Production method of normal-temperature instant cooked rice

Abstract

The present disclosure discloses a production method of normal-temperature instant cooked rice and belongs to the technical field of food processing. The method of the present disclosure comprises the main steps of rice washing and soaking, flavor blending, sub-packaging, cooking, sterile vacuum sealing, cooling and crystallization and normal-temperature storage, wherein an aqueous solution containing flavor substances is adopted to perform flavor blending, and a fast cooling mode is adopted to perform cooling and crystallization. The normal-temperature instant cooked rice obtained through the production method provided in the present disclosure can keep the original flavor after being stored for 90 days.

Claims

1. A method of cooking rice, which comprises: washing the rice, soaking the rice, blending the rice with flavor substances comprising volatile odor components in an aqueous solution, packaging the rice into containers, cooking the rice, sterile vacuum sealing the rice, and cooling the rice quickly thereby crystallizing starch within the rice, wherein cooling is performed at a rate of 5 to 11° C. per minute at a temperature of −70 to −10° C., such that the rice reaches a final temperature of 15 to 30° C., wherein the volatile odor components released from the cooked rice 90 days after cooking and cooling the rice when stored at room temperature are retained as compared with the volatile odor components released from the cooked rice on the day of cooking and cooling the rice, and wherein the volatile odor components comprise one or more of pyridines, pyrroles, esters, and alcohols.

2. The method of claim 1, wherein the cooling comprises applying an air cooling mode and a refrigeration house cooling mode.

3. The method of claim 1, wherein the concentration of the flavor substances is 0.001 to 10 mg/kg in the aqueous solution.

4. The method of claim 1, wherein the aqueous solution comprising the flavor substances comprises the following solutes (per kilogram of flavor substances/per kilogram of water): 0.000004% to 0.000009% of 2-acetyl-1-pyrroline, 0.0000002% to 0.0000004% of 2-acetylpyridine, 0.0000005% to 0.0000009% of ethyl 2-methylpentanoate, 0.000002% to 0.000004% of gamma-decalactone, 0.0000003% to 0.0000005% of linalool, 0.0000001% to 0.0000003% of alpha-terpineol, 0.0000002% to 0.0000004% of 1-octen-3-ol, and 0.0000004% to 0.0000006% of phenethyl alcohol.

5. The method of claim 1, wherein of washing and soaking is achieved with drinking water at a temperature of 10 to 40° C.

6. The method of claim 1, wherein: (a) washing and soaking the rice comprises: washing the rice with drinking water at 10 to 40° C. to provide washed rice, soaking the washed rice in the drinking water, and then, draining the drinking water from the rice; and (b) blending the rice with flavor substances comprises: (aa) preparing a stock solution comprising 4% to 9% of 2-acetyl-1-pyrroline, 0.2% to 0.4% of 2-acetylpyridine, 0.5% to 0.9% of ethyl 2-methylpentanoate, 2% to 4% of gamma-decalactone, 0.3% to 0.5% of linalool, 0.1% to 0.3% of alpha-terpineol, 0.2% to 0.4% of 1-octen-3-ol, and 0.4% to 0.6% of phenethyl alcohol, (bb) diluting the stock solution by 10.sup.6 times, (cc) adding the rice to the aqueous solution at a ratio of 1:1.0 to 1:1.8, and (dd) incubating the rice at 10 to 40° C.

7. The method of claim 1, wherein packaging comprises placing the cooked rice into environment-friendly, high-temperature-resistant, and high-pressure-resistant packaging boxes.

8. The method of claim 1, wherein the average cooling rate of the cooling step is 9 to 11° C. per minute, 7 to 9° C. per minute, or 5 to 7° C. per minute.

9. A cooked rice produced by the method of claim 1.

Description

BRIEF DESCRIPTION OF FIGURES

(1) FIG. 1 is a PCA analysis diagram of a fast gas chromatography electronic nose for comparing instant cooked rice with normal cooked rice according to three examples.

(2) FIG. 2 is a headspace solid-phase microextraction-gas chromatography-mass spectrometry diagram immediately after the rice without adding the aqueous solution containing the flavor substances is cooked.

(3) FIG. 3 is a headspace solid-phase microextraction-gas chromatography-mass spectrometry diagram of the normal-temperature instant cooked rice stored for 90 days in the example 1.

