Summary of Gel Properties of Different Hydrocolloids
At present, hydrophilic colloids are widely used as food additives, mainly as thickeners, stabilizers, etc. The gel characteristics and influencing factors of several commonly used hydrophilic colloids are discussed.
Characteristics of several commonly used hydrophilic colloid gel systems
Different hydrocolloid systems have different gel conditions. The following are the characteristics and influencing factors of commonly used hydrocolloid gels.
Pectin can be divided into high-ester pectin (High Methoxyl Pectin) and low-ester pectin (Low Methoxyl Pectin) according to the degree of methylation.
(1) Characteristics of High Methoxyl Pectin Gel
The basic conditions for the high-ester pectin gel system to meet the gel formation are pH2.0~3.8, 55% soluble solids, and the following factors affect the gel formation and strength:
1. Pectin quality and DE value: The quality of pectin directly affects the gelling ability. The higher the DE value, the greater the degree of dehydration, and the better the gelation in the bonding area formed by dehydration between pectin molecules;
2. Pectin content: The higher the pectin content in the system, the easier it is to form a bonding area with each other, and the better the gel effect;
3. The content and type of soluble solids: the content and type of soluble solids are different, the intensity of competition for water molecules is different, and the impact on gel formation and strength is different;
4. Temperature duration and cooling rate: The faster the cooling rate, the lower the gel formation temperature. On the contrary, the system temperature is slightly higher than the gel temperature for a long time, which will cause the gel formation temperature to rise.
(2) Characteristics of Low Methoxyl Pectin Gel
Similar to the high-ester pectin system, the gel formation conditions, gelation temperature, and gel strength of low-ester pectin are also restricted by the following factors:
1. Pectin quality: the quality directly affects the gelling ability and strength;
2. DE and DA values of pectin: When the DE value increases, the gelation temperature decreases; when the DA value increases, the gelation temperature also increases, but if the DA value is too high, the gelation temperature will exceed the boiling point of the system, making The system immediately forms a pre-gel;
3. The content of pectin: the increase of the content will increase the gel strength and gelation temperature, but if it is too high, it will lead to the formation of pre-gel, and the opposite will reduce the gel strength.
4. Ca2+ concentration and Ca2+ alloying agent: when the Ca2+ concentration increases, the gel strength and gelation temperature both rise; after reaching the optimum gel strength, the calcium ion concentration continues to increase, and the gel strength begins to become brittle and weak, and finally forms a pre-coagulation Glue; Ca2+ chelating agent can reduce the effective concentration of Ca2+ and reduce the risk of pre-gel formation, especially when the solid content in the system is high.
5. Content and types of soluble solids: high soluble solids content increases the gel strength and gelation temperature, but if it is too high, it is easy to form pre-gel; and the different types will affect the degree of binding ability of pectin and Ca2+ different.
6. System pH value: The pH value of gel formation can be in the range of 2.6~6.8. When the pH value rises, more pectin or calcium ions are needed to form the same quality gel, and the gelation temperature can be lowered at the same time.
2. Xanthan gum
In terms of gel properties, xanthan gum solution has good heat resistance, salt resistance, and acid and alkali resistance stability. The viscosity rises rapidly with the increase of concentration. The viscosity of the gel solution containing NaCl is between pH 2.5 and 12. has little impact.
Zhu Guilan et al. studied the rheological and gel properties of the gellan gum and xanthan gum compound system with different proportions of 1% mass fraction, and preliminarily discussed their interaction mechanism. The results show:
1) Dynamic frequency scanning showed that xanthan gum could improve the viscoelasticity and fluidity of the gellan gum-xanthan gum compound system, and the content of xanthan gum played a decisive role in the dynamic rheological properties of the compound system.
2) In the temperature scanning experiment, as the proportion of xanthan gum increases, the storage modulus G' and loss modulus G″ increase, and the gel temperature increases. It shows that there is a gap between gellan gum and xanthan gum molecular chains. Certain interactions.
3) Gellan gum is the decisive factor for the gel hardness of the gellan gum-xanthan gum compound system, and the addition of xanthan gum will improve the viscoelasticity, cohesion and water holding capacity of the compound system.
3. Gellan gum
Gellan gum has various excellent properties of xanthan gum, pectin and carrageenan, and is an indispensable hydrophilic colloid in modern times. Its gel properties mainly include the following points:
(1) High-quality gel can be formed at low concentration (0.05%~0.25%);
(2) It is very stable under heating and low pH conditions, and can form gels between pH 3.5 and 7.0;
(3) The gel formed by sodium or potassium ions can be restored after adding, while the gel of magnesium or calcium salt cannot be restored;
(4) It can be used in combination with other gums, such as modified starch, xanthan gum, locust bean gum, etc.;
(5) Gellan gum has good compatibility with other compounds.
Carrageenan is a multifunctional food additive that can hold water, hold oil, thicken, stabilize and promote gel formation, etc. It is often used in dairy products, sweets, beverages, jellies and meat products. The gel formed by carrageenan is relatively hard, so it needs to be used in conjunction with other food colloids to increase the elasticity of the gel. In recent years, the application of carrageenan in dairy products, soft candies, and jellies has basically replaced traditional gelatin and agar gum, etc., but the application of carrageenan is closely related to the gel properties of carrageenan. The performance and its change law under various conditions are of great significance to production and application.
