A method for preparing oil powder

Abstract

The present invention relates to the field of food and medicine, and specifically discloses a method and product for preparing a fat-coated product powder by using a complex coagulation multilayer coating technology. A fat-gelatin emulsion is mixed with sodium hexametaphosphate to form a complex coagulation layer; a modified starch substance is then added, and the obtained suspension is dried to obtain a fat powder coated with a starch salt and gelatin double layer. The powder has a high bulk density and tap density, is a low water activity product, and reduces the oil loading and increases the oil encapsulation rate.

Description

Technical Field

[0001] The invention relates to the field of food and medicine, and specifically discloses a method for preparing oil-coated product powder by using a composite coacervation technique and a product. Background Art

[0002] For oil, encapsulation is an important and effective method to increase its solubility in water, reduce the smell / taste of the oil, and improve its physical and chemical stability to environmental factors (such as light, humidity, air and heat). Many types of oils have been developed and applied to encapsulation research, such as fish oil, vegetable oil and essence. Among these oils, fish oil is an important source of ω-3 polyunsaturated fatty acids, with good physiological activity, medical prevention, medical nutrition and disease treatment functions. Therefore, fish oil capsules are increasingly attracting attention from the food and medical communities.

[0003] Gelatin is the main protein for interaction with oppositely charged molecules in complex coacervation for oil encapsulation due to their favorable advantages such as pH-dependent charge density, sufficient charge density on the chain, and unique gelling properties. Complex coacervation is a very promising encapsulation technology in the fields of food, pharmaceutical, and textile industries. Many types of anionic chemicals such as gum arabic, polyphosphates, or sodium hexametaphosphate have been used to interact with gelatin for oil encapsulation. However, the encapsulation efficiency (EE) of these products usually shows unsatisfactory results. For example, gelatin / gum arabic is 52.83–76.66%, gelatin / polyphosphate is 24.3–49.6%, and gelatin / sodium hexametaphosphate is 88.03%.

[0004] Therefore, further research should be aimed at increasing the EE of oil-encapsulated products. In addition, since different gelatins are derived from abundant animals (such as mammals and fish) and tissues (such as bones, skins, and scales), further research should also explore the potential effects of different gelatins on the preparation and properties of oil-encapsulated products.

[0005] There are several methods to process oil-in-liquid encapsulated materials into powders, such as spray drying, spray cooling, freeze drying (also known as lyophilization), and fluidized bed technology. Among these techniques, freeze drying is a good method for processing colloidal drug delivery systems containing heat-labile chemicals such as oils. Starch has been used as a drying aid for freeze drying homogenous gelatin emulsions due to its low viscosity. However, complex coacervation and freeze drying combined with adjuvants have not been applied to the encapsulation of oils.

[0006] Starch sodium octenyl succinate (SSOS) is a modified starch produced by esterification of hydrophobic starch with hydrophilic octenyl succinic anhydride followed by neutralization with sodium hydroxide. It is a common food additive that has been approved by the FDA, EFSA, and FDA (EFSA Panel on Food Additives and Nutrient Sources added to Food, Mortensen, Aguilar, Crebelli, Di Domenico, Dusemund, et al., 2017; Long, Bi, Pu, Xu, Xue, Fu, et al., 2022). As such, it is a reliable emulsifier and thickener and one of the most widely used starch esters. Recently, it has also been developed as a fat substitute for full-fat mayonnaise (Bajaj, Singh, & Kaur, 2019), as a composite film component to encapsulate essential oils for fruit preservation (Long, et al., 2022), and as a composite film component to encapsulate functional active substances for controlled release. Therefore, SSOS has broad prospects in the fields of food and pharmaceuticals. There is no report on the use of modified starch in the preparation of liquid oil solid powder. Summary of the invention

[0007] The present invention aims to provide a method for preparing oil powder.

[0008] The technical solution is a method for preparing oil powder, the steps comprising:

[0009] (1) mixing the oil-gelatin emulsion with sodium hexametaphosphate (SHMP) to form a complex coacervate layer;

[0010] (2) adding modified starch and dissolving it in the suspension; and drying to obtain a fat powder double-layered with starch salt and gelatin.

