Compositions and Methods for Inhibiting Browning of Processed Produce

FIGS. 1-4 are photographs illustrating the comparison of the test samples of Examples IV-VII, respectively.

In general, the present invention is directed to methods for treating produce pieces to minimize browning upon subsequent processing, handling and storage, as described above, wherein the produce pieces are immersed in an aqueous solution containing a sulfiting agent followed by treatment with an aqueous solution containing cysteine, preferably prior to processing which involves dehydration. Alternatively, the produce pieces are treated with an aqueous solution containing discoloration inhibitors including synergistic amounts of cysteine and sulfite effective to prevent browning of the produce.

In accordance with the present invention, the method for treating produce to minimize browning upon subsequent processing, handling, and storage involves exposing produce to a discoloration inhibitor selected from the group consisting of a source of available cysteine, and a mixture consisting of a source of available cysteine and a sulfiting agent, preferably wherein the step of exposing the produce to the discoloration inhibitor is accomplished in a step selected from the group of steps consisting of immersing the produce in a solution containing the discoloration inhibitor and spraying the produce with the solution. For purposes of the present invention the solution includes discoloration inhibitors preferably selected from the group of consisting of an amount up to about 0.5% cysteine and more preferably 0.2-0.5% cysteine; and an amount up to about 0.5% cysteine and an amount up to about 0.1% sulfiting agent and more preferably 0.2-0.5% cysteine and 0.50-0.1% sulfiting agent although the solution may contain discoloration inhibitors in an amount up to about 0.1% sulfiting agent, and an amount up to about 0.5% sodium acid pyrophosphate. More preferred are solutions containing discoloration inhibitors selected from the group consisting of 0.2-0.5% cysteine; 0.2-0.5% cysteine and 0.05- 0.1% sulfiting agent; 0.025-0.5% cysteine, 0.025-0.5% sodium acid pyrophosphate 0.05-0.1% sulfiting agent. Subsequently the produce treated with the previously mentioned discoloration inhibitors may be processed by a procedure selected from the group consisting of dehydrating, cooking, canning, aseptic, refrigerating and freezing.

In the embodiments where potatoes are sprayed aqueous solutions containing cysteine, and cysteine with sodium acid pyrophosphate, and cysteine with sodium acid pyrophosphate, and a sulfiting agent, the aqueous solution preferably include an amount of cysteine to result in a cysteine content of less than 0.1% in the dry product, contains cysteine and sodium acid pyrophosphate to result in a cysteine content of less than 0.1% and a sodium acid pyrophosphate content less than 0.2% in the dry product; or contains cysteine, sodium acid pyrophosphate, and a sulfiting agent to result in a cysteine content of less than 0.1%, a sodium acid pyrophosphate content of less than 0.2% and a sulfite content (as sulfur dioxide) of less than 0.003% in the dry product.

Preferred products produced in accordance with the present invention include potato products containing cysteine provided by extraneously added cysteine and less than about 30 ppm sulfur dioxide exhibiting a color measured by an Agtron reflectance meter rating of above 40, preferably wherein the Agtron reflectance rating is above 50, and the sulfur dioxide is present in amounts less than 10 ppm, and most preferably wherein the products contain essentially no sulfur dioxide. Preferred potato products are selected from the group consisting of dehydrated potato pieces and dehydrated mashed potato products wherein the dehydrated mashed potato products are selected from the group consisting of dehydrated potato granules, dehydrated potato flakes and agglomerates of dehydrated potato granules, and preferably dehydrated potato granules.

A suitable composition for treating produce in accordance with the present invention contains an amount up to about 0.5% cysteine and an amount up to about 0.1% sulfiting agent, and preferably 0.2-0.5% cysteine and 0.05-0.1% sulfiting agent.

Another suitable composition for treating produce in accordance with the present invention includes an amount that the dehydrated produce contains up to about 0.2% cysteine, and amount up to about 0.2% calcium chloride, and an amount up to about 0.2% sodium acid pyrophosphate, i.e., 0.025-0.2% cysteine, 0.025-0.2% calcium chloride, and 0.025-0.2% sodium acid pyrophosphate; and more preferably 0.1-0.15% cysteine, 0.1% calcium chloride, and 0.1% sodium acid pyrophosphate.

