PROCESSING METHOD FOR SWEET POTATO ENABLING LONG-TERM PRESERVATION AT ROOM TEMPERATURE AND SWEET POTATO PROCESSED FOOD PREPARED THEREFROM

Abstract

A sweet potato processed food can be preserved at room temperature for a long period of time while maintaining the taste, palatability, or the like acquired right after preparation procedures, given that the processed food is prepared by a process including: (1) washing and drying a sweet potato; (2) packaging each sweet potato of the step (1) in a laminated foil packaging sheet; and (3) pasteurizing the packaged sweet potato of the step (2) at 121 to 150 C. for 25 to 35 minutes. It is therefore expected to increase the income of sweet potato farmers and ensure high industrial availability by using the method for processing sweet potatoes into baked or steamed sweet potatoes that are readily consumable without trouble to conduct a separate cooking procedure, distributable at room temperature, and preservable for a long period of time.

Claims

1. A processing method for sweet potato enabling long-term preservation of a sweet potato at room temperature with enhanced quality using penetration of flavor and active ingredients of plant leaves into a sweet potato, the processing method comprising: (1) washing and drying a sweet potato; (2) wrapping the sweet potato of the step (1) with plant leaves and packaging each sweet potato in a laminated foil packaging sheet; and (3) pasteurizing the packaged sweet potato of the step (2) at 121 to 150 C. for 25 to 35 minutes.

2. The processing method for sweet potato as claimed in claim 1, wherein the washing of the step (1) is spraying ultrasonic wash water at high pressure.

3. The processing method for sweet potato as claimed in claim 1, wherein the drying of the step (1) is infrared drying.

4. The processing method for sweet potato as claimed in claim 1, wherein the plant leaves are selected from the group consisting of mulberry leaves, lotus leaves, mandarin melon berry leaves, Siberian ginseng leaves, kalopanax leaves, kudzu leaves, basil leaves, yerba mate leaves, Camellia sinensis (green tea) leaves, and pine tree leaves.

5. The processing method for sweet potato as claimed in claim 1, wherein the processing method for sweet potato further comprises baking the sweet potato of the step (1) to prepare a baked sweet potato.

6. The processing method for sweet potato as claimed in claim 5, wherein the baked sweet potato is prepared by placing the sweet potato in a kiln filled with a layer of red clay or covering the sweet potato with red clay in a kiln, and then baking the sweet potato at 150 to 160 C. for 80 to 100 minutes.

7. The processing method for sweet potato as claimed in claim 1, wherein the long-term preservation lasts 12 to 18 months.

8. A sweet potato processed food prepared by the processing method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0056] FIG. 1 presents experimental results showing the degree of decay in sweet potato processed foods prepared by the processing method for sweet potato according to the present invention and stored at 20 to 25 C. for five days.

DETAILED DESCRIPTION OF THE INVENTION

[0057] The processing method for sweet potato that enables long-term preservation of a sweet potato at room temperature, and the sweet potato processed food prepared therefrom according to the present invention involve: (1) washing and drying a sweet potato; (2) wrapping the sweet potato of the step (1) with plant leaves and packaging each sweet potato in a laminated foil packaging sheet; and (3) pasteurizing the packaged sweet potato of the step (2) at 121 to 150 C. for 25 to 35 minutes, thereby having the flavor and active ingredients of the plant leaves to penetrate into the sweet potato and enhance the sweet potato processed food in quality.

[0058] Hereinafter, a detailed description will be given as to the present invention in connection with preferred embodiments. It should be understood that the embodiments are not construed to limit the scope of the present invention but intended to cover all modifications. The embodiments of the present invention are given to make the disclosure of the present invention complete and enable those skilled in the related art to completely understand the conception of the present invention.

Examples 1 to 4: Preparation of Sweet Potato Processed Foods

[0059] (1) Washing and Drying of Sweet Potatoes

[0060] After harvest, raw sweet potatoes were washed with a high-pressure spray of ultrasonic wash water for removal of foreign materials such as soil, dirt, bacteria, etc. An infrared drying machine was used to dry the sweet potatoes and completely remove water from the surface of the sweet potatoes.

