A low gi lychee fruit powder base and a method of making the same

Abstract

The application discloses a low GI litchi fruit powder base and a preparation method thereof, and belongs to the technical field of food processing and functional food. The preparation method specifically comprises the following steps: (1) litchi pretreatment; (2) fruit pulp enzymolysis; (3) fruit pulp fermentation; and (4) drying and powdering. The litchi cell wall pectin structure is directionally depolymerized and modified by pectinase and arabinanase, then lactic acid bacteria fermentation is utilized to realize sugar metabolism, polysaccharide restructuring and metabolite conversion, and finally the low GI litchi fruit powder base is obtained.

Description

Technical Field

[0001] This invention relates to the field of food processing and functional food technology, and more specifically to a low-GI lychee fruit powder base and its preparation method. Background Technology

[0002] Lychees are rich in nutrients such as glucose, fructose, sucrose, polyphenols, and dietary fiber, giving them high nutritional value. However, the high content of available sugars in ripe lychees results in a high glycemic index (GI), limiting their use as a base material in people with diabetes, obesity, and functional health foods.

[0003] Existing low-GI fruit products mainly achieve their blood sugar-lowering effect by adding dietary fiber, sugar substitutes, or simply fermenting with lactic acid bacteria. However, most of them focus on reducing sugar content and lack research on the remodeling of fruit pulp cell wall structure and polysaccharide components. Moreover, it is difficult to achieve synergistic regulation of reducing available sugar, increasing functional polysaccharides, and enriching functional metabolites.

[0004] Currently, research on pectinase and arabinogalactanase in fruits mainly focuses on improving juice yield, reducing pulp viscosity, and improving juice clarity. Lactobacillus is mainly used to develop probiotic beverages. There is little research on the low-GI mechanism formed by the synergistic remodeling of sugar components, cell wall polysaccharides, and metabolites when these two enzymes and Lactobacillus work together in litchi pulp. There is also a lack of technical solutions for constructing low-GI litchi fruit powder base materials based on component remodeling.

[0005] Therefore, how to develop a low-GI litchi fruit powder base material based on the synergistic effect of pectinase, arabinogalactanase and lactobacillus to induce the remodeling of litchi pulp components and its preparation method is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a low-GI litchi fruit powder base and its preparation method, so as to overcome the shortcomings of the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a low-GI litchi fruit powder base material specifically includes the following steps: (1) Lychee pretreatment Peeled and pitted fresh lychee pulp is blended and homogenized to obtain lychee pulp. (2) Enzymatic hydrolysis of fruit pulp Add pectinase and arabinogalactase to litchi pulp, hydrolyze, sterilize, and obtain enzymatically hydrolyzed litchi pulp; (3) Fruit pulp fermentation Lactobacillus was inoculated into enzymatically hydrolyzed litchi pulp, and fermentation was carried out to obtain fermented litchi pulp. (4) Drying and grinding Fermented lychee pulp was pre-frozen, vacuum freeze-dried, and pulverized to obtain low-GI lychee fruit powder base material.

[0009] Furthermore, in step (1) above, the pulping equipment is a high-speed disperser with a rotation speed of 8000 rpm and a time of 5 min; the homogenizing equipment is a high-shear homogenizer with a rotation speed of 10000 r / min and a time of 30 s.

[0010] Furthermore, in step (2) above, the amount of pectinase added is 0.05%-1.0% of the mass of litchi pulp, preferably 0.5%.

[0011] The further beneficial effect of the above-mentioned method is that pectinase acts on the cell wall of litchi pulp, causing partial degradation of homogalacturonan (HG) and partial depolymerization of the cell wall, which releases pectin polysaccharides rich in arabinose, galactose and galacturonic acid into the soluble components; at the same time, it promotes the release of bound polyphenols.

[0012] Furthermore, in step (2) above, the amount of arabinogalactase added is 0.01%-0.5% of the mass of litchi pulp, preferably 0.3%.

[0013] The further beneficial effect of the above-mentioned method is that arabinogalactase further acts on the arabinogalactan side chain of rhamnogalacturonic acid polysaccharide-I (RG-I) to produce arabinooligosaccharides, which reduces the degree of pectin polymerization and thus improves its bioavailability and lactic acid bacteria fermentation efficiency.

[0014] Furthermore, in step (2) above, the enzymatic hydrolysis temperature is 35-55℃ and the time is 1-6h; the sterilization method is pasteurization, the temperature is 72℃ and the time is 10min.

