Patent applications entitled Starch-Based Products for Microwave Cooking or Heating by Victor T. Huang et al¬ and also Method of Microwave Heating of Starch-Based Products by K. H. Anderson et al. filed simultaneously herewith and to be assigned to the assignee of the present invention are incorporated by reference herein.

Microwaves are at the lower energy end of the electromagnetic radiation spectrum which includes gamma rays, X-rays, ultraviolet, visible light, near infrared, infrared radiation, microwaves and radio waves. Microwave processing offers advantages over conventional oven heating for some food products because it produces rapid product heating without excessively high surface temperatures. However, this type of heating is "opposite to" conventional cooking of foods with respect to moisture and heat transfer.

Convenience is the key to the popularity of microwave ovens. Consumer surveys have shown that microwave penetration has reached 70% of the population with projections for growth through the 1990 's. Along with the increase in penetration of the microwave oven into the home has come a demand for microwaveable food products.

There has been a large expansion in the number of microwave foods available on the market. However, typically this has amounted to the inclusion of microwave directions and not food reformulations for textural attributes. Particularly in the area of bread-like foods, little, if any, improvement in textural attributes has been made in commercially available products. It has thus not been desirable to reheat or cook such products in a microwave oven. Both precooked and uncooked products may exhibit excessive toughening and firming when exposed to microwave radiation.

The present invention relates to solutions for two problems attendant with heating pre-cooked dough-based products or cooking dough products in a microwave oven.

These problems relate to crumb texture i.e. toughening and firming.

The main technical difficulty for microwaving bread- like products is the development of the aforediscussed unacceptable texture. The outer crust layer may become so tough that it is difficult to tear such a product. The inner crumb becomes very difficult to chew. Also, the textural quality can deteriorate much faster than that o ,i- a conventional oven- baked product during the course of cooling. Overcooking in a microwave oven may exacerbate the problem while a reduction in overall cooking or reheating may reduce toughening and firming.

It has been reported that Oscar Mayer & Co. developed a microwaveable sandwich by using a specific type of starch, and a precise ratio of starch to fat to flour in the dough (Anonymous, 1987). Another method of dealing with texture problems was to use a specially designed protein system in the dough which has been reported not to become tough during microwave treatment (Moore, 1979). In U.S. Patent No. 4,463,020 the use of long grain rice flour in the dough is suggested to alleviate these problems. In

U.S. Patent No. 4,560,559 a problem-solving approach is suggested in which requires the addition of starch granules having an average size of less than approximately 20 microns. It has been reported that fat in combination with other substances reduced toughness in microwaveable dough-based items (Kimbrell, 1987). The tenderizing effect of fat has been attributed to the "shortening effect-".

Toughness can be defined and assessed in sensory terms as a leathery or rubbery eating texture. For example, a bagel is tough while a croissant is tender. Firmness can be defined and assessed in sensory terms as the force required to bite through the sample without tearing or pulling. A "stale" dough-based product can be characterized as firm while fresh bread immediately after conventional cooking would be considered non-firm.

Whether or not a product is tough or firm, or more accurately is objectionably tough or firm, depends on the product type and the consumer. For example, the expectation for bread is that it should be soft and not tough. If bread had a bagel texture it would be objectionable because of the toughness. However, a bagel, even though it is tough, is not objectionable since the expectation is for a product that has a tough texture. Thus, the type of product and the consumer will set the standard for what level of toughness or firmness is objectionable or desirable.

One of the complicating factors in dealing with dough-based systems is that minor changes in the formula or process can change the product identity from one product to another product. For example, further development of a biscuit dough will produce a baked product which is more of a bread and frying of a yeast leavened product will produce a doughnut while baking of the same yeast leavened dough will produce a bread-like

product. Thus, a careful balance must be made in the processing and the formula to solve product problems and not change the product identity.

Three criteria are the major determining factors for product identity. Those criteria are: the flour type and its protein content; the amount of fat; and the degree of dough development. See Figure 1 for examples.

Additional factors may affect product identity. Some of these factors include, for example: type of fat; type of leavener; dough formation method; method of fat inclusion; method of cooking the product e.g., steaming, frying, baking, etc; method of assembling the dough product, for example, laminating versus nonlaminating, etc. These and many related factors and principles are discussed in Hoseney (1986).

Further, the same cereal grain can provide major differences in the product. For example, changing from a soft wheat to a hard wheat can significantly change the product identity. Dough-based products may be prepared from one cereal grain flour or mixtures of several cereal grain flours. For dough-based products the cereal flour should be capable of forming a viscoelastic continuous protein matrix upon hydration and mixing.

It has surprisingly been found that the present invention easily permits maintenance of product identity while being able to freely manipulate toughness and firmness. Toughness and firmness can be reduced from any point along scales ranging from non-tough and non-firm products to very firm and very tough products. More specifically, the present invention involves methods to reduce toughness and firmness to the desired degree relative to a similar formula product when heated in a microwave oven. The present invention provides the latitude to manipulate toughness and firmness regardless

of the original toughness and firmness for a similar non- invention product.

The present invention involves methods to reduce the above mentioned toughening and firming of dough-based products upon heating, e.g. reheating or cooking in a microwave oven. In one aspect the present invention involves product compositions with a reduced degree of gluten development to permit product preparation for consumption by the application of microwave energy.

Embodiments of the invention can provide good quality microwaveable bread-like products including unleavened and leavened products. Leavened products include those leavened by microorganisms such as yeast, chemicals, and steam, etc. as known in the art. By use of the present invention, therefore, a good quality microwaveable product including reconstitutable dry mix, fresh or raw dough, frozen dough or precooked bakery products may be prepared in the microwave oven.

The present invention can be practiced with starch containing or starch-based dough products. Dough-based products will exhibit toughness and often firmness as a textural problem. Dough-based can be defined as a product which has a continuous matrix of gluten. Preferably such products have at least 4% gluten by weight in the dry flour. More preferably a dough-based product will have 6% or more gluten by weight of dry flour. As hereinafter discussed, toughening is predominantly a protein related phenomenon, more specifically a gluten related phenomenon. Also as hereinafter discussed, firming is a predominantly starch related phenomenon. For the practice of the present invention, any cereal grain based product from which a dough can be made, can be utilized.

