Rosa Helena Luchese

Psychrotrophic bacteria in milk: How much do we really know?

The occurrence of psychrotrophic bacteria in raw milk is studied worldwide due to the difficulties associated with controlling their growth during cold storage and the consequent negative effects upon fluid milk or dairy products. Among the psychrotrophic bacteria, the genus Pseudomonas (represented primarily by P. fluorescens) has been highlighted as the cause of numerous defects in dairy products. In light of its perceived predominance, this species has frequently been chosen as a model organism to assess the effects of psychrotrophic bacteria on milk or to evaluate the efficacy of control measures. However, recent findings derived from the application of molecular biological techniques have exposed a number of deficiencies in our knowledge of the biology of milk-associated psychrotrophs. Furthermore, it has been revealed that microbe to microbe communication plays a significant role in determining both the identities and the extent to which different groups of microbes develop during cold storage. The application of molecular identification methods has exposed errors in the classification of members of the genus Pseudomonas isolated from cold stored milk and has stimulated a reevaluation of the presumed status of P. fluorescens as the predominant milk-associated psychrotrophic species. This article presents a succinct review of data from studies on psychrotrophic bacteria in milk, some of which contest established theories in relation to the microbiology of cold stored raw milk, and poses the question: how much do we really know?

Inhibitory effect of acetic acid on bioconversion of xylose in xylitol by Candida guilliermondii in sugarcane bagasse hydrolysate

Sugarcane bagasse hydrolysate (initial acetic acid concentration = 3.5g/L), was used as a fermentation medium for conversion of xylose into xylitol by the yeast Candida guilliermondii FTI 20037. Acetic acid (2.0g/L) was added to the medium at different times of fermentation, with the aim of evaluating its effects on the bioconversion process. The addition of acetic acid to the medium after 12h of fermentation resulted in the strongest inhibition of the yeast metabolism. In this case, the xylose consumption and cell growth were, respectively, 23.22 and 11.24% lower than when acid was added to the medium at the beginning of fermentation. As a consequence of the inhibitory effect, lower values of the xylitol yield (0.39g/g) and productivity (0.22g/L.h) were observed, corresponding to a reduction of 36 and 48%, respectively, in relation to the values obtained with the addition of acetic acid after other fermentation times. The results obtained allowed to conclude that, under the experimental conditions employed in this work, the inhibitory effect of acetic acid on the xylose-xylitol bioconversion depends on the fermentation time when this acid was added, and not only on its concentration in the medium.

Aflatoxin production in a meat mix model system in the presence of Pediococcus and Lactobacillus

The effect on aflatoxin production by Aspergillus parasiticus of eight individual strains of Pediococcus and Lactobacillus was determined. The study was conducted in an axenic cultural system in which irradiated meat was employed in the formulation of a meat medium. The medium composition and incubation temperatures were simulations of Brazilian salami processing conditions. All single cultures of A. parasiticus supported aflatoxin production. More aflatoxin was produced in samples treated by the addition of lactic acid than in nontreated ones. Aflatoxin was not detected when A. parasiticus was grown with lactic acid bacteria, although visible mold growth was observed in all such cultures.

Efeito prebiótico do mel sobre o crescimento e viabilidade de Bifidobacterium spp. e Lactobacillus spp. em leite

To be considered prebiotic, a microorganism must fulfill a series of requirements and the maintenance of viability is a major one. Probiotic cultures of Lactobacillus spp. and Bifidobacterium spp. were cultured in 12% (w/v) reconstituted nonfat dry milk containing 3% (w/v) of pasteurized honey. Controls without honey were prepared. All cultures remained viable for up 46 days at 7 °C conforming to the regulation requirement. The higher cell number of L. casei-01 and L. casei Shirota (>9.0 log10 CFU.mL-1) were maintained in the presence of honey. The titratable acidity produced by these cultures was of 1.44%. On the 46th day of storage, the number of L. acidophilus Sacco® viable cells in the presence of honey was significantly higher (p < 0.05) compared to the control. Considering the overall storage period, honey exerted significant positive effect (p < 0,05) only on Bifidobacterium cultures. The lowest growth and acidity on the 46th day was observed with Bf. Lactis Bb12, being 7,63 log10 CFU.g-1 and 0,61% of acidity in the presence of honey and 6.11 log CFU.mL-1 and 0,30% of acidity in the control. Differently, Bf. lactis Sacco® cultures reached counts of 9,11 log10 CFU.mL-1 and produced 1.11% acidity.