(4) FIG. 4 is a headspace solid-phase microextraction-gas chromatography-mass spectrometry diagram of the normal-temperature instant cooked rice stored for 90 days in the example 2.

(5) FIG. 5 is a headspace solid-phase microextraction-gas chromatography-mass spectrometry diagram of the normal-temperature instant cooked rice stored for 90 days in the example 3.

(6) In FIGS. 2 to 5, the retention time of each flavor substance is as follows: 2-acetyl-1-pyrroline, about 10.5 min; 2-acetylpyridine, about 5.3 min; ethyl 2-methylpentanoate, about 19.8 min; gamma-decalactone, about 27.9 min; linalool, about 13.9 min; alpha-terpineol, about 12.2 min; 1-octen-3-ol, about 16.6 min; phenethyl alcohol, about 5.5 min.

DETAILED DESCRIPTION

(7) The method for detecting the flavor substances in the cooked rice adopts the TSQ Quantum XLS gas chromatograph-mass spectrometer produced by the Thermo Fisher Scientific. Detection conditions: a solid-phase microextraction column carboxen/polydimethylsiloxane (1 cm, 75 μm, CAR/PDMS) and a DB-WAX separation column (30 m, 0.25 mm, i. d. 0.25 μm) are adopted. Chromatographic conditions: the injection port temperature is 270 DEG C., and the split ratio is 20:1; the initial temperature is 40 DEG C. and is kept for 3 min, then the initial temperature of 40 DEG C. is raised to 90 DEG C. at the rate of 5 DEG C./min, the temperature of 90 DEG C. is kept for 5 min and is then raised to 230 DEG C. at the rate of 10 DEG C./min, and the temperature of 230 DEG C. is kept for 7 min and resolved for 40 min; the carrier gas is He, the flow rate is 1 mL/min, the ionization mode is EI, the electron energy is 70 ev, and the ion source temperature is 230 DEG C.; the quadrupole temperature is 150 DEG C., and the transmission line temperature is 230 DEG C.; the scanning range is 35-350 m/z. The retention time of each flavor substance is as follows: 2-acetyl-1-pyrroline, about 10.5 min; 2-acetylpyridine, about 5.3 min; ethyl 2-methylpentanoate, about 19.8 min; gamma-decalactone, about 27.9 min; linalool, about 13.9 min; alpha-terpineol, about 12.2 min; 1-octen-3-ol, about 16.6 min; phenethyl alcohol, about 5.5 min.

(8) A preparation method of fresh cooked rice comprises the following steps: washing rice twice with drinking water at about 20 DEG C., then putting the rice into a proper amount of drinking water to be soaked for 30 min, draining off the rice, sub-packaging the rice by adopting environment-friendly, high-temperature-resistant and high-pressure-resistant packaging boxes under the condition that the mass ratio of the rice to the water is 1:1.4, cooking the rice for 30 min at normal pressure, and naturally cooling the cooked rice at normal temperature.

Example 1

(9) Washing rice twice with drinking water at about 10 DEG C., and then, putting the rice into a proper amount of drinking water to be soaked for 30 min; preparing a stock solution of an aqueous solution containing 4% of 2-acetyl-1-pyrroline, 0.2% of 2-acetylpyridine, 0.9% of ethyl 2-methylpentanoate, 2% of gamma-decalactone, 0.5% of linalool, 0.2% of alpha-terpineol, 0.2% of 1-octen-3-ol and 0.5% of phenethyl alcohol; diluting the stock solution by 10.sup.6 times to obtain the aqueous solution containing the flavor substances;

(10) mixing the rice with the aqueous solution containing the flavor substances in a mass ratio of 1:1.4, and soaking the rice; sub-packaging the rice by adopting environment-friendly, high-temperature-resistant and high-pressure-resistant packaging boxes, cooking the rice for 30 min at normal pressure, and then, performing sterile vacuum sealing; after the sealing is finished, fast cooling the cooked rice by adopting a refrigeration house cooling mode in the low temperature environment of −70 DEG C. at the average cooling rate of 9 to 11 DEG C./min until the central temperature of the cooked rice is reduced to 15 DEG C., and then, storing the cooked rice at normal temperature;

(11) and after the cooked rice is stored for 90 days at normal temperature, analyzing volatile odor components of the obtained instant cooked rice and fresh cooked rice by utilizing the headspace solid-phase microextraction-gas chromatography-mass spectrometry technology. As shown in FIG. 1 and FIG. 2, the contents and varieties of the volatile smell components released by the instant cooked rice obtained by the example and the fresh cooked rice are approximately identical. The fast gas chromatography electronic nose is utilized for detecting the flavors of the instant cooked rice obtained by the example and the fresh cooked rice, and the results show that the two flavors have no significant difference.

