role of lipids in taiwanese flaky snack

ROLE OF LIPIDS IN TAIWANESE FLAKY SNACK

ALBERT LINTON CHARLES', CHI-TANG H02 and TZOU-CHI HUANG'x3

'Department of Food Science National Pingtung

University of Science and Technology Pingtung, Taiwan

2Department of Food Science Rutgers University

65 Dudley Road New Brunswick, NJ 08901

Received for Publication March 7 , 2001 Accepted for Publication April 16, 2001

ABSTRACT

Flaky snack, a popular Taiwanese snack, was prepared and subjected to force deformation tests, to investigate thefunctional roles of lipids and the ideal ratio of solid to liquid fat in layer development. It was observed that increasing the lard content of the dough resulted in a relative increase in the sofness of the final structure texture. A ratio of 3510 (w/w), solid to liquidfat gave intermedi- ate intensities compared with the various levels of lipid content in doughs. Light microscopy tests revealed the Remazobrilliant blue R (RBB}-colored lipids of the inner skin (Yousu} absorbed on the suij5ace of the intact starch granules while the remaining lipids were on the Youpi layers. Force deformation curves depicted increasing fracture intensities with increasing sugar content, indicating the effects of sucrose on dough rheology of the snack. Samples stored at low temperatures depicted shalp hardness increases of varying deflections and modijkations as the temperature parameters increased. It was concluded that the activity of lipids in the flaky snack was to achieve layers separation in order to improve the jlaky snack fracturability and crispy traits.

'Corresponding author. Fax: 886-87740213; E-mail: tchuangQmail.npust.edu. tw

Journal of Food Lipids 8 (2001) 115-130. All Rights Reserved. OCopyright 2001 by Food & Nutrition Press, Inc.. Trumbull, Connecticut. 115

116 A.L. CHARLES. C.-T. HO and T.-C. HUANG

INTRODUCTION

The flaky snack, a popular light biscuit of Taiwan, is one of the many novel snacks that are contributing to the many cereal products of Chinese cuisine. This particular snack uses a fold-in method, which spreads a layer of lard onto a sheet of dough used as the outer hide (Youpi). A mixture of lard, soy oil and flour is used in the inside hide (Yousu) to improve flow characteristics. This flaky snack product may vary in type of fat used, quantity of sugar and processing to such an extent that would cause the layered snack to exhibit varying lnstron fractures, taste and sensory crispy gradient.

The main function of the margarine/shortening in the production of puff pastry is to separate the thin layers of the dough, and to produce a uniform flaky texture and a high volume in the pastry. In order to obtain pastry with good functional properties, it is necessary that the fat blend for pastry margarine has good plasticity and consistency so that it does not penetrate into the dough during manufacture; furthermore, it must be resistant to the mechanical strain of the rolling process. The melting point must be high enough to keep the thin layers of the dough apart from each other during the initial stage of the baking process, but without giving the consumer the impression that the final product has the unpleasant characteristic associated with the presence of high melting fats (Tamstorf et al. 1988).

In cookies (biscuits), and to some extent in crackers, the fat is one of the main ingredients that influences lubrication, aeration, spread, and eating quality. The solid/liquid fat ratio affects the texture of snacks resulting in smoother dough and lowered mixing time and the risk of gluten development. Addition of fat gives the finished product a large volume with improved keeping quality (softness) as well as a tendered and more uniform crumb structure (Vetter 1984). Fats have been known to alter drastically the physical characteristics of starches, producing effects that have been utilized in the food industry. Textural effects are generally recognized to be due primarily to the formation of a complex between the fat and the linear fraction of starch (Okechukwu el al. 1992; Whistler and Daniel 1985). It was originally proposed by Carlson (1981) that soluble, surface active proteins were present at the gas cell surface, but was later refuted by Gan ef al. (1990), who proposed that wheat lipids found closely associated with the liquid phase of dough (Rajapaka et al. 1983), could assist in the foamability of dough by forming a lipid monolayer at the gadliquid interface (Tamstort el al. 1988), that is unsupported by the starch-gluten matrix.

Sugars similarly may be present in different mounts limiting gluten formation or contribute to the formation of a sugar glass (Blanshard 1985). Paton et al. (1981) reported on the influence of individual ingredients and concluded that sugar and lard have tenderizing effect on the cake structure. Sugar’s ability to limit the water available to the starch is thought to delay

ROLE OF LIPIDS IN TAIWANESE FLAKY SNACK 117

gelatinization (Spies er al. 1982). Hodge (1977) also reported on increasing crumb firming during the first few hours after baking and continued under storage conditions. He also reported that the main factor responsible for cake firming is a migration of water from gluten to starch, thus the observed increase in hardening of the matrix.

