Global agricultural activities generate a substantial amount of organic waste, particularly from fruit and starch-based residues. This study investigates the anaerobic acidification (AC) of these wastes using microbiota derived from rumen fluid, aiming to produce value-added bioproducts such as lactic acid (LA) and volatile fatty acids (VFAs) for sustainable waste management. The AC process was conducted over 48 hours at 35 ± 0.5 °C without pH control, utilizing six digesters with varying substrate-to-inoculum ratios. Results showed that starch-based substrates led to higher lactic acid accumulation compared to fruit waste, while both substrate types produced VFAs in comparable concentrations. LA and VFA accumulation ranged from 2–6 and 20–60 mmol/L, respectively. These findings underscore the feasibility of converting organic waste into economically viable, value-added products through bioconversion, with implications for environmental sustainability and resource efficiency. Further research is recommended to optimize the process and assess its scalability for industrial applications.