Balivo, Andrea (2024) Effect of fresh forages in the diets of different ruminant species on the chemical, physical, and sensory properties of dairy products: raw milk, cheese, and ice cream. [Tesi di dottorato]

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Abstract

Sustainable and ethical dairy production systems are increasingly demanded by consumers and present opportunities for developing competitive products. This trend has driven research toward the adoption of innovative practices, such as the use of fresh hydroponic forages and the certification of extensive grazing systems, in order to meet this demand. However, changes in animal feeding systems can significantly affect the chemical, physical, and sensory properties of dairy products. This doctoral thesis explores the effects of using fresh forages, both as pasture and hydroponic feed, on small and large ruminants, focusing on Saanen goats and Italian Mediterranean buffaloes in two distinct studies compared to traditional conserved forages (hay and maize silage). Goat milk was selected as a representative model for small ruminants, while buffalo milk was chosen for large ruminants, allowing a comprehensive analysis of the impact of these feeding practices on milk and their respective cheeses. Dairy products from grazing goats were certified according to the Metodo Nobile guidelines, which specify a high forage-to-concentrate ratio (at least 70:30), low animal density, and limits on daily milk production. Furthermore, grazing must occur on pastures containing at least five different forage plant species. For the production of ice cream, which is explored in the final part of this thesis, cow cream was used as it is the most commonly employed ingredient in both industrial applications and scientific studies. This choice ensures consistency with existing literature, facilitates comparisons, and enhances relevance to industrial practices. E-nose analysis was conducted on raw milk to discriminate between milk from fresh forages and that from conserved forages. Sensory and volatile compound analyses further elucidated the observed differences. For the cheeses (semi-hard goat caciotta and buffalo mozzarella PDO), analyses were carried out on chemical composition, fatty acids, volatile compounds, colour, texture, and sensory properties. Overall, the results did not show significant differences in chemical composition (protein, fat, lactose). However, the use of fresh forage reduced saturated fatty acids and increased mono- and polyunsaturated fatty acids, improving the nutritional profile of the cheeses. There was an increase in oleic acid, α-linolenic acid, vaccenic acid, and rumenic acid (CLA), as well as a higher total polyphenol content in goat caciotta cheeses from certified pasture. The sensory profile and texture of the cheeses were influenced by these changes, with reduced hardness observed both in mozzarella from buffaloes fed hydroponic forage as a substitute for maize silage and in goat cheeses from grazing goats. Cheese colour did not vary significantly, as goat and buffalo milk, compared to cow milk, contains negligible amounts of carotenoids, which are enzymatically converted to retinol. In milk and cheeses from grazing goats, some terpenes were exclusively identified, which could represent potential chemical markers for pasture-fed ruminants. In mozzarella, few volatile compounds differed significantly between sample groups. The use of hydroponic forage resulted in higher levels of 1-octen-3-ol, a secondary alcohol with mushroom aroma characteristic of buffalo mozzarella, and certain linear aldehydes such as octanal, volatile compounds derived from the catabolism of unsaturated fatty acids. Conversely, there were lower levels of volatile acids and ketones. The inclusion of hydroponic barley forage in dairy buffalo farming reduced water consumption and increased milk yield compared to traditional methods, although production costs were higher than for maize silage produced in Southern Italy under current conditions. However, it is important to consider that the costs associated with this new technology could decrease or be amortized over time as production processes are optimized and adoption scales up. In the last case study of this dissertation, the effects of different creams, including a certified "pasture-fed" (Metodo Nobile) cream, on the physical properties of ice cream mixes and final products were examined. The pasture-fed cream exhibited a lower solid fat content, lower melting temperature, and lower crystallization enthalpy, with differences in melting rate and hardness explained by varying kinetics of fat globule destabilization/aggregation in emulsions during frozen storage. In conclusion, this thesis demonstrates that the use of fresh forages, whether as certified pasture or hydroponic feed (which does not require soil for cultivation), improves the fatty acid profile of dairy products, albeit with some variations in physical properties and minimal changes in the sensory profile. These practices could also offer significant environmental benefits. The adoption of certified pastures with low animal densities, as specified by the Metodo Nobile, helps protect plant and animal biodiversity. This approach minimizes competition with crops destined for human consumption, reduces energy use and production inputs, lowers feed costs, and effectively utilizes grasslands otherwise unsuitable for human use. At the same time, hydroponic forages offer the advantage of requiring less land and water than traditional forage production, further supporting sustainable agricultural practices.

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