The importance of wheat starch granule surfaces in determining cake textures, e.g., the degree of springiness and gumminess has been studied by Seguchi et al. (1977). Hall and Sayre (1970), Fannon ef at. (1992), and Fannon and BeMiller (1993) found surface pores along the equatorial groove of the large wheat starch granules. Seguchi (1995) used wheat starch granules stained with Remazolbrilliant Blue R (RBB) dye, prepared in sodium dodecyl sulfate (SDS) to study the surface of the granules; he reported that the sodium dodecyl sulfate (SDS) solution gradually penetrated the granules, thus creating a hollow structure.

In this study, the lipid fraction of the Yousu was colored with the RBB solution so as to study the activities of lipids in the layered structure of the flaky snack and the functional roles of the intact starch granules surface as absorption points punctuated by pores. Furthermore, the use of the RBB dye would elucidate the relationship between lipids and the intact starch granules in texture development of the flaky snack.

MATERIALS AND METHODS

Sample Preparation

Flaky snacks were prepared in a pilot factory and included a series of processing activities. The outer layer (Youpi) was routinely prepared by mixing the ingredients (Table 1) into a loose hide and rested for 30 min. In the experimental design, 10, 20 and 40% lard was used in the Youpi formula to investigate the activities of lipids on the physical properties of the snack. The inner hide (Yousu) that plays an important role in developing the flaky structure, required a unique preparation in that, lard and soy oil were first blended and then mixed into low gluten flour, which were then gently mixed until attaining a smooth texture. This stage does not require kneading and no water is added. Both lipid sources for the two skins were colored with food coloring, for ease of identifying the location of the fat in the layered structure.

Lard and soy oil in ratios of 10:35, 35:10, 0:45 and 45:O (w/w) were blended and gently mixed into low gluten flour to form the inner hide (Yousu), which was then rolled into a ball. The balled Yousu was folded over by the (Youpi) outside hide, and was gently flattened to 1.5-2 cm. The dough was flattened using a dough rolling machine (Esmach s.p.a.; SFBOOL, Italy). Sugar

118 A.L. CHARLES, C.-T. HO and T.-C. HUANG

was sprinkled on the surface and the flattened dough was folded 3 times and flattened consecutively. For proper layer development, it was necessary to ensure the Youpi hide remains intact to prevent the soft Yousu from spilling to the surface. Sesame seeds were sprinkled on the surface and the dough was cut into square pieces of 5 cm x 5 cm. The rough side of the dough pieces was placed down on the baking pan. The flaky snack was baked at a top temperature of 170C and a bottom temperature of 140C for 15 min. In the last 5 min, they were turned. Upon a light browning of the outer skin, the baking process was completed.

TABLE 1. FLAKY SNACK FORMULAS

Outside Layer Inside Layer Batter Composition Batter Composition

Ingredients % Weight, g Ingredients % Weight, g Medium gluten flour 70 210 Low gluten flour 100 230 "Law gluten flour 30 90 Sugar 35 80 Water 45 135 Soy oil 10 25 Sugar I5 45 Lard 35 80 hLard 20 60

"CNS: high gluten flour = 12% gluten; medium gluten flour = 9.5%; low gluten flour = 7% b,Lard was used in 10,20 and 40% proportions in the Youpi.

- ... -

Texture Profiling Analysis

Force-deformation tests were performed by using an Instron Universal Testing Machine (UTM; Model 4301, Instron Ltd., High Wycombe, U.K.) interfaced with a PC for automatic data collection (software Instron Series IX, Automated Materials Testing System). The apparatus was equipped with a three- point bending fixture with a 36-mm span bridge, 100 N load cell. Hardness was defined as the fracture force determined using a crosshead speed of 30 mm/min. The maximum force required to break the snack samples (breaking strength), hardness and the initial slope of the force deformation curve (crispness), were determined. Moisture content was determined of 5 g samples of powdered product sample by infrared radiation at 1OOC.

Microscopic Observations of RBB-stained Starch Granules

In another baking process, a solution (20 mL) of 0.5% RBB (Remazolbril- liant Blue R, Sigma Chemical Co., St Louis, MO) dissolved in ethanol was


prepared and added to the liquidholid fat of the Yousu hide. The Yousu inner layers were then separated from the Youpi outer layers, and examined by a Nikon light microscope fitted with a Kodak camera (Sigma Chemical Co., St. Louis, MO).

