Sidonia Martínez

Thermal inactivation of Bacillus cereus spores formed at different temperatures

The effects of the sporulation temperature in the range 20-45 degrees C on the D and z values of three isolates of Bacillus cereus (ATCC 4342, 7004 and 9818) were investigated. The strains were found to differ in their response. Higher D100 values (around 10-fold) were obtained with isolates 4342 and 9818 when the sporulation temperature increased from 20 to 45 degrees C. With isolate 7004 (the least heat resistant of the three strains), however, the most thermal tolerant spores were obtained at 35 degrees C. The z values were not significantly modified (P > 0.05) by the sporulation temperature. Mean z values of 7.46+/-0.22 degrees C for isolate 4342, 7.80+/-0.40 degrees C for 7004 and 8.09+/-0.33 degrees C for 9818 were obtained.

The effects of ripening stage and processing systems on vitamin C content in sweet peppers (Capsicum annuum L.)

Morrón pepper of ‘Fresno de la Vega’ (Capsicum annuum L.) is a big sweet variety cultivated in the province of León (northwestern Spain). Changes in vitamin C content of this variety of pepper as a function of ripeness, storage and different preservation systems were studied. The ascorbic acid content increases in peppers as they ripen. For green mature, breaker and red peppers values of 107.3±1.84, 129.6±3.11 and 154.3±7.56 mg/100 g edible portion were found. The vitamin C content for green mature and breaker peppers stored at room temperature (20°C) increased up to 10 days of storage, reaching similar values as those obtained for red peppers direct from the plant. However, stored red ripe peppers showed a significant loss in vitamin C content, around 25%. Refrigeration at 4°C for up to 20 days did not change the ascorbic acid content, except for red peppers, which showed losses around 15%. The ascorbic acid content was altered in response to the preservation procedures assayed. Reductions of 12% and 20–25% during the water blanching and canning process, respectively, were observed. Ascorbic acid retention during freezing was 60%, increasing when the product was previously blanched (87%). Dehydration of peppers resulted in an 88% decrease in ascorbic acid content, whereas freeze-drying did not cause significant losses.

Thermal inactivation of Bacillus cereus spores affected by the solutes used to control water activity of the heating medium

The heat resistance of B. cereus spores (ATCC 7004, 4342 and 9818) over a wide temperature range (92-125 degrees C) in aqueous solutions of NaCl, LiCl, sucrose and glycerol at different water activities (1.00-0.71) was investigated. Sodium chloride in the heating medium tended to protect the spores of B. cereus against heat. The z-values increased significantly (P < 0.05) at and above a concentration of 4.0 M. The effects of LiCl were lower than those caused by the NaCl at the same a(w) values. An increase in z-values was observed. but the differences were only statistically significant (P<0.05) at the highest concentration tested (5.0 M). A concentration of sucrose 0.87 M caused in all cases a reduction in D-values, which was most pronounced for strains 4342 and 9818. With increasing concentration of sucrose ( > 0.87 M), the D-values showed an increase, although only those obtained for strain 4342 in sucrose solutions 2.22 M were higher than those found in pure water. The z-values were significantly higher (P < 0.05) when sucrose was added at concentrations above 1.42 M, except for strain 4342. When a(w) was lowered from 0.96 to 0.71 with glycerol, D-values obtained gradually increased, about 30, 50 and 60 fold for 4342, 7004 and 9818 strains, respectively. No significant effect on z-values were detected.

Thermal inactivation of Enterococcus faecium: effect of growth temperature and physiological state of microbial cells.

Aims:  To provide data on the effects on culture temperature and physiological state of cells on heat resistance of Enterococcus faecium, which may be useful in establishing pasteurization procedures.

Biogenic amine content during the manufacture of dry-cured lacón, a spanish traditional meat product : Effect of some additives

The content of nine biogenic amines (agmatine, tryptamine, 2-phenylethylamine, putrescine, cadaverine, histamine, tyramine, spermidine and spermine) was determined throughout the manufacture of dry-cured lacón, a traditional dry-salted and ripened meat product made in the north-west of Spain from the fore leg of the pig following a similar process to that of dry-cured ham. The effect of the use of additives (glucose, sodium nitrite, sodium nitrate, sodium ascorbate and sodium citrate) on the biogenic amine content during manufacture was also studied. Tryptamine and spermine were the main biogenic amines in fresh meat, while tryptamine and cadaverine were the most abundant at the end of the manufacturing process. During ripening the total amine content increased significantly (P<0.05) in the batches made both without and with additives. The use of additives significantly (P<0.05) increased the total amine content and the content of tryptamine, tyramine and histamine. The total biogenic amine content at the end of the manufacturing process was low as expected for a product in which there is little active microbial metabolism during manufacture.

