Crystal fingerprinting: elucidating the crystals of Cheddar, Parmigiano-Reggiano, Gouda, and soft washed-rind cheeses using powder x-ray diffractometry

Abstract

Crystals in cheese may be considered defects or positive features, depending on the variety and mode of production (industrial, artisanal). Powder x-ray diffractometry (PXRD) offers a simple means to identify and resolve complex combinations of crystals that contribute to cheese characteristics. The objective of the present research was to demonstrate the application of PXRD to study crystals from a range of different cheese types, specifically Cheddar, Parmigiano-Reggiano, Gouda, and soft washed-rind (smear ripened) cheeses. In studies of Parmigiano-Reggiano and long-aged Gouda, PXRD has confirmed that hard (crunchy) crystals that form abundantly within these cheeses consist of tyrosine. Furthermore, PXRD has tentatively identified the presence of an unusual form of crystalline leucine in large (up to 6 mm in diameter) spherical entities, or “pearls”, that occur abundantly in 2-year-old Parmigiano Reggiano and long-aged Gouda cheeses, and on the surface of rindless hard Italian-type cheese. Ongoing investigations into the nature of these “pearls” are providing new insight into the roles that crystals play in the visual appearance and texture of long-aged cheeses. Crystals also sometimes develop profusely in the eyes of long-aged Gouda, which have been shown by PXRD to consist of tyrosine and the aforementioned presumptive form of crystalline leucine. Finally, crystals have been shown by PXRD to form in the smears of soft washed-rind cheeses. These crystals may be associated in some cheeses with gritty mouth feel and with zonal body softening that occurs during ripening. Heightened interest in artisanal cheeses highlights the need to better understand crystals and their contributions to cheese characteristics.

Ion-Exchange Chromatographic Method for the Determination of the Free Amino Acid Composition of Cheese and Other Dairy Products: an Inter-Laboratory Validation Study

“…Indeed, these FAAs represent reagents or products of specific metabolic pathways of some LAB species, and their content gives interesting information (D'Incecco et al 2016a;Brasca et al 2016). RSD r values exceeding 5.0 were also observed for tyrosine, whose high RSD r values (sample 2 and sample 3) (already observed during the homogeneity test) are most likely due to the low solubility of this AA, which is known to appear as white crystals in many types of ripened cheeses (Tansman et al 2015;D'Incecco et al 2016b). For 71 out of the 84 determined single FAA contents (85%), the RSD R values were lower than 10.0, and values exceeding this level all referred to the same FAA with the lowest amounts above mentioned.…”

“…Threshold values exceeding 0.3 were observed for tyrosine in samples 3 and 4, where its concentration was highest, probably because of the low solubility of this AA, which tends to crystallize in ripened cheeses (Tansman et al 2015;D'Incecco et al 2016b). …”

New insight on crystal and spot development in hard and extra-hard cheeses: Association of spots with incomplete aggregation of curd granules

“…Spots can become so numerous and conspicuous that they may influence the visual appeal of the cheese. Spots have been very little studied, and results have been inconsistent (Giolitti and Mascherpa, 1970;Bianchi et al, 1974;Tansman et al, 2015).…”

“…Previous studies about specks reported that they contain clusters of tyrosine, cysteine, other FAA, calcium lactate, and magnesium (Shock et al 1948) or tyrosine and phenylalanine (Giolitti and Mascherpa, 1970). More recently, Bottazzi et al (1994) and Tansman et al (2015) identified the specks in extra-hard cheeses as tyrosine crystals.…”

“…The increasing solute (salt, ions, FAA) concentration in the cheese water phase may give rise to aggregation and crystallization phenomena that result in the different types of structures in the interior and on the surface of different cheese varieties observed by some authors (Bianchi et al, 1974;Agarwal et al, 2006a;Tansman et al, 2015). Although the earliest studies date back to the 1900s (Babcock et al, 1903;Tuckey et al, 1938), a clear and unambiguous characterization of these structures has not yet been achieved.…”