Keto acid decarboxylase and keto acid dehydrogenase activity detected during the biosynthesis of flavor compound 3-methylbutanal by the nondairy adjunct culture Lactococcus lactis ssp. lactis F9

Abstract

3-Methylbutanal is one of the primary substances that contribute to the nutty flavor in cheese. Lactococcus strains have been shown to have higher aminotransferase and α-keto acid decarboxylase activities compared with other microbes, indicating that they might form a higher amount of 3-methylbutanal by decarboxylation. Several dairy lactococcal strains have been successfully applied as adjunct cultures to increase the 3-methylbutanal content of cheese. Moreover, compared with dairy cultures, the nondairy lactococci are generally metabolically more diverse with more active AA-converting enzymes. Therefore, it might be appropriate to use nondairy lactococcal strains as adjunct cultures to enrich the 3-methylbutanal content of cheese. This study thereby aimed to select a nondairy Lactococcus strain that is highly productive of 3-methylbutanal, identify its biosynthetic pathway, and apply it to cheese manufacture. Twenty wild nondairy lactococci isolated from 5 kinds of Chinese traditional fermented products were identified using 16S rRNA sequence analysis and were found to belong to Lactococcus lactis ssp. lactis. The nondairy strains were then screened in vitro for their production of 3-methylbutanal and whether they met the criteria to become an adjunct culture for cheese. The L. lactis ssp. lactis F9, isolated from sour bamboo shoot, was selected because of its higher 3-methylbutanal production, suitable autolysis rate, and lower acid production. The enzymes involved in the catabolic pathway of leucine were then evaluated. Both α-keto acid decarboxylase (6.96 μmol/g per minute) and α-keto acid dehydrogenase (30.06 μmol/g per minute) activities were detected in nondairy L. lactis F9. Cheddar cheeses made with different F9 levels were ripened at 13°C and analyzed after 90 d by a combination of instrumental and sensory methods. The results showed that adding nondairy L. lactis F9 significantly increased 3-methylbutanal content and enhanced the nutty flavor of the cheese without impairing its textural properties. Thus, nondairy L. lactis F9 efficiently enhanced the biosynthesis of 3-methylbutanal in vitro and in manufactured cheese.

Formation of 3-Methylbutanal and 3-Methylbutan-1-ol Recognized as Malty during Fermentation in Swiss Raclette-Type Cheese, Reconstituted Milk, and de Man, Rogosa, and Sharpe Broth

“…salivarius subsp. thermophilus . Production or inhibition of these compounds could be altered through alteration of the redox potential , or adding dissolved oxygen .…”

“…thermophilus. 17 Production or inhibition of these compounds could be altered through alteration of the redox potential 18,19 or adding dissolved oxygen. 20 However, there are not many other reports about the control of these reactions available.…”

Direct Rub Inoculation of Fungal Flora Changes Fatty Acid Composition and Volatile Flavors in Dry-Aged Beef: A Preliminary Study

“…Moreover, among aldehydes, the peak counts of six compounds (3-methylbutanal, heptanal, benzaldehyde, octanal, nonanal, and 2-nonenal) were significantly higher in DAB (+) than in DAB (−). Notably, 3-methylbutanal and benzaldehyde have been reported to have “nutty” [ 27 ], “almond,” and “burned sugar”-like odors [ 28 ]. Nutty and brown roasted-like odors are used as a common and representative aroma description that characterizes DAB [ 7 ].…”

“…*** p < 0.001; ** p < 0.01; * p < 0.05. The following literature was used as reference for aroma descriptions: a [ 37 ]; b [ 25 ]; c [ 26 ]; d [ 38 ]; e [ 39 ]; f [ 29 ]; g [ 27 ]; h [ 28 ]; i [ 30 ]; j [ 31 ]; k [ 32 ]; l [ 40 ]; and m [ 41 ].…”

Characterization of major odor‐active compounds responsible for nutty flavor in Cheddar cheese according to Chinese taste

“…Cheese with no nutty aroma (‘blank cheese’) in the sensory analysis and containing no 2‐methylbutanal, 3‐methylbutanal, or benzaldehyde in the GC‐MS results was used as the matrix. The concentrations of 2‐methylbutanal, 3‐methylbutanal, and benzaldehyde in the cheese samples were quantified by comparison with their respective standard curves, where these were established using solutions of 3‐methylbutanal and 2‐methylbutanal standard at concentrations of 6.25 to 500 μg/kg and benzaldehyde standard at concentrations of 11.25 to 720 μg/kg 19 . These solutions were diluted with ethanol.…”