Abstract
Food fermentation under pressure has been studied in recent years as a way to produce foods with novel properties. The purpose of this work was to study kefir production under pressure (7–50 MPa) at different temperatures (17–32 °C), as a case study of unconventional food fermentation. The fermentation time to produce kefir was similar at all temperatures (17, 25, and 32 °C) up to 15 MPa, compared to atmospheric pressure. At 50 MPa, the fermentation rate was slower, but the difference was reduced as temperature increased. During fermentation, lactic and acetic acid concentration increased while citric acid decreased. The positive activation volumes (Va) obtained indicate that pressure decreased the fermentation rate, while the temperature rise led to the attenuation of the pressure effect (lower Va). On the other hand, higher activation energies (Ea) were observed with pressure increase, indicating that fermentation became more sensitive to temperature. The condition that resulted in a faster fermentation, higher titratable acidity, and higher concentration of lactic acid was 15 MPa/32 °C. As the authors are aware, this is the second work in the literature to study the combined effect of pressure and temperature on a fermentative process.
Highlights
Kefir is a lightly carbonated, low-alcohol dairy beverage with a creamy consistency and a pH ≈ 4.2–4.6 [1,2,3] that is produced by milk fermentation with starter cultures or kefir grains that contain lactic acid bacteria; yeasts; and, in some cases, acetic acid bacteria [4,5]
After the study of fermentation at control temperature, we studied the effect of pressure at different fermentation temperatures
Kefir production under unconventional conditions of higher pressure showed that the time needed to produce kefir was similar at all temperatures (17, 25, and 32 ◦ C) at 7 and 15 MPa compared to
Summary
Kefir is a lightly carbonated, low-alcohol dairy beverage with a creamy consistency and a pH ≈ 4.2–4.6 [1,2,3] that is produced by milk fermentation with starter cultures or kefir grains that contain lactic acid bacteria; yeasts; and, in some cases, acetic acid bacteria [4,5]. Kefir quality is affected by different fermentation parameters, such as type of kefir culture, inoculation ratio, time, and temperature [1]. New applications for HP have been studied, such as the use of sub-lethal pressures (5–100 MPa) in the microbial fermentation processes [10,11,12,13,14,15,16]. Only few studies have been published about fermentation under HP, it was reported that when microorganisms are under these levels of pressure they can develop specific stress response mechanisms, such as
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