A yet another suitable composition for treating produce in accordance with the present invention includes an amount up to about 0.2% cysteine, an amount up to about 0.003% sulfiting agent, an amount up to about 0.2% calcium chloride, and an amount up to about 0.2% sodium acid pyrophosphate, and preferably 0.025%-0.2% cysteine, 0.001-0.003% sulfiting agent, 0.025-0.2% calcium chloride, and 0.025-0.2% sodium acid pyrophosphate, and most preferably 0.05-0.15% cysteine, less than 0.001% sulfiting agent, 0.1% calcium chloride, and 0.1% sodium acid pyrophosphate.

The process of the present invention has been developed in an attempt to substantially reduce and essentially eliminate the use levels of sulfiting agents in the processing of produce, and particularly potatoes, which are subjected to elevated temperatures, and particularly temperatures to which the produce are exposed during dehydration.

In this regard, it has been discovered that exposing produce to discoloration inhibitors including cysteine preferably together with sulfite, and more preferably also calcium chloride and sodium acid pyrophosphate, in synergistically effective amounts, essentially eliminates the need for treating the produce with sulfiting agents at conventional levels and yet minimizes browning and discoloration of the produce upon subsequent processing, handling and storage. In accordance with the present invention, therefore, produce may be processed by a method which involves treating the produce in a manner so as to result with a finished product which contains less than about 50 ppm, and preferably less than about 30 ppm, and most preferably less than 10 ppm or essentially no sulfiting agent.

As used herein, "cysteine" is provided by any suitable source of cysteine. Related to this, "extraneously added cysteine" is used to designate cysteine which is not naturally present in the produce being processed in accordance with the present invention. The common or usual name of cysteine used in accordance with the present invention is L-cysteine hydrochloride monohydrate, the chemical name for which is L-2-amino-3-mercaptropropanocic acid hydrochloride monohydrate having the following structural formula:

The L-cysteine hydrochloride monohydrate is manufactured by first extracting L-cysteine from keratine which is then dissolved in HCl, subjected to electrical reduction, concentrated, crystallized, and centrifuged to result in L-cysteine hydrochloride monohydrate.

Although the discovery of the present invention may be used in conjunction with processing various fruits, such as apples, apricots, avocados, bananas, peaches and pears; vegetables such as beans, bell peppers, carrots, celery, corn, garlic, horseradish, leek, lentils, lima beans, mushrooms, onions, parsnips, peas, pimentos, tomatoes and turnips; and tubers, such as Russet, Kennebec, Hilite, Norkotah and Norgold varieties of solanum tuberosum, into dehydrated piece products, such as slices, dices, strips, shreds and the like, the present invention finds special utility in the processing of potatoes such as the previously mentioned varieties of solanum tuberosum into dehydrated mashed potato products, such as granules, flakes and agglomerates. Accordingly, the detailed description of the present invention will be given with respect to the processing of potatoes, and particularly with respect to the production of dehydrated potatoes, such as potato pieces, potato granules, and potato flakes.

As previously indicated, the present invention is based on the discovery that the need for sulfite can be substantially reduced or essentially eliminated in the processing of produce without sacrificing the organoleptic characteristics of the finished product by exposing the produce to an effective amount of cysteine to minimize browning upon subsequent processing, handling and storage, particularly as part of a process which involves subjecting the produce to elevated temperatures.

For purposes of the present invention, the elevated temperatures to which the produce are subsequently subjected fall within the range of about 70.degree. F.-575.degree. F. and typically within the range of 120.degree. F.-550.degree. F., for example as a result of subjecting the produce to a process step selected from the group of steps consisting of blanching, cooking, dehydrating, a sequence of blanching and dehydrating steps, and a sequence of cooking and dehydrating steps, preferably wherein the blanching step involves subjecting the produce to a medium selected from the group consisting of water, steam and a mixture of water and steam at temperatures within range of about 120.degree. F.-212.degree. F.