[0015] The further beneficial effect of the above-mentioned method is that pasteurization can not only inactivate the original microorganisms in the litchi pulp, but also inactivate the pectinase and arabinogalactase in the system, thus preventing further enzymatic hydrolysis.

[0016] Furthermore, in step (3) above, the lactobacillus is *Lactobacillus plantarum* (scientific name: *Lactobacillus plantarum*). Lactiplantibacillus plantarum ATCC 14917 strain suspension, Lactobacillus fermentum (scientific name: Limosilactobacillus fermentum GDMCC strain 1.1796 bacterial suspension or Lactobacillus rhamnosus (scientific name: Lactobacillus rhamnosusGDMCC 1.2223 strain suspension (all purchased from Guangdong Provincial Microbial Culture Collection Center), preferably Lactobacillus plantarum ATCC14917 strain suspension, concentration 10. 8 CFU / mL, the inoculation amount is 2% of the volume of enzymatically hydrolyzed litchi pulp (volume ratio v / v).

[0017] The further beneficial effects of the above-mentioned method are that the remodeling of litchi pulp components induced by Lactobacillus fermentation mainly involves three aspects: 1) Sugar component remodeling: Lactobacillus fermentation leads to a decrease in the content of glucose, sucrose, and fructose, resulting in a decrease in the total available sugar content; 2) Cell wall polysaccharide remodeling: Lactobacillus fermentation further promotes the partial degradation of water-insoluble polysaccharides in the cell wall into water-soluble polysaccharides, leading to an increase in the content of water-soluble polysaccharides and an increase in the content of arabinogalactan; 3) Metabolite remodeling: Lactobacillus fermentation leads to an increase in organic acids such as lactic acid, the release of bound polyphenols, and an increase in the total phenol content.

[0018] Furthermore, in step (3) above, the fermentation temperature is 37°C and the time is 3 days.

[0019] Furthermore, in step (4) above, the pre-freezing temperature is -80℃ and the time is 12 h.

[0020] Furthermore, in step (4) above, the vacuum freeze drying is specifically as follows: the first drying is set to cold trap -80℃ and vacuum 10-15 Pa; the shelf temperature is gradually increased from -30℃ to -20℃ and lasts for 28-32 h; the second drying is 20-25℃ and vacuum 5-10 Pa and drying for 6-8 h.

[0021] This invention also claims protection for a low-GI litchi fruit powder base obtained by the above preparation method, which has at least three of the following characteristics: (1) Estimated glycemic index (eGI) ≤ 55; (2) The glucose content decreased by more than 30% compared with that before fermentation; (3) The sucrose content is reduced by more than 20% compared with that before fermentation; (4) The content of water-soluble polysaccharides is increased by more than 30%; (5) The total phenol content is increased by more than 10%; (6) The lactic acid content increased by more than 3 times.

[0022] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: (1) Remodeling of sugar components: The combined enzyme and lactobacillus fermentation leads to a decrease in the content of glucose, fructose and sucrose in the litchi pulp system, reducing the content of high GI sugars in the system and reducing the potential for glycemic increase from the source.

[0023] (2) Reconstruction of cell wall polysaccharides: The complex enzymes work together with Lactobacillus fermentation to promote the conversion of water-insoluble polysaccharides in litchi cell walls into water-soluble polysaccharides, thereby enriching arabinogalactan and reconstructing the RG-I structure.

[0024] (3) Promote the release of phenols: Fermentation promotes the release of bound polyphenols, increases the total phenol content, and enhances the system's ability to inhibit glycoside hydrolases.

[0025] (4) Promote the accumulation of organic acids: Organic acids such as lactic acid and acetic acid are produced during fermentation, which can delay sugar absorption and improve blood sugar response.

[0026] (5) Constructing a low-GI system: The synergistic effect of compound enzymes and Lactobacillus fermentation-induced sugar component remodeling, cell wall polysaccharide reconstruction and metabolite remodeling results in a significantly reduced eGI value of the obtained litchi fruit powder base material.

