RESUMO
Chitooligosaccharides (COSs) have been clinically evaluated for their immunostimulating effects after oral intake. Similar to dietary supplements, prebiotics and biopreservatives, these water-soluble bioactives are easily incorporated into dairy products and beverages. Notwithstanding, the use of COS in fermented foods would be limited by its antimicrobial properties. In order to study the interaction with yoghurts as a model of fermented food, the effects of COS on chemical composition, viability, morphology and metabolism of lactic acid bacteria, fatty acid profiles and conjugated linoleic acid (CLA) were assessed over 28 days and after chemical digestion. There were no significant differences between the nutritional composition of controls and yoghurts supplemented with concentrations up to 0.1% w/w of COS. However, the acidification of milk decreased at 0.5% (p < 0.05) and the formation of yoghurt failed at 3.0%, without affecting viable counts. Lipid hydrolysis of yoghurts supplemented with 0.1% COS was not affected by chemical digestion. No significant differences were found between CLA percentages of controls and supplemented yoghurts after digestion. Although the nutritional composition, fatty acids and viable counts were not significantly modified after COS supplementation, the present study shows that COS diminishes bacterial acidification at concentrations higher than 0.1%, thus limiting the amounts that could be added to yoghurt.
Assuntos
Reatores Biológicos , Quitina/análogos & derivados , Digestão/efeitos dos fármacos , Valor Nutritivo/efeitos dos fármacos , Iogurte , Animais , Quitina/farmacologia , Quitosana/química , Decápodes/química , Suplementos Nutricionais , Ácidos Graxos/metabolismo , Hidrólise/efeitos dos fármacos , Ácido Láctico/metabolismo , Lactobacillaceae/metabolismo , Ácidos Linoleicos Conjugados/metabolismo , Metabolismo dos Lipídeos/efeitos dos fármacos , Oligossacarídeos , Iogurte/microbiologiaRESUMO
Pseudomonas syringae pv. tomato DC3000 (Pto DC3000) causes bacterial speck of tomato, a widely spread disease that causes significant economical losses worldwide. It is representative of many bacterial plant diseases for which effective controls are still needed. Despite the antimicrobial properties of chitosan has been previously described in phytopathogenic fungi, its action on bacteria is still poorly explored. In this work, we report that the chitosan isolated from shrimp exoskeletons (70 kDa and 78 % deacetylation degree) exerts cell damage on Pto DC3000. Chitosan inhibited Pto DC3000 bacterial growth depending on its concentration, medium-pH, and presence of metal ion (Mg(+2)). Biochemical and cellular changes resulting in cell aggregation and impaired bacterial growth were also viewed. In vivo studies using fluorescent probes showed cell aggregation, increase in membrane permeability, and cell death, suggesting the chitosan antibacterial activity is due to its interaction as a polycation with Pto DC3000 membranes. Transmission electron microscopic analysis revealed that chitosan also caused morphological changes and damage in bacterial surfaces. Also, the disease incidence in tomato inoculated with Pto DC3000 was significantly reduced in chitosan pretreated seedlings, revealing a promising action of chitosan as nontoxic biopesticide in tomato plants. Indeed, a wider comprehensive knowledge of the mechanism of action of chitosan in phytopathogenic bacterial cells will increase the chances of its successful application to the control of spread disease in plants.