[0061] (2) Preparation of Baked Sweet Potatoes

[0062] The raw sweet potatoes washed and dried in the step (1) were baked in a kiln to prepare baked sweet potatoes. For this, the sweet potatoes were placed in a kiln filled with a layer of red clay or covered with red clay in a kiln, and then baked at 160 C. for 80 minutes.

[0063] (3) Preparation of Sweet Potato Processed Foods

[0064] Each of the raw sweet potatoes washed and dried in the step (1) or the baked sweet potatoes prepared in the step (2) was packaged in a laminated foil packaging sheet, or wrapped with a mulberry leaf or a lotus leaf and then packaged in a laminated foil packaging sheet. The packaged sweet potato was pasteurized at 121 C. for 30 to 35 minutes. As shown in Table 1 below, the pasteurization process resulted in cooking the raw sweet potato into a pasteurized sweet potato processed food in the form of a steamed sweet potato and the baked sweet potato into a pasteurized sweet potato processed food in the form of a baked sweet potato. The laminated foil packaging sheet was a packaging sheet with a single foil laminate.

TABLE-US-00001 TABLE 1 Div. Sweet potato processed food Example 1 Pasteurize a raw sweet potato placed in a laminated foil packaging sheet. Example 2 Pasteurize a raw sweet potato wrapped with a mulberry or lotus leaf and then placed in a laminated foil packaging sheet. Example 3 Pasteurize a sweet potato baked with red clay and then placed in a laminated foil packaging sheet. Example 4 Pasteurize a sweet potato baked with red clay, wrapped with a mulberry or lotus leaf and then placed in a laminated foil packaging sheet

Experimental Example 1: Preservability of Sweet Potato Processed Food

[0065] In order to examine the preservability of the sweet potato processed food of the present invention, the sweet potato processed foods of Examples 1 to 4 were kept at 20 to 25 C. and measured in regards to the time required to have decay. The decay time was averaged. The results are presented in Table 2 and FIG. 1. Referring to FIG. 1, the sweet potatoes given in Table 2 below were kept at 20 to 25 C. for 5 days and then evaluated in regards to the degree of decay.

TABLE-US-00002 TABLE 2 Average Div. Sweet potato processed foods time to decay Test Group 1 Raw sweet potato washed and dried 20 days Test Group 2 Sweet potato baked without red clay 2 days Test Group 3 Sweet potato baked with red clay 4 days Test Group 4 Sweet potato processed food from 3 days pasteurization of a raw sweet potato not placed in a package Test Group 5 Sweet potato processed food from 4 days pasteurization of a sweet potato baked with red clay and not placed in a package Test Group 6 Sweet potato processed food from 1.5 month pasteurization of a raw sweet potato placed in a packaging sheet without a laminated foil Test Group 7 Sweet potato processed food from 6 months pasteurization of a sweet potato baked with red clay and placed in a packaging sheet without a laminated foil Example 1 Sweet potato processed food from 18 or more pasteurization of a raw sweet potato months placed in a laminated foil packaging sheet Example 2 Sweet potato processed food from 18 or more pasteurization of a raw sweet potato months wrapped with a mulberry or lotus leaf and then placed in a laminated foil packaging sheet Example 3 Sweet potato processed food from 18 or more pasteurization of a sweet potato baked months with red clay and then placed in a laminated foil packaging sheet Example 4 Sweet potato processed food from 18 or more pasteurization of a sweet potato baked months with red clay, wrapped with a mulberry or lotus leaf and then placed in a laminated foil packaging sheet

[0066] As can be seen from Table 2, decay appeared normally within four days of storage at 20 to 25 C. in the baked sweet potatoes (Test Groups 2 and 3), the sweet potato processed food from pasteurization of a raw sweet potato not placed in a package (Test Group 4), and the sweet potato processed food from pasteurization of a baked sweet potato not placed in a package (Test Group 5). In contrast, the sweet potato processed foods from pasteurization of sweet potatoes placed in a package (Test Groups 6 and 7, and Examples 1 to 4) had no decay in one or more months of storage at 20 to 25 C. The sweet potato processed foods using a laminated foil packaging sheet (Examples 1 to 4) had a noticeably longer shelf life at 20 to 25 C. than those not using a laminated foil packaging sheet (Test Groups 6 and 7).

