Nutrients Quality Improvement of Agro-industrial Citric Acid Residues by Fermentation with Yeast Waste from Bioethanol Processing to be Used as Ruminant Feed

The purpose of this study was to investigate the effect of improving the nutritional quality of agro-industrial citric acid waste (CW) by fermenting it with yeast waste (YW) from bioethanol processing. The study was conducted with two sub-experiments: Experiment (i) was performed to assess the yeast cultivation growth from YW in different conditions and at different cultivation times with a 12 × 15 factorial experiment design that was conducted and arranged according to a completely randomized design (CRD). Experiment (ii) was assessing the nutrient quality of CW fermented products with a 2 × 4 factorial in CRD. The growth rate of yeast cells displayed that there are interaction effects between various treatments and incubation time (p < 0.05), which were greater in 20 g of molasses (M) + 50 g of urea (U) and 25 g of M + 50 g of U after 16 h of cultivation. Moreover, the study revealed that the addition of YW to CW fermented products (CWYW) at 14 days revealed greater protein and lower fibers (p < 0.05). CWYW at 14 days was revealed a greater yeast population, whereas the population of aerobic bacteria and lactic acid bacteria was lower (p < 0.05). This study recommends that 20 g of M and 50 g of U at 16 h of cultured time be used as the condition medium and that keeping CWYW for 14 days could improve nutritional value.