Activity Of Starter Cultures Research Articles

Daqu regulates the balance of saccharification and alcoholic fermentation to promote Chinese baijiu fermentation

Saccharifying activity of starter culture plays a key role on the simultaneous saccharification and fermentation of Chinese baijiu fermentation. However, the regulation of alcoholic fermentation by Daqu starter or saccharifying enzymes still remains unclear in the baijiu fermentation. In this study, we identified 13 proteins, affiliated to 4 saccharifying enzymes (including alpha-amylase, beta-amylase, glucoamylase and beta-glucosidase) as the key saccharifying enzymes in Daqu by metaproteomic and culture-dependent analysis. These enzymes were metabolized from plant substrate (13.4%) and microbial metabolism (86.6%), and especially alpha-amylase and glucoamylase from Aspergillus and Rhizopus were dominant in Daqu bio-system. Furthermore, we observed the dynamic of saccharifying activity of Daqu (from 241 to 395 U) was driven by the combinations of isolated saccharifying microbes responsible for key enzymes releasing, indicating AR7 group (with a ration of Rhizopus oryzae: Aspergillus oryzae in 10:1) presented the highest saccharifying activity (395 U) in a simulative Daqu production. However, the highest ethanol production (80.5 mg/g) was obtained from the fermentation driven by AR8 group (with a ration of Rhizopus oryzae: Aspergillus oryzae in 50:1) with the saccharifying activity of 389 U. These results indicated that a proper combination of saccharifying microbes could enhance the saccharifying activity of Daqu and then promote ethanol production in baijiu fermentation, as it did not always exhibit a positive correlativity between saccharifying activity and alcoholic fermentation. Our findings should provide a potential approach to regulate the alcoholic fermentation by optimizing the saccharifying microbes or enzymes of starter cultures for baijiu and other fermented food.

Enhancing Bifidobacterium and lactic acid bacteria activity, and improving oxidative stability in functional algal concentrated yoghurt with Spirulina platensis powder

The purpose of this study was to examine the growing demand for healthy functional dairy products by investigating the incorporation of Spirulina platensis into concentrated yoghurt and evaluating its impact on starter cultures and product properties. A comprehensive analysis demonstrated the potential of spirulina to enhance bifidobacteria growth, acidity, PUFA content, and antioxidant activity in yoghurts, indicating its potential to improve the nutritional quality and oxidative stability of dairy products. The study investigated the impact of different Spirulina ratios on the activity of yoghurt starter cultures, including Lb. casei, Lb. plantarum, Lb. acidophilus, and Bifidobacterium mix. Three concentrated yoghurt samples were prepared, including a control, a probiotic sample, and a sample incorporating Spirulina powder. The findings suggest that while Spirulina did not significantly affect lactic acid bacteria, it noticeably stimulated the growth of Bifidobacterium. Treated samples showed increased acidity and TVFAs, with pH values displaying an inverse trend compared to the control. Clear differences in colour parameters and sensory evaluations distinguished control from treated samples. Additionally, Spirulina supplementation demonstrated a pronounced effect in enhancing antioxidant activity, as observed through DPPH radical scavenging activity, and influencing the peroxide value, reflecting improved oxidative stability in the yoghurt. This successful utilisation of Spirulina suggests its potential application in diverse edible algae in the food sector, especially in dairy products, enhancing both nutritional and sensory aspects, as well as contributing to improved oxidative stability

A review on fermented vegetables: Microbial community and potential upgrading strategy via inoculated fermentation.

Fermentation is a traditional method utilized for vegetable preservation, with microorganisms playing a crucial role in the process. Nowadays, traditional spontaneous fermentation methods are widely employed, which excessively depend on the microorganisms attached to the surface of raw materials, resulting in great difficulties in ideal control over the fermentation process. To achieve standardized production and improve product quality, it is essential to promote inoculated fermentation. In this way, starter cultures can dominate the fermentation processes successfully. Unfortunately, inoculated fermentation has not been thoroughly studied and applied. Therefore, this paper provides a systematic review of the potential upgrading strategy of vegetable fermentation technology. First, we disclose the microbial community structures and succession rules in some typical spontaneously fermented vegetables to comprehend the microbial fermentation processes well. Then, internal and external factors affecting microorganisms are explored to provide references for the selection of fermented materials and conditions. Besides, we widely summarize the potential starter candidates with various characteristics isolated from spontaneously fermented products. Subsequently, we exhibited the inoculated fermentation strategies with those isolations. To optimize the product quality, not only lactic acid bacteria that lead the fermentation, but also yeasts that contribute to aroma formation should be combined for inoculation. The inoculation order of the starter cultures also affects the microbial fermentation. It is equally important to choose a proper processing method to guarantee the activity and convenience of starter cultures. Only in this way can we achieve the transition from traditional spontaneous fermentation to modern inoculated fermentation.

