Drying method suitable for just-picked oranges

Abstract

The invention relates to a drying method suitable for freshly picked oranges, which comprises the following steps: step 1, washing the freshly picked oranges, and then blowing the oranges with cold air until no water drops exist on the surfaces of the oranges; step 2, placing the oranges at the environment temperature of 35-40 DEG C and the environment humidity of 50-55% RH for standing for 24-36 hours; 3, hot air with the temperature of 35-40 DEG C is used for blowing the oranges for 3-5 hours, and the ventilation quantity of the hot air is 2.2-2.7 m < 3 > / s; step 4, placing the oranges and tangerines under the environment temperature of 45-50 DEG C and the environment humidity of 40-45% RH for standing for 12-24 hours; and step 5, blowing the oranges for 7-9 hours by using hot air at the temperature of 25-30 DEG C, wherein the ventilation quantity of the hot air is 1.8-2.1 m < 3 > / s.

Description

Technical Field

[0001] The invention relates to the technical field of citrus processing, and in particular to a drying method suitable for freshly picked citrus. Background Art

[0002] This section provides background information related to the present application which does not necessarily constitute prior art.

[0003] Citrus belongs to the Rutaceae family and the genus Citrus. Citrus contains a relatively rich amount of flavonoids. The content of flavonoids in different parts of citrus is from peel to pulp to juice, and the composition of bioactive substances is also the richest in the peel. Citrus flavonoids (such as polymethoxyflavones rich in citrus peel) play an important role in anti-oxidation, anti-inflammatory, liver protection and anti-tumor.

[0004] After the citrus fruits used to prepare tangerine peel are picked, they are dried to reduce their moisture content in order to extend the storage period. Existing drying methods mainly include airing, drying, refrigeration, etc. Drying citrus fruits after picking is a key step in maintaining their quality, and by reasonably removing excess moisture from citrus fruits, the storage period of citrus fruits can be extended. However, existing drying methods have the following technical problems:

[0005] 1. Although removing an appropriate amount of water from citrus fruits after preliminary treatment is beneficial, the existing drying methods are prone to excessive water removal from citrus fruits, which in turn reduces the quality of citrus fruits;

[0006] 2. The antioxidant effect of citrus peel will be significantly weakened after drying;

[0007] 3. For the purpose of improving economic benefits, the citrus pulp used to prepare tangerine peel is used to extract limonin compounds after being separated from the peel (the citrus pulp contains a variety of limonin compounds, such as limonin), but the content of limonin compounds in the citrus pulp that has been dried will be significantly reduced. Summary of the invention

[0008] The present invention aims to provide a method for drying citrus, which is suitable for processing citrus just picked. Using the drying method to process citrus has at least the following beneficial effects:

[0009] 1. The amount of moisture removed from the citrus treated by the drying method is 15%-20%, which can extend the storage period of the citrus. It should be noted that the amount of moisture removed recorded in the present invention should be understood as the weight reduction rate of the citrus treated by the drying method based on the weight of the citrus just picked;

[0010] 2. Compared with the antioxidant effect of the peel of citrus fruits just picked, the antioxidant effect of the peel of citrus fruits treated by the drying method is less weakened, and the antioxidant effect of the peel is positively correlated with the flavonoid content in the peel;

[0011] 3. Compared with the content of limonoid compounds in the pulp of citrus fruits just after picking, the content of limonoid compounds in the pulp of citrus fruits treated by the drying method is less reduced.

[0012] To achieve the above object, the present invention adopts the following technical solution: A drying method suitable for freshly picked citrus, comprising the following steps:

[0013] Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits;

[0014] Step 2, placing the citrus fruits at an ambient temperature of 35-40° C. and an ambient humidity of 50-55% RH for 24-36 hours;

[0015] Step 3: Use hot air at a temperature of 35-40℃ to blow the citrus for 3-5 hours, with a ventilation volume of 2.2-2.7m 3 / s;

[0016] Step 4, placing the citrus fruits at an ambient temperature of 45-50° C. and an ambient humidity of 40-45% RH for 12-24 hours;

[0017] Step 5: Use hot air at a temperature of 25-30℃ to blow the citrus for 7-9 hours, and the ventilation volume of the hot air is 1.8-2.1m 3 / s.

[0018] In one or more embodiments, in step one, an aqueous solution of sodium chloride (the content of sodium chloride is 0.01-0.02 g / ml) is used to wash the freshly picked citrus.

[0019] Adopting the above technical scheme can shorten the drying time for freshly picked citrus, effectively reduce the impact on the quality of citrus, and increase the storage period of citrus.

