Browsing by Author "Guerra, Nelson P."
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- Chestnut purée: a possible growth media for probiotic microorganisms – Preliminary resultsPublication . Afonso, Maria João A.P.S.; Guerra, Nelson P.; Pereira, Ermelinda; Ramalhosa, ElsaPortugal and Spain are important chestnut producers. It is crucial to valorize this nut by using small-size and broken fruits that are usually discarded or used to produce animal feed. In this way, the production of chestnut purés seems to be an excellent alternative to valorize these fruits. Considering that chestnut does not contains lactose and its gluten-free, the present work aimed to use chestnut purée as a growth medium for probiotic microorganisms to obtain in the future a probiotic product that lactose-intolerants and celiac people could consume. In the present work, chestnut purées were produced and inoculated with Lactobacillus casei subsp. casei CECT 4043, Lactococcus lactis subsp. lactis CECT 539 and kefir grains. The following parameters were determined: Colony forming units per millilitre (CFU/mL), pH, total sugars, protein, total phosphorous and total nitrogen. Previously, a rheologic study was also performed to understand the flow behaviour of the chestnut purée when subjected to different temperatures (15, 25, 50 and 75 °C). The chestnut purée showed a pseudoplastic behaviour, as the viscosity decreased with the shear rate. Nevertheless, at the lowest temperatures, some time-dependency was observed. A hysteresis was detected between the loading and unloading curves, suggesting the existence of thixotropy. However, this behaviour was not so evident at high temperatures at 50 and 75 °C. Furthermore, the viscosities of chestnut purées decreased with temperature due to starch gelatinization. Regarding the growth of the microorganisms, Lb. casei and L. lactis reached approximately 109 and 108 UFC/mL of chestnut purée, respectively, after 26 hours fermentation. Concerning the fermentation with kefir, bacterias and yeasts were detected, being the first in higher number than the second at the end of fermentation. At this time, bacteria counts higher than 107 UFC/mL of chestnut purée were achieved. In all fermentations, it was observed a reduction in pH. The initial pH of the chestnut purée was around 6.4, decreasing to 4.7 for Lb. casei and L. lactis, or 3.7 for the kefir grains, at the end of the fermentation. In conclusion, the chestnut purée seems to be a good growth media for probiotic microorganisms.
- Effect of stirring and ultrasound assisted extraction conditions in flavonoids, tannins, antioxidant and antimicrobial activities of chestnut outer shells (Castanea sativa Miller)Publication . Afonso, Maria João A.P.S.; Dias, Rolando; Gomes, Catarina; Pereira, Ermelinda; Guerra, Nelson P.; Ramalhosa, ElsaPortugal is one of the main producersof chestnut in Europe.
- Effect of stirring and ultrasound-assisted extraction conditions in flavonoids, tannins, antioxidant, antimicrobial activities of the outer skin of chestnuts (Castanea sativa Miller)Publication . Afonso, Maria João A.P.S.; Dias, Rolando; Gomes, Catarina; Pereira, Ermelinda; Guerra, Nelson P.; Ramalhosa, ElsaThis study aimed to evaluate the presence of bioactive antioxidant molecules in chestnut outer shells. For this proposal, several extraction procedures were used, specifically different solvents (water, ethanol:water (80:20) and acetone:water (80:20)) combined with two extraction methods (stirring and ultrasounds (US)) and times of extraction. Several chemical assays were applied to evaluate the flavonoids, hydrolysable and condensed tannins contents, and the antioxidant activity by total reducing capacity, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, and reducing power. Some individual compounds were identified by HPLC-UV detection. Furthermore, the antimicrobial activity of the obtained extracts was screened using different microorganisms, namely Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, Proteus mirabilis, Klebsiella pneumoniae), as well as fungi (Candida albicans). The mixture acetone:water (80:20) was the best solvent to extract condensed tannins and flavonoids. It was with this mixture that the best total reducing capacity, (DPPH) radical scavenging activity and reducing power were determined. The highest extraction yield was also obtained with this mixture. Only for the hydrolysable tannins, the most suitable extraction solution was ethanol:water (80:20). The presence of gallic and tannic acids was detected by HPLC-UV. Concerning the extraction methods, only the extracts obtained by the US exhibited antimicrobial activity. The ethanolic extract showed antimicrobial activity against the Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Enterococcus faecalis) and the extracts with acetone:water (80:20) and water showed antimicrobial activity against Proteus mirabilis. The results of this study demonstrated that the chestnut outer shell is a promising source of bioactive compounds.
- Evaluation of the kefir potential to produce a fermented product from chestnut purée: a preliminary studyPublication . Afonso, Maria João A.P.S.; Guerra, Nelson P.; Río, Pablo G.; Martins, Fátima; Baptista, Paula; Pereira, Ermelinda; Ramalhosa, ElsaThe concept of functional food as a source of energy and nutrients, promoting healthy benefit and reducing the disease risk
- Production of nondairy fermented products with chestnut puree as substrate and milk kefir grains or two lactic acid bacteriaPublication . Afonso, Maria João A.P.S.; Ramalhosa, Elsa; Del Río, Pablo G.; Martins, Fátima; Baptista, Paula; Pereira, Ermelinda; Guerra, Nelson P.This work aimed to study the production, for the first time, of three fermented products of chestnut puree (CP) withmilk kefir grains, a higher nisin-producing (Lactococcus (L.) lactis CECT 539) and a higher lactic acid-producing (Lactobacillus (Lb.) casei CECT 4043) lactic acid bacteria (LAB). After studying the CP rheology, the ability of the two LAB to assimilate the carbon sources (starch, sucrose, glucose, and fructose) present in the CP was assayed. The two LAB grew well on glucose, fructose, and sucrose, but they did not use starch. Fermentation of CP with the two LAB and kefir grains allowed us to obtain three fermented products that contained no alcohol and low levels of sugars, lactic, and acetic acids, as well as viable cell counts. After 24 h of fermentation, bacterial counts increased by 2.12 log10 cycles for Lb. casei and 2.44 log10 cycles for L. lactis. Although the final counts for both LAB were very similar (p > 0.05), L. lactis grew faster than Lb. casei and produced a higher concentration of lactic acid. The total microbial counts for kefir increased by 1.16 log10 cycles, after 28 h of incubation, indicating that the microorganisms of the kefir grains adapted well to the composition of the CP. As no ethanol was detected, these results suggest the possibility of producing healthy, nonalcoholic, and low-calorie CPs.