3.1.5. Sanitary Chemical Research

Materials intended for contact with food products were subjected to sanitary chemical studies for the migration of low-molecular-weight substances.

Organoleptic studies at temperatures of 20, 40 and 60 ◦C for 7, 14, 21 and 28 days showed that, in the analyzed extracts from all the materials, there was no sediment, turbidity or color change in the extracts. However, there was the increase in the intensity of odor from materials with the increase in BBE concentration and temperature to 60 ◦C, while the average value was no more than 1 point, which is allowed for the materials contacting food products.

The results of the study of the migration of low-molecular-weight substances from the materials are presented in Table 6.


**Table 6.** Results of sanitary chemical research of extarcts of various model environments of materials based on polyethylene with 2.0% content of birch bark extract and the use of ultrasonic treatment.

When using a model medium of 3.0% lactic acid solution, the increase in the migration of methyl alcohol and formaldehyde is observed, although its value does not exceed permissible norms (Table 6). A study of the migration of low-molecular-weight components from developed materials with BBE

shows that migrating substances do not exceed permissible norms. It was found that ultrasonic treatment of the melt and the content of the additive at the concentration of up to 5% do not affect the formation of low-molecular-weight substances that can migrate into the food product upon contact.

Based on the carried out rheological, physico-mechanical, antimicrobial and sanitary chemical studies, it is proposed to use 2% BBE with ultrasound treatment as the packaging material for contact with food products. This material has sufficient physico-mechanical properties, has antimicrobial properties and complies with sanitary chemical standards. The use of the ultrasound treatment makes it possible to obtain material with uniformly distributed additive, and the content of 2% BBE is justified by the economic factor.

#### 3.1.6. Study of the Permeability of the Packaging Materials

When studying the vapor permeability of polymeric compositions based on PE and BBE, it was found that the introduction of a filler increases the vapor permeability by about 8–12% in comparison with the control samples. For example, the vapor permeability of PE without BBE is 0.18–0.21 g/m2. When the BBE content is 5% in the polyethylene composition, the vapor permeability is about 0.23–0.25 g/m2.

When studying the oxygen permeability of the samples, it was found that oxygen permeability coefficients for the compositions based on PE and BBE 5% are 1.42 <sup>×</sup> <sup>10</sup>−<sup>10</sup> cm3 cm/m2 s Pa. For the PE film without BBE, the oxygen permeability coefficient is 1.2 <sup>×</sup> <sup>10</sup>−<sup>10</sup> cm<sup>3</sup> cm/m<sup>2</sup> s Pa.

#### *3.2. Packed Product Storage Studies*

The results of storing chilled meat are presented using broiler chicken carcasses' parts as an example. Packed product samples were stored at 0 ± 2 ◦C. The quantity of mesophilic aerobic and facultative anaerobic microorganisms (QMAFAnM) was determined by the accelerated method of seeding on test plates—petrifilms containing dehydrated nutrient gel-like chromogenic substrate.

In the process of storage, the quantity of mesophilic aerobic and facultative anaerobic microorganisms increases in the packed parts of poultry carcasses (Table 7). The acceptable content of QMAFAnM in chilled poultry is 1 <sup>×</sup> 103 CFU/g. It was found that during the storage of poultry carcasses at the temperature of 0 ± 2 ◦C for 4 days in a packaging material based on pure polyethylene (PE), the QMAFAnM index approaches a critical value and significantly exceeds it by 5 days. The use of such products for food is considered unsafe for health. During the storage of poultry carcasses at the temperature of 0 ± 2 ◦C, the QMAFAnM index approaches the critical value on the 5th day. The rate of accumulation of the quantity of mesophilic aerobic and facultative anaerobic microorganisms is higher in a product packaged in pure polyethylene compared to a product packaged in plastic film with birch bark extract. This is due to the fact that upon the contact of the packaging material containing BBE with the product, partial suppression of the growth of microorganisms located on its surface occurs.

**Table 7.** Change in the content of the quantity of mesophilic aerobic and facultative anaerobic microorganisms, CFU/g, in parts of poultry carcasses during storage.


The data obtained show that the use of the developed PE BBE material in the packaging technology of chilled meat (poultry meat in particular) leads to the increase in shelf life.

*3.3. Investigation of the E*ff*ect of Ultrasonic Treatment on the Properties of Polyethylene Compositions Based on Birch Bark Extract and Thermoplastic Starch*

At this stage of the work, the development of polymer composite materials (PCM) with antimicrobial properties and biodegradability was carried out. In this work, compositions based on PE, thermoplastic starch and BBE were obtained. In PCM, the amounts of thermoplastic starch were 20%, 40% and 60%. The amount of BBE in PCM ranged from 0% to 12%.

The obtained film samples were investigated by rheological and physico-mechanical properties (Tables 8 and 9).


