Abstract
The study focuses on rapid determination of free amino acids produced during the ripening of cheese, by using near infrared spectroscopy. Analyses of 96 samples of Edam cheese (30% and 45% of fat in dry matter) were performed at monthly intervals up to the ripening age of 6 months. In total, 19 amino acids were analysed with infrared spectrometer using two different methods, either in the regime of reflectance in the integrating sphere of the apparatus or using a fibre optic apparatus with the fibre optic probe. Reference data based on high-performance liquid chromatography were used for calibration of the spectrophotometer. Calibration models were developed using a partial least square algorithm and tested by means of cross-validation. When measured with the integrating sphere and with the probe, the values of correlation coefficients ranged from 0.835 to 0.993 and from 0.739 to 0.995, respectively. Pairedt-test did not show significant differences between the reference and predicted values (P< 0.05). The results of this new calibration method showed the possibility of near infrared technology for fast determination of free amino acids, which occur during the ripening of Edam cheese. The content of free amino acids allow us to prepare Edam cheese quickly and efficiently for sale or to prepare the material for processed cheese.
Highlights
The key factor of ageing in cheese is its chemical composition
The highest correlation coefficients were found in models for phenylalanine (0.993) and tryptophan (0.992) in samples of Edam cheese measured in the integrating sphere and for phenylalanine (0.995) and ornithine (0.993) measured by the probe
NIR spectroscopy shows good ability to set values of fats, water content and proteins in natural and processed cheese and the obtained results correlate well with other reference methods (Rodriguez-Otero et al 1995; McQueen et al 1995; Adamopoulos et al 2001; Curda et al 2001; McKenna 2001). These methods are of interest especially when monitoring the process of cheese ageing because they enable analysis of changes in their composition
Summary
The key factor of ageing in cheese is its chemical composition. The water content is one of the most important factors in regulation of curd hydrolysis and microbial growth in manufactured cheese (Janštová et al 2010). Changes in and analysis of major compounds presented in young cheese are not good indicators of the course of ripening. This is because these cheese components are stable and more or less unchanging (Hering et al 2008). The type and quantity of free amino acids present in cheese influences its taste and indicates the degree of ageing and its progress. The composition and spectrum of free amino acids change depends on the type and age of cheese. The aim of the study was to evaluate the possibility of using near infrared spectrometry for determination of free amino acids which arise during the ripening of Edam cheese as an important indicator for the production of processed cheese. The results obtained by measurements performed in the integrating sphere and by probe were compared
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