Example 2

(12) Washing rice twice with drinking water at about 40 DEG C., and then, putting the rice into a proper amount of drinking water to be soaked for 30 min; preparing a stock solution of an aqueous solution containing 9% of 2-acetyl-1-pyrroline, 0.4% of 2-acetylpyridine, 0.5% of ethyl 2-methylpentanoate, 4% of gamma-decalactone, 0.3% of linalool, 0.1% of alpha-terpineol, 0.4% of 1-octen-3-ol and 0.4% of phenethyl alcohol; diluting the stock solution by 10.sup.6 times to obtain the aqueous solution containing the flavor substances;

(13) mixing the rice with the aqueous solution containing the flavor substances in a mass ratio of 1:1.4, and soaking the rice; sub-packaging the rice by adopting environment-friendly, high-temperature-resistant and high-pressure-resistant packaging boxes, cooking the rice for 30 min at normal pressure, and then, performing sterile vacuum sealing; after the sealing is finished, fast cooling the cooked rice by adopting an air cooling mode in the low temperature environment of −40 DEG C. at the average cooling rate of 7 to 9 DEG C./min until the central temperature of the cooked rice is reduced to 25 DEG C., and then, storing the cooked rice at normal temperature;

(14) and after the cooked rice is stored for 90 days at normal temperature, analyzing volatile odor components of the obtained instant cooked rice and fresh cooked rice by utilizing the headspace solid-phase microextraction-gas chromatography-mass spectrometry technology. As shown in FIG. 1 and FIG. 3, the contents and varieties of the volatile smell components released by the instant cooked rice obtained by the example and the fresh cooked rice are approximately identical. The fast gas chromatography electronic nose is utilized for detecting the flavors of the instant cooked rice obtained by the example and the fresh cooked rice, and the results show that the two flavors have no significant difference.

Example 3

(15) Washing rice thrice with drinking water at about 25 DEG C., and then, putting the rice into a proper amount of drinking water to be soaked for 30 min; preparing a stock solution of an aqueous solution containing 6% of 2-acetyl-1-pyrroline, 0.3% of 2-acetylpyridine, 0.7% of ethyl 2-methylpentanoate, 3% of gamma-decalactone, 0.4% of linalool, 0.3% of alpha-terpineol, 0.3% of 1-octen-3-ol and 0.6% phenethyl alcohol; diluting the stock solution by 10.sup.6 times to obtain the aqueous solution containing the flavor substances;

(16) mixing the rice with the aqueous solution containing the flavor substances in a mass ratio of 1:1.4, and soaking the rice; sub-packaging the rice by adopting environment-friendly, high-temperature-resistant and high-pressure-resistant packaging boxes, cooking the rice for 30 min at normal pressure, and then, performing sterile vacuum sealing; after the sealing is finished, fast cooling the cooked rice by adopting an air cooling mode in the low temperature environment of −10 DEG C. at the average cooling rate of 5 to 7 DEG C./min until the central temperature of the cooked rice is reduced to 30 DEG C., and then, storing the cooked rice at normal temperature;

(17) and after the cooked rice is stored for 90 days at normal temperature, analyzing volatile odor components of the obtained instant cooked rice and fresh cooked rice by utilizing the headspace solid-phase microextraction-gas chromatography-mass spectrometry technology. As shown in FIG. 1 and FIG. 4, the contents and varieties of the volatile smell components released by the instant cooked rice obtained by the example and the fresh cooked rice are approximately identical. The fast gas chromatography electronic nose is utilized for detecting the flavors of the instant cooked rice obtained by the example and the fresh cooked rice, and the results show that the two flavors have no significant difference.