[0020] The following describes the invention in conjunction with specific embodiments. DETAILED DESCRIPTION

[0021] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0022] [Example 1]

[0023] The embodiment of the present invention provides a drying method suitable for freshly picked citrus fruits, comprising the following steps:

[0024] Step 1: Wash the freshly picked citrus fruits with an aqueous solution of sodium chloride (the content of sodium chloride is 0.01 g / ml), and then blow the citrus fruits with cold air until there are no water droplets on the surface of the citrus fruits;

[0025] Step 2: placing the citrus fruits in a constant humidity and thermostat for 24 hours, wherein the ambient temperature inside the constant humidity and thermostat is 40° C. and the ambient humidity is 55% RH;

[0026] Step 3: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 35°C to blow the citrus fruits for 5 hours. The ventilation volume of the hot air is 2.2m 3 / s;

[0027] Step 4: placing the citrus fruits in a constant humidity and thermostatic box for 24 hours, wherein the ambient temperature inside the constant humidity and thermostatic box is 45° C. and the ambient humidity is 45% RH;

[0028] Step 5: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 30°C to blow the citrus fruits for 7 hours. The ventilation volume of the hot air is 1.8m 3 / s.

[0029] [Example 2]

[0030] The embodiment of the present invention provides a drying method suitable for freshly picked citrus fruits, comprising the following steps:

[0031] Step 1: Wash the freshly picked citrus fruits with an aqueous solution of sodium chloride (the content of sodium chloride is 0.02 g / ml), and then blow the citrus fruits with cold air until there are no water droplets on the surface of the citrus fruits;

[0032] Step 2: placing the citrus fruits in a constant humidity and thermostat for 36 hours, wherein the ambient temperature inside the constant humidity and thermostat is 35° C. and the ambient humidity is 50% RH;

[0033] Step 3: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 40°C to blow the citrus fruits for 3 hours. The ventilation volume of the hot air is 2.7m 3 / s;

[0034] Step 4: placing the citrus fruits in a constant humidity and thermostat for 12 hours, wherein the ambient temperature inside the constant humidity and thermostat is 50° C. and the ambient humidity is 40% RH;

[0035] Step 5: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 25°C to blow the citrus fruits for 9 hours. The ventilation volume of the hot air is 2.1m 3 / s.

[0036] [Example 3]

[0037] The embodiment of the present invention provides a drying method suitable for freshly picked citrus fruits, comprising the following steps:

[0038] Step 1: Wash the freshly picked citrus fruits with an aqueous solution of sodium chloride (the content of sodium chloride is 0.015 g / ml), and then blow the citrus fruits with cold air until there are no water droplets on the surface of the citrus fruits;

[0039] Step 2: placing the citrus fruits in a constant humidity and thermostat for 30 hours, wherein the ambient temperature inside the constant humidity and thermostat is 38° C. and the ambient humidity is 52% RH;

[0040] Step 3: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 38°C to blow the citrus fruits for 4 hours. The ventilation volume of the hot air is 2.6m 3 / s;

[0041] Step 4: placing the citrus fruits in a constant humidity and thermostat for 20 hours, wherein the ambient temperature inside the constant humidity and thermostat is 48° C. and the ambient humidity is 43% RH;

[0042] Step 5: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 28°C to blow the citrus fruits for 8 hours. The ventilation volume of the hot air is 2.0 m 3 / s.

[0043] [Comparative Example 1]

[0044] The drying method provided in this comparative example is:

[0045] Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits;

[0046] Step 2: Place the citrus fruits in a constant humidity and thermostat for 62 hours, where the ambient temperature inside the constant humidity and thermostat is 48° C. and the ambient humidity is 43% RH.

[0047] [Comparative Example 2]

[0048] The drying method provided in this comparative example is:

[0049] Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits;

[0050] Step 2: Place the citrus fruits in the drying chamber of the hot air drying device, and use a blower to blow hot air into the drying chamber. Use hot air at a temperature of 38°C to blow the citrus fruits for 62 hours. The ventilation volume of the hot air is 2.6m 3 / s.

[0051] [Comparative Example 3]

[0052] The drying method provided in this comparative example is:

[0053] Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits;

[0054] Step 2: Place the citrus fruits in the drying chamber of the hot air drying device, and use a blower to blow hot air into the drying chamber. Use hot air at a temperature of 28°C to blow the citrus fruits for 62 hours. The ventilation volume of the hot air is 2.0 m 3 / s.

[0055] [Comparative Example 4]

[0056] The drying method provided in this comparative example is:

[0057] Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits;

[0058] Step 2: placing the citrus fruits in a constant humidity and thermostat for 50 hours, wherein the ambient temperature inside the constant humidity and thermostat is 38° C. and the ambient humidity is 52% RH;

[0059] Step 3: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 38°C to blow the citrus fruits for 12 hours. The ventilation volume of the hot air is 2.6m 3 / s.

