The response surface methodology and canonical analysis were employed to find the most suitable conditions for Lactobacillus helveticus to produce lactic acid from cheese whey in batch fermentation. The analyzed variables were temperature, pH, and the concentrations of lactose and yeast extract. The experiments were carried out according to a central composite design with three center points. An empiric equation that correlated the concentration of lactic acid with the independent variables was proposed. The optimal conditions determined by the canonical analysis of the fitted model were 40°C, pH？6.8, 82？g/L of lactose, and 23.36？g/L of yeast extract. At this point, the lactic acid concentration reached 59.38？g/L. A subsequent fermentation, carried out under optimal conditions, confirmed the product concentration predicted by the adjusted model. This concentration of lactic acid is the highest ever reported for Lactobacillus helveticus ATCC 15009 in batch process using cheese whey as substrate. 1. Introduction 1.1. Cheese Whey as a Pollutant Cheese whey is the liquid remaining after the precipitation and removal of milk casein during cheese making. This byproduct represents 85–90% of the milk volume and retains 55% of milk nutrients. Among the most abundant of these nutrients are lactose (4.5–5.0%？w/v), soluble proteins (0.6–0.8%？w/v), lipids, and mineral salts [1]. It is produced in large amounts by the dairy industry. To produce 1？kg of cheese are produced, on average, 9？kg of whey. Because it is a byproduct of low economic value, formerly the cheese whey was simply dumped in watercourses without any previous treatment. This caused the whey to become a serious environmental problem due to its high content of organic matter, with BOD = 30,000–50,000？mg/L and COD = 60,000–80,000？mg/L [2]. 1.2. Cheese Whey as a Resource The whey produced in the dairy industry has two destinations: disposal or utilization. Disposal here means launching over the field, pumping in water courses, and treatment in effluent systems. In the first case, the use of whey as a fertilizer can over time unduly increase soil salinity. The pumping of untreated whey in watercourses is an environmentally incorrect solution and it is banned in several countries. Although it solves the legal problems associated with the launch in watercourses, treating whey as an effluent increases production costs and brings no economic return to the producer [3, 4]. The recovery of nutrients from whey and its transformation into higher value-added compounds are better alternatives than the disposal.
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