Abstract
In this work, the individual and interactive effects of temperature and pH on the proteolytic activity of Lactococcus lactis LCL strain in milk were studied by quadratic Response Surface Methodology. The effects of the selected variables have been analysed using a Central Composite Design and the maximum response (proteolysis rate) under the optimum values of variables and of a satisfactory fit model was realized. The mathematical relationship of the proteolytic activity on the two significant independent variables can be approximated by a nonlinear polynomial model. Predicted values were found to be in a good agreement with experimental values (R2 = 0.937) demonstrating the good significance of the model. The result of optimization predicted by the model has shown that the maximal result for the proteolysis rate revolved around of 43.7 ± 1.4 % at the optimal condition (30°C and pH 7).
Highlights
Lactic acid bacteria belong to a well-known group of bacteria that presents a high biotechnological potential, have been used as mixtures of selected bacteria as starter or adjunct cultures in food production, especially in fermented dairy products, in the milk, vegetables, ensilage and meat industries (González et al 2010; Konings et al 2000; Ni et al 2015)
To grow at a high cellular density, lactic acid bacteria need to overcome their auxotrophy for certain amino acids by hydrolyzing milk caseins to benefit from an amino acid source
This study is essentially based on the using of a simple technique widely used in laboratories, whose main scope relates to the qualitative aspect (SDS-PAGE), and by coupling it to a subsequent image analysis using the free software ImageJ of NIH (USA); we erected it at a quantitative technique grade by minimizing during this transition its background noise. This experimental way combined with that of the use of Box-Wilson Central Composite Experimental Design (CCD), allowed us to establish a methodological approach, to our knowledge not documented until now for this area of interest using the whole cells as source of proteolytic enzymes to optimize their activity in milk, by seeking the appropriate physicochemical conditions, interacting at the same time for a maximum activity of interest, the aim of which is a probable release of a set of acids amines and peptides of interest. This experimental approach is certainly characterized by a background noise who would may be not negligible, and by using this methodological approach, we have significantly reduced this background noise, justified by the obtained correlation coefficient (R2 = 0.937), which means that the model proposed for the proteolytic activity in milk by Lactococcus lactis LCL strain, is correct and fulfills the robustness criteria of a model
Summary
Lactic acid bacteria belong to a well-known group of bacteria that presents a high biotechnological potential, have been used as mixtures of selected bacteria as starter or adjunct cultures in food production, especially in fermented dairy products, in the milk, vegetables, ensilage and meat industries (González et al 2010; Konings et al 2000; Ni et al 2015). These bacteria have been used by mankind for centuries due to their ability to produce desirable sensory characteristics, to improve digestibility and to inhibit pathogenic and spoilage microorganisms. Milk proteins may be a source of functional ingredients, especially the caseins, as the main precursors of biologically active peptides, which are encrypted in their primary structure, who cannot modulate physiology of the consumer only after their proteolytic release (Bhat and Bhat 2011; Silva and Malcata 2005)
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