The effect of seed germination and Bacillus spp. on the ripening of plant cheese analogs.

The development of novel plant-based fermented food products for which no traditional templates exist requires the development of starter cultures. Although the principles of microbial flavor formation in plant-based analogs partially overlap with dairy fermentations, the composition of the raw materials and thus likely the selective pressure on the activity of starter cultures differs. Experiments that are described in this study explored the use of seed germination, the use of lactic acid bacteria, and the use of bacilli to reduce hygienic risks, to acidify plant milk, and to generate taste-active compounds through proteolysis and fermentative conversion of carbohydrates. The characterization of fermentation microbiota by culture-dependent and culture-independent methods also confirmed that the starter cultures used were able to control microbial communities throughout 90 d of ripening. Taken together, the results provide novel tools for the development of plant-based analogs of fermented dairy products.

Верификация оптимальных условий и параметров биотрансформации мышечной ткани филе рыб бактериальными заквасочными культурами

The article describes the relevance and expediency of using a method of biotechnological processing, namely biotransformation of fish raw materials by bacterial starter cultures, which is a priority of developing areas according to the Strategy of improving the quality of food products in the Russian Federation until 2030. The studied method of processing will positively affect the shelf life of fish products, its organoleptic properties and nutritional value due to the formation of metabolites of the vital activity of bacterial starter cultures, which are the main factor of bioconservation, synthesis of vitamins and other biologically active substances. Probiotic properties of bacterial starter cultures will have a significant impact on the optimization of the internal microflora of the gastrointestinal tract, thereby strengthening the human body and its immune system as a whole, which supports the principles of a healthy lifestyle. In accordance with this, studies have been conducted to study the possibility of using bacterial starter cultures for the biotransformation of fish raw materials in order to further obtain a probiotic food product based on it. Data on the effect of bacterial starter cultures on organoleptic microstructural, physico-chemical and functional-technological characteristics of fish raw materials are presented. The number of residual cells of bacterial starter cultures in the muscle tissue of fish fillets, which meets the requirements for probiotic products, was revealed. The survival rate under the influence of temperatures and the dynamics of changes in the number of bacterial starter cultures during storage in fish fillet muscle tissue samples were determined, the data on which will be used to develop and adjust the thermal treatment modes of the final product. The influence of bacterial starter cultures on the changes in total viable count after biotransformation and during storage is analyzed, on the basis of which the effect of bioconservation is justified. The results of the conducted studies became the basis for the selection of the most suitable bacterial starter cultures, as well as verification of optimal conditions and parameters predicted by mathematical modeling algorithms for biotransfor-mation of the muscle tissue of fish fillets. At the next stage, research will be conducted to study the possibility of using fish raw materials treated with bacterial starter cultures in the formulations of “fast food” products containing functional components, which is justified by the accelerated rhythm of life and the desire of modern society to monitor their nutrition by eating foods that correspond to a healthy lifestyle.

A Metagenomics Approach to Enumerate Bacteriophages in a Food Niche.

Dairy fermentation relies on the activity of starter cultures composed primarily of lactic acid bacteria such as Lactococcus and Streptococcus thermophilus strains to produce consistent, high-quality products. Bacteriophages are a constant threat to the industry, often causing slowed or failed fermentation resulting in significant economic losses. To ensure the continuation of reliable fermentation practices, it is important to detect and monitor the phage populations impacting different starter cultures. This has traditionally been done primarily through culture-dependent methods but has since expanded into viral metagenomics. Here we outline a protocol for a targeted virome extraction from a dairy whey sample, followed by subsequent sequencing and phageome analysis of the sample.

