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ABSTRACT Short-chain carboxylic acids (SCCAs) that are naturally produced by microbial fermentation play an essential role in delaying microbial spoilage. SCCAs are structurally diverse, but only a few of them are routinely used in food biopreservation. This study investigated the effects of environmental pH and intrinsic properties of 21 structurally different SCCAs on the antimicrobial and antibiofilm activity against Salmonella enterica. Inhibition of SCCA toward planktonic and biofilm growth of S. enterica was higher in an acidic environment (pH 4.5) that is common in fermented products, and for SCCA that possessed both a high acid dissociation strength (pKa) (>4.0) and a positive hydrophobicity [octanol/water partition coefficient (log Kow)]. Crotonic and caproic acids were identified as SCCAs with potential as biopreservatives even at near-neutral pH. SCCA with hydrophilic groups such as lactic acid did not inhibit S. enterica at concentrations up to 50 mM, while SCCA with benzene or methyl groups or a double bond prevented S. enterica growth and biofilm formation. Stimulation of biofilm formation was observed for formic, acetic, and propionic acid close to the minimum inhibitory concentration to reduce 50% of cell density (MIC50) of planktonic cells, and for citric and isocitric acid with an MIC50 of ≥50 mM. The presence of low concentrations of formic and propionic acids during biofilm formation conferred protection during eradication possibly due to a pre-adaptation effect, yet two consecutive acid treatments were successful in eradicating biofilms if the first acid treatment was two- to threefold of the MIC50.IMPORTANCEThis study provides a systematic comparison on the antimicrobial and antibiofilm activity of more than 20 structurally different SCCAs against a common food pathogen. We tested the antimicrobial activity at controlled pH and identified the structure-dependent antimicrobial effects of SCCA without the confounding influence of acidification. The combined effect of pKa and log Kow was identified as an important feature that should be considered when deciding for a specific SCCA in the application as antimicrobial. Our results imply that additional phenomena such as the use of SCCA as substrate and cellular pre-adaption effects have to be taken into consideration. We finally present a two-step treatment as an efficient approach to eradicate biofilms, which can be applied for the disinfection of contact surfaces and manufacturing equipment. Results obtained here can serve as guidelines for application of SCCA to avoid the growth of food pathogens and/or to develop biopreserved food systems.

Abstract Biopreservation refers to the use of natural or controlled microbial single strains or consortia, and/or their metabolites such as short‐chain carboxylic acids (SCCA), to improve the shelf‐life of foods. This study aimed at establishing a novel Lactobacillaceae‐driven bioprocess that led to the production of the SCCA propionate through the cross‐feeding on 1,2‐propanediol (1,2‐PD) derived from the deoxyhexoses rhamnose or fucose. When grown as single cultures in Hungate tubes, strains of Lacticaseibacillus rhamnosus preferred fucose over rhamnose and produced 1,2‐PD in addition to lactate, acetate, and formate, while Limosilactobacillus reuteri metabolized 1,2‐PD into propionate, propanol and propanal. Loigolactobacillus coryniformis used fucose to produce 1,2‐PD and only formed propionate when supplied with 1,2‐PD. Fermentates collected from batch fermentations in bioreactor using two‐strain consortia (L. rhamnosus and L. reuteri) or fed‐batch fermentations of single strain cultures of L. coryniformis with rhamnose contained mixtures of SCCA consisting of mainly lactate and acetate and also propionate. Synthetic mixtures that contained SCCA at concentrations present in the fermentates were more antimicrobial against Salmonella enterica if propionate was present. Together, this study (i) demonstrates the potential of single strains and two‐strain consortia to produce propionate in the presence of deoxyhexoses extending the fermentation metabolite profile of Lactobacillaceae, and (ii) emphasizes the potential of applying propionate‐containing fermentates as biopreservatives.

Objective The aim of this study was to characterize the exopolysaccharides (EPS)-producing lactic acid bacteria from Taiwanese ropy fermented milk (TRFM) for developing a clean label low-fat fermented milk. Methods Potential isolates from TRFM were selected based on the Gram staining test and observation of turbid suspension in the culture broth. Random amplified polymorphic DNA-polymerase chain reaction, 16S rRNA gene sequencing, and API CHL 50 test were used for strain identification. After evaluation of EPS concentration, target strains were introduced to low-fat milk fermentation for 24 h. Fermentation characters were checked: pH value, acidity, viable count, syneresis, and viscosity. Sensory evaluation of fermented products was carried out by 30 volunteers, while the storage test was performed for 21 days at 4°C. Results Two EPS-producing strains (APL15 and APL16) were isolated from TRFM and identified as Lactococcus (Lc.) lactis subsp. cremoris. Their EPS concentrations in glucose and lactose media were higher than other published strains of Lc. lactis subsp. cremoris. Low-fat fermented milk separately prepared with APL15 and APL16 reached pH 4.3 and acidity 0.8% with a viable count of 9 log colony-forming units/mL. The physical properties of both products were superior to the control yogurt, showing significant improvements in syneresis and viscosity (p

Our previous studies indicated that Lactobacillus kefiranofaciens HL1, isolated from kefir grain, has strong antioxidant activities and anti-aging effects. However, this strain is difficult to use in isolation when manufacturing fermented products due to poor viability in milk. Thus, the purpose of this study was to apply a co-culture strategy to develop a novel probiotic fermented milk rich in L. kefiranofaciens HL1. Each of four selected starter cultures was co-cultured with kefir strain HL1 in different media to evaluate their effects on microbial activity and availability of milk fermentation. The results of a colony size test on de Man, Rogosa and Sharpe (MRS) agar agar, microbial viability, and acidification performance in MRS broth and skimmed milk suggested that Lactococcus lactis subsp. cremoris APL15 is a suitable candidate for co-culturing with HL1. We then co-cultured HL1 and APL15 in skimmed milk and report remarkable improvement in fermentation ability and no negative impact on the viability of strain HL1 or textural and rheological properties of the milk. Through a co-culture strategy, we have improved the viability of kefir strain HL1 in fermented skimmed milk products and successfully developed a novel milk product with a unique flavor and sufficient probiotics.