Process for producing a freeze-thaw stable microwaveable pre-fried foodstuff

Batter coated, pre-fried microwaveable foodstuffs characterized by improved freeze/thaw stability are provided by employing as a dry predust, prior to batter application, a composition comprising greater than 20%, by weight, of an hydroxypropylmethyl cellulose ether having a methoxyl content greater than 22% and an hydroxypropyl content of at least 5%, by weight.

BACKGROUND OF THE INVENTION 
This invention relates to the use of a dry predust comprising an effective 
amount of a hydroxypropylmethyl cellulose derivative and the improved 
freeze/thaw stability provided to breaded and non-breaded convenience 
foodstuffs which are coated with the predust prior to the application of 
an aqueous batter mix, pre-fried, frozen, and ultimately cooked in a 
microwave oven. 
Batter coated fried foods have a broad appeal. Among the most popular 
batter coated foods are fried chicken and fish as well as other meat 
products, however, a wide variety of other foods, such as vegetables, and 
even fruits can be coated and then cooked by frying. Deep-fried food 
batters, whether for use with fresh or frozen foods, consist primarily of 
farinaceous materials such as starches and/or flours along with other 
optional ingredients such as egg solids, baking powder, cream of tartar, 
preservatives, seasonings, coloring matter and milk solids. These mixtures 
are combined with water so as to obtain a desired coating viscosity 
whereupon they are applied to the food ordinarily by means of a dip, spray 
or cascade technique. Before frying, the batter coated food may be coated 
with a breading such as corn meal, cracker crumbs, bread crumbs or the 
like if so desired. 
Prior to batter application, a foodpiece often will undergo a predusting 
step. Predusting has primarily been performed in order to create a surface 
which is more conducive to the physical adhesion of a wet batter. Applying 
a predust has always been a challenge in the coating industry because of 
the need to apply a thin, uniform layer. Where absent, the batter will not 
adhere evenly to the foodpiece. Similarly, the batter is unable to hydrate 
large lumps of the predust resulting in batter film break away causing 
voids in these areas. 
Typical predust materials have included farinaceous-based materials such as 
very fine cereal flour, a flour combination, starch or the dry batter 
itself. 
In order to obtain a fried product, a batter-coated food piece must be 
cooked in the presence of frying oils or melted fat at elevated 
temperatures. Foods thus prepared may be immediately consumed or may be 
packaged and quick frozen so that the ultimate consumer may prepare the 
foodstuff merely by reheating. In many cases, the food may only receive a 
partial cooking or "pre-frying" at this point, whereupon it is packaged 
and quick frozen with the cooking of the pre-fried frozen foodstuff 
completed at a later time by the consumer. 
A growing trend to spend less time on food preparation has lead to a great 
demand for time-saving "ready-to-heat" frozen food products now on the 
market. The wide use of microwave ovens, now a standard feature in many 
homes and restaurants, has further led to the reduction in cooking time 
spent by consumers. Many products cooked by means of microwaving or baking 
are indistinguishable from each other. Unfortunately, frozen prefried 
foodstuffs have shown strong differences when comparisons are made between 
final products which have been fried, baked and most particularly 
microwaved. Microwaved pre-fried products have tended to be undesirably 
soggy, and as such have not been recommended for microwaving. 
It had generally been accepted that frozen pre-fried products which were 
subsequently cooked by microwave radiation would be inferior in crispness 
to those products cooked in an oven. There are at least two reasons for 
which the inferiority of the microwaved products has been attributed. 
Firstly, the transfer of heat to a food piece during frying or baking is 
opposite that for microwaving. Microwave radiation cooks food pieces by 
heating the water contained therein which in turn acts to cook the entire 
piece. For this reason, it is often explained that microwave radiation 
cooks products from the interior outwards, resulting in the coating of a 
pre-fried piece being the last part to be cooked. During microwaving, the 
moisture in the food piece is driven outwards towards the surface, which 
can cause the food piece to become soggy. During frying or baking, on the 
other hand, the outer coating receives the most exposure to cooking 
temperatures while the interior receives the least, thus providing a 
crispy outer coating. 
