Abstract
The method based on the determination of the amount of active amino groups using o-Phthaldialdehyde (OPA method) can be applied in practice to assess accurately the degree of proteolysis in cheeses. The work establishes that the OPA method gives results that strictly correlate (R2 > 0.80, p < 0.01) with the results of assessing the degree of proteolysis by the Kjeldahl method. The results of the OPA method, expressed in the absorption intensity of the colored sample at a wavelength of 340 nm (OD340), can be converted to the content of soluble nitrogenous substances in cheese (WSN), using the calibration relationship between these indicators.The accuracy of the calibration relationship between WSN and OD340 can be increased (R2 > 0.91, p< 0.01) when using the OPA method in relation to a homogeneous group of cheeses produced by the same technology using the same type of milk clotting enzyme and lactic acid starter culture and having a similar shape of the molecular mass distribution of proteolysis products.The OPA method can be used to assess the content of proteolysis products, which form cheese flavor, in EMС. The results of assessing the degree of proteolysis by the OPA method (OD340) are proportional to both the total content of soluble nitrogen and the proportion of nitrogenous substances in it with a mass of less than 0.5 kDa, which make the greatest contribution to the formation of cheese flavor.The advantage of using the OPA method for assessing proteolysis in cheeses and EMC instead of the Kjeldahl method is a simpler measurement procedure and the possibility of studying more samples in less time.
Highlights
The traditional criterion for assessing proteolysis in cheeses is the ratio of the amount of water soluble nitrogen (WSN) to the amount of total nitrogen (TN) in the cheese with the determination of nitrogen forms by the Kjeldahl method
The degree of proteolysis in cheeses was expressed as a percentage of the absolute content of water soluble nitrogen (WSN) relative to the absolute content of total nitrogen (TN)
The accuracy of the calibration relationship between WSN and OD340 can be increased (R2 > 0.91, p < 0.01) when using the OPA method in relation to a homogeneous group of cheeses produced by the same technology using the same type of milk clotting enzymes (MCE) and lactic acid culture and having a similar shape of molecular mass distribution of proteolysis products
Summary
The traditional criterion for assessing proteolysis in cheeses is the ratio of the amount of water soluble nitrogen (WSN) to the amount of total nitrogen (TN) in the cheese with the determination of nitrogen forms by the Kjeldahl method This is a laborious and time-consuming method. The OPA method has not yet found widespread use in assessing the degree of cheese maturity This is due to the well-established tradition of assessing the degree of proteolysis in cheeses by the WSN content, as well as the absence of a strict relationship between the optical density of the colored complexes at a wavelength of 340 nm (OD340) and the WSN content in cheeses. For the introduction of the OPA method into widespread use, it is necessary to develop a method for accurately recalculating the OD340 indicator obtained using the OPA method into the WSN indicator obtained using the Kjeldahl method
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