Drying method of whole grape fruit puree and dried whole grape fruit product

Abstract

The invention provides a drying method of whole grape fruit puree and a dried whole grape fruit product, and belongs to the technical field of fruit drying. The whole grape puree is sequentially subjected to hot air drying and microwave vacuum drying. The problems that local hot spots are caused when semi-solid / liquid food and a high-sugar, high-moisture and high-viscosity system are subjected to microwave vacuum drying, and liquid is splashed under the condition that internal pressure is increased are solved, hot air drying and microwave vacuum drying are combined to control the viscosity of the puree to be before a blasting point which can bear the internal pressure, so that a puffing effect is generated, and the puree has a good taste. Compared with a raisin product prepared through traditional sun-drying or drying, the dried fruit product with the interior puffed is obtained, due to the fact that the dried fruit product contains the grape skin and the grape seeds, the dried fruit product is rich in nutrition, the puffed whole dried fruit product is creatively prepared, and the shape and taste of the dried fruit product are superior to those of a traditional rigid flat dried fruit product.

Description

Technical Field

[0001] The present invention relates to the technical field of fruit drying, and particularly relates to a drying method for whole grape puree and a dried whole grape product. Background Art

[0002] In addition to fresh consumption, grapes are mainly used to produce products such as fruit juice, jam, jelly, and raisins. Currently popular grape products basically do not contain grape seeds and grape skins. However, polyphenols with antioxidant activity are mainly stored in grape skins (28 - 35 wt%) and seeds (60 - 70 wt%). Therefore, grape seeds can be used for the research and development of health products, such as grape seed extracts sold on the market. In addition, grape seeds contain fiber, protein, and fatty acids, and grape skins contain a high level of anthocyanins, which can be used as natural colorants. Therefore, using the whole grape, including seeds and skins, to develop new dried whole grape products can add dietary fiber, protein, essential fatty acids, and more polyphenols to natural high-sugar grape products, and prepare healthy foods rich in dietary fiber, protein, unsaturated fatty acids, and carbohydrates.

[0003] Traditionally, grapes are dried by solar energy. Solar drying is the oldest drying method for raisin production, but it has many disadvantages, such as microbial spoilage, debris contamination, and most importantly, difficulties caused by bad weather. With the continuous progress of technology, freeze-drying technology, spray-drying technology, and microwave vacuum drying (MVD) have been widely promoted. Freeze-drying removes moisture from frozen fruits by sublimation, thus maintaining color, texture, and nutrition, and producing high-quality products. However, due to the refrigeration and vacuum systems, this process requires more energy and longer time than other traditional methods. Since whole grape puree has the characteristics of high sugar, high moisture, and high viscosity, and contains grape seeds, it is not suitable for spray drying. Moreover, a high-sugar, high-moisture, and high-viscosity system will cause local hot spots in vacuum microwave drying, and liquid splashing will occur when the internal pressure increases, so it is also not suitable for directly drying whole grape puree. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a drying method for whole grape puree and a dried whole grape product. The drying method for whole grape puree of the present invention combines hot air drying and microwave vacuum drying, solves the problems of excessive hot spot temperature and liquid splashing, has good drying effect, and can produce an expansion effect that cannot be formed by other drying methods, and prepares a dried fruit product with internal expansion.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a drying method for whole grape puree, comprising the following steps:

[0007] The whole grape puree is subjected to hot air drying and microwave vacuum drying in sequence. The temperature of the hot air drying is 50 - 70°C, the time is 150 - 300 min, and the wind speed is 1 - 2 m / s. The power density of the microwave vacuum drying is 1 - 4 W / g.

[0008] Preferably, the power of the microwave vacuum drying is 5 - 20 kW.

[0009] Preferably, the power of the microwave vacuum drying is 10 - 15 kW.

[0010] Preferably, the whole grape puree is obtained by a method including the following steps:

[0011] The grapes are frozen and then crushed to obtain an initial puree;

[0012] The initial puree is sheared to obtain the whole grape puree.

[0013] Preferably, the temperature of the crushing does not exceed 18°C.

[0014] Preferably, the particle size of the grape seeds in the whole grape puree is below 50 μm.

[0015] Preferably, the rotation speed of the shearing is 9800 - 13000 revolutions per minute, and the time is 5 - 10 min.

[0016] Preferably, the temperature of the crushing does not exceed 18°C.

[0017] The present invention also provides a dried whole grape product prepared by the drying method described in the above technical solution.

