LACTIC ACID BACTERIA AND THEIR ROLE IN THE MEAT PROCESSING

Lactic acid bacteria (LAB) play in meat processing a positive but also a negative role. The principal advantage of LAB in the production of dry fermented sausages lies in the fermentation of saccharides, i.e. the creation of lactic acid and the subsequent fall in pH. The role of LAB in fresh meat spoilage is still controversial. Several species are able to dominate the meat system in VP and MAP storage conditions and can release odor-impact molecules. On the other hand they can provide favorable antagonistic activity against other undesired microorganisms. LAB are important spoilage agents in cooked meat products. Аннотация Молочнокислые бактерии (МКБ) играют в мясной промышленности как положительную, так и отрицательную роль. Основная польза МКБ в производстве сухих ферментированных колбас заключается в ферментации сахаридов, т.е., образовании молочной кислоты и последующем падении рН. Роль МКБ в порче сырого мяса всё ещё неоднозначная. Несколько видов способны доминировать в мясной системе в условиях хранения в вакуумных упаковках и в модифицированной атмосфере и могут выделять молекулы, оказывающие влияние на запах. С другой стороны, они могут проявлять благоприятную антагонистическую активность против нежелательных микроорганизмов. МКБ являются важными возбудителями порчи в варёных мясопродуктах. DOI 10.21323/2114-441X-2016-1-25-31


Introduction
Lactic acid bacteria constitutes a group of gram-positive bacteria united by certain morphological, metabolic and physiological characteristics.They are nonsporulating, nonrespiring but aerotolerant, catalase negative cocci or rods, which produce lactic acid as one of the main fermentation products of carbohydrates (Leroi, 2010; von Wright and Axelsson, 2012).Due to their aerotolerant anaerobic nature, LAB occupy a wide range of natural environments including gastrointestinal tract of humans and animals (Toomey et al., 2010).LAB have traditionally been associated with food and feed fermentation, and are generally considered beneficial microorganisms.Human has empirically used LAB for natural fermentation ofmilk, meat, vegetables and fruits for thousands of years that led to a new stabilized product.The acidification process due to the lactic acid production as the major end-metabolite of the carbohydrate fermentation is one of the most desirable side effects of their growth, inhibiting micro-organisms including the most common human pathogens (Leroi, 2010).
In the meat processing LAB can play a positive but also negative role.The positive effect is connected with the growth of the LAB during fermentation and ripening of dry fermented sausages.The negative role can be associated with the meat spoilage, production of biogenic amines and distribution of antimicrobial resistance genes (Talon and Leroy, 2011;Toomey et al., 2010).

МКБ в ферментированных мясных продуктах
Ферментированные пищевые продукты имеют более продолжительный срок хранения по сравнению anaerobic microbial growth using internally supplied electron acceptors and generating ATP mainly through substrate level phosphorylation (Kim and Gadd, 2008).LAB play the predominant role in fermenting the batter made for the preparation of dry fermented sausages.LAB, however, make up just part of the total microbial population in meat under natural conditions.
The initial population of LAB is usually low in the raw material (3 to 4 log CFU/g) but it becomes dominant during the fermentation step (8 log CFU/g) in traditional sausages (Talon and Leroy, 2011).Following the addition of starter cultures, LAB can multiply from an initial population of 6.5 log cfu g -1 to 8.0-9.0 log cfu g -1 over the first few days (Kameník et al., 2013;Matagaras et al., 2015).Połka et al. (2015) found a LAB population from <2 log cfu g -1 to 4.52 log cfu g -1 in samples of Piacentino sausages (northern Italy) without starter cultures immediately after their filling into casings.The addition of starter cultures caused an increase in LAB from the beginning of fermentation to values of between 5.63 and 6.82 log cfu g -1 .After three weeks of ripening, the LAB population reached values of between 8.15 and 8.89 log cfu g-1; at this time there was no evident difference in the number of LAB seen between sausages in which starter cultures were used and sausages in which they were not used.During tests on minisalami filled into cellulose casings of a diameter of 25 mm, Gareis et al. ( 2010) recorded an increase in the LAB population (with the addition of starter cultures) of two logarithmic orders during the first three days.The number of LAB did not fall beneath 8 log cfu g -1 at any time during the course of the experiment (42 days).
The principal advantage of LAB in the production of dry fermented sausages lies in the fermentation of saccharides, i.e. the creation of lactic acid and the subsequent fall in pH.This is not, however, the only positive effect of this group of bacteria.It is also important in releasing other active aromatic (taste) substances and producing antimicrobial compounds.During their lifetime, LAB excrete substances into the external environment, many of which have a direct antibacterial effect.These may be hydrogen peroxide or organic acids.Bacteriocins have a more complicated structure (de Souza Barbosa et al., 2015).