**Table 8.** Dependance of the melt flow rate index (MRF) on the composition of polymeric compositions material, received with (with US) and without the use of ultrasonic treatment (without US).

**Table 9.** Physico-mechanical properties of composite polymeric films (PC) according to the content of birch bark extract (BBE) and the use of ultrasonic treatment (US).


From the results obtained, it is clearly seen that the ultrasonic treatment increases the melt flow rate by approximately 2 times compared with the control samples obtained without ultrasonic treatment. It is clearly seen that the introduction of up to 5% BBE has little effect on the physico-mechanical properties of PCM. The introduction of thermoplastic starch is of great importance; its amount reduces the breaking stress and elongation at break. It has been established that the processing of PCM melts increases the physico-mechanical properties of the materials, which is especially noticeable when comparing the elongation at break. The values of this indicator are approximately 1.5–2 times greater for PCMs obtained with ultrasonic treatment of the melt as compared to control samples. To determine the optimal concentration of BBE in PCM, studies were conducted to determine the shelf life of food products in packages. Dependence of the relative increase in shelf life on the concentration of BBE in polymer compositions containing thermoplastic starch is shown in Figure 10.

**Figure 10.** Dependence of the relative increase in shelf life of the food product on the contents of birch bark extract (BBE) in composition material (PCM): (1—content of thermoplastic starch 20% in PCM; 2—content of thermoplastic starch 30% in PCM; 3—content of thermoplastic starch 60% in PCM; 4—desired value to increase product storage).

Based on the data obtained, BBE concentration of 8% was selected.

Next, the research was conducted using the PCM method of composting (Table 10). As the criterion for evaluating the properties, the change in elongation at break after 6 months of composting was used.


**Table 10.** Change in relative elongation at break of composite polymeric materials (PC) containing birch bark extract (BBE), received with (with US) and without the use of ultrasonic treatment (without US).

It is worth noting that the samples obtained with ultrasonic treatment showed more noticeable change in relative elongation at break after composting than those without ultrasonic treatment. This indicates that the effect of ultrasound treatment accelerates the decomposition of polymer materials in the environment due to the uniform distribution of the filler in the polymer matrix and the increase in oxygen-containing groups in polymers, which was noted in the [27]. It should be noted that the introduction of BBE in PCM leads to the decrease in this indicator. This can probably be attributed to the action of BBE as the antimicrobial supplement.

Special attention should be paid to the material based on PE containing 60% starch and 8% BBE, in which, after 6 months of composting, the elongation at break changed by 60–68%. This is a good criterion for obtaining biodegradable PCMs.

### **4. Conclusions**

The influence of ultrasonic treatment of melts of the polymer compositions based on PE and BBE, as well as PE, thermoplastic starch and BBE, was investigated. Packaging materials in the form of films based on polymer compositions were obtained. A comparison of identical PCM compositions obtained with and without ultrasonic treatment of the melts revealed that the ultrasonic treatment increases the fluidity of the melts of polymer compositions. Using electron microscopy, it was found that ultrasonic treatment of the melts of polymer compositions contributes to the production of materials with the uniform distribution of the components of the composition, as shown by the example of a PE sample containing 2% and 5% BBE. When studying oxygen and water vapor permeability of polymeric compositions based on PE and BBE, it was found that the introduction of the filler increases vapor permeability and oxygen permeability by about 8–12% compared to control samples without the addition of BBE. Ultrasonic treatment of polymer compositions does not affect these indicators. It was established that the processing of PCM melts increases the physico-mechanical properties of the materials, which is especially noticeable when comparing the elongation at break. The values of this indicator are approximately 1.5–2 times higher for PCMs obtained with ultrasonic treatment of the melt as compared to control samples. It is predetermined that the BBE content of 1.0% and above in the composition of PE provides packaging materials with antimicrobial properties. The optimal concentration of BBE in compositions based on PE and thermoplastic starch was determined. To obtain biodegradable materials with antimicrobial properties based on PE and thermoplastic starch, it is advisable to introduce BBE in the amount of greater than 8%. It was found that the extension of the shelf life of the food products stored in packaging materials based on PE and BBE in the amount of 2.0% and PE containing thermoplastic starch (60%) and BBE (8%), was greater than 50%, when compared with the control samples without additives. It was revealed that ultrasonic treatment of polymer compositions leads to the acceleration of their biodegradation. The introduction of BBE into PCM leads to the decrease in the biodegradation time, which is associated with the action of BBE as the antimicrobial supplement.

**Author Contributions:** Writing—review and edit, I.K.; writing—preparation of the original project, Y.F.; conceptualization, O.B. (Olga Beznaeva); verification, D.M.; research, I.T. and V.R.; methodology, O.B. (Olga Bannikova); visualization, D.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** The study was carried out as part of the implementation of the federal target program, the unique project identifier RFMEFI57418X0191.

**Conflicts of Interest:** The authors declare no conflict of interest.