RESULTS AND DISCUSSIONS

Functional Role of Lipids in Layer Development

In processing the Yousu, no water was added to the dough and kneading was undesirable at this processing stage in order to reduce the mixing time and to avoid the risk of excess gluten development (Tamstorf et al. 1988). Hence optimum lubrication of the dough depended on the best mix of the so1id:liquid fat ratio. To obtain layer separation, which is an important characteristic of this product in terms of its functional properties, the composition and blend of the fats were considered as being most important for meeting these requirements. From preliminary studies, the solid liquid ratio of 35: 10 (w/w) for lipids in the snack resulted in a better layer separation and development, and a better sensory acceptability, though not significantly differing (p > 0.05) from the other ratios tested under force deformation tests (Table 2). The fat mixture that represented the Yousu was observed to have melted and remained on the Youpi layers, resulting in a clearly defined and well separated thin layers. The Yousu layers colored by the RBB dye were easily separated from the Youpi layers which formed wall-like structures separating the Yousu layers occurring in groups. Therefore, within at least 3 folds of the Youpi skin, 8 individual Yousu layers were counted. At least 24 layers were observed to have formed upon baking (Fig. 1A). Samples with high liquid fat (0:45 and 10:35, w/w) demonstrated that as the proportion of the liquid fat increased, hardness and fracturability increased. Similarly, for crispness, high liquid fractions resulted in increased crispness, but taste scores decreased. An increase in solid lipid content (35: 10; 45:O (w/w)) reduced crispness scores but taste scores increased when solid fat content was reduced (Table 2).

Tamstorf et al. (1988) reported that during kneading, the liquid portion of the fat is retained within a matrix by the solid fat component, thus strengthening the dough during proofing. This is supported by the Instron tests of Fig. 2 where different shapes of the curves give some information on the structure of the texture. This would presumably directly relate to the effect of the varying proportions of lipids content in the samples. The jagged surface of force curves of Fig. 2B of 20% fat exhibits higher fraction intensities than that of 5% and 40% curves. These qualifications were also defined by Bourne (1975) who attributed those jagged areas to layered structures collapsing in highly aerated


products such as the corn curl or from our hypothesis of the intact starch granule creating a discontinuous phase within the starch-gluten matrix network. The positioning of the fat fractions within the layer structure was also highlighted as important for separation of the thin layers of the dough, and these were identified by microscopic tests.

TABLE 2. SENSORY AND INSTRON TEXTURE PROFILE PARAMETERS ON DIFFERENT LIPID CONTENT OF Yousu

Y o u ~ i LiDid Content

Yoiwr Solid:Liquid Lipid Conlcnt Parameters 0:45 'Control 35:lO 45:O Fracturability I .07a o.9sa I .0ga 0.83a

Crispness '4.90h 4.80b 5.50"h 7.20a Hardness 2.88" 1 .87hC 2.1 5h 1 .79c

Taste 5.00' 6.Snh 7.00" 5.+ - 'Control snack contains 1035 (w/w) so1id:liquid lipid; all samples contain 20% lipid. 'Means followed by like letters do not differ (P>O.OS) 'Means of 15 panelists.

Microscopical examination (1B) showed the formation of individual layers in the flaky snack, and lipids absorbed on the surface of the intact starch granules. Large masses of RBB stained lipids are observed to be surrounding the starch granules and suspended in the starch-gluten matrix. The micrographs also indicate the RBB dye dispersed in the lipid mass, hence apparently not all the lipids were absorbed by the starch granules. This may be the result of the starch granules reaching a saturation level of absorption of lipids. Furthermore, the absorption of the lipids on the surface of the starch would indicate the porosity of the granule surface of the granules as well as the activity of the lipids in the layers of the flaky structure. This finding is supported by Flint et al. (1970) who showed that the fat in short sweet doughs does not occur as discrete globules or masses but instead forms part of the starch-protein matrix. However, examination of the finished snacks showed contrasting results in that the fat were present as globules embedded together with the starch granules in the protein matrix.

Thus, in the flaky snack the solid fat appears to play an important structural role in separating the layers that would contribute to desirable pastry requirements such as increasing fracturability intensities of the snack. However, increasing the solid fat was observed to reduce the hardness as a result of separating the layers to an extent that the panelists found unfavorable. In


FIG. 1 . A. LAYER FORMATION IN THE FLAKY SNACK; (1B) LIGHT MICROGRAPHS OF REMAZOLBRILLIANT BLUE R (RBB) STAINED STARCH GRANULES (RBB-LIPIDS)


4 ....................................... f . . . . . . . . . . . . . . . .I ..........................