More specifically, one embodiment of the present invention is directed to the production of dehydrated potato pieces, such as dices, slices, shreds, strips and the like. The following description is a representative example of a process for producing such dehydrated potato piece products modified to provide for a treatment with the discoloration inhibitors in accordance with the present invention.

Potatoes are first cut, after having been washed, trimmed and optionally peeled, into large pieces which may have a size of about 1/2 inch.times.1/2 inch.times.1/2 inch. The potatoes may also be cut into pieces having other shapes and sizes, such as 1/16-3/8 inch slices and dices, in addition to strips, for example french-fry cuts, and shreds, suitable for hashbrowns. The potato pieces are then immersed in a holding tank of water which contains certain additives found to be effective in minimizing the discoloration of the potatoes in this stage of the process. Suitable additives include cysteine, and sulfiting agents, such as sodium sulfite and sodium bisulfite. Acids, such as citric and phosphoric acids, may also be included in the holding tank, preferably in lieu of sulfiting agents.

The potato pieces may then be subjected to treatments which include heating with steam or water having a temperature within the range of 120.degree.-212.degree. F., and preferably between about 165.degree.-200.degree. F., for between 2 to 75 minutes, optionally followed by cooling in tap water to a temperature below about 80.degree. F. Most preferably, the pieces are blanched in steam or water at 200.degree. F.-212.degree. F. for between 2 to 12 minutes. After blanching, or blanching and cooking the potatoes under such conditions, the potatoes are treated with a discoloration inhibitor containing between 0.015% and 0.15% cysteine. Particularly preferred results are achieved, however, by using a solution containing synergistically effective amounts of cysteine and sodium acid pyrophosphate (SAPP) within the ranges of up to about 0.2% and preferably about 0.025%-0.2% cysteine and SAPP. The potatoes may be sprayed with or dipped in the solution. Alternatively, the discoloration inhibitors in accordance with the present invention may be included in the blanch water so as to eliminate a separate treatment for this purpose. The heat-treated potato pieces are then fed into a conventional dryer, such as cabinet, tunnel, and conveyor dryers, and most preferably continuous belt or conveyor dryers. Typically air temperatures within the range of about 130.degree.-285.degree. F. are used. Drying times and temperatures are normally controlled so as to avoid scorching the finish-dried product. Thus temperatures are generally within the range of 140.degree. F.-225.degree. F. so as not to raise the product temperature to an unacceptably high level. Also the temperatures and times may be varied in the various stages of drying as is conventional in the art. In any event, the potato pieces are permitted to remain in the dryer for a sufficient period of time to reduce their moisture content to a storage stable extent of less than about 10%, i.e. about 7%.

Upon extended storage, it is observed that the dehydrated potato pieces treated with discoloration inhibitors in accordance with the present invention do not discolor to an appreciable extent, but maintained a substantially light color despite containing essentially no sulfite, i.e., a sulfite content of less than 10 ppm. Thus, the present invention produces acceptable products wherein the solution in the holding tank contains essentially no sulfiting agent, i.e., an amount of sulfite in the holding tank which results in a finish dried product containing less than about 10 ppm sulfite.

The discovery of the present invention is particularly suitable in the production of dehydrated mashed potato products, such as potato granules. A typical process for the production of potato granules involves first preparing raw potatoes for cooking in a usual manner, for example by washing, trimming and cutting, and optionally peeling. The prepared pieces of potato are then transferred to a holding tank containing water and conventional additives, such as a sodium bisulfite solution, to prevent discoloration. As disclosed in U.S. Pat. No. 3,986,260, the holding tank normally contains an aqueous solution of sodium bisulfite present in an amount of at least 0.5% by weight of sulfite. In contrast to conventional potato granule production methods, including the process which is referred to as a low-additive process by U.S. Pat. No. 3,986,260, the present invention uses less than about 0.5%, and preferably on the order of 0.1%, sulfiting agent in the solution of the holding tank. In accordance with the present invention, a source of cysteine may be substituted for all or part of the sulfiting agent in the holding tank. This results in a SO.sub.2 content in the finished product which is less than about 30 ppm sulfite, and preferably less than 10 ppm sulfite, i.e., essentially no sulfite, in contrast to the sulfite content of conventional mashed potato products which typically contain at least 200-500 ppm SO.sub.2. Thus, processing potatoes in a manner in accordance with the present invention results in a finished product containing sulfites at levels far below the amount normally found in dehydrated instant mashed potato products.