[0027] In summary, this invention uses pectinase and arabinogalactanase to directionally depolymerize and modify the pectin structure of litchi cell walls, and then uses lactobacillus fermentation to achieve sugar metabolism, polysaccharide reconstruction and metabolite conversion, ultimately obtaining a low-GI litchi fruit powder base material. Attached Figure Description

[0028] Figure 1 The monosaccharide composition of the polysaccharides in the litchi fruit powder base materials of Examples 1-3 and Comparative Example 1 is shown. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the following examples, pectinase was purchased from Shanghai Ruiyong Biotechnology Co., Ltd.; arabinogalactase was purchased from Newgene Biotechnology (Shanghai) Co., Ltd.; Lactobacillus plantarum ATCC 14917, Lactobacillus fermentum GDMCC 1.1796 and Lactobacillus rhamnosus GDMCC 1.2223 are all prior art and were purchased from Guangdong Provincial Microbial Culture Collection Center (GDMCC), located at 5th Floor, Experimental Building, No. 100 Xianlie Middle Road, Yuexiu District, Guangzhou, Guangdong Province.

[0031] Example 1 The preparation method of low-GI litchi fruit powder base material specifically includes the following steps: (1) Lychee pretreatment First, place the peeled and pitted fresh lychee pulp in a high-speed disperser and blend at 8000 r / min for 5 min; then place it in a high-shear homogenizer and homogenize at 10000 r / min for 30 s to homogenize the pulp system and obtain lychee pulp. (2) Enzymatic hydrolysis of fruit pulp Add 0.5% by weight of pectinase and 0.3% by weight of arabinogalactase to litchi pulp, enzymatically hydrolyze at 45℃ for 3 hours, and then pasteurize at 72℃ for 10 minutes to obtain enzymatically hydrolyzed litchi pulp. (3) Fruit pulp fermentation Inoculate 2% (v / v) 10% concentration into enzymatically hydrolyzed litchi pulp. 8 A CFU / mL suspension of Lactobacillus plantarum strain ATCC14917 was then fermented at 37°C for 3 days to obtain fermented litchi pulp. (4) Drying and grinding First, the fermented lychee pulp was pre-frozen at -80℃ for 12 h; then, it was freeze-dried under vacuum: the first drying was set at -80℃ in the cold trap and 12 Pa in the vacuum; the shelf temperature was gradually increased from -30℃ to -20℃ for 30 h; the second drying was at 22℃ and 8 Pa in the vacuum for 6 h; finally, it was pulverized to obtain the low-GI lychee fruit powder base.

[0032] Example 2 The preparation method of low-GI litchi fruit powder base material specifically includes the following steps: (1) Lychee pretreatment First, place the peeled and pitted fresh lychee pulp in a high-speed disperser and blend at 8000 r / min for 5 min; then place it in a high-shear homogenizer and homogenize at 10000 r / min for 30 s to homogenize the pulp system and obtain lychee pulp. (2) Enzymatic hydrolysis of fruit pulp Add 1.0% by weight of pectinase and 0.5% by weight of arabinogalactase to litchi pulp, enzymatically hydrolyze at 45℃ for 3 hours, and then pasteurize at 72℃ for 10 minutes to obtain enzymatically hydrolyzed litchi pulp. (3) Fruit pulp fermentation Inoculate 2% (v / v) 10% concentration into enzymatically hydrolyzed litchi pulp. 8 A suspension of Lactobacillus fermentum strain GDMCC1.1796 with a concentration of CFU / mL was prepared and fermented at 37°C for 3 days to obtain fermented litchi pulp. (4) Drying and grinding First, the fermented lychee pulp was pre-frozen at -80℃ for 12 h; then, it was freeze-dried under vacuum: the first drying was set at -80℃ in the cold trap and 12 Pa in the vacuum; the shelf temperature was gradually increased from -30℃ to -20℃ for 30 h; the second drying was at 22℃ and 8 Pa in the vacuum for 6 h; finally, it was pulverized to obtain the low-GI lychee fruit powder base.

