Preparation method of new agaro-oligosaccharide yoghurt

Abstract

The preparation method comprises the following steps: preheating cow milk to 60 to 70 DEG C, then adding cane sugar and new agaro-oligosaccharide, dissolving, standing, and uniformly stirring to obtain a mixed solution; heating the mixed solution to 90 DEG C, maintaining for 5-10 minutes for sterilization treatment, and cooling to 42 DEG C; and inoculating lactic acid bacteria into the cooled mixed solution, uniformly stirring, sub-packaging into sterilized glass containers, fermenting in a constant-temperature incubator at 42 + / -1 DEG C for 6 hours, taking out, and performing post-fermentation in a refrigerator at 0-4 DEG C for 6-8 hours to obtain the new agaro-oligosaccharide yoghurt. According to the method, the new agaro-oligosaccharide is applied to the preparation process of the yoghurt, the yoghurt with the functions of resisting oxidation and reducing blood sugar is prepared, and the physicochemical properties of the yoghurt in the storage period are improved.

Description

Technical Field

[0001] The invention relates to the technical field of yogurt, and in particular to a method for preparing a new agar oligosaccharide yogurt. Background Art

[0002] Yogurt is a dairy product made from fresh milk fermented by lactic acid bacteria, which has health functions such as maintaining intestinal flora balance, preventing constipation, and lowering cholesterol. Coagulated fermented milk products often have adverse phenomena such as reduced viscosity, whey precipitation, and poor taste during long-term storage and transportation. When yogurt with a longer shelf life is stored at room temperature, its nutritional components are easily destroyed. Summary of the invention

[0003] In order to solve the above problems, the present invention proposes a method for preparing a new agar oligosaccharide yogurt, which applies the new agar oligosaccharide to the production process of yogurt to prepare yogurt with antioxidant and blood sugar lowering functions, and improves the physical and chemical properties of the yogurt during storage.

[0004] In order to achieve the above object, the present invention provides a method for preparing a new agar oligosaccharide yogurt, which comprises the following steps:

[0005] Preheat the milk to 60-70°C, then add sucrose and neoagar oligosaccharide, dissolve, let stand, stir evenly, and obtain a mixed solution;

[0006] The mixed solution is heated to 90°C and maintained for 5-10 minutes for sterilization, and then cooled to 42°C;

[0007] The lactic acid bacteria were added to the cooled mixed solution, stirred evenly, and divided into sterilized glass containers. The mixture was fermented in a constant temperature incubator at 42±1°C for 6 hours, and then taken out and placed in a refrigerator at 0-4°C for post-fermentation for 6-8 hours to obtain agar oligosaccharide yogurt.

[0008] According to a method for preparing a new agar oligosaccharide yogurt of the present invention, the new agar oligosaccharide is applied to the production process of yogurt. It has been verified that the prepared yogurt has antioxidant and blood sugar lowering effects, and improves the physical and chemical properties of yogurt during storage, such as water retention, hardness, elasticity, cohesion, viscosity, etc., to improve the taste of coagulated yogurt.

[0009] In addition, the method for preparing a new agar oligosaccharide yogurt according to the present invention may also have the following additional technical features:

[0010] Optionally, the added amount of the new agar oligosaccharide is 0.6% w / v.

[0011] Optionally, the inoculation amount of the lactic acid bacteria is 0.1%.

[0012] Optionally, the novel agar oligosaccharide is prepared by enzymatic hydrolysis of agar with β-agarase.

[0013] Further, 100 mL of 0.5% (w / v) agar substrate solution was taken, 40 U of purified β-agarase was added, and the reaction was carried out in a constant temperature water bath at 50°C; the solution was shaken every 15 minutes to allow sufficient enzymolysis, and the reducing sugar content of the system was measured until the reducing sugar content remained constant; after heating at 100°C for 10 minutes to terminate the reaction, 3 times the volume of anhydrous ethanol was added, and the solution was allowed to stand at 4°C overnight; the undegraded agar in the system was removed by suction filtration, the anhydrous ethanol and excess water were removed by a rotary evaporator, and then the solution was freeze-dried to obtain new agar oligosaccharides.