[0018] The present invention provides a drying method for whole grape puree, including the following steps: The whole grape puree is subjected to hot air drying and microwave vacuum drying in sequence. The temperature of the hot air drying is 50 - 70°C, the time is 5 - 30 min, the wind speed is 1 - 2 m / s, and the power density of the microwave vacuum drying is 2 - 4 W / g.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The present invention innovatively develops an economical, efficient and high-quality drying method for drying whole grape puree containing grape seeds and grape skins, solving the problems that local hot spots will be caused when microwave vacuum drying semi-solid / liquid foods and high-sugar, high-moisture and high-viscosity systems, and liquid splashing will occur when the internal pressure increases. The combination of hot air drying and microwave vacuum drying controls the viscosity of the puree before the bursting point of the tolerable internal pressure, thereby producing an expansion effect and obtaining a dried fruit product with internal expansion. Compared with traditional raisin products made by sun drying or baking, it is not only more nutritious because it contains grape skins and grape seeds, but also creatively prepares an expanded whole fruit dried product, with a better shape and taste than traditional rigid flat dried fruit products; and the combination of hot air drying and microwave vacuum drying takes the shortest time, and the contents of protein, crude fiber, trace elements and total fatty acids are much higher than those of traditional raisin products, with good nutritional quality and the least energy consumption.

[0021] The present invention also provides a whole grape dried product, which is an expanded whole fruit dried product, with a better shape and taste than traditional rigid flat dried fruit products. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a physical picture of the whole grape dried product prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention provides a drying method for whole grape puree, comprising the following steps:

[0024] The whole grape puree is subjected to hot air drying and microwave vacuum drying in sequence. The temperature of the hot air drying is 50-70 °C, the time is 150-300 min, the wind speed is 1-2 m / s, and the power density of the microwave vacuum drying is 1-4 W / g.

[0025] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0026] In the present invention, the whole grape puree is prepared from Fuan thorn grape (Vitis davidii (Rom. Caill.) )). The seeds of the Fuan thorn grape are smaller and softer, with lower energy consumption during crushing and processing. The whole grape dried product prepared by adding grape seeds has significantly higher contents of crude protein, dietary fiber and total fatty acids compared with traditional raisin products made from seedless grapes, and is more nutritious.

[0027] In the present invention, the whole grape puree is preferably prepared by a method comprising the following steps:

[0028] Freeze the grapes and then crush them to obtain the initial puree;

[0029] Shear the initial puree to obtain the whole grape puree.

[0030] In the present invention, the temperature of the crushing is preferably not more than 18 °C.

[0031] The present invention preferably freezes the grapes and stirs them in a food processor for 20 - 30 minutes, so that the grape seeds are crushed into fine particles. During the crushing process, the container is preferably placed in ice cubes to reduce the ambient temperature.

[0032] In the present invention, the rotation speed of the shearing is preferably 9800 - 13000 revolutions per minute, specifically it can be 9800, 10000, 11000, 12000 or 13000 revolutions per minute, and the time is preferably 5 - 10 minutes, specifically it can be 5, 6, 7, 8, 9 or 10 minutes.

[0033] In the present invention, the particle size of the grape seeds in the whole grape puree is preferably below 50 μm, obtaining a whole grape puree with good fluidity, smooth taste in the mouth and no granular feeling.

[0034] In the present invention, during the shearing process, it is preferably paused every two minutes to prevent the system temperature from rising too fast and too high.

[0035] In the present invention, the temperature of the hot air drying can specifically be 50, 55, 60, 65 or 70 °C, the time can specifically be 160, 180, 200, 220 or 240 minutes, and the wind speed can specifically be 1, 1.5 or 2 m / s.

[0036] In the present invention, the power density of the microwave vacuum drying can specifically be 1, 1.5, 2, 3 or 4 W / g.

[0037] In the present invention, the power of the microwave vacuum drying is preferably 5 - 20 kW, more preferably 10 - 15 kW.

[0038] In the present invention, microwave vacuum drying is carried out after hot air drying, which greatly shortens the drying time, and the produced product is better than that using hot air drying alone.

[0039] In the present invention, the microwave vacuum drying is preferably carried out in a microwave vacuum dryer.

[0040] After the microwave vacuum drying is completed, the obtained whole grape dried product is preferably packaged and stored in a vacuum bag.

[0041] The present invention also provides a whole grape dried product prepared by the drying method described in the above technical solution.

[0042] The following will clearly and completely describe the technical solutions in the present invention in combination with the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0043] The test method in the present invention:

[0044] 1. Color:

[0045] The appearance color is obtained by color comparison and filling in the form by 10 sensory evaluation personnel.