[0011] The oil is a liquid oil, including vegetable oil, animal oil, or a liquid oily substance containing nutrients or medicines; preferably, the vegetable oil is algae oil, and the animal oil is fish oil.

[0012] The gelatin is mammal gelatin or aquatic animal gelatin. The aquatic animal gelatin is fish skin gelatin (FG); the mammal gelatin is pig skin gelatin (PSG) or cow skin gelatin (BSG).

[0013] In step (1), the particle size of the oil-gelatin emulsion is 1-10 μm.

[0014] In step (1), the pH is adjusted to 4-4.8, preferably 4.4-4.8.

[0015] In a preferred embodiment of the present invention, when the gelatin is pig skin gelatin, the pH is adjusted to 4.7, when the gelatin is cow skin gelatin, the pH is adjusted to 4.4, and when the gelatin is fish skin gelatin, the pH is adjusted to 4.8.

[0016] In step (1), the method for preparing the oil-gelatin emulsion is as follows: adding oil to the gelatin solution and homogenizing. The ratio of gelatin to oil is 1:0.5-2.

[0017] In the gelatin solution, the weight ratio of gelatin to water is 2-15:100, preferably 5-10:100.

[0018] In step (1), the mass ratio of SHMP to gelatin is 1:8-20. Preferably, when the gelatin is pigskin gelatin or cowskin gelatin, the mass ratio of SHMP to gelatin is 1:8-20; when the gelatin is fishskin gelatin, the mass ratio of SHMP to gelatin is 1:8-12.

[0019] The drying in step (2) is freeze drying.

[0020] In step (2), the ratio of gelatin to modified starch is 1:0.5-5, preferably 1:1-5. In a preferred embodiment of the present invention, the ratio is 1:1.

[0021] The modified starch material includes pregelatinized starch, sodium starch octenyl succinate (SSOS), carboxymethyl starch, oxidized starch, composite modified starch and the like.

[0022] The obtained fat-gelatin emulsion powder can be used as capsule powder and instant powder for food, nutrition and medicine.

[0023] The invention also relates to the use of modified starch in preparing a drying aid for freeze drying of emulsion complex coacervates.

[0024] Application of modified starch in the preparation of oil-gelatin emulsion powder.

[0025] The modified starch material includes pregelatinized starch, sodium starch octenyl succinate, carboxymethyl starch, oxidized starch, composite modified starch and the like.

[0026] The present invention adopts a method combining complex coacervation and auxiliary freeze drying to prepare oil powder, and uses modified starch as a drying aid to prepare oil powder double-layered with starch salt and gelatin. The powder has a high bulk density and tap density, is a low water activity product, and reduces the LC value and increases the EE value; the results show that the method is an effective method for preparing oil capsule powder with extremely high EE value, especially fish oil capsule powder. The in vitro digestion behavior of the powder is analyzed in the simulated stomach and small intestine stage, and the results show that fish oil molecules can be released from the powder in the digestive tract.

[0027] The invention can encapsulate liquid fat and make it into dry solid powder, which will help expand the potential application of fat nutrients such as fish oil in the development of powdered foods such as milk powder and instant powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The physicochemical properties of four types of gelatin: pig skin gelatin (PSG), bovine skin gelatin (BSG), fish skin gelatin (FG) and cold water fish skin gelatin (FSG); (A): SDS-PAGE results, the band on the left is the protein standard; (B): ATR-FTIR spectrum; (C): Gelatin samples in freezing bottles and their gel strength values.

[0029] Figure 2 Preparation and morphological characterization of SSOS powder coated with fish oil gelatin-SHMP complex coacervates. (A): Preparation process of powders, from left to right: emulsion in a 150 mL glass beaker (13.3 cm high, 6.3 cm in diameter), sodium hexametaphosphate (SHMP) solution, mixture, pH adjustment, sodium starch octenyl succinate (SSOS) added to a 500 mL glass beaker (12.3 cm high, 9.5 cm in diameter). Freeze-dried sample in a glass Petri dish (1.9 cm high, 9.0 cm in diameter). (B): Digital camera images of powders in plastic Petri dishes (1.5 cm high and 4.0 cm high). (C): Scanning electron microscope images of powders. White arrows indicate surface roughness. Black arrows indicate surface roughness. The black scale bar indicates 30 μm for these images. Fish oil@PSG-SHMP@SSOS, fish oil

[0030] @BSG-SHMP@SSOS and fish oil @FG-SHMP@SSOS powders were prepared at a SHMP: gelatin mass ratio of 1:15 and different pH values ​​of 4.7, 4.4, and 4.8, respectively. (D): Schematic diagram of the preparation of fish oil @ gelatin-SHMP@SSOS powders. Yellow represents fish oil. Blue represents gelatin. Green represents SHMP. Cyan represents the interaction of gelatin (blue) with SHMP (green), and red represents SSOS.

