Growth Of Undesirable Microorganisms Research Articles

Assessment of Starters of Lactic Acid Bacteria and Killer Yeasts: Selected Strains in Lab-Scale Fermentations of Table Olives (Olea europaea L.) cv. Leccino

Olives debittering, organoleptic quality and safety can be improved with yeasts and lactic acid bacteria (LABs) selected strain starters, that allow for better fermentation control with respect to natural fermentation. Two selected killer yeasts (Wickerhamomyces anomalus and Saccharomyces cerevisiae) and Lactobacillus plantarum strains were tested for olive (cv. Leccino) fermentation to compare different starter combinations and strategies; the aim was to assess their potential in avoiding pretreatments and the use of excessive salt in the brines and preservatives. Lactobacilli, yeasts, molds, Enterobacteriaceae and total aerobic bacteria were detected, as well as pH, soluble sugars, alcohols, organic acids, phenolic compounds, and rheological properties of olives. Sugars were rapidly consumed in the brines and olives; the pH dropped quickly, then rose until neutrality after six months. The oleuropein final levels in olives were unaffected by the treatments. The use of starters did not improve the LABs’ growth nor prevent the growth of Enterobacteriaceae and molds. The growth of undesirable microorganisms could have been induced by the availability of selective carbon source such as mannitol, whose concentration in olive trees rise under drought stress. The possible role of climate change on the quality and safety of fermented foods should be furtherly investigated. The improvement of olives’ nutraceutical value can be induced by yeasts and LABs starters due to the higher production of hydroxytyrosol.

Alterantes microbianos atípicos en yogures argentinos: mohos gasógenos y bacterias del género Gluconobacter

Microbial food alterations lead to unfit products for consumption, and their discarding, to significant economic losses for the food industry. During storage, fresh foods offer available niches for the survival and growth of undesirable microorganisms. In dairy products, data regarding spoilage and/or pathogenic bacteria is better documented than those for molds and yeasts. Dairy products are less susceptible to mold's contamination than products such as fruits and vegetables, due to their refrigerated storage; their elaboration from heat-treated milk and, for fermented ones, the dominant microbiota that acidifies the medium. However, even cheeses and yogurts may be susceptible to mold contamination. Atypical cases of yogurt samples containing spoilage microorganisms not previously reported (molds producing gas and bacteria of the genus Gluconobacter) in Argentinean fermented milks are presented here. For yogurt, in particular, the “classic” altering organisms were always being yeasts, and in other countries, molds belonging to the genus Aspergillus.

Biotechnological methods to improve the quality and safety of milk

The foremost task of milk producers and processors is to prolong the shelf life of dairy products. One of the high-tech and innovative ways to address this issue is to suppress the growth of undesirable microorganisms. EMR milk treatment is proposed as one of such promising methods of product exposure in order to reduce the total microbial count, improve the milk’s chemical composition, and, ultimately, improve the quality and safety of milk and dairy products. The requirements of regulatory documents for the safety of milk and dairy products prohibit the direct introduction of preservatives into milk. In this regard, it is advisable to look for ways to use preservatives in packaging materials’ composition while observing the safety of the packaging itself. The purpose of our study was to identify the effect of electromagnetic treatment and preservatives, both direct application and in the composition of polyethylene packaging, on the physicochemical and microbiological parameters of milk at various storage temperatures. It was established that preservative’s introduction into the packaging film did not affect the chemical parameters of milk; the content of lactic acid bacteria in the product after a day of storage in modified polyethylene amounted to 1.4x106 CFU/cm3, while their number amounted 8.1x106 CFU/cm3 when stored in glass packaging.