Dough may be defined as a viscoelastic substance. As used herein, the term "dough-based product" includes

products that are partially cooked and were in a dough form just prior to cooking by any means. The term "dough-based product" also includes products that are dough prior to cooking in a microwave oven. The products when cooked typically have a composition by weight of product of about 20% to about 85% flour, about 15% co about 45% total water and about 0 to about 50% total fat.

The cooked products have a specific volume greater than about 1.5 cm 3/g, preferably greater than about 2.0 cm3/g

3 and more preferably greater than about 2.5 cm /g. The products in their uncooked conditions typically have a composition by weight of about 20% to about 80% flour, about 18% to about 55% total water and 0 to about 20% dough fat. What is meant by dough fat is fat, present preferably in the range between about 5% and about 18%, which is added to the dough during formation of the dough mass to act as a plasticizer. Additional fat can be added to the dough after mixing and this is generally referred to as lamination fat. With the additional fat, the total fat content of the product in the uncooked condition can be from 0 to about 45% total fat. Pie crust has a high dough fat content generally around 20% to about 40% and typically contains total water of less than about 25% by weight. Typical pie crust are undeveloped in which undevelopment is due to the high dough fat content and the extremely low degree of dough mixing. Pie crust dough or cooked pie crust is known to not toughen if heated in a microwave oven when they are not adjacent to a high moisture filling which results in moisture pickup during heating or cooking. Further, pie crusts are generally considered to be an unleavened product and have a low « specific volume of abour 1 cm /g. However, some expansion of the product can occur due to the evolution of steam during heating.

Firming in dough-based products may be improved by practice of this invention. Products containing, on a cry flour basis, at least 4% gluten may utilize the invention

to reduce toughening. Combinations of cereal grains can also be utilized to form a dough. Cereal grains include wheat, corn, rye, barley, oats, sorghum, triticale, etc.

As used herein bread-like product is not limited to breads as defined in the standards of identity under the Food, Drug and Cosmetic Act. Bread-like products include such foods as breads, biscuits, cornbread, pastries, sweet rolls, pita bread, pizza crust, pasta, dumplings, etc. A product intermediate is a dough-based product whenever formed. It may be, for example, partially cooked, uncooked (raw) and baked prior to exposure to microwave irradiation for cooking or reheating.

Dry mix as used herein means a mixture of ingredients normally used to make a dough from as is known in the industry. Such mixes can come in any package size and are generally sold through recail, food service or commercial outlets. The dry mix has added to it liquid ingredients such as water and fats, which are plasticizers, and other optional ingredients such as eggs, etc.

An acceptable texture is similar to the texture of a conventionally cooked equivalent ^' or similar product as is known in the industry. Conventional cooking includes convection, conduction, non-microwave irradiation like radiant heat cooking, electrical resistance heating i.e., the food product or bread-like product is used to conduct current, etc. The invention product texture is better than the texture of an equivalent product that does not use the invention. For puposes of this disclosure, a similar or equivalent product is a product that has substantially the same formula and is analogously processed, except for degree of development as hereinafter described, i.e., it is processed in the same way and precooked and or heated the same.

It is preferred that the improvement in product with the invention relative to a similar product without the invention being distinguishable to a consumer and is at least about 5, preferably at least about 10 or more preferably at least about 15 points on a 0-60 organoleptic relative sensory testing scale (with 60 representing high toughness or firmness) using a trained panel. Such a testing procedure is known in the art. It is preferred that the improvement in the product with the invention relative to a similar product without the invention is at least about 10%, preferably at least about 20%, and more preferably at least about 30% improvement on the relative sensory testing scale as described herein.

It is preferred that the degree of dough development as measured by light microscopy as hereinafter described with the invention relative to a similar product that does not use the invention is at least about 5, preferably at least about 10 and more preferably at least about 15 points on a 0-60 relative testing scale of the degree of development (with 60 representing high degree of development using a trained panel) as measured by light microscopy. These values are for cooked and uncooked products.

It is preferred that the reduced degree of development as measured by the reduction in energy required to break the dough as hereinafter described with the invention relative to a similar product that does not use the invention is at least about 0.3 J, preferably at least about 0.6 J and more preferably at least about 0.9 J (using Extensograph method). However, when the dry protein/total water ratio increases, the energy required to break the dough also increases even though the degree of development is much lower as shown on Figure 9. These ranges are applicable to a dough with a fat content of 0% to about 20% and a protein to water ratio of 0.15 to 0.3

The amount of work input required to develop a dough is dependent upon the type of mixer and the formula of the particular dough. Also, a product, as identified by name, for example, biscuits can have a wide range of degree of development and still produce a similar product with a similar formula. The traditional methods of measuring dough development are an effective tool to evaluate a dough. However, because of the test's dependency on formula, definitive comparisons are made with certain restrictions, those include, comparing the same formula and a specific product identity. The traditional dough development tests i.e. those performed on the Extensograph and the Farinograph because of the above limits are not as effective as one which indicates the ability of protein to interact within the system. Thus, the above described light microscopy test was developed which provides a better indication of and a better correlation to textural attributes over a broad range of product formulas, processing conditions and the degrees of development than do the traditional test methods. It provides a better indication of the ability of the proteins to interact and cause toughness and also a better indication of the degree of development which also reduces firmness.

The products of the present invention comprise flour and sufficient plasticizer to form a dough. The dough can include aqueous and nonaqueous plasticizers. Nonaqueous plasticizers include fats. However, in some products, added fat is not necessary, for example, with French bread. The water content used herein, unless otherwise indicated is total water. It is to be understood that flour contains approximately 14% water by weight of flour.