The next stage of processing involves cooking the prepared potatoes. As will be appreciated by one skilled in the art, any conventional method of cooking potatoes to completion can be employed at this stage of the process. Although it is preferred to cook with atmospheric steam, hot water, and in certain instances even hot oil, may be used with satisfactory results.

Prior to subjecting the potatoes to cooking, however, it is preferred to subject the prepared potatoes to pre-cooking and cooling steps. It is generally recognized in the art that this particular sequence of steps results in a tougher cell structure that resists rupture during processing and results with a more mealy finished mash. Notwithstanding the preference of this sequence of steps, the process of the present invention can be carried out by eliminating the pre-cook and cool steps prior to cooking if this is so desired.

The next stage of processing involves separating the cooked potato cells by partially mashing the cooked potatoes, as by ricing. This is the step wherein additives, such as starch complexing emulsifiers, e.g., glycerol monostearate, are incorporated into the mash. It is this stage of processing wherein it is preferred to expose the potatoes to discoloration inhibitors including a source of available cysteine in accordance with the present invention. Accordingly, the potatoes at this stage of processing are exposed to discoloration inhibitors in accordance with the present invention, including a source of available cysteine, in addition to other additives such as calcium chloride, other calcium salts, EDTA, sodium acid pyrophosphate, and/or optionally a sulfiting agent. The discoloration inhibitors in accordance with the present invention are preferably incorporated into the potatoes at this stage of processing in amounts which result in the following synergistic amounts by total weight of the potato product: an amount up to about 0.2% and preferably in the range of about 0.025-0.2% cysteine, an amount up to about 0.2% and preferably in the range of about 0.025-0.2% calcium chloride, and an amount up to about 0.2% and preferably in the range of about 0.025-0.2% sodium acid pyrophosphate. If a sulfiting agent is introduced to the potatoes at this stage of processing, it is added in an amount to result in preferably less than 100 ppm sulfite, and more preferably less than 30 ppm sulfite, and most preferably less than about 10 ppm or essentially no sulfite in the finish-dried product. In those instances where sulfite has been included in the holding tank, as previously described, the discoloration inhibitors used at this stage of processing preferably result with about 0.05-0.15% cysteine, about 0.1% calcium chloride and about 0.1% sodium acid pyrophosphate in the finish-dried product. More preferably, the discoloration inhibitors used at this stage of processing result with about 0.1% cysteine, about 0.1% calcium chloride, and about 0.1% sodium acid pyrophosphate in the finish-dried product.

As the discoloration inhibitors, as well the starch complexing emulsifiers and other additives, are introduced during this stage of processing, the potatoes are continuously mixed to accomplish complete cell separation. In so doing, the emulsifier, as well the discoloration inhibitors in accordance with the present invention, are uniformly distributed throughout the mash, and the separated cells are uniformly exposed to and coated with the additives.

The next stages of processing follow conventional add-back dehydrated potato granule processing which is well-known to those skilled in the art of potato dehydration.

For example, the process of the present invention may be applied to any potato dehydration process, such as processes for producing dehydrated granules disclosed by TALBURT & SMITH, Potato Processing, Chapter 12 entitled "Dehydrated Mashed Potato Granules", AVI Publishing Co., Westport, Conn., Third Edition, 1975, pp. 443-459.

Granules made in accordance with the present invention may then be used to form a variety of granular-based dehydrated potato products suitable for forming mashed potatoes or reconstituted into a formed potato product.

