**1. Introduction**

Fermentation is one the most ancient methods of food preparation that exploits the growth and metabolic activities of microorganisms to preserve and transform food materials [1,2]. During this process, growth of spoilage and pathogenic organisms is inhibited by secondary metabolites produced by fermenting organisms, preserving and extending the storage of perishable foods [3,4]. Beyond conservation, fermentation gives to food a characteristic aroma and taste and enhance their organoleptic profiles and palatability, digestibility of proteins and carbohydrates, and the bioavailability of vitamins and minerals [4–7]. Since ancient times, fermented foods and beverages have been a fundamental part of human diet and their beneficial effects in reducing cholesterol levels and blood pressure, boosting immune system, protecting from toxic pathogens and in the prevention of carcinogenesis, osteoporosis, diabetes, cardiovascular and hepatic diseases have been widely characterized [8]. Moreover, fermented foods and beverages have a strong impact on human gu<sup>t</sup> microbiota. It is well established that intestinal bacteria modulate the metabolic profile of the host, also influencing the immune system [9,10] and maintaining the structure and function of the intestinal tract [11,12]. The interactions between ingested fermented food and microbiota constitute a rapidly expanding field of study, focusing in particular on human health impact [12–16].

More than 100 years ago Metchnikoff, Nobel prize winner for the discovery of macrophages, already claimed that the longevity of some populations of Eastern Europe was due to the high quantity of fermented food in their diet [17] and more recently it has been shown that microbiota in the elderly is strongly influenced by diet, opening up that healthy ageing is associated with microbial diversity [18,19].

Fermented Papaya Preparation (FPP®, Immun'Âge®) is one of the fermented foods that have proven positive effects on brain health; FPP® is a product resulting from yeas<sup>t</sup> fermentation of non-genetically modified *Carica Papaya* Linn, which is marketed as a natural dietary functional health supplement under the brand name of Immun'Âge® [20,21]. FPP® is a powerful antioxidant and nutraceutical adjuvant in combined therapies against various diseases [22–29], including cancer [22,25, 30]. The FPP® more documented actions are as a free radical regulator [31], as immunomodulator [32– 36] and as antioxidant [37,38]. In fact, FPP® has shown a powerful *in vitro* anti-oxidative activity on brain cells [39], as well on *in vivo* experimental model of epilepsy consistently reducing neural release of epileptogenic monoamine [40]. Moreover, FPP® showed a clear action in reducing the derangement of oxidant/antioxidant balance at the brain level in elderly rats and in experimental ischemia-reperfusion model [20,41,42]; FPP® modulates oxidative DNA damage, protecting brain from oxidative damage in hypertensive rats and reducing genotoxic effect of H2O2 [43], and protecting the body from the aging-related diseases [44–47], including neurodegenerative diseases [47–49]. However, a clear *in vivo* action of FPP® on the molecular signature of aging, such as telomerase activity and telomeres length has not been provided yet.

In this study we investigated the role of in vivo FPP® administration in the induction of an antioxidant action together with an anti-aging effect. The experimental design provided that the mice received the FPP® in water either from 6 weeks (ET-FPP® group: early treatment with FPP®), or from 51 weeks of life (LT-FPP® group: late treatment with FPP®), as compared to mice receiving FPP®-free tap water (CTR group). For both treatment groups, at the end of treatment period (10 months), we evaluated antioxidants (Total Antioxidant Capacity, SOD-1 and GSH), ROS and telomerase activity levels in blood samples, and telomeres length in single cell suspensions from the bone morrow and the ovaries of the mice. Our results showed the effect of FPP® in inducing a clear systemic antioxidant reaction (higher of SOD-1 and GSH plasma levels) along with an increased telomerase activity and longer telomeres in both the bone marrow and the ovaries of the treated mice. Lastly, FPP® was more effective when it starts at an early age as compared to late treatment.
