IMPROVEMENT OF THE FERMENTATION PROCESS OF KARAKUL SKINS BASED ON A RESOURCE-SAVING TECHNOLOGY USING SOY WHEY

ABSTRACT

The article discusses the development of a resource-saving technology for fermenting Karakul skins by partially replacing the traditional aqueous fermentation bath with soy whey, a by-product of the soy processing industry. The presence of water-soluble proteins, carbohydrates, vitamins and mineral substances in soy whey enables its use as a biologically active medium. The introduction of soy whey into the fermentation process made it possible to save salt, barley grits, water and time resources. At the same time, it was found that the physico-mechanical and chemical properties of the resulting fur fully meet the requirements of the relevant standards.

АННОТАЦИЯ

В статье рассматривается разработка ресурсосберегающей технологии квашения каракулевых шкурок, путем замены традиционного водного квашенного раствора с соевой сывороткой, побочным продуктом соеперерабатывающей промышленности. Наличие в соевой сыворотке водорастворимых белков, углеводов, витаминов и минеральных веществ позволяет использовать ее в качестве биологически активной среды. Введение соевой сыворотки в процессе ферментации позволило сэкономить соль, ячменную крупу, воду и прочие ресурсы. При этом установлено, что физико-механические и химические свойства полученного меха полностью соответствуют требованиям действующих стандартов.

Keywords: soy whey, karakul skin, fermentation process, resource-saving technology, water saving, barley grits, physic-mechanical properties.

Ключевые слова: соевая сыворотка, каракульская шкура, процесс ферментации, ресурсосберегающая технология, водосбережение, ячневая крупа, физико-механические свойства.

Introduction. In recent years, reducing the environmental impact and high demand for natural resources in the global leather, footwear and fur industry has become one of the priority tasks. In particular, the large volumes of water consumed at the stages of hide and skin processing cause serious environmental problems. The significant amount of water used in technological processes not only hinders the rational use of existing water resources, but also leads to an increase in the volume of wastewater. Therefore, the efficient and rational use of resources in leather processing and the development of innovative technologies and solutions in this direction remain among the key areas of modern research.

It should be noted that a very large amount of water is required in the leather and fur industries [1], especially in the processing of pelts intended for fur production [2]. In particular, the use of 8–15 times more water relative to the mass of raw material leads to excessive consumption of water resources and a sharp increase in wastewater volume. This, in turn, aggravates environmental problems and raises production costs and product cost price. From this point of view, the development of alternative, water-saving and resource-efficient technologies for leather processing is an urgent task.

Within the framework of the present study, instead of using traditional water in the fermentation stage, the possibility of applying soy whey – a secondary product formed in the soy industry – was investigated [3]. Such an approach, on the one hand, helps to sharply reduce water consumption and save water resources in the Karakul fur industry, and on the other hand, contributes to environmental sustainability by reusing waste from the food industry.

Soy whey is the liquid fraction obtained during the production of soy protein isolates, tofu and other soy-based products. In practice, it is often treated as a technological waste and disposed of without further processing. However, such an approach does not reflect the real value of soy whey, since it contains water-soluble proteins, various vitamins and minerals, and can be considered as a natural raw material rich in biologically active components. The high content of organic substances in soy whey allows it to be used as a valuable nutrient substrate. Scientific publications substantiate the possibility of using soy whey as a nutrient medium for cultivating bifidobacteria [4]. In this case, the natural nutrients present in whey create favourable conditions for the growth of microorganisms without the need for expensive additional components.

There are also reports on the processing of soy whey for the production of non-alcoholic beverages [5] and low-alcohol fermented products [6]. Such technologies, on the one hand, make it possible to create added value from a secondary product of the soy industry, and on the other hand, expand the range of functional foods and beverages.

Thus, soy whey, which is usually regarded as a waste product, in fact has high nutritional value and is a promising raw material that can be efficiently used in biotechnology, the food industry and, potentially, other fields (including as an auxiliary technological medium in the leather and fur industry). This fully corresponds to resource-saving approaches aimed at rational use of resources and reduction of waste.

In Karakul fur technology, fermentation is a traditional processing stage that exerts a complex effect on the skin tissue, simultaneously softening and fermenting it, and increasing the flexibility and pliability of the dermal fibres. Barley flour and bread yeast prepared on the basis of NaCl have been used for many years as a standard method for the delicate skins of Karakul lambs, since, compared to rapid pickling in mineral acids, they provide a more stable and “slow” effect. Classic literature sources [7] describe fermentation as a method that ensures high quality indicators in the fur industry, and specifically note that in Karakul skins the dermal fibres are split into finer structural elements as a result of fermentation, which significantly improves the lightness and softness of the product.

Barley grits flour is characterised by its high content of fermentable starch and natural cereal enzymes, including amylase and maltase [8]. Amylase hydrolyses starch to maltose and glucose; these monosaccharides are then converted by lactic acid bacteria during fermentation into lactate and a certain amount of acetic acid. As a result, the acidity of the medium gradually increases and the pH decreases within an optimal interval, which promotes loosening and opening of the dermal fibre structure. Taking into account these properties of barley grits, it was considered expedient to use it partially in fermentation experiments based on soy whey.