[0014] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Determination of water holding capacity of yogurt according to an embodiment of the present invention;

[0016] Figure 2 Determination of pH of yogurt according to an embodiment of the present invention;

[0017] Figure 3 The titratable acidity of the yogurt according to the embodiment of the present invention is measured;

[0018] Figure 4 Determination of DPPH free radical scavenging rate of yogurt according to an embodiment of the present invention;

[0019] Figure 5 is the ABTS of the yogurt according to the embodiment of the present invention + Determination of free radical scavenging rate;

[0020] Figure 6 Determination of α-glucosidase inhibitory activity of yogurt according to an embodiment of the present invention;

[0021] Figure 7 is the relationship between the apparent viscosity and shear rate of the yogurt according to the embodiment of the present invention;

[0022] Figure 8 This is a frequency analysis of yogurt scanning according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. The change or adjustment of the relative relationship thereof shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0024] In order to better understand the above technical scheme, the exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0025] The test materials used in the present invention are all common commercial products and can be purchased in the market.

[0026]

[0027]

[0028] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0029] Example 1

[0030] Preparation of new agar oligosaccharide: Take 100mL, 0.5% (wv) agar substrate solution, add 40U purified β-agarase (β-agarase Y3R1 is selected, derived from Catenovulum agarivorans sp.YM01T, GeneBank accession number: WP_086933634.1), and react in a constant temperature water bath at 50°C. Shake well every 15 minutes to allow it to be fully enzymatically hydrolyzed, and measure the reducing sugar content of the system until the reducing sugar content remains constant. After heating at 100°C for 10 minutes to terminate the reaction, add 3 times the volume of anhydrous ethanol and let it stand overnight at 4°C. Remove the undegraded agar in the system by suction filtration, remove the anhydrous ethanol and excess water by rotary evaporator, and then freeze-dry and freeze-dry to obtain new agar oligosaccharide powder.

[0031] Example 2

[0032] A new agar oligosaccharide yogurt comprises the following components: 120 mL of milk, 0.12 g of new agar oligosaccharide, 7.2 g of sucrose, and 0.1% of lactic acid bacteria inoculation amount.

[0033] The specific production method comprises the following steps:

[0034] Preheat the milk to 60°C, add sucrose and neoagar oligosaccharide, dissolve, let stand, stir evenly, and obtain a mixed solution.

[0035] Heat the mixed solution to 90°C and maintain for 5-10 minutes for sterilization, then cool to 42°C for later use.

[0036] The glass container was sterilized at 85°C.

[0037] Add lactic acid bacteria to the cooled mixed solution and stir evenly; divide into sterilized glass containers, ferment in a constant temperature incubator at (42±1)°C for 6 hours, take out, and then place in a refrigerator at 0-4°C for post-fermentation for 6 hours to obtain yogurt.

[0038] Example 3

[0039] A new agar oligosaccharide yogurt comprises the following components: 120 mL of milk, 0.36 g of new agar oligosaccharide, 7.2 g of sucrose, and 0.1% of lactic acid bacteria inoculation amount.

[0040] The specific production method comprises the following steps:

[0041] Preheat the milk to 70°C, add sucrose and neoagar oligosaccharide, dissolve, let stand, stir evenly, and obtain a mixed solution.

[0042] Heat the mixed solution to 90°C and maintain for 5-10 minutes for sterilization, then cool to 42°C for later use.

[0043] The glass container was sterilized at 85°C.

[0044] Add lactic acid bacteria to the cooled mixed solution and stir evenly; divide into sterilized glass containers, ferment in a constant temperature incubator at (42±1)°C for 6 hours, take out, and then place in a refrigerator at 0-4°C for post-fermentation for 7 hours to obtain yogurt.

[0045] Example 4

[0046] A new agar oligosaccharide yogurt comprises the following components: 120 mL of milk, 0.72 g of new agar oligosaccharide, 7.2 g of sucrose, and 0.1% of lactic acid bacteria inoculation amount.