The present invention is also useful in minimizing browning of potatoes processed into dehydrated mashed potato flakes. In this regard, the discoloration inhibitors in accordance with the present invention are added to the potatoes at the stage in an otherwise conventional flake production process wherein additives, such as sulfites, antioxidants and the like, are normally introduced.

Suitable processes for purposes of the present invention are disclosed by TALBURT & SMITH, Potato Processing, Chapter 13 entitled "Potato Flakes", AVI Publishing Co., Westport, Conn., Third Edition, 1975, pp. 463-512.

In such a conventional flake production process, potatoes are first peeled and trimmed in a conventional manner prior to being sliced, for example, into one-half inch slabs. The potato pieces are then preferably pre-cooked in water followed by first cooling prior to cooking and then mashing, ricing for example by using conventional equipment for this purpose.

Additives, such as agents to improve the flavor, stability and texture of the product, are normally incorporated into the riced material before drying. In conventional potato flake processes, a source of sulfite, such as sodium sulfite or sodium bisulfite, is normally used to prevent oxidative changes during processing and to improve shelf life. Typically, sulfite is used in amounts so as to result in 400-500 ppm SO.sub.2 in the riced potatoes. Inasmuch as subsequent processing by dehydration removes some of the previously added SO.sub.2, conventional dehydrated potato flakes normally contain about 150-200 ppm SO.sub.2. Other additives which are normally included into the riced potatoes at this stage of processing include antioxidants and monoglycerides. In accordance with the present invention, therefore, cysteine, preferably in combination with SAPP in synergistically effective amounts within the ranges of up to about 0.2% and preferably 0.025%-0.2% cysteine and SAPP are mixed with the riced potatoes at this stage of processing in lieu of a source of sulfite. The resultant dehydrated potato product, therefore, is essentially sulfite-free.

Following addition and mixing of the potatoes with the discoloration inhibitors in accordance with the present invention, the potato mash is then fed to a conventional drum dryer on which the mash is spread into a thin film and dehydrated to a storage stable moisture content. The dried sheet of mashed potato is then peeled away from the drum and subdivided into pieces which are further broken into random-sized flakes which are then packaged for subsequent storage, handling and shipping.

The following examples are intended to be representative of the processes and products of this invention. It will be apparent, however, that the details of the examples are not to be regarded as limitations, as they may be varied to a certain extent, as will be understood by one skilled in the art.

For purposes of the present invention, the sulfite content of the products has been analyzed using a procedure known as the "Monier-Williams Procedure" mentioned in 21 C.F.R. 101 (Appendix A--Monier-Williams Procedure for Sulfites in Food). In brief, the AOAC official method for sulfites has been modified by the Monier-Williams Procedure to facilitate the determination of sulfites at or near 10 ppm in food. Thus, the methodology used in analyzing the sulfite content of products produced in accordance with the present invention is the technique which has been approved by the FDA as being effective in detecting as little as 10 ppm of sulfite in a finished food product.

The Agtron reflectance meter readings for purposes of the present invention, were determined by using an Agtron Model M-500A, an Agtron M-300A wide angle viewer, Agtron calibration disks M-56 and M-68, and a sample cup for a wide angle viewer; the Agtron Meter is first set to read on the blue mode and calibrated before each use. To calibrate the Agtron Meter, the M-56 calibration disk is first placed inside the sample cup, and the Relative Spectral Reflectance meter is adjusted to a reading of 24. Following this, the M-68 calibration disk is placed in the sample cup and the meter is adjusted to a reading of 95. In so doing, the needle for determining the low and high set points is verified at the low and high set points by repeating each disk several times. After the Agtron Meter has been calibrated, the calibration disk is removed and the sample cup is filled at least half full with the test sample, i.e., potato granules. The value, i.e., Agtron reflectance meter reading, is then read by lining the needle up with the mirrored reflectance so that the image is overlapped and looks like a single needle reading; once this is observed, the Agtron reflectance meter reading is recorded.

