Date of Award
Master of Science (MS)
Nutrition and Food Sciences
Paul S. Kindstedt
John M. Hughes
With the rising popularity of artisanal cheese in the United States, the soft washed rind category has emerged as a fast-growing segment of the marketplace. There is much anecdotal evidence to suggest a common sensorial defect in soft washed rind cheese is a gritty/sandy texture attributed to crystal growth on the rind of these cheeses
A preliminary study was undertaken to develop a set of criteria to visually identify crystals found on soft washed rind cheeses. Single crystal identities were presumptively determined using polarized light microscopy (PLM), and cross-checked using powder x-ray diffractometry (PXRD). Two distinct crystal groupings were determined based on these metrics. Group 1 crystals had high birefringent coloring, angle of extinction (AE) ≈ 90°, and were smaller and less circular than Group 2 crystals (P<0.05). Group 2 crystals had no birefringent coloring and AE ≈ 18°. Using established mineralogical data, Group 1 and Group 2 crystals were identified to be struvite and ikaite, respectively. These crystalline bodies are situated in an amorphous cheese matrix (i.e. smear), which create difficulties when examining via PLM and PXRD, leading to high background noise. To remedy these issues, a novel method for harvesting crystals was developed. Smear scrapings were immersed in NaOH (pH=10) to dissolve smear material, which resulted in improved PLM and PXRD performance.
A subsequent observational study was conducted to understand the prevalence of surface crystals and grittiness associated with washed rind cheeses sourced from the U.S.A. and Europe. Crystal types were identified via PXRD and PLM. Crystal size and shape (circularity) metrics were determined via PLM and image analysis. A descriptive sensory panel (n=12) was used to evaluate grittiness presence and intensity. Identified crystal types included ikaite, struvite, calcite, and brushite. Mean crystal length and area ranged from ~30μm to ~1100μm, and ~500μm2 to ~200,000μm2, respectively. Sensory perception threshold for grittiness occurred at a mean crystal length of ~70μm and mean crystal area of ~2900μm2. Below these threshold levels, cheeses presented with negligible grittiness. Above these threshold levels, grittiness was highly correlated with crystal length and area (r=0.93 and 0.96, respectively; P<0.001). These results indicate surface crystals have a direct impact on the sensorial quality of soft washed rind cheeses.
Number of Pages
Polowsky, Patrick, "Analysis of surface crystals on soft washed rind cheeses using polarized light microscopy and their effect on the sensory perception of grittiness" (2018). Graduate College Dissertations and Theses. 864.