (Chen et al. 1994; United States Department of Agriculture 2007). Also, during storage, flaxseed products retained moisture and softness more efficiently than control products (Pohjanhemo et al. 2006). In this study, recipes for bread were not adjusted to compensate for the oil content of flaxseed. Reducing 35% of the total weight of flaxseed from additional oil called in a recipe (Carter 1993; Vaisey-Genser & Morris 1997) is recommended. Different properties exist between milled and ground flaxseed. Milling exposes more oil from the hull and increases water absorption capacity. Products made with milled flaxseeds compared with ground flaxseed tend to have an oily texture and heavy crumb, necessitating recipe adjustments (Vaisey-Genser & Morris 1997). Milled and ground flaxseeds are not interchangeable in baking applications, and ground flaxseeds seem more appropriate because of their potential for improving sensory characteristics and allowing for higher levels of substitution (Vaisey-Genser & Morris 1997). Thus, in this study ground flaxseed was used as opposed to milled flaxseed.
As in many sensory evaluation studies, in this study, data generated using sensory organs tend to be variable between subjects because it is difficult to control the sources of variation. Factors such as panel's mood and motivation level, their physiological response to sensory stimulation, and their history and familiarity with the flaxseed products may have been responsible for introduction of variation (Lawless & Heyman 1999). Additionally, freezing of samples may have affected tenderness, moistness, nuttiness and acceptability of breads and muffins, leading to overall low scores across the samples. Because of the small panel size, sensory results are suggestive.