Lactoferrin's potential application in enhancing yoghurt's microbial and sensory qualities, with emphasis on the starter culture activity.

This research paper aimed to examine the antibacterial activity of lactoferrin (LF) as a potential natural alternative in the dairy sector, by measuring its minimum inhibitory concentration (MIC) against a number of common food-borne pathogens as well as Pseudomonas aeruginosa, one of the major dairy product spoiling microorganisms. Additionally, a viability experiment was applied to laboratory-manufactured set yoghurt to assess its impact on the activity of starter culture, sensory properties and STEC survivability. The findings demonstrated that LF exhibited significant antimicrobial activity, particularly against E. coli and S. typhimurium with MIC values of 0.0001 and 0.01 mg/ml, respectively. However, P. aeruginosa and B. cereus were quite resistant to LF requiring higher concentrations for MIC (2.5 mg/ml). By the third day of storage, LF at 0.0001 and 0.001 mg/ml significantly reduced the survivability of Shiga toxin-producing E. coli STEC by 70 and 91.6%, respectively, in the lab-manufactured yoghurt. Furthermore, LF enhanced the sensory properties of fortified yoghurt with a statistically significant difference in comparison to the control yoghurt group. There was no interference with the activity of the starter culture throughout the manufacturing process and the storage period. In conclusion, the potent antimicrobial effect of LF opens a new avenue for the dairy industry's potential applications of LF as a natural preservative without negatively influencing the sensory properties and starter culture activity of fermented products.

Investigation of the biochemical activity of starter compositions enriched with propionic acid bacteria on various raw materials

Currently, there is a need to develop an assortment of low-lactose or lactose-free dairy products and plant-based products due to an increase in the number of consumers with lactase deficiency, allergic to cow's milk components, cholesterol problems, etc. For the development of plant and lactose-free bioproducts, it is possible to use various starter cultures enriched with probiotics. Various starter cultures were used in the work, propionic acid bacteria were used as a probiotic. The objects were lactose-free milk and vegetable bases: rice milk, oat milk and coconut milk; the control was selected milk. A comparative analysis of the fermentation process of various compositions of starter cultures enriched with propionic acid bacteria on various raw materials was carried out. The duration of fermentation of vegetable raw materials is 8-10 hours, the acid-forming activity of combined starter cultures is quite high. The number of viable cells of lactic acid and propionic acid bacteria in the obtained bioproducts has a high value and amounts to 107-108 K.O.E. /cm3. This confirms that the nutrient medium for the cultivation of selected starter compositions is favorable, the microflora of the starter composition develops harmoniously. Lactic acid microorganisms and propionic acid bacteria make it possible to obtain fermented biological products with a variety of taste characteristics inherent in a certain type of raw material. According to the results of the research, the developed starter compositions meet the requirements for starter cultures, have valuable technological properties that allow expanding the range of plant and lactose-free biological products.

Preliminary Studies of Bio-Fortification of Yoghurt with Chromium

Yoghurt is a delectable fermented milk product suitable for all ages. Chromium (Cr), a trace mineral is found in two forms: trivalent and hexavalent. Recent studies have shown that the Cr (III), or chromium picolinate (Cri), is beneficial for carbohydrate metabolism. Thus, Cr supplements are used to treat diabetes and manage blood sugar. However, the effect of the incorporation of Cri on starter growth and the quality of yoghurt still needs to be determined. In this study, we aim to produce Cr (CrPi)-fortified yoghurt to fulfil the proposed recommended daily allowance (RDA) of Cr (35–50 µg/day for adults). Additionally, it might act as a nutraceutical for persons with special medical conditions, such as patients with obesity or type 2 diabetes mellitus disease. In this respect, the effect of different concentrations of CrPi, (1, 2, 5, 10, 20 ppm) chromium chloride [Cr (III)] (1, 2, 3, 4, 5 ppm), and potassium chromate [Cr (VI)] (1, 2 ppm) on the activity of yoghurt starter culture were investigated in vitro on de Man, Rogosa, and Sharpe (MRS) media. Compared to the control (without Cr), the obtained data revealed significant inhibition of the yoghurt starter culture by Cr (VI) at 2 ppm compared to Cr (III), which did not affect the bacterial growth up to 5 ppm and was comparable with CrPi [Cr (III)]. We also produced yoghurt supplemented with two doses of Cr (0.25 and 0.5 ppm). We did not observe any significant differences in the physicochemical, rheological, microbiological, and sensory properties of the Cr-fortified yoghurt and the control up to 2 weeks in cold storage. These results clearly indicate that CrPi (0.25 and 0.5 ppm) can be used to manufacture yoghurt with the RDA for intact Cr without affecting its quality.

