Measurement of water activity aw of sterile liquid and solid samples was performed with the LabMaster®-aw instrument (Novasina AG, Switzerland). The measurement is based on resistive electrolytic humidity analysis. System parameters were set at 5 min stabile observation time for temperature and water activity and measurement was performed at 25 °C. A volume of 5 ml per sample was filled in a dry and clean sample cup (Ø 40 mm, 12 mm, polypropylene, ePW sample cups, Novasina) and each sample was treated 10 min in the pre-condition chamber of the instrument before measurement.
Labmaster aw instrument
Manufactured by Novasina
Sourced in Switzerland
The LabMaster®-aw instrument is a precision instrument designed for the measurement of water activity (aw) in various samples. It provides accurate and reliable water activity readings, which are essential for quality control and product development in various industries.
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6 protocols using labmaster aw instrument
1
Water Activity Measurement of Sterile Samples
2
Water Activity Measurement of Minced Meat
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Portions of meat without fat were separated for sample preparation. The water activity of minced meat was measured triplicate in samples of 10 g at 20 °C in the Lab-master aw instrument (Novasina AG, Lachen, Switzerland). The apparatus was calibrated using standard salts in the aw range of 0.7 to 1.
3
Physicochemical properties of chilled fuets
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Technological properties were evaluated during the chilled storage of the fuets, at 0, 15 and 30 days.
The pH was determined (in quadruplicate) at room temperature in water in a ratio of 1:10 (w/v) using a 827 Metrohm pH-meter (Metrohm AG, Zofingen, Switzerland).
Water activity (Aw) was measured (in triplicate) at 25 °C, after removing the casing, in a LabMaster-aw instrument (model 1119977, Novasina AG, Lachen SZ, Switzerland).
Colour was measured (ten times) in fuet cross-sections using a Konica Minolta CM-3500 D spectrophotometer (Konica Minolta Business Technologies, Tokyo, Japan) set to D65 illuminant/10° observer. The CIELAB colour space was used to obtain the colour coordinates L* (black (0) to white (100)), a* (green (–) to red (+)), and b* (blue (–) to yellow (+)).
Texture profile analysis (TPA), as described by Bourne [32 ], was carried out using a TA-XTplus Texture Analyzer (Stable Micro Systems Ltd., Godalming, UK) equipped with a 30 kg load cell. Six cores (diameter = 12 mm, height = 20 mm) per sample were axially compressed to 50% of their original height at a crosshead speed of 0.8 mm/s to calculate hardness (N). The tests were performed on the samples at room temperature immediately after refrigeration at 3 °C.
The pH was determined (in quadruplicate) at room temperature in water in a ratio of 1:10 (w/v) using a 827 Metrohm pH-meter (Metrohm AG, Zofingen, Switzerland).
Water activity (Aw) was measured (in triplicate) at 25 °C, after removing the casing, in a LabMaster-aw instrument (model 1119977, Novasina AG, Lachen SZ, Switzerland).
Colour was measured (ten times) in fuet cross-sections using a Konica Minolta CM-3500 D spectrophotometer (Konica Minolta Business Technologies, Tokyo, Japan) set to D65 illuminant/10° observer. The CIELAB colour space was used to obtain the colour coordinates L* (black (0) to white (100)), a* (green (–) to red (+)), and b* (blue (–) to yellow (+)).
Texture profile analysis (TPA), as described by Bourne [32 ], was carried out using a TA-XTplus Texture Analyzer (Stable Micro Systems Ltd., Godalming, UK) equipped with a 30 kg load cell. Six cores (diameter = 12 mm, height = 20 mm) per sample were axially compressed to 50% of their original height at a crosshead speed of 0.8 mm/s to calculate hardness (N). The tests were performed on the samples at room temperature immediately after refrigeration at 3 °C.
4
Fungal Growth at Low Water Activity
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Measurements of the growth of fungi at lower steady-state aw were done as described by Segers et al. (40 (link)). Fungi were grown on malt extract agar (MEA) complemented with 0 to 50% glycerol (aw of 0.99 to 0.75) to assess the lower limits of growth with respect to aw. The aw values for the glycerol-agar mixtures were determined before and after growth experiments by using a Novasina labmaster-aw instrument (Novasina, Lachen, Switzerland) as also described by Segers et al. (40 (link)). Cultures were inoculated with 3 μl of a spore solution containing 1 × 106 conidia ml−1. These conidia were harvested from a 7-day-old culture by use of a T spatula (VWR, Amsterdam, The Netherlands), using ice-cold sterile 10 mM N-(2-acetamido)-2-aminoethanesulfonic acid, 0.02% Tween 80 (ACES; pH 6.8). The colony diameter was measured 3 times a week for 3 weeks. The growth speed was determined from the regression coefficients based on graphs of each colony.
5
Inhibition of A. flavus Growth on Gouda Cheese
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One cm thick wedges of commercial Gouda type cheese of 10 cm 2 were dipped in ethanol and dried in a laminar flow cabinet (Bio Flow II, Telstar, Tarrasa, Spain). Three sample wedges were separately placed in pre-sterilized containers after vapour-liquid equilibrium with a saturated KCl solution, to reach a w values of 0.84, similar to those found in the rind at the final stage of cheese ripening (Rüegg and Blanc, 1981) . Next, PgAFP was added in 200 mL PBS to treated samples at two concentrations (18 and 35 mg/cm 2 ) and left to dry in a flow cabinet. The non-treated batch received the same volume of PBS but with no PgAFP. Then, a volume of 100 mL of a suspension of A. flavus spores was spread onto the upper surface of cheese wedges to reach c.a. 10 5 conidia/cm 2 . The containers were incubated for 96 h and growth of the resulting mycelia was assessed. This test was performed in triplicate. Water activity (a w ) was determined in cheese wedges by a LabMASTER-aw instrument (Novasina AG, Lachen, Switzerland) both before inoculation and after 96 h incubation. This test was run in three independent trials.
6
Evaluating Pâté's Water Activity, pH, and Color
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The water activity was determined in polyethylene capsules with circa 5 g of pâté were placed in a Labmaster-aw instrument (Novasina, Lachen, Switzerland). Analyses were performed at 25 °C. The pH was evaluated by mixing 10 g of pâté with 100 mL of distilled water and then stirring the mixture in a magnetic plate. pH measurements were made by using a pH Basic 20 instrument (Crison, Barcelona, Spain). The color of the pâtés was measured by using a CR-400 Chromameter (Konica Minolta, Tokyo, Japan), and the L*, a* and b* parameters were registered, as specified by the International Commission on Illumination. The total color difference over the time between samples was evaluated with the ΔE*ab parameter, following Equation (2) [19 (link)]:
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