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Impact of Potassium Substitution for Sodium on pH, Proteolysis, Organic Acids, and Microbial Populations During Storage of Cheddar Cheese
Sodium reduction in cheese can assist in reducing dietary Na intake, yet saltiness is an important aspect of cheese flavor. Our objective was to evaluate impact of substitution of KCl for NaCl on cheese pH, organic acid content, extent of proteolysis as water soluble nitrogen (WSN) and protein profiles using urea-PAGE in Cheddar cheese in relation to changes in starter lactic acid bacteria (LAB) and nonstarter LAB (NSLAB) during 9 mo storage. Cheddar cheeses with molar salt contents equivalent to 1.7% salt and Na replacement of 0% (control), 10%, 25%, 50% and 75% were manufactured as well as a low-salt (0.7% NaCl) negative control cheese. The 1.7%-salt cheeses had mean composition of 352 g/kg moisture, 259 g/kg protein, 17.5 g/kg salt (measured as Cl<sup>-</sup>) and 50% fat on a dry basis. After salting there was a faster initial drop in pH in the 0.7%-salt cheese and cheeses with high levels of K substitution and the pH remained lower throughout storage. No difference in intact casein levels or %WSN levels between the various cheeses was observed with %WSN increasing from 5% at d 1 to 25% after 9 mo. There was a greater decrease in intact αs1-casein than β-casein, and a linear relationship was observed between the ratio of αs1-casein (f121-199) to αs1-casein and storage time suggesting this ratio could be used as an index of cheese ripening. Lactic acid content increased with K substitution and throughout storage. Propionic acid concentration in the cheese increased earlier in the control cheese than in cheeses with ≥25% K substitution or cheese with only 0.7% salt. This increase corresponded to the time after NSLAB numbers in the cheeses became dominant. There were few other obvious trends in organic acid concentration observed as a function of Na or K content. Typical changes in bacteria microflora occurred during storage with lactococci gradually decreasing and NSLAB increasing. Lowering the Na content, even with K replacement, extended crossover time when NSLAB became the dominant microflora from 4.5 mo to 5.2, 6.0, 6.1 and 6.2 mo for cheeses with 10%, 25%, 50% and 75% K substitution. This was, however, still shorter than the 7.3 mo for the low-salt cheese. By 9 mo, NSLAB levels in all cheeses had increased from initial levels of ≤102 to ~106 CFU/g. Lactococci remained at 106CFU/g in the low-salt cheese even after 9 mo storage.
Keywords: cheese, sodium, potassium