[0046] 2. Hardness:

[0047] The hardness is measured by using a texture analyzer. The dehydrated sample is cut in half on a grooved insert supported by a BHK blade. The test speed is 1 mm / s and the penetration depth is 5 mm. The hardness is expressed as the peak compression force. At least 3 measurements are carried out on a group of treatments, and the average value is reported as the hardness in kilograms.

[0048] 3. Porosity:

[0049] The apparent density (ρ a ) is calculated by dividing the weight (m) of ten samples by their corresponding volume (cm 3 ); the sample volume is determined by the volume difference of millet in a 100 mL beaker with and without 10 samples using a graduated measuring cylinder, and the calculation method is as shown in formula (1):

[0050]

[0051] The true density (ρ) is calculated according to formula (2):

[0052]

[0053] (2) where X W and X CH are the masses of water and carbohydrates in the dehydrated sample respectively, and ρ w (0.9976 g / cm 3 ) and ρ CH (1.4246 g / cm 3 ) are their corresponding densities;

[0054] The porosity is calculated according to formula (3):

[0055]

[0056] 4. Rehydration characteristics: water absorption index

[0057] Use an electric grinder to grind the dehydrated grape samples into fine powder. Mix the powder with DI water in a 50 mL centrifuge tube at a ratio of 1:10 (w / w). After brief vortexing, place all centrifuge tubes in a water bath shaker and rehydrate overnight at 30 °C and 200 rpm. The rehydrated samples are used for determination.

[0058] Water absorption index (WAI):

[0059] Mix the total mass of 3 g of powder (mo) obtained as described above with 30 mL of deionized water in a 50 mL centrifuge tube. All samples are equilibrated in a water bath shaker at 30 °C and 200 rpm for 30 min. After homogenization, centrifuge the samples at 10,000 rpm for 15 min. Pour the supernatant into an aluminum weighing dish and then dry it at 105 °C for 4 h. The mass of the remaining solid after centrifugation is recorded as ms. WAI is calculated as the percentage of ms to mo.

[0060] 5. Particle size distribution (D0.9) of the rehydrated samples:

[0061] Measure the particle size of the rehydrated samples using a particle size analyzer. The refractive index is measured using a refractometer. Using distilled water as the dispersant, measure the samples when the added sample concentration reaches 5% obscuration. Measure the particle size values in triplicate.

[0062] 6. Phenolic compound content and antioxidant activity:

[0063] 6.1. Sample extraction:

[0064] Grind the dehydrated samples into fine powder and mix with acidified methanol (1 wt% HCl) at a solvent ratio of 1:10 (w / v). After brief vortexing, shake the test tubes in a water bath shaker at 70 rpm for 2 h at room temperature. Then centrifuge the samples at 9,500 rpm for 10 min at 4 °C. Transfer the supernatant to an opaque sample bottle and store it at -20 °C for chemical analysis.

[0065] 6.2. Total phenolic content (PC):

[0066] All results are expressed as milligrams of gallic acid equivalents (GAE) per liter of extract (mg / L).

[0067] 6.3. Total anthocyanin content (AC):

[0068] Expressed as cyanidin-3-glucoside (cyd-3-glu) equivalents (CGE) per liter of extract (mg / L):

[0069]

[0070] Where A = (A 520nm -A700nm ) pH 1.0 -(A 520nm -A 700nm ) pH 4.5 ; The molecular weight is 449.2 g / mol; DF (dilution factor) = 25; ε is the molar extinction coefficient of cyd-3-glu = 26,900 L -1 × cm -1 × mol -1 ; L (path length) = 1 cm; 10 3 is the conversion from g to mg.

[0071] 6.4. In vitro antioxidant activity (ABTS free radical scavenging activity):

[0072] The free radical scavenging ability is calculated as the inhibition percentage (%) according to formula (5):

[0073]

[0074] A control is the absorbance of the blank, and A sample is the absorbance of the sample. The higher the inhibition rate, the stronger the antioxidant activity.

[0075] 7. The total fiber, total protein, and total fatty acid contents were detected according to the methods of approximate composition analysis. The crude fiber and crude protein were analyzed according to AOAC 954.02 and AOAC 992.23. The total fatty acid profile was analyzed by gas chromatography-mass spectrometry.