Cenouras minimamente processadas em embalagens com atmosferas modificadas e tratadas com radiação gama: avaliação microbiológica, físico-química e química

As cenouras sao as principais fontes de origem vegetal em carotenoides provitaminicos A (a e o b-caroteno) e podem ser transformados em vitamina A dentro do organismo animal. Segundo a Pesquisa de Orcamento Familiar realizada na regiao Sudeste do Brasil, no grupo de raizes e tuberculos, a cenoura e amplamente consumida. As cenouras minimamente processadas foram acondicionadas em embalagens com atmosferas modificadas de 5% O2/10% CO2 e 21% O2 (ar sintetico), e tratadas com radiacao ionizante gama, fonte de cesio, nas doses de 0,25, 0,50, 0,75 e 1,00kGy. Os produtos apos o emprego da radiacao foram armazenados em refrigeracao de 5°C durante 24 dias. Os diferentes tratamentos da cenoura e o grupo controle foram avaliados atraves das analises de pH, solidos soluveis totais (SST), acidez total titulavel (ATT) e microbiologia. Os resultados de microbiologia evidenciaram que os produtos tratados com as doses de 0,50, 0,75 e 1,0kGy apresentaram reducao de 3 a 4 ciclos logaritmicos na contagem total de mesofilos (CTM) logo apos a irradiacao e uma vida-util de 20 dias. Nao foram detectados coliformes totais e E. coli ate o 24o dia. Os patogenos B. cereus, Salmonella e Estafilococos coagulase positivos em 0,1g do produto, tambem nao foram detectados. As contagens de bacterias laticas mantiveram-se menores que 100UFC/g. O processo de irradiacao em baixas doses mostra-se promissor na manutencao da qualidade e apresenta-se como uma medida alternativa na reducao de perdas pos-colheita.

Effect of three different types of culture conditions on Spirulina maxima growth

Growth of Spirulina maxima was studied in three types of culture conditions with four replicates each: 1) manual aeration with natural sunlight; 2) manual aeration with artificial light; and 3) constant aeration with an aquarium compressor and artificial light. After 185 days of incubation, growth declined in the first two treatments, while in the third treatment, higher growth was observed with average optical density of 3.7 against 1.8 and 1.9 in the first and second treatment, respectively. This was probably due to the fact that under constant aeration the salts were suspended avoiding the crystallization what could cause a decrease in the availability of the necessary nutrients for the growth. Also, the constant stirring allowed all the cells to receive the same amount of light promoting photosynthesis and consequently, a larger growth and characteristic green coloration. Culture with constant aeration under artificial light should be used for S. maxima cultivation because, besides reducing labor hours, it could be a more effective method for improving the economic income.

Survival of free and microencapsulated Bifidobacterium: effect of honey addition.

Abstract This study evaluated the effect of honey addition on the viability of free and emulsion encapsulated cells of two strains of Bifidobacterium that underwent simulation of human upper gastrointestinal transit. In the control condition, without honey, free cells were drastically reduced after exposure to gastrointestinal conditions. The reduction was more pronounced with Bifidobacterium J7 of human origin. On the other hand, when cells were encapsulated, the viability reduction was higher for strain Bifidobacterium Bb12. The microencapsulation improved the viability maintenance of both Bifidobacterium strains, in recommended amounts for probiotic activity, after exposure to simulated gastrointestinal conditions. Moreover, suspending free cells of both Bifidobacterium strains in honey solutions resulted in a protective effect, equivalent to the plain microencapsulation with sodium alginate 3%. It is concluded that microencapsulation and the addition of honey improved the ability of Bifidobacterium to tolerate gastrointestinal conditions in vitro.