Интеграция бактериальных заквасочных культур с рыбным сырьем: подбор и обоснование

An important aspect of the technology of processing fish raw materials is the development of food products of various directions using modern methods of biotechnological processing. In this regard, in food biotechnology, special attention is paid to biotransformation by promising strains of bacterial starter cultures to produce food products with improved quality characteristics, and in particular with a functional orientation. The use of bacterial starter cultures in the production of fish food products can be a way to extend the shelf life due to the formation of metabolites of their vital activity (acids and bacteriocins), which are the main factor of bioconservation. At the same time, the biochemical activity of bacterial starter cultures will contribute to improving the organoleptic and structural-mechanical properties of raw materials, as well as increasing the nutritional value and synthesis of vitamins and other nutrients, and giving the final product probiotic properties. This trend is a response to the interest of the population of the Russian Federation in probiotic products, which allows to normalize the indigenous microflora of the gastrointestinal tract, thereby strengthening the human body and its immune system as a whole. In this regard, the analysis of data on the justification of the use of bacterial starter cultures for the biotransformation of fish raw materials was carried out, and the necessary strains of microorganisms were selected. The analysis of scientific and technical databases has shown the prospects of scientific developments on the use of bacterial starter cultures as protective microorganisms and the study of the influence of the conditions of cultivation and preservation of bioactivity of a living cell under the influence of physical and chemical factors during the technological process of production and subsequent storage of products, which is of particular importance for the creation of probiotic food products. The conducted research will be used in the construction of mathematical models of the process of biotransformation of fish raw materials as a basis for the development of technological processing parameters for its subsequent use in the formulations of "fast food" products containing functional components, which is justified by the accelerated rhythm of life and the desire of modern society to monitor their nutrition by eating products that support a healthy lifestyle.
 In food biotechnology, special attention is given to biotransformation of promising strains of bacterial starter cultures for the production of food products with improved quality characteristics and functional orientation. In this regard, the analysis of data on the justification of the use of commercial, potentially commercial fish types for biotransformation by bacterial starter cultures and the selection of the necessary strains of microorganisms, which will be used in the construction of mathematical models of the process of biotransformation of fish raw materials as a basis for the development of technological parameters of processing.

Probiotic Yoghurt Made from Milk of Ewes Fed a Diet Supplemented with Spirulina platensis or Fish Oil

PurposeYoghurt is a widely consumed dairy product around the world. It has healing properties and characteristics that are important for human health. Our goal was to see how using ewes' milk fed Spirulina platensis (SP) or fish oil (FO)-supplemented diets affected the chemical, physical, and nutritional properties of yoghurt, as well as the activity and survival of starter and probiotic bacteria during storage.MethodsThe collected milk from each ewe group was preheated to 65 °C and homogenized in a laboratory homogenizer, then heated to 90 °C for 5 min, cooled to 42 °C, and divided into two equal portions. The first portion was inoculated with 2.0% mixed starter culture (Lactobacillus bulgaricus and Streptococcus thermophilus, 1:1), whereas the second was inoculated with 2% mixed starter culture and 1% Bifidobacterium longum as a probiotic bacteria.ResultsSP yoghurt had the highest levels of short chain-FA, medium chain-FA, mostly C10:0, and long chain-FA, namely C16:0, C18:2 and the lowest levels of C18:0 and C18:1, followed by FO yoghurt. The addition of SP or FO to ewes' diets resulted in yoghurt with higher viable counts of L. bulgaricus and S. thermophilus, which were still >107 cfu/g at the end of storage, as well as a higher level of acetaldehyde content (P<0.05) as a flavor compound, than the control (C) yoghurt. The viscosity of SP yoghurt was higher than that of FO and C yoghurt; the difference was not significant. The addition of B. longum, a probiotic bacteria, to all yoghurt samples, improved antioxidant activities, particularly against ABTS• radicals, but reduced SP yoghurt viscosity. When B. longum was added, acetaldehyde content increased from 39.91, 90.47, and 129.31 μmol/100g in C, FA, and SP yoghurts to 46.67, 135.55, and 144.1 μmol/100g in probiotic C, FA, and SP yoghurts, respectively. There was no significant difference in sensory qualities among all the yoghurt samples during all storage periods.ConclusionsSupplementing the ewes' diets with Spirulina platensis or fish oil can change the fatty acid composition of the resulting yoghurt. The starter culture's activity, flavor compounds, and some chemical, physical, and antioxidant properties of milk produced from these diets can all be improved, particularly in yoghurt treated with probiotic bacteria (B. longum).