Carrageenan is stable under neutral and alkaline conditions, but under acidic conditions (pH3.5), carrageenan molecules will degrade, and heating will accelerate the degradation rate. Carrageenan can form a gel at a concentration of more than 0.5% in an aqueous system, and the gel-forming concentration in an emulsion system can be as low as 0.1% to 0.2%. Carrageenan can interact with protein, and the result depends on the isoelectric point of the protein and the pH value of the solution. For example, in neutral beverages, carrageenan can form a weak gel with milk protein to maintain the suspension of particles and avoid rapid deposition of particles; carrageenan The interaction with protein can also be used to remove undesired protein in the system; some carrageenan also has the function of rapidly forming protein-polysaccharide floc deposition, but the deposition is easy to redisperse in the flow.
5. Sodium alginate
Sodium alginate is a polysaccharide carbohydrate extracted from brown algae kelp or sargassum, and is composed of 1‚4-poly-β-D-mannuronic acid and α-L-guluronic acid. It is a kind of linear polymer, which is one of alginic acid derivatives, so it is sometimes called sodium alginate or kelp gum and seaweed gum. Its molecular formula is (C6H7O6Na)n, and its relative molecular weight is about 32,000 to 200,000. The molecular weight of its structural units The theoretical value is 198∙11. Sodium alginate can undergo a rapid ion exchange reaction with divalent metal ions other than magnesium and mercury to form alginate gel, among which the gel film formed with calcium chloride has the greatest strength. The performance of the formed gel is significantly different due to the M/G value, the concentration of sodium alginate, the amount of combined calcium, and the conditions of gelation .
Gelatin is an animal-derived colloid, and its gel system features are: gelatin is a very elastic colloid; gelatin has a low dissolution and solidification temperature, and it is a heat-unstable gel, acid-stable Poor, will harden when refrigerated.
Chen Haihua studied the effects of concentration, pH value, sucrose, calcium chloride, and sodium chloride on the gel strength of gelatin, and the effect of polysaccharides on the gel properties of gelatin. The results showed that the gel strength of gelatin increased with the increase of gelatin concentration; When the sucrose concentration is lower than 1%, the gel strength of gelatin increases with the increase of sucrose concentration, and when the sucrose concentration is higher than 1%, the gel strength of gelatin decreases with the increase of concentration. The gel strength of gelatin decreases with the increase of sodium chloride concentration and increases with the increase of calcium chloride concentration. Adding polysaccharides such as carrageenan, CMC or sodium alginate can improve the gel properties of gelatin and increase its gel strength .
Xie Ranyi et al. studied the properties of gelatin gel and the influence of various external factors, such as time, temperature, pH value, etc. on the properties of gelatin gel. The conclusions show that:
1) When the gelatin is dissolved in water at 70°C and incubated in a water bath at 70°C for 15 minutes, the gel strength of the gelatin body is the largest;
2) When the system pH=4, the greater the concentration of the gelatin solution, the more conducive to the formation of its gel;
3) When the concentration of sodium citrate in tap water is only 0.04%, the gelatin gel is formed well;
4) When the gelatin system contains 10% white granulated sugar or 25% maltose syrup, the gel formed is stronger;
5) When the ratio of white sugar and maltose syrup in the gelatin system is 5:2, and the concentration is about 25%, a strong gelatin gel can be formed.
Agar, also known as agar gel, belongs to seaweed gum like alginate and carrageenan. The characteristics of its gel system are: poor heat/acid stability, smooth but opaque texture, and is a thermally unstable gel Body, the amount used in the general system is relatively high.
Liu Shilin et al. used low-field nuclear magnetic resonance and texture analyzer to discuss the factors affecting the strength and relaxation properties of agar gel, and analyzed its gel mechanism. The results showed that the strength of agar gel increased with the increase of agar mass fraction; pH 6.0-7.0 was the optimum condition for the formation of agar gel; appropriate additions of potassium chloride, xylitol, and sucrose could increase agar gel formation. Glue strength, the effect is best when adding mass fractions of 0.2% ~ 0.3%, 9% and 6%, respectively; appropriate proportion of konjac gum, carrageenan and locust bean gum can produce synergistic effect with agar, respectively in their When the ratio is 15%, 5%, and 10%, the synergistic effect with agar is the strongest; calcium chloride, sodium chloride and β-cyclodextrin hinder the formation of gel and reduce the strength of agar gel. The relaxation time T23 of the agar gel has a very significant (p <0.01) negative correlation with the gel strength, that is, the smaller the water mobility in the gel, the greater the gel strength.
8. Konjac gum
The gel system of konjac usually needs to be hydrated for a long time, the viscosity of the system is high, it can gel by itself, and the effect of compounding with carrageenan is better, but the thermal stability is poor. Viscosity and strength relationship: related to the modified conditions and modified products; viscosity and water holding relationship: generally there is no water separation problem (water separation phenomenon occurs in acidic double protein beverages).