[0047] The specific production method comprises the following steps:

[0048] Preheat the milk to 70°C, add sucrose and neoagar oligosaccharide, dissolve, let stand, stir evenly, and obtain a mixed solution.

[0049] Heat the mixed solution to 90°C and maintain for 5-10 minutes for sterilization, then cool to 42°C for later use.

[0050] The glass container was sterilized at 85°C.

[0051] Add lactic acid bacteria to the cooled mixed solution and stir evenly; divide into sterilized glass containers, ferment in a constant temperature incubator at (42±1)°C for 6 hours, take out, and then place in a refrigerator at 0-4°C for post-fermentation for 8 hours to obtain yogurt.

[0052] Example 5

[0053] A new agar oligosaccharide yogurt comprises the following components: 120 mL of milk, 1.08 g of new agar oligosaccharide, 7.2 g of sucrose, and 0.1% of lactic acid bacteria inoculation amount.

[0054] The specific production method comprises the following steps:

[0055] Preheat the milk to 70°C, add sucrose and neoagar oligosaccharide, dissolve, let stand, stir evenly, and obtain a mixed solution.

[0056] Heat the mixed solution to 90°C and maintain for 5-10 minutes for sterilization, then cool to 42°C for later use.

[0057] The glass container was sterilized at 85°C.

[0058] Add lactic acid bacteria to the cooled mixed solution and stir evenly; divide into sterilized glass containers, ferment in a constant temperature incubator at (42±1)°C for 6 hours, take out, and then place in a refrigerator at 0-4°C for post-fermentation for 6 hours to obtain yogurt.

[0059] Comparative Example 1

[0060] A yogurt comprises the following components: 120 mL of milk, 7.2 g of sucrose, and 0.1% of lactic acid bacteria inoculation amount.

[0061] The specific production method comprises the following steps:

[0062] Preheat the milk to 70°C, add sucrose, dissolve it, let it stand, stir it evenly, and obtain a mixed solution.

[0063] Heat the mixed solution to 90°C and maintain for 5-10 minutes for sterilization, then cool to 42°C for later use.

[0064] The glass container was sterilized at 85°C.

[0065] Add lactic acid bacteria to the cooled mixed solution and stir evenly; divide into sterilized glass containers, ferment in a constant temperature incubator at (42±1)°C for 6 hours, take out, and then place in a refrigerator at 0-4°C for post-fermentation for 6 hours to obtain yogurt.

[0066] Comparative Example 2

[0067] A yogurt comprises the following components: 120 mL of milk, 0.12 g of agar, 7.2 g of sucrose, and 0.1% of lactic acid bacteria inoculation amount.

[0068] The specific production method comprises the following steps:

[0069] Preheat the milk to 70°C, add sucrose and neoagar oligosaccharide, dissolve, let stand, stir evenly, and obtain a mixed solution.

[0070] Heat the mixed solution to 90°C and maintain for 5-10 minutes for sterilization, then cool to 42°C for later use.

[0071] The glass container was sterilized at 85°C.

[0072] Add lactic acid bacteria to the cooled mixed solution and stir evenly; divide into sterilized glass containers, ferment in a constant temperature incubator at (42±1)°C for 6 hours, take out, and then place in a refrigerator at 0-4°C for post-fermentation for 6 hours to obtain yogurt.

[0073] Test example

[0074] The performance index tests were performed on the yogurts of Examples 2-5 and Comparative Examples 1-2:

[0075] 1. Determination of water holding capacity

[0076] Take a 50mL empty centrifuge tube and weigh it as m (g). Add the yogurt sample into the centrifuge tube and weigh it as m1 (g). Centrifuge at 8000r / min for 20min at 4℃. Pour out the supernatant and weigh the centrifuge tube as m2 (g).

[0077] Water holding capacity (%) = ((m2-m) / (m1-m)) × 100;

[0078] Where: m is the mass of the empty centrifuge tube (g); m1 is the mass of the centrifuge tube filled with yogurt sample (g); m2 is the total mass of the centrifuge tube and the remaining sediment after discarding the supernatant (g).