[0033] Example 3 The preparation method of low-GI litchi fruit powder base material specifically includes the following steps: (1) Lychee pretreatment First, place the peeled and pitted fresh lychee pulp in a high-speed disperser and blend at 8000 r / min for 5 min; then place it in a high-shear homogenizer and homogenize at 10000 r / min for 30 s to homogenize the pulp system and obtain lychee pulp. (2) Enzymatic hydrolysis of fruit pulp Add 1.0% by weight of pectinase and 0.5% by weight of arabinogalactase to litchi pulp, enzymatically hydrolyze at 45℃ for 3 hours, and then pasteurize at 72℃ for 10 minutes to obtain enzymatically hydrolyzed litchi pulp. (3) Fruit pulp fermentation Inoculate 2% (v / v) 10% concentration into enzymatically hydrolyzed litchi pulp. 8 A CFU / mL suspension of Lactobacillus rhamnosus GDMCC1.2223 strain was then fermented at 37°C for 3 days to obtain fermented litchi pulp. (4) Drying and grinding First, the fermented lychee pulp was pre-frozen at -80℃ for 12 h; then, it was freeze-dried under vacuum: the first drying was set at -80℃ in the cold trap and 12 Pa in the vacuum; the shelf temperature was gradually increased from -30℃ to -20℃ for 30 h; the second drying was at 22℃ and 8 Pa in the vacuum for 6 h; finally, it was pulverized to obtain the low-GI lychee fruit powder base.

[0034] Comparative Example 1 The preparation method of untreated litchi fruit powder base material specifically includes the following steps: (1) Lychee pretreatment First, place the peeled and pitted fresh lychee pulp in a high-speed disperser and blend at 8000 r / min for 5 min; then place it in a high-shear homogenizer and homogenize at 10000 r / min for 30 s to homogenize the pulp system and obtain lychee pulp. (2) Drying and grinding First, the lychee pulp was pre-frozen at -80℃ for 12 hours; then, it was freeze-dried under vacuum: the first drying was set at -80℃ in the cold trap and 12 Pa in the vacuum; the shelf temperature was gradually increased from -30℃ to -20℃ for 30 hours; the second drying was at 22℃ and 8 Pa in the vacuum for 6 hours; finally, it was pulverized to obtain the untreated lychee pulp base material.

[0035] Performance testing 1. Sugar content Fermented lychee pulp prepared in Examples 1-3 and untreated lychee pulp prepared in Comparative Example 1 were used to test the contents of glucose, fructose and sucrose by ion chromatography. The results are shown in Table 1.

[0036] Table 1. Sugar content of fermented lychee pulp in Examples 1-3 and untreated lychee pulp in Comparative Example 1.

[0037] As shown in Table 1, the contents of glucose, fructose and sucrose in untreated litchi pulp were all high. The contents of glucose, fructose and sucrose in litchi pulp could be reduced to varying degrees by compound enzyme-Lactobacillus plantarum fermentation treatment, compound enzyme-Lactobacillus fermentation treatment and compound enzyme-Lactobacillus rhamnosus fermentation treatment. Among them, the contents of the three sugars were the lowest after compound enzyme-Lactobacillus plantarum fermentation treatment, and the sugar-reducing effect was the best.

[0038] 2. Acid content Fermented litchi pulp prepared in Examples 1-3 and untreated litchi pulp prepared in Comparative Example 1 were used to test the contents of acetic acid, malic acid, lactic acid and citric acid by high performance liquid chromatography. The results are shown in Table 2.

[0039] Table 2. Acid content of fermented lychee pulp in Examples 1-3 and untreated lychee pulp in Comparative Example 1.

[0040] Table 2 shows that untreated litchi pulp contains small amounts of acetic acid, malic acid, lactic acid, and citric acid. After treatment with compound enzyme-Lactobacillus plantarum fermentation, compound enzyme-Lactobacillus fermentation, and compound enzyme-Lactobacillus rhamnosus fermentation, the content of various organic acids in the litchi pulp changed. Overall, the acetic acid content increased, the malic acid content decreased, the lactic acid content increased, and the citric acid content changed relatively little. Among these, the acetic acid content increased the most in the litchi pulp fermented with compound enzyme-Lactobacillus fermentation, and the corresponding malic acid content decreased the most significantly; the lactic acid content increased the most in the litchi pulp fermented with compound enzyme-Lactobacillus plantarum.

[0041] 3. eGI value The eGI values ​​of fermented litchi fruit powder base materials (low-GI litchi fruit powder base materials) prepared in Examples 1-3 and untreated litchi fruit powder base materials prepared in Comparative Example 1 were tested respectively, and the results are shown in Table 3.