[0060] [Comparative Example 5]

[0061] The drying method provided in this comparative example is:

[0062] Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits;

[0063] Step 2, Step 4, placing the citrus in a constant humidity and thermostat for 50 hours, the ambient temperature inside the constant humidity and thermostat is 48° C. and the ambient humidity is 43% RH;

[0064] Step 3: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 28°C to blow the citrus fruits for 12 hours. The ventilation volume of the hot air is 2.0m 3 / s.

[0065] [Comparative Example 6]

[0066] The drying method provided in this comparative example is:

[0067] Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits;

[0068] Step 2: placing the citrus fruits in a constant humidity and thermostat for 50 hours, wherein the ambient temperature inside the constant humidity and thermostat is 38° C. and the ambient humidity is 52% RH;

[0069] Step 3: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 28°C to blow the citrus fruits for 12 hours. The ventilation volume of the hot air is 2.0m 3 / s.

[0070] [Comparative Example 7]

[0071] The drying method provided in this comparative example is:

[0072] Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits;

[0073] Step 2: placing the citrus fruits in a constant humidity and thermostatic box for 50 hours, wherein the ambient temperature inside the constant humidity and thermostatic box is 48° C. and the ambient humidity is 43% RH;

[0074] Step 3: Place the citrus fruits in the drying chamber of the hot air drying device, and use the blower to blow hot air into the drying chamber. Use hot air at a temperature of 38°C to blow the citrus fruits for 12 hours. The ventilation volume of the hot air is 2.6m 3 / s.

[0075] [Drying effect test]

[0076] Pick 100 oranges of similar size and weight and group them into groups of 10, labelling them as groups AK.

[0077] The citrus fruits in group A were treated using the drying method provided in Example 1.

[0078] The citrus fruits in group B were treated using the drying method provided in Example 2.

[0079] The citrus fruits in group C were treated using the drying method provided in Example 3.

[0080] The citrus fruits in group D were treated using the drying method provided in Comparative Example 1.

[0081] The citrus fruits in group E were treated using the drying method provided in Comparative Example 2.

[0082] The citrus fruits in Group F were treated using the drying method provided in Comparative Example 3.

[0083] The drying method provided in Comparative Example 4 was used to treat the citrus fruits in Group G.

[0084] The drying method provided in Comparative Example 5 was used to treat the citrus fruits in Group H.

[0085] The drying method provided in Comparative Example 6 was used to treat the citrus fruits in Group I.

[0086] The drying method provided in Comparative Example 7 was used to treat the citrus fruits in Group J.

[0087] The citrus fruits in group K served as the blank control group and were not subjected to drying treatment.

[0088] The following tests were conducted on the citrus fruits of groups AJ that had completed the drying process:

[0089] 1. Weigh the weights of the citrus fruits in groups AJ before and after drying, obtain the difference, and calculate the ratio of the difference to the weight of the citrus fruits before drying, and then obtain the average value a (%), which can be approximately equivalent to the amount of water removed from the citrus fruits after drying;

[0090] 2. The dried citrus fruits of group AJ and the undried citrus fruits of group K were treated as follows: the peel and pulp of the citrus fruits were separated, the separated peel was crushed, and then an extraction solvent was added to obtain a mixture, the ratio of the peel to the extraction solvent was 1g:15mL, and the extraction solvent was selected from ethanol with a volume concentration of 55%; then the mixture was placed in an ultrasonic-microwave processor for simultaneous extraction to obtain an extract, and the conditions for the ultrasonic-microwave processor simultaneous extraction were: the extraction temperature was set to 50°C, the ultrasonic-microwave coordination time was 4min, the ultrasonic power was 450W, and the microwave power was 300W; after the extraction, the extract was concentrated and dried to obtain extract B. The flavonoid content in extract B was determined by existing liquid chromatography (HPLC), and the results are shown in Table 1. The specific method for determining the flavonoid content in extract B is as follows:

[0091] (1) Drawing of standard curve: accurately weigh 0.010g of rutin standard, dissolve in 70% ethanol and dilute to 50mL; accurately pipette 1.0, 2.0, 3.0, 4.0, 5.0, 6.0mL of rutin standard solution into a 25mL volumetric flask, add 1mL of 5% NaNO2 solution, shake well and let stand for 6min; then add 1mL of 10% Al(NO3)3 solution, shake well and let stand for 6min; then add 10mL of 4% NaOH solution, dilute to scale with 70% ethanol, shake well and let stand for 15min, use the solvent as blank reference solution, and measure the absorbance at a wavelength of 510nm; draw a standard curve with concentration as the horizontal axis and absorbance as the vertical axis. The standard curve of total flavonoids was measured as: y=0.0106x+0.0335, R2=0.9999.

