Antifungal effect of kefir fermented milk and shelf life improvement of corn arepas

GAMBA, RAÚL RICARDO; CARO, CARLOS ANDRÉS; MARTÍNEZ, OLGA LUCÍA; MORETTI, ANA FLORENCIA; GIANNUZZI, LEDA; DE ANTONI, GRACIELA LILIANA; LEÓN PELÁEZ, ÁNGELA MARÍA

INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 235 p. 85 - 92

0168-1605

Fungal contamination negatively affects the production of cereal foods such as arepa loaf, an ancient corn bread consumeddaily in several countries of Latin-America. Chemical preservatives such as potassium sorbate are applied in orderto improve the arepa´s shelf life and to reduce the health risks. The use of natural preservatives such as natural fermentedproducts in food commodities is a common demand among the consumers. Kefir is a milk fermented beverage obtainedby fermentation of kefir grains. Its antibacterial and probiotic activity has been exhaustively demonstrated.Our objectives were to determine the antifungal effect of kefir fermented milk on Aspergillus flavus AFUNL5 in vitroand to study if the addition of kefir fermented milk to arepas could produce shelf life improvement.We determined the antifungal effect on solid medium of kefir cell-free supernatants (CFS) obtained under differentfermentation conditions. Additionally, we compared the antifungal effect of kefir CFS with that obtained with unfermentedmilk artificially acidified with lactic plus acetic acids (lactic and acetic acids at the same concentration determinedin kefir CFS) or with hydrochloric acid. Finally, kefir was added to the corn products either in the loaf recipe (kefir-bakedarepas) or sprayed onto the baked-loaf surface (kefir-sprayed arepas). The loaves´ resistance to natural and artificial fungalcontamination and their organoleptic profiles were studied.The highest fungal inhibition on solid medium was achieved with kefir CFS produced by kefir grains CIDCA AGK1at 100 g/L, incubated at 30 °C and fermented until pH 3.3. Other CFS obtained from different fermentation conditionsachieved less antifungal activity than that mentioned above. However, CFS of milk fermented with kefir grains, untilpH 4.5 caused an increase of growth rates. Additionally, CFS produced by kefir grains CIDCA AGK1 at 100 g/L, incubatedat 30 °C and fermented until pH 3.3 achieved higher antifungal activity than CFS from artificially acidified milkwith organic acids (CFS L + A) at the same concentration of kefir CFS. Besides, CFS from milk acidified with hydrochloricacid (CFS HCl) showed no fungal inhibition. On the other hand, kefir-baked arepas exhibited significant resistanceto natural and artificial fungal contamination. Finally, both kefir-baked and kefir-sprayed arepas retained the organolepticcharacteristics of the traditional corn product, but with certain tastes imparted by the kefir fermentation. This workconstitutes the first study on fungal inhibition by kefir-fermented milk extending to the protection of corn products ofmass-consumption and the possible application as a food preservative.