[0042] The method for determining the eGI value includes the following steps: (1) External oral gastrointestinal digestion Oral stage: Accurately weigh 0.20 g of lychee fruit powder base and white bread flour (reference food) into an Erlenmeyer flask, add 5 mL of preheated simulated saliva (pH 7.0) at 37℃, and 25 μL of 0.3 mol... L -1 CaCl2 After shaking the 2H2O solution well, use 1 mol L -1 Adjust the pH of the system to 7.0 with hydrochloric acid or sodium hydroxide, then add 0.5 mL of α-amylase solution (1500 U). mL -1 Add sterile water to bring the final volume to 10 mL. Quickly transfer the conical flask to a 37°C shaker and incubate in the dark for 5 min.

[0043] Stomach stage: Immediately after the simulated oral digestion is completed, add 8 mL of preheated simulated gastric juice (pH 3.0) at 37°C and 5 μL of 0.3 mol / L solution. L -1 CaCl2 After shaking the 2H2O solution well, use 1 mol L -1 Adjust the pH of the system to 3.0 with hydrochloric acid, then add 0.5 mL of gastric digestive enzyme solution (8000 U pepsin). mL -1 1000 U of gastric lipase mL -1 Add sterile water to bring the final volume to 20 mL. Quickly transfer the conical flask to a 37°C shaker and incubate in the dark for 2 hours.

[0044] Small intestine stage: Immediately after the simulated stomach digestion is completed, add 8.5 mL of preheated simulated intestinal fluid (pH 7.0) at 37°C and 40 μL of 0.3 mol / L solution. L -1 CaCl2 After shaking the 2H2O solution well, use 1 mol L -1 Adjust the pH of the system to 7.0 with sodium hydroxide, then add 2.5 mL of porcine bile salt (3.84 mg). mL -1(Prepared to simulate intestinal fluid), 5 mL pancreatic enzyme solution (1000 U trypsin) mL -1 ), 48mg glucoamylase (106 U) g -1 Add sterile water to bring the final volume to 40 mL. Quickly transfer the conical flask to a 37°C shaker and incubate in the dark for 3 hours.

[0045] (2) Determination of reducing sugar content in digestive fluids from the small intestine in vitro 500 μL of digestion solution was collected at 0, 10, 20, 30, 60, 90, 120, and 180 min during simulated small intestine digestion. 2 mL of anhydrous ethanol was immediately added to terminate the reaction. The mixture was then incubated in a boiling water bath for 5 min to inactivate the enzymes, followed by 4500 r... min -1 The supernatant obtained after centrifugation for 5 min was used as the sample solution. The reducing sugar content was determined using the 3,5-dinitrosalicylic acid (DNS) method. 1 mL of the sample solution was accurately transferred, 0.75 mL of DNS reagent was added, and the mixture was vortexed until homogeneous. After heating in a boiling water bath for 5 min, the mixture was quickly transferred to an ice-water bath to cool to room temperature. Then, 10.75 mL of distilled water was added, and the mixture was vortexed until homogeneous. The absorbance of the sample solution was measured at 540 nm. A standard curve was established with the glucose standard concentration as the abscissa (y = 0.4495x + 0.0379, R0). 2 = 0.9996), with distilled water as a blank control. The corresponding reducing sugar content was calculated based on the standard curve, and three technical replicates were set for each group.

[0046] (3) Calculation of the predicted glycemic index The available sugar release rate of the sample and the reference food (ref-F) was calculated by using the reducing sugar content in the small intestinal digestion fluid in vitro. The relationship between available sugar release rate and time was plotted, and the area under the curve (AUC) was calculated using the "linear trapezoidal method". The hydrolysis index (HI) of the sample was then calculated according to the following formula.

[0047] HI = AUC s / AUC r ×100%, where: HI The hydrolysis index is %; AUC s The total area covered by the sample curve, in min·mg·mL -1 ; AUC r For the reference food (white bread), the total coverage area under the curve is expressed in min·mg·mL.-1 .

[0048] Calculate the estimated glycemic index (eGI) using the following formula.

[0049] eGI =39.71+0.549× HI In the formula: eGI To estimate the glycemic index; HI The hydrolysis index is %.

[0050] Table 3 eGI values ​​of fermented lychee fruit powder base materials in Examples 1-3 and untreated lychee fruit powder base material in Comparative Example 1

[0051] As shown in Table 3, the eGI value of the untreated litchi fruit powder substrate was 64.51. After treatment with compound enzyme-Lactobacillus plantarum fermentation, compound enzyme-Lactobacillus fermentation and compound enzyme-Lactobacillus rhamnosus fermentation, the eGI value of the litchi fruit powder substrate decreased significantly. Among them, the eGI value of the litchi fruit powder substrate fermented with compound enzyme-Lactobacillus plantarum was the lowest at 48.27.