[0079] like Figure 1 As shown, Figure 1The water holding capacity changes of the control yogurt, yogurt with 0.1% new agar oligosaccharide (NAOs-1), yogurt with 0.3% new agar oligosaccharide (NAOs-2), yogurt with 0.6% new agar oligosaccharide (NAOs-3), yogurt with 0.9% new agar oligosaccharide (NAOs-4), and yogurt with 0.1% agar (AG) during 21 days of storage at 4°C were shown. The results showed that the water holding capacity of yogurt decreased significantly during the entire storage period, but the water holding capacity of yogurt with new agar oligosaccharide and agar was significantly higher than that of the control group, among which, when the new agar oligosaccharide was added at 0.6%, the water holding capacity of yogurt was significantly higher than that of other groups.

[0080] 2. pH and titratable acidity determination

[0081] Weigh 10 g of yogurt sample and measure the pH of the sample using a pH meter.

[0082] Weigh 10g of yogurt sample, mix with 20mL of distilled water, add an appropriate amount of phenolphthalein indicator, and then titrate with 0.1mol / L sodium hydroxide standard solution until it turns slightly red and does not fade within 30s. The titration is completed. The titratable acidity value of the sample is calculated as follows:

[0083] Titratable acidity (°T) = c × V × 100 / m × 0.1;

[0084] Where: c is the concentration of sodium hydroxide solution (moL / L); V is the volume of sodium hydroxide standard solution consumed (mL); m is the sample mass (g).

[0085] like Figure 2 As shown, Figure 2 The pH of the control yogurt, yogurt with 0.1% new agar oligosaccharide (NAOs-1), yogurt with 0.3% new agar oligosaccharide (NAOs-2), yogurt with 0.6% new agar oligosaccharide (NAOs-3), yogurt with 0.9% new agar oligosaccharide (NAOs-4), and yogurt with 0.1% agar (AG) during storage at 4°C for 21 days was shown. The results showed that the pH of the yogurt decreased significantly during the entire storage period, and the pH of the yogurt with the addition of new agar oligosaccharide was significantly lower than that of the control group, among which the pH of the yogurt with the addition of agar was significantly higher than that of the other groups.

[0086] like Figure 3 As shown, Figure 3The titratable acidity of the control yogurt, yogurt with 0.1% new agar oligosaccharide (NAOs-1), yogurt with 0.3% new agar oligosaccharide (NAOs-2), yogurt with 0.6% new agar oligosaccharide (NAOs-3), yogurt with 0.9% new agar oligosaccharide (NAOs-4), and yogurt with 0.1% agar (AG) during 21 days of storage at 4°C was shown. The results showed that the titratable acidity of the yogurt gradually increased during the entire storage period, the addition of new agar oligosaccharide increased the titratable acidity of all yogurts, and the titratable acidity of the yogurt with the addition of agar was lower than that of the other groups, and its maximum value appeared on the 28th day of refrigeration. The new agar oligosaccharide added to the yogurt can be used as a prebiotic for lactic acid bacteria, thereby making the lactic acid and organic acid significantly higher than the control group.

[0087] 3. Determination of DPPH free radical scavenging rate

[0088] Add 500 μL of yogurt sample to a 2 mL test tube, add 1500 μL of 0.2 mmol / L DPPH solution, shake well, place in the dark at room temperature for 30 min, centrifuge at 12000 r / min for 2 min, take the supernatant to measure the absorbance at 517 nm (A0), use vitamin C as the positive control, and replace the sample solution with an equal volume of anhydrous ethanol as the control group (A1). Each group of experiments was repeated 3 times and calculated according to the following formula:

[0089] DPPH free radical scavenging rate (%) = A1-A0 / A1×100%.