Materials and methods. Experimental work was carried out at the “Omad Aziz” LLC, located in Romitan district of Bukhara region, which is specialised in processing Karakul skins. As the research object, eight black Karakul skins were selected after soaking and washing according to the factory’s technological scheme. A container with a capacity of 50 L was used as the working bath, where fermentation processes were carried out using soy whey as the main medium and, partially, barley grits. The technological parameters of fermentation are given in Table 1.

Table 1.

Technological parameters of the fermentation process

Initial experiments showed that when only soy whey is used as the fermentation medium, the required amount of acid does not accumulate sufficiently fast and steadily. This is mainly due to the nature of the carbohydrates in soy whey, the strong buffering capacity of the medium and the presence of certain plant components that inhibit microflora activity. As a result, although lactic acid is formed, the required technological effect on the dermal tissue appears later than expected. For this reason, on the second day of fermentation, barley grits were additionally introduced into the bath at a dosage of 5 g/L.

During fermentation in soy whey, sodium chloride was added stepwise to the 14-litre bath, increasing the NaCl concentration from 9 g/L on day 1 to 41 g/L on day 4, and to 45 g/L on day 8, thus ensuring a stable operating regime in the range of 35–45 g/L. No salt was added on days 5 and 7, since the process was evaluated not only by salt analysis, but also through organoleptic control and pH measurement. Reaching a salt concentration of 45 g/L by day 8 indicated the stability of the ionic strength and osmotic protection of the bath, which created favourable conditions for fermentation and ensured a gradual decrease in pH to 4.5–5.0.

The pH value of the fermentation liquor is one of the main technological indicators in controlling the fermentation of Karakul skins, as it directly reflects the activity of lactic acid bacteria, hygienic stability and the condition of the dermal fibres [9]. Changes in pH during fermentation in soy whey were monitored under production conditions, and the results are shown in Fig.

Figure 1. Graph of pH control during fermentation in soy whey

Results and discussion. In practice, the fermentation process began at pH 5.3, and during the active fermentation phase, pH decreased steadily within the range of 4.5–5.3. The stability of the medium within this range limits the development of spoilage microflora, maintains the predominance of lactic acid bacteria and ensures the integrity of hair follicle bonds. If pH remains above 5.0 for a long time, this indicates a slowdown in fermentation and an increased hygienic risk. In such cases, it is necessary to stabilise the temperature within 28–30 °C, mix in barley grits (for example, 5 g/L) and maintain the sodium chloride concentration at 35–45 g/L.

The fermentation variant using soy whey with partial addition of barley grits proceeded faster than fermentation carried out solely on barley grits. In particular, fermentation with soy whey + barley grits was completed on day 9 (216 hours), while in the barley-grits-only method the process lasted up to day 11 (264 hours). Thus, the duration of fermentation was reduced by 2 days (48 hours).

After the fermentation stage, all subsequent technological operations for both the control and experimental batches of skins were performed according to the standard scheme adopted at the enterprise. Organoleptic assessment showed no noticeable differences in the external appearance of the Karakul fur products from the control and experimental batches: the fur side was soft and fine, and the flesh side was sufficiently supple. Samples from both variants were taken, and their chemical composition and physico-mechanical properties were determined and compared with each other and with the requirements of the relevant standard; the results are presented in Table 2.

Table 2.

Chemical composition and physic-mechanical properties of karakul fur samples from the control and experimental options

Analysis of the results for the control and experimental variants shows that the main quality indicators are stable in both cases. In particular, the shrinkage temperature is 80.9 °C in the control and 79.4 °C in the experimental variant, and both values fully meet the requirements of GOST 9296-74 (≥ 70 °C). The moisture content is 12.4 % and 13.1 %, respectively, which is within the standard range.

The mass fraction of chromium oxide (Cr₂O₃) relative to dry matter is 1.61 % in the control and 1.52 % in the experimental variant, which exceeds the minimum standard requirement of “not less than 1.0 %”; the approximate difference of 0.09 percentage points between the variants is technologically acceptable. Tensile strength is also high: 63.7 N in the control and 61.8 N in the experimental variant, both significantly above the standard requirement of 49 N. Elongation and relative elongation at break are slightly higher in the experimental variant (28.0 MPa and 37.3 %, respectively). No noticeable differences were revealed between the batches in organoleptic assessment.

Thus, the fermentation method based on soy whey does not adversely affect the quality of the finished fur and fully ensures compliance with the standard requirements. According to the results obtained, this method reduces water consumption by 100 %, salt consumption by 51.4 %, barley grits consumption by 96.5 %, and shortens the technological time by 48 hours, while the quality indicators of the product are not inferior to those of the control samples.

Conclusion. The results of this study show that the use of soy whey as a technological medium for fermenting Karakul skins is a practically viable and efficient solution. Under the regime with soy whey, water consumption associated with the traditional aqueous bath was completely eliminated, the volume of wastewater was reduced, salt consumption was cut by more than half, and barley grits consumption was almost completely reduced. At the same time, the duration of the fermentation process decreased from 11 to 9 days, which shortened the technological cycle by 2 days and contributed to an increase in production efficiency.

Analysis of physico-mechanical and chemical indicators demonstrated that the finished fur obtained using soy whey fully meets the requirements of GOST 9296-74 in terms of shrinkage temperature, chromium oxide content, tensile strength, elongation and moisture content, and does not differ significantly in organoleptic characteristics from samples produced by the traditional method.

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