Secondly, food pieces which are cooked in the presence of hot fat or oil by 
frying are usually cooked at temperatures of at least 350.degree. F. 
(176.degree. C.) to about 425.degree. F. (218.degree. C.) preferably 
375.degree.-395.degree. F. (190.degree.-202.degree. C.) which are 
sufficiently high to fry the food piece. It is recommended that pre-fried 
food pieces be oven baked at comparable frying temperatures so that 
residual oil, contained on the surface of all pre-fried foods, will 
continue to cook the food piece. Microwave ovens, on the other hand, are 
limited to cooking temperatures such that the residual oil retained on a 
food piece after pre-frying will not continue to cook the piece. 
In addition to crispness, another desirable property of a microwaved 
pre-fried product is an undifferentiable interface between the batter 
coating and the food piece. The crispness of a food piece becomes 
overshadowed as the interface worsens by going from thin and dry to 
floury, bready and finally to pasty. Weepage is also an important concern. 
Fluid migration during freezing or microwaving due to gravity may result 
in the pooling of some fluid on the underface of the product resulting in 
a product which is soggy beneath a crispy coating. 
U.S. Pat. Nos. 4,529,607 and 4,595,597 (issued on July 16, 1985 and June 
17, 1986 respectively to J. Lenchin et al.) disclose a batter mix 
formulation for coating pre-fried microwavable foodstuffs. The batter mix, 
which advantageously employs about 50 to 80% of a high amylose flour, 
based on batter mix solids, provides a crispy pre-fried foodstuff which 
remains crispy after freezing and subsequent subjection to microwave 
cooking. The disclosures of the above references are hereby incorporated 
herein by reference. 
Most frozen pre-fried, convenience food products are produced and packaged 
to have an optimum shelf life of about three months. During this time 
period, it is not uncommon for storage temperatures to fluctuate causing 
the frozen products to undergo one or more partial or complete freeze/thaw 
cycles during transportation and storage. Due to the deleterious effect 
repeated freezing and thawing cycles has on a frozen pre-fried foodpiece 
causing a significant exudation of moisture therefrom, the freeze/thaw 
stability of a product is a serious concern in the frozen food industry. 
Freeze/thaw stability of a pre-fried foodpiece is especially important for 
products ultimately reconstituted by microwave cooking. As discussed 
above, the high cooking temperatures of oven reconstitution enables a 
significant amount of moisture present on the exterior of a foodpiece 
which could result in a soggy product to be removed. Microwave cooking, on 
the other hand, is conducted at a temperature which does not allow for the 
easy removal of excess water pooled on the underface of the product. 
Frozen pre-fried chicken pieces prepared employing a conventional predust 
and the batter mix of J. Lenchin et al. (described above) are unable to 
withstand one freeze/thaw cycle with the pre-fried coating exhibiting a 
poor interface with severe weepage. 
There is therefore a need in the convenience food industry for a method of 
providing freeze/thaw stable microwavable pre-fried foodstuffs. The 
ability to provide a microwaveable pre-fried chicken piece which is able 
to withstand three freeze/thaw cycles would be recognized in the 
convenience food industry as a significant improvement. 
Accordingly, it is an object of the present invention to provide a dry 
predust which is capable of improving the shelf-stability of a 
microwaveable pre-fried foodstuff. 
It is further an object to provide a method for preparing a microwaveable 
pre-fried foodstuff which is capable of withstanding repeated freeze/thaw 
cycles. 
SUMMARY OF THE INVENTION 
The present invention provides an improved process for preparing a 
freeze/thaw stable batter coated, pre-fried microwaveable foodstuff. By 
applying a batter formulation capable of providing a pre-fried foodstuff 
with acceptable crispness after subjection to microwave cooking and, prior 
to batter application, applying a dry predust comprising greater than 20% 
by weight of an hydroxypropylmethyl cellulose ether having a methoxyl 
content greater than 22% and a hydroxypropyl content of at least 5%, an 
acceptable microwaveable pre-fried foodstuff is provided which is capable 
of withstanding repeated freeze/thaw cycles. 