Роль МКБ в порче мяса
Мясо считается одним из наиболее скоропортящихся продуктов.Это обусловлено его химическим составом, который благоприятствует росту микроорга-layers of meat.The remaining 20-30% in the modified atmosphere is CO.Carbon dioxide inhibits bacterial growth by extending the lag phase and generation time.A twenty-five percent CO concentration is close to the maximum inhibition of aerobic microflora, which then decreases at <20%.Thanks to the mixture of gases used, the usual shelf life of MAP meat is 10 to 14 days.The second type of preservative packaging is vacuum packing (VP, CVP).The typical shelf life of vacuum-packed beef and pork is 28 and 21 days, respectively.An alternative and a relatively modern type of retail meat packaging is vacuum skin packaging (VSP).This relatively new method of vacuum packaging involves placing the product on a tray and wrapping it in a film under a vacuum at an elevated temperature.The heat causes the softening of the top film which then tightly covers the product, hence the designation of "skin".This procedure allows a gentler use of vacuum.The result is a decrease in purge loss and a longer shelf life in comparison with conventional vacuum packaging.Kameník et al. ( 2014) compared microbiological properties of vacuum skin packaged beef and pork with beef and pork packaged in conventional vacuum packaging and modified atmosphere packaging (Table 1).
The total viable count on day 35 of storage for beef was between 6.3 and 7.8 log 10 cfu.g -1 , with no significant differences between individual types of packaging.In pork, the bacterial population on day 21 was between 5 and 6 log 10 cfu.g -1 .Comparable values were found in the population of psychrotrophic bacteria.Differences between individual types of packaging were, however, reflected in the representation of selected bacterial groups.Vacuum packaging clearly enhanced the development of LAB.LAB counts determined in pork and beef packed in a modified atmosphere were significantly lower than those found in pork in CVP and VSP (P = 0.044 and 0.018, respectively) and beef in CVP and VSP (P = 0.006 and 0.003, respectively).From day 14 of storage onwards, the LAB population in meat samples in CVP and VSP was 2 log 10 larger than that in MAP meat.The differences remained unchanged throughout the experiment.
Currently, the role of LAB in fresh meat spoilage is still controversial.On one side, several species are able to dominate the meat system in VP and MAP storage conditions and can release odor-impact molecules, which may alter the sensory profile of raw or cooked meat, albeit this is not the case in all documented reports.The spoilage character of some LAB taxa is ambiguous and probably correlated with specific spoilage-associated capacities of individual strains that cannot be attributed collectively to the respective species.Moreover, for the LAB with negligible role in sensory spoilage, a bioprotective function in meat can be hypothesized as they can provide favorable antagonistic activity against other undesired microorganisms ( Pothakos et al., 2015).
On the other hand, there is also a large group of cooked meat products in which the presence of microorganisms and their metabolic activity is undesirable, as they induce spoilage and therefore reduce the shelf life of the given meat products.Psychrotrophic lactic acid bacteria have a crucial part to play in these negative effects (Slongo et al., 2009;Audenaert et al., 2010).Their presence is often connected with secondary contamination during packing or slicing, as they are not capable of surviving the heating involved in the cooking process (Franz, von Holy, 1996).Thermal resistant species also exist, however, which are not destroyed by higher temperatures (generally 70 °C), в вакуумную упаковку и вакуумную скин-упаковку (P = 0,044 и 0,018, соответственно), и говядине, упакованной в вакуумную упаковку и вакуумную скин-упаковку (P = 0,006 и 0,003, соответственно).