3 ................. ;, .................. j ........................................ i ............ I A. Lard5% i

2. .........

1 .................. .............

0 0 5 10 15 20

Time (sec)

3 ........................................ : B. Lard20% : ..................... ..................... ...............

2 fi;; .................... ; ..................... :... ................ : ................... ; .............

1 . . . . . . . . . . . , .................. .; .................... ; .............. I...; ..............

0 0 5 I 0 15 20

Time (sec)

4 .............................................................. 1 ............................... i C. Lard40% i

3 ................... .;. ................... .;. ................... :, ................... ;. ..........

2 ................... ; ..................... ; .................... ; .................... ; ............ 1 f l l !

............................... I .................. . ,1 .1 .................. i ............

0 I

0 5 10 15 20 Time (sec)

FIG. 2. TPA CURVES DEPICTING EFFECT OF LARD ON FLAKY SNACK TEXTURE


contrast, the liquid fat is responsible for contributing to hardness of the final product. Panelists however expressed their preference for a lipid blend with a higher solid fat that significantly contributed to desirable snack traits of the flaky snack.

Functional Role of Lipids in Youpi after Baking

At a low proportion of lipids in the snack food matrix, high hardness intensities were observed at 2.5 kg (Fig. 2A). However, at 20 and 40%, (Fig. 2 and 3), the hardness intensities were reduced to 1.8 and 1.7 kg, respectively. When fat coats the flour prior to hydration, gluten network formation is inhibited. When the fat level is high, the lubricating function in the dough is so pronounced that it influences aeration, consistency and eating quality of short dough (Olewnik ef al. 1984; Vetter 1984; Miller 1985). Lard, on the other hand, showed a direct effect on the hardness intensities of the flaky snack; as lipid content increased, hardness showed a relative decrease. These results demonstrate that the alteration of texture by increased lipid content is manifested by an increased softening of the samples; the Instron deformation curves (Fig. 2) exhibited and supported those changes in the distribution of fracture

2 LI

m

v) v) Q,

1.5 2

= I 2 m

0.5

0 10% 20% 40%

Lard (%)

Fracturability 0 Hardness 0 Crispness

FIG. 3. FRACTURE INTENSITY DISTRIBUTIONS FOR THE EFFECT OF FAT


intensities. The curves were typical of crispy foods defined as a highly valued and universally liked characteristic that signifies freshness and high quality (Jackson et al. 1996). The steepness exhibited by most curves indicated the resistance of the flaky snack to bending. A crisp flaky snack has a steep slope and is more resistant to bending than a less crisp snack.

Similar results were sensory evaluation (Table 3) demonstrated similar results for the 20% snack (control). However, this was significantly different (p C0.05) from other test levels in terms of crispness and total acceptability. The Youpi with 40% lipid was judged to exhibit higher crispness and reduced hardness (Instron test results) which show the important role of lipids in binding and structure setting of the Youpi skin.

TABLE 3. FRACTURARlLlTY AND SENSORY TESTS ON DIFFERENT LIPID CONTENT OF YOUPI'

Youpi Lipid Content, % 10 20 40

Fracturability 11.19a 0.76b 1 . 1 % Crisoness 6.19a 5.13b 6.44a

__ Totai Acceptability 6.SOa S.7Sb 6.3 la 'Means of 3 replications of IS panelists, 2Means followed by like letters do not differ (P>0.05); Solid: Liquid lipid content of Yousu was 10:35 (w/w) for all cases.

Wade (1988) reported that the addition of fat to the dough effectively reduces the amount of water required to make a dough of workable consistency and of making the product more tender. Thus, with increasing addition level of lard to the dough formula there was a relative decrease in hardness intensities (Fig. 2) and varying fracturability intensities (Table 3). Starch granules play an important role in the structure of biscuit skins as 'filler' in the matrices sites for absorbing migrating water. Furthermore, we observed starch granules surfaces stained and surrounded by the RBB-stained lipids resting on the Youpi layers. However, varying sizes of starch granules were noticeable and we assumed that the loss of birefringence may be due as much to the heat application in the baking process as to the absorption of water from denatured protein or from Youpi or of the lipid fractions on the granular surface. From the data of Table 3, a positive interrelationship existed between the oil content and starch granules affecting the final texture characteristics of the product.


