Spontaneously fermented curly kale juice: Microbiological quality, nutritional composition, antioxidant, and antimicrobial properties

Abstract

Nondairy fermented products, such as fruit and vegetable juices, are gaining popularity among consumers worldwide for health-related and economic reasons. The purpose of this study was to determine the changes in microbiological quality; antimicrobial and antioxidant activity; and phenolic, vitamin C, minerals, and cadmium content occurring during spontaneous fermentation of curly kale juice. The fermentation process contributed to a significant growth of lactic acid bacteria, enterococci, and yeasts, while no pathogens of Escherichia coli and Salmonella spp. were observed. The antimicrobial properties of the obtained juice improved during fermentation for all indicator microorganisms. Total phenolic content and antioxidant activity increased from 48 to 116 mg gallic acid equivalent/100 mL and from 4.5 to 6.8 mM Trolox/100 mL, respectively, while the content of vitamin C decreased. The results indicated that 100 mL of juice provided a significant contribution to the recommended mineral intake. Moreover, the content of heavy metal Cd was within acceptable limit (6 µg/kg). Overall, our findings indicate that fermented curly kale juice may become popular in the functional food sector, especially among vegetarians and consumers with lactose intolerance or allergy to milk proteins.Practical Application: As the market for fermented fruit and vegetable products grows, new plant materials rich in biologically active compounds are being sought. Considering the high demand for sauerkraut, the fermentation of other cruciferous vegetables seems interesting. One example is curly kale, which has been classified as "superfood" due to its numerous beneficial health properties, such as strong antioxidant activity, high vitamins, and minerals content. In addition, a market niche exists due to a lack of fermented green curly kale products on the market, making our study particularly relevant.

Probiotic potential of lactic acid bacteria obtained from fermented curly kale juice

“…In the subsequent stages of fermentation and storage, a decrease in the Leuconostoc population corresponded with the succession of Lactobacillus species, notably L. plantarum, L. coryniformis, and L. sakei. As was shown in our previous research, a drop in pH value from 5.08 on day 2 to 4.08 on the last day of fermentation was observed (Szutowska et al 2020). Therefore, it can be concluded that, bacteria of the genus Lactobacillus acted as strong acid producers.…”

“…As shown in our previous studies on fermented curly kale juice (Szutowska et al 2020), after 48 h of spontaneous fermentation, obligate aerobic microorganisms and fungi decreased, while the number of LAB, enterococci, and yeasts increased significantly. Thus, the initial microbiota activity resulted in the creation of an optimal environment for other microorganisms, responsible for stronger acidification of the product and the successful completion of the fermentation process (Szutowska et al 2020). In the subsequent stages of fermentation and storage, a decrease in the Leuconostoc population corresponded with the succession of Lactobacillus species, notably L. plantarum, L. coryniformis, and L. sakei.…”

“…At the initial stage of fermentation (often called the heterolactic or gaseous phase), these bacteria are capable of significantly lowering the pH of the product, producing CO 2 in appropriate amounts, and therefore inhibiting the growth of non-lactic or spoilage microbiota (Hutkins 2019). As shown in our previous studies on fermented curly kale juice (Szutowska et al 2020), after 48 h of spontaneous fermentation, obligate aerobic microorganisms and fungi decreased, while the number of LAB, enterococci, and yeasts increased significantly. Thus, the initial microbiota activity resulted in the creation of an optimal environment for other microorganisms, responsible for stronger acidification of the product and the successful completion of the fermentation process (Szutowska et al 2020).…”

Bacterias ácido lácticas de bebidas vegetales fermentadas: Producción de metabolitos y propiedades antimicrobianas

“…En fermentaciones espontáneas hay menor control sobre los microorganismos que pueden crecer, un ejemplo de ello es el jugo de zanahoria, que tiene mayor cantidad de BAL en comparación con las enterobacterias, 8 de 20 cepas identificadas por secuenciación pertenecen a Leuconostoc y Lactobacillus 110 ; igualmente en la fermentación espontánea de jugo de col rizada se encuentra mayor conteo de BAL y un nulo crecimiento de E. coli y Salmonella spp., la actividad antimicrobiana mejora durante la fermentación contra diferentes cepas patógenas (E. coli, S. enteritidis, Y. enterocolitica, P. aeruginosa, entre otras) 4 .…”

“…Este proceso de fermentación ha sido utilizado en este tipo de alimentos para mejorar su conservación, y determinar los cambios sobre las propiedades nutricionales de la actividad metabólica y enzimática de los microorganismos sobre el producto fermentado 3 . De los procesos fermentativos, el más estudiado es el del ácido láctico producido por las BAL, éstas son las más utilizadas en la fermentación de jugos y hortalizas debido a su inocuidad y beneficios a la salud humana 4 .…”