Percorrer por autor "Couto, J. A."
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- Cell membrane damage induced by phenolic acids on wine lactic acid bacteriaPublication . Campos, F. M.; Couto, J. A.; Figueiredo, A. R.; Tóth, I. V.; Rangel, António O. S. S.; Hogg, T. A.
- Chitosan as natural food preservative for sauces: a proof of conceptPublication . Costa, E. M.; Silva, S.; Silva, N.; Couto, J. A.; Gomes, A. M.; Pintado, M. M.Introduction: Nowadays, consumers demand more natural, nutritionally balanced, less caloric, and minimally processed foods leading to the emergence of sauces with low fat content and without chemical preservatives. This market pressure has led to the modification of a well-established and microbiologically stable matrix, triggering the search for new antimicrobial compounds of natural origin, compounds whose inhibitory efficacy must be studied [1]. Chitosan has attracted attention as a potential food preservative of natural origin due to its antimicrobial activity against a wide range of foodborne pathogens and contaminants. However, the antimicrobial capacity of chitosan, despite being extensively reported, is primarily based upon in vitro trials, where the compound, unimpeded, acts upon microorganisms. Currently, inclusion of chitosan in a food matrices is in its early steps with works reporting the application of chitosan in bread, egg, fruits, vegetables, juices, meat, milk and others, with various degrees of success [2]. In food sauces examples of chitosan application are few and scarce, as most works report on the usage of chitosan as an emulsifier or a emulsifier stabilizer and only Roller and Covill [3] described the successful usage of a chemically altered chitosan as a food preservative. As such, in this work we sought to ascertain the potential of chitosan as a viable, natural, alternative to traditional food preservatives used in food sauces, namely ketchup, mayonnaise and mustard, through assessment of the effect of chitosan containing sauces on the inhibition of lactic acid bacteria isolated therefrom and sensorial analysis of the developed prototypes.
- Cultivars of vitis vinifera used for white wine production: initial characterisation of selected portuguese varietiesPublication . Guedes, P.; Pina, C. M. G.; Santos, C.; Vasconcelos, I.; Hogg, C.; Couto, J. A.; Cunha, L. M.; Hogg, T. A.
- Determinação potenciométrica de efluxo de potássio em bactérias lácticas do vinho sujeitas a stress químicoPublication . Campos, F. M.; Couto, J. A.; Hogg, T. A.; Rangel, António O. S. S.; Tóth, I. V.
- Efeito de vários factores ambientais no crescimentoe produção de 4-etilfenol por leveduras do género Dekkera/BrettanomycesPublication . Silva, I. S.; Coelho, A. L.; Campos, F. M.; Ferreira, A. C.; Couto, J. A.; Hogg, T. A.
- Effect of food matrix on antimicrobial activity upon food spoilage Lactic Acid BacteriaPublication . Costa, E. M.; Silva, S.; Matias, C.; Matias, O.; Couto, J. A.; Gomes, A. M.; Pintado, M. M.Lactic acid bacteria (LAB) have been used in foodstuffs due to the desirable effects on the organoleptic and functional characteristics; however they can also cause food spoilage by producing off-flavours, carbon dioxide and textural changes. In such circumstances, their intrinsic high resistance to acidic conditions and antimicrobials poses a problem to the food industry. So it is important to select amongst the food additives those that assure LAB inhibition in acid and complex food matrices assuring safety and quality preservation. In this work we describe the antimicrobial efficiency of sodium diacetate in two prototypes of mayonnaise and ketchup. To that end both matrices (ketchup and mayonnaise) formulated with the selected antimicrobial agent were inoculated with a LAB isolated from previously spoiled sauces and the capability to reduce their initial viable cell numbers was evaluated. The results obtained showed that the inclusion of this antimicrobial into both matrices was not completely successful. While in the ketchup prototype revealed high antimicrobial activity reducing, in 24 h, LAB viable counts by 5.37 log CFU/g, in the mayonnaise only 1 log CFU/g reduction was observed in the same time frame. A probable cause for this discrepancy is the higher fat content of mayonnaise that may be blocking the antimicrobial activity. In conclusion the results obtained show the need to adapt the antimicrobial solution to different complex matrices, since several interactions between food matrix and antimicrobial components may occur
- Effect of malolactic fermentation on the volatile profile of winesPublication . Moreira, N.; Ruão, P.; Couto, J. A.; Vasconcelos, I.; Pinho, P. Guedes de
- Effect of malolactic fermentation on the volatile profile of winesPublication . Moreira, N.; Ruão, P.; Couto, J. A.; Vasconcelos, I.; Pinho, P. Guedes deThis work aimed to evaluate the influence of malolactic fermentation (MLF) on the composition of the volatile fraction of wines (alcohols, esters, fatty acids and heavy sulphur compounds). Red grape must vinifications were performed at industrial scale from a single grape cultivar (Touriga Franca-TF) and a mixture of cultivars (MC) of the Douro Region. Wine samples were collected before and after spontaneous MLF. Results show that the concentration of certain volatile compounds was clearly affected by the MLF. It was found that the content of 2-phenylethyl acetate, hexyl acetate, ethyl hexanoate, ethyl lactate and methionol increased while the levels of total ethyl esters and S-(methylthio)acetate decreased in both wines. The impact of MLF in some compounds was found to be wine dependent. For example, the concentration of 3-mercapto-1-propanol increased in the MC wine while it decreased in TF wine. No significant differences were observed for trans-2-methyltetrahydrothiophene-3-ol, 4-(methylthio)-1-butanol and 3-(ethylthio)-1-propanol.
- Effect of phenolic acids on glucose and malic acid metabolism of Lactobacillus hilgardiiPublication . Campos, F. M.; Couto, J. A.; Hogg, T. A.
- Ethanol-induced changes in the fatty acid composition of Lactobaci//us hilgardii, its effects on plasma membrane fluidity and relationship with ethanol tolerancePublication . Couto, J. A.; Rozès, N.; Hogg, T.The effect of environmental ethanol concentration on the fatty acid composition of strains of Lactobacillus hilgardii, differing in their tolerance to ethanol, was determined. A marked increase in the proportion of lactobacillic acid (a cyclopropane fatty acid) and a decrease in oleic and vaccenic acids with increasing ethanol concentration was observed. The amount of lactobacillic acid determined at standard conditions (25°C, 0% ethanol) was found to be proportional to the ethanol tolerance of the strains studied. The effect of this alcohol on plasma membrane fluidity was studied by differential scanning calorimetry. The adaptive response to growth in the presence of high concentrations of ethanol produced membranes which, within the limits of ethanol tolerance, maintained the fluidity and integrity in an environment which tends to increase membrane rigidity. When pre-adapted cells are analysed in the absence of environmental ethanol there is a measurabie increase in fluidity. It is proposed that this phenomenon may be correlated with the increase in the proportion of lactobacillic acid. The existence of a relationship between membrane fluidity and ethanol tolerance is discussed.
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