Bacteria from the Propionibacterium genus consists of two principal groups: cutaneous and classical. Cutaneous Propionibacterium are considered primary pathogens to humans, whereas classical Propionibacterium are widely used in the food and pharmaceutical industries. Bacteria from the Propionibacterium genus are capable of synthesizing numerous valuable compounds with a wide industrial usage. Biomass of the bacteria from the Propionibacterium genus constitutes sources of vitamins from the B group, including B12, trehalose, and numerous bacteriocins. These bacteria are also capable of synthesizing organic acids such as propionic acid and acetic acid. Because of GRAS status and their health-promoting characteristics, bacteria from the Propionibacterium genus and their metabolites (propionic acid, vitamin B12, and trehalose) are commonly used in the cosmetic, pharmaceutical, food, and other industries. They are also used as additives in fodders for livestock. In this review, we present the major species of Propionibacterium and their properties and provide an overview of their functions and applications. This review also presents current literature concerned with the possibilities of using Propionibacterium spp. to obtain valuable metabolites. It also presents the biosynthetic pathways as well as the impact of the genetic and environmental factors on the efficiency of their production.

BackgroundIn 2014, apple production in EU countries amounted to 11.8 million tonnes. A constant increase in the production of these fruits will lead to the accumulation of thousands of tonnes of apple pomace (production waste). The amount of industrial apples is the highest — their proportion on the market is estimated at 50–60%, of which over 95% is processed into juice. The proportion of pomace in the traditional pressing method accounts for 20% of fruits used.ResultsAnalysis of the growth dynamics of wild strain Propionibacterium freudenreichii T82 in micro-cultures using different carbon sources showed that the highest bacterial growth occurs in an environment with fructose and the most intense biosynthesis of metabolites was found in medium containing only saccharose. It has been found that P. freudenreichii T82 used apple pomaces as a source of carbon. Propionic acid biosynthesis reached its maximum value in the 120th hour of cultivation (1.771g/L). At this time, the content of the acetic acid produced reached the level of 7.049g/L.ConclusionsUtilization of by-products is a significant challenge for manufacturing sites and the natural environment. The solution to this problem may involve the use of pomace as a medium component for microorganism cultivation, which is a source of industrially useful metabolites. This study examined the possibility of using apple pomace as a carbon source in the process of propionic-acetic fermentation via wild strain Propionibacterium freudenreichii T82 bacteria

Sequential optimization of propionate production using apple pomace was studied. All experiments were performed in a static flask in anaerobic conditions. Effect of apple pomace as nitrogen source against conventional N sources (yeast extract, peptone) was studied. The double increase was observed in propionic acid production while using yeast extract and peptone (0.29 ± 0.01 g/g), as against the use of only apple pomace extract (APE) (0.14 ± 0.01 g/g). Intensification of propionic acid fermentation was also achieved by increasing the pH control frequency of the culture medium from 24-(0.29 ± 0.01 g/g) to 12-hour intervals (30 °C) (0.30 ± 0.02 g/g) and by increasing the temperature of the culture from 30 to 37 °C (12-hour intervals of pH control) (0.32 ± 0.01 g/g). An important factor in improving the parameters of fermentation was the addition of biotin to the medium. The 0.2 mg/L dose of biotin allowed to attain 7.66 g/L propionate with a yield of 0.38 ± 0.03 g/g (12-hour intervals of pH control, 37 °C).

The purpose of this study was to determine the potential for biosynthesis of propionic acid and vitamin B12 by Propionibacterium freudenreichii T82 in a medium containing various sources of carbon (glucose, fructose, and saccharose). These sugars are present in apple pomaces, which are the waste from the production of apple juice. Using statistical analysis design of experiments (DoE), the results allowed us to determine which sugars (carbon sources) exert the most beneficial influence on the biosynthesis of propionic acid and cobalamin. The highest production of propionic acid by the tested bacterial strain was obtained in a medium in which glucose accounted for at least 50% of the available carbon sources. Depending on the culture medium, the concentration of this metabolite ranged from 23 to 40 g/L. P. freudenreichii T82 produced the smallest amount of acid in medium in which the dominant nutrient source was saccharose. The results obtained indicated an inverse relationship between the amount of acid produced by the bacteria and vitamin B12 biosynthesis. Because of the high efficiency of propionic acid biosynthesis by P. freudenreichii T82, the prospect of using this strain to obtain propionate with the simultaneous disposal of waste materials (such as apple pomaces) which contain glucose and/or fructose is very promising.

Propionic acid bacteria are the source of many metabolites, e.g., propionic acid and trehalose. Compared to microbiological synthesis, the production of these metabolites by petrochemical means or enzymatic conversion is more profitable. The components of microbiological media account for a large part of the costs associated with propionic fermentation, due to the high nutritional requirements of Propionibacterium. This problem can be overcome by formulating a medium based on the by-products of technological processes, which can act as nutritional sources and at the same time replace expensive laboratory preparations (e.g., peptone and yeast extract). The metabolic activity of P. freudenreichii was investigated in two different breeding environments: in a medium containing peptone, yeast extract, and biotin, and in a waste-based medium consisting of only apple pomace and potato wastewater. The highest production of propionic acid amounting to 14.54 g/L was obtained in the medium containing apple pomace and pure laboratory supplements with a yield of 0.44 g/g. Importantly, the acid production parameters in the waste medium reached almost the same level (12.71 g/L, 0.42 g/g) as the medium containing pure supplements. Acetic acid synthesis was more efficient in the waste medium; it was also characterized by a higher level of accumulated trehalose (59.8 mg/g d.s.). Thus, the obtained results show that P. freudenreichii bacteria exhibited relatively high metabolic activity in an environment with apple pomace used as a carbon source and potato wastewater used as a nitrogen source. This method of propioniate production could be cheaper and more sustainable than the chemical manner.

This study assesses whether thermal imaging can be utilized for detecting and monitoring the level of plant product contamination with apples used as an example. The growth of Penicillium expansum, Botrytis cinerea, and Rhizopus stolonifer on apples contaminated with these fungi was investigated by measuring temperature changes using a thermovision camera. The results showed a significant relationship between the temperature of apples and the growth of microorganisms, as well as that the temperature changes occurred in two stages (temperature of the contaminated apples increased on the first day but then decreased). Significant differences were found between the temperature of the apples showing microbial growth and the noncontaminated control sample, which indicates that the thermal imaging technique has a potential application in microbial quality control. Automation of the production process and attempts on the intensification of production capacity have resulted in the need to improve individual stages of product quality control. Thermovision-based methods have a high potential in this field, as they represent an innovative and noninvasive alternative to conventional microbiological diagnostic methods.