[0031] Figure 3 Effect of pH on the formation of fish oil gelatin stable emulsions and fish oil gelatin SHMP complex coacervates. The morphology of the samples was photographed using an upright optical microscope with 10× and 40× objectives. The black scale bar in the 40× image represents 20μm. The black scale bar in the 10× image represents 100μm. (A): PSG. (B): BSG. (C): FG. (D): FSG.

[0032] Figure 4The effect of SHMP: gelatin mass ratio on the formation of fish oil gelatin stable emulsions and fish oil gelatin-SHMP complex coacervates. The morphology of the samples was photographed using an upright optical microscope with 10× and 40× objectives. The black scale bar in the 40× image represents 20 μm. The black scale bar in the 10× image represents 100 μm.

[0033] (A): PSG. (B): SG. (C): FG. (D): FSG. The pH values ​​of PSG, BSG, FG and FSG are 4.5, 4.4, 4.8 and 4.7, respectively.

[0034] Figure 5 The physicochemical properties of fish oil@gelatin-SHMP@SSOS powder. (A): Bulk density. (B) Tap density. (C): Water content. (D) Water activity. (E): Fish oil loading. (F) Fish oil encapsulation efficiency. Different lowercase letters indicate significant differences between samples (p<0.05).

[0035] Figure 6 In vitro digestion of fish oil@gelatin-SHMP@SSOS powder. (A–C): Digital camera images and optical microscope images after in vitro digestion. The glass vial is 30 mL (7.25 cm high, 2.75 cm in diameter). The black scale bar represents 20 μm. (D): Percentage of free fatty acids (FFA) released in the small intestine. DETAILED DESCRIPTION

[0036] Reagent: PSG (Type A, Vetec TM , gel strength ~300g Bloom) and FSG (biological reagent grade). BSG (type A, biological reagent grade), FG (biological reagent grade) and SSOS (biological reagent grade) were purchased from Shanghai Yuanye Biotechnology Co., Ltd. SHMP (purity 97%) was purchased from Shanghai Dibai Biotechnology Co., Ltd.

[0037] Data are presented as mean ± standard deviation (n=3). Statistical comparison was performed using one-way ANOVA (p value < 0.05).

[0038] Example 1 Physicochemical properties of four gelatins

[0039] (1) Molecular weight

[0040] The molecular weight (MW) distribution of gelatin was analyzed by SDS-PAGE gel electrophoresis (Zhang, Sun, Ding, Li, Tao, Wang, et al., 2020). 2 mg / mL gelatin was prepared in ultrapure water at 45 °C for 1 h. The pH was adjusted to 7.0. Then, 4 μL of 5× SDS-PAGE sample loading buffer (Guangzhou Jiebei Biotechnology Co., Ltd.) was added to 16 μL of gelatin solution and boiled for 5 min. Then, the sample (10 μL) was loaded into an 8% SurePAGE Bis-Tris gel (Nanjing GenScript Biotechnology Co., Ltd.) in a DYCZ-24KS electrophoresis pool (Beijing Liuyi Biotechnology Co., Ltd.). The gel was processed using a DYY-6D electrophoresis instrument (Beijing Liuyi Biotechnology Co., Ltd.) at a voltage of 120 V. After 80 min, the gel was stained with a mixture of 0.1% (w / v) Coomassie Brilliant Blue R-250, 25% (v / v) isopropanol and 10% (v / v) acetic acid for 3 h, and destained with a mixture of 20% (v / v) ethanol and 10% (v / v) acetic acid. The obtained gel was photographed using a digital camera.

