Waste valorization practices have attracted a significant amount of attention in recent years with the aim of managing waste in the most sustainable way. Food waste constitutes a largely under-exploited residue from which a variety of valuable chemicals can be derived. The operation in global yoghurt market provokes frequently the reject and withdrawn of yoghurt derivates out of shelf life. This work comprises a contribution on the valorisation of this high polluting waste of the dairy

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... based on the production of lactic acid using residual yoghurt whey as raw material. Response surface methodology (RSM) based on central composite design (CCD) was used to evaluate the effects of fermentation parameters for lactic acid production by Lactococcus lactis subsp. in batch experiments. The critical factors selected for the investigation were: sugars concentration (X 1 ), yeast extract concentration (X 2 ) and inoculum size (X 3 ). The experimental results were fitted with a second order polynomial equation by a regression analysis and 93 % of the variation could be predicted by the model. A maximum lactic acid production (6.80 g/l) was obtained under following optimal conditions: sugars concentration 57 g/l, yeast extract concentration 10.8 g/l and inoculum size 10 %. Moreover, the maximum of lactic acid production predicted by the model was 6.61 g/l. These results confirmed the validity of the model, and the experimental values were quite close to the predicted values.