The predust preferably comprises from about 25-100% of an 
hydroxypropylmethyl cellulose ether having a methoxyl content of from 
27-31% and an hydroxypropyl content of from 6-12%, and 0-75% of an 
inhibited oxidized corn starch. 
The batter formulation preferably employed is a farinaceous-based aqueous 
batter slurry comprising about 50-80%, based on batter mix solids, of a 
high amylose flour containing at least 50% amylose, based on the starch 
content of the flour.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The hydroxypropylmethyl cellulose ethers useful herein are those cellulose 
ethers having a methoxyl content greater than 22%, preferably 27-31% and 
an hydroxypropyl content of at least 5%, preferably 6-12%. The 2% aqueous 
solution viscosity of the useful cellulose ether derivatives is preferably 
in the range of 3200-5600 cps. The Dow Chemical Company of Midland, Mich. 
produces a variety of cellulose ether derivatives. Those particularly 
useful herein are sold under the tradename Methocel E4M and Methocel F4M. 
Biddle Sawyer of New York City also produces useful cellulose derivatives 
with the product referred to as Metolose 60SH-4000 being particularly 
useful herein. 
The hydroxypropylmethyl cellulose ethers useful herein may be employed as 
the sole predust component or may be employed in the form of a blend in an 
amount greater than 20% by weight of the total predust composition with 
one or more suitable materials which do not deleteriously effect the 
freeze/thaw stability and thus the ultimate texture of the pre-fried 
foodstuff after microwaving. Suitable materials useful in the predust 
blend include, for example, various modified and unmodified flours and 
starches, seasonings and flavorants. While unmodified corn flour and corn 
starch are useful in the blend, a particularly useful modified starch is a 
sodium hypochlorite-oxidized, adipic-acetic inhibited corn starch 
obtainable as BATTER BIND.RTM.S from National Starch and Chemical Corp. 
For economic reasons, a predust composition containing as little as 25% of 
an appropriate hydroxypropylmethyl cellulose ether which provides a 
microwaveable pre-fried food piece with acceptable freeze/thaw stability 
is preferably employed. 
In order to obtain a freeze/thaw stable pre-fried microwaveable foodstuff 
of the present invention, any suitable batter formulation capable of 
providing a pre-fried foodstuff with acceptable crispness after subjection 
to microwave cooking may be applied to the foodpiece subsequent to predust 
application. The high amylose flour-containing batters described in U.S. 
Pat. Nos. 4,529,607 and 4,595,597 (discussed above) are preferably 
employed. 
Suitable high amylose flours useful in the batter formulation are those 
flours with an amylose content of at least 50%, preferably about 70%, 
based on the total starch content of the flour. Although high amylose corn 
flour is preferably employed, high amylose flours derived from sources 
other than corn which contain concentrations of at least 50% amylose may 
be employed with similar results expected. Suitable flours would include 
those flours produced from any high amylose plant species of, for example, 
wheat, rice, rye, potato, oats, barley, pea, and millet. 
Modified or unmodified high amylose flour or combinations of both may be 
employed in the batter formulation. Typical flour modifications include 
treatment with heat and/or acids or with oxidizing agents. The flour may 
also be chemically derivatized by means of esterification or 
etherification reactions. Preferred modified flours useful herein include 
acid converted dextrins of high amylose corn flour prepared by 
conventional techniques known in the art and described in the "Handbook of 
Water-Soluble Gums and Resins", Robert L. Davidson, editor, McGraw-Hill 
Book Co., New York (1980) pp. 34-36. It has been found that such 
dextrinized flour, preferably uncharred after dextrinization, when used in 
concentrations of about 1 part dextrin to about 4 to 6 parts, preferably 5 
parts, of unmodified high amylose flour provide added crispness and 
improved interface to microwaved pre-fried foodstuffs. In higher 
concentrations, the dextrinized flour may cause unacceptable lacing 
resulting in crumbly coatings as well as cause the resultant foodstuff to 
be unacceptably dark in color. Moreover, when using the higher 
concentrations, it becomes increasingly difficult to achieve adequate pick 
up of the batter onto a food piece. 
