A Chewing Gum Containing Heyndrickxia coagulans SNZ1969® and Volatile Sulphur Compounds: An Exploratory Secondary Analysis of a Double-Blind Randomized Controlled Trial

Background: Chewing gum may reduce oral malodor through salivary stimulation and may also serve as a carrier for oral probiotics. Evidence on Heyndrickxia coagulans in this setting is lacking. Methods: This exploratory secondary analysis used data from a randomized, blinded, placebo-controlled study in which 52 healthy adults were assigned to a sugar-free gum with H. coagulans SNZ1969® or to a matched placebo gum for four weeks. Hydrogen sulphide (H2S) and methyl mercaptan (CH3SH) were measured by OralChroma™ at baseline (T0), during intervention (T1–T2), and one week after gum discontinuation (T3). Dental plaque 16S rRNA profiles from the parent trial were re-analysed in relation to VSC values. Results: Forty-four participants completed follow-up. H2S and CH3SH concentrations did not differ between probiotic and placebo groups at any visit, and changes from baseline were also similar between arms. In the probiotic group, H2S was lower than baseline at T2 (p = 0.008) and T3 (p = 0.031), but this within-arm decrease was not greater than the change seen with placebo. Taxon-level analyses suggested nominal associations with taxa plausibly linked to sulphur metabolism, mainly for H2S, but no association survived false-discovery-rate correction. Conclusions: The probiotic gum did not show a statistically significant additional effect on VSC concentrations compared with the placebo gum. The within-arm H2S decrease and microbiome signals are exploratory and require confirmation in trials designed for participants with clinically established halitosis.