(18) TABLE-US-00001 TABLE 1 contents (mg/kg) of eight flavor substances in examples 1-3 Influence on contents (mg/kg) of typical flavor substances in cooked rice by cooling rate: 1 2 3 4 5 6 7 8 Fresh 0.0491 ± 0.0195 ± 0.0512 ± 0.0483 ± 0.0685 ± 0.1194 ± 0.1529 ± 0.1639 ± cooked rice 0.0047 0.0027 0.0053 0.0035 0.0049 0.0106 0.0092 0.0137 Example 1 0.0420 ± 0.0180 ± 0.0397 ± 0.0353 ± 0.0510 ± 0.1087 ± 0.1180 ± 0.0890 ± 0.0070 0.0026 0.0055 0.0065 0.0056 0.0152 0.0085 0.0106 Example 2 0.0842 ± 0.0321 ± 0.0528 ± 0.0639 ± 0.0416 ± 0.0907 ± 0.1504 ± 0.1402 ± 0.0021 0.0036 0.0067 0.0058 0.0047 0.0133 0.0081 0.0112 Example 3 0.0669 ± 0.0301 ± 0.0625 ± 0.0426 ± 0.0573 ± 0.1009 ± 0.1634 ± 0.1723 ± 0.0072 0.0046 0.0093 0.0068 0.0039 0.0156 0.0126 0.0089

(19) Washing rice twice with drinking water at about 10 DEG C., and then, putting the rice into a proper amount of drinking water to be soaked for 30 min; preparing a stock solution of an aqueous solution containing 4% of 2-acetyl-1-pyrroline, 0.2% of 2-acetylpyridine, 0.9% of ethyl 2-methylpentanoate, 2% of gamma-decalactone, 0.5% of linalool, 0.2% of alpha-terpineol, 0.2% of 1-octen-3-ol and 0.5% of phenethyl alcohol; diluting the stock solution by 10.sup.6 times to obtain the aqueous solution containing the flavor substances;

(20) mixing the rice with the aqueous solution containing the flavor substances in a mass ratio of 1:1.4, and soaking the rice; sub-packaging the rice by adopting environment-friendly, high-temperature-resistant and high-pressure-resistant packaging boxes, cooking the rice for 30 min at normal pressure, and then, performing sterile vacuum sealing; after the sealing is finished, fast cooling the cooked rice by adopting a refrigeration house cooling mode in the low temperature environment of −70 DEG C. at the average cooling rates of 1 to 3 DEG C./min, 3 to 5 DEG C./min, 5 to 7 DEG C./min, 7 to 9 DEG C./min or 9 to 11 DEG C./min until the central temperature of the cooked rice is reduced to 15 DEG C., and then, storing the cooked rice at normal temperature; and after the cooked rice is stored for 90 days at normal temperature, analyzing volatile odor components of the obtained instant cooked rice and fresh cooked rice by utilizing the headspace solid-phase microextraction-gas chromatography-mass spectrometry technology. The results are as shown in table 2.

