Effect of Zinc Oxide integration on milk and cheese quality of lactating dairy cows

Zinc importance was first discovered with Aspergillus niger, but it took over 75 years to realize its importance as a trace element for rats and another 30 years to acknowledge that this also applies to humans. In the adult body, around 2 to 3 grams of Zinc can be found, distributed in organs, tissues, bones, fluids, and cells (Kaur et al., 2014). Zinc is a mineral that is involved in practically every function of the body, and its importance has earned it the epithet “calcium of twenty-first century (Mir et al., 2020). Zinc, an essential component of life in the three domains; around 5-6% of proteins in prokaryotes and 9-10% of proteins in eukaryotes require Zinc to carry out their biological functions (Andreini et al., 2006). A bioinformatics analysis revealed that over 50% of proteins that bind to Zinc are enzymes, and in most cases, Zinc plays a catalytic role in these enzymes (Andreini & Bertini, 2012). Roughly 20% of Zinc-binding proteins use the metal as a structural component, while in a small percentage of them, it regulates or acts as a substrate for enzymatic activity (Banci et al., 2002; Debela et al., 2006). Zinc is the second most abundant trace metal in biological systems after iron, it is a redox-inert trace element that has only one valence state, Zinc (II), and is involved in a variety of biological processes, as a structural, catalytic, and intracellular and intercellular signaling component (Maret, 2013). A process of selection was carried out to randomly allocate 24 cows of the Friesian breed into two groups (CTR: control and TRT: treated group). The aim was to ensure uniformity in terms of age, body weight, number of lactations, and lactation phase (mid lactation: 140-160 days). CTR diet contained 38 mg/kg of Zinc and TRT diet was supplied with 120 mg/kg of complete feed. Zinc was integrated by adding ZnO powder. This supplementation lasted for 60 days. During this time, the animals received a combination of unifeed, hay and concentrate. For the administration of Zinc, a different formulation of the concentrate was provided. To the CTR group was supplied by the farmer’s standard concentrate while for the TRT group the concentrate was formulated by adding ZnO powder for a total of 120 mg/kg. Both groups continued to follow the same diet with the only difference in the content of ZnO. The concentrate ration was administered manually to the animals, with each cow receiving 500 g, which was subtracted from the total TMR ration formulation. It is important to note that the standard diet adequately fulfilled the nutritional requirements of lactating cows, while the TRT group received an additional supplementation of 80 mg of Zinc. The dosage given adhered to the instructions specified in Regulation (EC) No. 1831/2003 of the European Parliament and the Council dated 22 September 2003 concerning additives utilized in animal nutrition (European Commission, 2003) (Regulation - 1831/2003 - EN - EUR-Lex, s.d.). The animals were fed a daily ration of approximately 22 kg of dry matter per head in the form of a total mixed ration (TMR) including 500 g of concentrate manually administered. TMR composition was determined based on the guidelines outlined in the eighth edition of Nutrient Requirements of Dairy Cattle (2021) (Nutrient Requirements of Dairy Cattle, 2021). During the trial, the monitoring of Zinc supplementation was conducted to ensure that it remained within the prescribed limit of 120 mg/kg of complete feed, as set by the European Union (Commission Implementing Regulation (EU) 2016/1095 of 6 July 2016). In this PhD project we evaluated the impact of integrating 120 mg/kg of Zinc in cows lactating diet on animal feed, bulk and individual milk and cheese. For animal diet which comprised TMR and concentrate were determined chemical composition, Zinc content and fatty acid profile. In addition to these three parameters for bulk milk were analyzed proteic and microbial profile. Chemical composition, proteic profile, Zinc, Iron, Copper content, lactoperoxidase and ceruloplasmin concentration were determined for individual milk samples. Regarding cheese samples, Zinc content, fatty acid, proteic and microbial profile, ammine content, pH, aw, dry matter, total lipid content, texture, sensory profile and oxidative stability were investigated. For individual milk and cheese direct and inverse correlations between some variables were founding by processing data by Pearson’s correlation. Some interesting relations were individuated. These could help to explain some statistically significant differences and understand the relationship between some physical and chemical parameters and food components which have shown to affect biochemical and microbiological reactions. In conclusion, ZnO integration at 120 g/kg DM in lactating cow diet did not affect milk composition, Zinc, Copper and Iron content, lactoperoxidase and ceruloplasmin concentration, and proteic profile of individual samples. Instead for caciotta cheese ZnO supplementation reduced mesophilic aerobic bacteria and Presumptive Pseudomonas spp. growth, proteolysis, biogenic amines content, lipid oxidation, odour intensity and sour and increased hardness, gumminess, chewiness, elasticity of cheese. Biogenic amines are considered an important aspect of food safety. ZnO integration in cow diet could represent a promising strategy for improving the quality, the safety and shelf-life of caciotta cheese. Further investigation is required to gain a comprehensive understanding of the intricate relationships between Zinc supplementation in animals, its influence on animal product composition, and ultimately, its implications on human health. Biochemical and microbial reactions that were took place during ripening period represent an important starting point to evaluate the possibility to analyse the metagenomic profile of cheese investigated. Finally, observing the effect of ZnO for caciotta cheese we can assert that ZnO could represent a promising strategy for improving the quality and safety of caciotta cheese and extending its shelf life.