The high amylose flour-containing batter mix useful herein comprises about 
50 to 80%, preferably 60-70%, of the high amylose flour, based on dry 
solids. Any suitable farinaceous material may be employed in conjunction 
with the high amylose flour. Suitable materials include starches derived 
from such sources as corn, sago, wheat, rice, potato, sweet potato, waxy 
maize, high amylose corn, tapioca, sorghum, or waxy sorghum starch, as 
well as components from these starches, viz, emylose and amylopectin. 
Derivatives of the above including esterified, etherified, inhibited, and 
converted starches are also applicable herein. Furthermore, flours derived 
from such sources as, for example, corn, wheat, or potato are also 
suitable in the batter compositions. 
In the preparation of the batter, the practitioner need merely prepare an 
aqueous slurry of the dry mix. The slurry will ordinarily contain about 
100 parts by weight of dry mix per 125 to 175 parts of water. The precise 
dry mix to water ratio will depend, of course, upon the type of foodstuff 
being prepared, the manner in which the batter mix is to be applied, and 
the particular mix composition being utilized. It is unnecessary to heat 
the batter mix slurry prior to its application of the foodstuff. The 
practitioner may add such seasoning, extenders, preservatives, or food 
colors to the batter mix slurry as are desired. The slurry is then kept 
under agitation prior to its application to the foodstuff so as to prevent 
settling from occurring. 
This invention encompasses the preparation of batter-coated foodstuffs 
which do not contain breading, referred to in the art as having a tempura 
type coating. The process of applying breading to batter coated foodstuffs 
is also encompassed, herein referred to as single-pass coating. Common 
breading mixtures employed in such single-pass applications include bread 
crumbs, corn meal, cracker crumbs and the like. 
In the process of the present invention, a thin uniform coating of the dry 
predust composition is applied to the food piece which may be either 
fresh, par-boiled, or frozen, with residual predust being removed by 
shaking or agitation. 
In order to assure adequate pick-up, some food pieces with little or no 
surface moisture may be dipped in water prior to the predust application 
step. 
After predusting, a suitable aqueous batter slurry is applied to the food 
piece by any convenient procedure such as by dipping, spraying or 
cascading. 
After draining off the excess batter, breading may optionally be applied 
before the foodstuff is pre-fried. The foodstuff need only be fried for a 
period of about 0.5-1.5 minutes depending on the foodstuff, preferably 
0.5-1.0 minutes. 
Thereafter the foodstuff is frozen to a temperature preferably between 0 
and 15.degree. F. (-17.degree. to -9.5.degree. C.) 
Pre-fried foodstuffs which will benefit from the present invention include 
fish, shell fish, poultry, meat and vegetable products including fish 
sticks, fish fillets, fish steaks, whole fish, scallops, oysters, clams, 
shrimp, lobster parts, chicken and turkey parts, veal, beef, pork, egg 
plant, and onion rings. 
The examples which follow will further illustrate the embodiment of the 
present invention. In the examples, all parts are given by weight and all 
temperatures are given in both degrees Fahrenheit and Celsius. 
Unless otherwise indicated, the following severe test procedure was used in 
order to evaluate the ability of various predust compositions to provide 
freeze/thaw stability to a microwaveable pre-fried foodstuff. 