Effects of organic acid-based products added to total mixed ration on performance and ruminal fermentation of dairy cows

An increase in total mixed ration (TMR) temperature is associated with a growth of undesirable microorganisms and decreases in feed intake in dairy cows. We evaluated the effects preservative products containing organic acids (OA) added to TMR on intake and digestibility of nutrients, rumen fermentation, milk yield and composition, nitrogen utilization, blood parameters, ingestive behavior of cows. Twenty-five Holstein cows (147.4 ± 87.9 days in milk, 668.7 ± 78.5 kg of body weight and 34.4 ± 4.2 kg/d milk yield), 10 of which were rumen-cannulated, were assigned to a 5 × 5 Latin square experiment containing the following treatments: control (CON), no OA added to TMR; and four preservatives composed mainly of either formic acid (FLE), sodium formate (SOL), propionic acid (SPE) in liquid form, or propionic acid (PER) in solid form added to TMR. The OA products used in this study were manufactured by Perstorp Waspik BV (Waspik, The Netherlands). Products were added daily to the TMR at 4 ml/kg natural matter (NM) for the liquid products (FLE, SPE, PER), and at 4 g/kg for the solid product (SOL). The experimental barn temperature, relative humidity, and temperature-humidity index during the experiment were 24.4 ± 4.29 °C, 75.0 ± 16.39%, and 72.7 ± 5.31 (mean ± SD), respectively. Each experimental period consisted of 14 days for adaptation to treatments and five days for sampling. Differences among treatments were studied using orthogonal contrasts, as follows: the effect of OA [control versus OA (SPE + SOL + PER + FLE)], the effect of OA composition [formic acid (FLE + SOL) versus propionic acid (PER + SPE)], the effect of different formic acid products (FLE versus SOL); and the effect of different propionic acid products (SPE versus PER). Organic acids increased feed intake (23.6 and 24.4 kg/d for CON and OA, respectively) and reduced sorting of feed particles with 8–19 mm size and shorter than 4 mm. Organic acids, however, decreased the total VFA concentration and increased pH of rumen fluid. Cows fed TMR with OA had greater fat-corrected milk production and milk protein content compared with CON. Organic acids avoided an increase in TMR temperature within 24 h air exposure. Organic acids, regardless of their composition, can maintain TMR temperature stable for longer periods and improve the performance of dairy cows.

AVALIAÇÃO DE DIFERENTES CULTURAS STARTERS NA ELABORAÇÃO DE SALAME TIPO ITALIANO

Resumo O Salame Tipo Italiano produzido no Brasil é predominantemente obtido de carne suína, com maturação aproximada de 30 dias, atingindo pH em torno de 5,4. O uso das bactérias do gênero Lactobacillus como culturas iniciadoras propicia o processo de fermentação e a obtenção de produtos uniformes e seguros, com redução do tempo de maturação devido à rápida formação de ácido lático, obtendo-se melhores características sensoriais, químicas e microbiológicas. Os estafilococos coagulase-negativos (comumente em produtos cárneos fermentados Staphylococcus xylosus e S. carnosus)possuem vantagens tecnológicas, como atividade de nitrito e nitrato redutase, consumo de oxigênio e atividade de catalase que melhoram a estabilidade de cor e diminuem o desenvolvimento de rancidez no produto, além de contribuírem para a geração de sabor devido à capacidade proteolítica e lipolítica. Portanto, este trabalho objetivou estudar a influência de diferentes culturas starters (S. xylosus, S. carnosus, L. sakei e L. plantarum)combinadascom diferentes concentrações de substrato de glicose (40,5 e 99,5%) na fabricação do Salame Tipo Italiano, bem como a influência da concentração destes no desempenho das culturas starters. Durante o processamento e shelf life, os salames foram avaliados quanto às características físico-químicas, microbiológicas e sensoriais. Em todas as amostras de Salame Tipo Italiano houve comportamento similar em relação aos parâmetros físico-químicos (umidade, proteína e gordura). Não houve crescimento de micro-organismos indesejáveis nas amostras analisadas após 60 dias de shelf life. Na análise sensorial, a amostra com menor concentração de substrato (40,5%), utilizando as culturas S. carnosus e L. sakei, foi a que recebeu as melhores notas e melhor aceitação pelos degustadores, além de apresentar valores de nitritos e nitratos de acordo com a legislação.