Potatoes prepared for processing in a conventional manner by washing, peeling and trimming were immersed in a holding tank. For the control run, no sulfite or other discoloration inhibitor was included in the holding tank water, and no cysteine was used in the process. In the other runs conducted for purposes of comparison, the amount of sulfite in the holding tank is indicated in the table below. The potatoes were then subjected to a cooking procedure which involved pre-cooking the potatoes to an internal piece temperature within the range of 150.degree. F.-180.degree. F., followed by cooling to a piece temperature within the range of 60.degree. F.-70.degree. F. Subsequently, the potatoes were cooked after which discoloration inhibitors in accordance with the present invention in the amounts listed in the table below were introduced. The cooked potatoes are mashed, mixed and conditioned prior to being introduced to an air-lift dryer, the air temperature in which is controlled such that hot air having a temperature within the range of 525.degree. F.-560.degree. F., when introduced into the air-lift dryer, exits at a temperature within the range of 150.degree. F.-220.degree. F., so as to effect a product temperature on the order of about 130.degree. F. The granular potatoes collected from the air-lift dryer are then finish-dried in a conventional fluid bed dryer using hot air at a temperature within the range of about 150.degree. F.-120.degree. F. which effects a product temperature of about 108.degree. F.-110.degree. F. until the moisture content is reduced to about 7-8%. Granular products in accordance with the previously described procedure were then measured for color using an Agtron reflectance meter, and judged by a taste panel for flavor. In this regard, Agtron reflectance meter readings, using the previously described procedure, above 40 are considered acceptable, and above 50 good to excellent. Flavor ratings of 3.0 are acceptable, and 4.0 are considered excellent. The results of these tests are tabulated below:

As can be seen, the control sample was unacceptable in color and marginal in flavor. The color and flavor of the dehydrated potato granules were improved somewhat when 0.1% sulfite was included in the holding tank. Treating the potatoes with a discoloration inhibitor solution containing cysteine showed markedly superior results, with the best results achieved when the potatoes are first exposed to a sulfiting agent in the holding tank, followed by treatment with a discoloration inhibitor solution containing cysteine, calcium chloride, and SAPP.

The following test was conducted to visually compare the effect of discoloration inhibitor solutions containing a combination of a minor amount of sulfite and L-cysteine in minimizing the discoloration of raw produce versus the use of a solution containing only sulfite and a solution containing only L-cysteine.

Russet Burbank potatoes were washed, trimmed, and peeled before being cut into French-Fry strips, and divided into even batches which were treated with aqueous solutions having the following compositions:

Each batch was immersed in a respective discoloration inhibitor solution for ten (10) minutes prior to draining to remove excess solution followed by storage for seven (7) days at 40.degree. F.

Following storage, each batch was evaluated by visual color change. Each of the strips treated with the 0.5% NaHSO.sub.2 solution had developed a moderately brown color over their entire surface. The strips treated with the 0.5% L-cysteine solution were even darker in color. In contrast, the strips of potatoes treated with the aqueous solution containing 0.45% L-cysteine and 0.05% NaHSO.sub.2, exhibited a uniformly light color which was not noticeably darker than the color of the fresh-cut slice.

The results of this test indicate that a discoloration inhibitor solution containing minor amounts of sulfiting agent together with a source of cysteine are synergistically effective in a manner superior to either sulfite or cysteine used alone in minimizing the discoloration of cut surfaces of raw potatoes upon storage.

The following tests were conducted to show the effectiveness of a solution containing a combination of relatively minor amounts of sulfite and cysteine in reducing enzyme activity responsible for browning of produce compared to solutions containing significantly greater amounts of only a sulfiting agent or cysteine.

Russet Burbank potatoes were left unpeeled and sliced raw prior to dividing into batches for treatment in the following solutions:

The slices of each batch were dipped in their respective discoloration inhibitor solutions and held for five (5) minutes. After draining to remove excess solution the slices were dipped in catechol for the purpose of assessing the enzymatic activity of the treated slices versus the control after 1 hour by visual color change.