Efeito do uso da cepa starter de Penicillium nalgiovense na qualidade de salames

The growth of filamentous fungi on the surface of salami during ripening is an important factor for the quality of the product quality because it helps the biochemical changes involved in the process. Nevertheless, some of these fungi can cause problems related to discolouration and off-flavour, as well as damage on the casings. In addition, some fungi are associated to health hazards due to toxin production. This work aimed to study the ability of the starter culture Penicillium nalgiovense (PN-2)R to control natural contaminants during ripening under factory conditions, the operation of the process and the general effect on organoleptical parameters as compared to the product obtained by the traditional process. The salami were produced in industrial scale, ripened for 30 days at 18°C and 80-60% ERH. Moisture, pH, free fatty acids (FFA), non-protein nitrogen (NPN), taste, texture and aroma were the ripening parameters studied. It was observed that at the end of ripening, samples from inoculated batches had an increase of 2,93% in FFA mean value as compared to the uninoculated control. This difference was significant at 5% level. The moisture loss occurred slowly and progressively, and no significant differences were observed among inoculated and non-inoculated batches at the end of the ripening period. Statistical difference was not observed among the batches related to pH, NPN and on the organoleptical attributes and acceptability. Microbiological analysis did not detect the presence of filamentous fungi other than the starter, and an almost complete cover by PN-2 culture was observed on the surface of the salami.

Hot topic: Holder pasteurization of human milk affects some bioactive proteins

The aim of this research was to investigate the effect of Holder pasteurization (HoP; 62.5°C, 30 min) on the protein profile and activities of glutathione peroxidase (GPx) and lysozyme (LZ) in human milk. Over 6 mo of lactation, human milk samples were analyzed before (raw) and after HoP for GPx and LZ activity and electrophoresis protein profile. Holder pasteurization reduced human milk lactoferrin, immunoglobulin fractions, and GPx activity. In addition, GPx activity, which is high in colostrum and transitional milk, was naturally reduced over the 6-mo lactation period. In contrast, HoP did not affect human milk LZ activity. Besides its critical cellular antioxidant role in protecting the organism from oxidative damage, GPx decreases the redox potential of milk, stimulating the growth of anaerobic microorganisms, such as the probiotic Bifidobacterium. Considering the role of lactoferrin in infant health, we conclude that an important part of its function has been inactivated by pasteurization. These compounds should be replaced by human milk banks after the HoP step to recover lost functionality. Otherwise, an alternative technology to HoP that better retains human milk properties should be used by milk banks to eliminate the risk of transmission of infectious agents.

Honey as a Functional Food

The most well‐known functional properties of honey are its antioxidant and antimicro‐ bial activities. The bioactive components of honey are affected by the flora from which it is produced and by geographical variations. Phenolic compounds promote, among other activities, high antioxidant action, being capable of minimizing intracellular oxida‐ tive damage associated with cellular aging, apoptosis and neurodegenerative diseases. A living cell system would provide a better platform for determining antioxidant activity, since the bioactive honey compounds can act modulating antioxidant defense gene expression. Indeed, phenolic compounds, amino acids and reducing sugars are among the substances responsible for honey antioxidant activity. Most of phenolic compounds also exert antimicrobial activity against a number of pathogens and spoilage microorgan‐ isms. The antimicrobial activity of honey is also due to the action of enzymes. In addition, honey was found to contain lactic acid bacteria (LAB), which itself produce a myriad of active compounds that remain in variable amounts in mature honey. In addition, these antioxidant compounds might play a key role as prebiotic, protecting and stimulating growth of probiotic bacteria. Oligosaccharides present in honey are well‐known prebi‐ otic substances stimulating growth, activity and protecting probiotic bacteria during pas‐ sage through the gastrointestinal tract and during storage of the products. This chapter describes the main bioactive components of honey, especially with respect to the pheno‐ lic compounds and their antioxidant activity and assay methods.