[0052] 4. Monosaccharide composition of polysaccharides Fermented lychee fruit powder base materials (low-GI lychee fruit powder base materials) prepared in Examples 1-3 and untreated lychee fruit powder base materials prepared in Comparative Example 1 were used to test the monosaccharide composition of their polysaccharides. The results are as follows: Figure 1 As shown.

[0053] The method for determining the monosaccharide composition of polysaccharides includes the following steps: 1) Extraction of polysaccharides: Weigh a certain amount of litchi fruit powder base material, add anhydrous ethanol at a material-to-liquid ratio of 1:20 (g / mL), vortex and shake well, then extract ultrasonically for 30 min, and finally extract at 8000 r. min -1 Centrifuge for 10 min and discard the supernatant. Wash the precipitate with 10 mL of 80% (v / v) ethanol, centrifuge, add 50 mL of water, and sonicate at 120 W for 30 min. Repeat the extraction twice. Combine the extracts and bring the volume to 10 mL to obtain the polysaccharide extract, which is stored at -20℃ for later use.

[0054] 2) Monosaccharide composition determination: Take 1 mL of polysaccharide extract, add 1.0 mL of 2.0 M trifluoroacetic acid solution, and seal with an alcohol burner. Hydrolyze at 120℃ for 2.0 h. After drying with nitrogen, redissolve in ultrapure water and bring the volume to 100 mL. The monosaccharide composition of the sample is determined using a high-performance anion exchange chromatography system equipped with a pulsed amperometric detector and a CarboPac PA10 sugar analysis column. The mobile phase consists of ultrapure water (solvent A), 200 mM sodium hydroxide (solvent B), and 200 mM sodium acetate (solvent C). The flow rate is 1.0 mL / min. The elution program is as follows: 0–15 min, 8% B and 0.3% C; 15–30 min, 8% B and 75% C; 30–45 min, 8% B and 0.3% C. The content of each monosaccharide is quantitatively analyzed using the external standard method.

[0055] Depend on Figure 1 It can be seen that the polysaccharides in the untreated litchi fruit powder substrate are mainly composed of galacturonic acid, glucose, galactose, arabinose, glucuronic acid, and mannose. After fermentation treatment with compound enzymes—Lactobacillus plantarum, Lactobacillus fermentum, and Lactobacillus rhamnosus—the content of arabinose, galactose, and galacturonic acid in the litchi fruit powder substrate was significantly increased. Compared with Comparative Example 1, the arabinose content in Examples 1-3 increased by 74.25%, 30.23%, and 67.42%, respectively; the galactose content increased by 34.01%, 12.72%, and 21.49%, respectively; and the galacturonic acid content increased by 35.24%, 27.21%, and 17.51%, respectively. Based on the changes in monosaccharide composition, the content of arabinose, galactose, and galacturonic acid in the litchi fruit powder substrate was significantly increased after enzymatic hydrolysis and Lactobacillus fermentation treatment, indicating that it was enriched with arabinogalactan.

[0056] 5. Total phenol content The total phenol content of fermented litchi fruit powder base materials (low GI litchi fruit powder base materials) prepared in Examples 1-3 and untreated litchi fruit powder base materials prepared in Comparative Example 1 were tested respectively, and the results are shown in Table 5.

[0057] The method for determining the total phenol content includes the following steps: (1) Extraction of polyphenols: The litchi fruit powder base was mixed with pre-cooled 80% acetone at a material-to-liquid ratio of 1:20 (g / mL), homogenized in an ice bath for 5 min (5000 r / min), centrifuged (4000 r / min, 8 min), and the supernatant was collected. The precipitate was extracted twice more under the same conditions. The supernatants were combined, concentrated under vacuum at 45℃, and the volume was adjusted to 10 mL. The extract was stored at -20℃ for later use. Then, 20 mL of 4 mol / L NaOH solution was added to the precipitate after the extraction of free phenols. The mixture was filled with nitrogen and sealed. The extract was shaken and extracted at room temperature for 1 h. Then, the pH of the extract was adjusted to 1 with 6 mol / L HCl solution. The extract was then extracted five times with 100 mL of ethyl acetate. The ethyl acetate phases were combined and concentrated to dryness under vacuum at 45℃. The extract was adjusted to 10 mL with distilled water and stored at -20℃ for later use.