Chicken thighs are par-boiled for twenty minutes. After cooling the thighs 
to a temperature at which they can be easily handled, the chicken is 
deskinned, dunked in ambient temperature water and thereafter the predust 
to be evaluated is evenly applied to each piece with any excess predust 
shaken free. The pieces are then dipped in an aqueous batter slurry 
allowing all the excess batter to run off. The batter coated pieces are 
pre-fried in oil at 385.degree. F. (196.degree. C.) for 1 minute, drained, 
placed in individual aluminum containers, covered and then frozen in a 
freezer maintained at 0.degree. F. (-17.degree. C.) for a minimum of about 
12 hours. After completion of the initial freezing period, the chicken 
pieces are thawed at room temperature for four hours and then refrozen, 
thus completing one freeze/thaw cycle. Freeze periods (at least 12 hours) 
and thaw periods (4 hours) are repeated for 5 cycles. After each cycle, 
one frozen sample is microwaved for about 1.5-2 minutes until an internal 
temperature of 150.degree. F. (66.degree. C.) is attained. Each sample is 
allowed to stand for 1 minute prior to being evaluated. An acceptable 
product has an interface which is preferably floury or bready and not 
pasty. An acceptable product also has a coating which is thin and which 
offers resistance upon application of pressure as opposed to being thick 
and wet to the touch and which leaves an impression where pressure is 
applied. The test is continued until an unacceptable product is obtained. 
The number of successful cycles completed before the predust fails is 
recorded for each sample. It is to be understood that this test is a 
relative indication of stability. 
EXAMPLE 1 
This example illustrates the improved freeze/thaw stability of a 
microwaveable pre-fried foodpiece employing the predust of the present 
invention. 
The predusts evaluated contained 0-100% of an hydroxypropylmethyl cellulose 
(HPMC) having an average methoxyl content of 29% and an average 
hydroxypropyl content of 10%, and 100-0% of an oxidized inhibited corn 
starch. 
A batter formulation capable of providing an acceptably crisp texture to a 
pre-fried foodstuff which is frozen and subsequently microwaved was 
prepared which contained the following ingredients. 
______________________________________ 
TS IN BATTER 
INGREDIENTS RECIPE 
______________________________________ 
High Amylose Corn Flour* 
50 
Dextrinized High Amylose Corn Flour** 
10 
Wheat Flour 38 
Acid Sodium Aluminum Phosphate 
1 
Sodium Bicarbonate 1 
Water 160 
______________________________________ 
*The flour contained approximately 70% amylose. 
**Acid converted dextrin of a flour containing approximately 70% amylose. 
Chicken thighs were prepared as described above. The texture of the samples 
was evaluated after microwaving subsequent to undergoing repeated 
freeze/thaw cycles with the results indicated in Table I. 
TABLE I 
______________________________________ 
Predust Composition Freeze/Thaw 
% HPMC* % Starch** 
Cycles 
______________________________________ 
0 100 0 
5 95 0 
15 85 0 
20 80 2 
25 75 4 
50 50 4 
75 25 4 
100 0 4 
______________________________________ 
*DOW METHOCEL E4M (obtained from the Dow Chemical Company) 
**BATTER BIND .RTM.S (obtainable from National Starch and Chemical Corp.) 
The results show that the hydroxypropylmethyl cellulose ether, when present 
in the predust composition in an amount greater than 20%, provided 
microwaveable pre-fried foodstuffs which were capable of withstanding 
repeated freeze/thaw cycles. No significant improvement was provided when 
amounts greater than about 25% of the hydroxypropylmethyl cellulose was 
employed. 
EXAMPLE 2 
This example illustrates the effect of employing other cellulose 
derivatives in a predust composition in a 25% concentration and their 
effect on providing freeze/thaw stability to a microwaveable pre-fried 
foodstuff. 
Chicken thighs were prepared as described above. The texture of the samples 
was evaluated after microwaving subsequent to undergoing repeated 
freeze/thaw cycles with the results indicated in Table II. 
