Residual yoghurt whey for lactic acid production

The operation in global yoghurt market provokes frequently the reject and withdrawn of yoghurt derivates out of shelf life. Yoghurts that have past their 'best before' date constitute a waste that has to be environmentally treated. Its use as a source for lactic acid production by Lactobacillus casei is studied in this work, being also a proposal that can reduce the end-of-cycle impact of the residue. Production of yoghurt generates a residue highly supplemented with sugar and fruits syrups that can be metabolized to lactic acid, but no data are available in the literature about this potential transformation into a commercial valuable lactic acid. Bioconversion of total sugars around 44% was achieved in pH controlled batch fermentation after 34 h. Control of pH and yeast extract supplementation in the preculture stage have shown a remarkable enhancement of fermentation performance due to the reduction in the toxicity and the increase in nitrogen content. Successive bioconversions of lactose, glucose and sucrose have been shown, with a sugar consumption profile giving a hierarchical mode consumption in the order glucose > sucrose > lactose.