Obtención de queso crema con propiedades funcionales suplementado con sólidos de lactosuero e inoculado con Lactobacillus casei

En la actualidad la industria alimentaria está enfocada principalmente en la diversificación de los productos probióticos debido a los efectos beneficiosos que estos proporcionan a la salud de los consumidores. El objetivo del siguiente trabajo de investigación fue elaborar un queso crema suplementado con sólidos de lactosuero e inoculado con Lactobacillus casei. Para lo cual se realizaron análisis fisicoquímicos al lactosuero y a la leche cruda, así como al queso crema, además se evaluó parámetros microbiológicos al producto final con el fin de estimar la calidad del mismo. Los resultados indicaron que es posible obtener un queso crema con calidad óptima ya que se obtuvieron resultados de proteína y grasa comparables con el producto comercial. Igualmente es importante destacar que Lactobacillus casei se conservó viable durante 15 días a las diferentes diluciones evaluadas, 10-4, 10-5 y 10-6, con valores de UFC de 1.79E+06, 1.35E+07 y 6.80E+07, respectivamente. El queso crema mantuvo calidad microbiológica debido a que no se apreció crecimiento de microorganismos indeseables.

발효오이의 산패예견표의 개발

발효된 오이의 산패는 원하지 않는 미생물의 2차적 생장에 의한 결과이며 장기보관을 원하는 발효오이 식품은 일반적으로 고농도의 염을 사용한다. 염의 농도를 최소한으로 하면서 산패를 방지할 수 있는 pH의 범위를 모색하기 위하여 다양한 조합의 pH와 NaCl 농도를 갖는 발효오이즙(FCS) 배양액에 3가지 종류의 산패액을 각각 접종하여 발효오이의 산패여부를 조사하였다. pH3에서는 NaCl의 첨가가 없더라도 산패는 일어나지 않는데 비하여 pH 5.0에서는 4%의 NaCl에서도 모두 산패가 진행되었다. pH 3.5, pH 4, pH 4.5 에서는 0%와 2% NaCl의 범위 내에서 다양한 결과를 보였다. 이 결과를 바탕으로 발효오이의 산패를 예견할 수 있는 조견표를 작성하였다. 조견표의 사용은 발효오이의 장기보관을 위한 적절한 산도와 염의 농도의 선택을 가능하게 할 것이다. Off-flavors and odors in fermented cucumbers result from the growth of undesirable microorganisms during the secondary fermentation. Under laboratory conditions using a sterile fermented cucumber slurry medium, the spoilage fermentations were reproduced. Using this system the salt and pH conditions that allow the spoilage to occur were determined by varying the NaCl concentration and pH of the slurry medium. At pH 3, no spoilage was observed, regardless of the salt concentration, while at pH 3.5, pH 4, and pH 4.5, spoilage occurred in the 0 and 2% NaCl samples. For pH 5.0 samples, spoilage products were seen for all NaCl treatments. Based on these results the Preservation Prediction Chart was developed. The Chart may be used for selection of proper pH value and salt concentration for long term storage of fermented cucumber.

The Leaf-Cutting ant Atta Sexdens rubropilosa, FOREL, 1908 Prefers Drier Chambers for Garbage Disposal

Leave cutting ants rely on a fungus garden as their main food supply. This garden produces debris that must be disposed by workers, as it may favor the contamination of the fungus. We assumed that the growth of undesired microorganisms on garbage would increase with humidity, therefore drier areas should be more suitable for garbage disposal. Accordingly, we tested the hypothesis that leave-cutting ants Atta sexdens rubropilosa choose drier chambers for garbage disposal. We found that 30 out of 30 sub-colonies tested for hygropreference chose drier chambers for garbage disposal when offered a choice between dry (RH=25±5% SD) and humid (RH=95±5% SD) chambers.

A new polymer inhibitor of lactobacillus growth in table olives

The bulky precipitate formed in the washwaters from the processing of Spanish-style green olives, as a consequence of HCl acidification, presented inhibitory activity against lactic acid bacteria growth, the intensity of the effect being influenced by the type of washwater, pH and inoculum size. The delay or complete inhibition of microorganism growth was confirmed for three strains of lactobacilli (Lactobacillus pentosus LP99, L. pentosus ATCC 8041 and L. plantarum ATCC 14917), and this phenomenon can allow growth of undesirable microorganisms during washwater fermentation. The inhibitory activity against lactobacilli in acidified washwaters disappeared when the bulky precipitate was eliminated by centrifugation or simply by sonicating the solutions. It seems that sonication modified the macromolecular structure of the precipitate and the biosorption of microorganisms in it did not occur. Also, the inhibitory activity of this precipitate was confirmed in brines of Spanish-style green olives. Therefore, this new lactobacillus growth inhibitor will have to be taken into account in the future for improving olive fermentation.