[0041] result Figure 1 A, clear bands at <30 kDa. PSG and FG show clear or fuzzy bands of collagen β chain (about 280 kDa), collagen α1 chain (about 140 kDa), and collagen α2 chain (about 125 kDa), which is consistent with the previous SDS-PAGE results of tilapia scale gelatin, silver carp scale gelatin (Xu, Zhang, Zhang, Yang, Nie, Tao, et al., 2021) and silver carp fin gelatin (L. Yang, Yang, Xu, Nie, Wu, Zhang, et al., 2022). It should also be noted that the molecular weight order of these gelatins is: BSG>PSG>FG>FSG.

[0042] (2) Structural groups

[0043] The structural groups of the four types of gelatin were analyzed by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR spectroscopy). The wavenumber range of the analysis was 4000-600 cm using a Perkin Elmer spot light 400 ATR-FTIR spectrometer (Perkin Elmer Inc.). -1 The structural characteristics of Figure 1 B. Amide A, B, I, II, and III bands are mainly related to NH stretching, CH2, and NH3 + Asymmetric stretching, C=O stretching vibration, NH bending coupled to CN stretching, and CH 2 The group swing vibration is related. PSG, BSG and FG show similar characteristic peaks (amide A at 3300cm-1 , amide B at 2935 cm -1 , amide I at 1636 cm -1 , amide II at 1540 cm -1 , amide III at 1235 cm -1 The peak centers of amide B, amide I, and amide III of FSG are similar to those of other gelatins, while amide A (3290 cm -1 ) and amide II (1526 cm -1 ) has a lower peak center position than other gelatins. This suggests that FSG has more NH groups involved in hydrogen bonding compared to other gelatins because of the lower peak position of amide A, and because of the lower peak position of amide II, the NH groups have more hydrogen bonds between α chains. Therefore, FSG contains more hydrogen bonds in molecular interactions than other gelatins.

[0044] (3) Gel strength

[0045] Gel strength was analyzed based on the British Standard 757:1975 method (Dille, Haug, & Draget, 2021; Shyni, Hema, Ninan, Mathew, Joshy, & Lakshmanan, 2014). Ultrapure water (105 mL) and gelatin (7.5 g) were added to a glass bottle. After 1 hour, the glass bottle was incubated (65°C) for 10 minutes to completely dissolve the gelatin. The solution was placed at 10°C for 16 hours and analyzed using a TA-XT Plus physical property analyzer (Stable Micro Systems, Godalming, Surrey, UK). The maximum force to press down 4 mm at a pressing rate of 1 mm / s is the gel strength (g Bloom). The results are shown in Figure 1 C. FSG solution could not form gelatin gel after being placed at 10℃ for 16h, so its bloom value could not be obtained. PSG, BSG and FG could form gel, and their gel strength values ​​(g Bloom) were: BSG (320±10)>PSG (290±10)>FG (270±10).

[0046] Example 2

[0047] Powder preparation process Figure 2 A, the emulsion is mixed with SHMP solution, the pH value is adjusted to complete the complex coacervation process, and then freeze-dried. Figure 2 D (yellow represents fish oil, blue represents gelatin, green represents SHMP, cyan represents the interaction between gelatin (blue) and SHMP (green), and red represents SSOS).

[0048] (1) Emulsion preparation

[0049] A gelatin-stabilized emulsion loaded with fish oil was prepared using a simple homogenization method. 8 g of gelatin was added to 100 mL of ultrapure water. After 30 min, the mixture was heated at 45 °C for 1 h to obtain an 80 mg / mL gelatin solution. 8 g of fish oil was added to the gelatin solution mixture and mechanically homogenized at 8000 rpm for 5 min using a T25 homogenizer (IKA, Germany, with a homogenizer blade of S18N-19G). The emulsion was observed using an ML-8000 upright optical microscope with a 40× objective lens (Minz Precision, Shanghai, China). Figure 3 .

[0050] The gelatins used were: pig skin gelatin (PSG), bovine skin gelatin (BSG), fish skin gelatin (FG) and cold water fish skin gelatin (FSG).

[0051] (2) Complex coagulation process

[0052] The emulsion obtained in step (1) is subjected to a complex coagulation process by a pH adjustment method.