In accordance with an aspect of the present invention, a good quality cooked or uncooked microwaveable product can be produced, such products can be distributed, and/or stored under conditions such as frozen, refrigerated (pressurized or unpressurized) , and shelf-

stable systems. It was also surprisingly found that a very underdeveloped dough such as described herein, as compared to a normally developed dough, did not grey as quickly when stored at 4.4' C in the presence of greater than 5% oxygen in the package headspace.

Unexpectedly, it was also found that a very underdeveloped dough resulted in a more acceptable product when cooked in a microwave oven than in the conventional oven, specifically in terms of product grain and specific volume.

One advantage of the present invention is that the treatment means, by way of process for the dough-based products, is effective in reducing microwave-induced toughness and firmness a distinguishable amount.

A further advantage of the present invention is that the treatment means for reducing toughness and/or firmness does not require special processing equipment to effectuate.

Yet another advantage of the present invention is that the treatment means is effective for reducing the toughness or firmness from any level of toughness or firmness for an equivalent product that does not utilize the treatment means.

It is yet another advantage of the present invention that a dough-based product can be made from any flour quality type with a range of total protein content.

Other advantages will become apparent from a review of the specification.

FIGURE 1 graphically illustrates different product identities and the corresponding product characteristics.

FIGURE 2 shows photomicrographs of a dough of low degree of development. (2A, 6.5 x and 2B, 106 x).

FIGURE 3 shows photomicrographs of a dough of high degree of development. (3A, 6.5 x and 33, 106 x).

FIGURE 4 shows photomicrographs of a dough of an intermediate degree of development. (4A, 6.5 x and 4B, 106 x) .

FIGURE 5 shows photomicrographs of a prebaked product at a low degree of development that was reheated in the microwave oven. (106 x) .

FIGURE 6 shows the effect of degree of dough development as measured by photomicroscopy on product toughness.

FIGURE 7 shows the effect of degree of dough development as measured by photomicroscopy on product firmness.

FIGURE 8 shows the effect of dough development as measured by rheology on product toughness.

FIGURE 9 shows the effect of protein/water ratio on the energy required to break the dough and on the resulting product toughness.

FIGURE 10 shows examples of products with different grain scores.

FIGURE 11 shows the difference in product grain of a dough at a low degree of development baked in the conventional and microwave oven.

FIGURE 12 shows an Extensograph of a lean dough formula at low degree of development.

FIGURE 13 shows a Farinograph of a lean dough formula.

As used herein all percents are by weight and all measurements are at 21 ^* C unless otherwise designated.

The present invention involves the discovery that control of the degree of dough development may be used to provide a product resistant to the development of undesired textural attributes during microwave heating. The degree of development may be controlled by the limitation of work input during dough formation from flour, water and other ingredients. By controlling the flour/water ratio in dough the degree of development may be controlled as well as effects of microwave cooking such as firmness and toughness. For a lean dough (approximately 5% or less fat) prepared with a relatively low work input a flour/water ratio of from about 1.3 to about.1.6 is preferred to obtain a properly undeveloped dough resistant to the negative effects of microwave cooking. For a rich dough (with 5-20% fat by weight of dough) a flour/water ratio of from abouc 1.2 to about 1.6 is preferred. Additionally, the control of flour particle size may have significant effects on the extent of dough development and quality product obtained by microwave cooking. For a rich dough containing more than about 5% fat by weight of dough, flour particle size is not as significant as it is with a lean dough. For a lean dough a flour particle size of at least 125 microns is preferred to obtain a product of good texture after microwave cooking.

Flour contains protein and since protein is indicated as the ingredient responsible for toughening, the control of the protein/water ratio is a good means to define the product formula. It is preferred that the protein/water ratio on a dry protein basis be in a range of between about 0.15 and about 0.3 preferably in the range of

between about 0.18 and about 0.24 and most preferably in the range of between about 0.18 and about 0.22.

The degree of dough development in uncooked products may be determined and utilized to assess likely negative effects of microwave irradiation. A preferred application of the dough development control of the present invention is for ^' the preparation of refrigerated doughs for product consumption. Such doughs may have their degree of development closely controlled prior to shipment to the retail outlet.

The present invention further involves a method for producing an edible starch based bread-like product having a desired reduced degree of toughness as compared to an equivalent product with a normal degree of development cooked by microwave irradiation. In one embodiment, the method comprises the steps of: working a mixture comprising water and flour to a low degree of development characterizing initial dough formation; preparing a product intermediate from said dough; and exposing said product intermediate to microwave irradiation for a time sufficient to produce a desired edible product.

During the process of the present invention, the degree of development may be monitored by photomicroscopic analysis of the mixture. When the mixture is a dough with some development and the photomicroscopically determined structural score is preferably between about 5 and about 35, more preferably between about 5 and about 30 and most preferably between about 5 to about 20. The mixture leading to a dough may be monitored by numerous other rheological means known to those of skill in the art. Such means include, for example, measurements in devices such as Farinographs (e.g., Model No. FZOLD0905 Brabender, Inc. Hackensack, N.J.) or Extensographs ( e.g., Model No. DM 90-40 Brabender, Inc. Hackensack, N.J.) which monitor

forces necessary to deform the semi-solid mixture and its doughy product.

A dough is most commonly composed of flour (preferably at least a majority of hard wheat flour), water, fat, sugar and leavening agent(s). A relatively lean formula contains 0% to 5% fat and 0% to 5% sugar and has a flour/water ratio of 1.1 to 1.3. An example of a relatively lean formula is shown in Example I. A mixture of these ingredients becomes a dough after a very short mix time. The specific length of this mix time for a given mixer is unique to each formula. The Farinograph, an instrument commonly used to assess dough and flour functionality. It measures the power needed to mix a dough at a constant speed, thus showing the dough's resistance to mixing. A typical example of the printout from a Farinograph is illustrated in Figure 13. Thus, as a dough is forming in the Farinograph mixing bowl, the mixture's resistance to mixing is increased. When the graph begins to plateau, as shown by the point labeled A in Figure 13 a dough begins to form. For example, the formula described in Example I plateaus after two minutes of mixing in the Farinograph bowl at speed 2. The resistance of the dough to mixing at this point is 600BUs.

