Print

Rajbhandari, Pallavi

Nutritional and Food Sciences

2005

MS

Calcium lactate crystal formation on the surface of cheese has been a concern to cheese manufacturers. Though not harmful, consumers mistake them for spoilage which causes financial loss to the industry. Crystallization behavior has been shown to be different for cheeses made from the same vat of milk. The objective of the first study was to compare the compositional differences of six pairs of naturally smoked cheeses. Each pair included one sample containing crystals and the other crystal-free and the pair originated from the same vat. Cheeses for the study were 5-6 months old and were obtained from a commercial source. These were stored for additiona1 5-13 months to insure the noncrystallized samples remained crystal-free. The crystals from the cheese were removed from the crystallized samples, weighed and analyzed for total lactic acid, L(+) and D(-) lactic acid, Ca, P, NaCl, moisture and crude protein. Crystallized and noncrystallized samples were then sectioned into 3 concentric subsamples (0 to 5mm, 6 to 10mm and greater than 10mm depth from the surface) and analyzed for moisture, NaCl, titratable acidity, L(+)and D(-) lactic acid, pH and total and water-soluble calcium. The data were analyzed by ANOVA according to a repeated measures design with 2 within-subjects variables. The crystalline material contained 52.1% lactate, 8.1% Ca, 0.17% P, 28.5% water and 8.9% crude protein on average. Both crystallized and noncrystallized cheese samples contained significant gradients of decreasing moisture from center to surface. Compared to noncrystallized samples, crystallized samples possessed significantly higher moisture, titratable acidity, L (+) lactate and water soluble calcium, and significantly lower pH and NaCl content. The data suggest that salt variation within vat allowed some cheese curds to accumulate more moisture, therefore, more lactose, resulting in more lactic acid, lower pH and more calcium ions. Therefore, excess of lactate and calcium ions then supersaturate the serum phase of the cheese and dehydration during smoking accelerated the formation of crystals.
The objectives of the second study were to develop and evaluate an objective method to measure the area occupied by calcium lactate crystals on the surface of smoked Cheddar cheese using image analysis. Coefficients of variation ranged from 1.19 to 4.8% for 5 replicate analyses of 3 different cheese surfaces that ranged from ca. 2 to 49% of total surface area occupied by crystals. Thus, results showed a high degree of repeatability for the 3 cheese surfaces, which ranged from very slight and geometrically simple to very heavy and geometrically complex crystal coverage. The method underestimated total area occupied by crystals on the 3 surfaces by 0.3 to 4.8% unless the fainter crystal regions that went undetected during initial thresholding were manually segmented and quantified. The wet weight of crystal substance collected per unit of surface area from 20 different cheese samples increased exponentially as the percentage of total surface area occupied by crystals increased. The area occupied by crystals on 6 different surfaces from 3 different cheese samples increased linearly (R2 = .94 to .99) during storage at 4°C for up to 33 wk. However, the rates of increase differed significantly among the 3 cheese samples. Image analysis may' serve as a useful tool to quantitatively evaluate the effects of factors such as cheese composition, packaging conditions, storage temperature, etc. on rate of crystal growth and time of crystal appearance during storage.