In Taiwan, daily beverages are extremely popular, and the sealing film on these drinks is an essential part of the culture. To make the consumption of probiotics more fun and convenient, we decided to integrate our 5-HTP-generating probiotics to alleviate negative emotions into the sealing film.
The idea is to sprinkle probiotic powder on an edible, water-soluble film attached to the bottom of the sealing film. The water-soluble film will dissolve to release probiotics into the drink, allowing consumers to consume it conveniently.
After reviewing various studies, we found that high-amylose starch films, wheat starch films, soy protein films, and sodium caseinate films each have distinct advantages and are promising materials for food packaging. Therefore, we conducted experiments to examine each type of film's dissolution rate, the state of the film dissolving in the liquid, whether they sediment out, coagulate, or dissolved. And stability in humid environments. Finally, we selected sodium caseinate films as our carrier.
High Amylose Starch [1]:
High-amylose starch is common in food applications. This type of starch is resistant to enzymatic digestion in the gastrointestinal tract and contains an increased fraction of resistant starch (RS), a kind of dietary fiber.
Wheat Starch [2]:
Wheat starch is a side product of gluten manufacture. The viscosity and gel strength are lower than corn starch. The principal use of wheat starch is baking.
Sodium Caseinate [3]:
Sodium Caseinate is a protein commonly found in milk. Casein proteins can be separated from milk and used independently as a supplement or additive to thicken, texturize, and stabilize various food products Unlike many proteins, casein is not coagulated by heat.
Soy Protein [4]:
Soy protein is a protein that is isolated from soybeans. Typically, soy protein is made from dehulled and defatted soybeans.
The proportion of starch and plasticizers:
According to the reference [1], an edible file containing 5% high-amylose starch takes approximately 7 minutes to fully dissolve in water, which is too slow for beverage applications [1]. Since the dissolution rate positively correlates with the starch concentration, we decided to examine whether 1% - 5% high-amylose starch film could be used for beverages. Plasticizers can increase the water solubility and elasticity of the edible film, so we selected 30% and 40% glycerol or sorbitol as plasticizers in high-amylose starch films.
Materials:
Experiment Steps:
The formulas for high-amylose starch are shown in Table 1.
| 1% starch | 2% starch | 3% starch | 4% starch | 5% starch | |
|---|---|---|---|---|---|
| 30% glycerol | 1 g starch 0.3 g glycerol |
2 g starch 0.6 g glycerol |
3 g starch 0.9 g glycerol |
4 g starch 1.2 g glycerol |
5 g starch 1.5 g glycerol |
| 40% glycerol | 1 g starch 0.4 g glycerol |
2 g starch 0.8 g glycerol |
3 g starch 1.2 g glycerol |
4 g starch 1.6 g glycerol |
5 g starch 2 g glycerol |
| 30% sorbitol | 1 g starch 0.3 g sorbitol |
2 g starch 0.6 g sorbitol |
3 g starch 0.9 g sorbitol |
4 g starch 1.2 g sorbitol |
5 g starch 1.5 g sorbitol |
| 40% sorbitol | 1 g starch 0.4 g sorbitol |
2 g starch 0.8 g sorbitol |
3 g starch 1.2 g sorbitol |
4 g starch 1.6 g sorbitol |
5 g starch 2 g sorbitol |
▲ Table 1: High-amylose Starch Film formulas
The proportion of starch and plasticizers:
Similar to high-amylose starch, the dissolution rate of 3% wheat starch is too slow for beverage applications. We selected 1%-3% wheat starch to examine whether they could dissolve quickly. Maltodextrin was selected as the plasticizer.
Materials:
Experiment Steps:
The formulas for wheat starch are shown in Table 2
| 1% wheat starch | 2% wheat starch | 3% wheat starch | |
|---|---|---|---|
| 20% Maltodextrin | 1 g wheat starch 20 g maltodextrin |
2 g wheat starch 20 g maltodextrin |
3 g wheat starch 20 g maltodextrin |
▲ Table 2: Wheat Starch Film Solution Ratios
The proportion of Sodium Caseinate and plasticizer:
Sodium caseinate films have good water solubility but are often brittle, which can be improved by adding plasticizers. Therefore, we selected 0.625% (w/v) glycerol as a plasticizer to stabilize the 2.5% (w/v) sodium caseinate film, according to the previous report [3].
Materials:
Experiment Steps:
The proportion of Soy protein and plasticizer:
Soy protein films have good film-forming properties but poor mechanical properties. Therefore, 2% (w/v) glycerol was selected as a plasticizer to stabilize 3% (w/v) soy protein film [4].
Materials:
Experiment Steps:
High Amylose Starch Film:
The 1% starch film does not form properly due to insufficient starch content, making gelatinization challenging. Starch films with more than 2% starch can gelatinize into a translucent, colorless, and tasteless film. 40% plasticizers led to excessively sticky films after drying, making removing them from the plate difficult.
▲ Figure: 2% high amylose starch, 30% sorbitol, High Amylose Starch Film.