The foregoing tests showed the slices treated with the discoloration inhibitor solution containing a combination of 0.1% NaHSO.sub.3 and 0.1% L-cysteine experienced only slight discoloration near the peel to an extent similar to slices treated with solutions containing 0.3% NaHSO.sub.3 and 0.5% L-cysteine lone. Thus, the combination of a sulfiting agent and a source of cysteine is synergistically effective in retarding enzyme activity and consequently enzymatic browning of raw produce.

The following examples are presented as an indication of the effectiveness of the L-cysteine compositions of the present invention for other fruits and vegetables by way of comparison with potatoes. In each of the following examples, a puree of the fruit, vegetable and potato was treated with amounts of L-cysteine HCl and compared to show the effectiveness of L-cysteine in minimizing discoloration.

Idaho Russet potatoes were peeled and ground into a puree in a Waring blender. Three samples were prepared. Sample 1 was the control which was not exposed to a discoloration inhibitor; 0.02% L-cysteine HCl was added to Sample 2; and 0.04% L-cysteine HCl was added to Sample 3. FIG. 1 is a photograph of the sample after exposure to air for two hours. As can clearly be seen, only Sample 3, with 0.04% L-cysteine added, remained substantially white.

Red delicious apples were peeled, cored and pureed in a Waring blender. Three samples were prepared. No additive was added to Sample 1; 0.015% L-cysteine HCl was added to Sample 2; and 0.03% L-cysteine HCl was added to Sample 3. FIG. 2 is a photograph showing the difference in color developed immediately after the puree was made. As clearly indicated in the photograph, Sample 3 has the most desireable color with enzymatic darkening substantially completely inhibited.

Apples were sliced about 1/8 inch thick and dried using 120.degree. F. air for 3 hours. Sample 1 was untreated. Prior to drying, Sample 2 was dipped in a 0.5% solution of L-cysteine for 15 minutes. The photograph of FIG. 3 clearly shows that the treated Sample 2 is much whiter than the untreated sample.

Avocados were peeled and the pits removed. The remaining pulp was ground to a puree in a Waring blender. Three samples were prepared. Sample 1 was treated with no additive, 0.035% L-cysteine HCl was added to Sample 2, and 0.07% L-cysteine HCl was added to Sample 3. FIG. 4 is a photograph of the three samples after exposure to air for 3 hours. As can be seen, only Sample 3, with 0.07% L-cysteine HCl added was satisfactory in color and flavor.

The previous examples show that L-cysteine HCl is effective in preventing color changes in purees and dried products made from fruits and vegetables, in addition to potatoes.

Table 2, appearing below, shows the level of L-cysteine most effective in apples, avocados and potatoes as tested. The level of addition that was effective in all three products was calculated to be 0.2% on a dry weight basis.

The following comparison is given to show that added cysteine is readily oxidized to its dimer form, i.e. cystine, is evidenced by the comparison of the relative cystine content of fresh potatoes (Table A), conventional dehydrated potato granules processed without extraneously added cysteine otherwise produced in accordance with the previously described process (Table B), and dehydrated potato granules processed with added cysteine in accordance with the present invention as disclosed herein (Table C):

As shown above in Table A, fresh potatoes average 3.22 mg cystine/100 g raw or about 16 mg cystine/100 g on a dry solids basis. Dehydrated potato granules average about 15 mg cystine/100 g (Table B); and dehydrated potato granules with 100 to 140 mg cysteine added/100 g dry average about 24 mg cystine/100 g (Table C).

In accordance with the present invention, the total cystine content of dehydrated potato granules is increased only 9 mg/100 g when 100 to 140 mg cysteine is added in process over what would otherwise be present in the potato granules. Nevertheless, despite such a small increase in the cystine content as a result of processing in accordance with the present invention, the use of cysteine in processing potatoes has been discovered to be effective in minimizing browning of potatoes which could otherwise occur, and has been found to be an effective substitute for sulfites in the prevention of browning.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, make various changes and modifications of the invention to adapt it to various usages and conditions.