TABLE II 
______________________________________ 
Freeze/ 
Thaw 
Cellulose Derivative Employed in Predust* 
Cycles 
______________________________________ 
Dow Methocel E4M 5 
(HMPC containing 29% methoxyl, 10% hydroxypropyl) 
Dow Methocel F4M 3 
(HPMC containing 29% methoxyl, 6% hydroxypropyl) 
Biddle Sawyer Metolose 60SH-4000 
5 
(HPMC containing 29% methoxyl, 10% hydroxypropyl) 
Dow Methocel K4M** 2 
(HPMC containing 22% methoxyl, 8% hydroxypropyl) 
Dow Methocel A4M** 2 
(methylcellulose) 
Hercules Klucel HF** 0 
(hydroxypropyl cellulose) 
Hercules Klucel GF** 0 
(hydroxypropyl cellulose) 
Hercules CMC 7H4XF** 2 
(carboxymethyl cellulose) 
Hercules CMC 7HXF** 0 
(carboxymethyl cellulose) 
______________________________________ 
*Present in a concentration of 25% with the remaining 75% comprising 
BATTER BIND .RTM.S. 
**Comparative 
The results show that a predust containing the hydroxypropyl cellulose 
ether derivatives having an average methoxyl content of about 29% provided 
superior freeze/thaw stability to microwaveable pre-fried foodstuffs in 
comparison to predusts containing other cellulose derivatives including an 
hydroxypropylmethyl cellulose ether having a lower methoxyl content. 
EXAMPLE 3 
This example illustrates the use of a predust composition containing a 
useful hydroxypropylmethyl cellulose in a blend with other optional 
materials. 
Chicken thighs were prepared as described above. The texture of the samples 
was evaluated after microwaving subsequent to undergoing repeated 
freeze/thaw cycles. The results may be found in Table III. 
TABLE III 
______________________________________ 
Freeze/Thaw 
HPMC* Predust Blend Cycles 
______________________________________ 
25% HPMC and 75% BATTERBIND .RTM.S 
4 
25% HPMC and 75% Corn Flour 
4 
25% HPMC and 75% Corn Starch 
3 
25% HPMC and 75% Wheat Flour 
0 
______________________________________ 
*Dow Methocel E4M 
The results show that corn flour and corn starch are also useful in a 
predust blend with the hydroxypropylmethyl cellulose. Wheat flour present 
in a high level in the blend had a deleterious effect on the freeze/thaw 
stability provided by the cellulose derivative. 
EXAMPLE 4 
This example illustrates that in order to provide acceptable freeze/thaw 
stable microwaveable products, the predust of the present invention must 
be employed in combination with a batter formulation capable of providing 
acceptable crispness to a pre-fried foodstuff after subjection to 
microwave cooking. 
A predust containing 25% METHOCEL E4M and 75% BATTER BIND.RTM.S was applied 
to chicken thighs. Thereafter the pieces were coated with an aqueous 
batter mix slurry and evaluated as described above. The batter mix 
compositions and the freeze/thaw results may be found in Table IV. 
TABLE IV 
______________________________________ 
TS BATTER 
MIX RECIPE 
INGREDIENTS A B C D 
______________________________________ 
High Amylose Corn Flour.sup.a 
50 0 0 0 
Dextrinized High Amylose 
10 0 0 0 
Corn Flour.sup.b 
Wheat Flour 38 97 0 47 
Corn Flour 0 0 97 50 
Acid Sodium Aluminum Phosphate 
1 1.5 1.5 1.5 
Sodium Bicarbonate 1 1.5 1.5 1.5 
Water 160 160 160 160 
Texture After 0 F/T Cycles 
good poor fair.sup.c 
poor 
Texture After 1 F/T Cycle 
good poor poor poor 
______________________________________ 
.sup.a The flour contained approximately 70% amylose. 
.sup.b Acid converted dextrin of a flour containing approximately 70% 
amylose. 
.sup.c The sample had a crisp surface texture with an unacceptable pasty 
interface. 
Summarizing, the present invention provides a process for preparing a 
freeze/thaw stable batter coated, pre-fried microwaveable foodstuff. 
Variations may be made in proportions, procedures, and materials without 
departing from the scope of this invention which is defined by the 
following claims.