В настоящее время роль МКБ в порче свежего мяса все еще противоречивая.С одной стороны, несколько видов способны доминировать в мясной системе в условиях хранения в вакуумной упаковке или вакуумной скин-упаковке и могут выделять оказывающие влияние на запах молекулы, что может изменять сенсорный профиль сырого или термообработанного  and which are capable of further growth under suitable conditions.Dušková et al. ( 2016) performed microbiological analysis of individual technological operations during the industrial production of cooked hams, focusing on LAB.Samples were taken during the course of the entire cooked ham production cycle in May-June (Experiment I) and November-December (Experiment II).A total of 215 samples were taken and subsequently tested.The difference in the occurrence of LAB in meat before thermal processing resulted from the initial level of contamination of the raw material.A reduction to the number of LAB from 4.0-5.0log cfu.g -1 of meat to a value of practically zero occurred during the thermal processing (core temperature of 70 °C/10 min).The LAB population increased during storage of the finished products.A level of 7.0 log cfu.g -1 was reached in slices of ham in the modified atmosphere after three (Experiment I) or two (Experiment II) weeks of storage, respectively.LAB of the genera Leuconostoc (Leuc.carnosum, Leuc.mesenteroides and Leuc.gelidum) occurred most frequently in samples of cooked ham after thermal processing.These species were also isolated from the production environment.Lactobacillus sakei, Lbc.curvatus and Weissella viridescens were other species of LAB that were isolated from samples after thermal processing (Dušková et al., 2016).The thermal resistance of Weissella viridescens was studied under laboratory conditions (0.9% NaCl; 50, 60 or 70 °C/5, 10 or 15 min.)and in dry cooked meat products (Kameník et al., 2015).Nine batches of hot smoked dry sausage were prepared differing in terms of the size of the inoculum of W. viridescens (3 log cfu.g -1 of sausage batter, 4 log cfu.g -1 ) and the addition of dextrose (0, 0.1, 0.2, 0.3 and 0.4%).W. viridescens was detected in samples with a lower concentration of inoculum only after 2 weeks of ripening.But in batches with a higher concentration of inoculum W. viridescens was detected immediately after cooking and the number of cfu exceeded 7 log.g - during ripening.The addition of dextrose did not influence the growth of Weissella.Survival of the species W. viridescens in hot smoked dry sausages was also demonstrated under the conditions of industrial production.Dušková et al. (2015) determined the potential spoilage agent in hot smoked dry sausages.A total of 87 Vysočina sausages obtained from eight producers in the Czech Republic were analysed.The number of LAB ranged from 2.00 to 7.88 log CFU/g.Weissella viridescens was found in 30 of the 42 samples positive for LAB (71.4%), in 23 cases (53.5%) as a monoculture of LAB.An analysis of the factory environment and raw materials (84 swab samples) for the presence of LAB was conducted in relation to three producers.The species W. viridescens was found in just 2.4% of all swabs.As total of four samples designated for reworking contained LAB, with three samples being positive for the presence of W. viridescens, authors suggested that the reworking process leads to subsequent growth of thermoresistant strains causing spoilage of the sausages (Dušková et al., 2015.мяса, хотя это не всегда происходило во всех документированных сообщениях.Характер порчи у некоторых таксонов молочнокислых бактерий неоднозначен и вероятно коррелирует со специфическими ассоциированными с порчей способностями отдельных штаммов, которые не могут быть коллективно приписаны соответствующим видам.Кроме того, для МКБ с незначительной ролью в сенсорной порче, можно предположить биозащитную функцию в мясе, так как они могут предоставить благоприятную антагонистическую активность против других нежелательных микроорганизмов (Pothakos et al., 2015).

УДК/UDC: 637.5:579.676 Abstract Lactic
acid bacteria (LAB) play in meat processing a positive but also a negative role.The principal advantage of LAB in the production of dry fermented sausages lies in the fermentation of saccharides, i.e. the creation of lactic acid and the subsequent fall in pH.The role of LAB in fresh meat spoilage is still controversial.Several species are able to dominate the meat system in VP and MAP storage conditions and can release odor-impact molecules.On the other hand they can provide favorable antagonistic activity against other undesired microorganisms.LAB are important spoilage agents in cooked meat products.