Coconut milk beverage fermented by Lactobacillus reuteri: optimization process and stability during refrigerated storage

Abstract

This study aimed to establish the optimal conditions of temperature (31–43 °C) and coconut pulp concentration in water 1:3–1:9 (w/v) for the growth of Lactobacillus reuteri LR 92 or DSM 17938 in coconut milk beverage, using a central composite face centered design. The optimized conditions were used for analysis of the viability during the fermentation process, pH, production of sugars and organic acids by High Performance Liquid Chromatography (HPLC) and reuterin production. Coconut milk provided adequate substrate for L. reuteri growth without supplementation. The optimal parameters for L. reuteri viability were: concentration 1:3 (w/v) and 37 °C for LR 92 and concentration 1:3 (w/v) and 34 °C for DSM 17938. Chemical analysis showed that the naturally occurring sucrose in the matrix (ca. 4.4 g/L) was used for cell multiplication and the strains differed in the production and content of organic acids. After fermentation until pH 4.5 ± 0.1, the samples were stored at 4 °C for 30 days and the final cell viability in coconut milk was 7.55 ± 0.07 log CFU/mL for L. reuteri LR 92 and 8.57 ± 0.09 log CFU/mL for DSM 17938. It was detected 0.15 ± 0.03 mM and 0.14 ± 0.04 mM of reuterin produced by DSM 17938 and LR 92, respectively. L. reuteri DSM 17938 presented a great decrease of pH and post acidification after storage. The LR 92 strain showed low post acidification. These results showed that coconut milk provides adequate matrix for the development of new fermented functional beverages.