Improvement of whey cheese matrices via incorporation of Lactobacillus acidophilus — proteolytic and glycolytic activities and their impact upon sensory analysis

Requeijão is a highly nutritious soft Portuguese whey cheese, yet with such organoleptic limitations as poor flavour and grainy texture. Furthermore, it offers excellent conditions for survival and growth of lactic acid bacteria, owing to its high water activity, pH above 5.0 and low salt content. The objective of this research effort was thus to study the contribution of Lactobacillus acidophilus LAC 1 to the improvement of the organoleptic quality of Requeijão, via its proteolytic and glycolytic activities. Experimental whey cheese matrices were produced, and subsequently inoculated with L. acidophilus; these matrices, as well as a control curd, were stored at 7 °C, and samples were taken at 0, 2, 7, 14 and 21 d. Cell viability, pH, and fat, protein and moisture contents were assessed. The contents of water-soluble nitrogen (WSN), nitrogen soluble in 12 %(w/v) trichloroacetic acid (TCA) and nitrogen soluble in 5 %(w/v) phosphotungstic acid (PTA), as well as of lactose and organic acids were also determined. Sensory analysis was finally performed, using a five-point scale for the various attributes. L. acidophilus viable cells number remained constant up to 21 d, while pH decreased by ca. 0,6; this was consistent with an increase in lactic acid content up to 28 mg/g of whey cheese. Values of TCA and PTA in L. acidophilus matrices indicated relevant proteolytic breakdown of whey proteins. These matrices received the highest overall preference scores in sensory evaluation.