Quantitative Analysis of DL-lactic Acid and Acetic Acid in Kefir Using near Infrared Reflectance Spectroscopy

Abstract

To be able to monitor in real time the concentrations of DL-lactic acid and acetic acid present in Kefir, a self-carbonated fermented milk product, near infrared (NIR) calibration models were constructed based on NIR spectra of 174 samples. Enzymatic tests and gas liquid chromatography were the reference methods used for DL-lactic acid and acetic acid, respectively. The fit of the models and their prediction power were evaluated using segmented cross-validation and an external validation set. The models obtained for DL-lactic acid were found to be acceptable for both cross-validation ( R2=0.90, SECV=0.110 g 100 mL−1 and RPD=3.16) and external validation ( r2=0.87, SEP=0.156 g 100 mL−1 and RPD=2.57). In contrast, the models for acetic acid were found to be unacceptable. The results obtained for both cross-validation ( R2=0.80, SECV=0.013g 100 mL−1 and RPD=2.21) and external validation ( r2=0.44; SEP=0.017 g 100 mL−1 and RPD=1.17) suggested this model requires further development. The application of principal component analysis (PCA) to the entire sample set showed Kefir prepared with laboratory Kefir grains (LG), traditional Kefir grains (TG) and mass cultured Kefir grains (MG) resulted in similar PCA score values in spite of the Kefir grains not having the same origin. PCA was also able to differentiate between fermented and “milky body-like” samples. The findings of this study could serve the dairy industry in monitoring more efficiently the acidity in terms of DL-lactic acid of fermented dairy products.

Digital technologies to assess yoghurt quality traits and consumers acceptability

“…The overtone for water, a major constituent of yoghurt, has previously been identified at 1940 nm, 34 consistent with this major peak. The absorption bands for lactic acid occur between 1800 and 2000 nm 35 but are not visible as a result of the overlapping broad water peak.…”

The Use of near Infrared Spectroscopy on Milk and Milk Products

“…Accuracy for the fat prediction was similar to previous studies on higher fat products of a similar nature. Kefir, a fermented dairy product, has also been assessed by NIR for pH and titratable acidity and lactic and acetic acids using diffuse reflectance across 1000-2500 nm 18,19 Predictive models suitable for screening purposes were developed, as is common with many studies on "real" samples obtaining a wide range of composition upon which to establish a correlation was challenging. The predictive model for lactic acid gave an RPD of 2.6 with an SEP of 0.16 g 100 mL -1 .…”

Acquisition Strategies for Fermentation Processes with a Low-Cost Miniaturized Nir-Spectrometer from Scratch: Issues and Challenges

“…No previous knowledge about the possibility to use low-cost handheld instrument in external reflectance mode to gain information about kefir fermentation is available in literature. Besides that, instrumentation covering the NIR spectral range was used already by Affane et al [18,22] in their works by showing the suitability of NIR spectroscopy to simultaneously estimate characterising parameters in kefir for screening purposes.…”