Method for adjusting porous structure and texture of freeze-dried pectin aerogel

Abstract

Disclosed is a method for regulating a porous structure and texture property of a freeze-dried pectin aerogel, which comprises the following steps of step 1: preparation of pectin/starch solution by mixing pectin powder and a gelatinized starch solution to form a stable pectin/starch mixed solution, a concentration of the pectin being 0.05% to 0.2% (w/v); step 2: induction of gel reaction by adding D-(+)-Glucono-δ-lactone and calcium carbonate into the stable pectin-starch mixed solution; and step 3: vacuum freeze of the starch/pectin composite gel subjected to the gel reaction to obtain the freeze-dried pectin/starch aerogel with an adjustable porous structure and an improved texture characteristic. Controllable regulation of the porous structure of the freeze-dried pectin aerogel is achieved by the method without complex pretreatment. Raw material ingredients applied in the method are cheap, easy-to-access, and has low-toxicity.

Claims

1. A method for regulating a porous structure and texture property of a freeze-dried pectin aerogel, comprising the following steps of: step 1: preparation of pectin/starch solution by mixing pectin powder and gelatinized starch solutions to form a stable pectin/starch mixed solution, wherein a concentration of the pectin is 0.05% to 0.2% (w/v); step 2: induction of gel reaction by adding D-(+)-Glucono-δ-lactone and calcium carbonate into the stable pectin-starch mixed solution; and step 3: vacuum freeze-drying of the starch/pectin composite gel subjected to the gel reaction to obtain the freeze-dried pectin/starch aerogel with an adjustable porous structure and an improved texture characteristic.

2. The method for regulating the porous structure and the texture property of the freeze-dried pectin aerogel according to claim 1, wherein in the step 2, in the stable pectin/starch mixed solution, the D-(+)-gluconic acid δ-lactone has a concentration of 30 mM, and the calcium carbonate has a concentration of 25 mM.

3. The method for regulating the porous structure and the texture property of the freeze-dried pectin aerogel according to claim 1, wherein in the step 2, the gel reaction is carried out at a temperature of 25° C. and is maintained for 12 hours.

4. The method for regulating the porous structure and the texture property of the freeze-dried pectin aerogel according to claim 1, wherein in the step 3, the specific method of the vacuum freeze drying comprises: under a vacuum pressure of 80 Pa, setting temperatures of a heating plate and a cooling trap to be −20° C. and −40° C. respectively, and carrying out the vacuum freeze drying for 3 days.

5. The method for regulating the porous structure and the texture property of the freeze-dried pectin aerogel according to claim 1, wherein in the step 3, before carrying out the vacuum freeze drying, the starch/pectin composite gel is frozen at −60° C. for 12 hours to form a starch-pectin composite gel system.

6. The method for regulating the porous structure and the texture property of the freeze-dried pectin aerogel according to claim 1, wherein in the step 1, starch is added into water at a solid-liquid ratio of 1:10, and gelatinized at a constant temperature of 60° C. for 2 minutes to 30 minutes.

7. The method for regulating the porous structure and the texture property of the freeze-dried pectin aerogel according to claim 1, wherein in the step 1, the pectin is low-fat pectin.

8. The method for regulating the porous structure and the texture property of the freeze-dried pectin aerogel according to claim 1, wherein the starch is potato starch.

9. The method for regulating the porous structure and the texture property of the freeze-dried pectin aerogel according to claim 1, wherein in the step 1, the pectin and the gelatinized starch solution are fully stirred by a rotary mixer for 12 hours to obtain the fully hydrated pectin-starch stable mixed sol solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of a method for regulating a porous structure and a texture property of a freeze-dried pectin aerogel in some technical solutions of the present invention.

(2) FIG. 2 is an SEM image of freeze-dried pectin/starch aerogels with different degrees of gelatinization.

(3) FIG. 3 is an influence table of the starch with different degrees of gelatinization on a pore diameter and a pore wall thickness of the freeze-dried pectin aerogels.

(4) FIG. 4 is an influence table of the starch with different degrees of gelatinization on a mechanical strength of the freeze-dried pectin aerogel.

DETAILED DESCRIPTION

(5) The present invention is further described in detail hereinafter, so that those skilled in the art can implement the present invention with reference to the specification.

(6) It should be understood that the terms such as “have”, “contain” and “comprise” used herein do not indicate the existence or addition of one or more other elements or combinations thereof

(7) It should be noted that experimental methods described in the following embodiments are all conventional methods unless otherwise specified. All the reagents and materials can be obtained commercially unless otherwise specified.

(8) In order to make those skilled in the art better understand the technical solutions of the present application, the following embodiments are now provided for description.

(9) A method for regulating a porous structure and a texture property of a freeze-dried pectin aerogel included the following steps.

(10) In step 1, starch was gelatinized: potato starch was gelatinized under water bath at a constant temperature of 60° C. for 0 min, 2 min, 8 min and 30 min. The starch might also be corn starch, sugarcane starch and other similar starch. When the starch was gelatinized, a solid-liquid ratio of the potato starch to water was 1:10.