[0090] like Figure 4 As shown, Figure 4 The DPPH radical scavenging rates of control yogurt, yogurt with 0.1% new agar oligosaccharide (NAOs-1), yogurt with 0.3% new agar oligosaccharide (NAOs-2), yogurt with 0.6% new agar oligosaccharide (NAOs-3), yogurt with 0.9% new agar oligosaccharide (NAOs-4), and yogurt with 0.1% agar (AG) during storage at 4°C for 21 days were shown. The results showed that during the entire storage period, the DPPH radical scavenging rates of yogurt with new agar oligosaccharide and agar added and control yogurt showed a downward trend, and the reduction of the radical scavenging rate of yogurt with new agar oligosaccharide was lower than that of control yogurt. During the 21-day storage, the DPPH radical scavenging rate of all yogurt samples reached the lowest, among which the radical scavenging rate of yogurt with 0.9% new agar oligosaccharide added was significantly higher than that of other groups. At the same time, with the increase of new agar oligosaccharide addition, the DPPH radical scavenging rate increased significantly, and the radical scavenging rate of yogurt with agar added was significantly lower than that of other groups.

[0091] 4. ABTS + Free radical scavenging rate

[0092] The ABTS solution was mixed with potassium persulfate and kept at room temperature in the dark for 15 hours to reach a stable oxidation level. The solution was then diluted with distilled water to an absorbance of 0.7 (± 0.02) at 734 nm. 180 μL of the ABTS solution was then mixed with 20 μL of the yogurt sample and placed on a 96-well plate.

[0093] After 6 minutes of reaction in the dark, the absorbance was recorded at 734 nm. Each group of experiments was repeated 3 times and calculated according to the following formula:

[0094] ABTS + Free radical scavenging rate (%) = A1-A0 / A1×100%;

[0095] Where: A0 is the absorbance of ABTS working solution and sample solution; A1 is the absorbance of ABTS working solution and distilled water.

[0096] like Figure 5 As shown, Figure 5 The results show the ABTS free radical scavenging rates of the control yogurt, yogurts with 0.1% new agar oligosaccharide addition (NAOs-1), yogurts with 0.3% new agar oligosaccharide addition (NAOs-2), yogurts with 0.6% new agar oligosaccharide addition (NAOs-3), yogurts with 0.9% new agar oligosaccharide addition (NAOs-4), and yogurts with 0.1% agar addition (AG) during 21 days of storage at 4°C. The results show that during the entire storage period, the ABTS free radical scavenging rate of yogurts with new agar oligosaccharide addition was significantly higher than that of the control yogurt, and the free radical scavenging rate of yogurts with agar addition was lower than that of the other groups. At the same time, the ABTS free radical scavenging rate increased significantly with the increase in the amount of new agar oligosaccharide addition, and there was no significant difference in the changes in the ABTS free radical scavenging rates of all yogurt samples during the 21-day storage period.

[0097] 5. α-Glucosidase inhibitory activity

[0098] Add 400uL of yogurt sample, 400uL of 0.04U / mL enzyme solution and 400uL of PBS (pH6.8, 0.1mol / L) to a 10mL test tube, and heat in a 37°C water bath for 5min; then add 200uL of 2.5mmol / L PNPG solution, mix well, continue to heat in a 37°C water bath for 30min, take out and add 500uL of 0.2mol / L Na2CO3 solution, mix well. After standing at room temperature for 5min, centrifuge at 5000r / min for 5min, take the supernatant and measure the absorbance at a wavelength of 405nm. Use phosphate buffer as blank to zero, replace the sample in the control group, the enzyme solution and sample in the blank control group, and the enzyme solution in the sample control group with phosphate buffer, and each group of experiments is parallel 3 times. The calculation formula is as follows:

[0099] α-glucosidase inhibition rate (%) = (1-(A 样品 -A 样品对照 ) / (A 对照 -A 空白对照 ))×100.

[0100] like Figure 6 As shown, Figure 6 The results show the inhibition rates of α-glucosidase in the control yogurt, yogurt with 0.1% new agar oligosaccharide addition (NAOs-1), 0.3% new agar oligosaccharide addition (NAOs-2), 0.6% new agar oligosaccharide addition (NAOs-3), 0.9% new agar oligosaccharide addition (NAOs-4) and 0.1% agar addition (AG) during storage at 4°C for 21 days. The results show that during the storage period of 1-14 days, all yogurt samples did not show a regular trend change. When the addition of new agar oligosaccharide was greater than 0.6%, the inhibition rate of glycosidase in the yogurt samples showed an upward trend. When the addition of new agar oligosaccharide was less than 0.6%, the inhibition rates of α-glucosidase in the yogurt samples with new agar oligosaccharide addition and the yogurt samples without oligosaccharide addition showed a downward trend. At 21 days, the inhibition rates of α-glucosidase in all yogurt samples showed a significant downward trend. The inhibition rate of yogurt with new agar oligosaccharide addition was higher than that of yogurt with agar addition and the control yogurt.