The composition of Arnoia peppers (Capsicum annuum L.) at different stages of maturity

‘Arnoia’ peppers (Capsicum annuum L. var. annuum cv. Arnoia) are cultivated in areas surrounding the Arnoia River, in Galicia (northwest Spain). Some physical and chemical changes associated with maturation and storage conditions have been reported. Changes in gross composition, the main physico-chemical parameters and mineral composition were evaluated in peppers collected directly from plants and at two different states of maturity (green and red fruits), and in commercially available peppers (green fruits). The total soluble solid content and titratable acidity increased significantly during ripening. The fat, ash and protein contents were generally significantly higher in the red pepper than in the green peppers. The total ascorbic acid in red peppers was 27% higher than that of green peppers. The vitamin C content of commercially available green peppers was up to 39% lower than in the freshly picked peppers. Potassium was the most abundant mineral in green and red peppers. Green peppers purchased in the supermarket contained higher amounts of calcium and sodium than the freshly picked peppers. The levels of zinc, manganese and copper were similar in all of the different samples.

Heat resistance of Bacillus cereus spores: effects of milk constituents and stabilizing additives.

Heat resistance of Bacillus cereus spores (ATCC 7004, 4342, and 9818) heated in different types of milk (skim, whole, and concentrated skim milk), skim milk containing stabilizing additives (sodium citrate, monopotassium phosphate, or disodium phosphate, 0.1%), and cream was investigated. Thermal resistance experiments were performed at temperatures within the range of 92 to 115 degrees C under continuous monitoring of pH. For strain 4342 no significant differences (P < 0.05) in D values were detected in any case. For strains 7004 and 9818 higher D values of about 20% were obtained in whole and concentrated skim milk than those calculated in skim milk. From all stabilizing additives tested, only sodium citrate and sodium phosphate increased the heat resistance for strain 9818. However, when the menstruum pH was measured at the treatment temperature, different pH values were found between the heating media. The differences in heat resistance observed could be due to a pH effect rather than to the difference in the substrates in which spores were heated. In contrast, when cream (fat content 20%) was used, lower D values were obtained, especially for strains 7004 and 9818. z values were not significantly modified by the milk composition, with an average z value of 7.95+/-0.20 degrees C for strain 7004, 7.88+/-0.10 degrees C for strain 4342, and 9.13+/-0.16 degrees C for strain 9818.

Sensitization of thermally injured spores of Bacillus stearothermophilus to sodium benzoate and potassium sorbate

The effects of sodium benzoate and potassium sorbate added to the recovery medium, at different pH values (6·5, 6·0 and 5·0), on the recovery rates and heat resistance of Bacillus stearothermophilus spores (ATCC 12980, 7953, 15951 and 15952) were investigated. Heated spores of strains 12980 and 7953 were inhibited by sorbate concentrations over 0·05%. Potassium sorbate at concentrations as low as 0·025%, and sodium benzoate at 0·1%, were very effective inhibitory agents for heat‐damaged spores. Their effectiveness always increased at pH 5·0, at which no growth occurred, with sodium benzoate for strains 7953, 15951 and 15952, and with potassium sorbate for strains 15951 and 15952. Decimal reduction times, whenever recovery was possible, were not significantly (P > 0·05) affected. None of these compounds modified the z‐values obtained for the spores of the four strains, which had a mean value of 7·53 ± 0·28.

Oxidation of edible animal fats. Comparison of the performance of different quantification methods and of a proposed new semi-objective colour scale-based method

The agreement among the results determined for the main parameters used in the evaluation of the fat auto-oxidation was investigated in animal fats (butter fat, subcutaneous pig back-fat and subcutaneous ham fat). Also, graduated colour scales representing the colour change during storage/ripening were developed for the three types of fat, and the values read in these scales were correlated with the values observed for the different parameters indicating fat oxidation. In general good correlation among the values of the different parameters was observed (e.g. TBA value correlated with the peroxide value: r=0.466 for butter and r=0.898 for back-fat). A reasonable correlation was observed between the values read in the developed colour scales and the values for the other parameters determined (e.g. values of r=0.320 and r=0.793 with peroxide value for butter and back-fat, respectively, and of r=0.767 and r=0.498 with TBA value for back-fat and ham fat, respectively).

Effects of different cooking methods on the antioxidant capacity and flavonoid, organic acid and mineral contents of Galega Kale (Brassica oleracea var. acephala cv. Galega)

Abstract Brassica spp. are good sources of bioactive substances, which are known to have beneficial health effects. The objective of this work was to evaluate the effect of different cooking methods (boiling, steaming, microwaving, pressure cooking and vacuum cooking) on the antioxidant capacity and on the flavonoid, organic acid and mineral contents of Galega kale. Results indicate that this vegetable has a high antioxidant capacity and high contents of total flavonoids, organic acids, and minerals such as potassium and calcium. All of the cooking methods yielded losses of antioxidant capacity and of total flavonoids, organic acids and minerals, relative to the contents in fresh kale. Steaming proved to be the best method of preserving the antioxidant capacity and bioactive compounds. Although cooking did not cause large losses of oxalic acid, the resulting oxalate:calcium ratio was rather low (<2). The present data demonstrate that the different cooking methods have different effects on the bioactive compounds in kale, and that it is important the optimisation of such methods in order to minimise losses of the nutritional properties.