Date of Award:

2007

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Advisor/Chair:

Donald J. McMahon

Abstract

Changes in cheese physical properties during aging are related to proteolysis by coagulant type, culture enzymes, and non-starter lactic acid bacteria (NSLAB). Storage temperature also affects aging rate. Cultures are important for flavor development , but less is understood about their role in melting and textural properties.

Our objective was to make Cheddar cheese using different cultures, to age it at 6 and 13°C, and measure physical and proteolytic properties over 12 mo to determine whether changes in texture and melting correlated with the extent of proteolysis that occurred during aging.

Cheese was manufactured using Lactococcus lactis starter culture either alone or combined with one or both of Lac Lc. Lactis or Lactobacillus helveticus adjunct cultures . Three replicates of cheese were made using 1500 lb of milk. Cheese composition was 35.5 ± 1.0% moisture, 52.5 ± 2.5% FDB, 1.65 ± 0.05% salt, and pH 5.2 ± 0.1. All cheeses were initially stored at 6°C, then half moved to l3°C after 21 d.

Texture profile analysis was performed using 25% and 60% compression and melting measured using a Meltmeter at 65°C. The data were analyzed based on culture and temperature over 12-mo storage time. The overall hardness decreased, while the cohesiveness decreased for all treatments. Extent of melting was significantly correlated with hardness (r = 0.62), cohesiveness (r = 0.40), and inversely with adhesiveness (r = 0.24). Correlations with adhesiveness and cohesiveness were not linear.

Proteins were extracted from cheese at 1 wk, 1, 2, 4, 6, 9, and 12 mo of aging using 500 mM sodium citrate solution containing 1% sodium chloride. Purified extracts were then applied to a high-performance liquid chromatography CS reverse phase column and large hydrophobic peptides and protein peaks monitored at 214 nm. Melting was inversely correlated with the amount of intact ɑs1-caserienm remaining in the cheese (r = -0.54) and directly correlated with what was thought to be ɑs1-casein (f 24 - 199) (r = 0.56).

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