305 The battle of yeasts: Ethanol or brewer’s yeast? How yeast processing impacts feline food preferences and flavor enhancement.

Abstract Yeast products derived from sugarcane or brewery industries can be used as functional ingredients in cat nutrition, enhancing diet palatability. Although both types of yeast share a similar nutritional basis, brewer’s yeast (BY) and ethanol yeast (EY) are produced under different pH conditions, influencing their protein content, digestibility, and flavor perception. Additionally, processing methods such as autolysis, enzymatic hydrolysis, and centrifugation can further modify their cellular composition, impacting bioavailability, digestibility, and feline acceptance. This study aimed to evaluate how different yeast sources and processing methods affect the palatability of dry cat food when used as a coating. Four palatability tests were conducted using dry diets coated with 0.5% yeast, comparing yeast origin and processing methods: inactive dried (ID), autolysis (A), hydrolysis (H), and centrifugation (to separate yeast extract - YE). The comparisons included YEEY vs. IDBY, YEEY vs. YEBY, HEY vs. YEBY, and AEY vs. YEBY. Food acceptance was assessed through preference and consumption tests, analyzing initial choice and total intake over a 4-day experimental period. Each test involved 20 cats, with 110 g of each yeast-coated diet offered per cat. Bowl positions were alternated daily to prevent side bias, and results were analyzed using a paired t-test at a 5% significance level. The YEEY was significantly preferred (P< 0.05; Figure 1) over IDBY, with a 2.67 preference ratio in total consumption, and favored on average by 38% of the cats. Similarly, in the YEEY vs. YEBY test, YEEY was again preferred (P< 0.05; Figure 2), with a 1.63 preference ratio, and 26% of the cats favored on average. In the HEY vs. YEBY test, HEY was significantly preferred (P< 0.05; Figure 3; Figure 4), with a 2.02 preference ratio, and favored by 36% of the cats. Conversely, in the AEY vs. YEBY test, no significant preference was observed (P >0.05), although AEY had a 1.29 preference ratio and was favored on average by 15% of the cats. These findings demonstrate that yeast palatability is strongly influenced by its production and processing methods. Hydrolysis, which uses exogenous enzymes, increases the concentration of nucleotides, free amino acids, and peptides, resulting in a more intense sensory impact compared to YE and autolyzed yeast, as observed by the highest preference for the HEY as kibble coating among the tested yeasts. Despite BY having slightly higher fat content and protein digestibility than EY, cats consistently preferred EY over BY, especially when comparing YEEY to IDBY. In conclusion, yeast processing significantly impacts cat food palatability, and HEY emerged as the most effective coating ingredient, improving feline diet acceptance.