The working of the dough described above may involve mixing with a dough hook. Other dough mixers are well known in the art and therefore are not described herein and any may be used.

A list of abbreviations used herein is as follows:

BU - Brabender unit cm - centimeter fat - dough fat (unless otherwise specified) flour - dry flour (unless otherwise specified) g - gram

J - Joule

m minute

RH relative humidity

SALP sodium aluminum phosphate

SAPP sodium acid pyrophosphate

S.D. standard deviation

SODA baking soda; sodium bicarbonate water total water (unless otherwise specified) work the amount of energy necessary to break dough during Extensograph measurement

Measuring of a value for toughness with mechanical measuring devices has been difficult. However, toughness can be easily measured by trained test panels of people and can be fairly accurately quantified on arbitrary toughness scales. Such techniques are well known in the food industry and are generally referred to as organoleptic testing.

A panel of trained people was used to evaluate products. The following procedure was used for both textural attributes and dough development evaluations. An initial training session was used to familiarize the panelists with the range of products that would be tested. Reference standards (low end and high end of the scale) were presented in this session to train the panelists to recognize the difference between the product attributes that were to be measured.

The trained panel marked two reference products used as standards on a 0-60 point line scale with 0 being the low end and 60 the high end. The standards were tasted or viewed prior to each evaluation session, and were marked on the score sheets. A separate score sheet as described above was used for the test samples.

A blind control was normally included with the test samples. The presentation of the marked control and blind control samples at each session was used as a method to

standardize responses made at different times. The mean score was reported. Evaluations by individual panelists which were significantly different from the remainder of the panel were eliminated from consideration. This testing procedure is more fully disclosed in Moskowitz (1983), the entire disclosure of which is incorporated herein by reference.

Two major textural attributes were tested: firmness and toughness. Firmness was assessed by the force required to bite through the sample without tearing or pulling. Toughness was assessed as the rate at which the sample comes apart during mastication.

Gluten becomes developed over time as it is exposed to water and a work input. As a result, a dough can be formed with different degrees of development. The gluten instead appears as a mudlike coating in which starch granules are imbedded. As the flour particles are mixed with water, gluten hydrates and forms a matrix. This process is described as dough development. Development is believed to be the formation of a network of protein molecules with occasional cross-links. The degree of development may be assessed by taking photomicrographs of the products. The photomicrographs reveal the degree of gluten hydration and the extent of fibril formation which are visible with protein staining. This information may be used to judge the degree of development by a trained observer.

Unhydrated flour particles are separate and distinct when viewed with a light microscope. The addition of water to flour with enough mixing to wet the particles results in the flour particle agglomeration, a disruption in their structure and limited gluten fibril growth. As the suspension is mixed further, no more intact flour particles can be observed. They become hydrated but not yet developed and gluten has no apparent direction in most

regions. Gluten fibrils attain more direction as the suspension is mixed further. At the stage of optimum development, many gluten strands are observed and appear continuous. In rheological terms, this is the point of minimum mobility. These changes are visible under the light microscope. A photomicrograph thus serves as evidence of the degree of product development.

Figure 2 is a photomicrograph of a product at the stage of low development. In this Figure, the gluten is separate and distinct with limited hydration. Figure 3 is the photomicrograph of a product at a high degree of development. In Figure 3, the protein is continuous and has direction.

Figure 4 represents a photomicrograph of a dough sample intermediate in the degree of development. In this Figure, gluten is hydrated but still distinct, there is limited formation of gluten fibrils and they have little to no direction.

Figure 5 is the photomicrograph of a prebaked product (at a low degree of development) reheated in the microwave oven.

Figures 6 and 7 illustrate the correlation between the degree of dough development, as measured by photomicroscopy, with toughness and firmness as measured

2 by sensory assessment. The correlation coefficients (R ) are 0.80 and 0.79, respectively. These results illustrate a fairly good correlation between the degree of dough development and toughness and firmness.

Proofed dough and precooked samples were frozen and specimens were cut from the center of each. The specimens were mounted on a stub for sectioning on a cryogenic microtome. Sections approximately 16 microns thick were cut and then allowed to air dry for a minimum of one hour.

Protein in the sample was stained by first fixing the sections in 2.5% glutaraldehyde for approximately 5 minutes and then rinsing with water for 1 minute. The samples were then stained with 1% light green SF yellowish protein stain, for example, that which is available from Aldrich (Milwaukee, WI.), for 5 minutes followed by a 5 minute water rinse. A cover slip was placed on top with a drop of "Aqua-Mount". The samples were then viewed with the light microscope and photomicrographs of representative fields were taken. Four photomicrographs were taken at 106X magnification and three taken at 6.5X.

The photomicrographs were then judged by a five member panel of trained people. An initial training session was used to familiarize the panelists with the range of photomicrographs that would be assessed. Reference standards were presented in this session to train the panelists to recognize the difference in the degree of product development. A standard 6-inch linear scale (0-60 points) was used to score the degree of development (low to high). Two reference standards (low end and high end of the scale) were judged prior to each evaluation session and was marked on score sheets. Each judge then evaluated the test photomicrographs and marked each on a separate score sheet. The scores are based upon a scale of 0-60 with 0 being the low end and 60 the high end of product development. Judgments were digitized and the mean score is reported. These are the same methods as used for standard sensory testing as discussed herein.

An underdeveloped sample as measured by the microscopic method is defined as the range where any sample in which the flour particles have remained separate and distinct (low end of the scale) to the point where no more intact flour particles can be observed, flour particles are hydrated and gluten has no apparent direction in. ost regions. As shown in Figure 4, this point would be judged about 35 on the 0-60 point scale.

For the lower and upper limits, Figures 2 and 3 were judged to be about 5 and about 55, respectively. Figures 2 and 3 represent the low end and high end standards given to the trained panel at the time* ^' of judging. Figure 4 represents the cutoff point between an acceptable and unacceptable product. All products with a score between 5 and 35 represent a texturally acceptable product.