[0076] Example 1

[0077] Whole Fuan thorn grapes (including seeds and skins) were selected. The cold grapes were stirred at high speed in a food processor for 20 min to break the grape seeds into fine particles. During the process, the container was placed in ice. The obtained initial puree was processed with a high-shear mixer at a speed of 98,000 revolutions per minute for 10 min, and paused every two minutes to prevent the system temperature from rising too fast and too high. Finally, the particle size of the grape seeds was mostly below 50 μm. The obtained whole fruit puree sample was transferred to a silica gel container and dried by hot air drying equipment for 240 min at a set temperature of 60 °C and a wind speed of 1 m / s. Then, it was dried by a 10 kW microwave vacuum dryer with a power density of 2 W / g for microwave vacuum drying. After that, the obtained dried whole fruit products of grapes were packed and stored in a vacuum bag.

[0078] Figure 1 Figure [ID number] is a physical picture of the dried whole fruit products of grapes prepared in Example 1. It can be seen that the dried whole fruit products of grapes prepared by the present invention are a kind of expanded dried whole fruit products, and their morphological and taste are superior to those of traditional rigid flat dried fruit products.

[0079] Example 2

[0080] Same as Example 1, except that the power density of microwave vacuum drying is 1 W / g.

[0081] Example 3

[0082] Same as Example 1, except that the power density of microwave vacuum drying is 1.5 W / g.

[0083] Comparative Example 1

[0084] Whole Fuan thorn grapes (including seeds and peel) were selected for vacuum freeze-drying, which was carried out by a freeze-dryer. The samples were freeze-dried at a final shelf temperature of 55 °C and a vacuum of 500 mTorr. The total processing time of freeze-drying was 30 h.

[0085] Comparative Example 2

[0086] Whole Fuan thorn grapes (including seeds and peel) were selected for hot air drying: hot air drying was carried out using a food dryer, the temperature was controlled at 60 °C, the time was 15 h, and it was dried until the weight change was less than 0.5 g.

[0087] The test results of the dried products prepared in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1. It can be seen from Table 1 that compared with the samples obtained by hot air drying, microwave vacuum drying after hot air drying can cause significant changes: lower hardness, higher antioxidant content (total phenols and total anthocyanins), and microwave vacuum drying can produce more nutritious puffed products, and the time of the present invention is much lower than that of vacuum freeze-drying. The drying time in Example 1 was reduced by 85% compared with Comparative Example 1, and only 15% of the time of Comparative Example 1 was used.

[0088] Table 1 Test results of the dried products prepared in Examples 1-3 and Comparative Examples 1-2

[0089]

[0090] Comparative Example 3

[0091] Same as Comparative Example 1, except that the whole Fuan thorn grapes selected do not include seeds.

[0092] The test results of the substance content of the dried products prepared in Example 1 and Comparative Examples 1-3 are shown in Table 2. It can be seen from Table 2 that the dried whole grape products with grape seeds added in the present invention have significantly higher total protein, total fiber and total fatty acid contents compared with the dried grape products made from traditional seedless grapes (Comparative Example 3).

[0093] Table 2 Test results of the substance content of the dried products prepared in Examples 1-3 and Comparative Examples 1-3

[0094]

[0095] The above are only the preferred embodiments of the present invention and do not impose any formal limitations on the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A drying method for whole grape puree, characterized in that, Comprising the following steps: Subjecting the whole grape puree to hot air drying and microwave vacuum drying in sequence. The temperature of the hot air drying is 50 - 70 °C, the time is 150 - 300 min, and the wind speed is 1 - 2 m / s. The power density of the microwave vacuum drying is 1 - 4 W / g.

2. The drying method according to claim 1, wherein The power of the microwave vacuum drying is 5 - 20 kW.

3. The drying method according to claim 2, wherein The power of the microwave vacuum drying is 10 - 15 kW.

4. The drying method according to claim 1, characterized in that, The whole grape puree is prepared by a method comprising the following steps: Freezing and crushing the grapes to obtain an initial puree; Shearing the initial puree to obtain the whole grape puree.

5. The drying method according to claim 4, wherein The temperature of the crushing does not exceed 18 °C.

6. The drying method according to claim 1 or 4, characterized in that, The particle size of the grape seeds in the whole grape puree is below 50 μm.

7. The drying method according to claim 4, wherein The rotation speed of the shearing is 9800 - 13000 revolutions per minute, and the time is 5 - 10 min.

8. The drying method according to claim 1, characterized in that, The whole grape puree is prepared from Fuan spiny grapes.

9. A whole grape dried product, characterized in that, Prepared by the drying method according to any one of claims 1 - 8.

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