Browsing by Author "Ho, Peter"
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- Changes in colour and phenolic composition during the early stages of maturation of port in wood, stainless steel and glassPublication . Ho, Peter; Silva, Maria da Conceição M.; Hogg, TimDifferences in colour and phenolic composition during the maturation of port in oak wood, stainless steel and glass were examined for a period of 311 days at 18 °C. Principal component analysis (PCA) was used in variable selection, data reduction and data analysis. Nine out of 13 colour and phenolic variables were heavily loaded on PC1 (76.1% of explained variance), and a plot of PC1 scores versus maturation time showed differences in colour and anthocyanins between ports matured in different containers. Ports matured in oak casks developed at a faster rate than the other ports. Total phenolics remained fairly constant in all ports, as monomeric anthocyanins were rapidly depleted during the time of maturation. Polymeric pigments formed during maturation contributed to increases in colour density, hue and the rate of browning. Differences in redox potential between wood matured ports and non-wood matured ports indicated that there were differences in dissolved oxygen which could have affected the maturation rate of these wines.
- Effect of skin contact and oxygenation of muts on the composition of white port winesPublication . Ho, Peter; Rogerson, Frank S.S.; Watkins, Steve J.; Silva, Maria da Conceição M.; Hogg, Tim; Vasconcelos, IsabelWhite port wine were made from Malvaela Fina and Rabigata gaps musts that were subjected to different combinations of skin contact and must oxygenation. Increasing skin contact times increased the total phenolics. Total hydroxycinnamoyl tartaric acid, total flavonoids and the formation of brown pigments in the tree-run musts. Both air exposure and hyperoxidation were effective in lowering the concentration of hydroxycinnamoyl tartaric acids and flavonoids it newly fermented wines. Hyperoxidation seemed more effective in removing this phenolic compounds and U1 reducing browning than air expo- sure In wines which had 8 and 25 h of akin contact. Phenolic compounds increased with wood ageing. Although the concentration of hydroxycinnamic acide were lower In all oxygenated wines than in the controls. However must oxygenation prior to fermentation could not prevent further browning of the wines, caused by the production of furans and the increase of flavonoids during that ageing it wood. increasing skin contact generally increased the total monoterpene alcohol concentration for hyperoxidised whesm with some increases it air exposed wines. Total monoterpene alcohol concentration was higher Hyperoxidised than in air exposed wines, made from musts with 8 and 25h of skin contact, after 18 months of wood ageing.
- Effects of various sugars added to growth and drying media upon thermotolerance and survival throughout storage of freeze-dried lactobacillus delbrueckii ssp. bulgaricusPublication . Carvalho, Ana S.; Silva, Joana; Ho, Peter; Teixeira, P.; Malcata, F. Xavier; Gibbs, PaulThe aim of this research effort was to investigate the role of various sugar substrates in the growth medium upon thermotolerance and upon survival during storage after freeze-drying of Lactobacillus bulgaricus. Addition of the sugars tested to the growth medium, and of these and sorbitol to the drying medium (skim milk) was investigated so as to determine whether a relationship exists between growth and drying media, in terms of protection of freeze-dried cells throughout storage. The lowest decrease in viability of L. bulgaricus cells after freeze-drying was obtained when that organism was grown in the presence of mannose. However, L. bulgaricus clearly survived better during storage when cells had been grown in the presence of fructose, lactose or mannose rather than glucose (the standard sugar in the growth medium). A similar effect could not be observed in terms of thermotolerance; in this case, the growth medium supplemented with lactose was found to yield cells bearing the highest heat resistance. Supplementation of the drying medium with glucose, fructose, lactose, mannose or sorbitol led in most cases to enhancement of protection during storage, to a degree that was growth medium-dependent.
- European FooD-Studies and Training Alliance (Erasmus+ Knowledge Alliance project)Publication . Schleining, Gerhard; Svacinka, Reiner; Pittia, Paola; Silva, Cristina L. M.; Costa, Rui; Ho, Peter; Dubois-Brissonnet, Florence; Braun, Susanne; Morais, Pilar; Jaume, Sola; Notarfonso, Mauricio; Drausinger, Julian; Cottilon, Christophe
- European FooD-Studies and Training Alliance (Erasmus+ Knowledge Alliance project)Publication . Schleining, Gerhard; Svacinka, Reiner; Pittia, Paola; Silva, Cristina L. M.; Costa, Rui; Ho, Peter; Dubois-Brissonnet, Florence; Braun, Susanne; Morais, Pilar; Jaume, Sola; Notarfonso, Mauricio; Drausinger, Julian; Cottilon, Christophe
- Impedimetric method for estimating the residual activity of freeze-dried Lactobacillus delbrueckii ssp. bulgaricusPublication . Carvalho, A. Sofia; Silva, Joana; Ho, Peter; Teixeira, Paula; Malcata, F. Xavier; Gibbs, PaulThe residual activity of Lactobacillus delbrueckii ssp. bulgaricus cultures was analysed using pH and various impedimetric methods (impedance detection time (IDT), conductance and capacitance) to quantify the loss in activity following freeze-drying. The large variation recorded in IDT values for similar levels of activity suggests that IDT is not an adequate parameter for estimating the culture's fermentative activity. Comparison of the impedance signals generated revealed that capacitance yields values that are more reproducible than those of conductance, and also gives a better correlation with pH. Statistical analysis (p<0.05) indicated that there are no significant differences between the capacitance and the pH method when attempting to estimate residual activity.
- Relevant factors for the preparation of freeze-dried lactic acidPublication . Carvalho, Ana S.; Silva, Joana; Ho, Peter; Teixeira, Paula; Malcata, F. Xavier; Gibbs, PaulThe industrial exploitation of lactic acid bacteria (LAB) as starter and/or probiotic cultures depends strongly on the preservation technologies employed, which are required to guarantee long-term delivery of stable cultures in terms of viability and activity. Freeze-dried preparations exhibit advantages relative to preparations made with other techniques in terms of long-term preservation, coupled with convenience in handling, storage, marketing and application. Degrees of survival of LAB cultures as high as possible, during drying and subsequent storage, are thus of nuclear importance, both technologically and economically. This review covers several factors, deemed relevant for preservation of freeze-dried LAB. The state of the art of the knowledge focussed on the improvement of LAB survival during freeze-drying and subsequent storage is presented, including specific discussion of the effects of (i) intrinsic factors, (ii) growth factors, (iii) sub-lethal treatments, (iv) drying media and (v) storage and rehydration.
- Survival of freeze-dried Lactobacillus plantarum and LactobacillusPublication . Carvalho, A. Sofia; Silva, Joana; Ho, Peter; Teixeira, Paula; Malcata, F. Xavier; Gibbs, PaulNo significant differences were observed in the viability of Lactobacillus plantarum and Lactobacillus rhamnosus cells during freeze-drying in the presence or absence of inositol, sorbitol, fructose, trehalose, monosodium glutamate and propyl gallate. However, survival was higher during storage when drying took place in the presence of these compounds. Sorbitol produced more significant effects than the other compounds toward maintaining viability of freeze-dried L. plantarum and L. rhamnosus.