Antimicrobial activity of açaí against Listeria innocua

Fermentation Kinetics, Microbiological and Physical Properties of Fermented Soy Beverage with Acai Powder

In this study, the effects of the fermentation kinetics, determination of the number of lactic acid bacteria, texture, water holding capacity, and color of fermented soy beverages with acai powder (3 and 6% w/v) were investigated. The addition of acai powder significantly influenced the fermentation kinetics based on changes in pH, accelerating fermentation in the initial period. The results showed that the acai additive did not affect the enumeration of Lactobacillus acidophilus and Bifidobacterium animalis subsp. lactis. The presence of acai inhibited the proliferation of Streptococcus thermophilus compared to the soy beverage without acai powder added. However, the higher the acai additive, the more Streptococcus thermophilus bacteria were detected: 4.39 CFU/g for 6% acai powder sample and 3.40 CFU/g for 3% acai powder sample. The addition of acai to the soy beverage reduced its firmness, consistency, cohesiveness, and viscosity index after fermentation. A slight difference was observed in the lightness and whiteness of fermented soy beverages with 3% and 6% acai powder.

QuiC2 represents a functionally distinct class of dehydroshikimate dehydratases identified in Listeria species including Listeria monocytogenes

Many Listeria species including L. monocytogenes contain the pathway for the biosynthesis of protocatechuate from shikimate and quinate. The qui1 and qui2 operons within these Listeria spp. encode enzymes for this pathway. The diversion of shikimate pathway intermediates in some Listeria species to produce protocatechuate suggests an important biological role for this compound to these organisms. A total of seven ORFs, including quiC2, were identified within qui1 and qui2, however only three proteins encoded by the operons have been functionally annotated. The final step in Listeria's protocatechuate biosynthesis involves the conversion of dehydroshikimate by a dehydroshikimate dehydratase (DSD). In this study, we demonstrate that QuiC2 functions as a DSD in Listeria spp. through biochemical and structural analyses. Moreover, we show that QuiC2 forms a phylogenetic cluster distinct from other functionally annotated DSDs. The individual phylogenetic clusters of DSD are represented by enzymes that produce protocatechuate for distinct biological processes. Similarly, QuiC2 is expected to produce protocatechuate for a novel biological process. We postulate that protocatechuate produced by DSDs found within the QuiC2 phylogenetic cluster provides an ecological niche for representative organisms.

Extraction of Anthocyanins and Total Phenolic Compounds from Açai (Euterpe oleracea Mart.) Using an Experimental Design Methodology. Part 1: Pressurized Liquid Extraction

Currently, açai is one of the most important fruits present in the world. Several studies have demonstrated its high content in phenolic compounds and anthocyanins. Both of them are responsible of interesting properties of the fruit such as anti-inflammatory, antioxidant or anticancer. In the present study, two optimized pressurized liquid extraction (PLE) methods have been developed for the extraction of anthocyanins and total phenolic compounds from açai. A full factorial design (Box–Behnken design) with six variables (solvent composition (25–75% methanol-in-water), temperature (50–100 °C), pressure (100–200 atm), purge time (30–90 s), pH (2–7) and flushing (50–150%)) were employed. The percentage of methanol in the extraction solvent was proven to be the most significant variable for the extraction of anthocyanins. In the case of total phenolic compounds, the extraction temperature was the most influential variable. The developed methods showed high precision, with relative standard deviations (RSD) of less than 5%. The applicability of the methods was successfully evaluated in real samples. In conclusion, two rapid and reliable PLE extraction methods to be used for laboratories and industries to determine anthocyanins and total phenolic compounds in açai and its derived products were developed in this work.

Bioactivity of Fucoidan as an Antimicrobial Agent in a New Functional Beverage

Seaweeds are a sustainable source of novel functional ingredients with applicability in pharmaceutics, biotechnology, and food science. The bioactivity of most of these marine compounds has scarcely been studied. The present study overviews the bioactivity of the polysaccharide fucoidan derived from Fucus vesiculosus brown algae as an antimicrobial agent against Listeria monocytogenes and Salmonella enterica serovar Typhimurium. The results obtained in vitro in reference medium reveal a bacteriostatic and bactericidal effect of fucoidan against both pathogens, this bioactivity being significantly dependent (p-value ≤ 0.05) on the concentration, 5–1000 μg/mL, temperature, 8–37 °C, and exposure time, 0–12 days. The results were validated in the formulation of a new functional pasteurized apple beverage to be commercialized under refrigeration. Fucoidan added at 25–100 μg/mL was highly effective against both pathogens. These results increase knowledge for the future formulation of new functional beverages that include marine compounds (high content in fibre, high content in protein; prebiotic and antioxidant properties), additionally revealing antimicrobial potential.

Selection of Surrogate Bacteria for Use in Food Safety Challenge Studies: A Review

Nonpathogenic surrogate bacteria are prevalently used in a variety of food challenge studies in place of foodborne pathogens such as Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, and Clostridium botulinum because of safety and sanitary concerns. Surrogate bacteria should have growth characteristics and/or inactivation kinetics similar to those of target pathogens under given conditions in challenge studies. It is of great importance to carefully select and validate potential surrogate bacteria when verifying microbial inactivation processes. A validated surrogate responds similar to the targeted pathogen when tested for inactivation kinetics, growth parameters, or survivability under given conditions in agreement with appropriate statistical analyses. However, a considerable number of food studies involving putative surrogate bacteria lack convincing validation sources or adequate validation processes. Most of the validation information for surrogates in these studies is anecdotal and has been collected from previous publications but may not be sufficient for given conditions in the study at hand. This review is limited to an overview of select studies and discussion of the general criteria and approaches for selecting potential surrogate bacteria under given conditions. The review also includes a list of documented bacterial pathogen surrogates and their corresponding food products and treatments to provide guidance for future studies.