title: Monitoring lactic acid production during milk fermentation by in situ quantitative proton nuclear magnetic resonance spectroscopy.
abstract: When fermenting milk, lactic bacteria convert part of α- and β-lactoses into d- and l- lactic acids, causing a pH decrease responsible for casein coagulation. Lactic acid monitoring during fermentation is essential for the control of dairy gel textural and organoleptic properties, and is a way to evaluate strain efficiency. Currently, titrations are used to follow the quantity of acids formed during jellification of milk but they are not specific to lactic acid. An analytical method without the use of any reagent was investigated to quantify lactic acid during milk fermentation: in situ quantitative proton nuclear magnetic resonance spectroscopy. Two methods using in situ quantitative proton nuclear magnetic resonance spectroscopy were compared: (1) d- and l-lactic acids content determination, using the resonance of their methyl protons, showing an increase from 2.06 ± 0.02 to 8.16 ± 0.74 g/L during 240 min of fermentation; and (2) the determination of the α- and β-lactoses content, decreasing from 42.68 ± 0.02 to 30.76 ± 1.75 g/L for the same fermentation duration. The ratio between the molar concentrations of produced lactic acids and consumed lactoses enabled cross-validation, as the value (2.02 ± 0.18) is consistent with lactic acid bacteria metabolism.
authors: INRA, UMR 1145 Ingénierie Procédés Aliments, Group of Molecular Gastronomy, F-75005 Paris, France; AgroParisTech, UMR 1145 Ingénierie Procédés Aliments, Group of Molecular Gastronomy, AgroParisTech, F-75005 Paris, France; Yoplait France, F-92641 Boulogne, France. Electronic address: romain.bouteille@yoplait.fr.
authors: R
authors: R
authors: Bouteille
authors: INRA, UMR 1145 Ingénierie Procédés Aliments, Group of Molecular Gastronomy, F-75005 Paris, France; AgroParisTech, UMR 1145 Ingénierie Procédés Aliments, Group of Molecular Gastronomy, AgroParisTech, F-75005 Paris, France.
authors: M
authors: M
authors: Gaudet
authors: Yoplait France, F-92641 Boulogne, France.
authors: B
authors: B
authors: Lecanu
authors: INRA, UMR 1145 Ingénierie Procédés Aliments, Group of Molecular Gastronomy, F-75005 Paris, France; AgroParisTech, UMR 1145 Ingénierie Procédés Aliments, Group of Molecular Gastronomy, AgroParisTech, F-75005 Paris, France.
authors: H
authors: H
authors: This
mesh_terms: D000818:Animals; D005260:Female; D005285:Fermentation; D019344:Lactic Acid / Q000096:biosynthesis*; D048668:Lactobacillus delbrueckii / Q000378:metabolism; D007785:Lactose / Q000032:analysis / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008892:Milk / Q000737:chemistry / Q000382:microbiology*; D048249:Streptococcus thermophilus / Q000378:metabolism
chemical_list: D019344:Lactic Acid; D007785:Lactose