Current Status, Recent Advances, and Main Challenges on Table Olive Fermentation: The Present Meets the Future

Table olives are among the most well-known fermented foods, being a vital part of the Mediterranean pyramid diet. They constitute a noteworthy economic factor for the producing countries since both their production and consumption are exponentially increasing year by year, worldwide. Despite its significance, olive’s processing is still craft based, not changed since antiquity, leading to the production of an unstable final product with potential risk concerns, especially related to deterioration. However, based on industrial needs and market demands for reproducible, safe, and healthy products, the modernization of olive fermentation processing is the most important challenge of the current decade. In this sense, the reduction of sodium content and more importantly the use of suitable starter cultures, exhibiting both technological and potential probiotic features, to drive the process may extremely contribute to this need. Prior, to achieve in this effort, the full understanding of table olive microbial ecology during fermentation, including an in-depth determination of microbiota presence and/or dominance and its functionality (genes responsible for metabolite production) that shape the sensorial characteristics of the final product, is a pre-requisite. The advent of meta-omics technology could provide a thorough study of this complex ecosystem, opening in parallel new insights in the field, such as the concept of microbial terroir. Herein, we provide an updated overview in the field of olive fermentation, pointing out some important challenges/perspectives that could be the key to the olive sector’s advancement and modernization.

A survey on antimicrobial resistance genes of frequently used bacteria in kefir and yoghurt

Antimicrobial resistance (AMR) is one of the foremost threats facing the treatment of infectious diseases worldwide. Recent studies have highlighted the potential for ntimicrobial resistance genes (ARGs) in fermented foods to contribute to AMR via horizontal gene transfer (HGT). The focus of our study was investigating the ARG content (resistome) and mobility potential of the ARGs (mobilome) of bacterial strains commonly used in probiotic products, namely yoghurt and kefir. We performed metagenomic analyses on freely available data sets (n=584) originating from various kefir and yoghurt strains using next generation sequencing (NGS) in order to gain an insight into the ARG diversity, frequency and mobility. Our study shows that kefir and yoghurt products carry diverse and significant amounts of ARGs and that these genes may often be associated with iMGEs or plasmids, conferring mobility. Certain bacteria species such as Bifidobacterium animalis and Streptococcus thermophilus were found to have higher ARG content. Overall, our results support the hypothesis that ARGs are present in fermented foods, namely yoghurt and kefir, and have the potential to contribute to AMR.

Exopolysaccharides Produced by Lactic Acid Bacteria: From Biosynthesis to Health-Promoting Properties

The production of exopolysaccharides (EPS) by lactic acid bacteria (LAB) has attracted particular interest in the food industry. EPS can be considered as natural biothickeners as they are produced in situ by LAB and improve the rheological properties of fermented foods. Moreover, much research has been conducted on the beneficial effects of EPS produced by LAB on modulating the gut microbiome and promoting health. The EPS, which varies widely in composition and structure, may have diverse health effects, such as glycemic control, calcium and magnesium absorption, cholesterol-lowering, anticarcinogenic, immunomodulatory, and antioxidant effects. In this article, the latest advances on structure, biosynthesis, and physicochemical properties of LAB-derived EPS are described in detail. This is followed by a summary of up-to-date methods used to detect, characterize and elucidate the structure of EPS produced by LAB. In addition, current strategies on the use of LAB-produced EPS in food products have been discussed, focusing on beneficial applications in dairy products, gluten-free bakery products, and low-fat meat products, as they positively influence the consistency, stability, and quality of the final product. Highlighting is also placed on reports of health-promoting effects, with particular emphasis on prebiotic, immunomodulatory, antioxidant, cholesterol-lowering, anti-biofilm, antimicrobial, anticancer, and drug-delivery activities.

Toxicological and safety evaluations of Weissella cibaria strain CMU in animal toxicity and genotoxicity

Weissella cibaria belongs to the Lactobacillaceae family and has been isolated from traditional fermented foods and saliva of children with good oral health. Previous investigations have shown that W. cibaria CMU (Chonnam Medical University) is expected to be safe based on results of in silico and in vitro analyses. However, there is a lack of studies assessing its safety in vivo. A toxicological safety evaluation of W. cibaria CMU was performed using an acute oral safety study in rats, a 14-day oral range finding study, a subsequent 13-week oral toxicity study in rats and a genetic toxicity battery (in vitro bacterial reverse mutation, in vitro chromosome aberration in Chinese Hamster Ovary cells and in vivo micronucleus study in mice). The results of the studies in rats showed that the acute lethal dose of W. cibaria CMU is > 5000 mg/kg body weight (bw)/day (1.8 × 109 CFU/kg bw/day) and the 14-day or 13-week no observed adverse effect level (NOAEL) is 5000 mg/kg bw/day (1.8 × 109 CFU/kg bw/day), the highest dose administered. W. cibaria CMU was non-mutagenic in the bacterial reverse mutation test and non-clastogenic or aneugenic in vitro and in vivo. In conclusion, the toxicological studies performed demonstrated W. cibaria CMU to be a safe strain to consume. This study is the first study examining the potential of a W. cibaria strain to cause genetic toxicity and subchronic toxicity in rats according to the Organization for Economic Cooperation and Development guidelines.

New application of microbial l-glutaminase as a flavor enhancing agent in beef burgers

L‑glutaminase (L‑glutamine amidohydrolase EC3.5.1.2) is the key enzyme in enhancing the taste and aroma of oriental fermented foods by increasing their glutamic acid content and as a result imparting a palatable taste. Beef burgers were prepared using different levels of the partially purified L- glutaminase (2.0 to10.0 U/100 g) prepared from Aspergillus oryzae NRRL 32567. Beef burgers treated with 6.0 U/100g and the others treated with monosodium glutamate (5000 ppm) were chemically, sensory and microbiologically evaluated and compared to untreated control during frozen storage at –18 ºC for 3 months. Treatment with L‑glutaminase (6 U/100g) resulted in an increase of 443% in glutamic acid and a reduction of 63% in glutamine contents resulting in an enhanced preferable taste and odor of the prepared beef burgers. Burgers treated with 6.0 U/100g exhibited the best odor, texture, taste and overall quality scores when compared to the untreated control and samples treated with monosodium glutamate (5000 ppm). During the frozen storage of all samples, an expected slight, but significant (p≤0.05), increase in the total mesophilic bacterial count was evident and such increase was quite acceptable since numbers did not exceed the limit of 5.7x103 cfu/g. Similarly, the total psychrotrophs did not exceed 3.7x102 cfu/g.