[0053] 0.533 g of SHMP was added to 100 mL of ultrapure water and dissolved at 50°C for 5 min to prepare a 5.3 mg / mL SHMP solution. Then, the prepared emulsion was mixed with 100 mL of SHMP solution (mass ratio of SHMP to gelatin was 1:15) and magnetically stirred (400 rpm) at 50°C for 1 min.

[0054] Subsequently, the pH was adjusted with 1 mol / L phosphoric acid solution and 1 mol / L NaOH solution. The sample was sealed with paraffin film and stirred continuously for 10 min. Then, the sample was stirred continuously at room temperature to form a complex coacervate.

[0055] When the gelatin is pig skin gelatin (PSG), the pH is adjusted to 4.7; when the gelatin is bovine skin gelatin (BSG), the pH is adjusted to 4.4; when the gelatin is fish skin gelatin (FG), the pH is adjusted to 4.8.

[0056] When the gelatin is cold water fish skin gelatin (FSG), the complex coacervate formed at pH 4.5-4.7 and SHMP: gelatin mass ratio of 1:10-1:20 floats and aggregates on the water phase to form a floating layer within 2 minutes after the magnetic stirring stops. The complex coacervate fails to form and cannot be freeze-dried to obtain fish oil@gelatin-SHMP@SSOS powder. Therefore, FSG cannot be used to prepare stable fish oil@FSG-SHMP complex coacervates and stable fish oil@FSG-SHMP@SSOS powder.

[0057] like Figure 3As shown in Figure 2, the size of the complex coacervate decreases with increasing pH. The fish oil@PSG-SHMP complex coacervate easily forms a continuous coacervate at pH 4.9 ( Figure 3 A). In addition, at pH 5.0 ( Figure 3 C) and pH 4.9 ( Figure 3 D), fish oil@FG-SHMP and fish oil@FSG-SHMP complex coacervates cannot form. As the pH increases, the charge of gelatin (NH3 + ) decreased, the interaction between SHMP and gelatin increased, and the size of the complex coacervate decreased.

[0058] The gelatin mass ratio mainly affects the yield of coacervate and has an important influence on the fish oil@PSG-SHMP( Figure 4 A) and fish oil @FG-SHMP( Figure 4 C) The size of the complex coacervates had no significant effect, whereas reducing SHMP may reduce the fish oil @BSG-SHMP ( Figure 4 B) and fish oil @FSG-SHMP( Figure 4 D) Size of complex coacervates. In particular, the fish oil@FSG-SHMP complex coacervates easily formed continuous coacervates when the SHMP: gelatin mass ratio was 1:15 and 1:20 ( Figure 4 D). Therefore, the SHMP: gelatin mass ratio is also a key parameter for controlling the size of the complex coacervate. However, the size of the complex coacervate and whether a continuous coacervate is formed do not affect the subsequent addition of sodium starch octenyl succinate (SSOS) to form a fat powder.

[0059] For the four types of gelatin, the complex coacervates consisted of spherical features ( Figure 3 , 4 : Coacervate (40 times)), which is comparable in size to the emulsion droplets ( Figure 3 , 4 : emulsion (40 times)). It was confirmed that SHMP can adsorb onto gelatin molecules in emulsion droplets and aggregate them to form fish oil@gelatin-SHMP complex coacervates. In addition, this also shows that the complex coacervation process did not significantly destroy the emulsion droplets. Therefore, during the complex coacervation process, SHMP can adsorb onto gelatin molecules in emulsion droplets stabilized by gelatin loaded with fish oil and aggregate them to form coacervates (such as Figure 2 D).

[0060] (3) Freeze-drying process

[0061] After complex coacervation, 8 g of SSOS was added to the suspension. The suspension was magnetically stirred at 400 rpm for 30 min at room temperature. Finally, the suspension was frozen and vacuum dried at -50 °C for 48 h. The freeze-dried sample was gently crushed by hand. Powders prepared with gelatin from different sources were placed in plastic petri dishes (1.5 cm high and 4.0 cm high). Digital camera images are shown in Figure 2. Figure 2 As shown in B.