Bacteriophage-host interactions as a platform to establish the role of phages in modulating the microbial composition of fermented foods

Food fermentation relies on the activity of robust starter cultures, which are commonly comprised of lactic acid bacteria such as Lactococcus and Streptococcus thermophilus. While bacteriophage infection represents a persistent threat that may cause slowed or failed fermentations, their beneficial role in fermentations is also being appreciated. In order to develop robust starter cultures, it is important to understand how phages interact with and modulate the compositional landscape of these complex microbial communities. Both culture-dependent and -independent methods have been instrumental in defining individual phage-host interactions of many lactic acid bacteria (LAB). This knowledge needs to be integrated and expanded to obtain a full understanding of the overall complexity of such interactions pertinent to fermented foods through a combination of culturomics, metagenomics, and phageomics. With such knowledge, it is believed that factory-specific detection and monitoring systems may be developed to ensure robust and reliable fermentation practices. In this review, we explore/discuss phage-host interactions of LAB, the role of both virulent and temperate phages on the microbial composition, and the current knowledge of phageomes of fermented foods.

Influence of Environmental Microbiota on the Activity and Metabolism of Starter Cultures Used in Coffee Beans Fermentation

Microbial activity is an integral part of agricultural ecosystems and can influence the quality of food commodities. During on-farm processing, coffee growers use a traditional method of fermentation to remove the cherry pulp surrounding the beans. Here, we investigated the influence of the coffee farm microbiome and the resulting fermentation process conducted with selected starter cultures (Pichia fermentans YC5.2 and Pediococcus acidilactici LPBC161). The microbiota of the coffee farm (coffee fruits and leaves, over-ripe fruits, cherries before de-pulping, depulped beans, and water used for de-pulping beans) was dominated by Enterobacteriaceae and Saccharomycetales, as determined by llumina-based amplicon sequencing. In addition, 299 prokaryotes and 189 eukaryotes were identified. Following the fermentation process, Pichia and the family Lactobacillaceae (which includes P. acidilactici) represented more than 70% of the total microbial community. The positive interaction between the starters resulted in the formation of primary metabolites (such as ethanol and lactic acid) and important aroma-impacting compounds (ethyl acetate, isoamyl acetate, and ethyl isobutyrate). The success competitiveness of the starters towards the wild microbiota indicated that coffee farm microbiota has little influence on starter culture-added coffee fermentation. However, hygiene requirements in the fermentation process should be indicated to prevent the high microbial loads present in coffee farm soil, leaves, fruits collected on the ground, and over-ripe fruits from having access to the fermentation tank and transferring undesirable aromas to coffee beans.

