Effect of agar-agar gelation on fermented coconut extract during in vitro digestion: probiotic survival and antioxidant activity (e-Latin Food 2020)
Coconut extract (CE) or commercially known coconut milk can be a growth medium for probiotic bacteria. These probiotics must survive during their passage through the digestive tract and reach their site of action. On the other hand, agar-agar (AA) is a gelling agent that could act by protecting biomolecules, however its effect on the survival of probiotics in food has not yet been studied. On the other hand, agar-agar (AA) is a gelling agent that may act as a biomolecule’s protector but its effect on the survival of probiotics in food is not yet studied. The aim of this work was to study the ability of agar-agar to protect probiotics and antioxidant molecules in a fermented coconut extract during an in vitro digestion. Fermentation with a lyophilized inoculum mix (1% w/v) of Bifidobacterium animalis ssp. lactis, Lactobacillus acidophilus y Lactobacillus delbrueckii ssp. bulgaricus in CE was carried on until pH 4.5 was reached. Two concentrations of AA (0.5 and 1.5% w/v) were evaluated to generate the gelation of the ferment. In vitro digestion of the gels was performed considering the gastric (GP) and intestinal phase (IP) by techniques previously reported. Probiotic survival was measured by plate count and antioxidant capacity (DPPH and ABTS methods), as well as total phenols content (Folin-Ciocalteu method), were assayed. The highest survival of probiotics at the end of the simulated digestion was observed in the sample with 0.5% AA (1.7x108±8.8x107CFU/g). All samples presented survival values above the recommended intervals for a probiotic food (106 to 107 CFU/g). In concern to the antioxidant activity, the control sample (0% AA) presented the highest percentage of ABTS radical inhibition (70.4±0.1%) at the end of the IP, while the lowest values were found in the 1.5% AA sample (54.9±0.5%). This behavior could be attributed to physicochemical interactions or obstructive effects between the AA matrix and the antioxidant compounds. Similar behaviour was observed concerning total phenols. Concentrations of AA above 0.5% could be generating overprotection of probiotics, phenolic molecules, and antioxidants. This could positively impact their survival during their transit through the digestive system, allowing them to reach their site of action and/or absorption.
Keywords: Agar-agar, coconut, in vitro digestion, probiotics.