[0062] The crushed samples were attached to a conductive adhesive, sputtered with a platinum layer, and observed using a scanning electron microscope (S-3400, Hitachi, Tokyo, Japan) at an accelerating voltage of 10.0 kV. Figure 2 C. White arrows indicate surface roughness, black arrows indicate surface roughness, and the black scale bar is 30 μm.

[0063] like Figure 2 A, from left to right: the emulsion is in a 150 mL glass beaker (13.3 cm high, 6.3 cm in diameter); sodium hexametaphosphate (SHMP) solution, emulsion (mixture), pH adjuster and sodium starch octenyl succinate (SSOS) are added to a 500 mL glass beaker (12.3 cm high, 9.5 cm in diameter); and the freeze-dried sample is in a glass petri dish (1.9 cm high, 9.0 cm in diameter).

[0064] Freeze-dried samples of PSG, BSG and FG were placed in plastic culture dishes (1.5 cm high and 4.0 cm high) as follows: Figure 2 B.

[0065] SEM images are shown in Figure 2 As shown in Figure C, the powder is mainly composed of particles with rough surfaces (μm-scale spherical protrusions), and a small amount of particles with smooth surfaces. Previous work found that there are two types of coacervates (B. Wang, Adhikari, Mathesh, Yang, & Barrow, 2019): coacervates coated on emulsion droplets (fish oil@gelatin complex coacervates) and free coacervates (gelatin complex coacervates). Therefore, we can reasonably assume that the powder obtained by this method is composed of two types of particles: (i) fish oil@gelatin-SHMP@SSOS particles, that is, fish oil@gelatin-SHMP complex coacervates with SSOS coating; (ii) gelatin-SHMP@SSOS particles, which are gelatin-SHMP complex coacervates with SSOS coating. The former has a rough surface due to the presence of emulsion droplet structure in the core, while the latter has a smooth surface due to the absence of emulsion droplet structure. This means that the SSOS coating has no obvious effect on the structure of the freeze-dried complex coacervate. Therefore, SSOS can be used as a drying aid in the freeze-drying of complex coacervates.

[0066] Preparation diagram Figure 2 D. After adding SHMP and adjusting the pH value, SHMP can adsorb onto the gelatin molecules in the emulsion droplets and aggregate them to form fish oil@gelatin-SHMP complex coacervates ( Figure 2 D (upper left, upper right and lower left structures in the second figure). In addition, SHMP can also adsorb onto free gelatin molecules in the aqueous phase and aggregate them to form a gelatin-SHMP complex coacervate ( Figure 2 D (lower right structure in the second image). Subsequently, during the freeze-drying process, water-soluble SSOS can be coated on the complex coacervate to form fish oil@gelatin-SHMP@SSOS blocks. After manual crushing, fish oil@gelatin-SHMP@SSOS powder was obtained, which mainly consisted of fish oil@gelatin-SHMP@SSOS particles ( Figure 2 D The upper left, upper right and lower left structures in the third image) and a small amount of gelatin-SHMP@SSOS particles ( Figure 2 D The upper left, upper right and lower left structures in the third image).

[0067] In step (2), when the amount of SHMP used is 0.4-0.8 g (the mass ratio of SHMP to gelatin is 1:10-20), fish oil@gelatin-SHMP@SSOS powder can also be obtained.

[0068] Example 3 Physicochemical Property Analysis

[0069] Three types of fish oil@gelatin-SHMP@SSOS powders (Example 2) were prepared using three types of gelatin (PSG, BSG and FG) at a SHMP:gelatin mass ratio of 1:15 and different pH values ​​of 4.7, 4.4 and 4.8, respectively, and then their physicochemical properties were analyzed: bulk density, tap density, moisture content, water activity, LC and EE.

[0070] (1) Bulk density and tap density

[0071] Bulk density and tapped density were determined by the measuring cylinder method (Botrel, Borges, Fernandes, & DoCarmo, 2014). Gently place the powder into a 50 mL measuring cylinder. Bulk density (g / cm 3 ) is determined by dividing the weight of the powder by the volume of the powder shown on the cylinder. Pour the powder freely into a 50mL cylinder and tap it repeatedly by hand to allow the sample to sink naturally until the volume no longer changes. Tap density (g / cm 3 ) is determined by dividing the powder weight by the tapped powder volume shown on the graduated cylinder.