The degree of dough development can also be assessed using rheology. For a given formula, the degree of development can be assessed as the amount of energy required to break the dough. For the assessments used in the presented data and the examples an Extensograph was used unless otherwise specified. The Extensograph is an instrument which is commonly used by those skilled in assessing dough rheology. The Extensograph is designed to measure dough extensibility and resistance to stretching. A 150 g sample of proofed dough was placed into the Extensograph molder. The dough sample is then held at 21" C for 15 minutes. The dough sample is then secured with dough clamps. The Extensograph hook then stretches the dough until it breaks. The extensibility of the dough and its resistance to extension were recorded. The area under the Extensograph curve as shown in Figure 12 was then calculated. This number refers to the amount of energy that was required to extend each dough piece to breakage by the Extensograph. The amount of energy is in units of Joules. Figure 8 shows that, in general, the higher the energy required to break the dough, the tougher the product will be. (a) shows that for a given formula, the amount of energy required to break the dough is proportional to the work input during mixing, and thus lower toughness; (b) shows that for a given formula base, the more dough development inhibitor(s) e.g. sugar, fat, inorganic electrolytes, (Salt, SAPP, Soda), high pH are present, the less energy required to break the dough, and thus lower toughness. As shown in Figure 9, the amount of energy required to break dough as measured by the

Extensograph increases as the protein/water ratio of the dough increases even though the degree of development is much lower.

These results illustrate a positive correlation between degree of development and toughness and firmness. The lower degree of development results in a lower degree of toughness and firmness.

Most grains, including cereal grains, oil seeds, etc., are predominantly comprised of protein, starch and fat with starch being the major component of all cereal grains. Tests were conducted to investigate causes of microwave-induced toughening. These tests included solvent testing of dough-based products that were pre-cooked and then reheated in a microwave oven. There were three protein interactions that could cause toughening. Those interactions are covalent bonding, hydrogen bonding, and hydrophobic interaction. In the case of covalent bonding, solubility tests using sodium dodecyl sulfate (SDS) and mercaptoethanol were conducted as well as electrophoresis testing as known in the industry. The solubility tests showed that very little protein was soluble using SDS alone. However, in the presence of SDS plus mercaptoethanol, all protein was solubilized. This indicated that no significant covalent bonding was occurring except for the disulfide bonding that is* characteristic of gluten proteins. This was consistent with the findings reported by Schofield et. al. (1983). It was found that there was no net increase in the number of disulfide bonds as a result of the microwave reheating (Table 1) .

TABLE 1. PROTEIN SOLUBILITY AS A FUNCTION OF MERCAPTOETHANOL CONCENTRATION

Soluble Protein (%)(+S.D.)

Mercaptoethanol Bread Microwave (%) Crumb Reheated

Electrophoresis tests were conducted to determine whether there were shifts in the molecular weight distribution of the gluten proteins. The proteins extracted from microwave reheated bread crumb had the same molecular weight distribution as proteins extracted from conventionally baked, non-reheated bread crumb.

In conclusion, neither the number nor the location of disulfide (covalent) bonds significantly changed as a function of microwave reheating.

To investigate a possible relationship of hydrophobic interactions and toughening or firming tests with several surfactants were conducted. If a surfactant reduced toughening, then it would be sound to conclude that preferential bonding was occurring between the surfactant and the protein rather than protein-protein interaction. The surfactant test indicated a reduction in toughening.

It appears that hydrophobic interaction is the cause of toughening in precooked dough-based products.

In regard to raw dough products which are cooked in the microwave oven, additional tests were conducted to determine the cause of toughening. Because raw dough product has a higher moisture content, there is higher mobility of protein molecules. This higher mobility may lead to even more toughening. As in the case of precooked products, the possible causes of toughening in dough products were also protein-protein interactions. Thus, it was surprisingly found that toughening of precooked and uncooked products was predominantly a protein related phenomenon.

Experiments were performed on doughs having different degrees of dough development. Unexpectedly, it was found that, as the degree of dough development was reduced, the magnitude of toughness and firmness were reduced. The limitation of the degree of dough development minimizes protein-protein interactions and thus reduces the microwave toughening of bread-like products.

The degree of dough development is dependent on the amount of work input during the dough formation and the amount of available water. It is also known that dough can develop somewhat over time without added work. Thus, the degree of dough development can be controlled by changing the amount of work input without changing the dough formula. In addition, the surface area of the flour particle can affect the time required for protein hydration to occur. The amount of flour particle surface area available for hydration is affected by the amount of fat in the dough and the flour particle size.

Other cereal grains, corn for example also contain gluten. However, corn gluten does not display the same ability of wheat gluten to form a protein matrix with the

presence of adequate water. Other cereal grains like corn can be added as a portion of the flour fraction to impede or retard the development of the dough and thereby limit microwave induced toughening. It is preferred for the ' present invention that the flour fraction be at least 50% wheat, more preferably at least 60% and most preferably at least 70% wheat flour.

Firmness may be characterized by the force required to bite through the sample without tearing. The reason that the dough of the present invention does not firm is similar to the explanation for why it does not toughen. Wheat flour particles are primarily composed of gluten and starch. In an underdeveloped system, the flour particles are not completely hydrated. Also, the starch in underdeveloped systems does not have the same opportunity for interaction as in developed systems. Thus, the amount of starch-starch interaction which results in microwave induced firming will be limited.

Insofar as protein-protein interactions account for microwave toughening of bread-like products, such toughening can be reduced by lessening the amount of those interactions. Protein-protein interactions can be inhibited by limiting the degree of gluten development in the dough. A fully hydrated flour particle that does not have a developed gluten matrix does not have a significant amount of protein-protein (gluten-gluten) interaction. Hence, an incompletely developed but fully hydrated product should not be tough after cooking by microwave irradiation.

The present invention is particularly applicable to those bread-like products which, when cooked either by conventional means or microwave radiation, may contain ingredients as described above and additional ingredients as are known in the art. The products herein described in

their uncooked state, may contain ingredients as described above and additional ingredients as are known in the art.

