A novel sensitive visual count card for detection of hygiene bio-indicator—molds and yeasts in contaminated food

A novel composite hydrogel matrix carrier guar gum@2-oxopropanoic acid sodium salt@konjac glucomannan for sensitive response to active mold and yeast

The synergistic effect of natural guar gum (GG), konjac gum (KGM) and sodium 2-oxopropanoic acid sodium (2-OAS) to designed a novel physical cross-linked three-dimensional network structure GG@2-OAS@KGM as a carrier of active microorganisms for mold and yeast sensitive detection. At the ratio of 6:2:2 (w/w/w), GG@2-OAS@KGM possessed a uniform porous structure. After treatment for 120 h, the hydrogel exhibits higher water holding capacity (WHC, 71.7 %) and swelling stability (SR, 667.5 %), and it also show a stable entrapment efficiency for chromogenic substrates as 95.7 % and 95.3 %, separately. Especially, the 2-OAS as a structural modifier of the free chromophore group indoxyl, to improve the surface rigidity of π-π conjugation effect to enhance the blue fluorescence characteristics of mold and yeast at 365 nm wavelength after incubated for 36 h. Compared with the national standard GB 4789.15-2016 agar plate method (≥5 d), the GG@2-OAS@KGM as active microorganisms carrier provided the fluorescent and visible detection methods can improve mold and yeast detection efficiency and reduce background interference of detection, obviously. This work provides a new reference for the microbial stimuli-responsive chromogenic hydrogel, with potential application in microbiological rapid detection method.

Short-Chain Carboxylates Facilitate the Counting of Yeasts in Sub-High Temperature Daqu

Sub-high temperature Daqu, a traditional solid fermenting agent used in Chinese strong-aroma Baijiu production, is abundant in diverse microorganisms, including bacteria, yeasts, molds, and actinomycetes. Among these, yeasts are pivotal for ethanol production and flavor formation. However, counting yeasts in Daqu is challenging due to interference from molds and bacteria. Antibiotics are employed to inhibit bacterial growth, but there is no practical way to suppress molds without affecting the growth of yeasts. In this study, short-chain carboxylates (C1-C6) were added to the culture medium at various pH conditions to investigate their effects on the growth of molds and yeasts. The results demonstrated distinct inhibitory effects of the short-chain carboxylates, depending on both pH and concentration. Several tested short-chain carboxylates effectively suppressed mold growth on agar plates while leaving yeast growth unaffected. This suggests a simple and feasible method for enhancing the efficiency of yeast isolation and counting in Daqu. Such an approach is valuable for studying yeasts in diverse and complex habitats.