[0072] Bulk density and tap density are commonly used to estimate the processability and flowability of powders by measuring the mass of powder in a given volume. Previous work has shown that the bulk density and tap density of particles are strongly affected by the composition of the wall material. Figure 5 As shown in A–B, the bulk density and tap density of the powders depend on the gelatin source. Fish gelatin has the highest bulk density and tap density. PSG has a higher bulk density and a tap density similar to BSG.

[0073] (2) Water content and water activity

[0074] For moisture content, 1.0 g of powder was treated in an oven at 105 °C to constant weight ( Acre, Viegas, Kurozawa, & Benassi, 2021). The moisture content (%) was determined by dividing the moisture weight by the powder mass (1.0 g) and then multiplying by 100. According to the company manual ( Acre, Viegas, Kurozawa, & Benassi, 2021), and water activity was determined using an AquaLab4TE instrument (Instrument Group, Pullman, WA, USA).

[0075] Moisture content and water activity are important parameters for predicting the stability of low-moisture products (Achata, Esquerre, O'Donnell, & Gowen, 2015). Figure 5 As shown in C–D, the moisture content and water activity depend on the gelatin source. In addition, the moisture content order is different from the water activity order. The maximum moisture content and water activity of fish oil@BSG-SHMP@SSOS powder are 4.3% and 0.086%, respectively. These results indicate that all the obtained powders are low water activity products.

[0076] (3) Loading capacity (LC) and encapsulation efficiency (EE)

[0077] The surface oil mass of the powder was measured by a simple dissolution-evaporation-weighing method (El-Messery, Altuntas, Altin, & 2020). Briefly, 0.500 g of powder was added to 10 mL of hexane in a 50 mL centrifuge tube and shaken for 2 min. Then, the mixture was filtered through filter paper. The centrifuge tube was washed with 10 mL of hexane and filtered. The washing-filtration process was repeated twice. Then, 10 mL of hexane was directly filtered to wash the surface of the filter paper. The collected hexane solution was evaporated at 50 °C, and then the sample in the vial was treated in an oven at 105 °C to constant weight, which was considered to be the surface oil mass of the powder (m 1 ).

[0078] The total oil mass of the powder (including surface oil and encapsulated oil) was measured by a simple rupture-dissolution-evaporation-weighing method (B. Wang, Adhikari, & Barrow, 2014). The powder (0.500 g) was added to 10 mL of HCl (4 mol / L) and 20 mL of hexane in a 50 mL centrifuge tube and magnetically stirred (400 rpm) overnight to extract the oil into the hexane phase. The mixture was allowed to stand for 30 min and the supernatant was filtered. Subsequently, hexane (20 mL) was added to the centrifuge tube and magnetically stirred (600 rpm) for 30 min, and the supernatant was filtered. The addition-stirring-filtration process was repeated twice. Then, 10 mL of hexane was directly filtered to wash the surface of the filter paper. The collected hexane solution was evaporated at 50 ° C, and then the sample in the vial was treated in an oven at 105 ° C to constant weight, which was considered to be the total oil mass of the powder (m 2 ).

[0079] LC and EE are calculated according to the following formula:

[0080]

[0081] The LC and EE of fish oil are key properties of fish oil loading system. A good oil loading system requires high oil LC and EE. Figure 5 As shown in E–F, the powders have similar fish oil LC values ​​(24.0–26.2%) and different fish oil EE values: PSG (98.4%) > FG (96.4%) > BSG (95.2%). In addition, the introduction of SSOS to coat the fish oil@gelatin-SHMP complex coacervate increased the total mass of the wall material and encapsulated part of the surface oil on the fish oil@BSG-SHMP complex coacervate, which reduced the LC value and increased the EE value compared with the fish oil@BSG-SHMP powder.