Refrigerated doughs are known in the industry. They 5 are raw or fresh dough stored in a substantially sealed container. When pressurized, the gauge pressure is in the range of betwen about one-half and about 2 atmospheres, preferably about 1 atmosphere. Refrigerated storage temperatures are less than about 5 " C and preferably in IDG tire range of between about 0 ^% C and about 5 ^* C. Storage time? rs typically six to twelve weeks.

Frozen doughs are stored at a temperature of less than 0 C and preferably less than about -10" C.

15

The invention furcher extends to a refrigerated or frozen dough product suitable for reheating or cooking by microwave irradiation, and to an edible product reheated or cooked by microwave irradiation, which products have

20 been produced using any of the methods of this invention. Products may be cooked to a set structure by microwave irradiation and browned or warmed by a consumer.

In one aspect, the doughs of the present invention 25 may be subjected to microwave irradiation to set structure and result in an acceptably textured bread-like product. When the same dough is subjected to conventional thermal baking, too much gas may escape and the product may have an unacceptably high density and low specific volume. 30

Product grain of selected samples were judged by a trained panel. An initial training session was used to familiarize the panelists with the range of products that would be tested. Reference standards were presented in 35 ^' . this- session to train the panelists to recognize the difference between the product attributes that were to be measured. A scale of 1-5 was used to grade the samples. A rating of 5 is the best possible score. Figure 10

illustrates the five samples with their respective grain size score. At each judging session standards were available for comparison. An article by Solle (1972) "A Descriptive System of Bread Scoring" describes the basis for grain judging as used by the panel.

The specific volume of selected samples was measured on a cooked sample at room temperature by rapeseed displacement. This method is well known to those trained in the art.

The grain and appearance of the conventional and microwave cooked product described in Example V is compared in Figure 11. The grain size score for each product is 4 and 3, respectively, while the specific volume of the product cooked in the conventional and microwave oven is 2.7 cm 3/g and 3.4 cm3/g, respectively.

Table 2 contains the specific volume of a typical yeast . leavened dough product baked in both the conventional and microwave oven. In this case, dough sample size was 22 g.

Most underdeveloped doughs result in very unacceptable products when baked in the conventional oven. Under these conditions, gluten has not developed to a high enough degree to entrap gas during the cooking cycle. The structure also sets, a phenomenon which involves the

gelatinization of starch, after most of the gas is lost from the product to the surrounding oven cavity. Thus, the product cooked in the conventional oven has an unacceptable grain size and specific volume. An acceptable bread or biscuit product has a specific volume, at least about 3.0. In contrast, during microwave cooking starch may gelatinize in a short time period. This results in less gas being lost from the product and therefore resulting in a higher specific volume. The entrapped gas also expands as the product cooks. The result is a product with an acceptable grain and appearance as illustrated in Figure 11. It was surprisingly found that an acceptable bread-like product can also be made from an underdeveloped dough containing 100% soft wheat flour. Product grain appeared relatively independent of flour quality type or protein content when an underdeveloped dough was cooked in the microwave oven.

Table 3 contains the specific volume and grain size scores of a lean dough formula as described in Example I mixed for different time periods with the exception that sample size was 250 g. These results show that specific volume is independent of the degree of dough development in this particular dough formula. The large sample size may explain the similiar performances in the Table. Example I mixed for 10 minutes has a specific volume of 3.5 when sample size is 22 g.

Table 3

Conventional Oven Microwave Oven Mix Specific Grain Specific Grain Times Volume Size Score Volume Size Score

2 2.8 cm /g 3 3.6 cm /g 4

6 2.8 cm ³ /g 3 3.6 cm /g 3

3

10 2.9 cm /g 3 3.5 cm /g 2

Following are examples showing effects of some of the manipulations discussed above on reducing toughness and firmness. It should be noted that all the examples describe products containing hard wheat flour (except for Sample H in Example III). The use of hard wheat flour serves as an illustration. A product containing soft wheat flour with a low degree of protein development does not become tough or firm during microwave cooking. The following examples are intended to illustrate aspects of the present invention, and are not to be construed as limiting the invention in any way.

EXAMPLE I

The effects of work input (mix time) on dough development and microwave baking or heating effects were evaluated.

Biscuits (chemically leavened) were prepared in the microwave oven by cooking the biscuits from raw dough, The biscuits had the following formula: ^•

PERCENT BY WEIGHT

INGREDIENTS SAMPLES A AND B Hard Wheat Flour 57.63 Water (added) 32.52 Dextrose 4.04 Fat 2.53

Sodiu Acid Pyrophosphate (SAPP) 1.51

Soda 1.11

Salt 0.66

Total 100.00

The biscuits were made according to the following procedures:

All ingredients were weighed (total 1000 g) and preblended in a Hobart (model # N50) bowl at low speed (#1) for 1.5 minute with dough hook. Molten fat was added during the preblending. Water was added and mixing continued for an additional minute. The mixing speed was changed to #2 and mixing continued for an additional 2 minutes (Sample A) or 10 minutes (Sample B).

The dough was rolled on lightly floured board and cut with an elliptical cutter (6.36 cm x 8.26 cm). The resulting dough pieces 'were each about 0.64 cm thick and weighed 22 g. The dough pieces were proofed for 30 minutes at 32 ^* C and 70% RH on a cookie sheet covered with plastic wrap.

The Extensograph work and photomicroscopy evaluation results obtained are displayed below:

PHOTOMICROSCOPY WORK

(J)

Sample A (2 minute mix) 32 0.9

Sample B (10 minute mix) 42 1.7

The proofed product may be stored by freezing or refrigerating prior to cooking.

The proofed dough pieces were baked by microwaving on high for 25-35 seconds. The microwaved products were then

evaluated by a sensory panel of 8 tasters with the results being tabulated below:

SENSORY SCORE Toughness Firmness

A - 2 minute mix 26 24

B - 10 minute mix 44 37

Sample A was judged to have a less tough and less firm texture than sample B. Sample A also has a lower degree of dough development than sample B as measured by photomicroscopy and rheological methods (Extensograph) .