Изучение свойств заквасок, приготовленных на основе нетрадиционных видов муки

Introduction. Bread and bakery products contain nutritional components that make an integral part of human diet. Starter cultures are a promising way to prepare bakery products. The research objective was to study the effect of non-traditional flours and their wheat mixes on the activity, sensory, and physicochemical properties of starter cultures.&#x0D; Study objects and methods. The research featured Lesaffre starter cultures (Saf-Levain LV1 and Saf-Levain LV4) with lentil flour and green buckwheat flour. It involved organoleptic, titrimetric, and photocolorimetric methods, as well as the “ball surfacing” method, to determine the fermentation activity of starter cultures and to assess the changes in their volume. The acid content of the flour was determined by titrating the aqueous solution of the sample. The amount of reducing sugars was determined by the photocolorimetric method based on the interaction of carbonyl groups of sugars in an alkaline medium with copper glycerate; the optical density of the resulting solution was performed using a photoelectrocolorimeter. The change in the volume of the starter cultures was determined by a non-standard method of using measuring cups in the process of thermostating. The research also included a sensory evaluation of the semi-finished products.&#x0D; Results and discussion. Green buckwheat flour had a positive effect on the activity of starter cultures based on Saf-Levain LV4 and LV1. The sensory properties of starter cultures with non-traditional flours differed from the control samples in aroma, taste, appearance, and inflation rate. The acidity of the samples varied depending on the flour, its quantity, and the starting culture. The greatest accumulation of acids occurred in the sample with 50% of green buckwheat flour and the samples with 25 and 50% of lentil flour. The most intense reduction in the amount of reducing sugars was observed in the samples with 25 and 50% of green buckwheat flour (from 1.9 to 3.9 times, depending on the sample). In the samples with lentil flour, it was 75 and 100% (from 2.7 to 7.5 times, depending on the sample). The difference in the samples with LV1 was greater than in the samples with LV4, which can be explained by the differences in their microbial composition. The inflation rate was higher in the test samples than in the control.&#x0D; Conclusion. The resulting starter cultures can be recommended for baking industry and further research. Starter cultures based on non-traditional flours will eventually reduce the fermentation time and produce bakery products with high consumer properties. The non-traditional flours can expand the range of bakery products and increase their nutritional value.

STUDY OF PROPERTIES OF YOGHURTS MADE USING VIVO STARTER CULTURES

The article presents the results of experimental studies of qualitative indicators of milk and fermented milk products (yoghurts) made using VIVO starter cultures. VIVO starter cultures contain thermophilic lactic acid bacteria Streptococcus thermophilus, Lactobacillus delbrueckii ssp., Lactobacillus acidophilus and others.&#x0D; The determination of organoleptic and physico-chemical parameters of cow's milk and dairy products based on it was carried out according to generally accepted methods. During the organoleptic evaluation of milk and lactic acid products, the appearance and texture, smell, taste and color of milk were examined. Determination of active acidity was carried out in accordance with GOST 26781. Titratable acidity in degrees Turner was determined according to GOST 3624. The content of fat, protein, dry matter was determined according to GOST 2661: 2010.&#x0D; A study was made of the organoleptic characteristics of yogurts obtained by fermentation by using of VIVO starter cultures. The high activity of VIVO starter cultures was established, the products on the basis of which have a pleasant taste characteristic of these products.&#x0D; The results of physico-chemical analysis of yogurt samples obtained by using of VIVO starter cultures confirmed their compliance with DSTU 4343: 2004.&#x0D; Lactic acid products made with VIVO sourdough are functional products. It is recommended to use yogurts based on VIVO starter cultures to restore intestinal microflora, normalize digestion, strengthen immunity, and reduce the risk of colds and SARS.

Chromatographic Characterization and In Vitro Bioactivity Evaluation of Lactobacillus helveticus Hydrolysates upon Fermentation of Different Substrates

Among various food sources, milk proteins remain the major vector for functional peptides endowed with several biological activities. Particularly, the proteolytic activity of lactic acid bacteria during milk fermentation has been one of the most followed strategies to produce bioactive peptides. In the present study, the exploration of the activity of several starter cultures, at different fermentation times, was firstly investigated by reversed phase-high performance liquid chromatography. Among the tested strains, Lactobacillus helveticus showed a higher proteolytic activity and it was submitted to further investigations by changing the fermentation substrate (skim milk, brain heart infusion, peptone water) as well as the extraction strategy (trichloroacetic acid vs. glass beads). The chromatographic analyses and the in vitro antioxidant and antihypertensive assays highlighted considerable differences for L. helveticus hydrolysates from different substrates, while a negligible impact by the two extraction protocols emerged. Furthermore, nano-high pressure liquid chromatography coupled with a high resolution mass spectrometry analyzer allowed the preliminary discrimination of fractions from fermented skim milk, likely responsible for the found activity. The obtained results suggest the possibility of varying the fermentation parameters in order to maximize the functional effects of the bioactive peptides.

