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The present invention relates to a process for microwave-induced food browning, and to a food product. Using principles of food science and, more specifically, the principles of food browning chemistry, a browning system has been achieved that may be used to brown select regions of foods upon exposure to microwave radiation. Further, the invention includes a process for making a food product using computer, food, and color science.
A major part of the appetizing appearance of conventionally heated foods is imparted by brown colors developed on their surfaces during preparation. Consumers have come to expect this appearance and consider it desirable in a variety of food products including meat, cheese, and cereal grain based products. It is not usually difficult to obtain a browned appearance using conventional cooking because the reactions leading to brown colors will proceed for the components comprising the surface of most foods under conventional baking conditions. However, it has been very difficult to obtain brown colors on the surfaces of foods prepared in microwave ovens without using browning devices.
Reasons why surfaces of microwave prepared products do not brown have been suggested (see for example, D.C.T. Pei, Baker's Digest, February 1982). This reference states that the heat in a conventional oven is transmitted from the oven environment to the food surface via convection and transmitted from the surface to the interior of the product via conduction. This process of heat transfer enables the food surface to dehydrate and rise above the boiling point of water by the end of the conventional bake time. Microwaves, however, penetrate the surface of the product and directly heat the interior of the product. This induces moisture transfer to the surface. Evaporation of the moisture from the surface to the microwave oven environment usually restricts the surface temperature to a maximum of about the boiling point of water during the microwave bake time. The resultant surface temperature is too low to enable the browning reactions to proceed at the necessary rate with the browning reactants inherent to the product surface. In addition to the depressed rate of microwave browning versus conventional browning due to the temperature conditions, microwave preparation times are generally much shorter than conventional preparation times. Therefore, according to the aforementioned reference, the surface conditions and preparation times, resulting from the basic differences in heat transfer mechanisms between microwave and conventional heating, create a very difficult problem for those desiring to effect browning in a microwave oven.
Generally, the solutions to microwave browning can be divided into the following categories: packaging aided, cosmetic, and reactive coating approaches. The first approach involves the use of microwave susceptors which heat to temperatures exceeding the boiling point of water and brown surfaces in close proximity or direct contact (see for example, U.S. Pat. No. 4,266,108). Limitations of commercially available susceptors include the requirement of close proximity or direct contact, their generally uncontrolled temperature profile, and their generally high cost. The second approach is cosmetic and includes various surface applied formulations that are brown prior to application (U.S. Pat. No. 4,640,837, and U.S. patent application Ser. No. 251,035 Zimmerman, filed on Sept. 26, 1988, now abandoned). The third approach involves coating the surface with a formula that will react to yield a brown color at the surface conditions described above. Two such variations of this approach are described in U.S. Pat. Nos. 4,735,812 and 4,448,791.
The disclosure in assignee's United States patent application for an invention relating to "Color System and Method of Use on Foods" to Ernst Graf, et al., filed contemporaneously herewith, is incorporated herein by reference.
A discussion of microwave heating can be found in U.S. patent application Ser. No. 085,125 to Pesheck, et, filed on Aug. 13, 1987, now U.S. Pat. No. 5,008,507.
The success of a product approach to browning requires control over the rate of the browning reaction. During the shelf life of a product, the rate of browning should be controlled or the product may brown prior to preparation by the consumer. This is usually unacceptable to the consumer. Then, on exposure to a microwave field, the rate should be sufficiently high to brown the product during the short preparation times generally encountered with microwave products.
The invention described herein is primarily based on the chemistry of Maillard browning. Non-enzymatic browning of this type is well characterized, the literature on the subject is extensive and it i the most common form of browning in heated food systems.
There are many reviews of Maillard browning and associated reactions (e.g., Carbohydrates, In: Food Chemistry, H. D. Belitz and W. Grosch, Chapter 4, second edition, 1987, this reference is incorporated by reference herein). Although the myriad of individual reactions leading to the development of the brown melanoidin polymers has been extensively studied, reactions after the initial few steps are not well characterized. This complex series of reactions may be divided into three major categories: the initial condensation of the amine and the carbonyl, the formation of colorless intermediates, and the formation of colored compounds (e.g., the melanoidin polymers). FIG. 4 illustrates this highly simplified reaction scheme.