The impact of lactic acid bacteria on sourdough fermentation

The baking of sourdough breads represents one of the oldest biotechnological processes. Despite traditionality, sourdough bread has great potential because of its benefits. Sourdough is a mixture of flour and water that is dominated by a complex microflora composed of yeasts and lactic acid bacteria that are crucial in the preparation of bread dough. Lactic acid bacteria cause acidification by producing lactic acid that increases the shelf life of bread by preventing the growth of undesirable microorganisms and affects the nutritional value of bread by increasing the availability of minerals. In addition to these advantages, the use of sourdough fermentation also improves dough machinability, breadcrumb structure and the characteristic flavour of bread. Lactic acid bacteria in sourdough fermentation are well known representing both homofermentative and heterofermentative bacteria. They may originate from selected natural contaminants in the flour or from a starter culture containing one or more known species of lactic acid bacteria. Sourdough can be cultivated in bakeries or obtained from commercial suppliers. However, many bakeries in Europe still use spontaneously fermented sourdoughs, which have been kept metabolically active for decades by the addition of flour and water at regular intervals. The impact of lactic acid bacteria on sourdough fermentation and their influence on dough and bread quality was discussed on the basis of research and literature data.

Ripening and seasonal changes in microbial groups and in physico-chemical properties of the ewes’ cheese Pecorino del Poro

Three batches of Pecorino del Poro, ewes’ cheese made from raw milk, were examined throughout a 28-day ripening time at three different seasons. High logarithmic counts per gram of cheese for mesophilic coccal-shaped lactic acid bacteria (6.70–12.45), mesophilic lactobacilli (4.82–11.73), thermophilic coccal-shaped lactic acid bacteria (2.30–9.90), and thermophilic lactobacilli (2.95–8.15) were found. Coccal-shaped lactic acid bacteria were the dominant microorganisms throughout ripening. The microorganisms used as an indicator of hygiene during manufacture of the cheeses, coliforms and Escherichia coli , were considerably lower, as were enterococci and yeasts. Coliforms and E. coli decreased sharply throughout ripening. Physico-chemical parameters such as pH (5.07–7.03), dry matter (46.34–72.79%), ether extract (31.35–51.84% of dry matter), crude protein (29.93–44.73% of dry matter), and chloride content (2.36–4.11% of dry matter) were also determined. Probably, the use of selected autochthonous mesophilic lactococci as a starter would control or suppress the growth of undesirable microorganisms. The results obtained suggest the need for improvements in milking and dairy conditions.

Fermented sausages

Abstract The fermentation processing of raw sausages controlled by metabolic activity of added microorganisms (starter cultures) has been known for several decades and is widespread in countries with developed meat industries. Its success is due to several factors, like rapid turnover, pleasant aroma and taste, and good safety record, to name just a few. The basic process is the bacterial breakdown of added carbohydrate, mostly dextrose and/or sucrose or any other mono‐ or disaccharides, as a result of which lactic acid is formed. In the presence of lactic acid the pH drops to a value close to the isoelectric point of muscle protein, in this way reducing water‐holding capacity and making rapid drying possible. By doing so, growth of undesirable microorganisms is inhibited, salmonellae and staphylococci being most important in this respect, and firm consistency is formed in a very short time. In addition to these basic processes other biochemical changes also take place, of which changes in N‐compounds and in lipids seem to be important in formation of aroma compounds. These changes thus play a definite role in the special palatability feature of raw fermented sausages, which is completely different from any other types of meat products. An interesting activity of starter cultures is their antagonism against undesirable (i.e., pathogenic and spoilage) microorganisms. It seems probable that in addition to acidity (presence of lactic acid formed) exhibiting a nonspecific inhibitive effect, undesirable bacteria are inhibited also specifically by, for example, antibiotics; but formation of hydrogen peroxide, depletion of nutrients, etc., may play a role too. The bacteriological safety of these products is provided by the combined effect of low pH (below 5.3) and low water activity (0.95 or below), which makes it possible to store them even at room temperature without health risk or spoilage.