[0101] 6. Texture determination

[0102] The TA-XT texture analyzer was used for the test, and the cylindrical probe TA / 0.5 was used. The test parameters were as follows: the pre-test speed was 2 mm / s, the test speed was 1 mm / s, the post-test speed was 2 mm / s, the test distance was 15 mm, the induction force was 5 g, and the hardness, elasticity, cohesion, and viscosity of the yogurt were tested. Each sample was tested three times.

[0103] The results are shown in Table 1, which shows the texture properties of control yogurt, yogurt with 0.1% new agar oligosaccharide (NAOs-1), yogurt with 0.3% new agar oligosaccharide (NAOs-2), yogurt with 0.6% new agar oligosaccharide (NAOs-3), yogurt with 0.9% new agar oligosaccharide (NAOs-4), and yogurt with 0.1% agar (AG) during 21 days of storage at 4°C. The results showed that AG fortified yogurt reduced the hardness of yogurt and significantly increased the viscosity. When the addition of NAOs was greater than 0.6%, the viscosity of yogurt decreased. The addition of new agar oligosaccharide did not significantly affect the cohesiveness and elasticity of yogurt, but increased the viscosity of yogurt. During the entire storage period, the viscosity values ​​of yogurt with added oligosaccharides and the control reached the maximum value at 7 days. From 7 to 21 days, the viscosity value of yogurt decreased. The viscosity value of yogurt with added new agar oligosaccharide was higher than that of the control yogurt. The viscosity value of yogurt with added agar showed a downward trend during storage. The hardness and viscosity were significantly higher than those of the control yogurt and yogurt with added new agar oligosaccharide. The hardness was too high, which affected the sensory perception of the yogurt.

[0104] Table 1

[0105]

[0106] 7. Rheological properties analysis

[0107] The rheological properties of yogurt were analyzed using a dynamic oscillation rheology analyzer. A 40 mm aluminum plate fixture was selected for measurement. The gap between the plates was 1 mm, and each sample was measured three times.

[0108] 7.1. Relationship between apparent viscosity and shear rate

[0109] The yogurt sample was heated at 25°C with a shear rate of 0.1 to 1000 s -1 The scanning was carried out in the range, the equilibrium time was 60S, and the shear rate was used as the horizontal axis and the apparent viscosity was used as the vertical axis to draw a curve of the relationship between the apparent viscosity and the shear rate.

[0110] The results are as follows Figure 7 As shown, Figure 7 The effects of shear rate and apparent viscosity of control yogurt, yogurt with 0.1% new agar oligosaccharide (NAOs-1), 0.3% new agar oligosaccharide (NAOs-2), 0.6% new agar oligosaccharide (NAOs-3), 0.9% new agar oligosaccharide (NAOs-4), and 0.1% agar (AG) at 4°C for 21 days were shown. The results showed that the apparent viscosity of all yogurt samples decreased with increasing shear rate, and these yogurts had the characteristics of shear-thinning fluids. As the shear rate continued to increase, the non-covalent bonds in the protein network structure were destroyed, and the electrostatic repulsion and hydrophobic interactions between molecules were weakened. The viscosity curve of AG-fortified yogurt fluctuated significantly, and the apparent viscosity dropped sharply. This may occur due to higher syneresis. When the shear rate is changed, the viscosity of NAOs-fortified yogurt is slightly higher than that of agar-fortified yogurt. When the NAOs addition amount is greater than 0.6%, the apparent viscosity decreases. This may be due to the fact that excessive neoagar oligosaccharides prevent the structural formation of casein gel and reduce the integrity of the gel structure, thereby reducing the viscosity of the yogurt.