A Comprehensive Study of the Impacts of Oat β-Glucan and Bacterial Curdlan on the Activity of Commercial Starter Culture in Yogurt.

This study provides important information about the impacts of various levels of oat (OBG) and bacterial (curdlan) β-glucan and fat contents in milk on survivability and metabolism of yogurt starter cultures. The results show that addition of β-glucans in the concentration higher than 0.25% reduced starter bacterial counts during storage and prolonged the milk acidification process. A significant increase in lactose consumption by starter cultures was noted in the yogurt samples with OBG addition up to 0.75%. The highest (by 567% on average) increase in lactic acid content was noted in the control yogurts. Whereas the lowest (by 351%) increase in lactic acid content was noted in yogurts with OBG. After 28-day storage, the acetic aldehyde content was significantly influenced by fat content, type and addition level of polysaccharide. A higher increase in acetoin content was noted in samples with 0.25% than in samples with 1% of polysaccharides. In turn, significantly lower increases in diacetyl and 2,3-pentanedione contents were observed in the yogurt samples with OBG than in these with curdlan, with diacetyl production increase along with the higher concentration of the polysaccharide. The addition of OBG and curdlan to milk contributed to differences in the starter culture metabolism, consequently, in the milk acidification dynamics.

Biotechnological potential of new strains of lactic acid bacteria

The paper presents data on the ferment effect of acid bacteria on model protein substrates in order to determine their proteolytic potential for biotransformation of fresh meat. The proteolytic activity of new starter cultures of lactic acid bacteria was evaluated. Strains of lactic acid bacteria Lbm. casei and Lbm. curvatus, exhibiting high proteolytic activity, can be recommended for inclusion in the composition of starter cultures.

Impact of Fluoridation of Milk on Manufacturing and Properties of Yoghurt

Fluoridation ( F ) of yoghurt milk ( YM ) was done by adding sodium fluoride to YM before ( treatment A ) and after ( treatment B ) the heat treatment applied on cow's milk . Activity of yoghurt starter culture (YSC) was followed during fermentation by measuring acidity and pH at different intervals up to the complete coagulation. The resultant control (C) and treated yoghurt were analysed when fresh and after 10 days of cold storage (5 ± 1 ⁰C).The attained results revealed that F had no pronounced impact on YSC, while the differences in acidity, pH, TS, fat and protein contents of the resultant yoghurt due to the applied treatments were slight. Curd syneresis (CS) of C kept for 10 and 30 min at room temperature (30 ± 1 ⁰C) was higher than the corresponding treated samples, while after 60 and 90 min the differences in CS were slight in fresh samples. The stored samples showed opposite trend of results. F of YM had no obvious impact on hardness, springiness and gumminess of yoghurt. Adhesiveness was higher in C, while the opposite was noticed for cohesiveness.Organoleptically, the fresh treated yoghurt ranked less scores for appearance and firmness while some improvement was recorded during storage of all samples. No adverse impact of F was noticed on flavour attributes.

Dextran modulates physical properties of rennet‐induced milk gels

SummaryPhysical properties of rennet‐induced milk gels as core intermediates of cheese production are mainly affected by milk composition, type and amount of coagulation enzyme and starter culture activity. We investigated model systems of reconstituted milk and dextran, which triggers effects on milk gels similar to exopolysaccharides from lactic acid bacteria. Furthermore, clotting activity (0.02 or 0.04 IMCU mL−1) and milk pH adjusted prior to renneting (6.5–5.7) were studied. A lower pH at renneting resulted in an earlier gelation onset, a higher gelation velocity and gel stiffness. The addition of dextran stabilised the gels especially at higher pH, and microstructural analysis revealed larger, more interconnected protein aggregates. However, at pH 5.7, a reverse effect was observed, indicating a destabilisation of the casein network. The current study indicates that altering milk pH and addition of polysaccharides gives the potential to change textural properties of cheese by affecting rennet‐induced gelation.