Abstract
The açai palm (Euterpe oleracea) is native to the Amazon basin, a humid tropical forest. High levels of total mesophilic bacteria with high diversity have been consistently reported in açai fruits. As local consumers have few digestive problems, the results of the present study reveal the lactic acid bacteria (LAB) recovered from açai fruits with characteristics that suggest they are possible candidates for probiotics and antagonistic potential against pathogens for the first time. Açai fruits were sampled from five different locations in the Eastern Amazonia floodplains. Sixty-six isolates were recovered from fruits and tested for some probiotic characteristics following FAO/WHO guidelines. Approximately 65% of the isolates showed no catalase or oxidase activity, Gram-positive staining or cocci and bacilli cell morphology. Furthermore, 48% of the isolates demonstrated preliminary characteristics that suggest safety for use, as they presented no coagulase enzyme activity or gamma-hemolysis. These strains were identified as belonging to the genera Lactiplantibacillus and Pediococcus, and 32 strains also presented resistance to vancomycin, ciprofloxacin and streptomycin. In addition, 28 isolates showed a survival rate, expressed as log cycle reduction, higher than 0.9 under gastric conditions (pH 2). All strains tested positive in bile salts deconjugation tests and showed a survival rate higher than 0.8 in the presence of this salt. Regarding antimicrobial activity against pathogens, all strains were able to inhibit Salmonella Typhimurium (ATCC® 14028TM) and 97% were capable of inhibiting Escherichia coli (ATCC® 25922TM). Concerning the results of in vitro antagonistic assays, three isolates (B125, B135, and Z183 strains) were selected for antagonistic tests using açai juice contaminated with these two pathogens. All tested LAB strains were able to inhibit pathogen growth in açai juice. In summary, açai fruits are a potential source of LAB isolates to be investigated as probiotics.
Highlights
The Amazon has the ideal climatic conditions for plant growth, especially for many types of palm trees
Sixty-six endophytic strains were isolated from açai fruit, 43 of which were selected for subsequent study taking into account their Gram positive, catalase negative and oxidase negative characteristics, among them 7 from Combú Island, Belém—PA (C21, C34, C35, C37, C38, C39, and C52), 6 from Abaetetuba— PA (A71, A72, A73, A74, A100, and A101), 24 from Breves—PA (B104, B105, B108, B109, B112, B113, B117, B118, B119, B120, B121, B122, B123, B125, B134, B135, B137, B138, B139, B140, B141, B142, B143, and B144), 2 from Santarém—PA (S150 and S153) and 4 from Zé Doca—MA (Z170, Z183, Z188, and Z190)
To the best of our knowledge, this is the first study on isolation and the genetic identification of a large number of endophytic lactic acid bacteria (LAB) of açai fruits, the evaluation of probiotic characteristics, the safety aspects for their use, and their antagonist activity against pathogens associated with foodborne infections
Summary
The Amazon has the ideal climatic conditions for plant growth, especially for many types of palm trees. Some of these palms are important for both the agricultural industry, which can offer a source of income for the local population, and for biotechnological purposes, which remains understudied. A large part of the population consumes the naturally fermented acai drink (called “past açai” or “açai sour”), which can be consumed directly or used in the production of porridges Those who consume past açai do not show clinical signs of food intoxication, so this phenomenon may be due to spontaneous fermentation that is primarily performed by lactic acid bacteria (LAB), which are desirable for the safe production of different foods (Aguiar et al, 2013)
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