Real-Time Monitoring of Chemical Changes in Three Kinds of Fermented Milk Products during Fermentation Using Quantitative Difference Nuclear Magnetic Resonance Spectroscopy

Abstract

Fermented milk products are rising in popularity throughout the world as a result of their health benefits, including improving digestion, normalizing the function of the immune system, and aiding in weight management. This study applies an in situ quantitative nuclear magnetic resonance method to monitor chemical changes in three kinds of fermented milk products, Bulgarian yogurt, Caspian Sea yogurt, and kefir, during fermentation. As a result, the concentration changes in nine organic compounds, α/β-lactose, α/β-galactose, lactic acid, citrate, ethanol, lecithin, and creatine, were monitored in real time. This revealed three distinct metabolic processes in the three fermented milk products. Moreover, pH changes were also determined by variations in the chemical shift of citric acid during the fermentation processes. These results can be applied to estimate microbial metabolism in various flora and help guide the fermentation and storage of various fermented milk products to improve their quality, which may directly influence human health.

Effects of applying Lactobacillus helveticus H9 as adjunct starter culture in yogurt fermentation and storage

“…The use of L. helveticus H9 increased lactate and acetate contents but decreased citrate content, which was also seen when other lactic acid bacteria were used, such as Lactobacillus plantarum (de Figueroa et al, 1996) and L. helveticus ATCC 15807 (Torino et al, 2005). Citric acid is an intermediate of the tricarboxylic acid cycle, which is produced from glucose through the glycolytic pathway and oxidative conversion of pyruvic acid into acetyl-CoA by pyruvate dehydrogenase (Lu et al, 2018). However, the concentration of citrate increased after 1 d of storage, perhaps due to the excessive pyruvic acid accumulated during milk fermentation, which was progressively metabolized into citrate at the beginning of the cold storage.…”

Metabolic profiling of natural and cultured Cordyceps by NMR spectroscopy

“…The quantitative 1 H NMR spectra were acquired with pre-saturation of HDO signal using a PRESAT pulse sequence as follows: 64K datapoints distributed on a 6,000 Hz spectral width, providing a spectral resolution of 0.183 Hz; acquisition time, 5.461 s; recycle delay, 20 s; and 32 scans. To obtain a proper recycle delay time value, the spin-lattice relaxation time ( T 1 ) was determined using the partial relaxation method 36,37 . The 13 C{ 1 H} NMR spectra were acquired with aid of S2PUL pulse sequence as follows: 64K datapoints distributed on a 32,000 Hz spectral width, providing a spectral resolution of 0.977 Hz; acquisition time, 1.024 s; recycle delay, 2 s; and 100,000 scans.…”

An NMR Metabolomics Approach to Investigate Factors Affecting the Yoghurt Fermentation Process and Quality

“…Pyruvate is mainly produced by ST. ST has a pyruvate-formate lyase, which LB lacks, therefore, ST can provide LB with the necessary formate for purine biosynthesis and for growth [ 21 ]. Moreover, pyruvate can be used to produce citrate [ 22 ], and through citrate metabolism it is also used by ST to produce acetate, formate, acetaldehyde and diacetyl, and it is thus very important in the aroma development of yoghurt [ 20 ]. The rapid decrease in pyruvate in samples containing LB, however, is probably caused by its employment for lactate production [ 23 ], also mirrored by the lactate increase in these samples at the same time-points.…”

“…Lactate shows an increase in concentration during fermentation with a faster slope after 4 h and a further increase in concentration from 8 to 24 h. ST is the strain that displays the lowest increase in lactate and the highest is observed for LB and MX in HT milk. Lactate is also produced through pyruvate [ 14 , 22 , 27 ], thus, the decrease in pyruvate for LB and MX can also be explained by lactate production.…”