(21) TABLE-US-00002 TABLE 2 influence on contents (mg/kg) of typical flavor substances in cooked rice by cooling rate 1 2 3 4 0 d 90 d 0 d 90 d 0 d 90 d 0 d 90 d Common 0.0570 ± NDb 0.0207 ± 0.0020 ± 0.0607 ± 0.0100 ± 0.0497 ± 0.0033 ± cooling 0.0056a 0.0035a** 0.0036b** 0.0081a** 0.0044c** 0.0042a** 0.0058d** (0.49 DEG C./min) 1~3 0.0577 ± 0.1367 ± 0.0200 ± 0.0080 ± 0.0603 ± 0.0200 ± 0.0503 ± 0.0073 ± DEG 0.0050a 0.1041a 0.0020a** 0.0036ab** 0.0045a** 0.0026bc** 0.0025a** 0.0025cd** C./min 3~5 0.0603 ± 0.0290 ± 0.0203 ± 0.0113 ± 0.0607 ± 0.0177 ± 0.0497 ± 0.0210 ± DEG 0.0057a** 0.0061ab** 0.0038a* 0.0032ab* 0.0097a** 0.0068bc** 0.0032a** 0.0066bc** C./min 5~7 0.0560 ± 0.0537 ± 0.0203 ± 0.0173 ± 0.0607 ± 0.0293 ± 0.0500 ± 0.0410 ± DEG 0.0096a 0.0100ab 0.0099a 0.0090a 0.0097a** 0.0012b** 0.0026a* 0.0046a* C./min 7~9 0.0563 ± 0.0543 ± 0.0220 ± 0.0187 ± 0.0600 ± 0.0557 ± 0.0503 ± 0.0483 ± DEG 0.0132a 0.0100ab 0.0088a 0.0075a 0.0115a 0.0135a 0.0074a 0.0081a C./min 9~11 0.0500 ± 0.0420 ± 0.0200 ± 0.0180 ± 0.0610 ± 0.0397 ± 0.0500 ± 0.0353 ± DEG 0.0115a 0.0070ab 0.0020a* 0.0026ab* 0.0095a* 0.0055b* 0.0096a 0.0065ab C./min 5 6 7 8 0 d 90 d 0 d 90 d 0 d 90 d 0 d 90 d Common 0.0700 ± 0.0097 ± 0.139 ± 0.0197 ± 0.1403 ± 0.0027 ± 0.1507 ± 0.0393 ± cooling 0.0044a** 0.0021c** 0.0127a** 0.0025d** 0.0100a** 0.0025c** 0.0126a** 0.0025c** (0.49 DEG C./min) 1~3 0.0693 ± 0.0117 ± 0.0996 ± 0.0537 ± 0.1417 ± 0.0380 ± 0.1503 ± 0.0573 ± DEG 0.0025a** 0.0025c** 0.0752a 0.0107cd 0.0075a** 0.0095b** 0.0029a** 0.0115bc** C./min 3~5 0.0701 ± 0.0323 ± 0.1373 ± 0.0803 ± 0.1403 ± 0.1083 ± 0.1527 ± 0.0733 ± DEG 0.0056a** 0.0023b** 0.0115a* 0.0251bc* 0.0060a* 0.0161a* 0.0092a** 0.0136ab** C./min 5~7 0.0697 ± 0.0563 ± 0.1470 ± 0.1220 ± 0.1417 ± 0.1170 ± 0.1493 ± 0.0753 ± DEG 0.0078a 0.0064a 0.0085a* 0.0124a* 0.0067a 0.0151a 0.0092a* 0.0055ab* C./min 7~9 0.0693 ± 0.0660 ± 0.1490 ± 0.1447 ± 0.1420 ± 0.1383 ± 0.1497 ± 0.0960 ± DEG 0.0051a 0.0061a 0.0061a 0.0038a 0.0087a 0.0100a 0.0080a* 0.0115a* C./min 9~11 0.0677 ± 0.0510 ± 0.1373 ± 0.1087 ± 0.1427 ± 0.1180 ± 0.1509 ± 0.0890 ± DEG 0.0091a 0.0056b 0.0085a 0.0152ab 0.0060a* 0.0085a* 0.0096a* 0.0106b* C./min Note: compound 1: 2-acetyl-1-pyrroline; compound 2: 2-acetylpyridine; compound 3: ethyl 2-methylpentanoate; compound 4: gamma-decalactone; compound 5: linalool; compound 6: alpha-terpineol; compound 7: 1-octen-3-ol; compound 8: phenethyl alcohol; data = average value ± standard deviation (n = 3). ND means not detected. The same English letters in the same column in the table indicate that the differences are not significant (p < 0.05), 0 day compared with 90 days, **indicates that the differences are extremely significant, *indicates that the differences are significant, and no mark indicates that there is no significant difference.

(22) As shown in table 2, at 0 day, with the increase of the cooling rate, the flavor components have no significant difference; and after the cooked rice is stored for 90 days, with the increase of the cooling rate, the contents of the flavor compounds firstly increase and then decrease, the reason is that fast cooling ensures fast nucleation of starch to promote coating of the flavor substances, but too fast cooling rate may cause the starch molecular chains to have no time to combine to each other, and the nucleation rate decreases so as to cause the loss of the flavor substances. Seen from table 1, the optimal cooling rate is 7 to 9 DEG C./min, and the secondary cooling rate is 5 to 7 DEG C./min. At the same cooling rate, the differences of the flavors at 0 day and 90 days are compared, the comparison results show that when a common cooling rate is adopted, the differences of all compounds are extremely significant; when the cooling rate of 7 to 9 DEG C./min is adopted, most of the flavor components at 0 day and 90 days basically have no significant difference; and when the cooling rate of 5 to 7 DEG C./min is adopted, the effect is secondary. In conclusion, the cooling rate is controlled to be 5 to 9 DEG C./min so as to be most favorable for keeping the flavor of the cooked rice.