The following table lists mix times of a relatively lean formula and toughness and firmness as assessed by a trained sensory panel. 2 minutes of mixing is the result of a work input of 57 J/g while 10 minutes of mixing is the result of 180 J/g.

Mix times Toughness Firmness

2 26 24

4 32 26

6 38 31

10 44 37

The formula that was used in this study is the relatively lean formula for Samples A and B. The relationship between work input and the magnitude of toughness and firmness would be different in a richer formula. A richer formula would be more tolerant to mixing, that is, would not become as developed with the same work input. The results described above thus represent the worst case. 10 minutes of mixing as described in Example I represents the amount of work input necessary to achieve a relatively more developed dough. Further mixing would lead to dough breakdown or overdevelopment. The micrograph value for 6 minutes of mixing is 27.

Example II

The effects of available water (flour/water ratio) on dough development and microwave baking or heating were studied.

Biscuits (chemically leavened) were prepared in the microwave oven by baking the biscuits from raw dough. The biscuits had the following formulas:

PERCENT BY WEIGHT

INGREDIENTS Sample C Sample D

Hard Wheat Flou (12% protein) 57.63 59.84

Water (added) 32.52 29.93 Dextrose 4.04 4.20

Fat - 2.53 2.63

SAPP 1.51 1.57

Soda 1.11 1.15

Salt 0.66 0.68

Total 100.00 100.00

Before cooking, the dough was measured for microscopic and Extensograph properties (work) . The photomicroscopy and Extensograph evaluations gave results displayed below:

PHOTOMICROSCOPY WORK

( J)

1.7 2.5

Sample D also has a lower degree of dough development as measured by photomicroscopy than the control (Sample C) .

The biscuits were made according to the procedure described for Sample B in Example I. The baked biscuit from Sample D was judged to have a less tough and less firm texture than that from Sample C. These product biscuits were evaluated for toughness and firmness with the results being tabulated below:

SENSORY SCORE

These results reflect the effect of flour/water ratio in a relatively rich formula as described in Example V. These doughs were mixed for 4 minutes.

Thus, an acceptable product with a relatively rich formula can be prepared if it has a flour/water ratio of less than about 1.8. As mentioned previously, a dough may not form if the flour/water ratio is greater than about 1.8. All dough flour/water ratios described in Table 3 would be classified as underdeveloped as measured by both the Extensograph and photomicroscopy. In a relatively lean formula, an acceptable product, in terms of both toughness and firmness, should have a flour/water ratio of at least about 1.3.

Example III

The effects of flour particle size on microwave- related product qualities were studied. Biscuits (chemically leavened) were prepared in the microwave oven

by cooking the biscuits from raw dough. The biscuits had the following formulas:

PERCENT BY WEIGHT

INGREDIENTS Sample E Sample F

Hard Wheat Flour 57.63

Hard Wheat Flour 57.63

Water (added) 32.52 32.52

Dextrose 4.04 4.04

Fat 2.53 2.53

SAPP 1.51 1.51

Soda 1.11 1.11

Salt 0.66 0.66

Total 100.00 100.00

E = 100% Flour that does not pass through a 145 micron sieve

F = 100% Flour that does not pass through a 107 micron sieve but passes through a 125 micron sieve

The photomicroscopy and Extensograph work results before cooking Samples E and F are displayed below:

PHOTOMICROSCOPY WORK (J)

Sample E 27 1.9 Sample F 47 2.5

The biscuits were made according to the procedure described for Sample B, Example I. Biscuits from Sample E were judged to have a less tough and less firm texture than biscuits from Sample F. The product biscuits were evaluated for •toughness and firmness with the results being tabulated below:

SENSORY SCORE Sample Particle Size Toughness Firmness

E >145 microns 32 18

F 107-125 microns 55 38

The following table contains toughness and firmness of microwave-cooked products with differently sized flours.-

Particle Size Toughness Firmness

> 145 microns 32 18

> 130 microns and < 145 microns 27 18

> 125 microns and < 130 microns 36 26 > 107 microns and < 125 microns 55 38

> 1 micron and < 200 microns 51 41

These samples were prepared as described above in this Example. The described formula is a relatively lean formula. The samples were mixed for 10 minutes. The effect of flour particle size on the rate of protein hydration will be much less in a richer formula. An acceptable product, in terms of both toughness and firmness, can be prepared from a flour with a particle size of greater than 125 microns in a relatively lean formula.

A discussion of flour particle size as a result of milling and thus grain processing can be found in "Wheat Chemistry and Technology" edited by Y. Pomeranz, 1978. A typical size distribution for hard wheat flour particles was determined by passage through successive screens (Rotap) . The following Table shows the resultant data.

This example illustrates that corn flour dough does not exhibit microwave-induced toughness while a wheat flour dough does.

PERCENT BY WEIGHT

INGREDIENTS Sample G Sample H

Hard Wheat Flour 57.63

Corn Flour 50.12

Water (added) 32.52 41.32

Dextrose 4.04 3.51

Fat 2.53 2.20

SAPP 1.51 1.31

Sodium Bicarbonate 1.11 0.97

Salt 0.66 0.57

Total 100.00 100.00

Dough G was made according to the procedure described for Sample B in Example I. Sample H was made according to the same procedure with the following exceptions:

1. The dough was mixed at speed #2 for 4 minutes; and

2. Dough pads were manually formed into 6.35 cm diameter disks having a weight of 35 g.

The product was photomicroscopically evaluated before cooking as displayed below:

PHOTOMICROSCOPY Sample

G 42 H 3

Cooked product from Sample H was judged to have a less tough and less firm texture than that from Sample G. The product from Sample H also had a lower degree of dough development as measured by photomicroscopy than Sample (G).