(11) In step 2, a starch/pectin solution was prepared: a series of gelatinized starch solutions were mixed with low methoxyl pectin, wherein a concentration of the low methoxyl pectin was generally 0.05% to 2.0% (w/v).

(12) In step 3, full mixing was carried out: the pectin and the gelatinized starch solution are fully stirred by a rotary mixer for 12 hours to avoid agglomeration, and a dissolved pectin/starch mixed solution was finally obtained.

(13) In step 4, D-(+)-gluconic acid δ-lactone and calcium carbonate were added into the stable pectin/starch mixed solution for galation for 12 hours. Ca.sup.2+ was an important factor causing the cross-linking of LMP and forming a gel network. A pH value of the solution was gradually reduced by using D-(+)-gluconic acid δ-lactone to release the Ca.sup.2+ slowly and achieving the slow gelling of the low methoxyl pectin, thus obtaining a gel system with a uniform structure. A content of the D-(+)-gluconic acid δ-lactone was generally 30 mM, and a concentration of the calcium carbonate was generally 25 mM. The gelation was maintained for 12 hours at 25° C.

(14) In step 5, pre-cooling was carried out at a low temperature: the starch/pectin composite hydrogel was frozen at −60° C. to obtain the frozen starch/pectin composite gel system. The gel system was frozen under a metal mold, and a freezing plate should not be directly contacted to achieve uniform ice crystal growth. The freezing process was controlled within 12 hours.

(15) In step 6, freeze drying was carried out: the obtained frozen starch/pectin composite gel was subjected to vacuum freeze drying to remove moisture in the gel system. The freeze drying was carried out under a pressure of 80 Pa for 3 days, and temperatures of a heating plate and a cooling trap were set to be −20° C. and −40° C., respectively. The drying process was controlled to last for 3 days.

(16) In step 7, packaging was carried out: the prepared freeze-dried aerogel was taken out of the mold, and then stored in a dryer.

(17) Observation results of freeze-dried pectin aerogels prepared by using the concentration of the low methoxyl pectin being 2.0% (w/v) and different degrees of gelatinization of the starch were as follows:

(18) Measurement method for microstructure:

(19) SEM images of the starch sample and cross-sections of cryogels were captured by a microscope (SU8010, Hitachi Co., Ltd, Tokyo, Japan) at 10 kV accelerated voltage. The fracture cross-section of aerogels was obtained by cutting with a blade. All samples were coated with gold-palladium prior to imaging using an ion sputtering apparatus (MCI000, Hitachi Co., Ltd, Tokyo, Japan).. Results were shown in FIG. 2.

(20) Measurement methods for specific surface area, pore diameter and pore wall thickness

(21) To study the microstructural properties of the aerogels, μCT imaging was performed by using a 3D X-ray microscopy (SkyScan 1272, Bruker, USA) with penetrative X-rays of 100 kV and 100 μLA. The pixel size was 10 μm with 700 ms of exposure time in a high-resolution mode. Tomographic reconstructions were performed using filtered back projection and the reconstructed slice stacks were visualized as 3D in the software package NRecon. This software allows the visualization of two-dimensional (2D) cross-sections and provides a complete 3D structure reconstruction without any sample destruction. The sample with a volume of 400 mm.sup.3 was defined as a representative reduced volume of interest (VOI). Pore size distribution was identified as the diameter equivalent to the area of the circle. Pore wall thickness was characterized according to the spatial thickness defined as the binarization within the VOI. The specific surface area was calculated according to a sum of two-dimensional areas of all solid objects and a percentage of the solid objects in a total mass of the samples. Results were shown in the table below.

(22) TABLE-US-00001 Specific Total surface porosity area Sample Process (%) (m.sup.2/g) Comparative Pure pectin aerogel 91.74 125.13 Example 1 Comparative  0 min - pectin/starch aerogel 86.57 129.08 Example 2 Example 1  2 min - pectin/starch aerogel 81.37 158.24 Example 2  8 min - pectin/starch aerogel 84.22 143.45 Example 3 30 min - pectin/starch aerogel 84.83 228.14

(23) Measurement method for hardness and brittleness of material

(24) Mechanical properties of all aerogels were measured through a compression experiment by using a TA-XT2i texture analyzer (Stable Micro Systems, Godalming, UK) equipped with a spherical probe TA/0.5S. The samples were compressed at a constant rate of 1.0 mm/s at a room temperature until maximum 60% strain. The mechanical property of the aerogel was determined by eight repeated force (N)—distance (mm) curves of each sample. The hardness was defined as a maximum magnitude of the force (N), and a number of fracture peaks were used to represent the brittleness. Results were shown in FIG. 4.

(25) A number of modules and a processing scale described herein are used to simplify the description of the present invention. The application, modification and variation of the present invention are obvious to those skilled in the art.

(26) Although the implementations of the present invention have been disclosed above, the implementations are not limited to the applications listed in the specification and the embodiments, and can be fully applied to various fields suitable for the present invention, and additional modifications can be easily implemented by those skilled in the art. Therefore, the present invention is not limited to the specific details and the embodiments shown and described herein without departing from the general concept defined by the claims and the equivalent scope.