[0092] (2) Determination of flavonoid content of extract B: Take 10 mL of the dissolved extract B in a 25 mL volumetric flask, measure the absorbance according to the above-mentioned standard curve method, and calculate the flavonoid content according to the following formula, thereby obtaining the average value of the flavonoid content in the peel of citrus fruits in different groups.

[0093] W=(c×V×n) / m

[0094] W is the content of total flavonoids in the sample, mg / g; c is the total flavonoid concentration of the extract, mg / mL; V is the volume of the fixed volume during the determination, mL; n is the dilution multiple; m is the sample weight, g.

[0095] 3. The dried citrus fruits of group AJ and the citrus fruits of group K that were not dried were treated as follows: the peel and pulp of the citrus fruits were separated, the separated pulp was squeezed and filtered in turn, the filtrate was taken, the volume was made up to 300 mL with double distilled water, and it was filtered again, 5 mL of the filtrate was added to a 50 mL centrifuge tube, 10 mL of dichloromethane was added, and it was shaken for about 20 minutes, and then ultrasonically extracted for 30 minutes, the lower layer liquid was taken and 10 mL of dichloromethane was added again to repeat the above steps, and the lower layer liquid was taken and concentrated to dryness to obtain extract C. The extract C was made up to 1 mL with acetonitrile solvent, filtered through a 0.22 μm microporous filter membrane to obtain a test sample, and then the existing liquid chromatography (HPLC) was used to determine the content of limonin in the test sample (i.e., the content of limonin in extract C), and the results are shown in Table 1. The specific method for determining the content of limonin in extract C is as follows:

[0096] Accurately weigh 0.025 g of a limonin standard, completely dissolve it in anhydrous ethanol and dilute it to 50 mL to prepare a 500 μg / mL limonin stock solution; take anhydrous ethanol and dilute the limonin stock solution to a concentration gradient of 6.25 μg / mL, 12.5 μg / mL, 25 μg / mL, 50 μg / mL, 100 μg / mL, 150 μg / mL and 250 μg / mL respectively; use a high performance liquid chromatograph, the mobile phase is pure water: acetonitrile (35%: 65%), isocratic elution, flow rate 1.0 mL / min, time 30 min, column temperature 30° C., injection volume 10 μL, detection wavelength 215 nm; under the above chromatographic detection conditions, determine the liquid chromatogram of the limonin content in the standard product, and draw a standard curve with concentration as the abscissa and absorbance as the ordinate. The standard curve of limonin was measured to be y=5568.2x+15480, R2=0.9995.

[0097] (2) Determination of limonin content in extract C: 25 μL of the test sample was taken and HPLC was used with a mobile phase of pure water: acetonitrile (35%: 65%), isocratic elution, flow rate 1.0 mL / min, time 30 min, column temperature 30°C, injection volume 10 μL, detection wavelength 215 nm ； The absorbance of the test sample was measured under the above chromatographic detection conditions, and the limonin content was calculated, thereby obtaining the average value of the limonin content in the pulp of citrus fruits of different groups.

[0098] According to the results in Table 1, it can be judged that the amount of moisture removed from the citrus treated by the drying method provided in the present application is within a reasonable range; taking the blank control group as a benchmark, compared with comparative examples 1-7, the citrus treated by the drying method provided in Examples 1-3 has a lower reduction in the content of flavonoids in the peel and the content of limonoid compounds in the pulp.

[0099] Table 1

[0100]

[0101] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0102] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A drying method suitable for freshly picked citrus fruits, characterized in that: The steps include: Step 1: Wash the freshly picked citrus fruits, and then blow cold air on the citrus fruits until there are no water droplets on the surface of the citrus fruits; Step 2, placing the citrus fruits at an ambient temperature of 35-40° C. and an ambient humidity of 50-55% RH for 24-36 hours; Step 3: Use hot air at a temperature of 35-40℃ to blow the citrus for 3-5 hours, with a ventilation volume of 2.2-2.7m 3 / s; Step 4, placing the citrus fruits at an ambient temperature of 45-50° C. and an ambient humidity of 40-45% RH for 12-24 hours; Step 5: Use hot air at a temperature of 25-30℃ to blow the citrus for 7-9 hours, and the ventilation volume of the hot air is 1.8-2.1m 3 / s.

2. The drying method according to claim 1, characterized in that In the step 1, a sodium chloride aqueous solution is used to wash the freshly picked citrus fruits, wherein the sodium chloride content in the sodium chloride aqueous solution is 0.01-0.02 g / ml.

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