The evaluations for toughness and firmness are tabulated below:

SENSORY SCORE

Sample Toughness Firmness

G 44 37

H 4 4

EXAMPLE V

The product thus far found to have the best sensory attributes is one which was underdeveloped and chemically leavened. It was prepared from a rich formula and had a high flour/water ratio (1.3) which makes the dough more tolerant to mixing. It may be prepared using a proof/punch/proof processing scheme which appears to establish the most uniform grain in the final product. The initial proof step resulted in an increase in the size of the air cells incorporated into the dough during mixing. The punch step resulted in the subdivision of air cells which reduced their number and size. The final

proof facilitated the expansion of the subdivided air cells. The dough thus contained small, evenly dispersed air cell nucleation sites which expanded during microwave cooking, resulting in a fine and even grained product. This processing scheme may also help reduce the magnitude of sensory-assessed firmness.

It has been found that thin cell walls also reduce firming. Calculations based on theoretical open structure foam show that decreasing the wall thickness reduces the firmness exponentially (Ashby, 1983). Thus, minor changes in cell wall thickness may have a significant effect on product attributes. Cell wall thickness is inversely proportional to the number of air cells per unit volume. Thus, a product with a fine, even grain should be less firm than a product with an large,uneven grain.

Bread loaves (chemically leavened) were prepared in the microwave oven by cooking the loaves from raw dough. The dough had the following formula:

PERCENT BY WEIGHT

INGREDIENTS Sample I

High Gluten Hard Wheat Flour(14% protein) 50.8 Water (added) 25.4

Sucrose 7.9

Fat 7.9

Nonfat Dried Milk 2.78

Sodium Bicarbonate 1.95 Sodium Aluminum Phosphate (SALP) 1.72

Salt 0.79

Sodium Pyrophosphate (SAPP) 0.66

Total 100.00

The loaves were made according to the following procedure:

All ingredients were weighed and each dough was mixed using a one stage mixing process. The dry ingredients- were first added to a 1500 g mixing bowl followed by the simultaneous addition of the molten fat and ambient temperature water. This combination was mixed for 4 minutes in a Hobart, Model N-50, equipped with a dough hook at high speed (#2). It was noted that even 18 minutes of mixing resulted in an acceptable dough.

Proofing was for 60 minutes at 32 ^* C and 70% RH in a bowl covered with plastic wrap. The dough was then punched to 1/2 its proof volume. Dough pieces of 250 g were then molded into loaf pans (12.7 cm x 7.62 cm x 5.08 cm) . The dough was then proofed for an additional 20 minutes.

The proofed product may be stored either frozen or refrigerated prior to cooking.

A typical microwave heating instruction was to microwave on high for 3-3 1/2 minutes. After cooling, the product was cut into 1 cm slices.

This formula provided was the most tender and soft product tested, with the exception of the corn based product. It was also judged to be very underdeveloped.

The above described product was evaluated for toughness and firmness with the results being tabulated below:

SENSORY SCORE

Sample Toughness Firmness

I 14 15

The above described product was also evaluated by photomicroscopy and the Extensograph (work) with the results displayed below:

PHOTOMICROSCOPY WORK

(J)

Sample

I 14 1.8

An underdeveloped dough system may also be preferred for a bread-like product designed for dual oven preparation. This type of product could be cooked in the microwave oven until the structure sets. The microwave cooked product could then be "finished" by conventional baking, frying, etc. The final step would promote the development of product crust and color. However, as discussed previously herein, when baked in a conventional oven a preferred underdeveloped dough system provides inferior results.

EXAMPLE VI

The effects of dough development upon the quality of microwave-heated prebaked products were evaluated.

Samples J and K were prepared as described for Example V (with the exception that a 22g sample was used) . The formula for Samples J and I are identical.

The formula for Sample K is listed below:

Percent by Weight Ingredients Sample K

High gluten hard wheat flour 55.2

Water (added) 27.6

Sucrose 8.6

Nonfat Dried Milk 3.0

Soda 2.1 SALP 1.9

Salt 0.9

SAPP 0.7

100 . 0

Dough samples were stored at 4.4" C and then conventionally baked under the following conditions: 232.2' C on a lightly greased pan for 10 minutes. The products were then cooled to room temperature. Samples were subsequently reheated in the microwave oven at high power for 15 seconds. All crust was removed from the samples prior to assessment using the sensory and photomicroscopy methods as described previously.

SENSORY SCORE

The Extensograph work value was also measured for the above described biscuits with the results displayed below:

Sample Work ±

J 1.8

K 3.4

These results indicate that as the degree of dough development is increased, as measured by the Extensograph work value, the toughness and firmness of a prebaked product is also increased.

The following references are incorporated by reference herein for the reasons cited.

References Cited

U.S. Patent Documents

Patent Date Inventor

4463020 07-31-84 Ottenberg, R. 4560559 12-24-85 Ottenberg, R.

OTHER PUBLICATIONS

Anonymous, (1987) "Lot Of Work And Research Went Into Zappetites Debut" World Food & Drink Report, October 8

Ashby, M.F., (1983) "The Mechanical Properties of Cellular Solids" Metallurgical Transaction A, 14A(9):1755

Hoseney, R. Carl, (1986) "Principles of Cereal Science and Technology" American Association of Cereal Chemists, Inc. St. Paul, MN.

Kimbrell, W. (1987) "Microwave Ovens Provide New

Opportunities for Bakery Companies" Bakery Production and Marketing, 22(11) :19

Moore, K. (1979) "Microwave Pizza Bows in Test Market; New Protein System Makes Crispy Crust" Food Product Development, 13 (10):20

Moskowitz, H. R. (1983) "Product Testing and Evaluation of Foods" Food & Nutrition Press, ^' estport, CT.

Pomeranz, Y. (Ed.) (1978) "Wheat Chemistry and Technology" American Association of Cereal Chemists, Inc. St. Paul, MN.

Solle, H. (1972) "A Descriptive System of Bread Scoring" Bakers Digest, 46:55

Schofield, J. D., Bottomley, R. C. , Timms, M. F., and Booth, M. R. (1983) "The effect of heat on wheat gluten and the involvement of sulphydryl-disulphide interchange reactions" J. Cereal Sci., 1:241

Changes may be made in the parts, elements and assemblies described herein or in the steps or the sequence of steps of the method described herein without departing from the concept and scope of the invention as defined in the following claims.