[0067] As can be seen from FIG. 1, the sweet potato baked with red clay (Test Group 3) had less severe decay under same storage conditions than the sweet potato processed food from pasteurization of a raw sweet potato not placed in a package (Test Group 4). The main reason for this presumably lies in that the baking process using red clay removed part of water from the sweet potato through evaporation to reduce the water content of the sweet potato and kept the sweet potato from decaying by the sterilizing action of the red clay.

[0068] As for the pasteurization process following the packaging of the baked sweet potato, as can be seen from FIG. 1, the baked sweet potato placed in a package and not pasteurized got water formed inside the packaging sheet and started to decay in 5 days of storage at 20 to 25 C.; whereas the baked sweet potato placed in a package and then pasteurized (Test Group 7) remained in the same condition of the baked sweet potato on the first day of preparation.

[0069] If not shown in the present invention, a pasteurization time of 5 minutes in the pasteurization step of the present invention resulted in a noticeable reduction of the shelf life of the sweet potato processed foods, and a pasteurization time of 20 or more minutes allowed the baked sweet potato to be preserved for one year or longer. As for the packaging sheet of the present invention, the larger number of foil laminates led to the longer shelf life of the sweet potato processed foods and was more favored to the maintenance of the processed foods in quality.

[0070] In conclusion, the sweet potato processed foods prepared by the processing method of the present invention were preservable at room temperature for a long time, distributable at room temperature in the case of food distribution, and thus easy to distribute with convenience.

Experimental Example 2: Sensory Evaluation of Sweet Potato Processed Food

[0071] The sweet potato processed foods of the present invention were subjected to a sensory evaluation in regards to taste, flavor, texture (mouthfeel), and ease of peeling.

[0072] 50 adult sensory panelists were assigned to evaluate the sweet potato processed foods of Table 2 in regards to taste, flavor, texture, and ease of peeling on a 7-point rating scale. For taste, sweet taste was captured as a reference attribute; for flavor, sweet flavor and less burnt flavor; and for texture (mouthfeel), less dense texture and less mushy texture. As for the samples, the sweet potato processed foods of Test Groups 2, 3 and 4 were sweet potatoes processed prior to the sensory evaluations, and those of Examples 1 to 4 were kept at room temperature for one month after preparation. The evaluation was conducted for steamed sweet potatoes and baked sweet potatoes separately. The degree of liking for each sample was marked using the number scale given by: 7=like very much, 6=like moderately, 5=like slightly, 4=neither like nor dislike, 3=dislike slightly, 2=dislike moderately, 1=dislike very much. Mean liking scores are presented in Tables 3 and 4 below.

TABLE-US-00003 TABLE 3 Processed foods in the form Ease of Div. of baked sweet potato Taste Flavor Texture peeling Test Group 2 Sweet potato baked without red 4.6 3.5 3.2 5.1 clay Test Group 3 Sweet potato baked with red 6.4 5.1 4.7 6.2 clay Example 3 Sweet potato processed food from 6.6 5.8 6.5 6.4 pasteurization of a sweet potato baked with red clay and then placed in a laminated foil packaging sheet Example 4-1 Sweet potato processed food from 6.5 6.5 6.4 6.6 pasteurization of a sweet potato baked with red clay, wrapped with a mulberry leaf and then placed in a laminated foil packaging sheet Example 4-2 Sweet potato processed food from 6.5 6.8 6.4 6.5 pasteurization of a sweet potato baked with red clay, wrapped with a lotus leaf and then placed in a laminated foil packaging sheet