[0082] Example 4 In vitro digestion process

[0083] A simulated gastrointestinal and small intestine model was used to analyze the digestive behavior of the powder (Tao, Xu, Chen, Liu, Zhang, Tao, et al., 2022). Briefly, simulated gastric fluid (2 g / L NaCl, 7 mL / L HCl, 3.2 g / L pepsin from porcine gastric mucosa, pH 1.2) was prepared. Subsequently, 0.1 g of powder was added to the fluid (15 mL) and the pH was adjusted to 2.0. The mixture (maintaining pH) was vibrated at 100 rpm for 2 h at 37 ° C (this stage was considered to be a simulated gastric stage). After the pH of the mixture was adjusted to 7.0, a porcine bile extract solution (3.5 mL, 54 mg / mL, Shanghai McLean, China) and a salt solution (1.5 mL; calcium chloride, 10 mM; sodium chloride, 150 mM) were added. After the pH was adjusted to 7.0, 2.5 mL was taken and dissolved in freshly prepared lipase phosphate buffer (75 mg / mL, pH 7.0). Finally, the mixture was shaken at 100 rpm in a 37°C water bath for 2 h (this stage was considered the small intestine stage), and the pH was maintained every 20 min using 0.5 mol / L NaOH. The samples were photographed and examined using an ML-8000 upright optical microscope.

[0084] If two free fatty acid molecules are produced per triacylglycerol, the percentage of free fatty acids (FFA) released during the small intestinal stage is calculated according to the following formula:

[0085]

[0086] Among them, V NaoH is the volume of NaOH required to neutralize the generated FFA, M NaoH is the molar concentration of NaOH required to regulate digestive juice (mol / L), the molecular weight of fish oil is 868g / moL, W 鱼油 is the total weight of fish oil (calculated by dividing the mass of sample required for digestion by the sample loading rate)

[0087] Digestive behavior is one of the most important properties of fish oil powder for potential food applications. In the past few decades, in vitro gastrointestinal systems have been widely used to simulate the human gastrointestinal tract and study the fate of food during digestion (Li, Yu, Wu, & Chen, 2020). In this work, digestive behavior was analyzed using a simulated gastrointestinal and small intestine model (Tao, et al., 2022): the powder was treated in a simulated gastric phase for 2 h and then in a simulated small intestine phase for 2 h.

[0088] After 2 h of the simulated small intestine stage, all solutions of fish oil@PSG-SHMP@SSOS, fish oil@BSG-SHMP@SSOS, and fish oil@FG-SHMP@SSOS powders were dark yellow and transparent in the digital camera images ( Figure 6 A–C). In addition, the sample in the optical microscope image consists of emulsion droplet-like structures ( Figure 6 A–C), which is similar to the emulsion droplets stabilized by gelatin loaded with fish oil ( Figure 3 and 4 ). Therefore, the SSOS layer and gelatin-SHMP interaction were disrupted, and only fish oil-loaded gelatin-stabilized emulsion droplets were present after the digestion process.

[0089] Fish oil digestion of the powder in the small intestinal phase was assessed by titrating the released free fatty acids. Figure 6 As shown in D, the percentage of FFA release after the small intestine stage was ≤55.5%, indicating that some fish oil molecules were released from the powder. Figure 6 A–C), we can assume that during digestion, the SSOS layer and gelatin-SHMP interaction were disrupted, and some emulsion droplets were broken to release part of the fish oil. In addition, the percentage of FFA release depended on the gelatin source: PSG (55.5% after processing) > FG (34.1% after processing) > BSG (27.0% after processing).

Claims

1. A method for preparing oil powder, characterized in that: The steps include: (1) mixing the fat-gelatin emulsion with sodium hexametaphosphate and adjusting the pH to 4-4.8 to form a complex coacervate; (2) adding a modified starch substance to dissolve in the suspension; and freeze-drying to obtain a fat powder double-coated with starch salt and gelatin; the modified starch substance is sodium starch octenyl succinate; the ratio of gelatin to modified starch is 1:0.5-5; the ratio of gelatin to fat is 1:0.5-2; The oil is vegetable oil or animal oil; the gelatin is pigskin gelatin, cowhide gelatin or fish skin gelatin; when the gelatin is pigskin gelatin or cowhide gelatin, the mass ratio of sodium hexametaphosphate to gelatin is 1:8-20; when the gelatin is fish skin gelatin, the mass ratio of sodium hexametaphosphate to gelatin is 1:8-12.

2. The method according to claim 1, characterized in that In step (1), the particle size of the oil-gelatin emulsion is 1-10 μm.

3. A grease powder, characterized in that: Prepared by the method according to claim 1 or 2.

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