[0111] 7.2 Dynamic Frequency Sweep Analysis

[0112] The yogurt samples were subjected to frequency scanning in the range of 0.1 to 100 Hz at 25°C, and the corresponding storage modulus (Gˊ) and loss modulus (G'') were recorded.

[0113] The results are as follows Figure 8 As shown, Figure 8The effect of new agar oligosaccharide on the scanning frequency of yogurt was shown for control yogurt, yogurt with 0.1% new agar oligosaccharide addition (NAOs-1), yogurt with 0.3% new agar oligosaccharide addition (NAOs-2), yogurt with 0.6% new agar oligosaccharide addition (NAOs-3), yogurt with 0.9% new agar oligosaccharide addition (NAOs-4), and yogurt with 0.1% agar addition (AG) at 4°C for 21 days. The G' and G" values ​​of yogurt increased with the increase of scanning frequency; compared with the control group, when the addition of NAOs was in the range of 0.1%–0.6%, the G' and G" values ​​of yogurt gradually increased, and the elasticity began to decrease when the addition amount was further increased to 0.9%. The results corresponded to the changes in WHC and apparent viscosity, indicating that the appropriate addition of NAOs can improve the viscoelasticity of yogurt and thus enhance the gel structure.

[0114] 8. Chromaticity value determination

[0115] After the colorimeter was calibrated, the yogurt samples were poured into the quartz glass dish dedicated to the spectrophotometer in triplicate to detect the parameters L*, a* and b*.

[0116] The chromaticity of the control yogurt, yogurt with 0.1% new agar oligosaccharide addition (NAOs-1), 0.3% new agar oligosaccharide addition (NAOs-2), 0.6% new agar oligosaccharide addition (NAOs-3), 0.9% new agar oligosaccharide addition (NAOs-4), and 0.1% agar addition (AG) during storage at 4°C for 21 days showed that when the addition of new agar oligosaccharide was greater than 0.6%, the L* and a* values ​​decreased significantly, and the b* value increased significantly. During the 21-day storage period, the color of the yogurt fortified with new agar oligosaccharide remained relatively stable. The b* value of the yogurt with agar addition and the yogurt with 0.9% new agar oligosaccharide addition showed a significant decrease. The addition of new agar oligosaccharides and agar reduced the brightness of the yogurt. New agar oligosaccharides and agar themselves have color.

[0117] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0118] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a new agar-oligosaccharide yogurt, characterized in that: The following steps are involved: Preheat the milk to 60-70°C, then add sucrose and neoagar oligosaccharide, dissolve, let stand, stir evenly, and obtain a mixed solution; The mixed solution is heated to 90°C and maintained for 5-10 minutes for sterilization, and then cooled to 42°C; The lactic acid bacteria were added to the cooled mixed solution, stirred evenly, and divided into sterilized glass containers. The mixture was fermented in a constant temperature incubator at 42±1°C for 6 hours, and then taken out and placed in a refrigerator at 0-4°C for post-fermentation for 6-8 hours to obtain agar oligosaccharide yogurt.

2. The preparation method according to claim 1, characterized in that The added amount of the new agar oligosaccharide is 0.6% w / v.

3. The preparation method according to claim 1, characterized in that: The inoculation amount of the lactic acid bacteria was 0.1%.

4. The preparation method according to claim 1, characterized in that: The new agar oligosaccharide is prepared by enzymatic hydrolysis of agar by β-agarase.

5. The preparation method according to claim 4, characterized in that: Take 100mL, 0.5% (wv) agar substrate solution, add 40U purified β-agarase, and react in a constant temperature water bath at 50°C; shake well every 15 minutes to allow sufficient enzymolysis, and measure the reducing sugar content of the system until the reducing sugar content remains constant; heat at 100°C for 10 minutes to terminate the reaction, add 3 times the volume of anhydrous ethanol, and let it stand overnight at 4°C; remove undegraded agar in the system by suction filtration, remove anhydrous ethanol and excess water by a rotary evaporator, and then freeze-dry to obtain new agar oligosaccharides.

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