TABLE-US-00004 TABLE 4 Processed foods in the form Ease of Div. of steamed sweet potato Taste Flavor Texture peeling Test Group 4 Sweet potato processed food from 3.9 3.8 2.7 3.4 pasteurization of a raw sweet potato not placed in a package Example 1 Sweet potato processed food from 4.2 4.3 3.9 4.4 pasteurization of a raw sweet potato placed in a laminated foil packaging sheet Example 2-1 Sweet potato processed food from 4.5 6.0 4.9 5.1 pasteurization of a raw sweet potato wrapped with a mulberry leaf and then placed in a laminated foil packaging sheet Example 2-2 Sweet potato processed food from 4.4 6.1 4.8 5.0 pasteurization of a raw sweet potato wrapped with a lotus leaf and then placed in a laminated foil packaging sheet

[0073] Referring to Table 3, as for baked sweet potatoes, the sweet potato processed foods prepared by the processing method of the present invention (Examples 3, 4-1 and 4-2), in spite of being stored for one month after preparation, were similar in taste and ease of peeling to the Test Group 3 and even superior in taste to the Test Group 2, where the Test Groups 2 and 3 were consumed immediately after the processing procedure. The reason of this presumably boils down to the use of red clay in baking sweet potatoes to enhance the taste of the sweet potatoes in Test Group 3 and Examples 3, 4-1 and 4-2. The sweet potato processed foods of the present invention were far superior in flavor and texture (mouthfeel) to the Test Groups 2 and 3.

[0074] Referring to Table 4, as for steamed sweet potatoes, the sweet potato processed foods prepared by the processing method of the present invention (Examples 1, 2-1 and 2-2), in spite of being stored for one month after preparation, were superior in taste, flavor, texture (mouthfeel), and ease of peeling to the Test Group 4.

[0075] In particular, the sweet potato processed foods using sweet potatoes wrapped in a plant leaf (e.g., a mulberry or lotus leaf) according to the present invention as in Examples 2-1, 2-2, 4-1, and 4-2 of Tables 3 and 4 were significantly superior in flavor to those using sweet potatoes not wrapped in a plant leaf. The reason of this presumably lies in that the process of pasteurizing the sweet potatoes wrapped in a plant leaf allowed the flavor of the plant leaf to penetrate into the sweet potatoes only to reduce the burnt smell of the baked sweet potatoes and increase the sweet flavor of the sweet potatoes. As implied from the penetration of the flavor of the plant leaf into the sweet potatoes, the active ingredients of the plant leaf were also presumably able to penetrate into the sweet potatoes during the pasteurization process.

[0076] If not shown in the present invention, the sweet potato processed foods prepared by the processing method of the present invention and stored for one year after preparation were similar in palatability associated with taste, flavor, texture (mouthfeel), and ease of peeling to those prepared by the processing method of the present invention and stored for one month.

[0077] Further, the baked sweet potatoes prepared by baking at 160 C. for 80 minutes in a kiln according to the present invention were sweeter and easier to peel than those prepared by a general baking method, namely, baking at 190 C. for 55 minutes.

[0078] In conclusion, the sweet potato processed foods prepared by the processing method of the present invention were capable of being preserved at room temperature for a long time, while maintaining the taste, flavor, texture (mouthfeel), or the like acquired right after preparation procedures.

[0079] As described above, the present invention ensures that a sweet potato processed food can be preserved at room temperature for a long period of time while maintaining the taste, flavor, texture (mouthfeel), or the like acquired right after preparation procedures, given that the processed food is prepared by a process including: (1) washing and drying a sweet potato; (2) packaging each sweet potato of the step (1) in a laminated foil packaging sheet; and (3) pasteurizing the packaged sweet potato of the step (2) at 121 to 150 C. for 25 to 35 minutes. Therefore, the present invention is expected to bring out an increase in the income of sweet potato farmers and thus acquire high industrial availability by using the method for processing sweet potatoes into baked or steamed sweet potatoes that are readily consumable without trouble to conduct a separate cooking procedure, distributable at room temperature, and preservable for a long period of time.