Abstract
The multifunctional properties of autochthonous lactic acid bacteria can be of use for enhancing the sensorial properties of food, as well as in food preservation. An initial screening for antimicrobial, proteolytic, and lipolytic capacities was done in 214 presumptive lactic acid bacteria isolates obtained from Chihuahua cheese manufacturing and during a ripening period of nine months. The antimicrobial screening was done by spot-on-the-lawn tests, using Listeria monocytogenes and Escherichia coli as indicator microorganisms; proteolysis was tested in casein-peptone agar and lipolysis in Mann–Rogosa–Sharpe (MRS)-tributyrin agar. More than 90% of the isolates hydrolyzed the casein, but only 30% hydrolyzed tributyrin; the inhibition of L. monocytogenes in the spot-on-the-lawn assay was used to select 39 isolates that had a bigger inhibition zone (>11.15 mm ± 0.3) than the control (Nisin producer Lactococcus lactis BS-10 Chr Hansen). The selected isolates were grown in MRS to obtain the neutralized cell-free supernatants and verify their antimicrobial activity by agar diffusion and the percentage of growth inhibition techniques. The selected isolates were also growth in casein peptone broth, and the cell-free supernatants were used for the determination of antioxidant activity by the radical scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) techniques. The results were analyzed to identify similarities by cluster analysis, based on their antimicrobial and antioxidant capacities. The isolates were arranged into six clusters; one cluster that included 12 isolates demonstrated L. monocytogenes (784–2811 mm2/mL AU by agar diffusion assay) and E. coli (41%–47% growth inhibition) antimicrobial activity. The isolates clustered in these groups also showed competitive inhibition of both radicals (11%–19% of DPPH and 50%–60% of ABTS). The isolates from cluster one were also identified by 16S rDNA amplification and were identified as Enterococcus faecium. Traditional products such as Chihuahua cheese can be a source or lactic acid bacteria with metabolic properties that can be used in food preparation and preservation.
Highlights
Lactic acid bacteria (LAB) are microorganisms widely dispersed in many environments that have shown desirable characteristics for the food, pharmacy, cosmetics, veterinary, and agriculturalFoods 2020, 9, 276; doi:10.3390/foods9030276 www.mdpi.com/journal/foodsFoods 2020, 9, 276 industries
Chihuahua cheese is a traditional dairy product that is manufactured by Mennonite and non-Mennonite communities in Chihuahua, Mexico, and until recently, they were using raw milk for its preparation
Manufacturing of artisanal Chihuahua cheese includes the use of unpasteurized milk, where autochthonous LAB contributes to the transformation of milk components thanks to enzymatic processes [24]
Summary
Lactic acid bacteria (LAB) are microorganisms widely dispersed in many environments that have shown desirable characteristics for the food, pharmacy, cosmetics, veterinary, and agriculturalFoods 2020, 9, 276; doi:10.3390/foods9030276 www.mdpi.com/journal/foodsFoods 2020, 9, 276 industries. LAB have been used from ancient times owing to their fermentative properties, but they are extensively studied lately for the multi-functional capacities, which include enzymatic and metabolite production, which are of importance in the food industry. LAB with different enzymatic activities can have multiple applications; in the case of proteolytic LAB strains, the generation of bioactive peptides from different protein matrices has gained considerable attention [2]. The bioactivities of these peptides include antioxidant and antimicrobial activity, immunomodulation, angiotensin-converting-enzyme inhibition, as well as anti-thrombotic capacity [3]. In vitro studies have shown that antioxidant peptides from LAB fermentation can participate as radical scavengers, lipid peroxidation inhibitors, metal chelators, and maintain cell viability in oxidative stress conditions [4,5,6]
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