Abstract
Plant proteases used in cheesemaking are easily available and could increase the acceptability of cheeses, otherwise hindered by ethical issues (e.g., religions, dietary habits, aversion to genetically engineered food and food ingredients). The milk clotting potential of Onopordum tauricum (Willd.) aqueous extract as an alternative to animal rennet was assessed for the first time in milk of different species (ewe, goat, cow). Among the aerial anatomical parts, i.e., receptacle, leaves, stems, and flowers, only the latter ones showed clotting properties. A response surface methodology (RSM) was used to explore the effects of three independent variables (temperature, pH, volume of coagulant) on the milk clotting activity (MCA) of the flower extract. A second-order polynomial model adequately described the experimental data and predicted a temperature value of 55 °C, a pH value of 4.9–5.7, and a volume of coagulant of 300–500 μL (added to 5 mL of milk) as optimal conditions to maximize the MCA. At a 35 °C temperature and natural milk pH of 6.7–6.8, the estimated MCA of the O. tauricum extract was 72–87, 69–86, and 75–151, in goat’s, ewe’s, and cow’s milk, respectively. In comparison, the MCA of calf rennet was 5.4–4.9, 3.3–14.7, and 4.9–16.7 times higher than that of the plant extract in goat’s, ewe’s, and cow’s milk, respectively.
Highlights
In Southern European and Western African countries, plant proteases have been used for centuries as milk coagulants in cheesemaking, especially for the curdling of raw ovine and caprine milks.Proteolytic activities have been found in the leaves, fruits, flowers, stems, seeds, and latex of several herbs, woody plants, and trees [1]
The results showed that the second-order model (Equation (2)) was significant for all milks, clotted by both the plant extract and animal rennet
(Taurian thistle, bull cottonthistle) flowers were tested in milk of different origin and compared with the clotting performance of commercial calf rennet
Summary
In Southern European and Western African countries, plant proteases have been used for centuries as milk coagulants in cheesemaking, especially for the curdling of raw ovine and caprine milks. The seeds, flowers, and leaves of O. turcicum Danin were found to contain proteolytic enzymes able to coagulate milk [9,10], but Onopordum tauricum Willd. No literature data are currently available about the proteases of Taurian thistle and their behavior as milk clotting agents. In this context, the highly specific caseinolytic activity of the aqueous extract from flowers of spontaneously grown O. tauricum was characterized for the very first time in milk of different species (ewe, goat, cow). A comparison with the performance of commercially available calf rennet was carried out
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