Wheat Starch Film:
Films made from wheat starch solutions of any ratio dry out and fragment directly, making them unsuitable for film formation.
▲ Figure: Wheat Starch + Maltodextrin Film (right: 1% starch, center: 2% starch, left: 3% starch)
Sodium Caseinate Film:
Forms a transparent, colorless film with a slight protein odor.
▲ Figure: 2.5% sodium caseinate, 0.625% glycerol, Sodium Caseinate Film
Soy Protein Film:
Forms a translucent, light brown film with no noticeable odor.
▲ Figure: Soy Protein Film.
The result of the street survey indicated that consumers are concerned about the dissolution rate of edible films and beverage's appearance and taste after adding edible films. The other important issue is the price of edible films. Accordingly, we conducted experiments to determine the dissolution rate of films and spectrophotometry to monitor the changes in the drink after adding films.
Results:
A preliminary examination indicated that crystal violet could not be released from edible films containing more than 4% high-amylose starch. Therefore, we could not conduct the dissolution rate experiment on films with more than 4% high-amylose starch. Since the edible film containing 40% plasticizer was too sticky for examination, we excluded them also. The wheat starch films were excluded due to their fragility.
Finally, we selected the following formulations for further experiments:
▲ Figure 6: Second Edible Film Dissolution Rate Experiment OD570 Value
The measurement of released crystal violet based on OD570 value indicated the solubility of soy protein film (SP) is poor. On the other hand, the maximal value of OD570 of dissolved high-amylose starch films and sodium caseinate film appears at 20 mins, suggesting complete dissolution.
However, further observation indicated that the high-amylose starch film released crystal violet without dissolution, as shown in the below figure.
▲ Figure 7: High amylose film settles at the bottom of the cup
Rationale:
The solution containing the dissolving membrane becomes turbid and reduces the intensity of transmitted light, leading to an increase in resistance and a decrease in current intensity . Therefore, we set up a photoresistor experiment to confirm the insolubility of high-amylose starch films.
Dissolution Rate Experiment 2 Steps:
Instruments:
▲ Figure 8: Microprocessor System: Arduino UNO R3
The conventional Arduino microprocessor
▲ Figure 9: Connected in a row of photoelectric (5549) group
▲ Figure 10: Circuit design
▲ Figure 11: A 3D-printed scaffold used for securing the film on the upper layer of the burnt cup.
▲ Figure 12: “Design of instruments for measuring dissolution rates”.
const int P_resistor = A0; //Read the photoresistor pins
int light = 0; //photoresistor value
void setup() {
pinMode (P_resistor, INPUT);
Serial.begin (9600);
}
void loop() {
light = analogRead (P_resistor);
Serial.println (light);
delay (100);
}
▲ Arduino code
Experimental Results:
1. The time required for complete dissolution of starch films is shorter with sorbitol as a plasticizer than with glycerol.
▲ Figure 14: Comparison of different plasticizers.
2. Based on the decrease in current intensity and direct observations, it is evident that only sodium caseinate films can fully dissolve without stirring.
▲ Figure 15: The comparison of the three types of films.
Transparency Experiment Steps:
Results:
By overlaying the OD value curves from different times with the OD chart of the tea without added sodium caseinate film, it was observed that the absorbance at different wavelengths over time almost perfectly overlapped. This indicates that the addition of sodium caseinate film to the commercially available beverage does not significantly affect the appearance and color of the drink.
Finally, we selected the sodium caseinate film as our carrier for mood-enhancing probiotics.
Viscosity:
According to the report, the viscosity of solution of edible films composed of 8% sodium caseinate is 10 mPa·s, while the viscosity of water is 1 mPa·s [5]. Since our edible film contains only 2.5% sodium caseinate, we believe that the viscosity of our film should be in the range between 1 and 10 mPa·s.
Cost:
We calculated the cost per gram of the raw materials required to produce sodium caseinate film and multiplied it by the amount of raw material needed for one piece of film. The result is that one sodium caseinate film costs approximately NT$ 0.62(Only the material costs are calculated, and the time and equipment costs for the production process are not included).
Storage Conditions:
Mold growth depends mainly on moisture, not temperature [6]. The mold grows significantly when moisture exceeds 60% and shows minimal growth at 40% moisture. The edible film must be stored below 40% moisture to stop mold growth effectively. The reduction of moisture and proper ventilation also reduce bacterial growth [7].
We found that sodium caseinate films meet all our requirements through experiments on dissolution rate and transparency. It dissolves quickly without affecting the beverage's appearance or texture.
Although the sodium caseinate film has the fastest dissolution rate among the components we've found, we hope to enhance this rate further. We might achieve this by lowering the sodium caseinate concentration or exploring other materials that dissolve more quickly.
Taiwan's humid climate makes it challenging for all stores to create the ideal preservation conditions for the film. In the future, we might develop individually packaged edible films or moisture-proof products to address hygiene concerns associated with sodium caseinate films.