Activity of Sugar on the Final Texture Characteristics

An increase in sucrose resulted in an observed increase in hardness (Fig. 4). Moreover, the texture profiling analysis (TPA) curves characteristically depicted fractured regions of the food internal structure. Samples treated with high levels of sucrose showed higher levels of hardness intensities, indicated by a sharp rise of the force (Fig. 4C) with varying deflections and a fewer number of peaks. The samples varied considerably as indicated by different fracture intensities exhibited (Fig. 5) by the sample at different treatments. In the same instances, average deformation resistance increased with added sucrose (40 and 10% for high and low samples, respectively) suggesting that the samples did not fail exclusively by brittle fracture. Additionally, the fine structured curves showing minimal jaggedness may be interpreted as the binding effect of the sucrose content (40%, Fig. 5B) increasing the T, or brittleness of the samples or lowering the ‘free water’ distributed within the food matrix. The quantity and quality of sugars have significant effects on the rheology of snack dough, as well as on the texture, appearance, and flavor of the finished product (Faridi el al. 1990). Large amounts of sugar in the dough tend to make it sticky and hard (Hoseney et al. 1986). Sucrose acts as a hardening agent by crystallizing as the snack cools, thus making the product crisp (Hoseney et al. 1986). However, dough with high levels of added sugar showed sharp increases in both consistency and cohesive properties as was reported by Olewnik and Kulp (1984). Steele (1977) reported that increased sugar levels cause dough firming.

Effect of Cooling Rates

The effects of cooling temperature on the stability of the samples were also evaluated. A decrease in hardness was observed in force intensities (Fig. 6) of the snacks stored at -5C, +5C and at room temperature 28C, respectively. The samples stored at the low temperatures present a sharp rise of the force with varying deflections and a larger number of peaks that originate in the progres- sive breakdown of the cellular structure of flaky snacks. On increasing the temperature parameters, the force-deformation curves were modified, i.e. the initial slope decreased and the height of peaks diminished. The samples stored at room temperature depicted lower hardness intensities. The addition of fat to the dough has the effect of reducing the amount of water required to make a dough of workable consistency (Wade 1988). As fat increased, the axial variation in firmness decreased indicating a reduction in the settling rate of flour particles due to increased viscosity of the suspension.


4 ............... ...; ................... A. Sucrose 10%

Time b e d

4 ................... i ................ ;.. . . . . . . . . . I . . . . . . . . . . . . . . I

i B. Sucrose 20% 3 .......... , ..

2 ....... , .......

1 ..............

0-

...........

..........

0 5 10 15 20 Time (sec)

C. Sucrose 40%

2 ................. : ................... i ................. i . . . . . . . . . .

.................... , ..................

0 5 I 0 15 20 Time (sec)

FIG. 4. TPA CURVES DEPICTING EFFECT OF SUCROSE LEVELS ON FLAKYSNACKTEXTURE


10% 2 0 O/O 40%

Sucrose ("/O)

Fracturability IHardness OCrispness

FIG. 5 . FRACTURE INTENSITY DISTRIBUTIONS FOR THE EFFECT OF SUCROSE CONTENT ON FLAKY SNACK TEXTURE

CONCLUSIONS

The role of lard and liquid: solid of lipids were clearly demonstrated as having functional roles in layer development of the snack and effects on the mechanical properties of the snack. Its absorption by the starch granules resulted in mechanical modifications as exhibited by force deformation curves showing hardness and fracturability gradients. Reduction in firming of the snack structure was related to the increasing percentages of the lipid fractions in the dough. The effect on the finished product of adding sugar to the formula was also significant with hardness intensities increasing with proportions of sugar content. Similarly, firmness increased during storage and force curves depicted varying deflections of the curve surface, indicating some form of mechanical or phase changes being sustained during storage or as a result of cooling rates within the layered structure of the flaky snack. The photomicrographs depicted intact and swollen starch granules stained by the lipid-RBB fractions, thus elucidating the presence and functional roles of the granules as absorption sites and as 'fillers' in the matrix network in the flaky snack. The lipids were then assumed to improve the mechanical and phenomenological properties of the intact starch granules in the snacks.


.............................. i A.Temperature28 C

0.8 .............................. i .............................. !. '".". ' '

........................................... ..........

Time (sec)

0.8 .............................. i :B. Temperature +5 C ......................................................................

0.4 .......

0.0 .......

0 10 20 I I

Time (sec)

........................................ 0.0 . . . . . I 1 4

................................................... : ....... I

20

0.8 .............................. j C. Temperature -5 C

0 10 20 Time (sec)

FIG. 6 . TPA CURVES DEPICTING EFFECT OF COOLING RATES ON FLAKY SNACK TEXTURE


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role of lipids in taiwanese flaky snack

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