Promotion of browning in a microwave oven is a difficult problem. Initially, attempts were made to develop a microwave Maillard browning system capable of browning refrigerated doughs (e.g., Pillsbury refrigerated buttermilk biscuits). However, as mentioned earlier, there exist several inherent problems with respect to accomplishing this task (e.g., short cook time, etc.). One browning system examined employed pectin gels as the browning agent carrier. Although the gel system did brown microwave-prepared biscuit dough samples to a limited extent, the prepared biscuit dough samples in this study were found to have less than optimal crumb structure and surface texture.
Other food approved carrier systems were used in an attempt to improve the surface textural properties of the microwave prepared biscuit samples. Shortening was found to be preferred due to its ease of manipulation and broad product system applicability. Biscuit dough samples were coated with a mixture of reducing sugar, soy protein, and shortening; placed in a microwave oven; and cooked for a time sufficient to brown the surface. Unfortunately, it was observed that during the microwave cooking cycle, the biscuit samples became very dehydrated and overdone. In a further attempt to improve the textural properties of the biscuit samples, the samples were placed into a sealed plastic pouch prior to microwave treatment. Surprisingly, the pouched biscuit samples not only remained moist and soft, but also browned to a much greater extent in a much shorter time, when compared to biscuit samples prepared without a pouch.
The disclosure in U.S. patent application Ser. No. 213,013 to K. Anderson, et al., filed on June 29, 1988, now U.S. Pat. No. 4,842,876 is incorporated herein by reference.
These observations led to the conclusion that steam-containing packaging, and possibly other means of enhancing browning, in conjunction with microwave browning ingredient formulation, could be used as a means to control the browning reaction in such a manner as to allow product browning to coincide with product textural development.
The literature (e.g., Color Science Concepts and Methods, Quantitative Data and Formulae, G. Wyszecki and W. S. Stiles, John Wiley and Sons, Inc. 1982, this reference is incorporated by reference herein), indicates that the measurement of color is a very complicated subject.
A Pacific Scientific Gardner XL-20 Colorimeter and Milton Roy Visible Spectrophotometer were used throughout the research for this invention. The following discussion of the primary responses is based upon the instruction manual for the Gardner instrument (Gardner Laboratory Inc., 5521 Landy Lane, Bethesda, Md.).
Three responses were recorded for a routine color measurement. L corresponds to a scale defining a range from black (L=0) to white (L=100). Another value, a.sub.L, defines the range from green (a.sub.L =-40) to red (a.sub.L =+40). Finally, b.sub.L defines a range from blue (b.sub.L =-40) to yellow (b.sub.L =+40). Subsequently, zero values for a.sub.L pl and b.sub.L correspond to white, grey, or black depending on the L value. Hue (type of color: orange, blue, etc.) and chroma (color intensity: vivid or dull) are defined by a.sub.L and b.sub.L. FIG. 1, which is from the Gardner manual, illustrates the three dimensional space describing this system.
The L a.sub.L b.sub.L system is only one system of describing colors. Others include the L a* b* system and the Y x' y' system. Equations are available to convert from one system to another.
The L* a* b* system (FIG. 2) is very similar to the L a.sub.L b.sub.L system in that the same relative scales apply (L* is white to black, a* is green to red, and b* is blue to yellow). The Y x' y' system (FIG. 3), however, adopts a somewhat different form. The x' and y' coordinates define a point on an irregular portion of an x' y' plane that is composed of various colors. The perimeter of this area is graduated in nanometers corresponding to the wavelength of the corresponding hue. Both hue and chroma are defined by x' and y'. Y, a scale running perpendicular to x' and y', is a measure of lightness, somewhat analogous to L or L*.