[0058] (2) Determination of polyphenols: The polyphenol content was determined using the Folin-Ciocalteu method. 0.125 mL of appropriately diluted free or bound phenol extract was added to 0.5 mL of distilled water and 0.125 mL of Folin-Ciocalteu reagent. After mixing, the mixture was reacted for 6 min. Then, 1.25 mL of 7% Na₂CO₃ solution (m / v) and 1 mL of distilled water were added. After mixing, the mixture was reacted in the dark for 90 min, and the absorbance of each reaction solution was measured at 760 nm. Standard curves were prepared using gallic acid standard solutions of different concentrations following the above procedure, and the content of phenolic substances in each sample was calculated. The content is expressed as the gallic acid equivalent (GAE) per 100 g of litchi fruit powder base material, i.e., mg GAE / 100 g.

[0059] Table 4. Polyphenol content of fermented litchi fruit powder base materials in Examples 1-3 and untreated litchi fruit powder base material in Comparative Example 1.

[0060] As shown in Table 4, compared with the untreated litchi fruit powder substrate, the polyphenol content of the litchi fruit powder substrate treated with compound enzyme-Lactobacillus plantarum, compound enzyme-Lactobacillus fermentum and compound enzyme-Lactobacillus rhamnosus fermentation were increased by 19.29%, 15.48% and 13.25%, respectively.

[0061] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a low-GI litchi fruit powder base, characterized in that, Specifically, the following steps are included: (1) Lychee pretreatment Peeled and pitted fresh lychee pulp is blended and homogenized to obtain lychee pulp. (2) Enzymatic hydrolysis of fruit pulp Add pectinase and arabinogalactase to litchi pulp, hydrolyze, sterilize, and obtain enzymatically hydrolyzed litchi pulp; (3) Fruit pulp fermentation Lactobacillus was inoculated into enzymatically hydrolyzed litchi pulp, and fermentation was carried out to obtain fermented litchi pulp. (4) Drying and grinding The fermented lychee pulp was pre-frozen, vacuum freeze-dried, and pulverized to obtain the low-GI lychee fruit powder base material.

2. The method for preparing a low-GI litchi fruit powder base according to claim 1, characterized in that, In step (1), the pulping equipment is a high-speed disperser with a rotation speed of 8000 rpm and a time of 5 min; the homogenizing equipment is a high-shear homogenizer with a rotation speed of 10000 r / min and a time of 30 s.

3. The method for preparing a low-GI litchi fruit powder base according to claim 1, characterized in that, In step (2), the amount of pectinase added is 0.05%-1.0% of the mass of litchi pulp.

4. The method for preparing a low-GI litchi fruit powder base according to claim 1, characterized in that, In step (2), the amount of arabinogalactase added is 0.01%-0.5% of the mass of litchi pulp.

5. The method for preparing a low-GI litchi fruit powder base according to claim 1, characterized in that, In step (2), the enzymatic hydrolysis temperature is 35-55℃ and the time is 1-6h; the sterilization method is pasteurization, the temperature is 72℃ and the time is 10min.

6. The method for preparing a low-GI litchi fruit powder base according to claim 1, characterized in that, In step (3), the lactobacillus is a suspension of Lactobacillus plantarum ATCC 14917 strain, a suspension of Lactobacillus fermentum GDMCC 1.1796 strain, or a suspension of Lactobacillus rhamnosus GDMCC 1.2223 strain, with a concentration of 10. 8 CFU / mL, the inoculation amount is 2% of the volume of enzymatically hydrolyzed litchi pulp.

7. The method for preparing a low-GI litchi fruit powder base according to claim 1, characterized in that, In step (3), the fermentation temperature is 37°C and the time is 3 days.

8. The method for preparing a low-GI litchi fruit powder base according to claim 1, characterized in that, In step (4), the pre-freezing temperature is -80℃ and the time is 12 h.

9. The method for preparing a low-GI litchi fruit powder base according to claim 1, characterized in that, In step (4), the vacuum freeze drying is specifically as follows: the first drying is set to cold trap -80℃ and vacuum 10-15 Pa; the shelf temperature is gradually increased from -30℃ to -20℃ for 28-32 h; the second drying is set to 20-25℃ and vacuum 5-10 Pa for 6-8 h.

10. A low-GI litchi fruit powder base material prepared by the preparation method according to any one of claims 1-9.

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